Membrane Reinforcement Strategy Using Robust Nanofibers for Durable and Safe AEM Water Electrolysis.

Anion exchange membrane (AEM) water electrolysis combines the advantages of alkaline water electrolysis and proton exchange membrane (PEM) water electrolysis, offering a cost-efficient solution with high performance. The catalyst layer (CL), a critical component of AEM cells, remains an area of active research and development, often drawing on insights from PEM fuel cells and electrolysers. Two primary methods for CL fabrication are catalyst-coated membrane (CCM) and catalyst-coated substrate (CCS). Due to the limited heat resistance of AEMs, CCS is more straightforward to fabricate compared to CCM, making it the preferred approach in many studies. However, comparative investigations of CCM and CCS in AEM water electrolysis are scarce.This study aims to address this gap by first exploring CCM fabrication techniques using various commercial membranes. Subsequently, a comprehensive comparison of CCM and CCS in AEM water electrolysis will be conducted under different operating conditions, including electrolyte and pure water supply. Performance metrics such as linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and durability will be evaluated. Microscopic imaging and theoretical analysis will be employed to elucidate performance differences between CCM and CCS under varied conditions. Furthermore, models of the CL, incorporating reactive site configuration and ion transport within and beyond the AEM, will be developed to provide deeper insights into optimizing AEM performance through appropriate CL fabrication methods. Additionally, the impact of catalyst distribution on specific activity will be investigated, focusing on configurations where catalysts are either sandwiched between the AEM and the porous transport layer or embedded within the porous transport layer. By providing a systematic comparison and theoretical framework, this work aims to guide future advancements in AEM water electrolysis with improved CL fabrication techniques.

Anion exchange membrane (AEM) water electrolysis is one of the most promising technologies to generate mass hydrogen. The employment of alkaline solution and non-noble metal electrocatalyst allows a relatively low cost to achieve high efficiency for hydrogen generation.1 The oxygen evolution reaction (OER) causes main energy loss because of the multistep electron transfer behaviors.2 In AEM water electrolysis, catalyst-coated-membrane (CCM) is one of the typical configurations for anode, which is significant for the performance of water electrolyzer. NiFe-based materials are popular as electrocatalyst towards OER, which inspires us to fabricate NiFe-based materials CCMs as anode materials. However, the interfacial reaction mechanism of NiFe-based materials CCM during alkaline OER is still unclear, and the understanding needs to be improved. In this scenario, in situ Raman spectroscopy is powerful to reveal the interfacial reaction mechanism, because it can get the fingerprint information in the interfacial area under operation conditions.Herein, a series of NiFeP catalyst-coated-membranes (CCMs) anode were synthesized on Tokuyama A-201 AEM via Pd-catalyzed electroless deposition. A self-developed cell was designed from the ground up for in situ Raman spectroscopy. Electrochemical measurements evaluated the performance of as-prepared CCMs in a reported water electrolyzer. The true active sites and behaviors of as-prepared CCMs were explored by characterizations, especially ex-situ and in-situ Raman spectroscopy. The ex situ characterizations showed that chemical dissolution of NiFeP CCMs happened on the surface all the time. The in situ Raman spectroscopy revealed the competition between the chemical dissolution and electrochemical oxidation under relatively low potential. With the potential increase, the electrochemical oxidation would be dominant, and obvious peaks of NiFe-hydroxide could be observed. At specific potential value, the NiFe-hydroxide would be transformed into NiFe-OOH, which plays significant role on the catalytic performance towards OER. The role of Fe and P contents was discussed as well. This work is expected to give a new insight into the CCM behaviors during OER in AEM water electrolysis, thus contributing to the development of AEM water electrolyzers. References C. Liu et al., Journal of Energy Chemistry, 90, 348–369 (2024).X. Xie et al., Adv Funct Materials, 32, 2110036 (2022).

This study explores a symmetric configuration approach in anion exchange membrane (AEM) water electrolysis, focusing on overcoming adaptability challenges in dynamic conditions. Here, a rapid and mild synthesis technique for fabricating fibrous membrane‐type catalyst electrodes is developed. Our method leverages the contrasting oxidation states between the sulfur‐doped NiFe(OH)2 shell and the metallic Ni core, as revealed by electron energy loss spectroscopy. Theoretical evaluations confirm that the S–NiFe(OH)2 active sites optimize free energy for alkaline water electrolysis intermediates. This technique bypasses traditional energy‐intensive processes, achieving superior bifunctional activity beyond current benchmarks. The symmetric AEM water electrolyzer demonstrates a current density of 2 A cm−2 at 1.78 V at 60°C in 1 M KOH electrolyte and also sustains ampere‐scale water electrolysis below 2.0 V for 140 h even in ambient conditions. These results highlight the system's operational flexibility and structural stability, marking a significant advancement in AEM water electrolysis technology.

One promising way to store and distribute large amounts of renewable energy is water electrolysis, coupled with transport of hydrogen in the gas grid and storage in tanks and caverns. The intermittent availability of renewal energy makes it difficult to integrate it with established alkaline water electrolysis technology. Proton exchange membrane (PEM) water electrolysis (PEMEC) is promising, but limited by the necessity to use expensive platinum and iridium catalysts. The expected solution is anion exchange membrane (AEM) water electrolysis, which combines the use of cheap and abundant catalyst materials with the advantages of PEM water electrolysis, namely, a low foot print, large operational capacity, and fast response to changing operating conditions. The key component for AEM water electrolysis is a cheap, stable, gas tight and highly hydroxide conductive polymeric AEM. Here, we present target values and technical requirements for AEMs, discuss the chemical structures involved and the related degradation pathways, give an overview over the most prominent and promising commercial AEMs (Fumatech Fumasep® FAA3, Tokuyama A201, Ionomr Aemion™, Dioxide materials Sustainion®, and membranes commercialized by Orion Polymer), and review their properties and performances of water electrolyzers using these membranes.

Anion exchange membrane (AEM) water electrolysis is a potentially inexpensive and efficient source of hydrogen production as it uses effective low-cost catalysts. The catalytic activity and performance of nickel iron oxide (NiFeOx) catalysts for hydrogen production in AEM water electrolyzers were investigated. The NiFeOx catalysts were synthesized with various iron content weight percentages, and at the stoichiometric ratio for nickel ferrite (NiFe2O4). The catalytic activity of NiFeOx catalyst was evaluated by linear sweep voltammetry (LSV) and chronoamperometry for the oxygen evolution reaction (OER). NiFe2O4 showed the highest activity for the OER in a three-electrode system, with 320 mA cm−2 at 2 V in 1 M KOH solution. NiFe2O4 displayed strong stability over a 600 h period at 50 mA cm−2 in a three-electrode setup, with a degradation rate of 15 μV/h. In single-cell electrolysis using a X-37 T membrane, at 2.2 V in 1 M KOH, the NiFe2O4 catalyst had the highest activity of 1100 mA cm−2 at 45 °C, which increased with the temperature to 1503 mA cm−2 at 55 °C. The performance of various membranes was examined, and the highest performance of the tested membranes was determined to be that of the Fumatech FAA-3-50 and FAS-50 membranes, implying that membrane performance is strongly correlated with membrane conductivity. The obtained Nyquist plots and equivalent circuit analysis were used to determine cell resistances. It was found that ohmic resistance decreases with an increase in temperature from 45 °C to 55 °C, implying the positive effect of temperature on AEM electrolysis. The FAA-3-50 and FAS-50 membranes were determined to have lower activation and ohmic resistances, indicative of higher conductivity and faster membrane charge transfer. NiFe2O4 in an AEM water electrolyzer displayed strong stability, with a voltage degradation rate of 0.833 mV/h over the 12 h durability test.

A high performance and durable electrocatalyst for the cathodic hydrogen evolution reaction (HER) in anion exchange membrane (AEM) water electrolyzers is crucial for the emerging hydrogen economy. Herein, we synthesized Pt–C core-shell nanoparticles (core: Pt nanoparticles, shell: N-containing carbon) were uniformly coated on hierarchical MoS2/GNF using pyrolysis of h-MoS2/GNF with a Pt-aniline complex. The synthesized Pt–C core-shell@h-MoS2/GNF (with 11.3 % Pt loading) showed HER activity with a lower overpotential of 30 mV at 10 mA cm−2 as compared to the benchmark catalyst 20 % Pt–C (41 mV at 10 mA cm−2) with improved durability over 94 h at 10 mA cm−2. Furthermore, we investigated the structural stability and hydrogen adsorption energy for Pt13 cluster, C90 molecule, h-MoS2 sheet, Pt13–C90 core-shell, and Pt13–C90 core-shell deposited h-MoS2 sheets using density functional theory (DFT) simulations. We investigated the Pt–C core-shell@h-MoS2/GNF catalyst active sites during HER performance using in-situ Raman analysis as well as DFT. We fabricated AEM water electrolyzers with cathode catalysts of Pt–C core-shell@h-MoS2/GNF and evaluated device performance with 0.1 and 1.0 M KOH at 20 and 60 °C. Our work provides a new pathway to design core-shell electrocatalysts for use in AEM water electrolyzers to generate hydrogen.

High-performance anion exchange membrane water electrolysis by polysulfone grafted with tetramethyl ammonium functionalities

Low cost hydrogen production by anion exchange membrane electrolysis: A review

We report on the optimization of nickel-copper catalysts for superior performance as a cathode catalyst in anion exchange membrane (AEM) water electrolysis. The bifunctional system of NiCu mixed metal oxide (MMO) nanosheets includes Ni metallic, NiO, and CuO oxides provide rapid kinetics for the hydrogen-evolution reaction (HER) of the Volmer step. In-situ Raman spectroscopy for NiCu MMO proved that nickel hydroxide was sustained under HER conditions for at least 30,000 s, which may explain why the exceptional activity of NiCu MMO as compared to other nickel-copper catalysts is maintained over time. The activity of the NiCu MMO for the HER activity in alkaline electrolytes increased as KOH concentration raised from 0.1 M to 1 M. The NiCu MMO nanosheets showed superior stability under alkaline HER conditions for 30 h. The use of Nafion ionomer in the ink resulted in a higher HER current density as compared to inks with a Fumion anion ionomer. The maximum HER performance was achieved at a Nafion ionomer to catalyst weight ratio of 0.5. Using Ir black as the anode, the NiCu MMO cathode gave an AEM electrolyzer performance of 1.85 A/cm2 at 2 V in 1 M KOH at 50 °C. The NiCu MMO catalyst developed here delivers AEM performance comparable to PEM water electrolysis.

Developing non-precious catalysts with long-term catalytic durability and structural stability under industrial conditions is the key to practical alkaline anion exchange membrane (AEM) water electrolysis. Here we propose an energy-saving approach to synthesize defect-rich iron nickel oxyhydroxide for stability and efficiency toward the oxygen evolution reaction (OER). Benefiting from in situ cation exchange, the nanosheet-nanoflake-structured catalyst is homogeneously embedded in, and tightly bonded to, its substrate, making it ultrastable at high current densities. Experimental and theoretical calculation results reveal that the introduction of Ni in FeOOH reduces the activation energy barrier for the catalytic reaction and that the purposely created oxygen defects not only ensure the exposure of active sites and maximize the effective catalyst surface but also modulate the local coordination environment and chemisorption properties of both Fe and Ni sites, thus lowering the energy barrier from *O to *OOH. Consequently, the optimized d-(Fe,Ni)OOH catalyst exhibits outstanding catalytic activity with long-term durability under both laboratory and industrial conditions. The large-area d-(Fe,Ni)OOH||NiMoN pair requires 1.795V to reach a current density of 500mA cm-2 at an absolute current of 12.5 A in an AEM electrolyzer for overall water electrolysis, showing great potential for industrial water electrolysis. This article is protected by copyright. All rights reserved.

Anion exchange membrane (AEM) water electrolysis can afford cheaper hydrogen (H2) production compared to the current state-of-the-art of proton exchange membrane (PEM) electrolysis. In AEM electrolysis, i.e., in alkaline environment, platinum group metal (PGM)-free catalysts can be adopted as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, contrary to the PEM electrolysis in which PGM-catalysts should be used. Furthermore, expensive titanium flow-field that is indispensable in acidic PEM electrolyzer can be replaced by inexpensive stainless flow-field. These advantages of AEM electrolysis make AEM electrolysis attractive technology to produce H2 in low cost. However currently performance of AEM electrolysis is much lower than that of PEM electrolysis. Therefore to make the AEM electrolysis technology viable, significant advancement in AEM electrolysis technology is needed. Many PGM-free OER catalysts measured in aqueous alkaline electrolytes, such as 0.1 M KOH or NaOH, have demonstrated as high activities as that of PGM IrO2 OER catalysts measured in an aqueous acid electrolytes in an electrochemical cell test. This implies that the low AEM electrolysis performance is possibly caused by some detrimental effect of AEM/anion exchange ionomer (AEI) onto catalysts. In this work we exploited different types of catalysts and AEIs to investigate the effect of catalyst-AEI interaction on AEM electrolysis performance. We observed that catalyst-AEI interaction substantially affects the AEM water electrolysis performance. The higher activity and durability of perovskite oxide OER catalyst than IrO2 OER catalyst in AEM water electrolysis can be explained by this catalyst-AEI interaction. In this talk, we will discuss the causes for low AEM electrolysis and possible pathways to improve AEM water electrolysis performance. Acknowledgements The authors gratefully acknowledge research support from the HydroGEN Advanced Water Splitting Materials Consortium, established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office.

Integrated inorganic membrane electrode assembly with layered double hydroxides as ionic conductors for anion exchange membrane water electrolysis

Alkaline anion exchange membrane (AEM) water electrolysis is a promising technology for producing hydrogen using renewable energies. However, current AEM electrolyzers still employ noble‐metal‐containing electrocatalysts, or have significant overpotential loss, or both. Here non‐noble‐metal electrocatalysts for both the hydrogen and oxygen evolution reactions (HER and OER) are developed. Both catalysts are made of a same NiMo oxide. Judicious processing of these materials in a mixed NH3/H2 atmosphere results in a NiMo‐NH3/H2 catalyst, which has superior activity in HER, delivering 500 mA cm−2 at an overpotential of 107 mV. Doping Fe ions into the NiMo‐NH3/H2 catalyst yields an Fe‐NiMo‐NH3/H2 catalyst, which is highly active for the OER, delivering 500 mA cm−2 at an overpotential of 244 mV. These catalysts are integrated into an AEM electrolyzer, which delivers 1.0 A cm−2 at 1.57 V at 80 °C in 1 m KOH. The energy conversion efficiency at this current density is as high as 75%. This work demonstrates high‐efficiency AEM electrolysis using earth‐abundant catalytic materials.

Experimental investigation of electrolytic solution for anion exchange membrane water electrolysis

Corrosion-engineered bimetallic oxide electrode as anode for high-efficiency anion exchange membrane water electrolyzer