Mott–Schottky Au/Co₃O₄ Decorated on a Carbon Cloth Substrate as an Efficiently Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution Reactions

Catalytic materials for water splitting must possess pivotal characteristics such as cost-effectiveness, robust stability, and high performance toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, we utilized a designed Mott–Schottky material, Au/Co₃O₄, developed in conjunction with a low-cost and robust material: carbon cloth. The findings revealed that 30 min of ultraviolet exposure is optimal for depositing Au nanoparticles, achieving the best balance between maximizing the Au loading content and minimizing the potential photochemical corrosion of Co₃O₄. The CC-30 material exhibited low overpotentials of 121 mV for the HER and 160 mV for the OER in 1.0 M KOH. Consequently, the overall water-splitting process necessitated a low cell voltage of 1.51 V. Remarkably, the electrode maintained excellent durability, with a negligible increase of 0.06 V after 100 h of continuous electrolysis in a 3 M KOH solution. Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy analysis during the reaction demonstrated that Au promotes faster charge transfer and stabilizes a higher Co²⁺ ratio during the HER, facilitating redox transformations. Notably, in the OER, the Au/Co₃O₄ interface accelerates the transition from Co³⁺ to Co⁴⁺, promoting the formation of a –C=O intermediate and enabling –O–O– detachment, which enhances gas evolution kinetics. Furthermore, density functional theory calculation revealed that various Au(111) and Co₃O₄(111) interface structures result in opposite charge redistributions at the interface.