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Due to increasing concerns about the ever increasing energy demand, the global energy system needs to transition away from fossil fuels, as they have been one of the main causes for climate change and air pollution. Fuel cells offer a good alternative to conventional thermal devices, as they usually use hydrogen and oxygen to produce electricity without greenhouse gases emissions. One of the main drawbacks to fuel cell commercialisation is the use of expensive catalysts, such as platinum, and their long-term stability under operation. Therefore, the design and study of cheap and durable catalysts is required to push the development of fuel cells. MXenes, a new family of two-dimensional transition metal carbides and nitrides materials, have shown some potential as support for ORR catalysts. However, the performance of electrocatalysts is directly related to the available surface where the electrochemical reaction could take place, and MXenes have pretty low specific surface areas compared to conventional supports used in the field of catalysis. This thesis reports the development of a synthesis method focused on improving the final catalyst surface area using MXene (Ti3C2) as support, by intercalating the precursors between the MXene layers before annealing. This is shown to lead to the formation of porous MXene structures, with increased surface area and decomposition products from the precursors on the surface of the MXene layers, which hindered the MXene layer restacking during thermal treatment. The samples where then tested in a three-electrode setup using the RDE method to evaluate the ORR performance of the synthesized materials. It was found that the addition of the precursors improved the overall performance of the materials. The different samples were also characterized to understand the connection between physico-chemical properties and electrochemical properties.

Pillared Ti3C2Tz MXene with a large interlayer spacing (1.75 nm) is shown to be promising for high-power Li-ion batteries. Pillaring dramatically enhances the electrochemical performance, with superior capacities, rate capability, and cycling stability compared to the nonpillared material. In particular, at a high rate of 1 A g–1, the SiO2-pillared MXene has a capacity over 4.2 times that of the nonpillared material. For the first time, we apply in situ electrochemical dilatometry to study the volume changes within the MXenes during (de)lithiation. The pillared MXene has superior performance despite larger volume changes compared to the nonpillared material. These results give key fundamental insights into the behavior of Ti3C2Tz electrodes in organic Li electrolytes and demonstrate that MXene electrodes should be designed to maximize interlayer spacings and that MXenes can tolerate significant initial expansions. After 10 cycles, both MXenes show nearly reversible thickness changes after the charge–discharge process, explaining the stable long-term electrochemical performance.

The demand of producing hydrogen energy in a more efficient and cleaner process has been a top priority for scientists as hydrogen energy is expected to be a splendid alternative of fossil fuel in many applications such as trains and airplanes. This thesis aimed to improve the efficiency of alkaline water electrolysis system by developing a low-cost catalytic coating on its anode that is made of stainless steel, where oxygen evolution reaction occurs. Nickel-iron based materials are main focus in this study due to their low price, high earth abundance and high activity towards OER. The thesis contained the cyclic voltammetry and linear sweep voltammetry results of metallic NiFe and NiFe (oxy)hydroxide prepared by electrodeposition and thermal deposition methods. Chronoamperometry was used to study the durability of the materials. The thesis also contains SEM images EDS mappings of coatings for morphological and elemental analysis. The most significant finding of the study is that NiFe hydroxide thin film prepared by electrodeposition improved OER drastically by showing 0.518 V overpotential at 10 mA cm-2. In a bench-scale single cell electrolyser test, the anode with NiFe hydroxide thin film generated 5.7 times as much columbic charge as electrode without coating when 1.6 V was applied for 30 minutes at room temperature and the electrolyte concentration was 0.1 M. These results indicate that the methodology can be applied to commercial scale of alkaline water electrolyser with stainless steel substrates for further testing.

Pollution reduction from waste management and energy generation is necessary to mitigate climate change and is one of the major challenges of the 21th century. This can be achieved through the development of innovative energy recovery technologies from biomass and wastes, such as microwave plasma gasification. An envelope of stable CO2 plasma operation is described, by varying working gas flow rate at applied microwave powers between 1 and 6 kW, whereas H2O plasma operation is possible with flow rate ranging from 20 to 50 g/min and microwave powers between 2.5 and 6 kW. The temperature generated in a large chamber connected to the plasma torch is recorded, reaching up to 850°C, showing a heterogeneous temperature distribution. In addition, optical emission spectroscopy measurements provide an insight into plasma chemistry and demonstrate the dissociation of CO2 and H2O molecules at extremely high temperatures of up to 6,300°C assuming local thermodynamic equilibrium. The experimental results demonstrate that the microwave plasma torch provides an ideal environment for gasification with high temperature and very chemically reactive species. This study provides valuable information for the design of microwave plasma gasification reactors with great potential for effective solid feedstock conversion into high quality syngas for energy production.

MXenes are a recently discovered class of two-dimensional materials that have shown great potential as electrodes in electrochemical energy storage devices. Despite their promise in this area, MXenes can still suffer limitations in the form of restricted ion accessibility between the closely spaced multistacked MXene layers causing low capacities and poor cycle life. Pillaring, where a secondary species is inserted between layers, has been used to increase interlayer spacings in clays with great success but has had limited application in MXenes. We report a new amine-assisted pillaring methodology that successfully intercalates silica-based pillars between Ti 3C 2 layers. Using this technique, the interlayer spacing can be controlled with the choice of amine and calcination temperature, up to a maximum of 3.2 nm, the largest interlayer spacing reported for an MXene. Another effect of the pillaring is a dramatic increase in surface area, achieving BET surface areas of 235 m 2 g -1, a sixty-fold increase over the unpillared material and the highest reported for MXenes using an intercalation-based method. The intercalation mechanism was revealed by different characterization techniques, allowing the surface chemistry to be optimized for the pillaring process. The porous MXene was tested for Na-ion battery applications and showed superior capacity, rate capability and remarkable stability compared with those of the nonpillared materials, retaining 98.5% capacity between the 50th and 100th cycles. These results demonstrate the applicability and promise of pillaring techniques applied to MXenes providing a new approach to optimizing their properties for a range of applications, including energy storage, conversion, catalysis, and gas separations.

Energy storage is a global critical issue and important area of research as most of the renewable sources of energy are intermittent. In this research work, recently emerged inorganic nanomaterial (MXene) is used for the first time with paraffin wax as a phase change material (PCM) to improve its thermo-physical properties. This paper focuses on preparation, characterization, thermal properties and thermal stability of new class of nanocomposites induced with MXene nanoparticles in three different concentrations. Acquired absorbance (UV-Vis) for nanocomposite with loading concentration of 0.3 wt.% of MXene achieved ~39% enhancement in comparison with the pure paraffin wax. Thermal conductivity measurement for nanocomposites in a solid state is performed using a KD2 PRO decagon. The specific heat capacity (cp) of PCM based MXene is improved by introducing MXene. The improvement of cp is found to be 43% with 0.3 wt.% of MXene loaded in PCM. The highest thermal conductivity increment is found to be 16% at 0.3 wt.% concentration of MXene in PCM. Decomposition temperature of this new class of nanocomposite with 0.3 wt.% mass fraction is increased by ~6%. This improvement is beneficial in thermal energy storage and heat transfer applications.

Energy storage is becoming a key challenge of the 21st century as the global energy system transitions away from the use of fossil fuels, which have been linked to damaging climate change and increasing air pollution. Electrochemical energy storage devices, such as batteries and supercapacitors, offer great potential to enable the clean energy transition, but require significant improvements to their performance characteristics such as energy density, power density and lifetime. The design and study of new electrode materials is key to achieving these improvements. MXenes are a new class of two-dimensional transition metal carbides and nitrides which have shown early promise in the field of electrochemical energy storage. Particularly interesting is the discovery of pseudocapacitive intercalation as their charge storage mechanism, since this could enable high power and energy densities with long cycling lifetimes into one device. However, the performance of MXene electrodes greatly depends on the electrode architecture, with multilayered or restacked MXenes showing unsatisfactory performances. This thesis reports on the development of pillaring techniques to increase the interlayer spacing between MXene (Ti3C2 and Mo2TiC2) sheets creating porous electrode architectures. This is shown to lead to large increases in the interlayer spacings, with up to 60-fold increases in the specific surface areas, among the highest reported for MXenes to-date. The pillared MXenes are then tested in a variety of systems for metal-ion capacitor applications, including organic Li-ion and Na-ion and aqueous Zn-ion systems. It was found that the pillared materials outperformed the non-pillared materials in each system studied, with improvements in capacities, rate capabilities, cycling stabilities and coulombic efficiencies. In addition, the pillaring and electrochemical mechanisms are studied using a combination of microscopy, spectroscopy and electrochemical techniques, providing import

Microwave-induced plasma (MIP) is an innovative technology with potential application for waste treatment and clean energy generation. The study presents the investigation of an MIP torch operated with carbon dioxide and steam. Optical spectroscopy measurements demonstrate the dissociation of CO2 and H2O molecules. This work shows that the MIP torch can generate a high temperature environment with very active chemical species, making it a promising technology for waste and biomass gasification.

Refers To Nuno Bimbo, Wesley Xu, Jessica E. Sharpe, Valeska P. Ting, Timothy J. Mays High-pressure adsorptive storage of hydrogen in MIL-101 (Cr) and AX-21 for mobile applications: Cryocharging and cryokinetics Materials & Design, Volume 89, 5 January 2016, Pages 1086-1094 The authors regret to inform that….. The Supplementary Information should have been included in the original paper and is now provided with this corrigendum. All the data and figures, contained in the manuscript and supporting information, are available and can be accessed free of charge at http://dx.doi.org/10.15125/BATH-00099. Any questions related to the data should be addressed to the corresponding author. Authors would like to apologize for the inconvenience caused.

Current state-of-the-art methods consist of containing highpressure compressed hydrogen in composite cylinders, with solid-state hydrogen storage materials an alternative that could improve on storage performance by enhancing volumetric densities. A new strategy that uses cryogenic temperatures to load hydrogen (cryocharging) is proposed and analysed in this work, comparing densities and final storage pressures for empty cylinders and containers with the high-surface area materials MIL-101 (Cr) and AX-21. Results show cryocharging as a viable option, as it can substantially lower the charging (at 77 K) and final pressures (at 298 K) for the majority of the cases considered. Kinetics are an equally important requirement for hydrogen storage systems, so the effective diffusivities at these conditions for both materials were calculated, and showed values comparable to the ones estimated in metal-organic frameworks and zeolites from quasielastic neutron scattering and molecular simulations. High-surface area materials tailored for hydrogen storage are a promising route for storage in mobile applications and results show that cryocharging is a promising strategy for hydrogen storage systems, since it increases volumetric densities and avoids energy penalties of operating at high pressures and/or low temperatures.

Current state-of-the-art methods consist of containing highpressure compressed hydrogen in composite cylinders, with solid-state hydrogen storage materials an alternative that could improve on storage performance by enhancing volumetric densities. A new strategy that uses cryogenic temperatures to load hydrogen (cryocharging) is proposed and analysed in this work, comparing densities and final storage pressures for empty cylinders and containers with the high-surface area materials MIL-101 (Cr) and AX-21. Results show cryocharging as a viable option, as it can substantially lower the charging (at 77 K) and final pressures (at 298 K) for the majority of the cases considered. Kinetics are an equally important requirement for hydrogen storage systems, so the effective diffusivities at these conditions for both materials were calculated, and showed values comparable to the ones estimated in metal-organic frameworks and zeolites from quasielastic neutron scattering and molecular simulations. High-surface area materials tailored for hydrogen storage are a promising route for storage in mobile applications and results show that cryocharging is a promising strategy for hydrogen storage systems, since it increases volumetric densities and avoids energy penalties of operating at high pressures and/or low temperatures.

Experimental hydrogen isotherms on several metal-organic frameworks (IRMOF-1, IRMOF-3, IRMOF-9, ZIF-7, ZIF-8, ZIF-9, ZIF-11, ZIF-12, ZIF-CoNIm, MIL-101 (Cr), NH2-MIL-101 (Cr), NH2-MIL-101 (Al), UiO-66, UiO-67 and HKUST-1) synthesized in-house and measured at 77 K and pressures up to 18 MPa are presented, along with N2 adsorption characterization. The experimental isotherms together with literature high pressure hydrogen data were analysed in order to search for relationships between structural properties of the materials and their hydrogen uptakes. The total hydrogen capacity of the materials was calculated from the excess adsorption assuming a constant density for the adsorbed hydrogen. The surface area, pore volumes and pore sizes of the materials were related to their maximum hydrogen excess and total hydrogen capacities. Results also show that ZIF-7 and ZIF-9 (SOD topology) have unusual hydrogen isotherm shapes at relatively low pressures, which is indicative of “breathing”, a phase transition in which the pore space increases due to adsorption. This work presents novel and more useful correlations using the modelled total hydrogen capacities of several MOFs. These total hydrogen capacities are more practically relevant for energy storage applications than the measured excess hydrogen capacities. Thus, these structural correlations will be advantageous for the prediction of the properties a MOF will need in order to meet the US Department of Energy targets for the mass and volume of on-board storage systems. Such design tools will allow hydrogen to be used as an energy vector for sustainable mobile applications such as transport, or for providing supplementary power to the grid in times of high demand.

Here we report direct physical evidence that confinement of molecular hydrogen (H-2) in an optimized nanoporous carbon results in accumulation of hydrogen with characteristics commensurate with solid H2 at temperatures up to 67 K above the liquid vapor critical temperature of bulk H2. This extreme densification is attributed to confinement of 112 molecules in the optimally sized micropores, and occurs at pressures as low as 0.02 MPa. The quantities of contained, solid-like H2 increased with pressure and were directly evaluated using in situ inelastic neutron scattering and confirmed by analysis of gas sorption isotherms. The demonstration of the existence of solid-like H2 challenges the existing assumption that supercritical hydrogen confined in nanopores has an upper limit of liquid H2 density. Thus, this insight offers opportunities for the development of more accurate models for the evaluation and design of nanoporous materials for high capacity adsorptive hydrogen storage.

We present results of investigations into improving methods by which gas sorption data are collected and reported. The focus is the accurate comparison of hydrogen storage capacities of different nanoporous materials. The aim is to produce a more rigorous approach to the assessment of the hydrogen storage capacities of different nanoporous materials through formulation of meticulous and systematic data collection routines for production of universally reproducible H-2 isotherms over a wide range of pressure and temperature conditions. Effects of a range of experimental variables are examined and recommendations for the optimisation of data collection routines are given. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

A robust, simple methodology for analysis of isotherms for the adsorption of fluids above their critical temperature onto nanostructured materials is presented. The analysis of hydrogen adsorption in a metal-organic framework is used as an example to illustrate the methodology, which allows the estimation of the absolute adsorption into nanoporous systems. Further advantages of employing this analysis are that adsorption systems can be described using a small number of parameters, and that excess and absolute isotherms can be extrapolated and used to predict adsorption behaviour at higher pressures and over different temperature ranges. Thermodynamic calculations, using the exact Clapeyron equation and the Clausius-Clapeyron approximation applied to the example dataset, are presented and compared. Conventional compression of hydrogen and adsorptive storage are evaluated, with an illustration of the pressure ranges in which adsorption facilitates storage of greater volumes of hydrogen than normal compression in the same operating conditions.