Exchange Membrane Electrolyzer Research Articles

A review of gas-liquid flow characteristics of anode porous transport layer in proton exchange membrane electrolysis cell

A review of gas-liquid flow characteristics of anode porous transport layer in proton exchange membrane electrolysis cell

Physics-Informed Neural Network for modeling and predicting temperature fluctuations in proton exchange membrane electrolysis

Physics-Informed Neural Network for modeling and predicting temperature fluctuations in proton exchange membrane electrolysis

Laser induced oxidation Raman spectroscopy as an analysis tool for iridium-based oxygen evolution catalysts.

The study of degradation behavior of electrocatalysts in an industrial context calls for rapid and efficient analysis methods. Optical methods like Raman spectroscopy fulfil these requirements and are thus predestined for this purpose. However, the iridium utilized in proton exchange membrane electrolysis (PEMEL) is Raman inactive in its metallic state. This work demonstrates the high oxidation sensitivity of iridium and its utilization in analysis of catalyst materials. Laser induced oxidation Raman spectroscopy (LIORS) is established as a novel method for qualitative, chemical and structural analysis of iridium catalysts. Differences in particle sizes of iridium powders drastically change oxidation sensitivity. Oxidation of the iridium powders to IrO2 occurred at a laser power density of 0.47 ± 0.06 mW μm-2 for the 850 μm powder and at 0.12 ± 0.06 mW μm-2 and 0.019 ± 0.015 mW μm-2 for the 50 μm and 0.7-0.9 μm powders respectively. LIORS was utilized to assess possible deterioration of an iridium electrocatalyst due to operation under electrolysis. The operating electrocatalyst exhibited higher oxidation sensitivity, suggesting smaller iridium particle size due to catalyst dissolution. Peak shifts of the IrO2 signal were utilized to assess differences in transformation temperatures. The operated electrocatalyst transformed to IrO2 at lower temperature (8 cm-1 redshift) relative to the pristine catalyst (10 cm-1 redshift), demonstrating that pre-oxidation of the iridium to amorphous IrOx during electrolysis diminishes the energy barrier needed for IrO2 formation. Thus, LIORS can be utilized as a straightforward screening method for the analysis of iridium electrocatalysts in the industrial application of PEMEL.

Recent Progress in Balancing the Activity, Durability, and Low Ir Content for Ir-Based Oxygen Evolution Reaction Electrocatalysts in Acidic Media.

Proton exchange membrane (PEM) electrolysis faces challenges associated with high overpotential and acidic environments, which pose significant hurdles in developing highly active and durable electrocatalysts for the oxygen evolution reaction (OER). Ir-based nanomaterials are considered promising OER catalysts for PEM due to their favorable intrinsic activity and stability under acidic conditions. However, their high cost and limited availability pose significant limitations. Consequently, numerous studies have emerged aimed at reducing iridium content while maintaining high activity and durability. Furthermore, the research on the OER mechanism of Ir-based catalysts has garnered widespread attention due to differing views among researchers. The recent progress in balancing activity, durability, and low iridium content in Ir-based catalysts is summarized in this review, with a particular focus on the effects of catalyst morphology, heteroatom doping, substrate introduction, and novel structure development on catalyst performance from four perspectives. Additionally, the recent mechanistic studies on Ir-based OER catalysts is discussed, and both theoretical and experimental approaches is summarized to elucidate the Ir-based OER mechanism. Finally, the perspectives on the challenges and future developments of Ir-based OER catalysts is presented.

Integrating Interactive Ir Atoms into Titanium Oxide Lattice for Proton Exchange Membrane Electrolysis.

Iridium (Ir)-based oxide is the state-of-the-art electrocatalyst for acidic water oxidation, yet it is restricted to a few Ir-O octahedral packing modes with limited structural flexibility. Herein, the geometric structure diversification of Ir is achieved by integrating spatially correlated Ir atoms into the surface lattice of TiO2 and its booting effect on oxygen evolution reaction (OER) is investigated. Notably, the resultant i-Ir/TiO2 catalyst exhibits much higher electrocatalytic activity, with an overpotential of 240 mV at 10 mA cm-2 and excellent stability of 315 h at 100 mA cm-2 in acidic electrolyte. Both experimental and theoretical findings reveal that flexible Ir─O─Ir coordination with varied geometric structure plays a crucial role in enhancing OER activity, which optimize the intermediate adsorption by adjusting the d-band center of active Ir sites. Operando characterizations demonstrate that the interactive Ir─O─Ir units can suppress over-oxidation of Ir, effectively widening the stable region of Ir species during the catalytic process. The proton exchange membrane (PEM) electrolyzer, equipped with i-Ir/TiO2 as an anode, gives a low driving voltage of 1.63 V at 2 A cm-2 and maintains stable performance for over 440 h. This work presents a general strategy to eliminate the inherent geometric limitations of IrOx species, thereby inspiring further development of advanced catalyst designs.

Modelling and analysis of multiphysics transport processes in proton exchange membrane electrolysis cell under marine motions

Modelling and analysis of multiphysics transport processes in proton exchange membrane electrolysis cell under marine motions

Anion exchange membrane electrolysis at work—Investigating impact of starting parameters and start-stop operation on cold start behavior and degradation

Water electrolysis is a key technology for the production of green hydrogen, with anion exchange membrane water electrolysis (AEMWE) showing promising properties. Future energy systems will require transient electrolysis operation to combine electrolysis with fluctuating renewably generated power. This study examines and optimizes the cold start process (ambient temperature and 0 V stack voltage) of an AEMWE stack system in terms of starting time, energy demand and degradation. The influence of relevant parameters such as voltage slope, target voltage, downtime and heating strategy on the starting process is experimentally quantified. A temporary increase in cell voltage during the starting process thereby represents a suitable compromise between acceleration of the startup and maintaining a low degradation. In addition, the start-stop degradation analysis with 150 cold starts per parameter set reveals that the degradation of the AEMWE stack during the starting process is independent of the maximum cell voltage and instead correlates with the steepness of the current slope. Using electrochemical impedance spectroscopy, the degradation is assigned to electrode processes. Under moderate starting conditions, degradation rates of 2–10 μV start−1 are observed. This shows that AEMWE is highly compatible with regular operational interruptions.

Engineering the Diaphragm to Minimize Gas Crossover in Alkaline Water Electrolysis

Hydrogen, a versatile energy carrier, is essential for the transition to renewable energy systems. Electrolytically produced hydrogen using renewable sources is a core technology for decarbonizing industries and societies. However, at the end of 2021, electrolysis contributed only about 4% of global hydrogen production [1].Various electrolytic hydrogen production techniques exist, including Proton Exchange Membrane Electrolysis (PEMEC), Solid Oxide Electrolysis (SOEC), Anion Exchange Membrane Electrolysis (AEMEC), and liquid Alkaline Water Electrolysis (AEL) [2]. AEL is the most mature and scalable technology, and it doesn't require precious metals. However, for efficiencies comparable to other techniques, AEL typically operates at low current densities of 0.2-0.5 A/cm2 (100% of rated current density). A porous diaphragm separates the produced hydrogen and oxygen in AEL.A key limitation to part-load operation of electrolyzers is hydrogen crossover into the oxygen stream, posing a safety hazard at concentrations exceeding 4%. Diffusion of dissolved gases through the diaphragm is the main crossover mechanism in balanced AEL systems and depends on electrolyte concentration and supersaturation [3]. Therefore, addressing supersaturation can significantly enhance AEL operational flexibility [4]. While crossover is marginally affected by current density, the 2% hydrogen-in-oxygen safety limit necessitates AEL shutdown at roughly 25% of rated current density to prevent hazardous mixtures.Stiesdal Hydrogen is a climate change company developing next-generation Alkaline Water Electrolysis systems. Our hydrogen electrolyzers operate within a pressure tank, eliminating the need for a hydrogen compressor and enabling direct production at up to 35 bar. To achieve operational flexibility below 25% of rated current density without sacrificing efficiency, we have engineered a novel diaphragm with a pore structure optimized to mitigate gas crossover.[1] IRENA Hydrogen Overview https://www.irena.org/Energy-Transition/Technology/Hydrogen downloaded on 17/04 2024 08:00 MET[2] J. Hnát et al 2020 New Perspectives on Hydrogen Production, Separation, and Utilization 91-117[3] P. Trinke et al 2018 J. Electrochem. Soc. 165 F502[4] M. T. de Groot et al 2022 Int. J. Hydrogen Energy 47 82

Investigation on the Interaction of Catalyst and Ionomer in AEM Electrolysis

In low temperature electrolysis, anion exchange membrane (AEM) systems combine the advantages of alkaline and proton exchange membrane (PEM) electrolysis in generating high purity hydrogen and reducing material costs from catalysts and component coatings [1]. Recent studies in AEM electrolysis have focused on improving cell performance, minimizing catalyst dissolution and mitigating ionomer/membrane degradation with different operating conditions. Ionomers play a critical role in the electrode because they provide ion conductivity, enhance mechanical support, and create preferred morphologies for electrolyte and produced gas to move [2, 3]. Optimizing catalyst-ionomer interactions by varying ionomer content, chemistries, and forms can accelerate the development of AEM electrolysis in terms of performance enhancement, cost and lifetime.In this work, different forms of ionomer (powdered and dispersed) with two polymer backbones were evaluated in AEM electrolysis cell testing. Ni- and Co-based oxides and IrO2 were applied as anode catalysts. In Figure 1, the anodes with powdered ionomer outperform the dispersed samples. With Co3O4 catalyst, the overpotential can be improved by 0.9 V at 1 A/cm2 (iR-free voltage of Co3O4 with powdered ionomer: 1.68 V at 1 A/cm2). By electrochemical diagnostic and modeling methods, the improved performance with powdered ionomer is attributed to better reaction kinetic from more active area between catalysts and ionomers, less ohmic overpotentials due to better contact between the electrode and the transport layer and preferred transport properties with higher porosity created by powdered ionomer. Scanning electron microscopy data verifies that the anodes with powdered ionomer provide more homogeneous distribution of catalysts and ionomer in the electrode, while dispersed samples have the issues of agglomerates and uneven coverage of catalysts, which could worsen the catalyst utilization and trigger mass transport issues.[1] Ayers, Katherine, et al. "Perspectives on low-temperature electrolysis and potential for renewable hydrogen at scale." Annual review of chemical and biomolecular engineering 10 (2019): 219-239.[2] Lee, Sol A., et al. "Anion exchange membrane water electrolysis for sustainable large‐scale hydrogen production." Carbon Neutralization 1.1 (2022): 26-48.[3] Favero, Silvia, Ifan EL Stephens, and Maria‐Magdalena Titirci. "Anion Exchange Ionomers: Design Considerations and Recent Advances‐An Electrochemical Perspective." Advanced Materials 36.8 (2024): 2308238. Figure 1

Sweet Spot in Oxidation Temperature Enhances Conductivity and Oer Activity for IrO2-Coated SnO2 Nanofibers

Solutions for effective energy conversion and storage are needed for the shift from fossil fuel-based, CO2-intensive energy production to a future sustainable energy-based economy. This way green energy from renewable sources, such as solar or wind power, may later be re-electrified. One option is to use water electrolysis to transform energy from renewable sources into chemical energy in the form of hydrogen. Proton Exchange Membrane (PEM) electrolysis is a potent, cutting-edge technique that leverages rare iridium-based catalysts to boost the oxygen evolution reaction (OER) to solve this issue. Reducing the total density of iridium-based catalysts for the OER requires minimizing the usage of rare and valuable iridium, which will enhance the PEM process's sustainability and economics.Here we present an investigation aimed to further reduce the iridium usage for proton-exchange membrane (PEM) electrolysis. First, SnO2 nanofibers are produced utilizing a water-free alkoxide route. A wet-chemical method is then used to deposit nanoparticulate IrO(OH) x on the filaments. After subsequent oxidation at various temperatures, the final OER active catalyst is obtained.With the emphasis on reaching high activity, stability, and conductivity at the laboratory level, ultra-small interconnected IrO x /IrO2 nanoparticles anchored to electrospun SnO2 nanofibers (IrO x /IrO2@SnO2) and associated percolation pathways are investigated. The utilization of transmission electron microscopy (TEM) in scanning mode (STEM) before and after electrocatalytic reactions provides insights into the oxidation and crystallization state of iridium oxide nanoparticles dependent on temperature and upon catalytic use. This enables an understanding of further possible reduction of iridium content by optimizing synthesis parameters. The data indicate that the optimal iridium utilization is achieved at 375°C oxidation temperature, with the highest resulting conductivity and electrochemical activity. Furthermore, TEM data reveal initiation of crystallization of IrO2 in the temperature window between 365 and 375°C. The pivotal role of conductivity in electron transport to active sites is underscored by cyclic voltammetry (CVA) measurements, which provide further insight regarding performance and stability with a view on future PEM electrolysis applications. These findings not only enhance our fundamental understanding but also offer practical strategies for advancing cost-effective and efficient electrolysis technologies.

Theory Guided Discovery of Superior Ru-Based Electrocatalyst for Durable Acidic Oxygen Evolution Reaction

Water electrolysis (WE) using hydrogen evolution reaction is widely recognized as a promising method for clean and sustainable hydrogen production. The currently dominant alkaline-based water electrolysis encounters several challenges including high ohmic resistance, limited current density, low efficiency, and poor long-term stability. Proton exchange membrane (PEM) electrolysis can tackle these challenges by providing efficient proton transfer. However, sluggish oxygen evolution reaction (OER) in acid has been a major long-existing obstacle in PEM systems and, therefore, has attracted great research interest.Due to its high activity and durability, IrO2 is currently considered the only practical OER electrocatalyst in PEM devices. However, Ir’s high cost and low global reserve limit its large-scale applications. Hence, less-expensive catalysts for acidic OER are in great demand. RuO2 has been recognized as an attractive alternative to IrO2 because Ru is ~100x abundant and costs ~10x less. Although RuO2 presents higher activity than IrO2, it deteriorates severely in a few hours due to its dissolution under oxidizing conditions. Its long-term stability remains a big challenge.To overcome the challenge of improving the stability of Ru-based oxides, in this work we provide a rigid theoretical framework of RuO2 dissolution under the influence of other metal species. We show that the stability of Ru-based oxides could be controlled by varying the properties of incorporated metal oxides as well as the synergy to form a complex oxide. Surveying the Materials Project database led to the rationalization of a series of metal elements that could positively improve the stability of RuO2. Guided by our theoretical approach, we conducted high-throughput screening and experimental evaluation of Ru-based oxides for acid OER.Our study discovered a novel Ru-based oxide with superior performance in acid OER application. A new wet-impregnation method was developed to synthesize the desired phase. The as-obtained product were uniform nanoparticles with diameters less than 5 nm in a single rutile structure. The new catalyst showed significantly better performance than pristine RuO2. In the rotating-disk-electrode experiment, our catalyst delivered a current density of 10 mA·cm-2 at an overpotential of less than 170 mV in 0.1 M HClO4. The catalyst exhibited a low degradation rate smaller than 25 μVh-1 for over 200 hours of operation at 10 mA·cm-2. Our results show great promise of Ru-based oxides as Ir-free electrocatalysts for acidic OER in PEM water electrolysis.

Combined Electrolysis and Steam Methane Reforming for Optimized, Sustainable Methanol and Green Hydrogen Production

The depletion of fossil raw materials and the environmental impact of their combustion is forcing the chemical industry to change. Increased social awareness and governmental regulations, supported by subsidies, accelerate this necessary change. In hard-to-abate sectors and chemical production processes where direct electrification is not applicable, green hydrogen is a key component for decarbonization. Green hydrogen, produced through water electrolysis powered by renewable energies, couples the power and chemical industries, realizing indirect electrification within the chemical industry.Methanol is an important hydrogen derivate, serving as a base chemical, fuel or gasoline additive, alongside its potential role as a hydrogen carrier and CO2 sink. Following ammonia, methanol is the second largest hydrogen consumer in the chemical sector, with growing demand in the future due to its use, e.g., as a drop-in fuel in overseas transportation. Traditionally, methanol is produced from fossil feedstocks such as natural gas. In a steam methane reforming or autothermal reforming process, natural gas and steam are converted to synthesis gas. This synthesis gas contains hydrogen, carbon monoxide and CO2 and reacts to methanol in a subsequent process step.Recent progress in catalyst development allows for economic methanol synthesis directly from green hydrogen and CO2, consequently replacing fossil feedstock with water, green electricity and CO2 from unavoidable or biological sources or captured from ambient air. The amount of green hydrogen produced by electrolysis to meet the overall demand for methanol requires a substantial scale-up of electrolysis technology and large amounts of green electricity, which is currently a long-term prospect. Therefore, transitional solutions with a reduced carbon footprint and, thus, a lower consumption of fossil raw materials are necessary to cover the demand for methanol in the short to medium term.We present a transitional solution that combines a proton exchange membrane (PEM) electrolysis parallel to a steam methane reformer to produce conventional synthesis gas mixed with hydrogen and CO2 for downstream methanol synthesis. This combination aims to produce both, low-carbon methanol and green hydrogen. It serves as a bridging solution to meet the growing methanol demand with today's limited availability and volatility of renewable energy until a sufficient technical readiness level and scale-up of electrolysis technology is achieved and renewable energy becomes more abundant.The combined process is investigated and optimized depending on its boundary conditions, such as power, natural gas or biogas availability, feedstock costs, direct and indirect CO2 emissions, product flexibility and intensive schemes. We will demonstrate the influence of these parameters on the overall process in order to determine whether a bivalent feed approach for sustainable methanol synthesis with a green hydrogen by-product is advantageous in certain scenarios.Results are obtained from a detailed process simulation of the overall process chain. Therefore, a PEM electrolysis model is developed on a cell level, and a flexible electrolysis plant following a fluctuating power profile is considered in the overall optimization model. Furthermore, PEM electrolysis is being assessed for its compatibility and integration with traditional processes. This evaluation includes studying the impact of varying synthesis gas compositions on the methanol production process, as well as the overall feasibility of the process concept.

Epitaxy Promotes OER Stability of IrO2-Coated SnO2 Nanoparticles in PEM Electrolysis

The transition from fossil fuel-based and CO2-intensive energy production to a future sustainable energy-based economy requires solutions for efficient energy conversion and storage for later re-electrification of green energy from a renewable source such as solar or wind power. One possibility is to convert energy from sustainable sources into chemical energy in the form of hydrogen by electrolysis of water. To meet this challenge, Proton Exchange Membrane (PEM) electrolysis is a powerful, state-of-the-art technology that uses scarce iridium-based catalysts to promote the oxygen evolution reaction (OER). To improve the sustainability and economics of the PEM process, it is necessary to minimize the use of rare and precious iridium to reduce the overall density of iridium-based catalysts for the OER.Here, we present different strategies for the synthesis of low-total iridium OER catalysts. In addition to the choice of support material and support morphology, we also consider the coating strategy to produce highly active and durable catalysts.The coating of corrosion-resistant high surface area metal oxide supports of various morphologies with an ultrathin layer of amorphous iridium hydroxide by a simple wet chemical synthesis at low temperature and ambient pressure or by a hydrothermal approach leads to the formation of interconnected amorphous hydrous iridium oxide particles. In a subsequent step, the amorphous phase is oxidized at elevated temperatures using an Adams fusion salt melt. This process allows a controllable phase transformation and crystallization to form a layer of interconnected partially crystalline IrOx nanoparticles of ≈1.5-2 nm domain size on the surface of the supporting metal oxides, thus providing an electrical percolation path in the catalyst layer.The appropriate choice of support material in terms of crystal lattice parameters can moderate the crystal growth of the iridium oxide in terms of epitaxy and significantly increase the stability due to tight anchoring to the support. The final core-shell nanostructures comprise highly active iridium oxide with total Ir weight fractions as low as 7at% on SnO2 nanoparticles, compared to a state-of-the-art benchmark catalyst with 56at% Ir supported on TiO2 nanoparticles. Transmission electron microscopy (TEM) imaging was used to elucidate the effect of different core-shell designs, particularly on iridium coating and crystallinity. Rotating disk electrode (RDE) measurements were performed to evaluate the electrochemical properties and assess the activity of respective catalyst as well as the cycling stability. Further, membrane electrode (MEA) polarization curves suggest enhanced stability of epitaxial catalyst layers.

A Low-Cost Bipolar Plate Comprising a Channeled Porous Transport Layer for Proton and Anion Exchange Membrane Electrolyzers

Hydrogen is gaining acceptance as a viable energy vector for renewable energy and as a green molecule for chemical synthesis, but its production in a sustainable, efficient, and affordable manner requires further optimization. Proton exchange membrane electrolyzers (PEMELs) can be efficient for hydrogen production. Within the PEMEL stack, the repeating unit cell consists of a bipolar plate, two porous transport layers (PTLs), two catalyst layers, and one proton exchange membrane (PEM). The oxygen evolution reaction at the anode creates a corrosive environment, therefore, titanium is used as the anode bipolar plate material. The anode bipolar plate is typically machined from a block of titanium for small volume production or stamped for large volume production, which is time-consuming and challenging due to frequent tool breakage resulting in high cost. Furthermore, ineffective in-plane water transport within the anode PTL can cause inadequate water supply to the catalyst layer resulting in unutilized catalyst. To alleviate these problems, we have designed a novel PEMEL cell containing channeled titanium foam enclosed within a PTFE frame that functions both as the bipolar plate and the PTL, termed channeled porous transport layer (CPTL). In our design, the channels face the current collector such that the water flows through the channels and the pores of the foam in both the through-plane and in-plane directions, thereby maximizing catalyst coverage and utilization. Similarly, the pores and channels of the CPTL provide an effective pathway for the evacuation of oxygen gas evolved at the anode catalyst layer. Most importantly, the channels in the titanium foam can be formed as part of the PTL production process which could greatly reduce PEMWE manufacturing costs and lower the cost of hydrogen. The same CPTL design can also be employed in anion exchange membrane electrolyzers (AEMELs) whose anode environment permits the use of nickel foam which further reduces material costs. We will present experimental results for PEMELs and AEMELs performance with this new design and compare them with those obtained with conventional bipolar plates.

Need for Speed: Fast Activation of PEM Electrolyzers for End-of-Line Testing

The Membrane Electrode Assembly (MEA) in a Proton Exchange Membrane Water Electrolyzer (PEMWE) requires an activation procedure (also known as initial conditioning or break-in) to reach its nominal stable performance, which can take up to several days. In large-scale industrial production of electrolyzers, this can create a bottleneck in the manufacturing process, as the functionality of each electrolyzer typically needs to be verified by activating and characterizing it in an end-of-line test.Although several activation methods for PEMWE can be found in the literature, to the authors' knowledge, none have been published with the goal of fast activation. The existing activation protocols are usually derived from PEMFC protocols or specified by the manufacturer without any information on how they were developed [1–4].The aim of this study is to gain a deeper understanding of the influencing factors of activation procedures in PEMWE in order to develop faster activation protocols for Begin of Life (BoL) characterization. To this end, we are conducting a Design of Experiment (DoE) parameter study in which we test different variations of galvanostatic activation protocols on PEM single cells. Each activation and characterization of a cell is followed by a short AST and a subsequent End of Life (EoL) characterization to see if the activation had an impact on degradation and final performance.The procedure followed for each test in the activation protocol is outlined in Figure 1a. All tests are performed on fresh MEA materials in a Baltic quickCONNECT cell with an active area of 7.2 x 7.2 cm and an active area compression of 2 MPa. The MEA consists of a state-of-the-art Catalyst Coated Membrane (CCM) sandwiched between a platinized titanium felt and Toray carbon paper. After integration into the test bed, the cell is flushed with water on both the anode and cathode sides while being heated to operating temperature, which takes a total of 6 hours. Galvanostatic activation is then performed over a period of 4 hours. This is followed by BoL characterization, during which polarization curves and electrochemical impedance spectra are recorded to evaluate initial performance. The cell is then subjected to an 80 hour Accelerated Stress Test (AST) where the potential is alternated between 0 and 2 V at 10 second intervals at 80 °C cell inlet temperature. Finally, an End of Life (EoL) characterization is performed to determine the final performance.The examined activation parameters, which are the input factors for the DoE, can be seen in Figure 1c. They are the anode inlet temperature, the maximum current density, a soft-start step (applying a lower current density of 0.2 A/cm² for the first 30 minutes), and the mode of current application (static or dynamic cycling between 100 % and 20 % of the maximum current density in 5-minute intervals). The full factorial DoE requires 16 experiments when each factor is varied between 2 states. The full test plan as seen in Figure 1b also includes 3 initial tests where the cell is activated according to the CCM suppliers' recommendation and 2 center points at the beginning and end of the full-factorial test plan. These additional tests show the reproducibility of the test results and any changes in cell performance over the duration of the test series.Through this experimental study, we show the influence of four activation parameters (Temp, current density, soft start, and current mode) on the quality of the activation, the BoL performance, and the initial degradation rate of PEMWE. This will lead to faster activation protocols for the end-of-line testing of PEMWE and will thus help the large-scale industrial production of electrolyzers.[1] Padgett E, Bender G, Alia SM. Membrane Pretreatment and Cell Conditioning for Proton Exchange Membrane Water Electrolysis. Meet. Abstr. 2021;MA2021-02(41):1252. https://doi.org/10.1149/MA2021-02411252mtgabs.[2] Bender G, Carmo M, Smolinka T, Gago A, Danilovic N, Mueller M et al. Initial approaches in benchmarking and round robin testing for proton exchange membrane water electrolyzers. International Journal of Hydrogen Energy 2019;44(18):9174–87. https://doi.org/10.1016/j.ijhydene.2019.02.074.[3] Wang W, Li K, Ding L, Yu S, Xie Z, Cullen DA et al. Exploring the Impacts of Conditioning on Proton Exchange Membrane Electrolyzers by In Situ Visualization and Electrochemistry Characterization. ACS Appl Mater Interfaces 2022;14(7):9002–12. https://doi.org/10.1021/acsami.1c21849.[4] Tomić AZ, Pivac I, Barbir F. A review of testing procedures for proton exchange membrane electrolyzer degradation. Journal of Power Sources 2023;557:232569. https://doi.org/10.1016/j.jpowsour.2022.232569. Figure 1

The Impact of Progressive Buildup of Trapped Gas Bubbles on the Performance of Oxygen Evolution Reaction Electrodes during Alkaline Water Electrolysis

Hydroxide exchange membrane electrolyzers (HEMELs) stand to be an effective means of achieving low-cost green hydrogen. However, HEMEL durability remains a substantial barrier to realizing this goal. The United States Department of Energy has set a durability target of a voltage increase of 2 µV/hr1. We have previously demonstrated constant current degradation rates of 1810 and 560 µV/hr with applied current densities of 500 and 200 mA/cm2, respectively, thus illustrating the substantial gap between our current achievable HEMEL durability and our target durability2.Gaseous products are formed at both electrodes in a HEMEL; by manipulating the wettability of the electrodes, recent studies have shown that the failure of gas bubbles to detach from the electrode surface leads to overpotentials associated with the loss of accessible reaction sites and exacerbated mass transport to those sites that remain accessible3,4. While these studies have demonstrated the impact of gas bubbles on acute water electrolyzer performance, we have found little work to investigate the impact of trapped gas bubbles from a durability perspective.Here we find that electrode wettability can change throughout the lifetime of a device. We investigate the durability of an FexNiyOOH – nF anode catalyst supported on nickel felt in a three-electrode setup with 1M KOH. We find that at a moderately low current density of 50 mA/cm2 the performance of this catalyst degrades by tens of mV over several hundred hours and that this performance loss is recoverable with the removal of oxygen bubbles adhered to the anode surface at open circuit. Moreover, when we resume the passage of current, the surface layer of oxygen (and associated performance loss) evolves more rapidly – suggesting that the wettability of the anode has decreased throughout the experiment. This is further supported by contact angle measurements of pre- and post-mortem anodes. Finally, we investigate whether the introduction of hydrophilic ion-conducting polymers can mitigate the emergent hydrophobicity of the anode catalyst layer. Technical Targets for Proton Exchange Membrane Electrolysis, Hydrogen and Fuel Cell Technologies Office. https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysis. J. Xiao et al., ACS Catal., 11, 264-270 (2021). R. Iwata et al., Joule, 5(4), 887-900 (2021). Z. Kang et al., Electrochimica Acta, 354 (2020).

PGM-Free Oer Catalyst for Water Splitting – an Interrogation on the Structural Dynamics of Catalyst during Reaction

Green hydrogen production through proton exchange membrane water electrolyzer (PEMWE) offers the advantages of high current density and high H2 purity with low footprint. At present, the platinum group metal (PGM) such as Ir are the catalysts of choice for the oxygen evolution reaction (OER) at PEMWE anode. The high cost and limited reserve of Ir add a significant cost to broad implementation of PEM electrolyzer.Replacing Ir with earth-abundant transition metals 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, we recently developed a nanofibrous cobalt spinel OER catalyst prepared from cobalt zeolitic methyl-imidazolate framework (Co-ZIF) doped with manganese and lanthanum. [1] A PEMWE containing this catalyst with the anodic loading of ~2.0 mg/cm2 demonstrated a current density of 2A/cm2 at 2.47 volts or 4A/cm2 at 3.00 volts. The catalyst also showed a promising stability under accelerated-stress-test (AST) through voltage cycling as well as galvanostatic tests at different current densities.To better understand the structure-function relationship, we conducted extensive structural characterizations and computational modeling. For example, our high-resolution electron microscopy study showed a catalyst morphology mimicking that of ZIF precursor but composed of cobalt spinel crystallites with an average size of 3.5 nm. The oxygen atoms on the top layer of the spinel surface are in the relaxed mode. X-ray absorption spectroscopy showed strong oxygen deficiencies around cobalt compared to standard spinel reference. Such deficiency became more predominant at higher cell voltage. Contrary to general perception, the cobalt oxidation state actually decreased instead of increasing at the escalating OER potential and fast turnover rate. Accompanying the change of oxidation state, reduction of oxygen coordination number surrounding Co and growth of Debby-Weller factor of Co-O shell were observed, indicating rapid exchange of the lattice oxygen in spinel during OER. On the other hand, no such changes were observed for the atomically dispersed Mn ion in the spinel as the dopant.In this presentation, we will discuss in our detailed findings and offer our perspective on the future research direction for PGM-free OER catalyst for PEM water electrolyzer application. 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)

Investigating Activity and Stability of Mixed-Metal Oxides (M-NiO) for Anion Exchange Membrane Electrolysis

Recent experimental studies suggest mixed oxides of Ni, Co, and Fe operated in basic media may be the strongest alternative to iridium.1, 2 However, the efficiency of these catalysts is strongly synthesis-dependent and there is no established understanding of the role of the different metals in operation with ionomers. Notably, Trotochaud, et al. observed catalyst efficiency in the order Ni0.9Fe0.1Ox > NiOx > NiyCo1-y, whereas Morales-Guio, et. al. ranked FeNiOx, CoFeNiOx > CoNiOx > NiOx.1, 2 Anderson et al. found in their RDE studies of commercial catalysts that NiFe2O4outperformed NiO, Co3O4 by 7 times kinetically. In low concentrations, these mixed-oxide materials may behave more closely to doped-catalysts, where dopants can increase activity, change selectivity, and even improve resistance to poisoning of active sites.3-6 Understanding how and why these catalysts work, and do not work, is critical to enabling these materials to achieve the Hydrogen Shot goal of $1/kg H2 in 1 decade. For our theoretical model, we limited our mixed material model to a single dopant to fully examine the geometric and electronic effects of a nearby transition metal e.g., Fe and Co dopants. Plane-wave density functional theory calculations elucidated the dopant-effects on both activity (the oxygen evolution reaction) and stability in anion exchange membrane electrolysis in the presence of experimentally-relevant ionomers (Georgia Tech, Nafion, Versogen, and Sustainion).(1) Trotochaud, L.; Ranney, J. K.; Williams, K. N.; Boettcher, S. W. Solution-cast metal oxide thin film electrocatalysts for oxygen evolution. Journal of the American Chemical Society 2012, 134 (41), 17253-17261.(2) Morales-Guio, C. G.; Liardet, L.; Hu, X. Oxidatively electrodeposited thin-film transition metal (oxy) hydroxides as oxygen evolution catalysts. Journal of the American Chemical Society 2016, 138 (28), 8946-8957.(3) Ha, M.-A.; Dadras, J.; Alexandrova, A. Rutile-deposited Pt–Pd clusters: A hypothesis regarding the stability at 50/50 ratio. ACS Cat. 2014, 4(10), 3570-3580.(4) Baxter, E. T.; Ha, M.-A.; Cass, A. C.; Alexandrova, A. N.; Anderson, S. L. Ethylene Dehydrogenation on Pt4, 7, 8 Clusters on Al2O3: Strong Cluster Size Dependence Linked to Preferred Catalyst Morphologies. ACS Cat. 2017, 7 (5), 3322-3335.(5) Ha, M.-A.; Baxter, E. T.; Cass, A. C.; Anderson, S. L.; Alexandrova, A. N. Boron switch for selectivity of catalytic dehydrogenation on size-selected Pt clusters on Al2O3. Journal of the American Chemical Society 2017, 139 (33), 11568-11575.(6) Halder, A.; Ha, M.-A.; Zhai, H.; Yang, B.; Pellin, M. J.; Seifert, S.; Alexandrova, A. N.; Vajda, S. Oxidative Dehydrogenation of Cyclohexane by Cu vs Pd Clusters: Selectivity Control by Specific Cluster Dynamics. ChemCatChem 2020, 12 (5), 1307-1315. DOI: 10.1002/cctc.201901795. Figure 1

(Digital Presentation) In-Situ Quantification of Individual Electrode Polarization and Depth Validation of the Distribution of Relaxation Times Methods Feasibility in PEM Fuel Cell

The article titled "Dynamics of anion exchange membrane electrolysis: Unravelling loss mechanisms with electrochemical impedance spectroscopy, reference electrodes and distribution of relaxation times" explores the challenges and mechanisms in anion exchange membrane water electrolysis (AEM-WE). The study by Matthias Ranz and colleagues employs electrochemical impedance spectroscopy (EIS), half-cell measurements using a reversible hydrogen electrode (RHE), and distribution of relaxation times (DRT) analysis to delve into the dynamics of AEM-WE cells.AEM-WE is gaining attention as a promising technology for hydrogen production due to its potential cost benefits over conventional electrolysis systems. However, its adoption faces obstacles such as efficiency issues and high degradation rates. To address these challenges, the research employs detailed electrochemical characterization techniques, providing new insights into the operational dynamics of AEM-WE cells.The study reveals five major loss mechanisms within AEM-WE systems: hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and ion transport losses, among others, occurring mostly within the catalyst layers. The findings also discuss the influence of various operating parameters on these loss mechanisms and how they can be systematically tracked and analyzed through EIS.A significant aspect of the research is the application of DRT analysis, a method not previously used in AEM-WE studies. This analysis method helps in identifying and quantifying the different electrochemical phenomena contributing to cell losses. By correlating these phenomena with their physicochemical origins, the study enhances understanding of the underlying processes within AEM-WE cells.Moreover, the use of equivalent circuit models in conjunction with EIS data provides a deeper understanding of the electrochemical behavior of the system. This combined approach allows for a more precise characterization of the impedance features and the differentiation of processes such as ion transport and electrochemical reactions.Ultimately, the research highlights the complexity of the AEM-WE process and emphasizes the need for advanced diagnostic tools to optimize performance and stability. By pinpointing the specific causes of efficiency losses and identifying opportunities for material and process improvements, the study contributes significantly to the development of more robust and efficient AEM-WE systems.In conclusion, the research not only elucidates the various loss mechanisms in AEM-WE but also showcases the potential of advanced electrochemical techniques like EIS and DRT in enhancing the understanding and optimization of this promising hydrogen production technology. This work sets a foundation for future studies aimed at overcoming the limitations of AEM-WE and advancing towards its commercial viability.

Investigating Ionomer Interactions on the Catalytic Interface of Model Catalysts (NiO, IrO2)

Anion exchange membrane electrolysis enables the use of earth abundant metals for the catalyst and other components of the membrane electrode assembly. However, earth abundant metal catalysts may be sensitive to poisoning and degradation due to the extreme pH of the electrolyte or interactions with the ionomer. Plane-wave density functional theory calculations probed the binding strength of different functional groups from popular ionomers (Nafion, Sustainion, tetramethylammonium-based ETFE/Gen 2/Georgia Tech, Versogen) on model catalysts such as Platinum Group Metal IrO2 and earth abundant NiO.1 We evaluated the stability of these various ionomers on these model catalysts, whether they remain intact or degrade, as well as their catalytic effects on the oxygen evolution reaction (OER) e.g. in the presence of OH*. These calculations allowed us to understand the poisoning of active sites: 1) if the functional group bound more strongly than key reaction intermediates, then the ionomer effectively blocked activity by displacing the reaction intermediate; 2) if the functional group introduced competing reactions, then the ionomer was consuming the OxHy* intermediates necessary for OER. Ideally, ionomers remain stable in contact with the catalyst and shuttle hydroxide ions from the cathode to the anode.1. S. Ghoshal, B. S. Pivovar and S. M. Alia, J. Power Sources, 2021, 488, 229433. Figure 1