Anode Catalyst Research Articles

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).

Investigation of Iridium Catalyst Degradation in PEM Water Electrolyzers: Current Density or Cell Voltage?

Proton exchange membrane (PEM) water electrolyzers represent a cornerstone technology in the sustainable production of green hydrogen. However, their large-scale commercialization is hindered by catalyst degradation, particularly the iridium-based anode, which compromises the efficiency and durability of the stack. This study delves into the degradation mechanism(s) of the Ir-based catalyst in the anode of PEM electrolyzers, focusing on the influence of operating conditions such as current density and cell voltage. We have utilized the state-of-the-art R&D platform “PEMI” at Plug Power to construct a rainbow stack that contains several 50 cm2 membrane electrode assemblies (MEAs) with different membrane thicknesses. This innovative approach enables identical current densities across different MEAs while varying the cell voltage on the anode catalyst layer, thereby isolating the effect of cell voltage from current on catalyst degradation.Our investigation seeks to clarify the puzzle whether it is the current density or the cell voltage that determines the transition and degradation of iridium-based catalysts. Preliminary results indicate that different oxidation states of Iridium exhibit significantly different kinetics and conductivity at varied cell voltages. This is corroborated by our synchrotron-based in situ X-ray absorption spectroscopy experiments that unraveled evolution of the anode catalyst layer at elevated cell voltages. By systematically analyzing the degradation patterns of MEAs with different membrane thickness under controlled conditions, we pinpointed the operational parameter that drives catalyst degradation. The finding provides in-depth understanding of the underlying principles that govern the iridium-based catalyst durability and points to strategies mitigating the degradation. It will pave the way for more resilient and efficient PEM water electrolyzers. Acknowledgement. This research used beamline 7-BM (QAS) of the National Synchrotron Light Source II, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory Contract DE-SC0012704. Beamline operations were supported in part by the Synchrotron Catalysis Consortium Grant DE-SC0012335.Keywords: PEM water electrolyzers, catalyst degradation, iridium, current density, cell voltage, MEAs.

Tuning the Bifunctional Properties of Cell Reversal-Tolerant Ir-Pt Electrocatalysts for HOR and Oer

Hydrogen starvation is still a big problem in PEM fuel cells [1]. In order to provide protons and electrons to the cathode during H2 starvation, the carbon oxidation reaction (COR) takes place at the anode [2]. To solve this issue, there are three main strategies: (i) utilization of corrosion resistant support materials, (ii) integration of extensive and complex system mitigation strategies and finally (iii) the addition of co-catalyst to promote the oxygen evolution reaction(OER) instead of COR. [3, 4]In this work, platinum-iridium (PtIr) nanoparticles (NPs) have been designed as a novel bifunctional electrocatalysts to accelerate either the hydrogen oxidation reaction (HOR) or the OER depending on the reaction conditions. Our catalyst concept is the combination of both functionality (HOR and OER) in single Pt-Ir alloy nanoparticles (NPs) deposited on the same support material. The Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different (colloidal and wet-impregnation) routes. Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size and mainly in the metallic state, while strongly oxidized NPs with ~2 nm size are produced by colloidal route. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for HOR and OER compared to pure commercial Pt/C and IrOx catalysts. Very interestingly, the bifunctionality of these Pt-Ir is highly reversible and is robust during accelerated stress tests. Operando Quick-X-ray Absorption Near Edge Structure (XANES) spectroscopy were performed to provide fundamental insights into the reversibility and catalytically active states of these bifunctional catalysts under the working conditions by jumping with the potential between HER and OER within few seconds. The combination of operando XANES, RDE and MEA data show that the bifunctional approach is a promising way to improve the cell reversal-tolerant properties of anode catalyst materials compared to the state-of-the-art Pt-IrOx catalyst materials.

Selectivity Study of Anodic Seawater Electrolysis Catalysts Using the Rotating Ring-Disc Electrode Method

Water electrolysis generating green hydrogen will play a vital role in achieving the net-zero 2050 goal; however, freshwater electrolysis will further strain an already strained supply of clean freshwater.1 If seawater electrolysis can be scaled successfully, it would provide an important source of green hydrogen. Current research on untreated, direct seawater electrolysis is limited, and only recently have studies emerged analyzing catalyst performance at near-neutral pH.2 At industrially-relevant current densities, the formation of corrosive hypochlorite must be considered as a secondary reaction.3 Hypochlorite forms through the chloride oxidation reaction (ClOR), which competes with the oxygen evolution reaction (OER) in seawater electrolysis.2 In this work, we discuss the limitations of the current methods for determining anodic catalyst selectivity between OER and ClOR. The short lifetime of hypochlorite can cause faradaic efficiency measurement methods such as titration or oxygen gas capture to become unreliable, as these tests require that the hypochlorite remain stable. Using a rotating ring-disc electrode (RRDE), we measure the selectivity of common OER catalysts in-situ (Figure 1a). Real-time hypochlorite sensing overcomes the challenge of measuring catalyst selectivity posed by the short lifetime of hypochlorite. Remarkably, a PtRu catalyst outperformed more common OER catalysts with the best in OER selectivity and low overpotential, a novel development in the field of near-neutral water electrolysis. We also determine that elevated heat and low chlorine concentration are conducive to improved OER selectivity on an IrO2 catalyst (Figure 1b). We hope this work will set the standard in catalyst benchmarking for seawater electrolysis catalysts and could lead to the development of catalysts for efficient, scalable, and sustainable hydrogen production from seawater. H. Jin et al., Sci Adv, 9, eadi7755 (2023) https://www.science.org/doi/10.1126/sciadv.adi7755.F. Dionigi, T. Reier, Z. Pawolek, M. Gliech, and P. Strasser, ChemSusChem, 9, 962–972 (2016) https://onlinelibrary.wiley.com/doi/full/10.1002/cssc.201501581.J. Guo et al., Nature Energy 2023, 1–9 (2023) https://www.nature.com/articles/s41560-023-01195-x. Figure 1. a) LSV profiles of common OER catalysts (solid line) and the corresponding faradaic efficiency (dashed line) for the OER, measured using the ring current of the rotating ring-disc electrode. Catalysts were tested in 0.5 M NaCl and buffered with KHCO3 to pH 8.5. b) A ternary plot depicting the effect of varying Cl concentrations and temperatures on the selectivity of an IrO2 catalyst at pH 8.5. Figure 1

Understanding Degradation Mechanisms in PEM Water Electrolysis Under Dynamic and Static Operating Conditions

Hydrogen production by electrolysis has great potential to enable a decarbonized economy, although further effort is needed to decrease its cost to meet ambitious targets, such as the US Department of Energy Hydrogen Earthshot goal of $1/kgH2.1 Achieving such low hydrogen production costs using polymer electrolyte membrane water electrolysis (PEMWE) will require decreasing the cost of input electricity while lowering capital costs through thrifting of iridium and other measures. An important opportunity to lower costs is the use of inexpensive intermittent electricity, either directly sourced from renewables or from grid leveling. However, previous studies have shown that dynamic cycling can accelerate degradation, especially when combined with low iridium catalyst loadings.2 It is therefore necessary to further understand the relevant degradation mechanisms, mitigation strategies, and implications for water electrolysis deployment.Here we present the results of investigations to understand the degradation mechanisms in PEMWEs under dynamic and static operating conditions. This presentation will discuss the attribution of voltage degradation observed during long-term, constant-current operation as well as comparison of the degradation observed under cycled and static test conditions, with select results illustrated in Figure 1. This includes experiments designed to understand the transition between static and dynamic degradation behavior, differences in the degradation mechanisms, and opportunities for mitigation of dynamic degradation. We will further present investigations into the impacts of porous transport layer-catalyst layer interactions on anode catalyst degradation. Finally, we will discuss the implications of these results for guiding research priorities in PEMWE and developing operational and materials-based mitigation strategies.Citations: Energy.gov https://www.energy.gov/eere/fuelcells/hydrogen-shot.S. M. Alia, S. Stariha, and R. L. Borup, J. Electrochem. Soc., 166, F1164–F1172 (2019). Figure 1: Voltage over time profiles for durability tests comparing different current densities and cycle/hold protocols. All tests use anode/cathode catalyst loadings of 0.4 mgIrcm-2/0.1 mgPtcm-2 and a Nafion N115 membrane, operating at 80°C. Figure 1

Improvements in Long-Term Durability of CO2 Electrolyzer Producing Formate Designed for Integration with Solar Cells for Artificial Photosynthesis

Artificial photosynthetic cells have been extensively studied for carbon neutrality, yet in lab-scale. We have previously constructed practically large-sized cells consisting of CO2 electrolyzers and crystalline silicon solar cells.1,2 Our CO2 electrolyzers adopt a facing cathode-anode configuration, using a Ru complex polymer (RuCP) catalyst realizing a low overpotential for CO2 reduction and an IrO x -based catalyst with a high catalytic activity for water oxidation.3 1000 cm2-sized cells achieved a solar-to-chemical energy-conversion efficiency (η STC) of 7.2%,1 and a further scaled-up 1 m2-cell demonstrated a higher η STC of 10.5%, yielding a large formate production rate of 1.2 mol/h.2 In the present study, we improved the long-term durability of the CO2 electrolyzer. We prepared the 75 cm2-sized CO2 electrolyzer using the improved cathode and the anode, and achieved high formate Faradaic efficiencies (FE) exceeding 80% and electricity-to-chemical energy-conversion efficiencies (η ETC) of around 60% even after 3000 h operation under practical conditions, as shown in Fig. 1.In the previous large-sized cells, the operating current gradually decreased during continuous operation within dozen of hours. We investigated the causes of the degradation and identified three key factors. Two of these factors were associated with the cathode electrodes: detachment of the RuCP catalyst from the carbon supports and peeling off of the carbon supports from the conducting Ti substrates. An introduction of a pyrrole derivative containing amino group in the RuCP, coupled with an application of a UV-ozone treatment to create carboxyl groups on the carbon supports, effectively reduced the detachment of the RuCP catalyst by forming strong chemical bonds. A newly-developed chemically-resistant graphite adhesive composed of graphite particles and a polyvinylidene fluoride (PVDF) binder prevented the carbon supports from peeling off from the Ti-plates. The post-loading process of the RuCP, i.e., RuCP-loading on the carbon supports already-bonded on the Ti-plates using the new adhesive eliminated the detrimental impact of the heat treatment for curing the adhesive. The third factor involved detachment of the anode catalyst of IrO x particles from the Ti-plates.4 Therefore, we replaced the IrO x anodes with highly durable counterparts comprising IrO x -TaO x /Pt-Metal oxide/Ti-plates.Another critical issue we addressed was the validity of laboratory-based evaluations for reflecting outdoor operations. In our previous study, we vertically installed the integrated CO2 electrolyzers and solar cells on the ground and evaluated their performance under continuous simulated sunlight (ca. 1 sun).2,3 This vertical setup was chosen to prevent a decrease in η STC caused by crossover reactions that would occur when the electrolyzers are inclined. Indeed, it has been reported that oxygen reduction reaction (ORR) of the O2 bubbles generated at the anode and transferred to the cathode can be substantial in a single-chamber water-splitting reactor.5 By contrast, although the present CO2 electrolyzer was installed at an inclined angle of 30 °, which is approximately the optimal value for receiving more solar energy, the crossover reactions were well-suppressed because the porous separator film inserted between the facing cathode and anode impeded the transfer of O2 bubbles from the anode to the cathode. However, the use of a separator film raised another issue: the O2 bubbles trapped on the film narrowed the effective film area. Intermittent operation corresponding to changes in solar energy during the day mitigates the detrimental impact of the second issue.Thus, we established the groundwork for the widespread use of integrated CO2 electrolyzers and solar cells for artificial photosynthesis, demonstrating high durability, exceptional FE, and η ETC.References N. Kato, et al., A large-Sized Cell for Solar-Driven CO2 Conversion with a Solar-to-Formate Conversion Efficiency of 7.2%, Joule, (2021) 5, 687.N. Kato, et al., Solar Fuel Production from CO2 using 1 m-square-sized Reactor with a Solar-to-Formate Conversion Efficiency of 10.5%, ACS Sustain. Chem. Eng.,(2021) 9, 16031.T. Arai, S. Sato, T. Morikawa, A Monolithic Device for CO2 Photoreduction to Generate Liquid Organic Substances in a Single-Compartment Reactor, Energy Environ. Sci., (2015) 8, 1998.M. Shiozawa, et al., Improved Durability of Highly Active IrO x Electrodes for Electrocatalytic Oxygen Evolution Reaction, Electrocatalysis, (2022) 13, 830.K. Obata, et al., Multiphase Fluid Dynamics Simulations of Product Crossover in Solar-driven, Membrane-less Water Splitting, Cell Rep. Phys. Sci, (2021) 2, 100358. Figure 1

Scanning Electron Microscopy Energy-Dispersive X-Ray Spectroscopy Analysis of Catalyst-Coated Porous Transport Layers

The transition of the United States energy infrastructure towards hydrogen energy involves the optimization of proton exchange membrane water electrolyzers (PEMWEs) for reliable hydrogen generation. PEMWE device typically consists of titanium porous transport layer (PTL) and an iridium-based anode catalyst layer. Several directions are being pursued to improve performance and to reduce the costs. To mitigate naturally occurring titanium passivation, protective coatings, typically platinum or other platinum-group metals (PGMs) are commonly applied to the PTLs. The drive to decrease the cost and the use of scarce materials has led to the development of catalyst layers with lower catalyst loadings. Reducing fabrication time and cost as well as increasing efficiency of the anode has led to the investigation of direct application of the iridium-based catalyst onto the Pt-coated Ti PTL. This motivated our investigation of porous-transport electrodes (PTEs) prepared with a variety of deposition methods, using different ink formulations, and targeting different catalyst loadings. There is need to develop a characterization approach that can be used to assess and compare quality of coatings across large parameter space or to monitor quality during production.Several sets of PTEs samples consisting of a titanium porous layer, platinum protective coating and iridium-based catalyst layer were prepared using a wide range of catalyst layer coating methods and parameters, including spray coating, gravure, airbrush and electrodeposition. All samples were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) to analyze the elemental composition and assess the distribution of elements of interest (Ti, Pt, and Ir). First, the atomic% of each element was used to calculate elemental ratios for quantitative assessment of the amount of deposited catalyst. However, it is crucial to recognize the limitations of relying solely on this information for assessing catalyst coating since it doesn’t account for heterogeneity of the coatings. Although elemental maps provide valuable insights into spatial distribution, they alone do not offer a complete picture. To better understand the catalyst coating distribution, each individual EDS elemental map was used to calculate the surface area, which served as a measure of PTL area covered by the catalyst. Further, surface area ratios (Pt/Ir) were calculated to determine variations in surface coverage. This poster will highlight differences between fabricated samples and will demonstrate that together, at% and surface area ratio values allow for a comprehensive quantitative assessment of the composition and distribution of catalyst surfaces that were produced through a wide range of fabrication variables. The implementation of proper characterization of these PTEs can help aid future decisions on which parameters should be used moving forward. This approach can also be used for quality control, enabling quick screening of commercially produced samples.

Mitigation of Performance Degradation of PEM Water Electrolyzers by Power Distribution Control of Fluctuating Renewable Energy

Introduction Hydrogen production by water electrolysis using renewable energy such as wind and solar power generation (i.e., green hydrogen production) has attracted considerable attention as a key technology towards decarbonization. Proton exchange membrane (PEM) water electrolyzers are often used in combination with renewable energy source since they show fast response to input power fluctuation. However, lifetime of PEM electrolyzer needs to be improved for reducing hydrogen production cost. Recently we reported a durability analysis of PEM electrolyzers under wind power voltage fluctuations, where the reversible and irreversible voltage losses were analyzed in terms of gas bubble transport and catalyst degradation [1]. We also developed a novel control strategy called the power distribution control (PDC) that controls the power converters so that the input fluctuating power is decomposed to several fluctuating patterns that less degrade the electrolyzers than the input pattern [2]. The purpose of this study is to validate the effect of the PDC on mitigation of performance degradation of PEM electrolyzers under wind power fluctuations. Experimental method A membrane electrode assembly (MEA) with an active area of 1 cm2 was prepared using Nafion 117 membrane, IrO2 anode catalyst and Pt/KB cathode catalyst. The catalyst loading for anode and cathode was 0.5 mg IrO2/cm2 and 0.3 mg Pt/cm2, respectively. A PEM water electrolysis cell was prepared by assembling the MEA into a cell holder. The cell temperature was kept at 80°C during the durability test.Figure 1a) and 1b) show a schematic system diagram for performing the PDC and the two voltage fluctuation patterns (A and B) used for the durability test, respectively. As in our previous study [1], actual 24-h voltage fluctuation of wind power turbine was used as the primary data. The pattern A was prepared from the primary data by (i) scaling down the maximum voltage by 1/100 and setting the minimum voltage higher than the standard potential of water electrolysis and (ii) accelerating the time scale by 5 times. The pattern B was prepared by applying the PDC, that is, converting the pattern A into an alternative sequence of a high-operating rate pattern and a low-operating rate pattern as described in Ref. [2]. Here we set the average voltage of the high-operating rate pattern (~2.4 V) and the low-operating rate pattern (~1.7 V) as the same value with the voltage of the pattern A (~2.05 V) for each time, ensuring that we model the situation in which the input fluctuating power is distributed between two series of electrolyzers as shown in Fig. 1a). We performed 240-h durability tests and analyzed performance degradation of the PEM cell for the pattern A and B, respectively. Results and Discussion Figure 2 summarizes the performance degradation of the PEM cell during the 240-h durability test. The cell current density at the cell voltage of 2.1 V showed a steep decrease during the initial ~30 h for both pattern A and B. For 30 – 240 h, the current density continuously decreased for the pattern A (−0.68 mAcm-2/h), while no distinguishable decrease was observed for the pattern B (+0.06 mAcm-2/h). Therefore we successfully demonstrated that performance degradation of the PEM electrolyzers can be effectively suppressed by the PDC when using actual wind power voltage fluctuation as the input power.To further investigate the performance degradation behavior, the increase in overpotential components of the PEM cell was analyzed. Figure 2b) shows the comparison of overpotential components before and after the 240-h test. For the pattern A, the diffusion overpotential (E diff) showed a significant increase after the test for the current density higher than 1.0 mAcm-2. In contrast, for the pattern B, increase in E diff was suppressed and confirmed only for > 1.4 Acm-2. Increase in the activation overpotential (E act) was small compared to increase in E diff for both pattern A and B. Furthermore, we confirmed that the performance degradation confirmed in this study was reversible, that is, the current density was almost recovered within 24-h rest time after the test. These results are consistent with our previous study [1] in that the reversible degradation is related to gas bubble transport, that is, the increase in E diff. Therefore it was shown that the PDC suppresses reversible degradation, which is important for mitigating irreversible degradation during long-term operation. Our results demonstrate that PDC is a promising technique for improving lifetime of PEM electrolyzers operating under fluctuating renewable energy.

Limiting Current Density in Water Vapor-Fed Polymer Electrolyte Membrane Electrolyzers

Polymer electrolyte membrane water electrolyzers (PEMWE) are a critical technology in development for addressing the need for efficient hydrogen production. In order to make hydrogen a cost-effective fuel or industrial feedstock, the overpotentials across the cell needs to be decreased and platinum-group metal loading reduced. Devising novel electrode structures that enable ultra-high current densities at low oxygen evolution reaction (OER) catalyst (e.g. Iridium oxide) loadings is one approach to achieving efficiency and cost targets. One of the overpotentials that needs to be addressed is due to mass transport limitations within the porous transport layer (PTL) and anode catalyst layer, which could be a limiting factor at ultra-high current densities. When operating at ultra-high current densities, the rate of the OER may reach a point at which oxygen gas bubbles fill the pores of the anode catalyst layer PTL, blocking access of liquid water to the anode catalyst layer. Because of this, there is a possibility that the cell will rely on water vapor diffusion through the evolving oxygen gas to deliver the water reactant to the OER catalyst. To assess the limitation of a PEMWE while relying on water vapor diffusion, a commercially manufactured membrane electrode assembly (MEA) was tested by flowing water vapor into the anode as the reactant. With the aim of identifying a limiting current density (LCD) of the electrolyzer under these conditions, potentiostatic polarization curves were obtained for a range of relative humidities (RH) and back pressures. The RH was varied to assess the impact of reactant concentration on the LCD, while the back pressure was varied to identify the impact of the molecular gas diffusion coefficient on the LCD. In this presentation, we will present our analysis of the significance of the water vapor diffusion transport resistance through the pressure-dependent resistance evaluation. Furthermore, we will discuss application of this approach to evaluating the impact of vapor operation on membrane water transport and OER reaction kinetics.

Comparative Study of Anion Exchange Membranes for Application in Advanced AEM Water Electrolysers

The chemical nature of hydrogen combined with its capability to be an energy carrier for energy conversion devices with zero- emission and its higher energy density than any other commercial fossil fuel-based energy source, make it unique [1]. The International Renewable Energy Agency has identified three of the most viable technologies for producing hydrogen in large volume, namely: alkaline water electrolyzers (AWEs), proton exchange membrane water electrolyzers (PEMWEs), and anion exchange membrane water electrolyzers (AEMWEs) [2]. Among the three types of electrochemical devices the AEMWEs are the newest and most promising, because they (i) have the same slim design of the PEMWEs, (ii) can operate at high current densities, and (iii) can use non-precious catalysts [3]. The durability and efficiency of the AEMWEs systems are significantly influenced by the anion exchange membranes (AEMs), which are currently under development. In addition, the used catalysts, as well as the methods for fabrication of the membrane electrode assemblies (MEAs) also impact substantially the electrolyzer’s performance. Catalyst-coated substrate (CCS) is one of the methods for fabrication of MEAs [4], while the other used method is known as catalyst coated membranes (CCMs). The Reactive Spray Deposition Technology (RSDT) is an innovative flame-assisted method that can be used for fabrication MEAs from both types [5].In this work, CCS are fabricated by the ultrasonic spray deposition method and 5 MEAs are assembled with various AEM membranes. This approach involves the application of Platinum Group Metal (PGM) catalysts, Pt/C and as cathode and anode catalyst layers, onto a Gas Diffusion Layer (C-GDL) and a porous transport layer (Ti-PTL). As fabricated CCSs are assembled with the three state-of-the-art commercially available AEMs, namely: FAA-3, Sustainion X-37, and TM1, and their performance is evaluated. In addition, CCSs with ultra-low PGM loadings in their catalyst layers are fabricated with the RSDT method and better performance in comparison to the baseline MEAs with high PGM loadings, is achieved. This comparative study provides valuable insights into the strengths and weaknesses of each membrane type for application in AEM water electrolysers. Reference: [1] M. G. Rasul, M. A. Hazrat, M. A. Sattar, M. I. Jahirul, and M. J. Shearer, “The future of hydrogen: Challenges on production, storage and applications,” Energy Conversion and Management, vol. 272, p. 116326, Nov. 2022, doi: 10.1016/j.enconman.2022.116326.[2] D. Yang et al., “Patent analysis on green hydrogen technology for future promising technologies,” International Journal of Hydrogen Energy, vol. 48, no. 83, pp. 32241–32260, Oct. 2023, doi: 10.1016/j.ijhydene.2023.04.317.[3] D. S. Falcão, “Green Hydrogen Production by Anion Exchange Membrane Water Electrolysis: Status and Future Perspectives,” Energies, vol. 16, no. 2, p. 943, Jan. 2023, doi: 10.3390/en16020943.[4] J. E. Park et al., “High-performance anion-exchange membrane water electrolysis,” Electrochimica Acta, vol. 295, pp. 99–106, Feb. 2019, doi: 10.1016/j.electacta.2018.10.143.[5] Z. Zeng, J. Xing, L. Bonville, D. R. Dekel, R. Maric, and S. Bliznakov, “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,” International Journal of Hydrogen Energy, p. S0360319923013721, Apr. 2023, doi: 10.1016/j.ijhydene.2023.03.249.

PGM-Free Oxygen Evolution Reaction Catalyst for PEM Water Electrolysis – a Mechanistic Study on Activity and Durability for Practical Applications

Low temperature proton exchange membrane water electrolyzer (PEMWE) represents a critical technology for green hydrogen production. It offers the advantages of significantly higher current density and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential. Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the platinum group metal (PGM) materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve add a significant cost barrier to PEM electrolyzer, which contributes to the overall expense of hydrogen production next only to the cost of electricity. Replacing Ir with earth-abundant transition metal oxides could help to reduce the electrolyzer system cost.For PEMWE application, a PGM-free anodic catalyst must be highly active to match the performance of Ir. Furthermore, it must be stable against oxidative acid corrosion. At Argonne National Laboratory, we recently developed a new PGM-free OER of a nanofibrous cobalt spinel catalyst co-doped with lanthanum and manganese (LMCF). [1] The catalyst was synthesized from the precursor of cobalt zeolitic methyl-imidazolate framework (Co-ZIF) doped with manganese and lanthanum. The Co-ZIF was mixed with a polymer solution and electrospun into nanofiber before being converted to fibrous cobalt spinel under low temperature oxidation to remove all the organics and carbon. The new PGM-free catalyst demonstrated a low overpotential of 353 mV (RHE) at 10 mA/cm2 and a low OER degradation over 360 hours in acidic electrolyte. A PEMWE containing this catalyst at its anode at ~2.0 mg/cm2 demonstrated a current density of 2000 mA/cm2 at 2.47 volts (Nafion® 115 membrane) or 4000 mA/cm2 at 3.00 volt (Nafion® 212 membrane). The membrane electrode was also subjected to accelerated-stress-test (AST) in both voltage cycling and galvanostatic run at different current densities. Low degradation rates under both ASTs were observed.In addition to catalyst design and synthesis, we also conducted extensive structural characterizations, stability measurement, as well as computational modeling. Our in situ study found that the OER process involves significant lattice oxygen movement, leading to lowering instead of raising the cobalt oxidation state during the electrolysis. The measurement of the stability number, combined with computational Pourbaix diagram, elucidated the importance of the operating potential in reducing catalyst dissolution. These findings offer in-depth understanding and direction of future development for PGM-free OER catalyst in PEM water electrolyzer. Acknowledgement: This work is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewal Energy, Hydrogen and Fuel Cell Technologies Office, and by Laboratory Directed Research and Development funding of Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DEAC02-06CH11357. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both U.S. Department of Energy Office of Science User Facilities, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.[1] “La- and Mn-doped cobalt spinel oxygen evolution catalyst for proton exchange membrane electrolysis” Lina Chong, Guoping Gao, Jianguo Wen, Haixia Li, Haiping Xu, Zach Green, Joshua D. Sugar, A. Jeremy Kropf, Wenqian Xu, Xiao-Min Lin, Hui Xu, Lin-Wang Wang, Di-Jia Liu, Science 380, 609–616 (2023)

Improvement of Reversal-Tolerance of Pt/Ti4O7-C Catalysts by the Addition of Oxygen Evolution Catalysts

When hydrogen is depleted in a polymer electrolyte fuel cell, the anode potential increases (cell reversal), which involves the oxidation of supported carbon (COR) and causes the growth of Pt particles, resulting in the deactivation of the anode catalyst. The addition of the oxygen evolution (OER) catalysts has been reported to suppress the degradation1. Though it has also been reported that the combination of Ti4O7 with Ir catalysts increased the reversal tolerance2, the combination of Pt/Ti4O7 and Ti4O7-supported OER catalysts has not been reported. We have reported that Pt catalysts supported on Ti4O7-C synthesized by the carbothermal process showed excellent performance3. In order to investigate how the distribution of the OER catalyst in the catalyst layer affects the reversal-tolerance, we compared the performance of the physical mixture of Pt/Ti4O7-C and Ti4O7-supported OER catalysts with the composite catalysts (Pt and OER catalyst supported on Ti4O7-C) in this study. The hydrogen starvation was carried out during the hydrogen pump tests in order to clarify the degradation on HOR. Experimental Preparation of catalysts: 20 wt% Pt/Ti4O7-C (11 wt% C) was prepared as previously reported3. RuO2 catalysts Ti4O7-C or Pt/Ti4O7-C was impregnated with RuCl3 solution, and precipitated at pH 8 with NaOH solution. The residue was washed, and dried at 150°C. 21 wt% RuO2/Ti4O7-C and 19 wt% Pt-2.0 wt% RuO2/Ti4O7-C were used for the physical mixture (abbreviated to catalyst-M) and for the composite catalyst, respectively. IrO2 catalysts Ti4O7-C or Pt/Ti4O7-C was impregnated in IrCl3 solution, and hydrothermally treated at 180°C. Afterwards, the solution was washed and dried at 80°C. 3.8 wt% IrO2 and 8 wt% Pt-3.7 wt% IrO2/Ti4O7-C were used for the physical mixture and the composite catalyst, respectively. Electrochemical measurement: The MEA was composed of Nafion NRE211 as the electrolyte membrane, a commercial heat-treated c-Pt/C (Pt loading: 0.5 mg-Pt/cm2) as the cathode, and the above-mentioned catalyst or a commercially available c-Pt/C (Pt loading: 0.2 mg-Pt/cm2) as the anode. The RuO2 and IrO2 loadings were 0.021- 0.042 mg/cm2 and are indicated in parentheses. The performance was evaluated with IV curves, the hydrogen pump, CV and LSV by flowing H2 gas to the cathode under 80°C fully humidified condition. The hydrogen starvation was performed by switching the anode supply gas to N2 (RH 100%) while the hydrogen pump was carried out at 0.2 A/cm2 for 10 minutes at a cutoff voltage of 2.7 V. After the test, a hydrogen pump, CV, LSV, and an IV test were performed. The second hydrogen starvation test was repeated in the same manner. Results and Discussion As shown in Table 1, the voltage of c-Pt/C quickly increased above 1.7 V, however, a plateau was observed at 1.8 V after the rapid voltage increase during the second hydrogen starvation, which indicated COR. After the second hydrogen starvation, the current at 0.4 V for the LSV increased from 7.1 mA/cm2 before the second test to 47.9 mA/cm2, indicating the damage of the membrane. The HOR activity also deteriorated after the hydrogen starvation. No improvement was observed for Pt/Ti4O7-C and Pt/Ti4O7-C+RuO2/Ti4O7-M (0.025) under this condition, however, the voltage rise to 1.7 V on the RuO2 composite catalyst was suppressed for the first starvation, due to the OER. This effect disappeared for the second hydrogen starvation. On the other hand, the catalyst physically mixed with IrO2/Ti4O7-C showed a voltage plateau from 1.50 to 1.75 V during the hydrogen starvation, indicating a significant improvement, and the increase in the IrO2 loading improved the reversal-tolerance. Furthermore, for the IrO2 composite catalyst, a plateau due to the OER was observed at 1.5 - 1.7 V for the two hydrogen starvation tests. The voltage increase of the hydrogen pump after the tests was also slight and the change in ECSA was small. Since the difference from the physical mixture was clearly observed, it was deduced that the OER catalyst in the vicinity of the Pt catalyst improved the reversal-tolerance.Acknowledgments: This work was supported by NEDO.(1) T. R. Ralph et al., Platinum Metals Rev. , 46, 117 (2002). (2) T. Ioroi et al., J. Power Sources, 450, 227656 (2020). (3) M. Chisaka et al., Chem. Comm. , 57, 12772 (2021). Figure 1

Exploring Low Temperature Proton Exchange Membrane Water Electrolysis Anode Catalyst Degradation Under Cathode Backpressure Conditions

Hydrogen is expected to play an important role in the decarbonization of the future energy landscape by integrating renewable, nuclear, and fossil fuels and using excess power from the grid to produce H2 that can then be stored and used for a variety of applications ranging from ammonia and steel production, stationary power, buildings, and transportation.1 In order to achieve low-cost hydrogen production that is competitive with steam methane reformation (SMR), it is necessary to decrease the capital cost and this can be done by leveraging variable renewable energy (VRE) as an electricity feedstock for LTE.2 However, cost, and durability are still current challenges in state-of-the art water electrolysis systems. More research is needed to better understand the effects of dynamic operation on electrolyzer degradation. Understanding the degradation mechanisms governing intermittent electrolysis operation can enable future improvements related to component design and system operation.In recent years, electrolyzer anode degradation has been investigated during continual intermittent operation at the single cell level. Square-wave potential cycling demonstrated higher anode degradation compared to the triangle-wave cycling over the same 525 hour test (21.9 d).3 Electrolyzers operating at differential pressures and producing electrochemically compressed hydrogen could decrease the hydrogen production cost by eliminating the need for equipment related to mechanical compression.4 This work investigates the dynamics of low-temperature proton exchange membrane (PEM) electrolyzers, with a specific focus on anode catalyst layer degradation from redox transition when subjected to hydrogen crossover from cathode backpressure conditions. While cathode backpressure and operation requirements are well understood from an industry perspective, its impact on degradation mechanisms and loss rates has been relatively underexplored when low-temperature electrolysis is focused on cost reduction and variable load.In this study, hydrogen cross-over rates were varied by cathode backpressure conditions (ambient to 30 Bar) and were compared to elucidate the impact hydrogen has on anode catalyst layer degradation. The durability test duration varied from 168 – 500+ hrs. Hydrogen cross-over rates were found to correlate to cell potential during operational shutdowns and loss rates during load cycling. Electrochemical impedance spectroscopy further demonstrates higher degrees of kinetic loss and the immergence of additional loss mechanisms. The findings presented in this research contribute to the fundamental understanding of low-temperature PEM electrolysis dynamics under cathode backpressure conditions. The implications of this research offer practical insights for the design and operation of efficient and durable electrolysis systems crucial for the advancement of sustainable hydrogen production technologies.(1) H2@Scale. Hydrogen and Fuel Cell Technologies Office. https://www.energy.gov/eere/fuelcells/h2scale.(2) Mark, R.; Jadun, P.; Gilroy, N.; Connelly, E.; Boardman, R.; Simon, A. J.; Elgowainy, A.; Zuboy, J. The Technical and Economic Potential of the H2@Scale Concept within the United States; NREL/TP-6A20-77610; National Renewable Energy Laboratory: Golden, CO, 2020.(3) Alia, S. M.; Reeves, K. S.; Yu, H.; Park, J.; Kariuki, N.; Kropf, A. J.; Myers, D. J.; Cullen, D. A. Electrolyzer Performance Loss from Accelerated Stress Tests and Corresponding Changes to Catalyst Layers and Interfaces. Journal of The Electrochemical Society 2022, 169 (5), 054517. https://doi.org/10.1149/1945-7111/ac697e.(4) Ragnhild Hancke, Thomas Holm, and Øystein Ulleberg, “The Case for High-Pressure PEM Water Electrolysis,” Energy Conversion and Management 261 (2022): 115642, https://doi.org/10.1016/j.enconman.2022.115642. Figure 1

Optimization of Transport Components and Electrode Interfaces for Low Iridium Oxide Loading PEM Electrolysis

Moving towards lower iridium oxide (IrOx) catalyst loadings for the anode side of polymer electrolyte membrane water electrolyzers (PEMWE) requires tuning of the catalyst layer-porous transport layer (PTL) interface. To see widespread deployment, PEMWE anodes need to lower the loadings from 1-2 mg/cm2 IrOx down to 0.1 mg/cm2 [1]. The catalyst layer can become less uniform and more disconnected at these lower loadings, so the addition and optimization of a microporous layer (MPL) onto the PTL to improve interfacial contact and in-plane connectivity is essential to move toward the more sustainable lower loadings [2]. First, a set of PTLs with MPLs are made such that morphological properties are varied between them. Then, the PTLs with MPLs are combined with anode catalyst layers with IrOx loadings of 0.7, 0.5, 0.3, and 0.1 mg/cm2 to create cells to record polarization curves, stability tests, and catalyst degradation rates. The morphology of the PTLs and MPLs is quantified using X-ray computed tomography (CT). The important morphological characteristics that can be varied and measured with X-ray CT include porosity, pore size distribution, tortuosity, and thickness for each the MPL and base PTL. Using operando X-ray CT and radiography, oxygen transport through the PTL and channel can be observed to provide further information to the performance of the novel PTLs and MPLs. By using a two-dimensional continuum PEMWE model, insights into the effects on the cell performance and the contact resistance present at the MPL-catalyst layer brought about from PTL and MPL morphology alterations can be extracted to help guide the optimization efforts. Through combining these results, an optimal set of manufacturing/morphological parameters can be found to tune PTL and MPL production for the low-loaded catalyst layers that are needed for the future of PEMWEs.

Investigating the Effect of KOH Feed Concentration on a Stainless-Steel Anode Using a 3-Electrode Anion Exchange Water Electrolyser Cell Set-up

Anion-exchange membrane water electrolysers (AEM-WE) have the potential to lower the capital cost of hydrogen production compared to proton-exchange membranes water electrolysers (PEM-WE). The alkaline conditions of AEM-WE result in: (i) a kinetically more favourable oxygen evolution reaction (OER), (ii) the ability to use platinum group metal (PGM)-free metal catalysts, and (iii) reduced cell component costs because of the less corrosive operating conditions. However, AEM-WE is held back from commercialisation by limited current density and durability.1 Compared to conventional alkaline water electrolysis, AEM-WEs have the advantage of lower ohmic resistance thanks to a solid polymer electrolyte which provides intrinsic ionic conductivity instead of relying on 6 M KOH and a porous separator. Most studies show, however, that a dilute KOH feed (< 1 M), rather than pure water, is critical to reaching a high current density in AEM-WE. Varying the concentration of KOH in the feed solution impacts catalyst activity and membrane resistance thereby making performance measurements in AEM-WE more complex. Moreover, the overpotential for the alkaline hydrogen evolution reaction (HER) is significant due to its sluggish kinetics. This means full-cell measurements are insufficient for understanding the behaviour of OER and HER catalysts in AEM-WE. It is therefore crucial to make half-cell measurements in AEM-WEs to decouple the effect of the anode and cathode electrocatalysts from the overall cell performance.In this context, our group recently demonstrated a 3-electrode, 5 cm2 membrane electrode assembly electrolyser cell2 that uses a reference electrode to decouple the anode and cathode contributions to the overall water splitting reaction. The technique was demonstrated for AEM-WEs and is soon to be published by Malone et al. (Figure 1A)3. In this study, we aimed to investigate the effect of KOH concentration in the feed solution on OER by using this 3-electrode cell setup. We used a stainless steel (SS)-felt at the anode as both catalyst and porous transport layer (PTL) in different concentrations of KOH feed while maintaining Pt/C as the cathode catalyst. We also repeated the tests with various anode catalyst layers (IrOx, NiFeOx) in combination with the SS PTL. For each test, full and half-cell polarisation curves and impedance spectroscopy were recorded before and after a sixteen-hour durability test at 1 A cm-2 at 40 °C. The results revealed the catalytic significance of the SS-felt in 1 M KOH as recently shown by Chen et al.4 Additionally, we demonstrated how the SS masks the performance of an IrOx catalyst layer in 1 M KOH. Reducing the KOH concentration to 0.18 M resulted in ≈ 7 % increase in the overall cell voltage at 1 A cm-2 (from 1.88 V to 2.00 V at 40 °C in Figure 1B). Aside from the ≈ 35 % increase in membrane resistance (e.g. 180 to 240 mΩ cm2 at 0.9 A cm-2) in 0.18 M KOH, the higher overpotential arose from the anode (Figure 1C), which could be attributed to the higher OER overpotential of SS-felt in a lower pH solution. Meanwhile, there was no appreciable change in cathode overpotential when the KOH concentration was reduced. These findings demonstrate the importance of 3-electrode cell measurements for understanding the impact of each component in an AEM-WE cell. Furthermore, the results reveal that both the choice of PTL material as well as the concentration of feed solution should be considered when testing different catalysts in AEM-WE.

A Spray-Drying Approach for Highly Active Amorphous NiFe2O4 for AEM Water Electrolysis

Water electrolysis, a key process for hydrogen production, holds immense potential in mitigating carbon dioxide emissions when powered by renewable energy sources, thereby contributing to a sustainable and clean energy future. Commercially available and widely recognized technologies for water electrolysis include the proton exchange membrane water electrolysis (PEMWE) and the traditional alkaline water electrolysis (AWE). In order to use the benefits of both systems, the anion exchange membrane water electrolysis (AEMWE) method is proposed, enabling the utilization of non-noble catalyst materials and achieving high current densities at low cell voltages [1].In the present work, the influence of a spray-drying approach compared to a co-precipitation method on the bimetallic non-noble NiFe2O4 catalysts on the oxygen evolution reaction (OER) activity is systematically investigated. State of the art catalyst for OER is Iridium oxide and so far, the best non-noble catalyst has not been found yet. A widely used non-noble catalyst is NiFe- layered double hydroxide but it suffers from low electric conductivity [2]. Another promising catalyst is the NiFe2O4, which also provides low OER overvoltage. However, amorphous oxides are said to have a higher activity than crystalline [3]. Furthermore, the use of a spray drying approach is highly reproducible, with which the crystallinity can be set very easily [4, 5].The experimental study of the catalysts was carried out in a commercial Baltic-Fuel Cell with a geometrical area of 25 cm² at 60 °C in 1 M KOH electrolyte and a contact pressure of 1.25 MPa. The electrodes were prepared by directly spray coating the desired amount of catalyst onto the anode and cathode substrates. A Bekipor® 2NI 18-0.25 nickel felt was used as the substrate for the anode, while AvCarb MGL370 carbon paper was employed for the cathode. As cathode catalyst Pt/C from Tanaka (TEC10E40E, 37.2 % Pt) was used, while a loading of 0.5 mg cm-2 Pt was targeted during the spraying procedure. On the anode, the NiFe2O4 loading was set to 2 mg cm-2. Both electrodes were separated by a Sustainion® X37-50 Grade T membrane. For determination of relevant catalyst activity data chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) were carried out.Figure 1 reveals that the spray-dried NiFe2O4 (amorphous, red curve) has a superior performance compared to the precipitated NiFe2O4 (green curve), which is partly crystalline. With the spray-dried catalyst, a reduction in overvoltage of approx. 60 mV at 1 A cm-2 can be achieved. With a cell voltage of less than 1.7 V at a current density of 1 A cm-2, our recently developed catalyst ranks among the most outstandingly described in the literature to date [6]. These findings can contribute to a further development of amorphous catalysts with even higher activity.[1] Cossar, E., Murphy, F. and Baranova, E.A. (2022), Nickel-based anodes in anion exchange membrane water electrolysis: a review. J Chem Technol Biotechnol, 97: 1611-1624.[2] Jeon, S.S., Lim, J. Kang, P.W., Lee, J.W., Kang, G., Lee, H. (2021), Design Principles of NiFe-Layered Double Hydroxide Anode Catalysts for Anion Exchange Membrane Water Electrolyzers. ACS Appl Mater Interfaces,13 (31): 37179-37186.[3] Shi, G., Arata, C., Tryk, D., Tano, T., Yamaguchi, M., Iiyama, A., Uchia, M., Iida, K., Watanabe, S., Kakinuma, K. (2023), NiFe Alloy Integrated with Amorphous/Crystalline NiFe Oxide as an Electrocatalyst for Alkaline Hydrogen and Oxygen Evolution Reactions. ACS Omega, 8: 13068−13077.[4] Kreitz, B., Arias, A. M., Martin, J., Weber, A. P., Turek, T. (2020), Spray-Dried Ni Catalysts with Tailored Properties for CO2 Methanation, Catalysts, 10 (12): 1410.[5] Arias, A. M., Weber, A. P. (2019), Aerosol synthesis of porous SiO2-cobalt-catalyst with tailored pores and tunable metal particle size for Fischer-Tropsch synthesis (FTS), J Aerosol Sci, 131: 1-12.[6] Du, N., Roy, C. Peach, R., Turnbull, M., Thiele, S. and Bock, C. (2022), Anion-Exchange Membrane Water Electrolyzers. Chem Rev, 122: 11830-11895. Figure 1

(Invited) Integrated Approach of Modeling, X-Ray and Electrochemical Characterization to Understand Low Iridium Loading Catalyst Layers Integration and Durability

Proton exchange membrane water electrolyzers (PEMWEs) will share more than 40 % of green hydrogen production market by 2050. Currently, iridium catalyst in the anode catalyst layers amounts to 1 mg/cm2. To enable low-loading (0.4 mg/cm2) or ultra-low loading (<0.1 mg/cm2) designs we need to better understand both integration of catalysts into catalyst layer and their durability. At low loadings catalyst layer in-plane electric conductivity can be compromised, requiring either supported catalyst layers or the need for microporous layer (MPL) design. For durability study it is necessary to understand the pathway of surface of IrOx transformation during accelerated stress tests (ASTs) and identify optimal beginning of life (BOL) structure for long-duration deployment. In this work we evaluate the structure and performance of amorphous and crystalline IrOx catalysts at the BOL and EOL to build structure-to-property relations. Rheology studies are conducted to identify the optimal ink recipe for each of the catalysts for blade coating deposition method. We use operando x-ray diffraction technique to evaluate catalyst structure evolution during AST cycling. X-ray computed tomography (CT) was used to evaluate catalyst layer – MPL interfaces under various operando conditions. The morphological information was integrated into the two-dimensional model to better understand interfaces for the low-loading PEMWEs.

All‐Aromatic Polymer‐Based Anion Conductive Ionomers with Different Ion Exchange Capacities for Water Electrolysis

Anion exchange membrane water electrolysis (AEMWE) is vital for efficient, environmentally friendly, and cost‐effective hydrogen production. Herein, fluorene‐based polymers containing alkyl ammonium groups with different ion exchange capacities (IECs) for use in anion exchange membranes (AEMs) and anion exchange ionomers (AEIs) are investigated. Among the AEMs tested, the AEM with an IEC of 2.2 meq g−1 shows the highest anion conductivity because of its efficient water uptake characteristics. The anode catalyst layers utilize AEIs and iridium oxide catalyst particles. It is essential to select AEIs with appropriate IEC and suitable solvents for high‐performance anodes in water electrolyzers. Morphological and physical property evaluations reveal that moderate hydrophilicity and suppression of water swelling of AEIs improve water electrolysis performance. The optimized catalyst layer achieves better water electrolysis performance (2.64 V, 1.8 A cm−2 at 30 °C) than the conventional catalyst layer (3.83 V, 1.8 A cm−2 at 30 °C). Although the water electrolysis performance in this study falls short of the final targets, further research on anion conductive polymers and catalyst layers, based on this study's findings, is expected to promote practical applications of AEMWEs.

Co-N-C/C Bifunctional Electrocatalyst for Dual Applications in Seawater Electrolysis and Catalyst in Hydrazine Fuel Cells.

The convergence of water electrolysis and alkaline fuel cells offers captivating solutions for sustainably harvesting energy. The research explores both hydrazine-assisted seawater electrolysis (hydrazine oxidation reaction (HzOR) and hydrogen production reaction (HER)), as well as alkaline hydrazine fuel cell reactions (HzOR and Oxygen reduction reaction (ORR)) by using a bifunctional cobalt polyaniline derived (Co PANI/C) catalyst. The catalyst shows excellent performance for hydrazine-assisted seawater electrolysis in harsh seawater environments to produce H2 as fuel with nearly 85% Faradaic efficiency and during alkaline HzOR, the bifunctional catalyst generates H2 with 95% Faradaic efficiency by acting as both anode and cathode side catalyst. Also, the same catalyst requires only a potential of 0.34V versus RHE and 0.906V versus RHE for HzOR and ORR, respectively, in 1m KOH, which makes this overall process useful for a Hz/O2 fuel cell.

Anode defects’ propagation in polymer electrolyte membrane fuel cells stack

This paper investigates how cell manufacturing defects can propagate within healthy areas of the same cell or to adjacent cells within a stack. To do so, a defective stack is assembled on the basis of 30 cells without defect and 5 defective cells with controlled lack of anode catalyst layer. The analysis of the degradation rate showed that the adjacent cells to the defective cells are the ones whose performance degraded the fastest, which implies that the presence of defects within the stack induces a propagation of the performance decrease. Post-mortem analyses are performed in the vicinity of the anode defect in the adjacent cell and highlight a significant degradation of perfluorosulfonic acid (PFSA) inducing hydrogen leakages through the membrane. The propagation of the degradation of the membrane in the surroundings of the anode defect to the adjacent cell can be discussed based on the stack design and operating conditions.