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

The well-known NiFe hydroxides show tremendous promise as low-cost oxygen evolution reaction (OER) cata-lysts, which however suffer from the rapid decline of activity at current densities exceeding 100 mAcm- 2. Herein, we constructed a sulfur-doped OER electrode ((Ni7Fe3)OOH-S) by facile sulfurization and anodic displacement processes. The as-prepared (Ni7Fe3)OOH-S electrode shows an overpotential of 238 mV at 10 mA cm-2 in 1 M KOH at 25 degrees 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 in-termediates, 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 (Ni7Fe3)OOH-S electrode. Furthermore, a solar-powered electrolyzer consisting of the (Ni7Fe3)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 degrees C. Overall, the combined sulfidation and anodic displacement approach could be a general approach to prepare efficient and durable catalysts for water electrolyzers.