Electrochemical hydroxidation of sulfide for preparing sulfur-doped NiFe (oxy) hydroxide towards efficient oxygen evolution reaction

• The low-cost (NiFe)OOH-S catalytic layer in situ grows on the NiFe foam by combining surface reconstruction and electrochemical oxidation. • (NiFe)OOH-S shows competitive alkaline catalytic OER performance (238 mV @ 10 mA cm -2 ). • The S doping results in the super hydrophilic surface (CA≈0 o ) and optimizes the free energy of the formation of OER intermediates, improving the OER activity. • A water electrolyzer driven by solar energy is operated at industrial conditions. The well-known NiFe hydroxides show tremendous promise as low-cost oxygen evolution reaction (OER) catalysts, which however suffer from the rapid decline of activity at current densities exceeding 100 mAcm -2 . Herein, we constructed a sulfur-doped OER electrode ((Ni 7 Fe 3 )OOH-S) by facile sulfurization and anodic displacement processes. The as-prepared (Ni 7 Fe 3 )OOH-S electrode shows an overpotential of 238 mV at 10 mA cm -2 in 1 M KOH at 25 o C, which is due to the high intrinsic catalytic activity, the super hydrophilic nature of the electrode for the S dopant. DFT calculations reveal that the S dopant changes the electronic structure and charge density (NiFe)OOH, thereby optimizing the OER rate-determining step, improving the binding energy for OER intermediates, which ensures the high intrinsic catalytic activity. In addition, the long-term stability (e.g., 200 h) at industrial-level current density (399 mV at 500 mA cm -2 ) holds the promise for the real application of the (Ni 7 Fe 3 )OOH-S electrode. Furthermore, a solar-powered electrolyzer consisting of the (Ni 7 Fe 3 )OOH-S anode and a 20% Pt/C@CC cathode operates successfully at a low voltage of 1.46 V(10 mA cm -2 ) in 10 M KOH at 75 o C. Overall, the combined sulfidation and anodic displacement approach could be a general approach to prepare efficient and durable catalysts for water electrolyzers.