Exchange Membrane Water Electrolysis Research Articles

Hydrophilic treatment of carbon paper for anodic porous transport layer in proton exchange membrane water electrolyzer

Hydrophilic treatment of carbon paper for anodic porous transport layer in proton exchange membrane water electrolyzer

Lower‐Temperature Synthesis of Nitrogen‐Rich Molybdenum Nitride/Nickel (Cobalt) Heterojunctional Assembly for the Effective Water Electrolysis

AbstractThe nitrogen‐rich molybdenum nitrides (N/Mo > 1) are promising for water electrolysis due to their increased activity and antioxidant ability. However, a higher temperature is needed in the usual synthesis for introducing more N, leading to the formation of large particles and the difficulty in controlling the morphology, thus limiting their catalytic performance. Here, a new strategy is reported based on the synergy of internal/external N sources (INS and ENS) toward Mo5N6‐based catalysts at a decreased temperature of 450 °C. The PMo12 clusters and Ni2+ (Co2+) are first combined with 2‐methylimidazole/melamine (INS) to give a flower‐like assembly. The subsequent pyrolysis under NH3 flow (ENS) gives the flowers composed of small Mo5N6/Ni (Co) heterojunctional particles that can expose more surface sites with an optimized electronic structure. The Mo5N6/Ni exhibits good HER activity close to Pt/C, and Mo5N6/Co shows superior OER performance to IrO2. The Mo5N6/Ni||Mo5N6/Co cell drives overall water splitting (OWS) at a low voltage of 1.397/1.74 V to achieve a current density of 10/100 mA cm−2 in the 1.0 M KOH. An anion exchange membrane water electrolyzer (AEMWE) based on the catalysts can achieve a current density of 450 mA cm−2 at 1.8 V with a long‐term stability of 120 h.

Atomic Phosphorus Sites for Anchoring Platinum–Tungsten Dimers to Facilitate Proton Transfer in All‐pH Hydrogen Evolution

AbstractBimetallic single‐atom‐dimer (SAD) with unique electronic structures and adsorption properties presents exceptional catalytic performance owing to atomic‐level synergistic effects from direct bonding between different metal atoms. However, inherent characteristics of substrate present great challenges in their synthesis and mechanism investigation. Herein, a unique phosphorus modified atomic layer deposition (P‐ALD) strategy is designed to synthesize P‐anchored Pt–W dimers, overcoming substrate limitation (Pt1W1–P/C). Motivated introduction of atomic P site via ALD can effectively anchor one‐to‐one AB bimetallic dimer structure on various substrates, confirmed by X‐ray absorption spectroscopy (XAS). Density functional theory reveals an interatomic synergistic adsorption mechanism, with W as primary hydrogen adsorption site extending to Pt, optimizing hydrogen coverage, leading to 60‐fold increase in mass activity compared to commercial Pt/C in both acidic and alkaline electrolytes. Anion exchange membrane water electrolyzer with ultra‐low loading Pt1W1–P/C (50 µgPt cm−2) catalyst operates durability at 1000 mA cm−2 for 550 h with ultra‐low degradation of 38 µV h−1. Operando XAS confirms hydrogen adsorption pathway between atoms and remarkable self‐healing ability of P–Pt–W–O sites under all‐pH conditions. These findings extend the application domain of SAD to catalytic manufacturing methods and aid in designing advanced materials with multi‐atomic active sites.

Modulating Carrier Oxygen Vacancies to Enhance Strong Oxide‐Support Interaction in IrO2/Nb2O5‐x Catalysts for Promoting Acidic Oxygen Evolution Reaction

AbstractGiven the pronounced dissolution of electrocatalysts in acidic environments, the quest for effective oxygen evolution reaction (OER) electrocatalysts suitable for proton exchange membrane (PEM) water electrolyzers persists as a formidable challenge. In this investigation, catalysts are synthesized by creating oxygen vacancies within various metal oxides (Nb2O5‐x, Ta2O5‐x, ZrO2‐x, TiO2‐x) through plasma‐assisted method, thereby facilitating the immobilization of IrO2 onto these defect‐rich surfaces. The findings unveil that IrO2/Nb2O5‐x manifests reduced overpotentials during acidic OER, achieving an overpotential down to 225 mV@10 mA cm−2, coupled with outstanding durability at multicurrent densities exceeding 200 h, attributed to strong oxide‐support interaction (SOSI) between the IrO2 catalyst and Nb2O5‐x substrate. Density functional theory (DFT) computations uncover intensified binding affinities between IrO2 and Nb2O5‐x, thus modulating the central energy levels of Ir's d orbitals toward favorable OER conditions, consequently bolstering the electrocatalytic activity and stability of the composite catalyst. Furthermore, employing IrO2/Nb2O5‐x as a PEM electrolyzer anode enables consistent operation at 1000 mA cm−2 for 200 h, with an Ir content of only 0.2852 mg cm−2 and an energy consumption of 4.34 kWh Nm−3 H2. This achievement substantially lowers the cost of hydrogen production to US$ 0.96 per kilogram, underscoring its potential for practical applications.

Surface oxygen-doping induced atom migration of iron-nickel sulfides with tailored d-band center for enhanced oxygen evolution

The rational design of tailored surface properties by surface doping is an efficient yet challenging method for enhanced OER performance. Herein, we propose atom migration effect, induced by surface O-doping to precisely control surface compositions of FeNiS2 (FNS). The FNS undergoes a surface sulfur/oxygen exchange to form FeNiS2-xOx (FNSO) structure after surface O-doping, while the bulk phases remain unchanged. In contrast, the surface Ni/Fe ratio is significantly increased due to the accelerated atom migration of nickel during surface O-doping. At elevated temperatures, the bulk phase is prone to transition into complex phases of FeNiS and FeNiO, leading to the decreased surface Ni/Fe ratio. The optimized FNSO demonstrates superior OER performance with a low overpotential of 256 mV at 100 mA cm−2, and the assembled anion exchange membrane water electrolyzer requires only 1.83 V at 1 A cm−2 with robust durability. Theoretical calculations reveal that this surface atom migration adjusts the d-band center level, optimizes surface adsorption/desorption behaviors, and expedites the OER kinetics. This work contributes to a deeper comprehension of surface modulation with desired surface properties of sulfides and other compounds for enhanced OER performance.

Stabilizing Pure Water-Fed Anion Exchange Membrane Water Electrolyzers through Membrane-Electrode Interface Engineering.

Nickel-iron (oxy)hydroxide (NiFeOxHy) stands as a cutting-edge nonprecious electrocatalyst for the oxygen evolution reaction (OER). However, the intrinsic thermodynamic instability of nickel and iron as anode materials in pure water-fed electrolyzers poses a significant durability challenge. In this study, an anion exchange ionomer coating was applied to NiFeOxHy to modify the local pH between a membrane and an electrode. This effectively extended the diffusion length of hydroxide anions toward the electrode, establishing an alkaline local pH environment. Stability tests with the ionomer coating showed reduced Ni dissolution. Moreover, locally resolved current density measurements were used to demonstrate a notably lower degradation rate during stability testing, revealing a 6-fold increase in stability with the ionomer on NiFeOxHy. In situ Raman spectroscopy in a neutral pH electrolyte confirmed inhibited Ni oxidation with the ionomer, mitigating Ni dissolution and enhancing stability of state-of-the-art NiFeOxHy catalysts in pure water-fed water electrolyzers.

Variance-based global sensitivity analysis of the performance of a proton exchange membrane water electrolyzer

This study is threefold objective. First, a nonlinear one-dimensional steady-state simulation model for hydrogen production from proton exchange membrane water electrolyzer (PEMWE) is established. The model comprehensively addresses activation, diffusion overpotentials and ohmic potential drop, and particularly incorporating Nafion membrane properties in the presence of liquid water. The model is enhanced by analyzing the hydrogen crossover, introducing corresponding diffusion equations to evaluate Faraday efficiency. The model accurately quantifies voltage efficiency, hydrogen production rate and specific energy consumption, and it is validated with published experimental data found in the scientific literature. Second, a variance-based global sensitivity analysis (GSA) on the model, is employed as a metric to assess the impact of operating conditions and material characteristics on three objective functions: the hydrogen production rate; the voltage efficiency and the specific energy consumption. Third, to support the GSA analysis, genetic algorithm (GA) technique is performed to maximize hydrogen production rate while minimizing specific energy consumption. In the course of this novel investigation, it was discerned that the number of cells, the cross-sectional area of the electrolyzer, the current density and temperature all exerted a significant impact on the three objective functions. This combined approach GSA-GA provides a thorough exploration of parameter influences and an efficient optimization strategy for enhancing the model's performance. These findings provide valuable insights that can guide analysis of the performance and the optimization of the PEMWE system.

Performance prediction of experimental PEM electrolyzer using machine learning algorithms

Proton exchange membrane water electrolyzer (PEMWE) is a sustainable energy conversion device that uses electrical energy to oxidize water and convert it into chemical energy (hydrogen and oxygen) and heat. Despite their numerous advantages, such as high current density, efficiency, high-purity hydrogen production, compatibility with renewable energy sources, and compact design, they have not yet matured due to durability, cost, and electrochemical performance deficiencies. Effective assessment of performance and durability is crucial for electrolyzer design and optimization. This study analyzes the electrochemical performance of PEMWE with artificial intelligence approaches using experimental data. Three different machine learning (ML) techniques − Multilayer Perceptron (MLP), Support Vector Machine (SVM), and Random Forest (RF) were trained and tested for predicting the hydrogen flowrate and current density for PEMWE using different input parameters. These input parameters include cell voltage, temperature, torque, and water flowrate. SVM was detected to be the best technique in predicting all output parameters with a Mean Absolute Error (MAE) of 0.0317 and 0.0671 for current density and hydrogen flowrate predictions in the test set, respectively. The study results show that machine-learning algorithms can optimize operational parameters in electrolyzer control systems.

Machine learning-powered performance monitoring of proton exchange membrane water electrolyzers for enhancing green hydrogen production as a sustainable fuel for aviation industry

Aviation is a major contributor to transportation carbon emissions but aims to reduce its carbon footprint. Sustainable and environmentally friendly green hydrogen fuel is essential for decarbonization of this industry. Using the extremely low temperature of liquid hydrogen in aviation sector unlocks the opportunity for cryo-electric aircraft concept, which exploits the advantageous properties of superconductors onboard. A significant barrier for green hydrogen adoption relates to its high cost and the immediate need for large-scale production, which Proton Exchange Membrane Water Electrolyzers (PEMWE) can address through optimal dynamic performance, high lifetimes, good efficiencies, and importantly, scalability. In PEMWE the cell is a crucial component that facilitates the electrolysis process and consists of a polymer membrane and electrodes. To control the required production rate of hydrogen, the output power of cell should be monitored which usually is done by measuring the cell’s potential and current density. In this paper, five different machine learning (ML) models based on different algorithms have been developed to predict this parameter. Findings of the work highlight that the model based on Cascade-Forward Neural Network (CFNN) is investigated to accurately predict the cell potential of PEMWE under different anodic material and working conditions with an accuracy of 99.998 % and 0.001884 in terms of R2 and root mean square error, respectively. It can predict the cell potential with a relative error of less than 0.65 % and an absolute error of below 0.01 V. The Standard deviation of 0.000061 for 50 iterations of stability analysis indicated that this model has less sensitivity to the random selection of training data. By accurately estimating different cell’s output with one model, and considering its ultra-fast response, CFNN model has the potential to be used for both monitoring and the designing purposes of green hydrogen production.

Ultrafine IrNi nanoparticles supported onto titanium nitride as low-iridium and highly active OER electrocatalysts for proton exchange membrane water electrolysis

The development of cost-effective and highly efficient iridium-based catalysts for the anode of proton exchange membrane water electrolyzers (PEMWEs) is urgently required. This study utilized a straightforward wet-chemical method to produce IrNi nanoparticles that were supported on titanium nitride (TiN), where the ultra-small particle size of 1.9 nm for IrNi nanoparticles and the structural support provided by TiN ensure the full exposure of catalytic sites. The electronic interaction between Ir-Ni and Ir-TiN enhances the intrinsic activity of the catalytic sites. The developed catalyst exhibits excellent oxygen evolution reaction (OER) performance, with an overpotential of just 267 mV at a current density of 10 mA cm−2, and a mass activity of 1.07 A mgIr−1 at 1.55 V versus reversible hydrogen electrode, which is more than 14 times that of commercial IrO2. Furthermore, its catalytic performance is validated in a PEMWE single cell, along with stable operation for 100 h. The proposed design of the supported iridium-based alloy catalysts in this study presents a novel and referential method for developing anode catalysts in PEMWEs.

Optimization of dual-layer flow field in a water electrolyzer using a data-driven surrogate model

Serious bubble clogging in flow-field channels will hinder the water supply to the electrode of proton exchange membrane water electrolyzer (PEMWE), deteriorating the cell performance. In order to address this issue, the dual-layer flow field design has been proposed in our previous study. In this study, the VOF (volume of fluid) method is utilized to investigate the effects of different degassing layer and base heights on the bubble behavior in channel and determine the time for the bubbles to detach from the electrode surface. However, it is very time-consuming to get the optimal combination of base layer and degassing layer heights due to the large number of potential cases, which needs to be calculated through computation-intensive physical model. Therefore, machine learning methods are adopted to accelerate the optimization. A data-driven surrogate model based on deep neural network (DNN) is developed and successfully trained using data obtained by the physical VOF method. Based on the highly efficient surrogate, genetic algorithm (GA) is further utilized to determine the optimal heights of base layer and degassing layer. Finally, the reliability of the optimization was validated by bubble visualization in channel and electrochemical characterization in PEMWE through experiments.

Electrocatalytic nitrogen reduction in continuous-flow cell via water oxidation at ambient conditions: Promising for ammonia or diazene?

Electrochemical nitrogen reduction reaction (eNRR) is recognized as an alternative green approach to the traditional energy-demanding and fossil-based catalytic processes (e.g. Haber Bosch). In this study, we implement eNRR in a proton exchange membrane (PEM) water electrolyzer in which nitrogen (N2) is fed in the cathode. This operation mode has been suggested as a way to overcome mass transfer limitations, however, there is a lack of developed evaluation protocols for appropriate product identification. Herein, we exemplify the spirit of the evaluation protocols for gas phase operation at the device level with a combination of online product analysis and isotopic labeling. Our protocol involves control experiments by replacing the cathodic N2 feed with (i) inert gas (i.e. Ar) and (ii) isotopic labeled 15N2 and by replacing the anodic water feed with isotopic labeled D2O. Taking advantage of the gas phase operation in the cathode product analysis is realized with online techniques i.e. quadrupole mass-spectrometer (QMS) and Fourier transform infrared (FTIR) spectrometer. This allows us to verify the production of diazene (N2H2) resulted from genuine N2 reduction, rather than from nitrogen-containing contaminants. Our methodology provides a pathway for how the false positive results can be eliminated in the gas phase study and a platform for follow-up studies using promising or exotic catalysts in the cathode, especially to validate the eNRR products or discover more products.

Accelerated Discovery of Multi-Metallic Nanostructured Catalysts for Anion Exchange Membrane Water Electrolyzers: Oxygen Evolution Reaction

The current reliance on platinum group metals (PGMs) as electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane (PEM) water electrolyzers, the current industry standard, presents a significant barrier to the widespread adoption of hydrogen as a clean energy carrier. The scarcity and high cost of PGMs necessitate the development of alternative materials and technologies that offer comparable performance at a reduced cost. In this context, anion exchange membrane (AEM) water electrolyzers have emerged as a promising alternative.This presentation addresses this imperative by focusing on the design and synthesis of nanostructured mesoporous multi-metallic catalysts for AEM water electrolyzers, leveraging earth-abundant materials as alternatives to the rare and expensive PGMs currently employed in PEM water electrolyzers. Transition metal oxides, sulfides, and phosphides are promising candidates to replace PGMs, given their abundance, low cost, and tunable catalytic properties conducive to high OER activity. The OER activity and durability of newly developed multi-metallic transition metal catalysts in an alkaline environment will be discussed in this presentation.Preliminary results demonstrate that the developed catalysts exhibit high OER activity, achieving a potential of <1.5 V versus RHE at a current density of 10 mA cm⁻² in 1.0 M KOH. Notably, this surpasses the performance of commercial OER catalysts in alkaline environments. Furthermore, the catalyst exhibits superior durability, with < 0.5 mV/h potential loss over 100 h durability test at 10 mA cm⁻² in 1.0 M KOH.AcknowledgmentsThis work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). Argonne is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under Contract DE-AC-02-06CH11357 .

High Efficiency and High Durability Proton Exchange Membrane Water Electrolyzers for Hydrogen Production with Advanced Catalyst Coated Membranes

Water electrolyzers and fuel cells can be used to create a closed loop system for space exploration. Electrolyzers allow for reliable self-sustainable generation of hydrogen and oxygen for energy storage, followed by conversion into electrical energy in a fuel cell. A first-order safety concern for water electrolyzer operation is hydrogen crossover. Transport of hydrogen to the oxygen rich anode in proton exchange membrane (PEM) water electrolyzers poses safety concerns when the hydrogen concentration in the anode flow field approaches the hydrogen lower flammability limit (LFL). Hydrogen storage efficiency relies on high hydrogen pressure, leading to pressure-driven hydrogen crossover. Mitigation of hydrogen crossover through research and development of a platinum metal recombination layer has been demonstrated in high performing, durable PEMWEs.1-4 Ouimet4 explored the use of a novel dual recombination layer configuration to mitigate PEM water electrolyzer hydrogen crossover. In addition, the current state of the art for PEM fuel cells and water electrolyzers rely on perfluoro-sulfonated acid (PSFA) based membranes. There are significant challenges facing the use of PSFA-based membranes; namely, environmental contamination and performance limitations. The use of a hydrocarbon membrane allows for the development of a PSFA-free system that shows higher efficiency and durability. Investigation of hydrocarbon membranes pave way for developing a PEM water electrolyzer that will demonstrate improved gas permeability resistance, mechanical strength, and thermal stability.5-8 There is a need for both hydrogen crossover mitigation strategies and durability testing with hydrocarbon membranes.The research outlined in this work is focused on the development of PSFA-free PEM water electrolyzers with low hydrogen crossover. In this work, the dual recombination layer configuration will be incorporated into a hydrocarbon membrane for PEM water electrolysis. Polarization, electrochemical impedance spectroscopy, electrochemical equivalent circuits, distribution of relaxation times, and materials characterization will be used to investigate the cell performance and durability. References G. Mirshekari, R. Ouimet, Z. Zeng, H. Yu, S. Bliznakov, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, and R. Maric, “High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment,” international journal of hydrogen energy, vol. 46, no. 2, pp. 1526–1539, 2021.Z. Zeng, R. Ouimet, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, A. P. Soleymani, J. Jankovic, H. Yu, G. Mirshekari, et al., “Degradation mechanisms in advanced meas for pem water electrolyzers fabricated by reactive spray deposition technology,” Journal of The Electrochemical Society, vol. 169, no. 5, p. 054536, 2022.A. Martin, D. Abbas, P. Trinke, T. Böhm, M. Bierling, B. Bensmann, S. Thiele, and R. Hanke-Rauschenbach, “Communication—proving the importance of ptinterlayer position in pemwe membranes for the effective reduction of the anodic hydrogen content,” Journal of The Electrochemical Society, vol. 168, no. 9, p. 094509, 2021.R. J. Ouimet, “Catalyst development by a novel fabrication process for energy applications,” University of Connecticut Doctoral Dissertation, 2021.P. Trinke, P. Haug, J. Brauns, B. Bensmann, R. Hanke-Rauschenbach, and T. Turek, “Hydrogen crossover in pem and alkaline water electrolysis: mechanisms, direct comparison and mitigation strategies,” Journal of The Electrochemical Society, vol. 165, no. 7, p. F502, 2018.P. Trinke, B. Bensmann, and R. Hanke-Rauschenbach, “Current density effect on hydrogen permeation in pem water electrolyzers,” International Journal of Hydrogen Energy, vol. 42, no. 21, pp. 14355–14366, 2017.H. Q. Nguyen and B. Shabani, “Proton exchange membrane fuel cells heat recovery opportunities for combined heating/cooling and power applications,” Energy Conversion and Management, vol. 204, p. 112328, 2020.C. Klose, T. Saatkamp, A. Münchinger, L. Bohn, G. Titvinidze, M. Breitwieser, K. D. Kreuer, and S. Vierrath, “All-hydrocarbon mea for pem water electrolysis combining low hydrogen crossover and high efficiency,” Advanced Energy Materials, vol. 10, no. 14, p. 1903995, 2020.

Evaluating the Impact of Cell Assembly and Operating Conditions on the Performance of Anion Exchange Membrane Electrolyzers

The alkaline water electrolyzer (AWE) and proton exchange membrane water electrolyzer (PEMWE) are the two dominant commercial platforms to produce hydrogen through electrolysis. Recent efforts have focused on combining the benefits of the two technologies, leading to the creation of the anion exchange membrane water electrolyzer (AEMWE). AEMWEs operate under high pH conditions, like AWEs, enabling the use of cost-effective materials as cell components and non-noble electrocatalysts. AEMWEs also utilize the same high-performance zero-gap design PEMWEs and also have the ability to operate at high differential pressures. Therefore, AEMWEs offer the opportunity to optimize both cost and performance, out-pacing both incumbent technologies after further development.As the “active” materials in AEMWEs, the anion exchange membranes and ionomers and the catalysts have been widely studied and a number of materials have been proposed and reported on in the literature and throughout the last several ECS meetings. However, such materials are only one piece of the overall puzzle when it comes to the operation of AEMWEs. There are several aspects of cell assembly and operation that go a long way to dictating the performance of an operating cell.Therefore, the overarching goal of this study was to investigate several operational variables for AEMWEs with a known high-quality set of anion-exchange materials, known commercially as Aemion+™ paired with commercially available catalysts – PtNi/C at the cathode and either IrOx or NiFeOx at the anode. For cell assembly, representative variables that were changed were the type of membrane and electrode pre-treatment, gasket thickness, cell torque and membrane thickness. Operationally, temperature, current density and break-in procedure were adjusted. This talk will link each of these variables to the polarization performance and galvanostatic durability

Composition-Dependent Dynamics of Nickel-Iron-Cobalt Metal Catalysts for Oxygen Evolution Reaction

Water electrolyzers, such as proton exchange membrane water electrolyzers (PEM) and anion exchange membrane water electrolyzers (AEM) are important technologies for sustainable electrochemical energy conversion. The oxygen evolution reaction (OER) at the anode is a pivotal half-reaction in these systems. Despite substantial progress over the years, OER kinetics remain a major source of inefficiency in these devices, necessitating the development of stable catalysts. Currently, precious metal-based catalysts dominate the landscape of OER catalysts for these devices. As non-precious alternatives, nickel-iron (Ni/Fe) catalysts have emerged as particularly promising in alkaline conditions. However, they exhibit dynamic behavior during electrocatalysis—for instance, oxidizing to an active oxyhydroxide phase during the OER. This dynamic nature makes it challenging to establish clear structure-activity-stability relationships. Incorporating cobalt (Co) into the catalyst composition has been found to influence the activity and material conversion of mixed Ni-Fe-Co oxides and (oxy)hydroxides. Methods for rationally activating and stabilizing Ni-Fe-based catalysts via electrochemical and chemical (e.g. composition) routes are necessary for enhancing scalability and accessibility in hydrogen production devices.Herein, our goal is to understand and exploit activation protocols to enhance the OER performance of as-synthesized nickel-iron-cobalt metal thin films, addressing three primary objectives: synthesizing and characterizing homogeneous metal catalysts, investigating the impact of different potential ranges and scan rates on catalyst oxidation and surface conversion from the metal, and assessing how the addition of cobalt influences conversion rates and current density of the catalyst. We use cyclic voltammetry to facilitate and disentangle conversion (integrated reductive peak for Ni and/or Co2+ → 3+ transition) and OER performance (current density (mA cm-2) at η = 350 mV). For all compositions tested of (Ni80Fe20)100-xCox, x = 0 - 5 % we observe that the most effective conversion requires both redox and oxygen evolution. To further investigate the relationship between conversion and performance catalysts were tested in varying electrolytes such as 1M KOH, 0.1M KOH, and an ionomer overlayer to understand how these impacted conversion.Subsequently, post-analysis techniques such as X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry optical emission spectroscopy (ICP-OES) were conducted to gain insights into the surface composition and elemental distribution of the catalysts following potential cycling. Additionally, electrochemical mass spectrometry (EC-MS) was employed to quantify the faradaic efficiency of oxygen, providing an understanding of at what point the catalyst begins converting and how much of the OER current is directed towards OER versus metal conversion.This project advances the fundamental understanding of NiFeCo catalyst conversion, shedding light on the critical role of catalyst composition and investigating the conditions that foster optimal conversion efficiency. The use of physical vapor deposition for thin film catalysts offers distinct advantages, making deposition and scaling processes facile. This capability, coupled with the gained insights into conversion dynamics, sets the stage for in situ optimization of the surface to achieve the active oxyhydroxide phase with the highest performance for AEM water electrolysis.

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.

Understanding Mechanisms and Reversibility of Anode Degradation in PEM Water Electrolysis

Water electrolysis is an important route toward sustainable industrial production of hydrogen, as well as mitigation of the CO2 emissions associated with current hydrogen production from natural gas. The industrial deployment of clean electrolytic hydrogen will depend on long-term electrolyzer durability under the intermittent operating conditions associated with coupling with renewable sources of electricity. Thus, understanding cell degradation mechanisms is required to develop mitigation strategies and minimize performance degradation over extended periods of operation.Here, we investigate the effect of temperature and intermittent conditions on proton exchange membrane (PEM) water electrolyzer performance over a variety of timescales. Performance losses consisting of both reversible losses and irreversible degradation accelerate quickly during holds at high current densities and low temperatures, reaching high cell voltages within several hours. However, the cell can be returned to near beginning-of-test performance by interrupting these current holds with a variety of intermittent states of operation, such as interruption of the applied current or operation at higher temperatures. Reversible losses can harm the overall cell efficiency without being captured in short-term polarization curves, and may also contribute to stressors causing long-term degradation. The impact of different shut-down and idle states on the catalyst layers and cell degradation will also be discussed. The presented insights could contribute to the development of accelerated stress test protocols as well as performance recovery strategies for long-term operation of PEM water electrolyzers.

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.

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.