The harsh corrosive environment and sluggish oxygen evolution reaction（OER） kinetics at the anode of proton exchange membrane water electrolysis（PEMWE） cells warrant the use of excess Ir,thereby hindering large-scale industrialization.To mitigate these issues,the present study aimed at fabricating a robust low-Ir-loading electrode via one-pot synthesis for efficient PEMWE.The pre-electrode was first prepared by alloying through the co-electrodeposition of Ir and Co,followed by the fabrication of IrCo oxide（Co-incorporated Ir oxide） electrodes via electrochemical dealloying.Two distinct dealloying techniques resulted in a modified valence state of Ir,and the effects of Co incorporation on the activity and stability of the OER catalysts were clarified using density functional theory（DFT） calculations,which offered theoretical insights into the reaction mechanism.While direct experimental validation of the oxygen evolution mechanism remains challenging under the current conditions,DFT-based theoretical modeling provided valuable perspectives on how Co incorporation could influence key steps in oxygen evolution catalysis.The Ir-Co oxide electrode with a selectively modulated valence state showed impressive performance with an overpotential of 258 mV at 10 mA cm -2 ,a low Tafel slope of 29.4 mV dec -1 ,and stability for 100 h at 100 mA cm -2 in the OER,in addition to a low overpotential of 16 mV at -10 mA cm -2 and high stability for 24 h in the hydrogen evolution reaction.The PEMWE cell equipped with the bifunctional Ir-Co oxide electrode as the anode and cathode exhibited outstanding performance(11.4 A cm -2 at 2.3 V cell ) despite having a low noble-metal content of 0.4 mgNM cm -2 .

The anode porous transport layer (PTL) is crucial in proton exchange membrane water electrolyzers (PEMWEs), facilitating efficient mass transport, electron conduction, and heat dissipation. This paper reviews advancements in PTL structural design and coating strategies, emphasizing their impact on cell performance, durability, and cost-effectiveness. The acid resistance of Ti-based PTLs has led to their widespread adoption; nonetheless, challenges such as increased ohmic resistance and catalyst delamination caused by oxidation to TiO2 remain. A comprehensive investigation into the relationship between PTL pore structure and PEMWE performance has yielded significant advancements, including gradient porosity design, optimized pore structures, as well as thin and planar PTLs. Furthermore, anti-corrosion coatings, predominantly comprising precious metal layers such as Pt and Ir, have enhanced durability and performance. However, high costs pose significant constraints, prompting the exploration of non-precious material alternatives, including Nb, Ti, and Ta. In addition, the emergence of porous transport electrodes has facilitated cost-effective, high-performance PEMWE systems by integrating the dual-functional roles of catalytic activity and corrosion prevention. This paper provides key insights into designing cost-effective and high-performance PTLs to support the future hydrogen economy.

Alkaline and anion exchange membrane water electrolysis (AEMWE) presents a promising approach for hydrogen production. However, the slow kinetics of the alkaline hydrogen evolution reaction (HER) remains a significant challenge. This study aimed to enhance HER activity by optimizing transition metal‐phosphorus compound catalysts, including Ni, Co, NiCo, NiP, CoP, and NiCoP. Their surface structure, crystallinity, electrochemical properties, and HER performance were meticulously studied. Among the catalysts, Ni 28 Co 62 P 10 exhibited exceptional HER performance, achieving a low overpotential of 48 mV at a current density of −10 mA cm –2 in 1 M KOH. X‐ray photoelectron spectroscopy analysis revealed that an optimal 1:1 balance of phosphate to phosphide is critical for achieving efficient HER. These findings emphasize the importance of balancing phosphorus species for optimal alkaline HER catalysis. Moreover, Ni 28 Co 62 P 10 demonstrated excellent durability, maintaining high performance after 5000 cycles. In AEMWE single‐cell tests, the catalyst achieved a cell voltage of 1.88 V at 1 A cm –2 , surpassing the performance of Ni/Co‐based catalysts from previous studies. The NiCoP‐based catalysts in this study presented considerable promise for AEMWE systems, paving the way to the development of more efficient and durable catalysts for hydrogen production and advancing hydrogen‐based renewable energy technologies.

Proton‐exchange membrane water electrolysis (PEMWE) powered by renewable energy sources is an eco‐friendly technology for the mass production of hydrogen. One of the major obstacles in the commercialization of PEMWE is the necessity of using precious metal catalysts under corrosive operating conditions, which can be partially mitigated by using nonprecious metal catalysts for the cathode, where the conditions are less harsh than those for the anode. However, the use of nonprecious transition metal catalysts limits both performance and durability. To overcome this limitation, a wide range of NiMoMn ternary alloy catalyst compositions were fabricated by electrodeposition, and their performances were evaluated. The best‐performing Ni 82.1 Mo 11.6 Mn 6.3 alloy catalyst exhibited an outstanding hydrogen evolution performance with an overpotential of 16 mV at −10 mA cm −2 , and with an increase of only 8 mV after 10,000 potential cycles for durability testing. The application of this material in a PEMWE single cell gave a favorable performance of 1.936 A cm −2 at 2.0 V cell , and an excellent degradation rate of 2.2 mV h −1 in a durability test performed at 1 A cm −2 . This high performance and excellent durability of the Ni 82.1 Mo 11.6 Mn 6.3 catalyst was attributed to the modulation of its electronic structure, in addition to a large electrochemical surface area, and stable Mn oxide formation on the surface. These results indicate the potential of this catalyst for use in lowering the hydrogen production costs associated with PEMWE.

The development of efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER) is of paramount importance for addressing energy challenges and achieving decarbonization. This paper reports the preparation of low cost NiMo/Co-nanowire (NW)/carbon paper (CP) catalysts using a simple two-step electrodeposition process. The Co-NW template was prepared by optimizing the Co deposition potential and time on a CP substrate. Next, binary NiMo was electrodeposited onto the Co-NW templates to prepare NiMo/Co-NW/CP catalysts. The developed catalyst exhibited high performance toward the HER in an alkaline environment, necessitating a mere 85 mV overpotential in 1 M potassium hydroxide to achieve a current density of-10 mA cm- 2 and sustaining high stability over 100 hat the same operating current density. This excellent performance can be attributed to a 1.66-fold increase in active site exposure, from 24.5 mF cm- 2 to 40.8 mF cm- 2, due to the use of the Co-NW template, as substantiated by electrochemical double-layer capacitance measurements. Consequently, the HER activity of NiMo/Co-NW/CP was markedly enhanced in relation to that of NiMo/CP. The NiMo/Co-NW/CP catalyst was employed as a cathode of an anion-exchange membrane water electrolyzer, which exhibited an exceptional performance of 1.52 A cm- 2 at 2.0 Vcell.

Water electrolysis is an eco-friendly technology that does not emit pollutants when connected to renewable energy and can obtain high purity hydrogen (>99.9%) through the process of electrochemically splitting water molecules into hydrogen and oxygen. Among them, proton exchange membrane water electrolysis (PEMWE) has the advantage of high current density, low gas crossover, high gas purity, and high pressure operation compared to existing alkaline water electrolysis.[1] The material that shows the best catalytic activity in the hydrogen evolution reaction (HER) is platinum (Pt), which has a low overpotential and high exchange current density. Therefore, it has been the subject of various studies in the fields of catalysis and electrochemistry to investigate the effect of the size and structure of Pt nanoparticles and nanostructures on electrocatalytic activity.[2,3] However, due to the limited resources and high cost of platinum, the use of platinum acts as an obstacle to commercialization of PEMWE. Accordingly, many studies have been conducted on the development of low-platinum hydrogen generation catalysts to reduce platinum usage and increase activity. has been in progress. In this study, a porous transport electrode incorporating a Ni catalyst in which Ru was atomically dispersed was fabricated through simple electrodeposition. The Ni98.1Ru1.9 catalyst doped with trace amounts of Ru showed a low overpotential of 35 mV at –10 mA cm-2 for hydrogen evolution and a low Tafel slope of 31 mV with excellent stability. It was found that optimized hydrogen adsorption strength and improved mobility of hydrogen adsorbates on the catalyst surface contributed to high performance through density functional theory calculations. As a result of further verifying the performance and durability by applying Ni98.1Ru1.9 to the hydrogen electrode of the PEMWE cell, it showed excellent performance of 6.0 A cm-2 at 2.25Vcell and high stability operating at 1 A cm-2 for 50 hours.[4] [References] [1] M. F. Kaya, N. Demir., Fuel Cells, 17 (2017) 37–47 [2] J. Solla-Gullón, R. Gómez, A. Aldaz, J.M. Pérezet., Electrochemistry Communications, 10 (2008) 319–322 [3] Maryam Bayati, Jose M. Abad, Craig A. Bridges, Matthew J. Rosseinsky, David J. Schiffrin, Journal of Electroanalytical Chemistry, 623 (2008) 19–28 [4] K-R. Yeo, H. Kim, K-S Lee, S. Kim, J. Lee, H. Park, S-K Kim, Applied Catalysis B: Environment and Energy, 346 (2024), 123738

Fuel cells are widely used for converting the energy released by fuel oxidation into electricity. Among the available fuels, hydrogen is particularly crucial for achieving carbon neutrality and is mainly produced by natural gas reforming, therefore containing ppm-level traces of carbon monoxide (CO). Despite its low concentration, CO interferes with the operation of hydrogen fuel cells by strongly binding to the anode catalyst and thus irreversibly decreasing its activity (poisoning). To address this problem, which cannot be solved without a deep understanding of all aspects, the present review examines the origins of CO poisoning and categorizes and discusses the related prevention methods, revealing the pivotal role of electrocatalyst design in poisoning research and mitigation. The presented evidence demonstrates that knowledge-driven approaches enable the practical applications of catalysts designed using the above methods and therefore help solve the problems posed by CO poisoning in fuel cells.

Proton exchange membrane water electrolysis (PEMWE) is an environmentally benign technology for large-scale hydrogen production. Despite many catalysts being developed to replace Pt, successful development of low-cost catalysts that meet the balance of performance and durability is limited. In this work, atomically dispersed Ru on Ni catalyst-integrated porous transport electrodes were fabricated by a simple electrodeposition. With a trace amount of Ru (< 0.05 mg(Ru)cm(-2)), the Ni98.1Ru1.9 cathode catalyst exhibited an overpotential of 35 mV at -10 mAcm(-2) with excellent stability. Density functional theory calculation revealed that the high performance was driven by optimized adsorption strength and improved mobility of hydrogen on the catalyst surface. The Ni98.1Ru1.9 electrode was further verified in a PEMWE cell and resulting performance (6.0 Acm(-2) at 2.25 V-cell) and stability (0.13 mVh(-1) decay rate at 1 Acm(-2)) surpassed previously reported non-Pt and even Pt electrodes, demonstrating its readiness as an advanced cathode to replace Pt.

Multicomponent electrocatalysts offer inherent advantages because of the synergistic effects among their constituents at the atomic scale, rendering them suitable for enhancing the catalytic activity of the hydrogen evolution reaction (HER). In this study, self-supported Co-Ni-Cu-Mn electrocatalysts are deposited on porous carbon paper via one-step electrodeposition. These electrocatalysts exhibit remarkable synergistic enhancements, resulting in both improved acidic HER activity and overall durability. This synergy arises from the development of hierarchical structures triggered by Cu and Mn-doped surface. During HER, Cu leaches from the catalyst surface, while simultaneously, surface - doped Mn synergistically prevents activity degradation and facilitates surface reconstruction. The combination of these interactions helps to achieve a low overpotential of 100 mV at 10 mA cm - 2 . The Co-Ni-Cu-Mn electrocatalyst is applied as a high-efficient cathode gas diffusion electrode for proton exchange membrane water electrolyzer (PEMWE). The PEMWE single-cell equipped with Pt-free cathode achieves an outstanding performance of 2.57 A cm - 2 at 2.0 V cell , with exceptional stability for 60 h under high current density of 2.0 A cm - 2 . The successful implementation of the quaternary electrocatalyst highlights its potential for tailoring catalytic properties for hydrogen production, effectively bridging the gap between fundamental understanding and practical realization for cost-efficient PEMWE.

Data-driven approaches now allow for systematic mappings from materials microstructures to materials properties. In particular, diverse data-driven approaches are available to establish mappings using varied microstructure representations, each posing different...

Replacing the oxygen evolution reaction in water electrolysis with ammonia oxidation reaction enables low voltage hydrogen production. Pt is a promising catalyst for the ammonia oxidation reaction due to its superior dehydrogenation and low affinity for *N, but N-ads poisoning deactivates the Pt surface. This study proposes a method to improve ammonia oxidation performance and stability through electrochemical activation, introducing cathodic corrosion and recovery conditions. The half-cell results showed a peak current density of 74.2 mA cm(-2) and retention ratio of 17 %. Adjusting the lower and upper cell voltage in a membrane electrode assembly based single cell optimized surface cleaning and inhibits further poisoning by O/OHads above 0.75 V-cell. Furthermore, incorporation of recovery conditions can enhance the stability of poisoned electrode compared to that in chronoamperometry test. The results of pulsed ammonia electrolysis tests incorporating recovery conditions suggested a novel approach to practical hydrogen production by stabilizing catalysts with a 83 % Faradaic efficiency at 0.1 A cm(-2).

Proton exchange membrane water electrolyzer (PEMWE) is the most promising green hydrogen production device suitable for responding to the intermittency of renewable energy sources [1]. However, anodes in acidic and oxidizing environments require the use of noble Ir that is resistant to harsh conditions. Although many efforts have been made to develop efficient and robust Ir-based catalysts, most have focused on developing catalysts in powder form and evaluating half-cells based on aqueous model systems consisting of three-electrode using rotating disk electrode (RDE). The membrane electrode assembly (MEA)-based PEMWE system has significant differences in operating conditions (temperature, electrolyte, catalyst loading, substrate type, etc.) from the half-cell system, and therefore, the high performance and durability in the half-cell system do not ensure the same results within the PEMWE system [2]. This means that the developed catalysts should be applied to a single cell and its compatibility assessed. In this study, a catalyst-integrated electrode was fabricated by forming an Ir-based catalyst on a Ti fiber felt used as an anode PTL in the PEMWE system, and applied directly to the anode without using a binder. The application of a powder-type catalyst to MEA is complicated through many steps such as powder production, ink preparation, and catalyst layer coating, requiring a lot of time and cost. In addition, when coating the catalyst layer, it is physically deposited together with a polymer binder, which not only blocks the active sites of the catalyst but also causes the problem of lowering the electrical conductivity of the catalyst layer [3]. On the other hand, the catalyst-integrated electrode is a simple method of growing on PTL, providing good electrical conductivity and excellent mechanical stability, and can be directly applied to the PEMWE system without using a binder. Our Ir-based catalyst-integrated electrode prepared through electrochemical reaction showed excellent OER activity (248 mV at 10 mA cm− 2) and durability (50 h at 200 mA cm− 2) in a half-cell system based on excellent physicochemical/electrochemical properties, and also showed the similar results when applied to a single-cell (performance of 6.5 A cm− 2 @ 2.0 Vcell with a degradation rate of only 1.58 mV h− 1 for 100 h stability test at 2 A cm− 2), showing feasibility for industrial use. [1] S. Shiva Kumar, V. Himabindu, Hydrogen Production by PEM water electrolysis – A review, Materials Science for Energy Technologies, 2 (2019) 442-454. [2] K. Ehelebe, D. Escalera-Lopez, S. Cherevko, Limitations of aqueous model systems in the stability assessment of electrocatalysts for oxygen reactions in fuel cell and electrolyzers, Current Opinion in Electrochemistry, 29 (2021) 100832. [3] W. Wang, L. Ding, J. Li, Z. Xie, M.M. Mench, F.-Y. Zhang, An ink-free integrated dual electrode assembly for economical proton exchange membrane water electrolysis at ultrahigh current densities, Chemical Engineering Journal, 494 (2024) 153015.

2D (2-dimensional) (100) plane β phase Ga2O3 (β-Ga2O3) flake based Pt Schottky diode is demonstrated for hydrogen sensing application. The (100) plane β-Ga2O3 flake was formed from the side wall of a mother (2̅01) plane β-Ga2O3 bulk substrate by the cost-effective mechanical exfoliation method. The hydrogen response of the (100) plane Ga2O3 flake based diode with the catalytic Pt Schottky electrode for hydrogen decomposition reaction was measured in the wide concentration range of 50–40,000 ppm hydrogen. The β-Ga2O3 flake based hydrogen sensor showed excellent responsivity of 2.32 × 108% for the 500 ppm hydrogen exposure at 25°C, and exhibited a reliable hydrogen sensing behavior up to 400°C. The decent cross-selectivity of the (100) plane β-Ga2O3 flake based Pt Schottky diode sensor over the other gases including N2, CO, CO2, CH4, NO2, NH3, and O2 was observed. In addition, the effect of the humidity on hydrogen sensing was investigated.

The development of high-performance non/less-precious metal-based electrocatalysts for the hydrogen oxidation reaction (HOR) in anion exchange membrane fuel cells remains a challenge. Here, we report a bimetallic Ni-Ir catalyst fabricated using electrodeposition and optimized to improve its HOR performance in an alkaline environment. Bimetallic Ni-Ir catalysts of various compositions are electrochemically deposited on a glassy carbon (GC) disk electrode and their HOR activity in 0.1 M KOH is examined. It is found that Ni47Ir53 has the highest HOR activity of 2.09 and 2.28 mA cm-2 at 0.05 and 0.10 VRHE, respectively, outperforming a commercial Pt/C electrode. This improved performance is ascribed to the larger electrochemical surface area and the modification to the electronic structure via alloying. Electrochemical analysis revealed a low Tafel slope and a large exchange current density for Ni47Ir53, suggesting the presence of the Tafel-Volmer mechanism and a rapid Volmer reaction. The balanced H binding and OH binding with Ni47Ir53 is a significant contributor to the higher HOR activity. During accelerated durability testing, the oxidation state and electronic structure of the catalyst become more unfavorable for the HOR due to Ni dissolution, which supports the strategy of employing a dissolution-resistive alloying metal with Ir for alkaline HOR catalysts.

A carbon matrix with desiccation cracks serves as a porous transport layer for PEMWE, enhancing the electrochemical performance and stability of Ir nanoparticles for the oxygen evolution reaction.

To reduce the fabrication cost of proton exchange membrane water electrolyzers (PEMWEs), low-loading platinum-based cathodes were fabricated through constant po-tential (-1.1 V-SCE) electrodeposition of Co, galvanic displacement with Pt in K2PtCl4 + NaCl solution, and subsequent chemical (immersion in 0.5 M H2SO4 for 5 min) or electrochemical dealloying (2000 potential cycles at-0.2 to-0.5 V-SCE in 0.5 M H2SO4) processes. These simple electrochemical steps produced a bimodal structure of layered Pt/Co/carbon paper (CP) and particulate Pt/CP catalysts on a porous transport layer of carbon fiber. Heat treatment of Co deposits (500 degrees C for 2 h, H-2/Ar atmosphere) prior to Pt displacement was found to strongly affect the stability of Co and the electronic structures of subsequently placed Pt, resulting in high activity (an overpotential of 18.4 mV at-10 mA cm(-2)) and durability (similar to 6000 potential cycles) of the electrochemically dealloyed catalyst in hydrogen evolution reaction. A single cell with this catalyst at low cathode Pt loading of 18.4 mg cm(-2) further demonstrated excellent performance of 2.39 A cm(-2) @ 1.9 V. The cathode Pt mass activity is superior to previous works on other low Pt electrode fabrication methods using pulse electrodeposition or self-terminated electrodeposition, providing a new lower limit of precious metal usage for PEMWE. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The costly price of Pt for the oxygen reduction reaction is the primary issue for the metal-air batteries or fuel cells. In this study, Fe, N, and S tri-doped non-precious metal catalysts are synthesized by varying different N and S doping sequences. The catalysts exhibit a higher graphitization degree than carbon black as proven by the XRD and Raman spectroscopy. The catalyst without S shows the Fe3C phase, while the Fe3C phase is not found in all the Fe-NSC catalysts. Furthermore, imaging and XANES studies show that the Fe metal particles are atomically dispersed in the S-doped NPMCs. XPS and XANES exhibit that the active sites concentrations, inactive Fe-S bond and the oxidation number of Fe species are varied by the N and S doping sequences. The Fe-NSC-1 catalyst with an onset potential of 0.96 V (vs. RHE) demonstrates fast reaction rate and high selectivity. After 10,000 potential cycles between 0.6 and 1.0 V, half wave potential for the Fe-NSC-1 catalyst decreased by ca. 3%. Methanol tolerance tests represent the negligible decrease in the current density for the Fe-NSC-1 catalyst. Therefore the doping sequence influences the chemical and electronic structure, which enhances the electrochemical performance and stability under operating conditions.

The primary challenge in the large-scale production of metal-air batteries or fuel cells is the high cost of Pt, which is used in the oxygen reduction reaction. To address this issue, we synthesized non-precious metal catalysts by doping Fe, N, and S in various sequences. X-ray diffraction and Raman spectroscopy proved that these catalysts had a higher degree of graphitization than carbon black. While the Fe3C phase was found in the catalyst without S, it was absent in all Fe-NSC catalysts. Imaging and X-ray absorption near edge structure (XANES) studies showed atomically dispersed Fe metal in the S-doped non-precious metal catalysts. X-ray photoelectron spectroscopy (XPS) and XANES reveal that the active site concentrations, inactive Fe-S bond, and oxidation number of the Fe species vary according to the N and S doping sequences. Fe-NSC-1 showed fast kinetics and high selectivity, with an onset potential of 0.96 V. Even after 10,000 potential cycles between 0.6 and 1.0 V, the half-wave potential for Fe-NSC-1 decreased by only 3%. Additionally, the Fe-NSC-1 catalyst showed a negligible decrease in current density during the methanol tolerance tests. Overall, this study found that the doping sequence plays a vital role in enhancing the electrochemical performance and stability of these catalysts under suitable operating conditions by influencing their chemical and electronic structures.

In this study, we investigated ternary transition metal catalysts composed of Cu, Ni, and Mo for application to hydrogen oxidation reaction (HOR) in alkaline electrolyte. A series of catalysts with a wide range of elemental compositions were fabricated by a simple electrodeposition method, and their material and electrochemical properties were investigated. In particular, to avoid inaccurate activity measurements due to oxidation and reduction of the transition metal-based catalysts during the HOR test, the electrochemical measurements were performed in both H2- and N2-saturated electrolytes, and the results were compared. The fabricated CuNiMo catalyst with an optimized composition exhibited an excellent HOR activity of 2.03 mA cm−2 at 0.1 VRHE, while the current density decreased only by 0.55 mA cm−2 after 3000 cycles. The enhanced HOR activity is attributed to the combined effects of the modified crystal structure, increased surface area, alloying effects beneficial to the hydrogen binding energy and OH− binding energy, and appropriate surface compositions between the H-adsorbing metallic state and OH-adsorbing oxophilic states. The characteristics of the catalyst demonstrated in this study can provide insights for the development of non-precious catalysts for HOR in alkaline electrolytes.

2D (2-dimensional) (100) plane /3 phase Ga2O3 (/3-Ga2O3) flake based Pt Schottky diode is demonstrated for hydrogen sensing application. The (100) plane /3-Ga2O3 flake was formed from the side wall of a mother (201) plane /3-Ga2O3 bulk substrate by the cost-effective mechanical exfoliation method. The hydrogen response of the (100) plane Ga2O3 flake based diode with the catalytic Pt Schottky electrode for hydrogen decomposition reaction was measured in the wide concentration range of 50-40,000 ppm hydrogen. The /3-Ga2O3 flake based hydrogen sensor showed excellent responsivity of 2.32 x 108% for the 500 ppm hydrogen exposure at 25 degrees C, and exhibited a reliable hydrogen sensing behavior up to 400 degrees C. The decent cross-selectivity of the (100) plane /3-Ga2O3 flake based Pt Schottky diode sensor over the other gases including N2, CO, CO2, CH4, NO2, NH3, and O2 was observed. In addition, the effect of the humidity on hydrogen sensing was investigated.