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Our energetic matrix is currently based on finite fossil fuels, leading to climate change and increasing hazardous air pollutants. Nevertheless, solid oxide cells have emerged as a feasible and profitable route for energy generation. Solid oxide electrolysis cells can convert the excess electrical energy into chemical energy, thereby decoupling the transport fuels and chemicals production from today's fossil fuels, while solid oxide fuel cells can convert chemical energy back into electricity, thus balancing energy availability and demand. Solid oxide electrolysis cells afford an opportunity for upgrading biogas through the internal dry reforming of biogas and carbon dioxide electrolysis, producing hydrogen and carbon monoxide. Solid oxide electrolysis cells with conventional Ni-YSZ cermet fuel electrode and yttria stabilized zirconia electrolyte were constructed and tested on the direct feed of simulated biogas mixture (i.e. CH₄/CO₂ = 60/40, 50/50 and 40/60) at 850 °C. Cell performance and outlet gases measurements were carried out under open-circuit and closed-circuit conditions. The current densities at 1.8 V are -0.448, -0.678 and -0.876 A cm⁻² for the gas mixtures of CH₄/CO₂= 60/40, 50/50 and 40/60, respectively. The short term durability tests were performed in these three gas mixtures at 850 °C and 1.4 V. The cell fed with high CO₂ content demonstrates stable performance. No carbon deposition was observed on the Ni-YSZ fuel electrode surface, which might be due to not reaching the thermodynamic equilibrium and the reverse Boudouard reaction. Nonstoichiometric perovskites with active metal nanoparticles exsolved on the surface have been proposed as the promising fuel electrode in solid oxide cells. Here, La₀.₄₀Ca₀.₄₀TiO₃ and La₀.₄₃Ca₀.₃₇MχTi₁-χO₃-γ (M = Ni₀.₀₅, Ni₀.₁₀, Mn₀.₁₀, Co₀.₁₀, Ni₀.₀₅Mn₀.₀₅, and Ni₀.₀₅Co₀.₀₅) perovskite oxides were synthesized. The in-situ exsolution of Ni, Co and NiCo metal nanoparticles from the perovskite oxide parents was successfully according to the X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The results demonstrate that the exsolved metal nanoparticles can enhance the electrical conductivity, catalytic activity toward the hydrogen oxidation end carbon dioxide reduction. The cell performance can be improved by employing high voltage electrochemical reduction and extending the electrochemical reduction time. The best cell performance in 3% H₂O/H₂ was achieved by La₀.₄₃Ca₀.₃₇Ni₀.₁₀Ti₀.₉₀O₃-γ, exhibiting the maximum power density of 1.50 W cm⁻² at 900 °C. La₀.₄₃Ca₀.₃₇Co₀.₁₀Ti₀.₉O₃-γ based solid oxide electrolysis cell displays the highest current density of 0.856 A cm⁻² at 1.4 V.

Monolayers of graphene and boron nitride with little to no defects are shown to allow only protons through them and block the transport of small ions. We exploit this property and employ graphene as an electrode to study water dissociation and electrolysis. An increase in the exchange current density is observed with increasing pH because the proton-selectivity of our graphene electrodes allows for spatial separation of proton-hydroxide pairs and so an increased electric field at zero-current is observed which accelerates water dissociation and at higher bias, full water electrolysis. The measured Tafel slopes in our alkaline regime for the hydrogen evolution reaction (or HER) do not change with pH and their values indicate that water dissociation becomes rate limiting due to the barrier associated with extracting the proton from water. These results have implications for alkaline electrolysers and are also relevant to the design of catalysts for HER in alkaline media. Finally, we use graphene to improve existing technology by incorporating CVD-grown graphene into the membrane of a proton exchange membrane fuel cell (PEMFC). Fuel crossover poses a significant problem for PEMFCs and leads to a reduction in performance. We demonstrate a significant decrease in hydrogen crossover with our scalable graphene-coated membrane.

To reduce the adverse effects of global warming, there is an international drive towards the rapid decarbonisation of the aviation and maritime sectors. Simultaneously, there is an opportunity for the maritime sector to assist with the decarbonation of the wider global energy system via the supply of low-carbon energy. There is potential to transport such energy from regions where natural renewable and low-carbon energy resources are in abundance to where they are scarce. In this thesis, utilisation of electricity grid derived liquid hydrogen (LH2) fuel for these purposes is investigated. Particular focus is dedicated to: (1) the geographical, situational and design niches for which the use of LH2 is favourable within aviation and shipping; (2) the ability of LH2 to power the global aviation and shipping fleets and the modifications required to accommodate the fuel; (3) the identification of technologies that are likely to significantly effect decarbonisation efforts; and (4) the influence of weather induced boil-off on LH2 ship design. Methods such as energy systems analysis, thermodynamic concepts and numerical methods (e.g., Monte Carlo simulations) are utilised to construct models of LH2 fuelled aircraft and ships. These models are applied to various scenarios to analyse the performance of LH2 from a component, vehicle, network and global energy systems perspective. Models of a single-fuel LH2 and a dual-fuel LH2- liquefied natural gas (LNG) aircraft are constructed from data on an existing Boeing 787-8. The aircraft are modelled to operate towards 2050, in which time: (1) LH2 technologies develop, (2) both the World-average and region-specific electricity grids used to produce the hydrogen are assumed to decarbonise and (3) the International Air Transportation Association emissions targets tighten and so aircraft emissions decrease accordingly. The model identifies certain niches within the 2050 aviation sector where use of LH2 is beneficial. Single-fuel LH2 aircraft can only travel further than LNG fuelled aircraft in North America, accounting for 17% of the global demand. However, under stricter emissions constraints, LH2 can also outperform LNG aircraft in Europe and Latin America which accounts for an additional 24% of the demand. These superior ranges are achieved at a reduced passenger number and an increased energy consumption. The use of the dual-fuel aircraft in place of single-fuel aircraft in all three of these regions leads to improved range, passenger number and energy consumption. The LH2 aircraft models based on the Boeing 787-8 are expanded to utilise a dataset of multiple, differently sized existing aircraft. The models are combined with an estimation of the global aviation passenger-range demand to represent a 2050 aircraft fleet that is fuelled by LH2. This process indicates that, to meet the global aviation demand in 2050 using LH2 fuel: (1) 1.76 times the internal volume of the largest existing fossil fuel aircraft is required to meet the maximum range, (2) different passenger and range combinations are required and (3) low-carbon energy is demanded in regions where such energy is scarce. Therefore, a combination of aircraft design, network and energy system changes are imperative. A Monte Carlo simulation is conducted to assess the uncertainty of the LH2 aircraft models and their sensitivity to the projected development of LH2 technologies. The analysis indicates that there is a 95% probability that the single-fuel LH2 fuelled Boeing 787-8 that employs electric propulsion and utilises World-average electricity in 2050 travels within - 44% and + 49% of the range predicted by the unperturbed model. The ability of LH2 aircraft to fill specific niches within the aviation industry and the design, network and energy system changes required to accommodate such aircraft are thus highly uncertain. Of all the technological parameters, the LH2 aircraft that employ electric propulsion are the most sensitive to the efficiency of the fuel cells and the ones that do not (e.g., the dual-fuel aircraft) are the most sensitive to the efficiency of electrolysis. It is thus recommended that fuel cells and electrolysers are the focus of future research and development. This will not only further the development of LH2 aircraft but will also further the development of transport systems with similar well-to-end-use pathways (e.g., LH2 fuelled ships). The First Law of Thermodynamics, ship motion equations and data on an existing LNG carrier are utilised to predict weather induced boil-off in an LH2 ship tank at different ship velocities, weather conditions and ship design configurations. It is found that weather induced boil-off heavily influences the design and operation of LH2 ships, so its estimation is essential for successful design. Firstly, the use of real time routing is essential to avoid significant boil-off at high Beaufort Number as, relative to LNG, LH2 boil-off is twice as sensitive to adverse weather conditions. Secondly, significant tank and ship redesign is required to accommodate LH2. The presence of a reliquefaction unit is essential: without it, 8 times the thickness of insulation is required relative to an LNG ship in calm weather. To deliver the same energy, an LH2 ship that is 1.7 times the volume of the existing LNG ship is required. Using this model of boil-off and low-carbon technology projections towards 2050, an energy systems model is constructed to compare grid derived LH2 with liquid ammonia (LNH3) for use in freight and low-carbon energy transportation. The analysis shows that, in terms of limiting well-to-end-use carbon dioxide emissions, LH2 is favourable for use in energy transportation and LNH3 is favourable for use in freight. The maritime transportation of LH2 can thus provide a means of conveying low-carbon energy to regions where such energy is in low supply. Among many other end-uses, the LH2 can thus be used directly as fuel for aviation or can be converted to LNH3 for maritime freight. However, the high energy demand of LH2 production means this process is reliant on a high availability of low-carbon energy at the source. Hence, the role of LH2 in both aviation and shipping is dependent on a complex interaction with the wider global energy system.

Materials for heterogenous catalysis as well as in anodes for solid oxide fuel cells are two innovative and relevant areas of research. The search for a replacement of traditional Ni-based anodes in solid oxide fuel cells has been an increasing area of study over the last 20 years. The use of template materials such as ordered mesoporous silica to provide higher surface area materials for heterogenous catalysis are also a hot topic. In this thesis nanocubic doped-ceria oxides (for anodes in SOFCS) and lanthanum ferrite (as a good catalyst for the oxidation of hydrocarbons), were synthesised and studied separately for their electrochemical, structural, and catalytic properties, respectively. Three different nanocubic ceria candidate materials were synthesised and tested by impedance spectroscopy for their electrochemical properties (Nanocubic ceria, La-doped ceria, and Pr-doped ceria). These materials were studied to determine the effect of dopants and nanostructure of the material on the resistances and conductivities. The electrochemical studies, by impedance spectroscopy yielded that La-doped ceria has the lowest resistance of the three materials. Problems were encountered both with the testing apparatus, as well as the printing and durability of the ink electrodes and this area of research was not pursued further. For the lanthanum ferrite (LFO) materials, different preparation methods were explored by using ordered mesoporous carbon (OMC) templates to nanocast 19 ordered mesoporous products with high surface areas and improved catalytic performance. The use of OMC templates is a novel, safer, and easier route for nanocasting than its ordered mesoporous silica (OMS) counterparts. The preparation methods included a citrate complexation method, two solid-liquid methods - one of which included the preparation of these materials with OMC templates calcined at different temperatures - and a vacuum impregnation method. These materials were characterised using x-ray diffraction, transmission (and scanning transmission) electron microscopy, and nitrogen physisorption. They were evaluated catalytically by temperature programmed reduction and light-off experiments. The crystallite size, BET specific surface area, particle size, pore volume, pore diameter, degree of nanorod-like and ordered mesoporous structure, the reducibility, and light-off temperatures were obtained for each material. The vacuum impregnation method was the most successful method out of the four tested, with the highest specific surface areas reported as well as the best catalytic activity for the oxidation of methane in light-off experiments. The citrate complexation method was ranked second behind this with high specific surface areas and improved catalytic activity. The solid-liquid methods reported the lowest surface areas and worst catalytic activity, as well as having high impurity phases in the final products.

In this thesis, first-principles calculations within the density functional theory (DFT) framework were utilized to investigate heterogeneous catalytic reactions in direct ethanol fuel cell. The ethanol electrooxidation on Pd and binary Pd systems are studied, concerning mainly on the activity and selectivity, respectively. Meanwhile, due to the high cost of Pt and Pd and the CO poisoning effect, we aim to reduce the loading of Pd and Pt in catalysts. In this thesis, three ways of improving electrocatalytic performance of catalysts have been studied: (i) using some additives to promote the catalyst; (ii) tuning the catalytic surface thickness to get higher active surface area; (iii) controlling the structure or shape of particles to form some extremely active sites. From our theoretical studies, some basic principle has been obtained for rational design of high performance ethanol oxidation reaction catalysts: (i) active surface sites for C-C bond breaking; (ii) a suitable surface composition to increase selectivity for CO2 formation; (iii) the ability to facilitate the adsorption and activation of water (OH*) for the initiation of reaction.

Proton Exchange Membrane Fuel Cell (PEM-FC) is a technology that is associated with three main challenges that can be summarised as cost, reliability and lifetime. Current global research in PEM-FC focuses on reducing the use of expensive precious materials to reduce costs. Research is also improving the way fuel cells internal subsystems (water management, thermal management, power conditioning unit, gas supply management) are being controlled, managed and operated to enhance reliability and lifetime. This thesis takes the FC research to a different level of abstraction to reduce FC internal degradation. The proposed work does not focus on current FC global research trends. Instead, it addresses the different fuel cell challenges by proposing new solutions to the external factors (dynamic of the load, battery size, etc.) affecting a FC during operation. The formulated thesis hypothesis is therefore: “ Reduce the FC internal degradation and address the above three FC challenges by looking at the overall FC system (FC, battery, DC/DC converter, load) and ignoring the FC internal subsystems and subcomponents (water, thermal management, power conditioning, gas supply management). This research differs from previous work as it does consider a FC as a black box and only work on how to better control external components that have a negative impact on the fuel cell durability. ” This research work proposed three main interrelated “antidotes” to address the PEM-FC premature failure, thereby reducing cost, reliability and lifetime issues: a) Development of an optimisation technique to size the intermediate battery buffer component within a fuel cell system. b) Devise a method to optimise the fuel cell electrical power output using the proposed double PID control system. c) Devise a method to optimise the fuel cells operation and reduce battery stresses using advanced predictive Artificial Intelligence (AI) technology. The outcome from this research work demonstrates how it is possible to reduce the fuel cell and battery degradation while feeding load requirements.

Hydrogen fuel cells, and notably the polymer electrolyte fuel cell (PEFC), present an important opportunity to reduce greenhouse gas emissions within a range of sectors of society, particularly for transportation and portable products. Despite several decades of research and development, there exist three main hurdles to full commercialisation; namely infrastructure, costs, and durability. This thesis considers the latter of these. The lifetime target for an automotive fuel cell power plant is to survive 5000 hours of usage before significant performance loss; current demonstration projects have only accomplished half of this target, often due to PEFC stack component degradation. Health management techniques have been identified as an opportunity to overcome the durability limitations. By monitoring the PEFC for faulty operation, it is hoped that control actions can be made to restore or maintain performance, and achieve the desired lifetime durability. This thesis presents fault detection and diagnosis approaches with the goal of isolating a range of component degradation modes from within the PEFC construction. Fault detection is achieved through residual analysis against an electrochemical model of healthy stack condition. An expert knowledge-based diagnostic approach is developed for fault isolation. This analysis is enabled through fuzzy logic calculations, which allows for computational reasoning against linguistic terminology and expert understanding of degradation phenomena. An experimental test bench has been utilised to test the health management processes, and demonstrate functionality. Through different steady-state and dynamic loading conditions, including a simulation of automotive application, diagnosis results can be observed for PEFC degradation cases. This research contributes to the areas of reliability analysis and health management of PEFC fuel cells. Established PEFC models have been updated to represent more accurately an application PEFC. The fuzzy logic knowledge-based diagnostic is the greatest novel contribution, with no examples of this application in the literature.

This thesis focuses on developing support materials for direct methanol fuel cell (DMFC) catalysts. The approach involves using graphene based materials including reduced graphene oxide (rGO), reduced graphene oxide-activated carbon (rGO-AC) hybrid and reduced graphene oxide-silicon carbide (rGO-SiC) hybrid as a support for Pt and Pt-Ru nanoparticles. Pt/rGO and Pt-Ru/rGO catalysts were synthesized by three chemical reduction methods: (1) modified polyol, (2) ethylene glycol (EG) reduction and (3) mixed reducing agents (EG + NaBH4) methods. The synthesized catalysts were characterized by physical and electrochemical techniques. The results demonstrated that Pt/rGO-3 and Pt-Ru/rGO-3 catalyst synthesized with Method-3 exhibit higher electrochemical active surface area (ECSA) than the other rGO supported and Vulcan supported commercial electrocatalysts. In addition, Pt/rGO-3 and Pt-Ru/rGO-3 catalysts showed better oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities, respectively. The DMFC tests under different cell temperature (30, 50 and 70°C) and methanol concentration (1, 2 and 4 M) conditions further demonstrated the higher catalytic activity of the catalysts. The peak power density obtained with Pt/rGO-3 cathode and Pt-Ru/rGO-3 anode catalysts at 70°C with 1 M methanol was 63.3 mW/cm2 which is about 59 % higher than that of commercial Pt/C and Pt-Ru/C catalysts. The enhanced performance was attributed to the highly accessible and uniformly dispersed nanoparticles on rGO support with large surface area and high conductivity. Pt/rGO-AC (reduced graphene oxide-activated carbon) and Pt-Ru/rGO-AC catalysts were synthesized with various rGO:AC support ratios by using biomass derived AC. The results showed that the catalysts with content of 20 wt. % AC support (Pt/rGO-AC20 and Pt-Ru/rGO-AC20) exhibited higher ECSA, better catalytic activity and stability among all the tested catalysts. With 1 M methanol and 70°C cell temperature, the MEA with Pt/rGO-AC20 cathode and Pt-Ru/rGO-AC anode catalysts gave 19.3 % higher peak power density (75.5 mW/cm2), than that of Pt/rGO-3 and Pt-Ru/rGO-3 catalysts. The better DMFC performance was due to the incorporation of AC particles into rGO structure which builds electron-conductive paths between rGO sheets, facilitates the transport of reactant and products and provides higher specific surface area for the uniform distribution of nanoparticles. Pt/rGO-SiC catalysts were synthesized with variable silicon carbide (SiC) content in the hybrid support. Pt/rGO-SiC10 (10 wt. % of SiC support) catalyst showed higher ECSA and better catalytic activity compared to the Pt/SiC, Pt/rGO-3 and Pt/rGO-SiC20 catalysts. In addition, the Pt/rGO-SiC10 gave 14.2 % higher DMFC performance than the Pt/rGO-3 catalyst in terms of power density. The high performance can be attributed to the insertion of the SiC nanoparticles into rGO structure that improves the conductivity and stability of the catalyst by playing a spacer role between rGO layers. In summary, the overall results showed that the catalytic performance of the catalysts followed the trend in terms of support material: rGO-AC20 > rGO-SiC10 > rGO > Vulcan. The study demonstrated that the novel rGO-AC and rGO-SiC hybrids are promising catalyst supports for direct methanol fuel cell applications.

Hydrogen fuel cells have the potential to dramatically reduce emissions from the energy sector, particularly when integrated into an automotive application. However, there are three main hurdles to the commercialisation of this promising technology; one of which is reliability. Cur- rent standards require an automotive fuel cell to last around 5000 h of operation (equivalent to around 150,000 miles), which has proven difficult to achieve to date. This hurdle can be overcome through in-depth reliability analysis including techniques such as Failure Mode and Effect Analysis (FMEA), Fault Tree Analysis (FTA) and Petri-net simulation. This research has found that the reliability field regarding hydrogen fuel cells is still in its infancy, and needs development, if the current standards are to be achieved. In this research, a detailed reliability study of a Polymer Electrolyte Membrane Fuel Cell (PEMFC) is undertaken. The results of which are a qualitative and quantitative analysis of a PEMFC. The FMEA and FTA are the most up to date assessments of failure in fuel cells developed using a comprehensive literature review and expert opinion. Advanced modelling of fuel cell degradation logic was developed using Petri-net modelling techniques. 20 failure modules were identfied that represented the interactions of all failure modes and operational parameters in a PEMFC. Petri-net simulation was used to overcome key pitfalls observed in FTA to provide a verfied degradation model of a PEMFC in an automotive application, undergoing a specific drive cycle, however any drive cycle can be input to this model. Overall results show that the modeled fuel cell's lifetime would reach 34 hours before falling below the industry standard degradation rate of more than 5%. The degradation model has the capability to simulate fuel cell degradation under any drive cycle and with any operating parameters. A fuel cell test rig was also developed that was used to verify the simulated degradation. The rig is capable of testing single cells or stacks from 0-470W power. The results from the verification experimentation agreed strongly with the degradation model, giving confidence in the accuracy of the developed Petri-net degradation model. This research contributes greatly to the field of reliability of PEMFCs through the most up-to-date and comprehensive FMEA and FTA presented. Additionally, a degradation model based upon Petri-nets is the first degradation model to encompass a 1D performance model to predict fuel cell life time under specific drive cycles.

With the achievements recorded in the development of fuel cell technology, arguably hydrogen-driven systems would replace the combustion fossil fuel-based systems in the nearest future for safer and pollution-free environment. The much desired renewable and sustainable hydrogen infrastructure to replace or complement the fast-depleting fossil-based hydrogen fuel for the full commercialisation of fuel cell could be achieved through catalyst development and gasification of by-product glycerol glut from biodiesel production activity seen as a waste at the moment. In this study, the development of catalysts for the conversion of biomass vegetable oil via transesterification reaction to biodiesel has been explored in parallel to the subsequent catalytic gasification of pure and by-product glycerol from biodiesel synthesis to generate hydrogen-rich gases for utilisation in fuel cells. Reaction of tricalcium aluminate (C3A) with adsorbed water vapour under controlled hydration process at elevated temperatures was found to modify its surface morphology by formation of strongly basic hydroxide products. This was found to increase its surface basic strength and ability to catalyse transesterification reaction to biodiesel for the first time. Furthermore, basic alkaline earth metal oxides MgO, SrO and transition metal oxide ZnO that are known to catalyses transesterification reaction but suffered deactivation due to profuse leaching were doped and incorporated into the non-hydrated tricalcium aluminate (C3A) lattice structure. The doped catalysts were found to be not only active and selective to biodiesel formation but also resistant to deactivation by leaching of the doped active metals for the first time. The rapid deactivation of the nickel-based catalyst Ni/Al₂O₃ due to carbon deposition; agglomeration and phase transformation especially during prolonged high temperature operations using feedstock glycerol in steam reforming was minimised through the use of promoters such as ceria (CeO₂) and LSCM (La₀.₇₅Sr₀.₂₅Cr₀.₅Mn₀.₅O[sub](3-δ)) and alternative supports such as samarium-doped ceria (Ce₀.₈Sm₀.₂O[sub](2-δ)) and zirconia-doped ceria (Ce₀.₇₅Zr₀.₂₅O₂). This led to the development of a new catalyst system NiLa₀.₇₅Sr₀.₂₅Cr₀.₅Mn₀.₅O[sub](3-δ)/ Ce₀.₇₅Zr₀.₂₅O₂ (Ni-LSCM/Ce-Zr) which was found to be very active and offered much better suppression of carbon deposition and agglomeration minimizing catalyst deactivation. However, the work revealed that, the 'traditional' wet impregnation method does not offer sufficient control over particle size, growth and distribution. It takes time, is costly and results in weak interaction between the active phase metal catalyst particles and support leading to agglomeration, instability and deactivation at times even where a promoter was used; hence this offered poor catalytic properties. This study has demonstrated for the first time the use of a new phenomenon called redox lattice reorganisation and already known redox exsolution as alternative methods to wet impregnation in the preparation of oxide-supported nickel-based metal catalysts in glycerol steam reforming (GSR). The work has revealed that unlike what happens with the traditional wet impregnated catalysts where metal catalyst superficially interact with the oxide support resulting in catalyst deactivation due to agglomeration and carbon deposition or phase transformation. Redox lattice reorganisation in spinel has shown that metal catalyst particles can be grown out from the support itself and firmly anchored on the spinel oxide support leaving behind elaborate macro porous channels. That provides good surface area, strong metal support-interaction and reduced tendency for catalyst deactivation by agglomeration and offered effective coking suppression and good catalytic behaviour. The work has further shown that particle size, population, metal-support interaction, size of the channels in redox lattice reorganisation can all be tailored for better catalytic behaviour by simple control of reduction temperature. The work revealed further that redox exsolution in perovskite; particle size and distribution, metal-support interaction and general morphology of the catalyst surface could be tailored for good catalytic performance through control of B-site doping, careful choice of dopant metals for both A-site and B-site cations and defect chemistry in glycerol steam reforming (GSR). The metal exsoluted catalyst systems were found to be not only active and selective toward the desired products but have also demonstrated great potentials to suppress carbon deposition.

Proton Exchange Membrane Fuel Cells (PEMFCs) present a promising alternative to the conventional internal combustion engine for automotive applications because of zero harmful exhaust emissions, fast refuelling times and possibility to be powered by hydrogen generated through renewable energy. However, several issues need to be addressed before the widespread adoption of PEMFCs, one such problem is the removal of waste heat from the fuel cell electrochemical reaction at high ambient temperatures. Automotive scale fuel cells are most commonly liquid cooled, evaporative cooling is an alternative cooling method where liquid water is added directly into the fuel cell flow channels. The liquid water evaporates within the flow channel, both cooling and humidifying the cell. The evaporated water, along with some of the product water, is then condensed from the fuel cell exhaust, stored, and re-used in cooling the fuel cell. This work produces a system level model of an evaporatively cooled fuel cell vehicle suitable for the study of water balance and heat exchanger requirements across steady state operation and transient drive cycles. Modelling results demonstrate the ability of evaporatively cooled fuel cells to self regulate temperature within a narrow region (±2°C) across a wide operating range, provided humidity is maintained within the flow channels through sufficient liquid water addition. The heat exchanger requirements to maintain a self sufficient water supply are investigated, demonstrating that overall heat exchange area can be reduced up to 40% compared to a liquid cooled system due to the presence of phase change within the vehicle radiator improving heat transfer coefficients. For evaporative cooling to remain beneficial in terms of heat exchange area, over 90% of the condensed liquid water needs to be extracted from the exhaust stream. Experimental tests are conducted to investigate the condensation of water vapour from a saturated air stream in a compact plate heat exchanger with chevron flow enhancements. Thermocouples placed within the condensing flow allow the local heat transfer coefficient to be determined and an empirical correlation obtained. The corresponding correlation is used to produce a heat exchanger model and study the influence different heat exchanger layouts have on the overall required heat transfer area for an evaporatively cooled fuel cell vehicle. A one-dimensional, non-isothermal model is also developed to study the distribution of species, current density and temperature along the flow channel of an evaporatively cooled fuel cell using different methods of liquid water addition. Results show that good performance can be achieved with cathode inlet humidities as low as 20%, although some anode liquid water addition may be required at high current densities due to increased electro-osmotic drag. It is also demonstrated that both good membrane hydration and temperature regulation can be managed by uniform addition of liquid water across the cell to maintain a target exhaust relative humidity.

Graphene, a one-atom-thick sheet of carbon atoms, is impermeable to all atoms and molecules; the same can be expected for other 2D crystals like hexagonal boron nitride (hBN). In this work we show that monolayers of graphene and hBN are highly permeable to thermal protons. As a reference, we show that monolayers of molybdenum disulphide as well as bilayers of graphene and tetralayers of hBN are not. Moreover, we show that water plays a crucial role in the transport mechanism. Because of the zero point energy of vibration in the oxygen-hydrogen bonds in water, protons face energy barriers smaller than previously predicted by theory. The effect, revealed by substituting hydrogen for deuterium, also shows that protons and deuterons transport at different rates across the membranes; establishing them as membranes with subatomic selectivity. Beyond the purely scientific implications, our results establish monolayers of graphene and hBN as a promising new class of proton conducting materials with potential applications in fuel cells, hydrogen purification and isotope enrichment technologies.

Current state-of-the-art fuel cells depend on relatively high quantities of platinum metal to function. For fuel cells to become economically feasible as a replacement for the internal combustion engine there needs to be a drastic reduction in the quantity of platinum used within them. ACAL Energy has developed a fuel cell that allows for an 80 % reduction in the quantity of platinum required. This is achieved by replacing the solid supported cathode with an aqueous catholyte solution that contains within it a non-precious metal catalyst. The work contained in this thesis explores a library of non-heme metal complexes as potential candidates for use as catalysts for the 4 electron oxygen reduction reaction at the cathode of the FlowCath® fuel cell. The catalysts chosen, Fe(II) TPEN, Fe(II) TRILEN and Fe(II) TPTCN, are super oxidise dismutase mimics and are known to effectively reduce oxygen in a homogeneous solution. These catalysts were studied in fuel cell-like conditions to gain an understanding of their effectiveness in reducing oxygen. Attempts to decorate the complexes with sulfonate groups led to the evolution of the isoquinoline-based complexes. The change from pyridine-based complexes to isoquinoline-based complexes led to the formation of six alternative complexes, Fe(II) 1-miq TQEN, Fe(II) 3-miq TQEN, Fe(II) 1-miq TRILEN, Fe(II) 3-miq TRILEN, Fe(II) 1-miq TQTCN and Fe(II) 3-miq TQTCN, four of which (1-/3-miq TRILEN and 1-/3-TQTCN) are new to the academic literature. These complexes were analysed for their use as catalysts in the oxygen reduction reaction. In addition to the synthetic and analytical work carried out, computational models of the complexes were created. This theoretical data gave a deeper insight into the molecular structure of the complexes studied and the spin states of the Fe(II) and Fe(III) species.

This thesis presents the development and redesign of a commercial electrochemical quartz crystal microbalance with dissipation (E–QCM–D). This was used to study factors affecting the efficiency of the four electron reduction catalysed by the fuel cell enzyme bilirubin oxidase from Myrothecium verrucaria immobilised on thiol modified gold surfaces. Within this thesis, the E–QCM–D was used to show that application of a constant potential to bilirubin oxidase adsorbed to thiol-modified gold surfaces causes activity loss that can be attributed to a change in structural arrangement. Varying the load by potential cycling distorts the enzyme by inducing rapid mass loss and denaturation. Attaching the enzyme covalently reduces the mass loss caused by potential cycling but does not mitigate activity loss. Covalent attachment also changes the orientation of the surface bound enzyme as verified by the position of the catalytic wave (related to the overpotential for catalysis) and reactive labelling followed by mass spectrometry analysis. The E–QCM–D was used to show how electrostatic interactions affect enzyme conformation where high pH causes a reduction in both mass loading at the electrode and a reduction in activity. At pH lower than the enzyme isoelectric point, there is a build up of multilayers in a clustered adsorption. When enzyme adsorbs to hydrophobic surfaces there is a rapid denaturation which completely inactivates the enzyme. Changing the surface chemistry from carboxyl groups to hydroxyl and acetamido groups shows that catalysis is shifted to more negative potentials as a result of an enzyme misorientation. Further to this, increasing the chain length of the thiol modifier indicates that an increased distance between surface and enzyme reduces activity, enzyme loading and results in a conformational rearrangement that permits electron transfer over longer distances.

Specifically, this thesis is an investigation into the use of Additive Manufacturing (AM) for the construction of a small rocket component whose fabrication by means of AM has not been researched extensively. In general, it is an example of how AM can be used to introduce complexity into simple, common parts for the purpose of innovation. AM is maturing into a disruptive technology allowing for the placement of payloads into Low Earth Orbit (LEO) and deep space with record-breaking cost reductions. Common AM practices allowing these cost reductions are the use of AM to produce whole systems with reduced amounts of material, manufacturing whole systems with fewer components, or constructing exotic geometries that are not obtainable by means of subtractive manufacturing but result in higher performance characteristics or efficiencies. During the preliminary literature review, it became apparent much of the research and development in the field of AM applications for spacecraft are on those systems providing opportunities for improved cost/benefit margins such as the propulsion system and human-spacecraft interfaces. However, I believe there is missed opportunity in terms of innovation by not researching the use of AM in the other systems. In April 2022, NBC News published an article stating that the cost of sending a pound of payload into space on the space shuttle cost nearly 30,000 USD (in 2021 dollars), while the emergence of modern rockets and their systems has allowed the cost to drop down to around 1,296 USD on the Falcon 9 rocket (Chow, 2022). While this 95.68% reduction in cost is significant, our imaginations are coming up with more expensive, capable, and heavier payloads which further drives our need to find additional ways to improve efficiency and reduce weight. One way we may be able to do this is by reevaluating systems that can be manufactured through AM processes and have a relatively uncomplicated function and construction. This lack of complexity implies that a new, and hopefully innovative, design approach will add little risk to performance, reliability, and safety while providing the opportunity to shave a few pounds. With the need to innovate in mind, I will design and manufacture artifacts representative of the traditional method by which modern spherical Pressure Vessels (PVs) are fabricated (essentially two hemispheres joined in the center by a weld) and a new, potentially innovative design only possible via AM and consisting of two unlike pieces that combine to form a spherical PV. The goal of this new design is to produce a PV that can withstand higher pressures as compared to a similar PV constructed through traditional means. Using FEA analysis and minor postprocessing, I will analyze both designs to evaluate if there is value in researching and re-thinking how we design, build, and use simple products. The results show both artifacts can withstand 100%, 125%, and 150% of their expected normal operating pressures. However, the “traditional” artifact will undergo catastrophic failure at a pressure that is about 2% greater than the point at which the “innovative” artifact experiences catastrophic failure.

In this work, the hexagonal perovskite of targeted composition Ba5In2+xAl2Zr1-xO13 (x=0, 0.1, 0.2) was synthesized via a solid-state synthesis route to study the impact of oxygen vacancy concentration in layered hexagonal perovskites. Precursor oxides were mixed in stoichiometric proportions, calcined between 800-1200℃ and sintered at 1475℃. The sintered pellets were crushed into fine powders to investigate the chemistry and structure through X-ray diffraction, neutron diffraction, inductively coupled plasma mass spectrometry, and nuclear magnetic resonance. Dense pellets were used to study conductivity properties using electrochemical impedance spectroscopy. The synthesis approach produced 100% phase pure material across a range of increasing indium content from 2.0 to 2.8, although not of the projected stoichiometries. Neutron diffraction and x-ray diffraction indicated fractional occupancy and site swapping of the indium and aluminum positions, which was not dependent on indium content and resulted in the newly detected O5 position. From nuclear magnetic resonance, aluminum was proven to retain a strictly tetrahedral coordination. Additionally, the existence of four bulk protons was observed. Eight distinct oxygen signals were detected, likely the result of protonated and unprotonated forms of the various oxygen sites. Impedance spectroscopy indicated a reduction of total conductivity at 600℃ from 10-4 to 10-5 S cm-1 from wet to dry air, with proton conduction consistent across the temperature range.

Hydrogen storage in lightweight hydrides continues to attract significant interest as the lack of a safe and efficient storage of hydrogen remains the major technological barrier to the widespread use of hydrogen as a fuel. The metal borohydrides Ca(BH₄)₂ and LiBH₄ form the subject of this thesis; three aspects of considerable academic interest were investigated by density functional theory (DFT) and molecular dynamics (MD) modelling. (i) High-pressure crystal structures of Ca(BH₄)₂ were predicted from a structural analogy between metal borohydrides and isoelectronic metal oxides. The structural stability of hydrogen storage materials under high pressure is an important aspect, as high-pressure polymorphs may provide structures with better hydrogen desorption properties. The isoelectronic analogue of Ca(BH₄)₂ is TiO₂, and structural equivalents of Ca(BH₄)₂ in the baddeleyite, columbite and cotunnite structures of TiO₂ were found to be stable at elevated pressure. Thermodynamic stability was evaluated by computing the Gibbs energy with respect to pressure and temperature. The pressure-dependence of the Helmholtz energy was determined to described a third-order Birch-Murnaghan equation of state, and the harmonic approximation was used to compute the vibrational energy levels and the Helmholtz energy as a function of temperature. The proposed structures are consistent with reports of two hitherto unidentified high-pressure phases observed experimentally. (ii) The disordered structure of the high-temperature phase of LiBH4 was studied by ab initio molecular dynamics (MD) at temperatures ranging from 200-535 K. It was found that the model emerging from analysis of the MD simulations properly accounts for dynamical disorder and fundamentally differs from the published experimental and theoretical structures. The validity of the MD model was corroborated by comparison of calculated pair distribution functions, vibrational spectra and a crystallographic model with neutron diffraction data; good agreement was found. A reassignment of the space group from P63mc to P63/mmc is proposed based on evidence for additional symmetry from MD simulations. (iii) Finally, a new MD-based method was developed to simulate fast ionic diffusion in LiBH₄. The colour diffusion algorithm - a nonequilibrium molecular dynamics method originally developed for the study of model fluids - was adapted and applied to self-diffusion of atoms in a solid for the first time. Calculated diffusion coefficients agreed very well with published measurements, and diffusion pathways that include collective particle effects were determined directly from the simulation results, thereby opening up a promising and efficient new method for the study of phenomena such as superionic conduction.

Fast oxide-ion and proton conductors are the subject of considerable research due to their technological applications in sensors, ceramic membranes and solid oxide fuel cells (SOFCs). This thesis describes the use of computer modelling techniques to study point defects, dopants and clustering effects in fluorite-and perovskitetype ion conductors with potential SOFC applications. Bi2O3 related phases are being developed with the objective of high oxide-ion conductivities at lower operating temperatures than 1000°C, as in current generation SOFC electrolytes. Doped Bi2O3 phases have shown promise as materials capable of accomplishing this goal. First, the Y-doped phase, Bi3YO6, has been investigated including the ordering of intrinsic vacancies. The defect and dopant characteristics of Bi3YO6 have been examined and show that a highly mobile oxygen sub-lattice exists in this material. A preliminary structural modelling study of a new Re-doped Bi2O3 phase was also undertaken. A comprehensive investigation of the proton-conducting perovskites BaZrO3, BaPrO3 and BaThO3 is then presented. Our results suggest that intrinsic atomic disorder in BaZrO3 and BaThO3 is unlikely, but reduction of Pr4+ in BaPrO3 is favourable. The water incorporation energy is found to be less exothermic for BaZrO3 than for BaPrO3 and BaThO3, but in all cases the results suggest that the proton concentration would decrease with increasing temperature, in accord with experimental data. The high binding energies for all the dopant-OH pair clusters in BaPrO3 and BaThO3 suggest strong proton trapping effects. Finally, a study of multiferroic BiFeO3 is presented, in which the defect, dopant and migration properties of this highly topical phase are investigated. The reduction process involving the formation of oxygen vacancies and Fe2+ is the most favourable redox process. In addition, the results suggest that oxide-ion migration is anisotropic within this system.

The purpose of this thesis was to carry out the experimental study of direct ammonia fuel cells. The use of hydrogen in fuel cells poses a lot of problems. There is a lot of safety, technical and economic issues to be overcome to make its use as a fuel widespread. Ammonia is being considered as a very promising source of hydrogen for fuel cells. However, until now its use in fuel cells has received very little attention. Ammonia presents many advantages over hydrogen and other potential sources of hydrogen such as an easy storage and a world-wide distribution network. Ammonia is a suitable hydrogen carrier and can be easily cracked at high temperatures such as those used in solid oxide fuel cells. The present study was conducting using ammonia as fuel and argon as carrier gas in different solid oxide fuel cell systems: an annular design, a planar design and a micro laminated reactor. The electrolyte materials were calcia stabilized zirconia and yttria stabilized zirconia. As far as the electrodes are concerned, silver, platinum and nickel cermet were used as anode/materials and silver was employed as cathode material. The cell yoltage was measured as function of reactor configuration, space time, ammonia flow rate and ammonia concentration. The results demonstrate the high potential of ammonia over hydrogen when nickel is used as anode material. Solid proton conducting fuel cells operating on ammonia fuel were also studied. The electrolyte materials were fabricated from neodymium and gadolinium doped barium and strontium cerates. The dopant fraction ranged from 1 to 20 wt%. Silver was employed as cathode and anode material and was spray deposited. The application of proton conducting electrolytes results in higher current densities for a given voltage than the using typical oxide ion conductors such as 8mol % yttria stabilized zirconia. The potential of the proton conducting materials for application in ammonia synthesis at atmospheric pressure was also studied. They demonstrated promising results and could prove to be an alternative to the common ammonia synthesis processes.

This thesis concerns the design, implementation and operation of a hydrogen energy storage facility that has been added to an existing renewable energy system at West Beacon Farm, Leicestershire, UK. The hydrogen system consists of an electrolyser, a pressurised gas store and fuel cells. At times of surplus electrical supply, the electrolyser converts electrical energy into chemical energy in the form of hydrogen. This hydrogen is stored until there is a shortage of electrical energy to power the loads on the system, at which point it is reconverted back to electricity by the process of reverse-electrolysis that takes place within a fuel cell. The renewable energy sources, supplying electrical power to domestic and office loads at the site, are photovoltaic, wind and micro-hydroelectric. This work is being carried out through a project, conceived and overseen by the author, known as the Hydrogen and Renewables Integration (HARI) project. The purpose of this study is to demonstrate and gain experience in the integration of hydrogen energy storage with renewable energy systems and, most importantly, to develop software models that could be used for the design of future systems of this type in a range of applications. Effective models have been created and verified against the real-world operation of the system. These models have been largely completed, although some minor details remain unfinished as the are dependant upon studies linked to this one which are yet to be concluded. Subject to some fine tuning that this would entail, then, the models can be used to design a stand-alone, integrated hydrogen and renewable energy system, where only the load profile and weather conditions of a site are known. Significant practical experience has been gained through the design, installation and two years' of operation of the system. Many important insights have been obtained in relation to the integration of the system and the design and operation of its components.

Heavy-duty vehicles (HDVs) are one of the largest contributors of both greenhouse gas (GHG) and criteria pollutant emissions in California. The burning of heavy diesel fuels and even the cleaner burning of natural gas within internal combustion engine (ICE) trucks are unsustainable. As such, as part of California’s goals to reach net zero GHG emissions by 2045, California has mandated that all drayage trucks must be zero-emission by 2035 and all other HDVs be zero-emission by 2045. This mandate will force the adoption of zero-emission technologies such as battery electric trucks (BETs) and fuel cell electric trucks (FCETs).While battery electric technology has begun to succeed in the light-duty vehicle (LDV) market, the challenges associated with battery power are exacerbated in HDV applications including long charge times, immense power demands on grid infrastructure, heavier vehicle weight, and limited vehicle range. Hydrogen fueled FCETs have the advantages of faster refuel times, lighter vehicles, and larger vehicles ranges, all of which are more comparable to the performance of modern diesel trucks. As such, hydrogen fueled FCETs will play a major role in all HDV vocations, likely dominating in long-haul applications. The major inhibition to the adoption of FCETs is the lack of refueling infrastructure, the subject of this thesis. To study and aid the initial deployment and rollout of Hydrogen Refueling Stations (HRSs), a model was developed in ArcGIS to spatially optimize HRS deployment within California and optimally support the predicted adoption of FCETs in the coming years. The model aims at optimizing refueling coverage to provide the most support possible and the least compromises of desired truck routing. The model also accurately informs the number of HRSs needed within the state to cover the anticipated fueling demands and how different station parameters might affect the performance of the network. While stations will be required to meet the total demand of the state, an initial subset of well optimized stations can effectively meet a majority of the trucking demand in California.

Fuel Cells using solid oxides for the electrolyte material, or Solid Oxide Fuel Cells (SOFCs), can operate at high temperatures and have many benefits when compared to other electrolyte material-based fuel cells. SOFCs can, however still have problems when operating at these high temperatures. (~1,000 degrees Celsius) At high temperatures, the SOFC electrolyte resistivity goes up making the ionic conductivity decrease and therefore a loss of performance. The inclusion of low level Yttria to Zirconium Oxide (the electrolyte material) has been known to help reduce the resistivity at high operating temperatures. In this study, a series of Yttria stabilized Zirconium Oxide thin films were grown by Pulsed Laser Deposition. The same series of films was deposited on Silicon, Zirconium and Alumina (Al2O3) substrates. Here, we will scrutinize these thin films using Secondary Ion Mass Spectroscopy or SIMS. SIMS is a depth profiling technique that is commonly used in materials characterization in the form of process monitoring, research and development or troubleshooting. We will be evaluating the compositions, film thicknesses, surface roughness, contamination and growth interfaces of these films, as well as correlating the SIMS data to the previous electrical measurements performed on these thin films.

Ever-increasing energy consumption and rising public awareness for environmental protection require the development of new technologies for renewable energy conversion and storage. The renewable energy, abundant but intermittent, is usually stored in stable chemicals that can be easily converted back to electrical energy. This process is similar to how Nature harvests and utilizes solar energy through photosynthesis and respiration.For energy conversion, one of the major technologies is fuel cells. A Fuel cell is an electrochemical device that converts chemical energy in fuels directly into electrical energy. A fuel cell separates a combustion reaction into two half-reactions (fuel oxidation and oxygen reduction), and these two half-reactions occur in two physically separated chambers. In commercialized fuel cells, both reactions require platinum catalysts. Oxygen reduction reaction requires large amounts of platinum catalysts to achieve high current density. Therefore, developing alternative, cheap catalysts for ORR is important for lowering the price of fuel cells. In nature, life-sustaining ORR is catalyzed by multicopper oxidases (MCOs), where O2 is captured and reduced at a tricopper cluster. MCOs are a group of enzymes which can selectively catalyze the reduction of oxygen to H2O with a high turnover frequency (560 s-1). In Chapter 1 and Chapter 2, a biomimetic tricopper complex, resembling the active site in multicopper oxidases (MCOs), was developed to understand how nature employs tricopper clusters to catalyze ORR at near-zero overpotential. In order to mimic MCO’s ability to reversibly store and deliver multiple electrons, a fully encapsulated tricopper complex was synthesized. Site isolation and intramolecular proton transfer site are further shown to be the two critical factors in lowering the overpotential of oxygen reduction reaction. Our work represents a significant step toward inexpensive and efficient copper catalysts for ORR.Another major technology that stores energy on a large scale is redox flow batteries (RFBs).3 In RFBs, at least one electrode contains redox-active liquid electrolyte that can be reduced or oxidized. After electrochemical reaction, the reduced or oxidized materials are pumped out of the electrochemical cell and stored in a large tank. The energy density of RFBs, one of the most important factors in evaluating the performance, is usually limited by the solubility of the energy storage material and the volume of the electrolyte. In Chapter 3, a new type of catholyte utilizing low-cost gaseous nitrogen oxides (NOx) was developed and investigated. With this material, the energy can be stored in a redox-active gas, which allows scale-up of storage capacity without increasing the concentration of the redox-active solute or the amount of electrolyte employed, which is one of the main cost drivers in non-aqueous RFBs.

Mass industrialization over the last few centuries has created a global economy which is dependent upon fossil fuels to satisfy an exponentially increasing demand for energy. Aside from the possible depletion of this finite resource, the combustion of fossil fuels releases greenhouse gases into the atmosphere which cause the global temperature to rise – a phenomenon which has already begun to create geologic and geopolitical instability and shows no signs of abatement. One proposed method to rid humanity of its dependence on fossil fuels is to use green hydrogen as an energy carrier. In this scheme, excess electricity from a robust renewable energy generation infrastructure is diverted to grid-scale electrolyzers which split water into hydrogen and oxygen. The hydrogen is in turn distributed via supply chain to end users who employ fuel cells to locally convert the energy stored in the chemical bond of hydrogen into electricity on-demand. This vision for an alternative global energy economy has been inhibited by several factors including the low utilization of renewable energy generating technologies, the considerable cost of precious metals required for electrolyzer electrodes, and the relatively low efficiency of the cathodic fuel cell reaction. This vi dissertation is a compilation of experimental work related to the development of materials and interfaces for enhanced electrocatalytic hydrogen evolution using non-precious materials and hydrogen utilization in highly-efficient proton exchange membrane fuel cells. Chapter 1 begins with an overview of the global energy diet and the problem of climate change followed by a discussion of renewable energy technologies, ending with a proposal of how the large-scale implementation of green hydrogen technologies may fit into the futuristic energy landscape. Chapter 2 presents a brief review of the mechanism of hydrogen evolution electrocatalysis including its thermodynamic, kinetic, and mass transport limitations. In Chapter 3, we demonstrate a simple and scalable fabrication process for highly-active non-precious molybdenum sulfide electrolyzer cathodes. Molybdenum sulfide and other transition metal dichalcogenides have received considerable attention in recent years as electrolyzer catalysts due to their environmental benignity, high stability, good catalytic activity, and low cost. Aside from the issue of low efficiency, industrial implementation of most reported molybdenum sulfide fabrication procedures is complicated by extreme and/or lengthy processing conditions. Our process is roll-to-roll amenable and produces a catalyst film in milliseconds without the use of harsh processing conditions or excessive chemicals. Ex-situ characterization of the resulting electrode confirms transformation of the precursor to molybdenum sulfide and reveals a hydrogen evolution reaction overpotential of 200 mV at 10 mA cm-2 which is comparable to that of other reported highly-active molybdenum sulfide catalysts. Chapter 4 deals with the development and ex-situ characterization of a novel non-precious electrocatalyst platform for hydrogen evolution based upon a nickel-centered thiosemicarbazone molecular framework. The enzyme hydrogenase, found in most forms of life, has served as a source of inspiration for researchers due to its ability to reversibly catalyze hydrogen evolution efficiently. However, efforts to translate the activity of the hydrogenase active site to an electrode have been limited in their success. We report a class of molecular catalysts inspired by previous work on hydrogenase active site analogues. Successful translation and retention of the catalyst to the electrode surface is confirmed, and ex-situ testing reveals a hydrogen evolution reaction overpotential of 450 mV at 10 mA cm-2 with remarkable stability – a promising milestone which lays the foundation for further development of this class of materials. Beginning in Chapter 5, the focus of the dissertation is shifted away from materials for hydrogen evolution and toward the development of highly-efficient proton exchange membrane fuel cell devices. Chapter 5 details the interplay between chemical transport, catalytic kinetics, thermodynamic considerations, and Ohmic losses which influence fuel cell efficiency. In Chapter 6, we introduce a structured proton exchange membrane fuel cell cathode which utilizes an array of bulk-like ionomer channels to improve the interface between the catalyst layer and membrane. The channels serve as conduits for rapid proton transport, dramatically decreasing the cathode sheet resistance and enabling a reduction in electrode ionomer content which attenuates active site inhibition from sulfonate adsorption. Using this approach, the mass activity of Vulcan carbon-based Pt viii catalyst is improved by up to 80 %, and the power density is improved by up to hundreds of mW cm-2 at benchmark cell potentials – particularly under arid conditions. Further performance gains may be realized by tuning the electrode geometry and/or applying this technology to other catalyst types including those based upon high-surface-area carbon. The results described in this dissertation 1) advance the understanding of materials and fabrication processes for hydrogen evolution electrodes and 2) provide a simple tool for mitigating chemical transport and catalyst poisoning limitations in the proton exchange membrane fuel cell cathode.

Energy and electricity are vital to modern society and our daily life. However, environmental pollution and global warming caused by fossil fuels have also become highly problematic in recent years. Hydrogen has the highest energy density, it can be produced directly from water, and the only by-product during the power generation is water. Therefore, hydrogen is considered to be the key to solving the current energy problem. However, the current mainstream hydrogen production methods also result in significant carbon emissions. In the meantime, the chemical reactions performed in water electrolysis and fuel cells rely heavily on expensive noble metal catalysts. Consequently, there is an urgent need to develop cheap and efficient catalysts to replace noble metals. Since 2009, nitrogen-doped carbon nanotubes have been proved to have a similar catalytic activity to platinum for oxygen reduction reactions (ORR) and better stability. Heteroatom-doped carbon materials have been developed rapidly over recent years and are now considered a promising alternative to noble metal catalysts. In addition to ORR, carbon materials can also catalyze hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with comparable performance to the commercialized noble metal catalysts while being cheaper to produce and more stable. This dissertation will be divided into several sections to discuss the application of functionalized carbon materials in various energy conversion and storage devices. Chapter 2 explore the potential application of functionalized graphene in the transport layer and active material for perovskite solar cells. Chapter 3 introduces a small project which combines perovskite material with electrospun fiber into a flexible photodetector. Chapters 4 and 5 investigate the multifunctional catalytic performance of nitrogen and sulfur co-doped 3D graphite networks (N, S-3DPG) in water splitting, fuel cells, dye-sensitized solar cells, and zinc-air batteries; we successfully used these low-cost carbon-based devices to build zero-emission clean hydrogen energy system that requires only sunlight and water to generate hydrogen and electricity. In the last part, we use inexpensive basic carbon materials to prepare large-area load-bearing supercapacitors with potential applications in flexible wearable devices.

The upcoming energy transition from fossil to renewable, clean energy requires multiple energy conversion and storage solutions to increase efficiency and reduce emissions in all energy-consuming sectors. Hydrogen, when produced from green electricity, can play a crucial role in this transition. Polymer electrolyte fuel cells (PEFCs) are the most efficient energy converters to re-electrify hydrogen, combining it with oxygen from the air to produce only water, electrical energy, and heat. They, therefore, are applied for both mobile and stationary applications. However, the high system cost of PEFCs has limited their wider use in the energy and mobility markets. Decreasing the cost per installed power requires indispensably material developments of all essential fuel cell components. In a PEFC, hydrogen and oxygen are supplied through gas channels from both sides of the polymer electrolyte membrane at the center. The gas diffusion layers (GDLs) distribute the feed gases homogeneously across the catalyst layers located at the membrane interfaces. Water accumulation in the porous gas diffusion layers increases the oxygen transport resistance to the cathode catalyst and thus prevents current PEFC technology from reaching higher current and power densities. This thesis thoroughly investigates water and gas transport in conventional and advanced GDL materials. It highlights the benefits of deterministic structures, as compared to today’s stochastic materials, leading product water more direct to the gas channel and thereby reducing the liquid water saturation in the pore space. On the one hand, deterministic modifications of stochastic materials, and, on the other hand, intrinsically deterministic structures are investigated and enable for proposing design guidelines for future materials. After the fundamentals and experimental means used are described, the results of this thesis are split into two parts. The first part investigates the potentials and limits of modifying conventional carbon fiber GDLs by laser perforation. This technique introduces deterministic, straight channels that locally direct liquid water. A wide variety of patterns was studied to evaluate the influence of the pattern geometry on fluid transport through porous materials. With this approach, a suitable descriptor was found that accurately relates the optimum perforation density with fuel cell performance. The competing effects of improved water transport (and thus reduced oxygen transport resistance) and increased membrane drying (by increasing the effective diffusivity) limit the maximum power density increase to 20%. Furthermore, the water transport through the laser-structured GDL of one specific perforation pattern was investigated with sub-second operando X-ray tomographic microscopy (XTM). The comparison with a conventional GDL showed that the total water saturation is similar for both gas diffusion layers. However, the perforations distribute product water more evenly, reducing the water saturation close to the catalyst layer, leading to increased current densities for the perforated GDL. These studies show that the introduced deterministic structure can direct and improve water transport in conventional, stochastic GDLs and thereby increase fuel cell power density. The second part follows a different approach and investigates the potential of novel, fully deterministic GDLs. Woven and gold-coated PET fabrics offer unique tuning properties, enabling a rational, bottom-up design of transport optimized gas diffusion layers. In a first study, these woven materials are successfully used for the first time in a polymer electrolyte fuel cell (PEFC), and their superior performance under cold and saturated operating conditions was analyzed. The water transport, investigated again by operando XTM, is fundamentally different. Water moves much faster through the structure, as it needs to pass only one pore throat before reaching the gas channel. The last study focuses on the thermal conductivity of GDLs, as heat removal is another essential transport duty. Different thickness of gold coatings enable changing the thermal conductivity independently of the pore structure. The strongly reduced thermal conductivity is unexpectedly not a performance limiting factor. It leads to significant thermal gradients across the GDL and thus drives through water evaporation a heat pipe. The temperature gradient is reduced by using product water evaporation as cooling power on the hot side. Thus, more water is transported in the vapor phase, and the GDL structure stays dry for improved oxygen transport. In comparison with a conventional GDL it was shown that the structure is the key to the improved performance and that the thermal conductivity, different by orders of magnitude, causes just smaller differences between the materials. Both approaches emphasize the benefits of designed, deterministic GDL structures that locally reduce liquid water saturation and facilitate oxygen transport. Future GDL development can therefore focus on optimizing the structure and tuning it to the locally heterogeneous operating conditions present in a fuel cell to further increase PEFC power density.

Due to the climate crisis, the importance of reducing greenhouse gas (GHG) has been recognized by governments, private companies and the general public alike. Yet carbon capturing-based approaches are difficult to integrate with transportation, which is one of the largest GHG producing sectors, Therefore, electrification is the only viable approach to reduce emissions from transportation, by greatly increasing the market share of electric vehicles (EVs). However, the mass adoption of either (or both) of battery EVs (BEVs) and fuel cell EVs (FCEVs) require a large amount of supporting infrastructures, particularly the construction of EV charging stations (EVCSs) for BEVs and hydrogen refuelling stations (HRSs) for FCEVs. The goal of this study is to provide effective approaches for the sizing and sitting of EVCSs and HRSs to facilitate the deployment of BEVs and FCEVs. The background and an overview of the thesis are provided in Chapter 1, where the gaps in the current research are pointed out and the objectives of the thesis are formulated. Chapter 2 reviewed the current state of technologies regarding the hydrogen life cycle as well as the popular planning models for EVCSs and HRSs. In Chapter 3, to achieve a competitive strategy from the perspective of private companies, a market-based framework is proposed for the problem of EVCS planning by leveraging Graph Convolutional Network (GCN) and game theory. In Chapter 4, a multi-objective planning model is developed for EVCSs and the expansion of distribution network with significant renewable components while considering uncertainties in EV charging behaviour. Additionally, in Chapter 5, a planning model of HRS maximises the long-term profit while considering different practical constraints. The HRS planning model also addresses short-term demand uncertainty via redistribution. The models that are developed in this study are validated using either synthetic or real-world case studies, and the simulation results showed the effectiveness of the proposed models. Finally Chapter 6 summarises the major achievements of the thesis and provides directions for further research.

Fuel cells are devices that can efficiently convert fuels into electricity without the limitation of the Carnot cycle. Particularly, hydrogen fuel cells have attracted enormous interest due to their high energy density, high efficiency, and low environmental impacts. The most widely adopted proton-exchange-membrane fuel cells (PEMFCs) use platinum (Pt) catalysts to drive both anode and cathode reactions. To date, the most significant roadblock to the broad dissemination of this green energy technology remains the acceleration and retention of the reaction rate of oxygen reduction reaction (ORR) at the cathode. Developing robust, active, and cost-effective ORR catalysts is the solution to this challenge.In my first work, I demonstrated a Cu doping strategy to enhance the intrinsic activity and durability of octahedral PtNi nanoparticles in the rotating-disk-electrode (RDE) setting. By a novel integration of simulations and growth tracking experiments, we uncover the beneficial role of increased surface Pt composition, which reduces the generation of surface vacancies and subsequent dissolution of sub-surface Cu and Ni atoms. Unlike the well-controlled RDE system, the critical role of mass transports in a practical membrane-electrode-assembly (MEA) system demands additional consideration in stability-enhancing strategies. Therefore, in my subsequent work, I recognized the critical challenge in MEA with ultralow Pt loading and designed a graphene-nanopocket-encaged platinum cobalt nanocatalyst with good electrochemical accessibility and exceptional durability in practical MEA testing. With the greatly improved rated power and durability, a 6.8 gram Pt loading is projected for a 90-kW PEMFC light-duty vehicle, approaching that used in a typical catalytic converter. Furthermore, I presented a unique design of ultrafine Pt nanocatalysts with embedded cobalt oxide clusters, which further improve the catalyst stability for durable PEMFCs. This endohedral-oxide design exploits the strong Pt/oxide interaction, which grants the catalyst its exceptional structural and chemical durability, without sacrificing activity. The developed nanocatalyst exhibits exceptional durability promising an outstanding projected lifetime of 15,000 hours.

The development of high efficiency and cost-effective bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical to a wide commercialization of metal-air batteries and unified regenerative fuel cells. Pt and IrO2 and their alloys have been applied as favorable catalysts due to their prominent performance. However, their high cost, low stability and susceptibility to poisoning greatly limit their widespread commercial adoption. Transition metal has been regarded as a good alternative to noble metal-based catalysts because of their tunable valence state, cost-effectiveness and variety of chemical composition, structure, and morphology. However, the catalytic activity of the transition metal electrocatalysts is largely hindered by their inherent corrosion and oxidation susceptibility. Therefore, my research mainly focusses on the development and modification of transition metal-based catalysts with enhanced catalytic activity towards ORR and OER.In the first project (Chapter 4), I propose to investigate the beneficial effect of atomic layer deposition (ALD)-derived incorporation of transition metal-based materials for electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Gas-evolving electrochemical reactions primarily occurs at the triple phase boundary regions where electrons, ions and reactant molecules meet altogether. Therefore, ALD-based dispersion of atomic-scale transition metal species can be an ideal approach for maximizing catalytically active sites. Our proposed research is to investigate the effect of ALD treatment of functionalized carbon-based materials with different transition metals on electrocatalytic ORR and OER reactions via both experimental and theoretical studies. In the first work, a mixed metal/metal oxide-integrated N-doped carbon is prepared by performing atomic layer deposition (ALD) of CeO2 nanodots on a three-dimensional Co and N co-doped carbon polyhedron nanostructure derived from zeolitic imidazolate framework (ZIF; a type of metal-organic framework). An optimally prepared hybrid catalyst achieved excellent bifunctional oxygen electrocatalytic performance comparable to or even better than noble metal-based benchmark catalysts (Pt/C for ORR and IrO2 for OER) thanks to the synergistic effect between Co and Ce, high-surface-area backbone structure, rich Co-Nx moieties and oxygen vacancies. This work proves the effectiveness of ALD in uniformly incorporating the second metal/metal oxide onto a monometallic system for enhanced electrocatalytic performance.In the second project (Chapter 5), I demonstrate a unique 3D core-shell nanostructure for efficient OER electrocatalysis. Two-dimensional (2D) layered double hydroxides (LDHs) are promising as an effective electrocatalyst towards OER, but their poor conductivity and tendency to stack together limits their activity and durability as an electrocatalyst. Herein, 3D core-shell structures are synthesized through a facile one-step reaction strategy, in which the terephthalic acid and urea is employed as the organic ligand for the metal organic framework (MOF) precursor and surface coordination buffer between LDH and MOF. Benefiting from the hierarchical 3D microstructure with uniform nanosheets grown on the surface, the as-prepared electrocatalyst exhibits rich carbon edge sites and high electrochemical surface area. The representative sample (CoNi-BDC@LDH) achieves an OER activity with the overpotential of 280 mV at 100 mA cm−2 and robust cyclic and chronoamperometric stability. A series of quasi-operando studies by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Raman and Fourier-transform infrared spectroscopy further elucidate that Co-Ni acts as the main active site while the high valence state of Ni facilitates O2 desorption from O-O bond linking metal sites. The high OER performance is additionally attributed to a high valence state of metal ions in γ-NiOOH/CoOOH, lattice edge sites of carbon, and a synergistic effect between neighboring metal atoms.In the third study (Chapter 6), a Co-Ni based LDH structure with thin layer coating of ceria and/or titania by ALD is synthesized. Benefiting from the result of the first two projects, ALD was applied to the LDH structure directly. The effects of tri-metal incorporation on the electrocatalytic properties of the resulting hybrid systems toward OER is further investigated. The primary electrochemical studies and XPS characterization results suggests the improved OER performance is mainly attributed to the synergistic effect between metal cations.

Polymer electrolyte fuel cells (PEFCs) provide a promising way to mitigate global warming since these power sources produce no emissions of greenhouse gases. PEFCs convert chemical energy of hydrogen and air to electricity via electrochemical pathway. For broad deployment of PEFCs in transportation sector cost and durability need to be addressed. At the heart of the fuel cell is the catalyst layer, where platinum (Pt) catalyst is used to catalyze oxygen reduction reaction (ORR). Pt is typically dispersed on carbon support and with ionomer (such as Nafion) to enable ORR. Understanding Pt-ionomer interface is critical to enable PEFCs with low Pt content. Therefore, in this work Pt- ionomer interfacial and transport properties within the catalyst layers were examined using variety of electrochemical diagnostic techniques. Optimizing electrode morphology with a more uniform ionomer distribution is key to reducing ohmic losses and increasing electrocatalyst utilization in PEFCs. For ionomer transport properties, we determined three different methods including direct current (DC) hydrogen pump (HP), HP electrochemical impedance spectroscopy (EIS) and H2/N2 EIS to investigate catalyst layer ionic conductivity, and it was the first and unique study to compare each method. Apart from that, we developed an 1D H2/N2 EIS impedance fitting model, which enable us to evaluate catalyst layer ionic conductivity with good accuracy. For Pt ionomer interfacial properties study, we first studied performance and electrochemical characterizations for MEAs containing novel high oxygen permeability ionomers (HOPIs) synthesized by Giner, and a comparison was made between novel ionomer and commercial Nafion ionomer. After that, we investigated some possible factors which influence cell performance and catalyst/ionomer interfacial properties using 3M materials including Pt loading, ionomer content and carbon support types, which would bring thoughts and inspirations to community regarding the design of optimal catalyst layer. Finally, we studied Pt ionomer transport and interfacial properties change during carbon corrosion accelerated stress tests (ASTs). We performed both in-situ and ex-situ measurements on MEAs containing different types of carbon support, which enable us to better understand the causes for drop of performance from ionomer interfacial properties perspective.

Proton exchange membrane fuel cells are important to the future of green energy as hydrogen can be made with green technologies and store energy for later use. Fuel cells can efficiently convert the hydrogen to electricity as needed. This study uses Solidworks simulation to make design improvements to the fuel cell before the prototype build stage of testing; this saves money and time by reducing the prototype builds needed. In this study, a multi-channel serpentine design with two outlets versus a single outlet is evaluated using CFD to investigate pressure drop. Lower pressure drops are desirable as less energy input is required to operate the fuel cell. A problem with the clamping of fuel cell end plates is that the forces are not evenly spread throughout the cell. To improve the clamping force problem, a two-piece end plate with embossments is designed and forces simulated. In the FEA, the embossments provided a more uniform force distribution. The findings show that the two-outlet bi-polar plate greatly reduces the pressure drop, which at same inlet pressure of 5 psi increases the mass flowrate by 54% . The analysis of the endplates with embossments shows an improvement in the uniformity of the forces applied to the fuel cell. This is visible by the stress contour plots of each design, which shows that the forces move from the edges of the cell to the inner area of the cell. This study demonstrates that Solidworks can be used to evaluate a PEMFC and that the design changes used in this study have promising possibilities in future PEMFC designs.

It is increasingly and urgently obvious that the world needs to move toward green, renewable energy sources. Key in realizing this infrastructure are energy-conversion devices such as hydrogen fuel cells and water electrolyzers. As their name suggests, these devices allow energy to be converted from one form (a fuel) to another (electricity), and vice versa, enabling a distributed and modular energy network. The efficiency and cost of these devices have vastly improved over the last few decades, but those gains (in particular for fuel cells) have stagnated in recent years due to performance limitations and high costs associated with their catalyst layers (CLs). This dissertation focuses on fuel-cell CLs, although the fundamental principles and insights gained are applicable to electrolyzers and other energy-conversion devices that rely on similar CL paradigms and architectures.CLs are heterogeneous porous electrodes comprised of agglomerates of catalyst particles (typically platinum supported on carbon), ion-conducting polymer (ionomer), and void space. The microstructure of the CL, including the size of the agglomerates, the ionomer coverage, porosity/tortuosity, etc. controls the complex gas, liquid, ion, and electron transport networks and impacts the overall kinetic, ohmic, and mass-transport performance of these devices. Characterization efforts have spanned micro-, meso-, and macro-scale techniques to probe structure-property-performance relationships of the CL. CLs are made from precursor CL inks, which are colloidal dispersions of the ionomer and catalyst particles, dispersed in solvent. CL studies are complicated by the multiple material types used (varying ionomer chemistry, catalyst loading, carbon support type, solvents) and disparate ink deposition and drying methods that render no two CLs alike; this makes it difficult to compare across these different studies. Additionally, within the community, CL fabrication has traditionally been treated as a black art, and the details of the fabrication process (ink composition, casting method, etc.) are typically inconsistently reported, because emphasis has been placed on understanding CL properties and performance and not the forces controlling that formation process. However, it is increasingly clear that simply being able to characterize CLs is not enough. To enable predictive control and rational design of CLs, it is vital to understand how and why (in addition to what) specific microstructures form. This dissertation sets out to uncover systematically the underlying fundamental interactions between the ink components in solution, which ultimately govern CL microstructure (agglomerate structures and sizes, ionomer coverages, etc.) and performance once cast. We begin by introducing all relevant parameters in the CL ink fabrication process and conducting a literature-based parameter screening to test correlation between ink variables and performance metrics. The analysis reveals that while no single parameter is controlling, solvent identity and ionomer-to-catalyst-particle ratio correlate well with performance metrics. This suggests ionomer/solvent, ionomer/particle, and ionomer/solvent/particle interactions merit further investigation. To probe the specifics of these interactions, we build our understanding piecewise. The first part of this dissertation is dedicated to the investigation of ionomer/solvent interactions. We use a range of water/propanol ratios to probe the influence of solvent on these interactions. Water/propanol ratios are chosen because they are (1) the most commonly used solvents, (2) represent a range of water contents (relevant for studying hydrophobic/hydrophilic interactions), and (3) encompass a wide range of dielectric permitivities. We first explore the solution structure of ionomer dispersed in various water/propanol ratios, and how these different conformations affect the in situ evolution of thin-film morphology via x-ray scattering. Higher-water-content dispersions exhibit enhanced ordering of primary ionomer aggregates, and fewer secondary aggregates, which affect the final structure of the films; this results in thin films and membranes with improved transport. Having established a strong link between ionomer/solvent dispersion interactions and the cast state, this dissertation focuses on additional details of the ionomer/solvent interaction and how it may influence catalyst-particle aggregation behavior. We uncover that solvent has a strong effect on the acidity of these dispersions, and that this acidity change is likely due to solvent-induced conformational differences. Additionally, this ionomer/solvent interaction is sensitive to ionomer concentration, wherein acidity does not scale linearly with ionomer concentration, again suggesting it is in part attributed to conformational differences (i.e. aggregation) across the different compositions. The increased acidity with increasing water content propagates to alter particle interactions: acidity strongly influences the electrostatic interactions between the ionomer and catalyst particles in an ink. These pH measurements are then used to probe a third dimension to this solvent/ionomer parameter space by considering the temporal stability of these dispersions. The ionomer slowly equilibrates to new solvent environments over the course of many days: lower ionomer concentrations and water/propanol composition extremes affect this change more drastically. Once again, these conformations persist to membranes upon casting and annealing.To study ionomer/particle interactions further, isothermal titration calorimetry measurements are used to extract quantitative binding affinities of ionomer to both platinum and carbon nanoparticle surfaces as a function of ionomer charge density. There exists a nonmonotonic relationship between the number of charged groups in the ionomer and its binding affinity. The binding affinity is modeled to extract the entropic and enthalpic contributions to the binding free energy, critically revealing that binding to both platinum and carbon surfaces is governed by a similar entropy-dominated mechanism. This finding is counter to the prevailing hypothesis in literature that ionomer/particle ink association is due to inherent, strong specific-ion (enthalpic) interactions between the ionomer and platinum, and it reveals that ink interaction mechanisms operate in different modes than those occurring operando in the fuel cell. Therefore, extrapolation from well-studied fuel cell systems to ink systems should be avoided because of differences in charge states of the platinum surface; this leads to a new reinterpretation of existing data. We compliment the calorimetry results with a wide parameter screening using quartz crystal microbalance: we probe ionomer adsorption from solution onto crystal surfaces with a range of different surface functionalities (varying hydrophobicity, metal type, and surface chemistry). Importantly, the findings from the above ionomer/solvent interaction studies inform this ionomer/particle interaction investigation by considering adsorption to these different surfaces both as a function of ionomer charge density as well as water/propanol ratio. In inks (under no applied potential) data reveal that higher-water-content dispersions promote adsorption to all surface types, and adsorption to hydrophobic surfaces (like carbon) is higher than adsorption to platinum. In sum, these ionomer/particle interaction investigations suggest that the ionomer/catalyst particle interactions in inks are dominated by ionomer/carbon interactions, rather than ionomer/platinum interactions.Finally, the results of the preceding sections are used to inform a case study examining the influence of platinum versus carbon nanoparticle surface area on ink interactions, CL microstructure, and fuel-cell performance. Catalysts with varying platinum loadings are used to explore the zeta potential of inks with varying ionomer-to-particle ratios. A direct correlation between ink zeta potential and CL local-transport resistance is established. Furthermore, we demonstrate that particles with higher carbon surface areas can support more ionomer, likely leading to more uniform coverage and lower CL transport resistance. The fundamental ink interactions uncovered here provide insights into CL performance and lay the groundwork for design rules to select for desired CL microstructures by manipulating ink parameters not only for fuel cells, but similar energy-conversion technologies from CO2 electrolysis to chemical synthesis to water treatment.

The conventional power system undergoes a massive change owing to the penetration of distributed generators into distribution networks and the standalone operation of microgrids. The characteristics of distributed generators largely depend on power electronic interfaces that are not matched with conventional synchronous machine-based generation systems. The changing behaviours of the distribution side of the electrical network continue to provide new challenges to power system design and operation engineers. To overcome such issues, the design of high-performance controllers plays a crucial role. In addition, investigation of the dynamic behaviours of the power electronic interfaces, including switching frequency is essential, which is the critical characteristic of the distributed generators. The first contribution of this dissertation is the design of a robust nonlinear controller to enhance the transient stability of distributed generators. In this work, the feedback linearization technique is used to linearize the standalone solar photovoltaic including battery energy storage, grid-connected fuel cell, and grid-connected solar photovoltaic including battery energy storage systems. Robust H_\infty mixed-sensitivity loop-shaping controllers are designed to stabilize the linearized part of the nonlinear feedback linearized control laws. The proposed robust H_\infty controller for the feedback linearized control scheme provides several benefits over the existing feedback linearization that is stabilized by the conventional PI controller. The second and unique contribution of this thesis is the developed single-input two-output feedback linearized control scheme based on the conventional single- input single-output feedback linearization approach. The third contribution of this dissertation is single-input two-output controller design for the islanded DC, AC, and hybrid DC/AC microgrids to enhance the voltage stability and minimize the circulating current among parallel-connected distributed generators. The fourth and final contribution of this work is the developed multi-frequency averaging based dynamic phasor model of a standalone, grid-connected, and two-stage distributed photovoltaic generators. The developed dynamic phasor models are provided with switching frequency-dependent characteristics, showing the switching frequency effect on the distributed generators. This contribution provides the idea of a suitable switching frequency range for power electronic interfaces.

Highly efficient electric power systems are crucial for the reduction of carbon emissions from fossil fuels, as well as, in a circular economy where renewable fuels like biogas, biomass and hydrogen need to be converted to electricity in an efficient manner to minimize the environmental footprint. Moreover, current thermoelectric electricity generation requires enormous amounts of water, primarily for cooling or heat rejection, which creates tensions and interdependencies between the electricity sector and the water sector. To address these concerns, this dissertation focuses on the design of highly efficient, economically viable solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid systems to minimize the environmental impact of electricity generation including the water use, and further addresses the system integration and the economics of flue gas water recovery technologies.Two of the greatest challenges to widespread adoption of SOFC technology are thermal cell management and costs. Applying a unique bottom-up SOFC cost approach, cell design parameters are identified that synergistically reduce thermal gradients and specific SOFC stack cost. Using this optimized cell design, the SOFC stack is integrated into a SOFC-GT hybrid system. Through research of this SOFCGT hybrid system over a wide range of pressure conditions, fuel utilization factors, and operating voltages, cost-competitive operating points and major cost driving factors contributing to the cost of electricity are identified while considering thermal SOFC and GT aerodynamics constraints associated with SOFC-GT systems. Based upon the results of the hybrid system design study, multiple water recovery technologies, such as an air-cooled condenser, a direct contact condenser, a LiBr absorption system, a monoethylene glycol absorption system and a transport membrane condenser, are integrated into the hybrid and studied in combination with various fuel types at numerous scales. In the studied configurations, the direct contact condenser and the transport membrane condenser suffer from low water recovery rates, while the air-cooled condenser’s large pressure drop leads to substantial system integration losses. The absorption systems achieve the highest water recovery rates and the LiBr absorption system exhibits the most favorable economics. The absorption systems are particularly advantageous in biogas scenarios where the latent heat can be upgraded and made available to the digester.

Energy crisis and climate change are the imminent challenges faced by mankind that demand instant solutions in replacing fossil fuels with alternative clean energy sources. To meet this demand, the hydrogen fuel cell industry has witnessed tremendous growth within the past decade. However, the broad dissemination of proton-exchange membrane fuel cells (PEMFCs) is still limited by the high cost originated from the high loading of platinum-group metals (PGM) based catalysts to accelerate the sluggish oxygen reduction reaction (ORR) at the cathode. Therefore, it is central to design high-performance ORR catalysts and validate their performance in the membrane electrode assembly (MEA). In the first chapter of my dissertation, by combining theoretical modeling and experimental observations, we developed a binary experimental descriptor (BED) that directly correlates with the calculated oxygen binding energy ∆E O on Pt-alloy catalyst surface. The BED captures both the strain and Pt-transition metal coupling contributions based on experimental parameters extracted from X-ray absorption spectroscopy. This leads to an experimentally validated Sabatier plot wherein the BED can be used to predict not only the catalytic activity but also the stability of a wide range of Pt-alloy ORR catalysts. Based on the BED, we further designed an ORR catalyst wherein high activity and stability are simultaneously achieved. The second chapter is an extension of the first chapter, in which I demonstrated that tetrahedral PtCuNi catalysts, as an efficient multifunctional catalyst, did not only showed excellent ORR performance but also exhibited high methanol/ethanol oxidation reaction (MOR/EOR) performance, which can be potentially used in the direct methanol/ethanol fuel cells (DMFCs/DEFCs). By tailoring the surface composition, the optimal catalyst with a composition of Pt56Cu28Ni16 showed a MOR and EOR specific activity (SA) of 14.0  1.0 mA/cm2 and 11.2  1.0 mA/cm2, respectively; and mass activity (MA) of 7.0  0.5A/mgPt and 5.6  0.6 A/mgPt for the MOR and EOR, respectively. In the third chapter, I applied some highly promising ORR catalysts in MEA. In specific, I developed an ultralow Pt loading (total loading of 0.072 mgPt/cm2) and high-performance MEA using ultrathin platinum-cobalt nanowires (PtCoNWs) as cathode catalysts. The PtCoNWs showed a high ECSA of 73.2 m2/gPt and achieved an unprecedented MA of 1.06 � 0.14 A/mgPt [0.9 ViR-free] at the beginning of life (BOL) stage in MEA. This MA is 3.3 times that of the commercial Pt/C (0.32 A/mgPt) and far surpasses the Department of Energy (DOE) 2020 target (0.44 A/mgPGM). The PtCoNWs reached a peak power density of 1016 mW/cm2, outperforming the PtNWs (830 mW/cm2) and Pt/C (773 mW/cm2) with comparable Pt loading. After the AST, the PtCoNWs showed a respectable end of life (EOL) MA of 0.45 A/mgPt, remaining above the DOE 2020 BOL target. In the last chapter, I tried to tailor the interfacial properties to further enhance the surface microkinetic. In brief, I developed a facile and controllable molecular surface modification approach using dimethylformamide (DMF) to successfully improve the ORR performance of Pt-based catalysts. Significantly, our molecular dynamics (MD) simulations elucidated that DMF can disrupt interfacial water hydrogen-bonding networks, therefore allowing accelerated water exchange kinetics, facile O2 transport towards Pt surface, increased interfacial oxygen concentration, and adsorption time (around twice compared to pure Pt(111) surface), justifying enhanced ORR activity. We further applied this approach to a model Pt-alloy catalysts (PtCuNi), which achieved an unprecedented SA of 21.8 � 2.1 mA/cm2 at 0.9 V versus the reversible hydrogen electrode (RHE), about 2.65 times improvement comparing to original PtCuNi catalysts, and nearly double previously reported the best value, leading to an ultrahigh MA of 10.7 � 1.1 A/mgPt. Importantly, after 20,000 cycles of accelerated degradation tests (ADT), surface-modified PtCuNi showed even better SA and MA than the initial performance of original PtCuNi, suggesting the surface modification can also considerably extend the lifetime of the catalyst.

Proton exchange membrane fuel cell (PEMFC) technology provides a sustainable power solution as it electrochemically converts the chemical energy stored in hydrogen molecules into electricity, heat, and water. The electrochemical reactions occurring in the catalyst layer (CL), however, requires the use of precious group metal (PGM) catalysts, such as platinum, which is a major factor contributing to the high cost of PEMFC technology. To reduce the cost, there have been extensive research efforts in developing low-PGM and PGM-free catalyst materials. Nevertheless, the CLs incorporating these novel materials are often found to suffer from severe mass transport resistance resulting in significant performance loss. Based on the literature, this undesired mass transport resistance is mainly attributed to the cathode oxygen transport due to the heterogeneous characteristics of the hierarchical microstructure of the CL. Although a standard CL only contains carbon supported catalyst and ionomer, understanding the formation of the structure and the origin of the structural characteristics have been very challenging due to its complicated preparation process. A CL is usually prepared by an ink casting method, which involves multiple steps. The catalyst ink consists of the CL constituent materials uniformly dispersed in a liquid medium forming a suspension, which has an opaque, heterogeneous, and highly time-sensitive nature making the experimental investigation on the particulate structure in the catalyst ink very challenging. Despite the long history of using the CLs, a principled framework for understanding the structure-property relationship of the CLs has not yet fully developed. To advance the design and development of low-cost and robust CLs, this research 1) conceptualized a physical process capturing the key aspects of the particulate structure formation with respect to the CL fabrication process, 2) based on the complex fluid nature of the catalyst ink, designed a holistic non-destructive hierarchical approach to investigate the particulate structure in the catalyst ink, and 3) qualitatively and experimentally established the formation-structure-process-functionality relationship for CLs. With the newly proposed framework, this research advances current understanding on the structure-property relationship of the CLs and provides novel and practical insights into the design of low-cost functionality-tailored CLs.

With the development of hydrogen fuel cell technology continuing to advance, rapid characterization of membranes is increasingly important for design purposes. Pressurized blister testing has been suggested as an accelerated characterization alternative to traditional relative humidity (RH) cycling tests, and is the focus of this project. Prior efforts to determine the stress state present in the pressurized membrane blister test, however, have required constitutive properties of the membrane (Young's modulus and Poisson's ratio), along with Hencky's classic model for circular membrane stresses. Herein we describe an analysis method and computer vision imaging technique that are capable of determining the stress state in a pressurized circular membrane based solely on simple equilibrium equations and geometric considerations. This analysis method is applied to an image of the blister during testing, and the only additional required data is the pressure at the time the image was taken. By pressurizing circular blisters, an equi-biaxial, mechanical stress state is induced, simulating membrane stresses experienced during fuel cell operation as humidity levels fluctuate. The analysis leverages membrane theory and the axisymmetric geometry to determine the stress state from a profile image of the inflated blister. As a check for the method, an elastomer with known constitutive properties was analyzed using both the previous Hencky's solution method, as well as the new computer vision imaging method. The comparison of stress calculation results show that the two methods agree within 5 percent. A primary mechanism of membrane failure through mechanical stressors is the growth of local defects (usually chemically induced) due to the cyclic equi-biaxial stress state. In order to better understand and characterize the effect of disparate initial defects on CCM, two primary methods to defect membranes were introduced. The first was a compression against sandpaper method meant to simulate GDL compression, and the second was a targeted method using a hypodermic needle to initiate a defect at a central location on the membrane prior to pressurization. Observing the pressure decay in these defected blisters as compared to undefected tests showed that, while undefected samples did not experience pressure decay until failure, defected samples began showing signs of leaking through pressurization cycle profiles and steady state pressures achieved. Pressure data showed that samples tended to lose pressure more quickly with increasing initial defect severity. Undefected samples exhibited no pressure loss until the moment of failure, which was often catastrophic and instantaneous. Sandpaper defected samples exhibited a slow decay in cycle steady state pressure throughout tests, with no increase in cycle pressurization time. Needle samples showed a slow decay in cycle steady state pressure as well as an increase in time for the cycles to reach steady state. The needle defects were the most locally severe and thus the pressure decay indicators were most significant out of all the samples tested. The blister test method rapidly cycles mechanical stresses in a CCM, and elucidates signs of leaking that correlate to flaw development in recorded pressure data. With further development, it might serve as a robust method to quickly test flaw growth rate and development in CCM samples.

In this dissertation, new electroanalytic measurements and electron microscopy observations are applied to obtain fundamental understanding of how the incorporation of bismuth (Bi) with platinum (Pt) either as an alloy or a surface adatom Pt enhances the dimethyl ether electrooxidation reaction (DMEOR). Previous works have shown that incorporating other metals into a Pt electrocatalyst, such as Ru, Cu, or Bi, enhances electrooxidation activity toward DME, formic acid, ethanol and other organic compounds. When incorporated in alloy form and then dealloyed, these metals can potentially benefit structure sensitive electro-oxidation reactions through both the electronic effect of alloying as well as by increasing the strain in the Pt lattice structure when dealloyed, altering the bond length. When surface adatoms or complexes are used, they can also prevent poisoning of the catalytic surface by promoting the oxidation of intermediate species such as COads through either bi-functional or ensemble effects. The role of atomic surface structure in Bi-modified catalysts on DMEOR activity has not been previously revealed. In addition, while previous research has demonstrated the improved durability of Bi-containing electrocatalyst during DMEOR, an explanation as regards how poison resistance correlated to surface reactivity was not provided.

Carbon-based composite materials have long been fabricated and extensively used in our daily lives. In the past decades, with rapid development of nanotechnology, these class of material have gained even more attention owing to their outstanding properties which directly results in their prospects to revolutionize technological development in many fields, ranging from medicine to electronics. Nevertheless, for certain applications, including electrochemical energy storage/conversion devices, the chemically inert nature of these materials creates obstacles and thus requires their coupling with other active species. This thesis explores the use of Laser Ablation Synthesis in Solution (LASiS) in tailoring promising strategies and pathways for the synthesis of carbon-based hybrid nanocomposites, more specifically herein I present (1) the synthesis of metal-oxide/ reduced-graphene-oxide hybrid nanocomposites and the rational-design of their structure–property for selective improvements in electrocatalytic/ and or supercapacitive properties, (2) the fabrication of nanoparticles within Metal-Organic Frameworks (MOFs) and characterization of their performance as electrocatalysts for Oxygen Reduction Reaction (ORR). For each synthetic route, a comprehensive analysis of reaction pathways, formation mechanisms and structure-property relationship is developed taking into account elemental, structural, physicochemical and morphological characterizations of the final products, setting the ground for use of LASiS for the rational design and synthesis of a wide library of diverse carbon-based nanocomposites structures in future.

In SOFCs, we observe that the porous electrodes tend to agglomerate and thus decrease the cell performance over time. The agglomeration (or sintering) of a porous oxide can be understood as the diffusion of the oxide atoms along the surface of a material to minimize the surface energy of the structure. Therefore, even an ultrathin overcoat is expected to deter the sintering process and thus maintain the porous geometry for longer period of time. In this thesis, the actual role of YSZ overcoat in the ORR process is presented through a series of electrochemical analyses. Without an overcoat, a nanoporous Pt is significantly agglomerated during a high-temperature operation, and ORR kinetics becomes limited by the availability of TPB. An ultrathin YSZ overcoat significantly suppressed the sintering kinetics and preserved the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic oxygen species-mediated chemical process(es), which used to be rate-limiting in the ORR of a non-coated Pt/YSZ system. In the next step, to understand the impact of spincoated layer on the interface of cathode/electrolyte, EIS data obtained at different temperatures and oxygen partial pressures. Beside SEM imaging and XRD, to support the hypothesis of ORR kinetics, infiltration and ALD coating also performed on different samples. We found out that spin-coated layer has smaller nanoparticle sizes and 3~4 times smaller nanocrystalinity that increase the active cites for dissosiative adsorption on the cathode side, comparing to the available cites on bare LNF. EIS data along with ALD coating also strongly support the hypothesis that ion conducting pass through the LNFGDC FL playes an important role in decreasing the polarization resistance comparing the bare LNF cathode as well. It helps the available cites not limited to the vicinity of GDC interlayer but be available in entire FL and the ion transport to the GDC interlayer through GDC nanoparticles paths. To sum up, a combination of nanoscale treatments including cathode infiltration, metal oxide ALD coating, and cathode-electrolyte interface spin-coating pursued to achieve a significantly enhanced performance and durability by addressing the issues. In addition, I also performed a systematic studies on the change in electrochemical kinetics and a possible shift of bottleneck process by the treatments to better understand the effect of each of this nano-functionalization on oxygen reduction catalysis process in SOFCs.

Fuel cells can potentially become a practical solution for solving the emerging energy crisis. Platinum nanoparticles are used as electrocatalyst for oxygen reduction reaction. Many synthesis methods exist that produce platinum nanoparticles supported by carbon support. The goal for synthesis is to increase its performance and reduce its loading. In this paper, we successfully synthesized Pt nanoparticles within 2.09 ± 0.76 nm range with the alternating current method. With this one-step, top-down method, Pt nanoparticles were produced by simply applying the square wave potential to the Pt wire without adding any additional chemicals. Besides, the rotating disk electrode (RDE) measurements suggest this method has a possibility to increase the performance of the Pt nano catalyst. Moreover, we explored the mechanism of the generation of nanoparticles and proposed the critical potential range for this method. And we first reported the Pt formation in neutral and acid electrolyte.

A techno-economic analysis was conducted for a 100% renewable energy-based standalone microgrid system comprising of solar PV, battery energy storage and Power to Hydrogen(P2H) system (comprised of Electrolyzer, Fuel Cell and Hydrogen Storage Tank). Hydrogen is gaining widespread interest globally as an energy carrier as well as a storage medium. This study evaluates the potential of hydrogen systems to utilize (in fuel cells) and store (in the form of compressed hydrogen) excess renewable electricity generated which otherwise would be curtailed.Four scenarios (including a diesel generator only base-case scenario) were investigated for a 25 year project lifetime period to select the most optimal set of energy technologies to meet load requirements of a microgrid in San Diego, CA. The microgrid had an electrical load of around 2900 kWh/day and peak annual load of 312 kW. The microgrid design optimization tool HOMER Pro was used to design, model, and simulate the energy technologies and to analyze and compare the energy balance, economics, and environmental emissions amongst the proposed scenarios. A sensitivity analysis was performed to evaluate design robustness against the uncertainty pertaining to fuel cell and electrolyzer costs. The simulation results showed that a hydrogen-battery based renewable hybrid energy storage system minimized total net present cost, and levelized cost of energy technologies. The proposed hybrid energy system has the potential to be deployed to a 100% renewable energy based standalone microgrid system, with low energy generation costs and facilitating in decarbonization efforts.

Laser powder bed fusion (LPBF), as a popular additive manufacturing (AM) technique, has gained a great deal of research attention and industrial application. Its capability of producing complicated shapes and structures enables this technique to be favored for manufacturing critical prototypes and complex parts. Meanwhile, LPBF techniques also have a significant advantage over many other AM processes that is they do not require support structure which allows more interest in producing parts with higher complexity since overhangs and unconnected islands are supported by surrounding unfused powder bed instead. However, in fabrication, the constant melting and cooling of metal powders by layers leads to a large gradient and rapid evolution of temperature, causing considerable residual stress and deformation. Fuel cells are widely regarded as a promising candidate as the next-generation energy device, which electrochemically converts the chemical energy in the injected fuel, such as hydrogen gas, directly to electricity. Fuel cell components are required to be free of distortion to avoid leakage of reactant gases and contaminants and interfacial resistance. In this study, a three-dimensional thermal analysis model is employed to numerically study the residual stress and deformation in the LPBF fabricated inlet/outlet of a fuel cell that connects to its bipolar plate. Inconel 718 and stainless steel SS316L are used as the powder materials, respectively. The results of distortion are validated against both experimental and other modeling data. Additionally, the validated tool is employed to investigate several major parameters in LPBF fabrication and their impacts on distortion, including the laser power, laser speed, and layer thickness. It is found that the laser power and speed have a significant impact on the distortion of the pipe wall, while the scan pattern shows little influence. Additionally, SS316L shows a much less distortion (about 40 µm) than that of In718 which is about 90 µm for the maximum distortion and a nearly 30% smaller average distortion at all measuring locations.

The world’s railway system is responsible for approximately 1% of the total anthropogenic carbon emissions [1]. Fuel cell hybrid systems can theoretically meet the power and dynamic operating requirements of locomotives and provide an efficient, low emission and potentially affordable way to decarbonize rail. In this work, different ways of hybridizing Solid Oxide Fuel Cells (SOFCs) are analyzed to determine the best way to power trains in the future. CO2First, the development of a Solid Oxide Fuel Cell-Reciprocating Engine (SOFC-RE) hybrid system model on MATLAB Simulink is reported. The steady state system efficiency while operating on natural gas is 68.8% compared to 66.1% for a stand-alone SOFC. The cell voltage in the SOFC is 0.802 V with a current density of 0.623 A/cm2. The SOFC-RE outperforms a stand-alone SOFC, but not an SOFC-Gas Turbine (SOFC-GT) hybrid system, which has an efficiency of up to 72.2%. The model and results can be used to predict the performance and aid in design of hybrid systems of this kind for both stationary and transportation applications. Second, the simulation of a Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT) hybrid system for a locomotive application is presented. Using MATLAB Simulink, a 2.8 MW SOFC system was combined with a 500 kW GT and simulated to travel the route from Bakersfield to Mojave in California. Elevation data was imported using the Google Application Programming Interface (API) and smoothed to calculate the dynamic power demand for the SOFC-GT system, assuming 480 tons of freight per 120-ton locomotive traveling at an average speed of 45 mph. The SOFC-GT system model follows this demand without causing a significant disruption to the speed of the locomotive. A lithium-ion battery was included into the system model to improve the net system efficiency with regenerative braking and make the operation smooth enough for the highly dynamic route power demands. The overall efficiency along the simulated route has been estimated as 57% operating on partially pre-reformed compressed natural gas (CNG) fuel. These results suggest that SOFC-GT systems are promising for the future of freight rail transportation throughout the United States. CO2 and particulate matter emissions are significantly reduced compared to current diesel-electric locomotives and it is also possible to operate the system on hydrogen to make it completely emission-free. Third, different scenarios for how to the use of a renewable hydrogen-powered hybrid SOFC-GT system used in both freight and passenger trains are considered. A techno-economic analysis is performed to evaluate the potential emission reductions and the direct costs associated with this conversion. The corresponding reduction in carbon dioxide emissions ranges from 1.07% to 3.05% of global carbon emissions and the expected demand for renewable hydrogen is annually between 30 and 50 million metric tons, with future costs ranging from $45-75 billion. Moreover, this technology offers the potential to reduce global carbon emissions by up to 15%, if more aggressive adoption occurs. A case study for the U.S. in which the necessary renewable energy infrastructure is designed. It is shown that in order to decarbonize the transportation sector, zero-emission hydrogen-powered trains are both essential and viable in terms of technical, economic, and practical feasibility.

Reducing greenhouse gas (GHG) emissions to mitigate the impact of climate change is a critical mission of policy makers in California. In September 2018, Senate Bill 100 (SB100) was ratified, requiring California to obtain 100% of its power from clean sources by 2045. This law also required utilities to generate 60% of their power from renewable sources by 2030.Transitioning to a zero-emission portfolio requires significant investments and should be accomplished in multiple stages. In each stage, the impact of changes in the system on the emitted GHG should carefully be analyzed. This will ensure the best transition path to achieve the goal of 100% renewable energy penetration in California is chosen. In this dissertation, first, the impact of change in throughput on the change in methane emissions, which is one of the major sources of GHG emissions, is studied. The analysis identifies major methane emissions sources from the upstream of natural gas system and their dependencies on time, event, and throughput. A new cause-based model is developed using the marginal methodology to estimate the change in methane emissions with the change in throughput. The impact of the marginal change in methane emissions when the total throughput changes by 5%, 15%, 30%, and 50% in either direction is studied. The effect of system expansion and reduction as well as the technological improvements is also considered. Next, the capacity of Southern California natural gas infrastructure to support a zero-emission portfolio is studied. A transient model is developed to determine the amount of additional solar farms, pipeline network capacity, and underground storage facilities that are required to achieve 100% renewable energy penetration. Different scenarios are analyzed, and the most cost-effective option is identified. Finally, the impact of injecting hydrogen in the existing natural gas infrastructure of Southern California is studied. It is shown that with hydrogen mix of 2% vol., all of the network constraints are met while increasing the hydrogen mix to 20% vol. requires some adjustments to the current pipeline network and compressor stations to ensure all the constraints are met. The effect of hydrogen injection location points on the hydrogen carrying capacity is investigated.

Multicopters are important tools in industry, the military, and research but suffer from short flight times and mission durations. In this thesis, we discuss three different ways to increase flight times and therefore increase the viability of using multicopters in a variety of missions. Alternate fuel sources such as hydrogen fuel and solar cells are starting to be used on multicopters, in our research we simulate modern fuel cells and show how well they currently work as the power source for multicopters and how close they are to becoming useful in Unmanned Aircraft System (UAS) technology. Increasing the efficiency in which the available energy is used can also increase mission duration. Two characteristics that affect the efficiency of a mission are the flight speeds of the multicopter and the payload it carries. These characteristics are well known in larger rotorcrafts but often ignored in smaller multicopters. In our research, we explore the effect of flight speed on the dynamics of a multicopter and show that higher speeds lead to higher flight times due to the effect of translational lift. Lastly, we developed an online updating multi-flight planning algorithm for stop and charge missions, a method that can potentially indefinitely extend a mission. The multi-flight planning algorithm, the variable resolution horizon, reduces the computing resources necessary to 15% to 40% of a typical optimal planner while having a maximum 5.6% decrease in expected future reward, a metric for accuracy. The results of this thesis help guide decisions in fuel type for multicopter missions show examples of how to increase flight time through increasing efficiency and develop the framework for multi-flight missions. Advisers: Justin Bradley and Carrick Detweiler

The purpose of this project is to model the operation of a proton exchange membrane (PEM) fuel cell during operation in weather as cold as -40 °C. The fuel cell must be kept above the freezing point of water, and it is hypothesized this can be done by utilizing the heat produced in the system. The system is being designed to provide off-grid power for operation of various scientific sensors requiring power output of 20 W at a potential of 12 V. A fuel cell combines hydrogen and oxygen to form water, heat, and electricity. Process steps include generating hydrogen from the alcoholysis and/or hydrolysis of sodium borohydride, creating electricity from the fuel cell to charge a battery, and preheating feed air to provide oxygen to the fuel cell. The project explores 1) modeling of the reaction kinetics for hydrogen production, 2) modeling the efficiency and kinetics of the catalytic reaction between the generated hydrogen and oxygen from air within the fuel cell, and 3) modeling heat flow within the system to preheat the incoming air and maintain good fuel cell temperature. The reaction kinetics show sufficient hydrogen production to keep the fuel cell running as specified. The modeled efficiency gives an average efficiency just above 50% for the conversion of chemical potential energy to usable power. The heat flow, assumed to be 1-dimensional, shows sufficient heat transfer to keep the area around the fuel cell above the freezing point of water as modeled.

Hydrogen fuel cells in fuel cell electric vehicles (FCEVs) are a promising technology to reduce, and eventually eliminate, carbon dioxide emissions from transportation. The Pt nanoparticles used to catalyze the fuel cell’s electrochemical reactions are an important limiting factor because at present levels, the cost of the Pt catalyst will prevent widespread adoption of FCEVs. Catalysts must be developed to reduce the amount of Pt while meeting vehicle power demands even after many years of use. Strategically improving catalysts requires detailed and statistically robust characterization of their microscopic structure to understand the connections between catalyst synthesis, structure, performance, and durability. This dissertation presents the development and application of (scanning) transmission electron microscopy ((S)TEM) techniques to guide advancement of catalysts through nanostructural characterization. We develop a robust strain mapping technique for complex catalyst specimens. We deploy a new exit wave power cepstrum (EWPC) transform to nanobeam electron diffraction (NBED) patterns to enable precise, high-throughput, dose-efficient strain measurement. This approach is suitable for statistically representative measurements of many particles without special requirements such as zone-axis orientation. We apply this strain mapping technique to core-shell Pt-Co nanoparticles in combination with a continuum elastic theory model and demonstrate two mechanisms contributing to the relaxation of strain at the catalyst surface: lattice dislocations and Poisson expansion due to the spherical geometry. Comparison with electrochemical measurements suggests that the geometrical Poisson relaxation accounts for the activity of catalysts with thin shells, but catalysts with thick shells experience additional activity loss from dislocation-driven relaxation. We then turn to the larger-scale catalyst structure, investigating the impact of porous carbon support morphology, local reactant transport, and catalyst durability. Using statistical analysis of STEM images, we compare Pt and Pt-Co catalysts on porous and solid carbon supports. Comparison of 3D tomographic images and electrochemical accessibility measurements indicated that carbon pores prevent ionomer adsorption for particles embedded within them, improving the catalyst activity, while allowing proton access through condensed water. By comparing images and composition maps before and after electrochemical stability tests, we find that porous carbon supports suppress Pt particle coalescence, accounting for improved overall durability.

The depletion of fossil fuels and global warming require the application of highly efficient and sustainable energy conversion devices, like fuel cells. However, the sluggish kinetics of the oxygen reduction reaction (ORR) on the cathode has significantly hindered the widespread implementation of fuel cells, which stimulates the development of highly active and durable electrocatalysts. Enormous progress has been made on both precious metal and non-precious metal catalysts, including Pt/Pd alloyed nanoparticles, transition metal oxides and nitrogen doped carbon materials. In this thesis, a bifurcated strategy involving the rational design and in situ mechanistic investigation has been proposed and conducted. Via different synthetic routes, a variety of nano-structured materials has been prepared, including Pt-based structurally ordered intermetallics, core-shell structured nanoparticles with Pt surface decoration, tri-metallic spinel oxides, bimetallic organic framework (BMOF) derived carbon materials and nitrogen-doped BMOF-derived Pt-Co nanoparticles. They are featured with distinctive properties to adapt various working conditions, for the ground transportation or stationary applications, for proton exchange membrane fuel cells (PEMFCs) or alkaline exchange membrane fuel cells (AEMFCs). For example, Pt-based catalysts exhibit excellent electrocatalytic activities with a relatively high Pt utilization efficiency, making them suitable as promising candidates in the acidic electrolyte for fuel cell vehicles. Precious-metal-free catalysts demonstrate high activity, robust durability and cost effectiveness, which can be potentially applied in alkaline media for stationary applications. The in situ mechanism analysis of these materials consists of two parts: the first reveals the structural evolution of structurally ordered bimetallic intermetallics at high temperature, from both microscopic and macroscopic levels to determine the optimized synthesis condition for the Pt3Co intermetallic nanoparticles. The second part couples the electrochemical reaction with X-ray adsorption spectroscopy to elucidate the working and degradation mechanism of trimetallic oxides, which indicates the synergistic catalysis by Co and Mn, with Fe serving as the stabilizing agent. These analyses, in return, provide valuable insights for designing and optimizing related materials in the future.