Commercial Membrane Electrode Assembly Research Articles

Constructing Highly Porous Low Iridium Anode Catalysts Via Dealloying for Proton Exchange Membrane Water Electrolyzers.

Iridium (Ir) is the most active and durable anode catalyst for the oxygen evolution reaction (OER) for proton exchange membrane water electrolyzers (PEMWEs). However, their large-scale applications are hindered by high costs and scarcity of Ir. Lowering Ir loadings below 1.0 mgcm-2 causes significantly reduced PEMWE performance and durability. Therefore, developing efficient low Ir-based catalysts is critical to widely commercializing PEMWEs. Herein, an approach is presented for designing porous Ir metal aerogel (MA) catalysts via chemically dealloying IrCu alloys. The unique hierarchical pore structures and multiple channels of the Ir MA catalyst significantly increase electrochemical surface area (ECSA) and enhance OER activity compared to conventional Ir black catalysts, providing an effective solution to design low-Ir catalysts with improved Ir utilization and enhanced stability. An optimized membrane electrode assembly (MEA) with an Ir loading of 0.5 mgIr cm-2 generated 2.0 A cm-2 at 1.79V, higher than the Ir black at a loading of 2.0 mgIr cm-2 (1.63 A cm-2). The low-Ir MEA demonstrated an acceptable decay rate of ≈40 µV h-1 during durability tests at 0.5 (>1200 h) and 2.0 A cm-2 (400 h), outperforming the commercial Ir-based MEA (175 µV h-1 at 2.0 mgIr cm-2).

Lattice Boltzmann Model Investigation of Simultaneous Imbibition/Evaporation in PEMFC Cathodic Catalyst Layer Using Reconstructed 3D Image Data from Transmission Electron Microscopy

Proton Exchange Membrane Fuel Cells (PEMFCs) are widely used and significant attention is directed towards optimizing of the cathode catalyst layer. The critical focus revolves around refining the multi-phase boundary of the electrically conducting carbon support, the ion-conducting ionomer, the catalyst particles as well as the pore space that can be either occupied by oxygen (feedstock) or water (product). Challenges related to mass transport limitations of oxygen towards these multiple-phase boundaries, also denoted as active sites, persist, especially when liquid water increasingly saturates the pore space (Fig. 1). Furthermore, the evaporated water additionally hinders oxygen transport in the gas phase1,2. This study focuses on the investigation of pore-scale transport mechanisms inside of the cathodic catalyst layer, taking into account the counter-current diffusion of oxygen and water vapor in the gas phase as well as the generation of liquid water that increasingly saturates the void space. For this purpose, a multi-phase and multi-component pore scale Lattice Boltzmann model (LBM), coupled to two-phase reaction, was implemented. The LBM is tailored based on previous works3,4, including the localized generation of water at constant current densities, the imbibition of the pore structure with water counter-currently to the diffusion of oxygen, and the simultaneous evaporation of water. An actual 3D cathode catalyst layer from a commercial membrane electrode assembly, reconstructed from transmission electron microscopy (TEM) image data, was employed. It was imaged using a source voltage of 200kV and a current of 2 nA. The scanned sample had an approximate total volume of 500 × 500 × 100 nm3. From this, a 3D domain of 138 × 138 × 58 nm3 was reconstructed for this study. A 2D cross-section of the reconstructed image is exemplarily shown in Fig. 1. The in-silico study of water and oxygen transport through the catalyst layer elaborates the relationship between the rates of water invasion and evaporation in dependence of current density and catalyst layer structure. The critical conditions for water flooding are evaluated for different process conditions. Fig. 1 Schematic representation of the cathode catalyst layer: The ionomer is represented in white; the carbon for electron connectivity is represented in gray; pore space for oxygen and water transport in yellow; the black circles represent the active sites, i.e., Pt-particles located at the multi-phase boundary of ionomer, carbon and oxygen-filled pores; the red circles represent the inactive sites, that have no connection to ion and/or oxygen transport pathways. References A. Suzuki et al., Int. J. Hydrogen Energy, 36, 2221–2229 (2011) https://www.sciencedirect.com/science/article/pii/S0360319910022913.M. El Hannach, M. Prat, and J. Pauchet, Int. J. Hydrogen Energy, 37, 18996–19006 (2012) https://www.sciencedirect.com/science/article/pii/S0360319912022069.S. Bhaskaran et al., Dry. Technol., 40, 735–747 (2022) https://doi.org/10.1080/07373937.2021.1898417.S. Bhaskaran et al., Int. J. Hydrogen Energy, 47, 31551–31565 (2022) https://www.sciencedirect.com/science/article/pii/S0360319922030932. Figure 1

Electrospun Nanofiber Catalyst Support for Polymer Electrolyte Membrane Fuel Cells

Increased energy demand and environmental concerns are driving the search for cleaner, more efficient power generation. Fuel cells (FCs) offer a solution by converting chemical energy from fuel and oxidant directly into electricity with high efficiency (40-70%) and zero carbon emissions. Enhancing the performance and durability of polymer electrolyte membrane fuel cells (PEMFC) while reducing costs remains a significant challenge. The current planar FC design presents various issues, including high costs and weight due to metal or graphite bipolar plates, high-pressure drop-in reactant gas diffusion channels, reactant gas transport losses in the agglomerate-type catalyst layers, water flooding, to name just a few. Exploring novel biomimetic designs may offer solutions to these challenges.This research is inspired by vascular plant structures to improve mass transport and efficiency. The cathode uses carbon nanofibers (CNF) made via electrospinning, with Pt nanorod catalyst on the surface in an open electrode layout. This CNF-type cathode was used to create a membrane electrode assembly (MEA), using a commercial membrane and typical anode. A number of parameters were varied, including overall Pt loading, Pt concentration on the fibers, design with and without gas diffusion layer, using CNF mat. The MEAs were tested to establish links between structure, properties, and performance. Performance was evaluated through polarization curves and electrochemical impedance spectroscopy, while beginning of test and end of test structure was investigated using microscopy. CNF-based MEAs achieved a higher current density compared to the commercial MEA at lower Pt loading. This suggests that reduced loading still maintained acceptable Pt utilization, reducing the Pt amount in the MEA. In summary, the CNF catalyst support displayed improved durability, mass transport, Pt utilization, and efficiency thanks to its porous mesh structure.

Advanced Porous Transport Electrode for High-Performance Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) hold great potential for supplying green hydrogen to support extensive energy storage and mobility in a future energy landscape centered on renewable energy sources.1,2 However, their contribution to global hydrogen production is currently limited, mainly due to their comparatively high cost.3 To improve the economic competitiveness of green hydrogen and foster broader market penetration, the Department of Energy (DOE) has launched the Hydrogen Earthshots, aiming for a substantial cost reduction to $2 per kilogram by 2025 and $1 per kilogram for green hydrogen by 2030.4 The high efficiency and prolonged durability are pivotal for the overall performance and cost reduction of the PEMWEs. This requires careful consideration of the interfacial contact between the porous transport layer (PTL) and the anode catalyst layer.5 One option for PEMWEs is to directly coat the anode catalyst layer onto the PTL, forming porous transport electrodes (PTEs). Recent literature suggests that it is feasible to manufacture PTEs with low precious metal loading, demonstrating both high performance and durability.6,7 In this study, an innovative reactive spray deposition technology (RSDT) is used to fabricate PTEs with low PGM loading (0.2 - 0.3 mgPGM cm-2) in both catalyst layers. The RSDT is a flame-based method that combines the synthesis and deposition of the catalyst in a single step, significantly reducing the fabrication time and cost of the membrane electrode assembly (MEA).8–11 The RSDT-fabricated PTEs are coupled with various membranes, and their performance has been assessed and compared to the state-of-the-art MEAs for PEMWEs. In addition, the performance loss in each cell has been studied and discussed in detail. Furthermore, a standard accelerated stress test (AST) protocol has been applied to assess the durability of the RSDT-fabricated MEAs, with one order of magnitude lower PGM loading in their catalyst layers in comparison to the commercial MEAs for PEMWEs.Reference1. Pham, C. Van, Escalera-López, D., Mayrhofer, K., Cherevko, S. & Thiele, S. Essentials of High Performance Water Electrolyzers – From Catalyst Layer Materials to Electrode Engineering. Adv. Energy Mater. 11, (2021).2. Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energy 38, 4901–4934 (2013).3. Buttler, A. & Spliethoff, H. Current status of water electrolysis for energy storage, grid balancing, and sector coupling via power-to-gas and power-to-liquids: A review. Renew. Sustain. Energy Rev. 82, 2440–2454 (2018).4. Styapal, S. et al. DOE Update on Hydrogen Shot, RFI Results, and Summary of Hydrogen Provisions. (2021).5. Peng, X. et al. Insights into Interfacial and Bulk Transport Phenomena Affecting Proton Exchange Membrane Water Electrolyzer Performance at Ultra-Low Iridium Loadings. Adv. Sci. 8, (2021).6. Xie, Z. et al. Ionomer-free nanoporous iridium nanosheet electrodes with boosted performance and catalyst utilization for high-efficiency water electrolyzers. Appl. Catal. B Environ. 341, 123298 (2024).7. Lee, J. K. et al. Ionomer-free and recyclable porous-transport electrode for high-performing proton-exchange-membrane water electrolysis. Nat. Commun. 14, 1–11 (2023).8. Zeng, Z. et al. Advanced nickel-based catalysts for the hydrogen oxidation reaction in alkaline media synthesized by reactive spray deposition technology: Study of the effect of particle size. Int. J. Hydrogen Energy 1–12 (2023) doi:10.1016/j.ijhydene.2023.03.249.9. Zeng, Z. et al. Degradation Mechanisms in Advanced MEAs for PEM Water Electrolyzers Fabricated by Reactive Spray Deposition Technology. J. Electrochem. Soc. 169, 054536 (2022).10. Xing, J. et al. Long-term durability test of highly efficient membrane electrode assemblies for anion exchange membrane seawater electrolyzers. J. Power Sources 558, 232564 (2023).11. Mirshekari, G. et al. High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment. Int. J. Hydrogen Energy 46, 1526–1539 (2021).

Open Circuit Voltage Hold Induced Degradation Under Dry Conditions and Recovery Strategies in PEMFC Electrodes

With regards to the decarbonization of the transportation sector in the near future, the importance of proton exchange membrane (PEM) fuel cells is shifting more and more from light-duty vehicles to heavy-duty vehicles, as well as to an application for maritime and aviation applications. With this change in the field of application, the requirements of the fuel cell system need to be adjusted towards an increased fuel efficiency and lifetime.1 Especially the targeted durability of 25,000 h for heavy-duty vehicles requires a detailed understanding of the degradation processes within the stack to be able to minimize performance losses or possible failure of the components.2 During the life cycle of a fuel cell electric vehicle, the stack encounters operation under increased temperature as well as under low relative humidity (RH). Both conditions are well known to lead to a degradation of the membrane electrode assembly (MEA).3,4 Deliberate operation under those conditions and at open circuit voltage (OCV) is commonly used to study the chemical degradation of the membrane. Here it is believed that gas crossover can lead to the formation of radicals, which attack the perfluoro sulfonic acid based ionomer chains and result in a variety of degradation products.5,6 Especially sulfonate group containing degradation species strongly adsorb on the Pt surface and reduce the oxygen reduction reaction (ORR) activity of the cathode catalyst. It was already shown that a suitable recovery step can restore of most of the observed performance losses.3,5 This work focusses on the chemical degradation and subsequent recovery strategies of a commercial MEA with an active area of 5 cm2 and a cathode loading of 0.4 mgPt/cm2. Although it is known that radical scavengers, like Ce3+ cations, minimize the chemical degradation within the membrane, we decided to use an MEA with a non-mitigated membrane (i.e., free of radical scavengers) in order to facilitate the degradation processes.5 As seen in the upper panel of Figure 1, the applied OCV hold for 72 h under H2/air (1000/1000 nccm) at 95 °C and at 30 % RH induces a voltage loss of ~115 mV (at 2.5 A/cm²) in the polarization curve after this accelerated stress test (AST), i.e., at end-of-degradation (EOD; red line/symbols), compared to the initial MEA performance at beginning-of-test (BOT; black line/symbols). In order to distinguish between reversible and irreversible losses, a subsequent recovery step at fully humidified conditions is implemented. The polarization curve at end-of-test (EOT; green line/symbols), i.e., after the recovery step, reveals that the majority of the observed losses is reversible. Provided that the applied recovery step accounts for all reversible effects, the remaining losses of ~45 mV (at 2.5 A/cm²) are of irreversible nature. On the one hand, those irreversible losses partially arise from a small increase in the high frequency resistance (HFR), which rises during the degradation period by ~2 mΩcm² (lower panel of Figure 1. On the other hand, the electrochemically active surface area (ECSA) is reduced by ~20 % over the course of the experiment, which leads to another unavoidable loss in performance. The comparison of the catalyst’s specific activity in units of mA/cm2 Pt, hence, accounting for the loss in ECSA, strongly suggests that the Pt surface at EOT approaches the initial state at BOT, which indicates a reversible degradation mechanism. References A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers and A. Kusoglu, Nat. Energy, 6(5), 462–474 (2021).Marcinkoski, R. Vijayagopal, J. Adams, B. James, J. Kopasz, R. Ahluwalia, Hydrogen Class 8 Long Haul Truck Targets, DOE Hydrogen Program Record# 19006, https://www.hydrogen.energy.gov/docs/hydrogenprogramlibraries/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf (2019).Du, T. A. Dao, P. V. J. Peitl, A. Bauer, K. Preuss, A. M. Bonastre, J. Sharman, G. Spikes, M. Perchthaler, T. J. Schmidt and A. Orfanidi, J. Electrochem. Soc., 167(14), 144513 (2020).Jomori, K. Komatsubara, N. Nonoyama, M. Kato and T. Yoshida, J. Electrochem. Soc., 160(9), F1067–F1073 (2013).Zhang, B. A. Litteer, F. D. Coms, R. Makharia, J. Electrochem. Soc., 159(7), F287–F293 (2012).A. Yandrasits, S. Marimannikkuppam, M. J. Lindell, K. A. Kalstabakken, M. Kurkowski and P. Ha, J. Electrochem. Soc., 169(3), 34526 (2022). Acknowledgements We gratefully acknowledge funding from the German Federal Ministry for Digital and Transport (BMDV) under the funding scheme H2Sky (funding code 03B10706). Figure 1

Comprehensive Effort on Electrode Slurry for Proton Exchange Membrane Water Electrolysis

Green hydrogen production through renewable energy-based water electrolysis is the most efficient technology for decarbonization, and demand has recently been rapidly increasing. Addressing this surge in demand requires the rapid development of reliable large-scale manufacturing methods for PEMWE membrane-electrode assemblies (MEAs).For reliable large-scale manufacturing, it is necessary to optimize electrode components, including catalysts, binders, solvents, and additives, as well as their dispersion methods. Particularly, ensuring the homogeneity and stability of the electrode slurry is crucial.In this study, we enhanced the stability of the electrode slurry to twice and five times that of the existing standard by selecting an appropriate dispersion method for the metal-oxide oxygen evolution reaction (OER) catalyst and by adjusting the OER catalyst (both support and particle size control), respectively. Additionally, we secured stable electrode coating characteristics by controlling the solvent composition and additives, based on the rheology of the slurry. By optimizing the composition, formulation, and preparation method of the electrode slurry to form an optimal catalyst layer, we achieved a 20% improvement in performance compared to commercial MEA products.

An Air Over-Stoichiometry Dependent Voltage Model for HT-PEMFC MEAs

In this work, three commercially available Membrane Electrode Assemblies (MEAs) from Advent Technology Inc. and Danish Power Systems, developed for a use in High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC), were tested under various Operating Conditions (OCs): over-stoichiometry of hydrogen gas (1.05, 1.2, 1.35), over-stoichiometry of air gas (1.5, 2, 2.5), gas oxidant (O2 or air) and temperature (140 °C, 160 °C, 180 °C). For each set of operating conditions, a polarization curve (V–I curve) was performed. A semi-empirical and macroscopic (0D) model of the fuel cell voltage was established in steady state conditions in order to model some of these experimental data. The proposed parameterization approach for this model (called here the “multi-VI” approach) is based on the sensitivity to the operating conditions specific to each involved physicochemical phenomenon. According to this method, only one set of parameters is used in order to model all the experimental curves (optimization is performed simultaneously on all curves). A model depending on air over-stoichiometry was developed. The main objective is to validate a simple (0D) and fast-running model that considers the impact of air over-stoichiometry on cell voltage regarding all commercially available MEAs. The obtained results are satisfying with AdventPBI MEA and Danish Power Systems MEA: an average error less than 1.5% and a maximum error around 15% between modelled and measured voltages with only nine parameters to identify. However, the model was not as adapted to Advent TPS® MEA: average error and maximum error around 4% and 21%, respectively. Most of the obtained parameters appear consistent regardless of the OCs. The predictability of the model was also validated in the explored domain during the sensibility study with an interesting accuracy for 27 OCs after being trained on only nine curves. This is attractive for industrial application, since it reduces the number of experiments, hence the cost of model development, and is potentially applicable to all commercial HT-PEMFC MEAs.

Long Term Evolution of MEA for AEM

Green hydrogen technology, aimed at revolutionizing clean hydrogen production, has recently garnered significant attention. However, the pursuit of cost-effective methods for obtaining clean hydrogen remains a substantial challenge for various industries. Anion exchange membrane water electrolysis (AEMWE) has emerged as a promising solution, leveraging low-cost materials and high efficiency, thus attracting extensive interest from both researchers and industries. Yet, the adoption of AEMWE faces two major hurdles: its relative immaturity as a technology and the limited exploration of its durability and stability. Within the Production, Use, and Storage of Hydrogen (PUSH) Research Center, a collaborative effort involving Chalmers Technical University, Lund University, Umeå University, and Research Institutes of Sweden (RISE), we are dedicated to addressing the scientific and technical barriers currently hindering the seamless integration of hydrogen into sustainable energy systems. Our comprehensive research strategy encompasses every facet of hydrogen, including production, storage, distribution, and utilization, all working synergistically in harmony. One of the ongoing projects in this research center, conducted in cooperation with RISE, around enhancing the durability of components and devices through advanced testing techniques applied to AEMWE. This study present the results of a 2000-hour lifetime test and Accelerated Stress Testing (AST) conducted on a commercial Membrane Electrode Assembly (MEA), showcasing the system's remarkable stability. It must be mentioned that in the next step, these results will be compared with lifetime test and AST from MEAs from other partners within PUSH Research Center.

Porous Electrode Optimization for PEMFCs Using 3D Printing Technology

Proton Exchange Membrane Fuel Cells (PEMFCs) represent a class of fuel cells that transform the chemical energy of fuels, ideally hydrogen and oxygen, into electrical power. Utilized in diverse applications, PEMFCs power vehicles and supply backup energy to buildings. The core of a PEMFC is the membrane electrode assembly (MEA), composed of a polymer electrolyte membrane, an anode, and a cathode. Oxygen, protons, and electrons merge at the cathode, forming water. One challenge PEMFCs face is water-induced cathode flooding at low temperatures, a consequence of the electrochemical reaction's water accumulation. This reduces the oxygen supply, potentially leading to decreased cell performance or even failure. This issue can have substantial undesired consequences, as PEMFCs depend on oxygen availability at the cathode to generate electricity.Gas Diffusion Layers (GDLs) serve as critical PEMFC components, providing porous structures that facilitate reactant access to the catalyst layer and enabling electron flow through the external circuit. GDLs also offer structural support and promote reactant distribution across the membrane surface. Water accumulation in the cathode may cause pore clogging within the GDL, restricting reactant flow, and reducing cell performance. Additionally, water build-up increases pressure drop across the GDL, hindering reactant access to the catalyst layer and diminishing fuel cell efficiency.Three-dimensional (3D) printing has emerged as a potential technique for fabricating GDLs in PEMFCs. 3D printing enables the creation of GDLs with ordered pore size structures, offering a more uniform surface than traditional GDLs with randomly oriented fibres. This uniformity enhances reactant distribution across the membrane surface and mitigates water accumulation risks. In addition, to prevent cathode flooding, 3D printed GDLs are immersed in PTFE solution to increase hydrophobicity.This talk delves into the creation and evaluation of 3D printed carbonized GDLs for PEMFC implementation. A desktop 3D printer constructed a polymer framework, which was subsequently carbonized in a high-temperature tube furnace. Isothermal thermogravimetric analysis (TGA) tests were performed to identify weight change across a temperature range of 30-900 °C under an N2 atmosphere, optimizing the carbonization step to reduce structural distortion and increase electrical conductivity.The 3D printed GDLs displayed pore size diameters spanning 80 to 120 μm and fibre radii of 20-30 μm. The 3D printing technique produced GDLs characterized by a consistent, planar structure without blocked pores that are normally caused by excess resin residue. Electrical conductivity assessments were conducted on the carbonized specimens, and tensile and compression tests measured their mechanical properties.GDLs possessing minimal pore sizes and thicknesses were integrated into membrane electrode assemblies (MEAs) and examined in low-temperature PEMFCs. Diverse spraying methodologies were investigated, involving either the catalyst being sprayed onto the 3D printed GDL or the membrane receiving a catalyst coating. Commercial MEAs, comprising Nafion membranes and platinum electrodes, acted as benchmarks for MEAs featuring 3D printed GDLs. Furthermore, the current challenges facing 3D printed GDLs, including material selection, production consistency, compatibility with other PEMFC components, costs, and scaling up are highlighted in the talk.These findings underscore the promise of 3D printed carbonized GDLs in boosting PEMFC performance, showing their potential as a cost-effective and proficient substitute for conventional carbon paper based GDLs. Figure 1

Analysis of PEM Membrane Electrode Assemblies Impact on the Levelized Cost of Hydrogen

Plug is building an end-to-end green hydrogen ecosystem to help its customers meet their business goals and decarbonize the economy. This hydrogen ecosystem is inclusive of production, storage, delivery, and energy generation. As the largest user of liquid hydrogen globally, Plug Power plans to build and operate green hydrogen production plants across North America and Europe. Plug’s hydrogen production plants are based on electrolyzer systems featuring internally developed proton exchange membrane (PEM) based water electrolysis membrane electrode assemblies (MEAs). This paper will review the state of commercial PEM water electrolysis MEAs and provide insight as to what advances in MEA technology are needed to produce hydrogen at a levelized cost of $1/kg.The cell polarization curves for two modeled PEM MEAs are shown in Figure 1. They represent the performance of both commercial and future PEM water electrolyzer technology. As the applied current density to the cell increases, so does the cell voltage, and thus the energy required to produce a kilogram of hydrogen. As the MEA technology in the stack matures, the applied current density, and thus, the hydrogen production rate can increase at a set efficiency. A 155 cell, 1,000 cm2 active area, electrolyzer stack featuring commercial MEAs would produce approximately 220 kg-H2/day at an efficiency of 49 kWh/kg-H2. With the future MEAs, this same stack, operating at the same efficiency, could produce as much as 1,200 kg-H2/day.A hydrogen plant with a production capability of 45 metric tons per day, featuring commercial MEAs, would produce hydrogen at a cost of approximately $6/kg when powered by energy at a price of $35/MWh. The MEA cost represents only a few percent of the total capital expenditure required to build a 45 metric ton hydrogen plant. Thus, MEAs would only contribute a few cents to the estimated $6/kg levelized cost of hydrogen (LCOH). They, however, are responsible for most of the energy consumed at a hydrogen plant. Therefore, the MEAs could account for 50%, or more, of the total cost to produce hydrogen. A savings of $328M to $410M can be realized or every $1/kg reduction in LCOH over the lifetime of a hydrogen plant. Thus, performance improvements in the MEA are paramount to making hydrogen production competitive with other energy carriers.The oxygen evolution catalyst featured in a future MEA would be required to achieve a greater than four-fold increase in activity. The PEM of the future MEA would also be required to support a substantial increase in proton transfer while maintaining its integrity for greater than 100,000 hours. These advances, as well as savings in hydrogen plant capital expenditures, are required to achieve a LCOH of approximately $1/kg at a fixed energy cost of $35/MWh. Even at the lowest projections for capital expenditures, most of the cost of hydrogen will be dominated by power consumption, further highlighting the importance of maturing PEM water electrolysis MEA technology. Figure 1

Investigating Proton Exchange Membrane Fuel Cell Durability at Intermediate Temperatures (80 – 120 °C)

For several applications the low operating temperature of 60-80 °C of proton exchange membrane fuel cells (PEMFCs) limit their potential use. Increasing this temperature above 100 °C would simplify the water management and increase the temperature of the produced heat which would allow for more effective cooling systems [1,2]. Further, increasing the operating temperature could potentially allow for other benefits, such as the employment of more affordable catalysts, as the reaction kinetics are enhanced at elevated temperatures. However, operating at higher temperatures can cause increased degradation on the utilized components [3].In this work we investigated how commercial proton exchange membrane electrode assemblies (MEA) aged at various temperatures when operating either using a load cycle (based on the New European Drive Cycle) or constant load. The state of health of the MEA was continuously monitored through cyclic voltammetry, electrochemical impedance spectroscopy, linear sweep voltammetry, CO-stripping measurements and polarization curves. The obtained ageing results were evaluated using a physics-based model using COMSOL to better understand what aging mechanisms were pronounced at higher operating temperatures. Finally, the aged MEA were characterized with SEM and TEM analysis.The results show that all samples underwent an ageing process and that the ageing was accelerated at higher temperatures, as can be seen in the figure . Further, the ageing was more pronounced at a higher load. The measurements showed that the main ageing is occurring at the cathode catalyst layer and a drastic reduction in the electrochemical active surface area of the catalyst was observed. The membrane properties were also altered by the ageing, and a minor reduction in the membrane conductivity was observed. Surprisingly, no significant increase in the hydrogen crossover was observed, suggesting that the elevated temperature does not cause significant pinhole formation.The results shed light on the rate and mechanisms for ageing at various temperatures and can be used to determine the cost and benefits of operating at elevated temperatures.

Soluble ultra-high molecular weight poly(4,4′-diphenylether-5,5′-bibenzimidazole) based membranes with remarkable mechanical strength and specific proton conductivity for high temperature proton exchange membrane fuel cells

Reducing the thickness of membrane electrolyte is one important direction to improve Ohmic polarization and the according performance of high-temperature proton exchange membrane fuel cells for its widespread applications. Herein, we report that robust thin membranes can be formed using a soluble ether-contained poly(4,4′-diphenylether-5,5′-bibenzimidazole) with an ultra-high molecular weight of 170 kDa. Due to the enhanced chain entanglement of high molecular weight polymers, the formed thin membrane exhibits promising mechanical strength, thermal and oxidation stability. The optimized membrane with thickness of 61 μm and phosphoric acid uptake of 606 wt% has the high specific proton conductivity of 25.9 S cm−2 at 160 °C under anhydrous conditions and mechanical strength of 11.2 MPa. The accordingly fabricated membrane electrode assembly delivers a peak power density of 0.544 W cm−2 with the open circuit voltage of 0.915 V at 160 °C using air as oxidant, outperforming the value of 0.522 W cm−2 for the commercial membrane electrode assembly with thickness of 250 μm and phosphoric acid uptake of 1018 wt%.

Carbon Monoxide-Resistant Anode Catalysts for Single-Cell Direct Carbon Monoxide Fuel Cells: Platinum-Ruthenium Anode Electrocatalysts

The objective of this paper is to present the results of experimentations on the state-of-the-art anode electrocatalysts and the membrane-electrode assemblies (MEAs) developed for direct carbon monoxide fuel cells (DCMFCs). The custom-made platinum-ruthenium (Pt-Ru) MEAs along with a commercial MEA were tested to evaluate the impacts of cell temperature, different types of fuel and oxidant, the flow rate of fuel and oxidant, and humidification temperature on the performance of the MEAs. It was shown that both the catalyst manufacturing process and the test procedure are repeatable. Also, it was shown that the performance of Pt-Ru cells when fueled by CO and CO-containing fuels was markedly inferior to that of hydrogen-fueled fuel cells. However, there were some promising signs that with the right catalysts and optimum operating conditions, the performance of DCMFCs can be significantly improved. It was also shown that increasing the operating temperature always improved the performance. While increasing the flow rates of the reactants improved the performance of the MEAs, there was a limit to this improvement. Furthermore, generally speaking, the performance of the MEAs was better when fed with CO rather than CO-N2 and O2 rather than air but the actual impact depended on other operating conditions.

Carbon Monoxide-Resistant Anode Catalysts for Single-Cell Direct Carbon Monoxide Fuel Cells: Binary, Ternary, And Quaternary Platinum Alloys as Anode Electrocatalysts

The objective of this paper is to present the results of experimentations on the custom-made anode electrocatalysts for direct carbon monoxide fuel cells (DCMFCs) inspired by catalysts commonly used for direct alcohol fuel cells. Seven different catalysts were fabricated and tested. The uniform and consistent manufacturing process and the test procedure allowed a meaningful comparison of the developed fuel cells. The results indicated that homemade Pt-Ru membrane-electrode assembly (MEA) could not compete with the Pt-Sn MEA. While the performance of the MEAs with Pt-Ru-Ni, Pt-Ru-Sn-Ni, and Pt-Ru-Sn-Co was not satisfactory, the Pt-Ru-Sn-Co-W MEA achieved the best performance among all MEAs with Nafion® 117 membrane. The last MEA was made of the Pt-Sn anode catalyst and Nafion® 212 membrane and outperformed all other MEAs by a wide margin. The experiments demonstrated that the performance of the best-developed MEA was three times better than the performance of the commercial Pt-Ru MEA. This means the performance of DCMFCs can be significantly improved by developing a suitable anode electrocatalyst, using a thinner membrane, and operating at optimum conditions. These results are not only applicable for DCMFCs but also are very useful for other proton exchange membrane fuel cells (PEMFCs) operating with CO-containing fuels.

Transport Properties of Iridium Oxide Catalyst Layers for Proton Exchange Membrane Water Electrolyzers

One of the current challenges of proton exchange membrane (PEM) water electrolyzers (PEMWE) is to reduce the high costs associated with iridium as the anode catalyst material. In commercial PEMWE membrane electrode assemblies (MEAs), loadings of iridium are as high as 2 to 3 mgIr/cm2. However, for PEMWE systems to match global energy demand, the Ir-specific power density must increase by ~ 50-fold [1, 2]. This can be achieved by decreasing iridium loadings and increasing the utilization of iridium. Previous work has determined that homogeneity of anode catalyst layers is generally favorable and even necessary for good electrochemical performance at lower iridium loadings [1-3]. However, gaining a better understanding of the important micro- and nano-scale features of iridium oxide (IrO2) catalyst layers is still needed for informing fabrication methods and achieving higher Ir-specific power density operation. Our previous work used nano-scale X-ray computed tomography (nano-CT) and plasma-focused ion beam cross sectioning with scanning-electron microscopy (pFIB-SEM) to characterize several IrO2 catalyst layers varying in coating methods and steps along the fabrication and testing lifetime, finding differences in morphological properties particularly of the pore size distributions. Our current work expands on this image-based characterization to elucidate transport properties between catalyst layers fabricated with different coating methods and iridium loadings. Using modeling and simulation techniques, effective transport properties for pore and solid phases such as oxygen diffusivity, conductance, and tortuosity will be examined using the high-resolution image-based data. The results presented in this work will help elucidate the transport phenomena through the IrO2 catalyst layer and the relationship between fabrication, morphology, and performance.This conference presentation was developed based upon funding from the Alliance for Sustainable Energy, LLC, Managing and Operating Contractor for the National Renewable Energy Laboratory for the U.S. Department of Energy.[1] Bernt, M., Siebel, A., & Gasteiger, H. A. (2018). Analysis of Voltage Losses in PEM Water Electrolyzers with Low Platinum Group Metal Loadings. Journal of The Electrochemical Society, 165(5), F305–F314. https://doi.org/10.1149/2.0641805jes[2] Kulkarni, D., Huynh, A., Satjaritanun, P., O’Brien, M., Shimpalee, S., Parkinson, D., Shevchenko, P., DeCarlo, F., Danilovic, N., Ayers, K. E., Capuano, C., & Zenyuk, I. v. (2022). Elucidating effects of catalyst loadings and porous transport layer morphologies on operation of proton exchange membrane water electrolyzers. Applied Catalysis B: Environmental, 308. https://doi.org/10.1016/j.apcatb.2022.121213[3] Taie, Z., Peng, X., Kulkarni, D., Zenyuk, I. v., Weber, A. Z., Hagen, C., & Danilovic, N. (2020). Pathway to Complete Energy Sector Decarbonization with Available Iridium Resources using Ultralow Loaded Water Electrolyzers. ACS Applied Materials and Interfaces, 12(47), 52701–52712. https://doi.org/10.1021/acsami.0c15687

The effect of oxygen partial pressure and humidification in proton exchange membrane fuel cells at intermediate temperature (80–120 °C)

The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles would be facilitated if operating temperatures above 100 °C were possible. In this work, the effect of temperature in the intermediate range of 80–120 °C is investigated for a commercial membrane electrode assembly (MEA) through polarization curves and electrochemical impedance spectroscopy. The importance of oxygen partial pressure on voltage is systematically studied by decoupling it from humidity and temperature. The results show that adequate operation at intermediate temperature is achievable if the oxygen partial pressure is sufficient. Although the cathode kinetics is faster with rising temperatures, the voltage gain is counteracted by the decreasing equilibrium potential. At intermediate temperature, the water transport is enhanced, levelling out the relative humidity difference between anode and cathode. However, ionic conductivity in the polymer can become limiting at high currents, due to a smaller relative humidity increase at these temperatures. To conclude, a higher operating temperature does not inherently cause a decrease in obtained current density. Rather, the difficulty to simultaneously have sufficient oxygen partial pressure and high relative humidity causes limitations within the cathode that to some extent can be solved by pressurizing the cell.

Efficient electrocatalytic desulfuration and synchronous hydrogen evolution from H2S via anti-sulfuretted NiSe nanowire array catalyst

Decreasing energy consumption of water splitting strategy by replacing oxygen evolution reaction (OER) with more facile sulfide oxidation reaction (SOR) to H2 evolution and value-added sulfur products is a promising technology. Nevertheless, the unsatisfactory catalyst long-term stability and passivation issues substantially limit the overall productivity. Herein, we report an anti-sulfuretted NiSe nanowire array catalyst on nickel foam (NiSe/NF), this catalyst exhibits a significantly reduced anode potential of 0.49 V vs. RHE at 100 mA cm−2 compared to the oxygen evolution reaction (1.78 V vs. RHE) and remains admirable stability for more than 500 h without passivation. Particularly, the skillful combination of UV–vis, in situ Raman, and attenuated total reflection Fourier transform infrared spectra, we reveal that S2-/HS- has been selectively converted to Sn2- and by-product S2O32- rather than sulfur, which avoids long-perplexing passivation issue of solid sulfur. For the first time, we demonstrate the feasibility of the system (SOR + HER) in a commercial membrane electrode assembly stack, which affords 19.0 mL min−1 H2 at a low cell voltage of 1.0 V with consuming the electricity of 2.63 kWh Nm−3 H2. This work provides a new avenue for low-cost H2 production by H2S electrooxidation desulfurization.

Large–Scale, High-Performance, Durable and Low-Cost Membrane Electrode Assemblies for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane (PEM) water electrolyzers, designed to produce hydrogen from intermittent renewable energy, will play a key role in future sustainable energy systems.1 However, the widespread commercialization of PEM water electrolyzers is obstructed by their high cost, low durability, and safety concerns related to the hydrogen crossover. Currently, the production cost of green H2 is in the range of $3-8 kg-1. In order to boost the commercialization of this clean energy devices and lower the production cost of green H2, DOE implemented targets of $2 kg-1 by 2025 and $1 kg-1 hydrogen by 2030.2 In addition, the durability of all electrolyzer components has to be improved in order to increase the lifetime of a PEM water electrolyzer stack to the targeted 80,000 hours. These challenging targets inspired the researchers all over the world to work on development of novel catalyst and catalyst layers with decreased platinum group metal (PGM) loadings, invent new cost-effective methods for fabrication of membrane electrode assemblies (MEAs), develop innovative designs for the MEAs capable of decreasing the hydrogen crossover, and improve the corrosion resistance of the cell hardware and the other stack components to enhance their durability.In this work, the unique Reactive Spray Deposition Technology (RSDT) is used to fabricate a high-performance, durable, and low-cost MEAs with geometric area of 680 cm2. These large scale MEAs have one order of magnitude lower PGM loadings in their catalyst layers in comparison to the state-of-the-art (SOA) commercial MEAs. The RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition in one step and thus substantially reduces the time and cost for MEAs fabrication.3–5 As fabricated large-scale MEAs with 680 cm2 geometric area of their electrodes, have loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode, which are 10 times lower than the loadings in the SOA MEAs. The MEAs of interest have been tested at steady-state conditions that are typical for an industrial hydrogen production system for over 1000 hours. The cell voltage transients, as well as the periodically measured polarization curves during the test, clearly show that as fabricated MEAs have excellent activity and durability performance. Furthermore, the RSDT fabricated MEAs have integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 % LFL at all measured current densities (from 0.58 to 1.8 A/cm2). In addition, the MEA was subjected to comprehensive post-test analysis to study the degradation mechanisms governing the performance loss during the long-term durability test, and the results obtained will be presented and discussed in this presentation.Reference1. C. Van Pham, D. Escalera-López, K. Mayrhofer, S. Cherevko, and S. Thiele, Adv. Energy Mater., 11 (2021).2. https://www.energy.gov/eere/fuelcells/hydrogen-shot-summit-proceedings-panel-session-1-electrolysis3. H. Yu, N. Danilovic, Y. Wang, W. Willis, A. Poozhikunnath, L. Bonville, C. Capuano, K. Ayers, and R. Maric, Appl. Catal. B Environ., 239, 133–146 (2018).4. G. Mirshekari, R. Ouimet, Z. Zeng, H. Yu, S. Bliznakov, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, and R. Mari, Int. J. Hydrogen Energy, 46, 1526–1539 (2021).5. H. Yu, L. Bonville, J. Jankovic, and R. Maric, Appl. Catal. B Environ., 260, 118194 (2020).

Impact of Accelerated Stress Tests on the Cathodic Catalytic Layer in a Proton Exchange Membrane (PEM) Fuel Cell Studied by Identical Location Scanning Electron Microscopy

Platinum is the most used electrocatalyst in proton exchange membrane fuel cells (PEMFCs). Nonetheless, it suffers from various types of degradation. Identical location electron microscopy has previously been used to observe local catalyst changes under accelerated stress tests (ASTs), giving insight into how individual catalyst particles degrade. However, it is important that such studies are carried out under relevant reaction conditions, as these can differ substantially between liquid half-cells and real PEMFC conditions. In this work, a single cell PEMFC was used to study the degradation of a commercial Pt-catalyzed membrane electrode assembly by performing square wave voltage ASTs in a potential range of 0.6 to 1.0 V. Identical location scanning electron microscopy (IL-SEM) was used to follow the degradation of the cathodic catalytic layer (CL) throughout 14,000 AST cycles. From the IL-SEM, we can conclude that the Pt nanoparticles degrade via Ostwald ripening, crystal migration, and coalescence. Small Pt nanoparticles agglomerate to larger particles or dissolve and redeposit to more stable particles, increasing the average particle size during the ASTs. In addition, cross-sectional TEM images show thinning of the ionomer layer during the AST procedure. The IL-SEM technique facilitates observation of local degradation of the CL in real PEMFCs, which will help to understand different degradation mechanisms, allowing for better solutions to be designed.

(Digital Presentation) Large–Scale High-Performance Low Catalyst Loaded Membrane Electrode Assemblies for Advanced Proton Exchange Membrane Water Electrolyzers

Hydrogen is regarded as the next-generation energy carriers for the future hydrogen economy.1 Among the hydrogen production technologies, proton exchange membrane (PEM) water electrolyzers is considered the favored approach for the implementation of the global hydrogen energy transformation due to its several benefits including high power density operation, low ohmic losses and differential pressure operation. However, (i) high cost mainly from the high platinum group metals (PGM) loading in the catalysts layers; (ii) low durability due to instability of the catalysts layers and membrane; and (iii) poor safety because of hydrogen crossover of PEM water electrolyzers have jeopardized their widespread commercialization. Currently, a new Department of Energy Consortium (H2NEW) has targeted hydrogen production from electrolysis, especially PEM water electrolysis, for use as a clean, sustainable fuel, which can achieve $2/kg hydrogen production cost by 2025.2 This requires a balance between the performance, durability and scale-up cost of membrane electrode assemblies (MEAs) for PEM water electrolyzers.In this work, we demonstrate the capability to fabricate large scale MEAs by the unique Reactive Spray Deposition Technology (RSDT), that have one order of magnitude lower PGM loadings in the catalyst layer than the state-of-the-art (SOA) designs, and activity and durability performance comparable to the SOA commercial MEAs. RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition processes into one step and thus substantially reduces the time and cost for their fabrication.3–5 The RSDT fabricated MEA with 680 cm2 geometric area electrodes, and loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode has been tested at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. The initial steady-state test for over 250 hours, clearly shows excellent activity and stability. In addition, the RSDT fabricated MEA has integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 %LFL at all current densities from 0.58 to 1.8 A/cm2.Reference1. M. Carmo, D. L. Fritz, J. Mergel, and D. Stolten, Int. J. Hydrogen Energy, 38, 4901–4934 (2013).2. https://www.energy.gov/sites/default/files/2021-09/h2-shot-summit-panel1-lte-status.pdf3. H. Yu et al., Appl. Catal. B Environ., 239, 133–146 (2018) https://doi.org/10.1016/j.apcatb.2018.07.064.4. H. Yu et al., Electrochim. Acta, 247, 1155–1168 (2017) http://dx.doi.org/10.1016/j.electacta.2017.07.093.5. G. Mirshekari et al., Int. J. Hydrogen Energy, 46, 1526–1539 (2021) https://doi.org/10.1016/j.ijhydene.2020.10.112.