Performance and Durability of Membrane Electrode Assemblies Using a Non-Precious Metal Catalyst on Both Electrodes and a Hydrocarbon-Based Electrolyte for Anion Exchange Membrane Water Electrolysis
Authors: Uchida Makoto , Takahashi Sayaka , Natori Soichiro , Iwataki Toshio , Asakawa Takayuki , Kakinuma Katsuyoshi , Miyatake Kenji 
Published: December 2024

Anion exchange membrane water electrolysis (AEMWEs) can use non-noble metal catalysts because the system is alkaline, and, like proton exchange membrane water electrolysis cells (PEMWEs), it has a membrane-electrode assembly (MEAs) structure. Therefore, it is expected to achieve both lower costs and higher output by using non-precious metals, including peripheral materials such as porous transfer layers (PTLs). Most of the research cases of AEMWEs are focused on the material development and physical property evaluation of electrocatalysts and anion-conductive polymers, and the deterioration mechanism of materials under actual operating AEMWE conditions remains largely unknown. In addition, many high-performance AEMWEs use noble metal catalysts for both the anode and cathode 1. Therefore, in this study, with the aim of converting AEMWEs cells to non-precious metals, we used Ni0.8Co0.2Ox catalyst 2 and Ni0.8Fe0.2Ox catalyst 3, which were independently developed at the University of Yamanashi, as electrocatalysts, and QPAF-4 4, an AEM that was also developed at the University of Yamanashi. We evaluated water electrolysis in a noble metal-free AEMWE cell using anion-conductive polymers for the electrolyte membrane and ionomer, aiming to achieve high electrolytic performance and durability.

The catalyst ink for the anodes was prepared by mixing the Ni0.8Co0.2Ox catalyst (University of Yamanashi) with solvent (water/methanol) and QPAF-4 (IEC = 2.0 meq g-1, University of Yamanashi) binder solution. The anode ink was 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. Catalyst inks for the cathodes were prepared by mixing Ni0.8Fe0.2Ox catalyst (University of Yamanashi) with solvent (water/methanol) and QPAF-4 (IEC = 2.0 meq g-1) binder solution. The cathode ink was coated by using PSS on the gas diffusion layer (GDL, TGP-H-120, Toray) to make the gas diffusion electrodes (GDEs) for the cathodes. Ni mesh (Bekaert.co.jp) was used for the anode GDLs. 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 initial performance results showed that the electrolytic performance tended to improve as the cathode I/C increased when both electrodes were supplied with aqueous KOH, as well as when only the anode was supplied with aqueous KOH (Fig. 2-a, b). Since the movement of cathode reactants and produced substances strongly depends on the amount and distribution state of ionomer in the catalyst layer, the increasing I/C levels helped to improve the effectiveness of the water electrolysis reactions, thus contributing to improving the performance. These results indicate the possibility of adopting non-precious metal catalysts for both electrodes in AEMWE, thereby significantly lowering the catalyst cost.

Acknowledgement

This work was partially based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and on GteX Program Japan Grant Number JPMJGX23H2.

References

1) A. W. Tricker et al., J. Power Sources, 567, 232967 (2023)

2) G. Shi et al., ACS Catal., 12, 14209 (2022).

3) G. Shi et al. ACS Omega, 8, 13068-13077 (2023).

4) H. Ono et al., J. Mater. Chem. A, 5, 24804 (2017).

Figure 1