Active sites engineering construction of spinel cobalt oxide based excellent bifunctional electrocatalyst for water splitting by modifying oxygen vacancy with S dopant

It is a significant and challenging work to endow transition metal oxide highly bifunctional electrocatalytic activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, the bifunctional electrocatalysts of S-doped FeCo2O4 ultrafine nanoparticles were fabricated by introducing rich oxygen vacancies (Vo) and then partially substituting the Vo by doping S atoms. The electronic structures and adsorption free energy of the active sites towards reactants were modulated by the strategy of doping sulfur atoms to modify oxygen vacancies. The catalysts were consequently endowed extraordinarily improved HER and OER electrocatalytic activities. The optimized catalyst S-doping FeCo2O4 (FCOS-10) exhibited 33 and 59 times of the turnover frequency as high as that of the pristine FeCo2O4 for HER and OER, respectively. Only 1.54 V of cell voltage for water electrolysis is needed to afford 10 mA cm−2. The catalyst also exhibited robust stability of 85.4% after 120 h i-t test for overall water splitting and high Faraday efficiency of 97.19%, thus it is a high promising catalyst for commercial water electrolysis. This work is one of the few examples that endow metal oxide with highly bifunctional activities for HER and OER, and it is an important reference for rational designing and fabrication of analogous catalysts.