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Thin foil based porous transport layers (PTLs) that contain highly structured pore arrays have shown promise as anode PTLs in proton exchange membrane electrolysis cells. These novel PTLs, fabricated with advanced manufacturing techniques, produce thin, tunable, multifunctional layers with reduced flow and interfacial resistances and high thermal and electric conductivities. To further optimize their design, it is important to understand their fundamental impact on the transport of protons, electrons, and liquid/vapor mixtures in the electrode. In this work, we develop a two-dimensional multiphysics model to simulate the coupled electrochemistry and multiphase transport in an electrolysis cell operated with the novel PTL architecture. The results show that larger pores improve access of water to the anode catalyst layer, which is beneficial for both the oxygen evolution reaction and membrane hydration. Larger pore sizes also improve oxygen gas transport from the catalyst layer, because generated oxygen gas is forced to travel in-plane through the anode catalyst layer until it reaches a pore opening that is connected to a channel. The discussed results confirm that the proposed thin foil based PTLs are fundamentally different from conventional PTLs, such as felts or layered meshes. The model developed in this work also provides generalizable insight into fundamental PEMEC phenomena, such as the competition between liquid and gas phase transport, membrane hydration and water management, and nonuniform electrochemical reactions, which are processes relevant to all PEMEC designs.

To achieve large-scale application of proton exchange membrane electrolyzer cells (PEMECs) for hydrogen production, it is highly desirable to reduce the manufacturing cost while enhancing cell performance. In the PEMPECs, a catalyst-coated membrane (CCM) is the vital component where electrochemical reactions and mass transport mainly occur. The fabrication methods and catalyst layer (CL) structure can significantly affect the cell performance. Herein, for the first time, a comparative study of CCM fabrications with decal transfer and direct spray deposition methods have been conducted by both ex-situ materials characterization and in-situ performance testing in PEMECs. It is found CCMs that are fabricated with a direct spray deposition method display enhanced cell performance compared to CCMs fabricated with a decal transfer method, mainly due to the largely reduced ohmic resistance and improved mass transport. More importantly, cell performance can be greatly enhanced by simply regulating the Nafion ionomer content at the anode CL. The optimal Nafion ionomer content of 10 wt% gives the best cell performance at 80 °C with a low cell voltage of 1.887 V at 2 A cm−2, outperforming the commercial CCM and most other previous publications. Our study provides a valuable guidance for fabrication and optimization of CCMs with significantly enhanced performance and reduced cost for practical application of the PEMECs.

As the most important part of electrochemical reaction in proton exchange membrane electrolysis cells (PEMECs) for water splitting, oxygen evolution reaction (OER) occurs at the anode catalyst layer (CL). The distribution of the OER site is affected by many factors, such as properties of CL, operation parameters, procedures, etc. To study the effects of properties of CLs on the distribution of OER site on the CL, and consequently affect the performance of PEMECs, CLs with different sheet resistances are tested under different operation conditions. The phenomena of OER on CLs are captured by a high-speed and micro-scale visualization system in-situ and analysed coupled with electrochemical results. The results show that both sheet resistance and wettability of CLs have significant impact on the distribution of the OER site, which can help optimize the design of membrane electrode assembly and improve the operating parameters for electrochemical devices.

The development of water electrolyzer is challenging as we approach theoretical limits arising from electrochemical reactions and micro-scale bubble dynamics. In this research, two-phase flow and bubble dynamics are in-situ studied in a special designed single-channel electrolyzer. The devices fabricated by a 3D printer provide a whole vision of the electrochemical reaction within the channel. In-situ observations of channel-scale hydrogen and oxygen micro-bubbles dynamics are conducted, and the whole process of hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) are simultaneously studied. The results indicate that all bubbles generate at the interface between the proton exchange membrane and the electrode wire, and the operating conditions have a great impact on the micro bubble evolution process. The bubble detachment diameter is inversely proportional to the flow velocity, but is in direct proportion to the current density. Finally, a mathematic model has been developed, and shows a good agreement with experimental data. Those results could help to better understand the bubble evolution mechanism, in order to further understand the electrochemical reaction.

Proton exchange membrane electrolyzer cells (PEMECs) have been considered one of the most promising devices for hydrogen generation and energy storage from water splitting, especially when coupled with sustainable energy resources. Microporous layers (MPLs), which have been widely used in fuel cells for better catalyst access and product/reactant removal, have limited investigations in PEMECs due to harsh environments and carbon corrosion. In this study, the MPLs with both irregular micro (∼5 μm) and spherical nano (30–50 nm) titanium particles are developed on novel thin/tunable liquid/gas diffusion layers (TT-LGDLs) and are investigated comprehensively both in-situ and ex-situ for the first time. The MPLs change the wettability of the TT-LGDLs and show super hydrophobic property. The results reveal that micro particle MPLs exhibit improved catalytic activity but increased ohmic resistances, and that nano particle MPLs do not impact catalytic activity meaningfully but exhibit even greater increases in ohmic resistance. The effects of the thickness of the MPLs are also investigated and the typical MPL is also studied by in-situ visualization in a transparent PEMEC with a high-speed and micro-scale visualization system (HMVS). The results indicate the strong feasibility of the TT-LGDLs with small pore size and large porosity for high-efficiency and low-cost PEMEC practical applications.

Gas bubble dynamics and two-phase flow have a significant impact on the performance and efficiency of proton exchange membrane electrolyzer cells (PEMECs). It has been strongly desired to develop an effective experimental method for in-situ observing the high-speed/micro-scale oxygen bubble dynamics and two-phase flow in an operating PEMEC. In this study, the micro oxygen bubble dynamic behavior and two-phase flow are in-situ visualized through a high-speed camera coupled with a specific designed transparent PEMEC, which uses a novel thin liquid/gas diffusion layer (LGDL) with straight-through pores. The effects of different operating conditions on oxygen bubble dynamics, including nucleation, growth, and detachment, and two-phase flow have been comprehensively investigated. The results show that temperature and current density have great effects on bubble growth rate and reaction sites while the influence of flow rate is very limited. The number, growth rate, nucleation site, and slug flow regime of oxygen gas bubbles increase as temperature and/or current density increases, which indicates that an increase in temperature and/or current density can enhance the oxygen production efficiency. Further, a mathematical model for the bubble growth is developed to evaluate the effects of temperature and current density on the bubble dynamics. A mathematical model has been established and shows a good correlation with the experimental results. The studies on two-phase flow and high-speed micro bubble dynamics in the microchannel will help to discover the true electrochemical reaction at micro-scale in an operating PEMEC.

The corrosion of low-cost, easily manufactured metallic components inside the electrochemical environment of proton exchange membrane electrolyzer cells (PEMECs) has a significant effect on their performance and durability. In this study, 316 stainless steel (SS) mesh was used as a model liquid/gas diffusion layer material to investigate the migration of corrosion products in the catalyst-coated membrane of a PEMEC. Iron and nickel cation particles were found distributed throughout the anode catalyst layer, proton exchange membrane, and cathode catalyst layer, as revealed by scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. The results indicate the corrosion products of 316 SS are transported from anode to cathode through the nanochannels of the Nafion membrane, resulting in impeded proton transport and overall PEMEC performance loss.

Additive manufacturing (AM) technology is capable of fast and low-cost prototyping from complex 3D digital models. To take advantage of this technology, a stainless steel (SS) plate with parallel flow field served as a combination of a cathode bipolar plate and a current distributor; it was fabricated using selective laser melting (SLM) techniques and investigated in a proton exchange membrane electrolyzer cell (PEMEC) in-situ for the first time. The experimental results show that the PEMEC with an AM SS cathode bipolar plate can achieve an excellent performance for hydrogen production for a voltage of 1.779 V and a current density of 2.0 A/cm 2 . The AM SS cathode bipolar plate was also characterized by SEM and EDS, and the results show a uniform elemental distribution across the plate with very limited oxidization. This research demonstrates that AM method could be a route to aid cost-effective and rapid development of PEMECs.

Multiphase transport inside a proton exchange membrane electrolyzer cell (PEMEC) plays an important role in its performance and design. Most PEMEC modeling studies so far have mainly focused on its electrochemical performance prediction and analysis, and fundamental understanding of the effect of multiphase transport on the cell performance is still lacking. In this study, a two-phase mathematical model is developed to investigate the transport properties inside liquid/gas diffusion layers (LGDLs) and to explore their effects on the PEMEC voltage and efficiency. Sudden changes in the PEMEC voltage and efficiency are captured for the first time as the current density reaches a limiting value, and the limiting current density is greatly impacted by the LGDL contact angle, porosity, and thickness. In addition, the liquid water distribution and cell performance in PEMECs with different important operating and physical parameters are examined and discussed in detail. Increasing the LGDL porosity or/and decreasing its surface contact angle will improve the PEMEC performance especially at the high current density. The thickness changes of the LGDL and membrane also have significant impacts on the cell voltage and efficiency. The model can effectively examine two-phase transport properties and provide useful information for design optimization of a PEMEC.

In this study, nitrogen and sulfur co-doped mesoporous carbon (N-S-MPC) materials are selected as the platform to demonstrate the potential of N-S-MPC to replace precious metal catalyst for fuel cell cathode oxygen reduction. Using both N-S-MPC and commercial available 40%Pt/C as cathode catalysts, the effects of catalyst and bonding layer in the catalyst layer (CL) on the power generation performances are thoroughly investigated for alkaline membrane fuel cells (AMFCs). Through single cell tests, several observations are reached as follows: (1) For N-S-MPC cathode, with increasing N-S-MPC loading from 1.00 to 5.00 mg cm−2, the power density reached the maximum (21.7 mW cm−2) when the catalyst loading is 3 mg cm−2. However, for Pt/C cathode the power density reached the maximum (21.3 mW cm−2) for a catalyst loading of 0.5 mg cm−2, with increasing loading from 0.3 to 0.5 mg cm−2; (2) Increasing the thickness of catalyst layer resulted in an increase in power density. Thus, raising the local hydroxyl ion concentration was in favor of the process of oxygen reduction reaction. (3) The bonding layer also has a significant influence on the MEA fabrications, where the MEA using 30 μL bonding layer produced a maximum power density of 20.8 mW cm−2.

A low-cost additive manufacturing technology, electron beam melting (EBM), is employed for the first time to fabricate titanium liquid/gas diffusion media with high-corrosion resistances and well-controlled multifunctional parameters, including two-phase transport and high electric/thermal conductivities. Its application in proton exchange membrane electrolyzer cells (PEMECs) has been investigated in-situ with modular galvano (MG) and galvano electrochemical impedance spectroscopy (GEIS) and characterized ex-situ with SEM and XRD. Compared with conventional woven and sintered liquid/gas diffusion layers (LGDLs), much better performance is obtained with EBM-fabricated LGDLs due to a significant reduction of ohmic losses. The EBM technology components exhibited several distinct advantages in fabricating LGDLs: well-controllable pore morphology and structure, rapid prototyping, fast manufacturing, highly customizable design, and economic. In addition, by taking advantage of additive manufacturing, it is possible to fabricate complicated three-dimensional designs of virtually any shape from a digital model into one single solid object faster, cheaper, and easier, especially for titanium components. More importantly, this development will provide LGDLs with well-controllable pore morphologies, which will be valuable to develop sophisticated models of PEMECs with optimal and repeatable performance. Furthermore, it could lead to a manufacturing solution that greatly simplifies the PEMEC/fuel cell components.

The lack of a fundamental understanding of the corrosion mechanisms in the electrochemical environments of proton exchange membrane (PEM) electrolyzer and/or fuel cells (ECs/FCs) has seriously hindered the improvement of performance and efficiency of PEM ECs/FCs. In this study, a stainless steel mesh was purposely used as an anode gas diffusion layer that was intentionally operated with high positive potentials under harsh oxidative environments in a PEMEC to study the corrosion mechanism of metal migration. A significant amount of iron and nickel cations were determined to transport through the anode catalyst layer, the PEM and the cathode catalyst layer during the PEMEC operation. The formation/deposition of iron oxide and nickel oxide on the carbon paper gas diffusion layer at the cathode side is first revealed by both scanning electron microscope and X-ray diffraction. The results indicate the corrosion elements of iron and nickel are transported from anode to cathode through the catalyst-coated membrane, and deposited on carbon fibers as oxides. This phenomenon could also open a new corrosion-based processing approach to potentially fabricate multifunctional oxide structures on carbon fiber devices. This study has demonstrated a new accelerated test method for investigating the corrosion and durability of metallic materials as well.

This paper presents a comprehensive computational model for the proton exchange membrane (PEM) electrolyzer cells, which have attracted more attention for renewable energy storage and hydrogen production. A new ohmic loss model of a PEM electrolyzer cell has been developed and the influence of different operating conditions and physical design parameters on its performance has been investigated, including operating temperature, pressure, exchange current density, electrode thickness, membrane thickness and interfacial resistance. The interfacial resistance between the membrane and electrode has been found to play an important part for electrolyzer performance and an overpotential is increased significantly with the interfacial resistance. At a current density of 1.5 A/cm2, the performance loss due to the interfacial resistance between the membrane and electrode comprises 31.8% of the total ohmic loss. Thickness changes in either electrode or membrane also have significant impacts on the electrolyzer performance mainly due to their contributions to the diffusion overpotential and ohmic loss. Increasing the operating temperature will result in lower electrolyzer overpotential, while increasing the operating pressure will lead to higher electrolyzer overpotential, which is mainly controlled by the open circuit voltage. Results obtained from the present model will provide a comprehensive understanding of design parameter effects and consequently improve the design/performance in a PEM electrolyzer cell.

A combined strategy via mixing Mg(BH4)2·6NH3 with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH4)2·6NH3. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH4)2·6NH3–6AB is achieved with the assistance of ZnCl2, which plays a crucial role in stabilizing the NH3 groups and promoting the recombination of NHδ+⋯HBδ−. Specifically, the Mg(BH4)2·6NH3–6AB/ZnCl2 (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.

In this paper, niobium-based ammine borohydride has been synthesized via a simple ball milling of NbCl 5 ·5NH 3 and MBH 4 (M = Li, Na) with a molar ratio of 1:5. Thermogravimetric analysis–mass spectrometry (TGA–MS) and temperature-programmed-desorption (TPD) results revealed that the dehydrogenation of NbCl 5 ·5NH 3 /5LiBH 4 and NbCl 5 ·5NH 3 /5NaBH 4 mixtures showed a two-step decomposition process with a total of 8.1 wt.% and 11.2 wt.% pure hydrogen evolution upon heating to 250 °C, respectively. Isothermal TPD results showed that over 6 wt.% and 10.4 wt.% pure hydrogen were liberated from NbCl 5 ·5NH 3 /5NaBH 4 within 60 min at 150 °C and 220 °C, respectively. Fourier transform infrared spectroscopy (FTIR) and isotope tagging measurements demonstrated that the dehydrogenation mechanism of niobium-based ammine borohydride is not only based on the combination reaction of BH and NH groups, but the BH⋯HB and NH⋯HN homo-polar interactions also contribute to the H 2 formation.

The penta-ammine vanadium (III) borohydride, i.e. V(BH4)3·5NH3, was successfully synthesized via ball-milling of VCl3·5NH3 and LiBH4 in a molar ratio of 1:3. This compound was shown to release 11.5 wt% hydrogen with a H2-purity of 85 mol% by 350 °C. To improve the dehydrogenation purity of V(BH4)3·5NH3, Mg(BH4)2 with various molar ratios was mixed with V(BH4)3·5NH3 to synthesize expected ammine metal-mixed borohydrides, among which the formed VMg(BH4)5·5NH3 was indexed to be a monoclinic unit cell with lattice parameters of a = 19.611 A, b = 14.468 A, c = 6.261 A, β = 93.678° and V = 1772.75 A3. Dehydrogenation results revealed that the Mg(BH4)2 modified V(BH4)3·5NH3 system presents significantly enhanced dehydrogenation purity. For example, in the case of V(BH4)3·5NH3/2Mg(BH4)2 sample, 12.4 wt% pure hydrogen can be released upon heating to 300 °C. Further investigation on the dehydrogenation mechanism of the VMg(BH4)5·5NH3 system by isotope tagging revealed that the interactions of homo-polar BH units also participated throughout the dehydrogenation process (onset at 75 °C) as complementary to the prime combination of BH···HN.

In the face of world-wide energy price fluctuation, energy supply security, and the energy crisis, it becomes an urgent issue to search for alternative methods for energy generation and to close the gap between the supply and demand of global energy. The current method of energy supply in Taiwan is through a centralized electronic power system, which is generated by a few large electronic power plants. Hydrogen fuel cell (HFC) has a characteristic of de-centralized electronic power supply system, which provides electronic power more reliably, efficiently and economically. Based on the output of Taiwan’s sewage, sludge, kitchen waste and biohydrogen technology, the preliminary market for biohydrogen fuel cell (BHFC) is positioning itself toward the supply of public electronic power within the housing communities. Based on the patent analysis of BHFC, this study finds that Taiwan pays more attention to the front-end manufacturing of raw materials and emphasizes the development of biohydrogen technology, while America and Japan mainly pay more attentions to rear-end product application and emphasize the application of hydrogen and fuel cells by integrating industrial opinions. Based on the market analysis of BHFC, this study finds that the product attributes, consumers’ characteristics and external variables strongly influence consumer’s purchase intention of biohydrogen technology products.

A pilot-scale high-rate dark fermentative hydrogen production plant has been established in the campus of Feng Chia University to develop biohydrogen production pilot-plant technology. This pilot-plant system is composed of two feedstock storage tanks (0.75 m3 each), a nutrient storage tank (0.75 m3), a mixing tank (0.6 m3), an agitated granular sludge bed fermentor (working volume 0.4 m3), a gas–liquid–solid separator (0.4 m3) and a control panel. The seed mixed microflora was obtained from a lab-scale agitated granular sludge bed bioreactor. This pilot-scale fermentor was operated for 67 days at 35 °C, an organic loading rate (OLR) of 40–240 kg COD/m3/d, and the influent sucrose concentration of 20 and 40 kg COD/m3. Both biogas and hydrogen production rates increased with increasing OLR. However, the biomass concentration (volatile suspended solids, VSS) only increased with an increasing OLR at an OLR range of 40–120 kg COD/m3/d, whereas it decreased when OLR was too high (i.e., 240 kg COD/m3/d). The biogas consisted mainly of H2 and CO2 with a H2 content range of 23.2–37.8%. At an OLR of 240 kg COD/m3/d, the hydrogen content in biogas reached its maximum value of 37% with a hydrogen production rate (HPR) of 15.59 m3/m3/d and a hydrogen yield of 1.04 mol H2/mol sucrose. This HPR value is much higher than 5.26 m3/m3/d (fermented molasses substrate) and 1.56 m3/m3/d (glucose substrate) reported by other pilot-scale systems. Moreover, HPR was also greatly affected by pH. At an optimal pH of 5.5, the bacterial community became simple, while the efficient hydrogen producer Clostridium pasteurianum was dominant. The factors of energy output compared with the energy input (Ef) ranged from 13.65 to 28.68 on biohydrogen, which is higher than the Ef value on corn ethanol, biodiesel and sugarcane ethanol but in the similar range of cellulosic ethanol.

A high-rate hydrogen production process able to produce H 2 at a maximum rate of 15 L/L/hwas successfully developed by the Feng Chia University (FCU) biohydrogen research team.This highly efficient hydrogen fermentation system includes a 400 L pilot-scale systemconstructed for determining scale-up operation parameters for commercializing the bioH 2 production technology. The pilot-scale system is composed of a feedstock tank, mixingsystem, fermentor, gas/liquid separator and automatic control system. The fermentor isfed with sucrose (20 g COD/L) and operated at 35 C. A batch strategy is used for systemstart-up. The fermentor was first operated in a batch mode for two days and then switchedto a continuous-feeding mode (HRT 12 h) for one month. During the continuous operation,pH notably affected H 2 production efficiency and bacterial community. For the first 14-dayoperation, the H 2 production rate increased from 0.017 to 0.256 L/L/h with a pH variationfrom 5.0 to 7.0. The DGGE results indicate the presence of two Clostridium species (namely,Clostridium butyricum and Clostridium pasteurianum) in the fermenter. Stable hydrogenproduction rate was obtained at pH 5.5–6.0 when C. pasteurianum became dominant in themixed culture.Crown Copyright a 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu.All rights reserved.