An oxygen vacancy-modulated bifunctional S-NiMoO₄ electrocatalyst for efficient alkaline overall water splitting

S-doped nickel molybdate nanorods grown on nickel foam (S-NiMoO₄/NF) were fabricated by a two-step hydrothermal method. The resultant S-NiMoO₄/NF exhibited remarkable bifunctional electrocatalytic activity, with overpotentials of 235 mV for the hydrogen evolution reaction and 150 mV for the oxygen evolution reaction at a current density of 50 mA cm^-2. Assembled into the two-electrode S-NiMoO₄/NF electrolyzer in alkaline electrolytes for overall water splitting, it required only low cell voltages of 1.55 V and 1.63 V to drive 50 mA cm^-2 and 100 mA cm^-2, respectively. No significant performance degradation occurred during the water electrolysis process. The experimental results confirmed that S-doping induced the increase of the oxygen vacancies, accelerating the reaction kinetics and thus improving the electrocatalytic performance. Meanwhile, more active sites exposure on the surface of S-NiMoO₄/NF enhanced the reactivity. This work may guide the development of efficient bifunctional catalysts in alkaline electrolysis through oxygen vacancy regulation.