Comprehensive Hydrogen Evolution Descriptors for Nonprecious Metal Oxide Electrocatalysts

Green hydrogen production via electrochemical water splitting has attracted significant attention as a key technology for future sustainable societies. There is a need for comprehensive descriptors for the cathodic hydrogen evolution reaction (HER) to develop promising electrocatalysts. We herein investigate the HER electrocatalysis on Fe‐, Co‐, and Ni‐based oxides with various elemental compositions and crystal categories and uncover the relations to their structural and electronic characteristics. Through machine learning analysis of the data obtained from 25 types of metal oxides, we find that the most critical parameter for HER is the number of d electrons in each catalyst. It is notable that influence of the number of d electrons on HER depends on kind of transition metals; i.e., larger and smaller numbers of d electrons are beneficial for Fe‐ and Ni‐based oxides, respectively. Contrarily, Co‐based oxides exhibit a volcano relationship. DFT calculations reveal that the trend of the number of d electrons correlates with hydrogen adsorption energies on the catalyst surface, which determines the HER activity. The discovered descriptor is a simple guideline for the efficient design of nonprecious metal‐based oxides with excellent HER catalytic activities and contributes to the establishment of a zero‐carbon society.