Membrane Electrode Assembly Design Research Articles

(Invited) Novel Design of Low-Loaded Membrane Electrode Assemblies for Advanced Low-Temperature Water Electrolyzers

Development of advanced low-temperature (LT) water electrolyzers (WEs) is of crucial importance for implementation of the Hydrogen Economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. “Green” hydrogen can be produced at large scale by integration of WEs with renewable energy sources. Currently, the low-temperature proton exchange membrane (PEM) and anion exchange membrane (AEM) WEs are considered to be the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for LTWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers; (ii) limited durability caused by the instability of the catalysts and the other cell components, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].This work is aimed on designing of novel MEAs for LTWEs with dramatically reduced catalysts loadings, enhanced durability, and improved H2 crossover capabilities. Reactive Spray Deposition Technology (RSDT) is used as an innovative methodology for designing of advanced catalysts, catalyst and recombination layers, and MEAs for LTWEs. The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs for application in LT fuel cells and water electrolyzers [5, 6]. As fabricated MEAs with ultra-low PGM catalysts loadings are tested at operating conditions typical for industrial PEM hydrogen production systems, and performance of 1.8 V at 3 A/cm2 is achieved. The MEAs of interest are tested for over 1000 hrs at steady-state conditions at 3 A/cm2. Comprehensive post-test characterization is performed by using high-resolution TEM, STEM, EDS, SEM, ICP, XRF, XCT, and digital optical microscopy and the governing degradation mechanisms are identified and discussed in detail. The impact of the design of low-loaded MEAs for LTWEs on their performance and durability is discussed in detail and their potential to meet and surpass the DOE 2030 targets is demonstrated.References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdfKlose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).

Rational design of membrane electrode assembly for anion exchange membrane water electrolysis systems

Anion exchange membrane water electrolysis (AEMWE) is a promising and potentially low-cost technology for producing green hydrogen, but a novel manufacturing technique with rational design of the electrodes is essential to improve the performance and stability. In this work, we investigate the effect of electrode structure on activity and the stability of AEMWEs by fabricating membrane electrode assemblies (MEAs). For the first time, the decal transfer method with platinum-group-metal-free (PGM-free) catalyst was successfully used in AEMWEs. With this method, deposition of a compact catalyst layer (CL) on the membrane was achieved without damaging neither the CL nor the membrane. The MEAs were designed for AEMWE using 1 M KOH as the electrolyte and the ionomer content was optimized for both cathode and anode. In the anode, a low ionomer loading improved activity and ionic conductivity, however, a higher ionomer content was beneficial for the cathode. Furthermore, the type of ionomer on the anode side has shown to be the major reason of loss of performance over time. An ionomer with low (1.4–1.7 meq g−1) Ion Exchange Capacity (IEC) and Nafion™ ionomer greatly improved the stability.

Exploring the sustainability of serpentine flow-field fuel cell, straight channel PEM fuel cells hight temperature through numerical analysis

This study focuses on investigating the performance dynamics of high-temperature Proton Exchange Membrane fuel cells, with an emphasis on critical design parameters. Utilizing a comprehensive mathematical model, the research explores concentration profiles, current density profiles, and polarization curves within a three-dimensional, isothermal, steady-state PEM fuel cell.The model incorporates the intricate processes of gas transport in anode and cathode channels, diffusion in catalyst layers, and the transport of water and hydronium ions in both the polymer electrolyte and catalyst layers. Additionally, it accounts for electrical current transport in the solid phase. Simulations conducted with Comsol Multiphysics 6.1 demonstrate a robust alignment between model results and experimental polarization data obtained at 180 °C. Optimal conditions for performance are outlined, specifying an inlet hydrogen gas velocity of 0.12 m/s and an inlet air velocity of 1.2 m/s, with consideration for a proton conductivity of 9.825 S/m.In a parallel investigation, numerical analysis assesses the sustainability of Serpentine Flow-Field PEM fuel cells, using critical parameters. The model applied in this research considers gas, water, and electrical current transport across various layers of the fuel cell, with a crucial focus on optimizing the membrane electrode assembly's design. The finite element method and ANSYS Fluent are employed for model solution.This study contributes significantly to the understanding of HT-PEM fuel cell dynamics, providing insights into the interdependencies of design parameters and their impact on system performance. The study emphasizes the pivotal roles of air and hydrogen inlet velocities in shaping fuel cell performance, elucidating the intricate dynamics dictating reactant distributions within diverse cell components.

A numerical analysis of the effect of layer-scale and microscopic parameters of membrane electrode assembly in proton exchange fuel cells under two-phase conditions

A multiphysics, multiphase, multiscale model of the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell (PEMFC) is presented. The model accounts for varying local effective transport that arise from assembly compression of the gas diffusion layer (GDL) and MEA microstructure, providing a more realistic description of heterogeneities. The model is validated against previous experimental data in terms of polarization curve, effect of inlet relative humidity on performance, and rib/channel saturation distribution. Then, a parametric analysis of layer-scale (compression and GDL thickness) and microscopic (pore radius and defect volume fraction) parameters is presented. The results show that performance can be improved by reducing compression under the rib (provided that electrical contact resistances are negligible), tailoring GDL thickness at intermediate values around 200μm, designing macroporous layer (MPL) and catalyst layer (CL) with pore sizes between 50–100nm and 0.5–1μm, respectively, and reducing large defect volume fractions in MPLs and CLs. To achieve these goals, an integral design of MEAs is necessary to minimize electrical contact resistances, cracks and defects, reduce inhomogeneous compression and produce highly porous multiscale structures with large continuum pore sizes at multiple scales.

Model-Driven Membrane Electrode Assembly Design for High-Performing Open-Cathode Polymer Electrolyte Membrane Fuel Cells

Open-cathode fuel cells use air cooling to effectively reduce system cost. However, due to the challenging hygrothermal environment, they generally suffer from low performance compared to conventional, liquid-cooled cells. A pre-validated, three-dimensional computational model is used in the present work to determine the effects of different sub-component designs, namely the polymeric membrane, composition of the cathode catalyst layer (CCL), and structure of the cathode microporous layer (CMPL), on the performance of an open-cathode fuel cell. This comprehensive parametric study performed on a total of 90 cases shows the increment in current density to be 7% and 31% by improvising the membrane and CCL design, respectively, at 0.6 V. A steep increase of 87% is also achieved by strategically modifying the CMPL design at 0.4 V operation. An overall increment of 119% and 131% in current density is achieved for the best membrane electrode assembly (MEA) design at 0.6 and 0.4 V, respectively, as compared to the baseline design. These improvements are achieved by collective improvements in kinetics, oxygen mass transport, ohmic resistance, self-heating, and water retention in the ionomer phase. The proposed MEA design could facilitate open-cathode fuel cell stacks with 2× higher power output or 56% lower weight and materials cost for a given power demand.

(Invited) Lowering the Noble Metal Requirement for PEM Water Electrolysis: Membrane Electrode Assembly and Porous Transport Layer Design Considerations

The Net Zero Emission scenario proposed by the International Energy Agency projects a required electrolytic generation of hydrogen equivalent to 3600 GW by 2050 [1], averaging to an annual installation of ~130 GW/a between 2023 and 2050. If this were to be provided by proton exchange membrane based water electrolyzers (PEM-WEs) based on platinum catalysts for the hydrogen evolution reaction (HER) and iridium catalysts for the oxygen evolution reaction (OER), the current PEM-WE noble metal requirements of ~0.7 gIr/kW and ~0.3 gPt/kW [1] would have to be drastically reduced in view of the noble metal supply constraints. As argued previously, for PEM-WEs to be sustainable on such a large scale would require to achieve platinum and iridium loadings of ~0.05 mg/cm2 electrode [2,3]. While the former can be easily achieved due to the fast HER kinetics on Pt, the latter requires either ultra-thin OER catalyst layers or improved OER catalysts with a substantially reduced iridium packing density (in units of gIr/cm3 electrode) [2], like the recently developed catalyst with a hydrous iridium oxide shell supported on a titanium oxide core (IrOx/TiO2) [4,5].In this contribution, we will discuss the effect of the design of membrane electrode assemblies (MEAs) and of the adjacent porous transport layers on PEM-WE performance. In general, the preparation of MEAs with low platinum loading cathodes is straightforward, due to the availability of carbon supported platinum catalysts (Pt/C) with a low Pt packing density. For the optimization of the ionomer content in the cathode electrode, however, its effect on the high current density performance and on the hydrogen permeation rate from cathode to anode have to be considered [6,7].With regards to the anode electrode, we will further discuss the MEA design challenges when targeting ultra-low iridium loadings. In the case of the ultra-thin catalyst layers that result when using conventional OER catalysts, additional contact resistances between the anode catalyst layer and the titanium based porous transport layer (Ti-PTL) are observed [2]. As will be shown, these can be largely mitigated by the use of a titanium based microporous layer (MPL) coated on the Ti-PTL, highlighting the importance of the interface between the PTL and the anode catalyst layer. In case of using the above described IrOx/TiO2 catalysts with low iridium packing density, their typically lower electrical conductivity also results in apparent contact resistances within and across the anode catalyst layer [4], which poses an additional constraint on the allowable range of the catalyst/ionomer ratio in the anode electrode. The interplay between the anode catalyst type, the anode ionomer content, and the type of interface between the anode electrode and the PTL (i.e., with and without MPL) will be discussed.

Rational Design of Membrane Electrode Assembly for Anion Exchange Water Electrolysis

In the framework of an increased interest for green hydrogen production, Anion Exchange Membrane Water Electrolysis (AEMWE) systems have attracted tremendous attention. Platinum group metal-free (PGM-free) catalysts can be effectively exploited with this technology to reach higher current densities compared to traditional alkaline electrolysis [1]. However, challenges are posed by the stability of the anion conducting polymer in the membrane and in the catalyst layers (CLs). Furthermore, the scarcity of works showing devices with stable performance which can work without a supporting electrolyte raises the question of whether or not it is possible to rely on ionomer conductivity for CL.Here, we focus on a method for the fabrication of catalyst coated membranes (CCMs). This strategy has the benefit of enhancing the interfacial contact between the CL and the membrane, reducing the cell resistance when low conducting electrolytes or pure water are used. Inspired by the industrial approach for proton exchange membrane (PEM) fuel cell fabrication, we applied the “decal transfer” method to AEMWE. In this approach, the CL is first coated on a substrate and then transferred on the membrane surface to fabricate the so-called MEA. This method is easy to scale up and allows for fine control of catalyst loading.In our work, we investigated the effect of ionomer content on the electrode performance. After optimizing the ionomer weight fraction for both anode and cathode, we studied the stability of MEAs at 200 mA/cm2 in 1 M KOH. It was found that when the anion conducting ionomer (AP-1-HNN8-00-X) in the anode CLs was replaced with Nafion, the electrode performance (Figure 1a) and stability were significantly improved (Figure 1b). Additionally, the electrode utilization was increased due to the higher density and lower water uptake of Nafion which reduces the volume fraction of Nafion in the CL. Reduced electrode resistance was also observed using Nafion when compared to the anion exchange ionomer (figure 1a). Since Nafion is chemically stable and does not suffer from excessive water uptake and dissolution, contrary to anion exchange ionomers [2], it can be easily used as a binder in AEMWE.These findings point out that MEAs for AEMWE can be manufactured with the “decal” method, however, their performance is limited by the catalyst surface area and ionomer stability. These two elements are fundamental towards pure water AEMWE.

Membrane electrode assembly design for lithium-mediated electrochemical nitrogen reduction

A feasible membrane electrode assembly (MEA) configuration is proposed for lithium-mediated electrochemical nitrogen reduction to ammonia, which shows the advantages of efficient gas transfer, reduced solvent consumption and compact configuration.

Characterizing Liquid Water Distribution in Polymer Electrolyte Fuel Cells Using Operando 2D and 3D X-Ray Imaging

The potential to reduce the cost of Polymer Electrolyte Fuel Cells (PEFCs) through high power density operation is limited by the attending water management challenges at such operating conditions [1]. Addressing PEFC water management requires detailed understanding of liquid water distribution characteristics of an operating fuel cell, to refine the design of membrane electrode assemblies (MEAs) for improved performance.Recent advances in X-ray operando imaging [2, 3] and custom hardware development [4], have enabled the visualization of liquid water in an operating PEFC, through the analysis of water phase segmented 3-dimensional (3D) images [2, 3] and 2-dimensional (2D) radiographs [5]. 2D image datasets may be acquired in a shorter time than 3D tomographic datasets but only provide grayscale information averaged through the thickness of the sample. 3D image datasets obtained from a reconstruction of many angular radiographs yield a 3D representation of the sample in addition to the grayscale information but take a long collection time. However, time dependent liquid water distribution characteristics such as channel water breakthrough, observable in the 2D image datasets, tend to be elusive to 3D imaging methods. Although efforts have been made to reduce the image acquisition time for 3D X-ray imaging by using Synchrotron sources and improved image processing techniques [2], these efforts tend to compromise image quality and are restricted to a brief temporal snapshot of liquid water distribution. Also, the brightness of the Synchrotron sources necessitates short exposure duration tests due to the likelihood of cell degradation caused by the sample’s exposure to radiation [4]. Given the unique capabilities of 2D and 3D imaging modes, we therefore focus on combining information accessible in both modes to further the understanding of PEFC liquid water distribution.In this work, an improved understanding of liquid water distribution in the PEFC is presented by integrating operando 2D and 3D image datasets acquired under the same cell operating conditions and using laboratory scale X-ray computed tomography (XCT) equipment which was interfaced with fuel cell testing and diagnostic tools. Analysis of 3D image datasets is extended beyond binary information to include the grayscale value (GSV) of liquid water to reveal a change in the through-plane values. These results, when combined with observed 2D liquid water breakthrough characteristics suggest that the change in GSV is indicative of the differences in the intermittency of liquid water presence in the different regions of the GDL; see Figure 1. These results therefore present a more complete interpretation of PEFC operando liquid water distribution, highlighting distinct characteristics from the microporous (MPL) region to the GDL-land interface. Unique findings and insight obtained using this methodology will be discussed. Acknowledgments Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, and Canada Research Chairs. References Jiao and X. Li, Progress in energy and combustion Science, vol. 37, no. 3, pp. 221–291, 2011.Xu, S. Nagashima, H. P. Nguyen, K. Kishita, F. Marone, F. N. Büchi, and J. Eller, Journal of Power Sources, vol. 490, p. 229492, 2021.Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu, and F. N. Büchi, Journal of Power Sources, vol. 435, p. 226809, 2019.T. White, F. P. Orfino, M. El Hannach, O. Luo, M. Dutta, A. P. Young, and E. Kjeang, Journal of The Electrochemical Society, vol. 163, no. 13, pp. F1337–F1343, 2016.R. Banerjee, N. Ge, J. Lee, M. G. George, S. Chevalier, H. Liu, P. Shrestha, D. Muirhead, and A. Bazylak, Journal of The Electrochemical Society, vol. 164, no. 2, p. F154, 2017. Figure 1

Electro-Conversion of Carbon Dioxide to Valuable Chemicals in a Membrane Electrode Assembly

Electro-conversion of carbon dioxide (CO2) into valuable chemicals is an efficient method to deal with excessive CO2 in the atmosphere. However, undesirable CO2 reaction kinetics in the bulk solution strongly limit current density, and thus it is incompetent in market promotion. Flow cell technology provides an insight into uplifting current density. As an efficient flow cell configuration, membrane electrode assembly (MEA) has been proposed and proven as a viable technology for scalable CO2 electro-conversion, promoting current density to several hundred mA/cm2. In this review, we systematically reviewed recent perspectives and methods to put forward the utilization of state-of-the-art MEA to convert CO2 into valuable chemicals. Configuration design, catalysts nature, and flow media were discussed. At the end of this review, we also presented the current challenges and the potential directions for potent MEA design. We hope this review could offer some clear, timely, and valuable insights on the development of MEA for using wastewater-produced CO2.

Overall design of novel 3D-ordered MEA with drastically enhanced mass transport for alkaline electrolyzers

A novel three-dimensionally (3D)-ordered membrane electrode assembly (MEA) based on highly porous catalyst layers with unique vertical channels, an ultrathin membrane layer and 3D interface structures was nanoengineered for alkaline electrolyzers.

Mitigation of mechanical membrane degradation in fuel cells – Part 1: Gas diffusion layers with low surface roughness

Hygrothermal variations that arise during dynamic fuel cell operation are known to generate mechanical stresses in the ionomer membrane. Previous research has indicated that membrane electrode assembly (MEA) interaction effects may influence membrane degradation under such loads. The present objective is therefore to evaluate novel MEA design strategies for mitigating mechanical membrane degradation in fuel cells. In this case (Part 1), a gas diffusion layer (GDL) with low surface roughness is applied to suppress buckling-driven membrane failures. Laboratory-based X-ray computed tomography is used in a customized, time-resolved workflow for non-invasive four-dimensional characterization of membrane damage evolution during accelerated stress testing. Membrane crack development is the key failure mode preceded by fracture of the cathode catalyst layer. In comparison to high surface roughness GDL, the severity of membrane buckling is substantially reduced by adoption of the smoother GDL, contributing 2x greater lifetime. Accompanying finite element simulations of the unit fuel cell assembly show plastic strain accumulation in the buckled membrane and identified a critical range of GDL void sizes that influence membrane buckling. Overall, the improvement in GDL surface demonstrates substantial mitigation effect against fatigue-driven mechanical membrane degradation and failure, which is also corroborated by the numerical simulation results. • Novel MEA design strategies are shown to mitigate mechanical membrane degradation • CCM buckling into GDL voids is identified as the key mechanism for membrane failure • 2× higher RH cycling lifetime is achieved with low surface roughness GDLs • Complementary finite element simulations corroborate the experimental findings • A critical GDL pore radius is demonstrated for CCM buckling to occur

Ti2Zr2O8 nanotube as an additive in the fuel cell membrane and catalyst layer for improved low humidity operation

The development of high-performance, low-cost and durable membrane electrode assembly (MEA) materials receives significant attention from the fuel cell community. A promising MEA design approach introduces a radical scavenging Ti 2 Zr 2 O 8 nanotubes additive (TZONT) in the polymer electrolyte membrane and cathode catalyst layer for fuel cells operating under dry conditions is described. The modified MEA operating at 20% relative humidity (RH) showed ~18% increase in the peak power density than its counterpart assembled with only a modified membrane. A fluoride emission rate (FER) analysis reveals that the TZONT additive in the Nafion ionomer protects it from radical attack and, thus, lowers the FER value to about 200-times the commercial Nafion-212 membrane. Finally, we revealed a promising approach to lower the Pt loading in the cathode catalytic layer without compromising its intrinsic activity in a relatively cost-competitive manner. • The radical scavenging effect of Ti 2 Zr 2 O 8 in Nafion matrix is reported. • Composite membranes show excellent mechanical strength and chemical stability. • Observed 200-times reduction of FER contributed by Ti 2 Zr 2 O 8 additive. • Promising approach for Pt reduction in the PEMFC cathode catalytic layer.

Iron Contamination and Local Distribution within a 50 Cm Single-Channel Proton Exchange Membrane Water Electrolysis Cell

Proton exchange membrane water electrolysis (PEMWE) will play a major role in the clean and versatile energy conversion in the near future.[1] Offering scalable solutions of PEMWE are of high industrial interest and have to provide a sufficient durability and reliability.[2] To achieve this, a better understanding of the impact of contamination on the PEMWE performance is very crucial. In this context, the membrane electrode assembly (MEA) is susceptible to several degradation processes like metallic cations (Fe3+/2+ stemmed from tubing). In particular, soluble and reduced iron species forming by Fenton reaction might attack via radicals the MEA.[3,4] Hence, analyzing impurities and their resulting impacts on e.g. the proton transport resistance and degradation mechanisms at different length scales and local distributions are of large interest.In this work, the influence of spatially resolved iron contamination in MEAs on the cell performance has been investigated using a 50 cm single-channel PEMWE cell equipped with local current density measurement setup.[5] Adding defined amounts of FeSO4 via the anode inlet feed, the changes on the three main regimes of overpotentials, i.e. kinetic, ohmic and mass transport, is correlated with the current density mapping as well as local and global electrochemical impedance spectroscopy (EIS) measurements. Ex-situ scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are used to detect the distribution and agglomeration of iron species within the MEA.With this combined approach of electrochemical and ex-situ physical methods, the contamination pathways and their effects of (spatially resolved) iron contamination on the overall performance of MEA are investigated as a function of degree of contamination and operating conditions. Especially, the (spatially resolved) overpotential-specific degradation processes along the 0.5 m channel, which mimic a technically relevant stack size, allow us to conclude on the optimum design of MEA, targeting use of mitigation strategies and development of accelerated stress test protocols.[1] M.A. Pellow, C.J.M. Emmott, C.J. Barnhart, S.M. Benson, Energy Environ. Sci. 8 (2015) 1938-1952.[2] P.K. Shen, C.-Y. Wang, S.P. Jiang, X. Sun, J. Zhang, Electrochemical Energy: Advanced Materials and Technologies, CRC Press, 2015.[3] X. Wang, L. Zhang, G. Li, G. Zhang, Z.-G. Shao, B. Yi, Electrochim. Acta 158(2015) 253-257.[4] C. Rozain, P. Millet, Electrochim. Acta 131 (2014) 160e167.[5] C. Immerz, B. Bensmann, P. Trinke, M. Suermann, R. Hanke-Rauschenbach, JECS 165 (16) (2018)

Designing AI-Aided Analysis and Prediction Models for Nonprecious Metal Electrocatalyst-Based Proton-Exchange Membrane Fuel Cells.

Traditionally, a larger number of experiments are needed to optimize the performance of the membrane electrode assembly (MEA) in proton-exchange membrane fuel cells (PEMFCs) since it involves complex electrochemical, thermodynamic, and hydrodynamic processes. Herein, we introduce artificial intelligence (AI)-aided models for the first time to determine key parameters for nonprecious metal electrocatalyst-based PEMFCs, thus avoiding unnecessary experiments during MEA development. Among 16 competing algorithms widely applied in the AI field, decision tree and XGBoost showed good accuracy (86.7 % and 91.4 %) in determining key factors for high-performance MEA. Artificial neural network (ANN) shows the best accuracy (R2=0.9621) in terms of predictions of the maximum power density and a decent reproducibility (R2>0.99) on uncharted I-V polarization curves with 26 input features. Hence, machine learning is shown to be an excellent method for improving the efficiency of MEA design and experiments.

Experimental studies on the effects of sheet resistance and wettability of catalyst layer on electro-catalytic activities for oxygen evolution reaction in proton exchange membrane electrolysis cells

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.

Disclosure of the internal transport phenomena in an air-cooled proton exchange membrane fuel cell—Part I: Model development and base case study

In this study, the internal transport phenomena and mechanism inside an air-cooled proton exchange membrane fuel cell (PEMFC) are investigated. It helps to understand the factors that affect the performance of an air-cooled PEMFC and optimize the design of Membrane Electrode Assembly (MEA) and the flow field. This series article contains two parts. In this paper, i.e., Part Ⅰ of this series, a three-dimensional, two-phase flow, non-isothermal, steady-state Computational Fluid Dynamics (CFD) model is established to investigate the liquid water generation mechanism and the species distributions inside an air-cooled PEMFC single cell with a Base Case flow field design. Dry hydrogen and ambient air (the relative humidity and the stoichiometry are 60% and 150 separately) are considered for the simulation and validation. It is found that the liquid water appears mostly inside the cathode electrode underneath the cathode rib. Inside the anode gas diffusion layer (GDL), the mass fraction of H2 underneath the cathode ribs is lower than that underneath the cathode channels, while the mass fraction of H2O shows the opposite. The distributions of O2 mass fraction and H2O mass fraction inside the cathode GDL have the same trend as those of H2 mass fraction and H2O mass fraction inside the anode GDL. The membrane water content is periodically distributed from channel to channel and its value underneath the cathode rib is much larger than that underneath the cathode channel. The current density distribution is affected by the distribution of water content, i.e., the part underneath the cathode rib shows a larger current density than that underneath the cathode channel.

Unraveling the cohesive and interfacial adhesive strengths of electrodes for automotive fuel cells

Despite the pressing need to develop highly durable electrodes for electric vehicles powered by polymer electrolyte membrane fuel cells (PEMFCs), evaluating the mechanical robustness of the electrodes in membrane electrode assemblies (MEAs) has proven challenging because the electrodes are intrinsically porous and brittle. Herein, we propose a novel technique for effectively quantifying the mechanical robustness of the electrodes using a surface and interfacial cutting analysis system (SAICAS). The SAICAS enables the separate quantification of cohesion and adhesion of PEMFC electrodes. We find that the adhesion at the interface is higher than the cohesion in the bulk owing to a larger intermolecular diffusion at the interface than in the bulk. Also, the SAICAS could reliably quantify the cohesion and adhesion of PEMFC electrodes having different ionomer contents and assembly temperatures. Our findings are intriguing and will be useful for the efficient and effective design and development of robust electrodes and MEAs.

Study of relative humidity on durability of the reversal tolerant proton exchange membrane fuel cell anode using a segmented cell

Cell voltage reversal resulted from hydrogen starvation at the anode is one of the factors that exacerbate the overall degradation of proton exchange membrane fuel cells (PEMFCs). An effective mitigation strategy is to involve oxygen evolution reaction (OER) catalysts into the anode to facilitate water electrolysis against carbon corrosion. As such, this paper aims to study the influence of relative humidity (RH) on the performance and durability of reversal-tolerant-anodes (RTAs) during hydrogen starvation. An advanced segmented technique is employed to examine the coupling reactions by simultaneously measuring current density, RH and temperature in a fuel cell with a large active area. It is found that the inlet of RTAs undergoes degradation earlier than the outlet and the membrane electrode assembly (MEA) with a RTA has an optimal humidity during cell reversal. Results also show that the failure of the RTA MEA is due to a loss of electron conduction medium rather than the deactivation of the OER catalyst. In addition, this work highlights the importance of plate flow field design and the OER catalyst gradient design of the RTA MEA.

(Invited) The Evolution of Membrane Electrode Assemblies for Automotive Applications

Membrane Electrode Assemblies (MEAs) have evolved significantly in recent years to become a complex piece of technology. Currently, MEAs incorporate a variety of catalyst types and supports which need to be integrated into layers for both anode and cathode electrodes. In addition, the additives used in the membrane have also become more complex, to mitigate gas crossover and degradation that can be caused by metal ion impurities, thus enabling the deployment of thinner membranes (<15 mm). Further, different approaches to maximising the power per cost lead to different power density requirements. For example, the performance target set by the US-DOE is 1.0 W/cm2, whereas in EU funded program GAIA1 the target is a demanding 1.8 W/cm2. This forces MEA developers to carefully design each component to enable mass commercialization. This presentation will document recent advances at JM in the design of MEAs for the transportation industry, with an emphasis on the integration of scaled-up alloy catalysts in cathode layers. Results from advanced catalyst characterisation using state of the art TEM and XPS facilities will be provided; these results have helped identify the mechanisms that compromise catalyst stability and activity and have allowed the synthesis of new materials and layers that will enable thrifting of Pt to levels that will help mass commercialization. In addition, with the help of 1D testing and the use of simulation tools such as OpenFCST, insights will be provided into proton and oxygen transport limitations at high current densities. Finally, a detailed analysis will also be provided that highlights the importance of understanding catalyst and ionomer surface compositions to give high kinetic activity whilst also enabling high performance at high current densities in H2/Air, in order to reach 1.8 W/cm2. References GAIA, Grant Agreement Number 826097, http://www.gaia-fuelcell.eu/ Acknowledgements The GAIA project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 826097. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research.