Adjusting the Composition of Novel Earth-Abundant Transition Metal-Based Oxide Nanoparticles for Electrocatalytic...

To produce green hydrogen through water electrolysis, highly efficient catalysts that use inexpensive, earth-abundant materials are required. In search of novel and inexpensive electrocatalysts, we investigate the adjustment of the composition of transition metal-based catalysts for the alkaline oxygen evolution reaction (OER) and evaluate the effects of both redox-active and -inactive elements. Based on the known synthesis of AFe₂O₄-type spinels (A = transition metal cation), we adjusted the composition of the A and B positions (B = Fe position), achieving a significant improvement in catalytic activity. Additionally, we are investigating the high-entropy effect, which is expected to enhance the activity and stability of electrocatalysts. Introducing cobalt and manganese and combining these elements with nickel and zinc formed a NiO/(NiZn)(MnCoFe)₂O₄ composite that reduced the overpotential for OER to 360 mV. However, increasing the number of A-cations in the spinel beyond six to reach a high-entropy spinel oxide had no positive effect on the overpotential. In terms of composition, the amount of nickel, and thus NiO, could be reduced to 5%, maintaining low overpotentials. The same applies to the proportion of cobalt, which does not scale linearly with activity.