Anodic/Cathodic Properties of Ni Based Catalysts for Anion Electrolyte Membrane Water Electrolysis

Anion electrolyte membrane water electrolysis (AEM WE) using non-precious metal catalyst is one of the most prospective systems for pure hydrogen generation. The Ni based oxide shows relatively lower overpotential of oxygen evolution reaction (OER) by adding the transition metals of Co, Fe and Mn, and approaches that of precious metal of Ir based oxide. Our previous study reported that the Ni-Co based catalyst was highest OER activity at operating temperature. The crystallized Ni-Co metal-based core particles with amorphous Ni oxyhydrates of top surface (shell) was confirmed to be preferable to obtain the higher OER activity by rotating disk electrode method, transmission electron microscopy and DFT calculation. Moreover, the fused aggregated network microstructure of Ni-Co based catalyst assisted to show a metallically electronic conductivity. In this study, we evaluated both OER and hydrogen evolution reaction (HER) activity of Ni based catalysts to confirm the prospective non-precious metal catalysts for AEM WE. Each Ni based catalysts with additive of transition metals were synthesized by the flame oxide-synthesis method. 1 The OER and HER activities of these catalysts were evaluated in 1 M KOH at 20 to 80 o C by use of the RDE. The Ni-Co based catalyst was highest OER activity in these Ni based catalysts obtained above. The amorphous top surface layer was correlated with a negative shift in the oxyhydroxide formation peak potential from the results of DFT calculations. 2 The HER activity of the Ni-Fe based catalyst also showed the higher OER activity. Especially, the Ni-Fe based catalyst had highest HER activity in these Ni cased catalysts above. The HER activity enhanced by the construction of well crystallized top surface in comparison with its amorphous or poorly crystalline ones. DFT calculation indicated that the defective or disordered surface was not as active for the HER. These results will provide a strategy of Ni based catalysts optimization for AEM. Acknowledgement This work was partially supported by funds for the JSPS KAKENHI (20H02839), and the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References Kakinuma, M. Uchida, T. Kamino, H. Uchida, and M. Watanabe, Electrochim. Acta , 56 , 2881 (2011). Shi, T. Tano, D. A. Tryk, A. Iiyama, M. Uchida, and K. Kakinuma, ACS Catal. , 11 , 5222 (2021). Figure 1