Ultrathin Iron-Cobalt Oxide Nanosheets with Abundant Oxygen Vacancies for the Oxygen Evolution Reaction

Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H₂ fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H₂ production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low-cost fabrication route. Herein, a facile solution reduction method using NaBH₄ as a reductant is developed to prepare iron-cobalt oxide nanosheets (Fe_x Co_y -ONSs) with a large specific surface area (up to 261.1 m² g^-1 ), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe₁ Co₁ -ONS measured at an overpotential of 350 mV reaches up to 54.9 A g^-1 , while its Tafel slope is 36.8 mV dec^-1 ; both of which are superior to those of commercial RuO₂ , crystalline Fe₁ Co₁ -ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe₁ Co₁ -ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH^- ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H₂ O onto nearby Co³⁺ sites.