S-doped Ni(Fe)OOH bifunctional electrocatalysts for overall water splitting

A larger overpotential being needed to drive overall water splitting, the poor stability of electrode materials and high cost caused by the scarcity of noble metal electrocatalysts are still important factors for restricting electrochemical water splitting. Developing high-activity, low-cost electrocatalysts to enhance hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a major challenge for overall water splitting. For this purpose, the S–Ni(Fe)OOH electrocatalyst was synthesized and used to perform HER and OER in 1.0 M KOH solution. The experimental results show that the overpotential of S–Ni(Fe)OOH is 22 mV and 198 mV, and the Tafel slope is 93.21 mV dec−1 and 17.50 mV dec−1 for HER and OER respectively. Electrochemical impedance spectroscopy (EIS) also shows that S–Ni(Fe)OOH has smaller Rct value of 2.71 Ω (HER) and 5.492 Ω (OER). The electrochemical active surface areas (ECSA) of S–Ni(Fe)OOH are 55.75 cm2 (HER) and 85.75 cm2 (OER), respectively. In addition, cyclic stability and chronoamperometry (i-t) tests prove that S–Ni(Fe)OOH catalyst has good stability with retention rates of 73.83% and 73.73% for HER and OER, respectively. In conclusion, the optimal S–Ni(Fe)OOH electrocatalyst exhibits a superior HER and OER activity, and can be used as a bifunctional electrocatalyst for the overall water splitting.