Amorphous MOFs with electrochemically tailored reversible reconstruction to boost industrial-scale oxygen evolution reactions

<p indent="0mm">China’s ambitious carbon peak and carbon neutrality strategic goals have largely pushed the advances of renewable energy technology. Hydrogen gas is a well-known clean fuel and feedstock in chemical industries, and has gained increased attention in establishing the renewable energy ecosystem. About 90% of the hydrogen gas in China, however, is generated through fossil fuels dependent strategies such as steam reforming. These conventional petrochemical routes contribute to a high carbon footprint and represent unsustainable hydrogen production methods. Low temperature water electrolysis driven by renewable electricity is an alternative way to produce hydrogen and the only byproduct is oxygen, making itself sustainable and carbon footprint free. The commercialized low temperature water electrolysis techniques include alkaline water electrolysis and proton exchange membrane (PEM) water electrolysis. Alkaline water electrolysis (AWE) is a mature electrolysis technology and allows for the non-noble metal-based catalysts. However, its voltage efficiency is insufficient when electrolysis current goes up beyond <sc>400 mA cm⁻².</sc> In addition, the long start-up time of AWE cannot match with the intermittent renewable energy. PEM water electrolysis incorporates the design of membrane electrode assembly (MEA) and its voltage efficiency is significantly higher than that of AWE at high-rate conditions (current density above <sc>400 mA cm⁻²),</sc> whereas the noble metal catalysts and PEM highly increase the costs of the electrolyzers. Anion exchange membrane (AEM) water electrolysis is a newly developed hydrogen generation technique, and it implements MEA design as well as non-noble metal-based catalysts in alkaline or neutral electrolytes. It thus shows unique advantages in both fast start-up and low costs. Nonetheless, the voltage efficiency of AEM water electrolysis is still not competing with PEM water electrolysis at high-rate conditions, and the sluggish kinetics and mass transfer of oxygen evolution reaction (OER) are critical limiting factors. To address the limitations, it is reasonable to both increase the intrinsic activity of the OER catalysts and enhance the mass transfer/bubble escape for improved performances under high-rate electrolysis. NiFe based electrocatalysts have exhibited appealing intrinsic activity due to the synergistic effects between Ni and Fe in optimizing the oxygen intermediates adsorption and bond formation of oxygen molecules. Anchoring intrinsically active NiFe OER catalysts on electrically conductive porous gas diffusion layer to form self-standing gas diffusion electrodes (GDEs) is one effective method to handle the challenges of high-rate OER for AEM water electrolysis, and has attracted much attention in this fast developed field over the past few years. In light of the importance of self-standing NiFe based GDEs and rapid development of AEM water electrolysis, we in this work review the representing major advances of this type of GDEs in recent years. The general background of OER for high-rate AEM water electrolysis including its challenges, activity and stability indicators and NiFe self-standing GDEs is briefly introduced. Following this section, we pay particular attention to different strategies in preparing the NiFe self-standing GDEs for high-rate OER toward AEM water electrolysis such as magnetron sputtering, cathodic electrodeposition, corrosion engineering and hydrothermal method reported so far. These technique routes are compared regarding their unique advantages and the associated NiFe self-standing GDEs prepared by these methods are analyzed regarding the microstructure and activity. Last but not least, we further outline the critical challenges and perspective in the development and operando characterizations of the NiFe self-standing GDEs for high-rate alkaline and pure-water fed AEM water electrolysis. With the review and discussions in this article, we hope it can serve as helpful references for our research community in developing self-standing GDEs for high-rate AEM water electrolysis.

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).

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

Anion exchange membrane water electrolyzers (AEMWEs) are regarded as a promising solution for green hydrogen generation, owing to their cost-effectiveness, outstanding electrolysis efficiency, robust operation, and fast response. However, the sluggish kinetics of the anodic oxygen evolution reaction (OER) severely limits the water electrolysis efficiency. Currently, precious-metal based oxides, such as IrO2 and RuO2, are used as benchmark catalysts for the OER. Yet, their scarcity and poor long-term durability severely hinder their industrial-scale application. Over the past few decades, metal-organic frameworks (MOFs) have emerged as ideal candidates for fabricating low-cost and high-performance electrodes owing to their exceptional physicochemical features. In this review, we focus specifically on pristine MOFs and their composites, aiming to highlight their inherent structural advantages toward water electrolysis. We first introduce the fundamentals of the alkaline OER and the evaluation criteria toward both the OER and AEMWEs. We then summarize recent advances in pristine MOFs and their composites for the OER. Finally, we discuss current research challenges and suggest future research directions.

Anion exchange membrane water electrolyzers (AEMWEs) represent an attractive technology for producing “green” hydrogen that enables operation on pure water using platinum group metal (PGM)-free electrocatalysts at both anode and cathode. Also, AEMWEs do not require the use of highly concentrated and corrosive alkaline electrolytes and PGM-based catalysts, which are the major drawbacks of the incumbent low-temperature liquid-alkaline and proton exchange membrane electrolyzers, respectively.1,2 In this context, the development of PGM-free electrocatalysts for oxygen evolution reaction (OER) in alkaline media has attracted considerable research interest. Among different types of transition metal-based oxides, Ni oxides doped with Fe have shown the highest OER activity in alkaline media.3,4 Recently, we have developed at Los Alamos National Laboratory (LANL) a series of Ni oxide-based aerogel materials that, primarily in combination with Fe in different proportions, have shown respectable OER performance in the electrochemical cell and at the AEMWE anode operating on either neat deionized water or with a supporting electrolyte, 0.1 M KOH or K2CO3.5 For application at the AEMWE anode, the catalyst integration into the electrode catalyst layer, i.e., combining the catalyst with anion exchange ionomer (AEI) and binding agents, is crucial to prevent catalyst layer delamination and to create a good catalyst/electrolyte interface, which in turn enables high OH- conductivity within the catalyst layer.6 This latter aspect is especially important for achieving high AEMWE performance in pure water operation. In this work, we investigate the impact of combining our Ni-Fe oxide aerogel catalysts with different AEIs (various backbone chemistries, OH- functional groups) and different binding agents (e.g., Nafion ionomer) on the AEMWE performance. We will show that full activation of the catalyst by phase transformation from the original Ni oxide-like structure to the active layered (oxy)hydroxide is essential for achieving high OER activity, and it can be influenced by the catalyst layer composition. By advanced characterization techniques such as high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and Mössbauer spectroscopy, we will shed light onto the phase transformation process that results in superior OER activity of these materials in alkaline media.Following our prior machine learning studies aimed at optimizing for the synthesis of oxygen reduction electrocatalysts,7,8 we will also show how to improve the synthesis of Ni oxide aerogel-based OER catalysts to maximize activity and stability. This work is further supported by density functional theory (DFT) modeling studies to better understand reaction mechanisms, active sites, and ultimately what role transition metal dopants (Fe and Co) play in modifying OER activity. Studies of in situ dissolution of these dopants using DFT-generated, phase-constrained Pourbaix diagrams9 will guide synthesis through understanding this likely materials degradation pathway. References H. A. Miller et al., Sustain. Energy Fuels, 4, 2114–2133 (2020).C. Santoro et al., ChemSusChem, 202200027 (2022).S. Fu et al., Nano Energy, 44, 319–326 (2018)D. Xu et al., ACS Catal., 9, 7–15 (2019).P. Zelenay and D. Myers, "ElectroCat (Electrocatalysis Consortium);” U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Program, 2022 Annual Merit Review and Peer Evaluation Meeting, June 6-8, 2022. https://www.hydrogen.energy.gov/pdfs/review22/fc160_myers_zelenay_2022_o.pdfL. Osmieri et al., J. Power Sources, 556, 232484 (2023).M. R. Karim et al., ACS Appl. Energy Mater., 3, 9083–9088 (2020).W. J. M. Kort-Kamp et al., J. Power Sources, 559 (2023).E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020).

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

Anion-exchange membrane water electrolyzers (AEMWEs) present a multitude of advantages, particularly in the utilization of non-platinum group (non-PGM) catalysts. While diverse catalysts have demonstrated notable electrocatalytic activity in alkaline conditions, the integration of the ionomer with the electrocatalyst at the active catalyst layer is crucial for enhancing overall AEMWE performance in practical device demonstrations by improving mass transport. However, the intrinsic instability of polymeric ionomers, leading to physical detachments or alkaline (chemical) degradation, poses a challenge that can potentially diminish performance. In this study, drawing inspiration from the aforementioned ionomer chemistry, we introduce non-PGM NiFe-based metal-organic frameworks (MOFs) incorporating quaternary ammonium (QA) cation moieties covalently functionalized to benzenedicarboxylic acid (BDC) ligands as promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline environments. Three specifically designed functional groups with varying ion exchange capacities (IEC) and alkaline stability—trimethylamine (TMA), N-methylpyrrolidine (C4N), and N-methylpiperidine (C5N)—were directly tethered to BDC ligands. The alkaline OER activity of Ni2Fe1-QA-MOF was meticulously assessed using rotating disk electrodes and AEMWE devices. These directly tethered QA groups markedly facilitated improved ionic transport of OH- ions at the catalyst/electrolyte interfaces compared to BDC ligands, ultimately leading to a significant enhancement in half-cell activity and AEMWE performance. In-situ IR/RAMAN spectroscopy revealed that QA moieties highly promoted local ionic transport at the interfaces, as evidenced by characteristic peaks indicating a robust interaction between QA and OH- ions. Unexpectedly, QA moieties not only contributed to ionic transport in local environments but also induced oxidation states of Ni metal sites, while Fe sites exhibited no changes during the applied potential in the OER region, as comprehensively revealed by synchrotron X-ray absorption spectroscopy (XAS). In comparison with conventional NiFe layered double hydroxide (LDH) structures, we posit that the substantial structural transformation of Ni moieties can be attributed to an increased degree of M-O bond interaction, enhanced by the local interaction between QA and OH- ions. Density functional theory (DFT) calculations also validate the balanced adsorption of OER intermediates on QA-MOFs. Finally, QA-NiFe-MOF was directly synthesized on a porous transport layer (PTL), and its AEMWE performance was evaluated without the use of any ionomer. At 1.0 M KOH, C4N, C5N, and TMA-based NiFe MOFs exhibited current densities of 9.35 A/cm2, 9.11 A/cm2, and 7.6 A/cm2, respectively. These current densities surpassed those of bare BDC-NiFe MOF and commercial IrO2 anode catalysts, which exhibited only 7.39 A/cm2 and 6.4 A/cm2, respectively. Consequently, we emphasize that the facilitation of local ionic transport could yield remarkable AEMWE performance, even in the absence of conventional polymeric ionomers.

Metal-Organic Frameworks (MOFs), praised for structural flexibility and tunability, are prominent catalyst prototypes for exploring oxygen evolution reaction (OER). Yet, their intricate transformations under OER, especially in industrial high-current environments, pose significant challenges in accurately elucidating their structure-activity correlation. Here, we harnessed an electrooxidation process for controllable MOF reconstruction, discovering that Fe doping expedites Ni(Fe) MOF structural evolution, accompanied by the elongation of Ni-O bonds, monitored by in situ Raman and UV/Visible spectroscopy. Theoretical modeling further reveals that Fe doping and defect-induced tensile strain in the NiO6 octahedra augments the metal ds-O p hybridization, optimizing their adsorption behavior and augmenting OER activity. The reconstructed Ni(Fe) MOF, serving as the anode in anion exchange membrane water electrolysis, achieves a noteworthy current density of 3300 mA cm-2 at 2.2 V while maintaining equally stable operation 500 mA cm-2 for 300 h and 1000 mA cm-2 for 170 h. This undertaking elevates our comprehension of OER catalyst reconstruction, furnishing promising avenues for designing highly efficacious catalysts across electrochemical platforms.

Limited by the strong oxidation environment and sluggish reconstruction process in oxygen evolution reaction (OER), designing rapid self-reconstruction with high activity and stability electrocatalysts is crucial to promoting anion exchange membrane (AEM) water electrolyzer. Herein, trace Fe/S-modified Ni oxyhydroxide (Fe/S-NiOOH/NF) nanowires are constructed via a simple in situ electrochemical oxidation strategy based on precipitation-dissolution equilibrium. In situ characterization techniques reveal that the successful introduction of Fe and S leads to lattice disorder and boosts favorable hydroxyl capture, accelerating the formation of highly active γ-NiOOH. The Density Functional Theory (DFT) calculations have also verified that the incorporation of Fe and S optimizes the electrons redistribution and the d-band center, decreasing the energy barrier of the rate-determining step (*O→*OOH). Benefited from the unique electronic structure and intermediate adsorption, the Fe/S-NiOOH/NF catalyst only requires the overpotential of 345 mV to reach the industrial current density of 1000mAcm-2 for 120 h. Meanwhile, assembled AEM water electrolyzer (Fe/S-NiOOH//Pt/C-60°C) can deliver 1000mAcm-2 at a cell voltage of 2.24V, operating at the average energy efficiency of 71% for 100 h. In summary, this work presents a rapid self-reconstruction strategy for high-performance AEM electrocatalysts for future hydrogen economy.

Anion exchange membrane water electrolysis (AEMWE) offers a cost‐effective and efficient platform for hydrogen production by enabling the use of non‐platinum group metal (non‐PGM) electrode materials. However, the sluggish kinetics of the oxygen evolution reaction (OER) remains a key challenge. In this study, a CoMo‐LDH OER electrode for AEMWE is developed via a sacrificial template strategy. The high valence state of Mo promotes oxygen vacancy formation, enhancing OER performance. Electrochemical reconstruction also induces a phase transition into active (oxy)hydroxide species during OER. Density functional theory (DFT) calculations show that the weak OH− adsorption energy of CoMo‐LDH lowers the energy barrier for OH− deprotonation, improving catalytic activity. The CoMo‐LDH electrode demonstrates superior performance in AEMWE compared to the PGM‐based IrO2 electrode. This study highlights the potential of sacrificial template‐based electrodes for high‐performance AEMWE.

To achieve carbon neutrality, extensive research is ongoing to produce green hydrogen via water electrolysis combined with renewable energy sources. Understanding and developing catalysts for membrane electrode assembly (MEA) type water electrolysis systems, such as proton exchange membrane water electrolysis (PEMWE) and anion exchange membrane water electrolysis (AEMWE), are critical steps toward this goal. Therefore, this presentation will focus on catalyst development for PEMWE and AEMWE, with emphasis on cost-effective catalysts.For oxygen evolution reaction (OER) catalysis in PEMWE, the primary challenge is to minimize iridium (Ir) usage for sustainable green hydrogen production. Layered monoclinic iridium nickel oxide (IrNiOx) platelets were synthesized using a molten salt method and employed for the OER. These platelets exhibited high OER activity with reduced Ni dissolution in acidic conditions. When applied in MEA, they demonstrated enhanced interconnectivity within the catalyst layer, promoting electron transfer. Even at low Ir loading (0.2 mgIr cm-2), the platelets showed good performance with an initial cell voltage of 1.70 V at 1 A cm-2 and minimal degradation over 100 hours. This highlights the effectiveness of incorporating transition metals into Ir oxide to reduce Ir usage in PEMWE.For oxygen evolution reaction (OER) catalysis in AEMWE, attention is focused on nickel iron (NiFe) hydroxide catalysts for their high activity and stability in alkaline conditions. However, the lack of initial electrical conductivity of as-prepared NiFe LDH limits its potential as an electrocatalyst. To address this issue, a monolayer structuring approach was proposed. This method improved mass transport to allow a high energy conversion efficiency of 72.6% with exceptional stability over 50 hours at 1 A cm-2. Additionally, lack of initial electrical conductivity hinders determination of electrochemically active surface area (ECSA) of NiFe LDH using conventional double layer capacitance method. Use of electrochemical impedance spectroscopy (EIS) at reactive OER potentials to extract the capacitance that is hypothesized to arise due to reactive OER intermediates (O*, OH*, OOH*) adsorbed on the catalyst surface was thus investigated. This allowed the estimation of ECSA and intrinsic activity of NiFe LDH, validating the methodology through rigorous catalyst loading and support studies.For hydrogen evolution reaction (HER) catalysis in AEMWE, replacing platinum (Pt) with Ni-based alloys containing molybdenum (Mo) species has shown promise. Dynamic active sites of Ni catalysts with Mo species require innovative approaches to maintain initial performance, warranting material innovation or careful manipulation of operating protocol. The approaches in which this is made possible is shortly presented, together with the innovations that allows probing of such phenomenon.

The sluggish kinetics of the oxygen evolution reaction (OER) critically limit the efficiency of anion exchange membrane water electrolysis (AEMWE). Herein, a Ce‐doped bimetallic Fe2P/NiCoP hybrid pre‐catalyst that undergoes dynamic reconstruction to activate a highly efficient OER pathway is designed. The optimized Ce0.1‐Fe2P/NiCoP exhibits an impressively low overpotential of 280 mV at 0.5 A cm−2 and a small Tafel slope of 55.3 mV dec−1 in a 1.0 M KOH. Remarkably, when integrated as the anode in an AEMWE electrolyzer, it delivers a low cell voltage of 1.812 V at 1.0 A cm−2 and maintains stable performance for over 500 h at 60 °C. In situ characterizations and density functional theory (DFT) calculations reveal that Ce‐doping enhances surface reconstruction and modulates the electronic structure, thereby reducing energy barriers for intermediates (ΔG*OH and ΔG*OOH) formation and accelerating OER kinetics. This work introduces a novel strategy to utilize catalyst reconstruction, advancing their applications in AEMWE systems.

Investigation of NiCoOx catalysts for anion exchange membrane water electrolysis: Performance, durability, and efficiency analysis

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 .

Anion exchange membrane water electrolysis (AEMWE) is a type of electrolysis that involves the use of an anion exchange membrane (AEM) to separate the anode and cathode compartments. During the electrolysis process, water is split into hydrogen gas (H2) at the cathode and oxygen gas (O2) at the anode. AEMWE is an emerging technology that has the potential to play a significant role in the production of green hydrogen, which is a promising energy carrier for a variety of applications, including fuel cells and transportation.One of the benefits of AEMWE is that it can be used with a variety of water sources, including seawater and wastewater. Additionally, AEMWE has the potential to be more energy-efficient and cost-effective than other types of water electrolysis because it can operate at lower voltages and use cheap Ni-based materials [1]. Recently, there has been a significant amount of interest in the development of anion exchange ionomers (AEI) that conduct hydroxide ions [2]. We recently investigated the PPO-LC-TMA ionomer (poly(2,6-dimethyl-1,4-phenylene oxide) [3] backbone with amine-functionalized by trimethyl amine) [4] as an ionomer for Ni-based catalysts in AEMWE. Commercial Aemion, Fumion, and Nafion AEI were compared to the lab-synthesized ammonium-enriched anion exchange ionomer PPO-LC-TMA as an anode catalyst layer for oxygen evolution reaction (OER).Cyclic voltammetry results showed that the NiFe catalyst layer with PPO-LC-TMA AEI showed higher Ni(OH)2/NiOOH peak current density, while current density obtained over Ni90Fe10 catalysts was 11%, 17%, and 39% for Nafion, Fumion, and Aemion AEI, respectively [5]. This resulted in increased OER activity of Ni90Fe10 with PPO-LC-TMA AEI and a lower overpotential of 151 mV at 10 mA cm-2 in 1 M KOH. Ex-situ Raman spectroscopy of as prepared and spent catalytic layer confirmed that the electrode transitioned to the Ni-OOH phase after polarization.NiFe anode catalytic layers were tested in a 5 cm2 single-cell alkaline membrane water electrolysis (AEMWE) with varying amounts of PPO-LC-TMA (7, 15, and 25 wt %). AEMWE results revealed that 25 wt% PPO-LC-TMA is the best ionomer loading, achieving a cell voltage of 1.941 V at 600 mA cm-2 in 1 M KOH at 50°C.Both three-electrode electrochemical cell and alkaline membrane water electrolysis (AEMWE) tests revealed that the PPO-LC-TMA ionomer stabilized NiFe catalyst and improved its performance compared to Fumion and Nafion ionomers. These results will be presented and discussed, along with details of electrochemical and physical characterizations.References E. Cossar, F. Murphy, E.A. Baranova, J Chem Technol Biotechnol, 97 (2022) 1611–1624.Wright, A. G.; Fan, J.; Britton, B.; Weissbach, T.; Lee, H.-F.; Kitching, E. A.; Peckham, T. J.; Holdcroft, S. Energy Environ. Sci. 9 (2016) 2130−2142.A.R. Nallayagari, E. Sgreccia, L. Pasquini, M Sette, P. Knauth and M. L. Di Vona ACS Appl. Mater. Interfaces, 14, 41 (2022) 46537–46547.R.-A. Becerra-Arciniegas, R. Narducci, G. Ercolani, E. Sgreccia, L. Pasquini, M. L. Di Vona, and P. Knauth, J. Phys. Chem. C, 124, 2 (2020) 1309–1316.E. Cossar, F. Murphy, J. Walia, A. Weck, E.A. Baranova, ACS Applied Energy Materials, 5 (2022) 9938−9951.