Simultaneous activity and stability gains in PEM electrolyzer via targeted Cr³⁺ occupation in spinel Co₃O₄ octahedral lattices

Iridium-based materials are less studied in proton exchange membrane water electrolyzers (PEMWEs), which are crucial for the generation of green hydrogen, due to their rarity and high cost. Herein, doping Cr with cobalt oxide resulted in rich oxygen vacancies with the Co²⁺/Cr³⁺ redox couples and surface hydroxyl groups, which considerably enhance the capacity of the material to adsorb and activate oxygen intermediates. Due to its structural and electrical characteristics, CrCo₈O_x has proven to be a stable and effective catalyst for acidic oxygen evolution reaction (OER) and high-performance PEMWEs applications. A high current density of 100 mA·cm⁻² was attained by the CrCo₈O_x anode catalyst and maintained for 130 h, whereas a current density of 300 mA·cm⁻² was maintained for 20 h. In situ Fourier transform infrared (FT-IR) spectroscopy combined with density functional theory (DFT) calculations corroborate the oxide path mechanism (OPM) over pristine Co₃O₄ rather than the associative electron mechanism (AEM) over Cr-doped CrCo₈O_x composites. Such outstanding results indicate a bright future for industrial deployment and provide broad recommendations for developing PEMWEs with high efficiency.