From bulk parameters to catalytic activity: descriptors for nonprecious metal electrocatalysts for water electrolysis

The mitigation of greenhouse gas emissions has become an urgent global challenge due to the accelerated progression of climate change, and the realization of a zero-carbon society requires great innovation in energy-conversion technologies. Specifically, green hydrogen production via water electrolysis powered by renewable energy has attracted significant attention as a key technology for future sustainable societies, because it enables the generation of hydrogen as a high-density energy carrier from abundant water without emitting carbon dioxide. However, achieving highly efficient water electrolysis critically depends on improving the activity of electrocatalysts, and reliable rational design strategies for promising catalyst materials are essential. Our research group has been working toward establishing comprehensive design guidelines for the efficient design of highly active catalysts. In this Feature Article, we highlight our recent efforts in the development of inexpensive nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER) at water-electrolysis anodes. Mainly, this review summarizes the interrelationships between OER catalytic activity and key material parameters, including crystal structures, electronic structures and surface adsorption energetics, and introduces systematic investigations across various classes of compounds, such as metal oxides, metal phosphates, metal-organic frameworks, and metal sulfides. Through these studies, reliable and easily available descriptors for the OER are proposed, and their mechanisms of determining OER activity are explained.