Performance and Durability Evaluation of Anion Exchange Membrane Water Electrolysis Cells Using Non-Precious Metal Catalysts and a Hydrocarbon-Based Electrolyte

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Anion exchange membrane water electrolysis (AEMWE) is operated in an alkaline environment and has a similar membrane-electrode assembly (MEA) structure to that of proton exchange membrane water electrolysis (PEMWE). The use of nonprecious metals as the electrocatalysts and operation at high current densities are inherently possible, so they are expected to be low-cost, high-performance candidates for next-generation water electrolysis systems.1 However, for practical use, high durability versus large load fluctuations, as well as even higher current densities, are required. In this study, with the aim of achieving high durability and high current density for AEMWE, we used Ni0.8Co0.2Ox 2 and Ni0.8Fe0.2Ox,3 which were developed at the University of Yamanashi (UY), as anode catalysts, and QPAF-44, a hydrocarbon-based electrolyte, which was also developed at UY, as the electrolyte membrane and binder.The catalyst inks for the anodes were prepared by mixing the Ni0.8Co0.2Ox catalyst (UY) or Ni0.8Fe0.2Ox catalyst (UY) with solvent (water/methanol) and QPAF-4 (IEC = 1.5 meq. g-1, UY) binder solution. The anode inks were coated by using pulse-swirl-spray (PSS, Nordson) on the QPAF-4 membranes (thickness 50 μm, IEC = 1.5 meq. g-1) to make the catalyst-coated membranes (CCMs) with the anode. The catalyst ink for the cathodes was prepared by mixing Pt/CB catalyst (TEC10E50E, Tanaka Kikinzoku) with solvent (water/methanol) and QPAF-4 (IEC = 1.5 meq. g-1) binder solution. The cathode ink was coated by using PSS on the opposite side of the CCM. Ni mesh (Bekaert.co.jp) and carbon paper (TGP-H-120, Toray) were used for the anode and cathode porous transport layers (PTLs) respectively. The single cell (Figure 1, cell structure developed by Yokohama National University) performances were measured while supplying 1 M KOH at 80 °C to both electrodes. The durability of these cells was tested by cycling between high electrolysis load (4 A cm-2, 10 s) and no electrolysis (0.1 V, 10 s) for 2000 cycles. Here, the no electrolysis mode is designed to simulate a situation where the anode potential drops to near 0 V due to hydrogen leakage from the cathode when the water electrolysis is stopped for a long time.Figure 2a shows the cell voltage at 4 A cm-2 of the cells using the Ni0.8Co0.2Ox catalyst or Ni0.8Fe0.2Ox catalyst for the anode and Pt/CB for the cathode. During 2000 cycles, the cell with Ni0.8Co0.2Ox catalyst showed a gradual increase in cell voltage. On the other hand, the cell with Ni0.8Fe0.2Ox catalyst showed no significant increase in cell voltage and maintained a cell voltage of less than 2 V during 2000 cycles. Figure 2b shows the I-V performance of these cells after 2000 cycles. The cell with Ni0.8Fe0.2Ox catalyst showed higher I-V performance than that of the Ni0.8Co0.2Ox catalyzed cell even after 2000 cycles, achieving a cell voltage of 1.96 V at a current density of 4 A cm-2. These results indicate the usefulness of Ni0.8Fe0.2Ox catalyst using Fe as a substitute material for the low-abundance metal Co and the possibility of further gains in high current density for AEMWE. Acknowledgement This work was partially based on results obtained from project JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and on GteX Program Japan Grant Number JPMJGX23H2. References 1) H. A. Miller et al., Sustain. Energy Fuels, 4, 2114 (2020).2) G. Shi et al., ACS Catal., 12, 14209 (2022).3) G. Shi et al. ACS Omega, 8, 13068 (2023).4) H. Ono et al., J. Mater. Chem. A, 5, 24804 (2017). Figure 1