Chromium-Induced High Covalent Co-O Bonds for Efficient Anodic Catalysts in PEM Electrolyzer.

The proton exchange membrane water electrolyzer (PEMWE), crucial for green hydrogen production, is challenged by the scarcity and high cost of iridium-based materials. Cobalt oxides, as ideal electrocatalysts for oxygen evolution reaction (OER), have not been extensively applied in PEMWE, due to extremely high voltage and poor stability at large current density, caused by complicated structural variations of cobalt compounds during the OER process. Thus, the authors sought to introduce chromium into a cobalt spinel (CoO) catalyst to regulate the electronic structure of cobalt, exhibiting a higher oxidation state and increased Co-O covalency with a stable structure. In-depth operando characterizations and theoretical calculations revealed that the activated Co-O covalency and adaptable redox behavior are crucial for facilitating its OER activity. Both turnover frequency and mass activity of Cr-doped CoO (CoCr) at 1.67 V (vs RHE) increased by over eight times than those of as-synthesized CoO. The obtained CoCr catalyst achieved 1500 mA cm at 2.17 V and exhibited notable durability over extended operation periods - over 100 h at 500 mA cm and 500 h at 100 mA cm, demonstrating promising application in the PEMWE industry.