Unveiling Role of Sulfate Ion in Nickel‐Iron (oxy)Hydroxide with Enhanced Oxygen‐Evolving Performance

The rational design of effective catalysts for sluggish oxygen evolution reactions (OERs) is desired but challenging. Nickel‐iron (NiFe) (oxy)hydroxides are promising pre‐electrocatalysts for alkaline OER. However, OER performances are limited by the slow reconstruction process to generate active species of high‐valance NiFe oxyhydroxides. In this work, a sulfate ion (SO42−) modulated strategy is developed to boost the OER activity of NiFe (oxy)hydroxide by accelerating the electrochemical reconstruction of pre‐catalyst and stabilizing the reaction intermediate of OOH* during OER. The SO42− decorated NiFe (oxy)hydroxide catalyst (NF‐S0.15) is fabricated via scalable anodization of NiFe foam in a thiourea‐dissolved electrolyte. The experimental and theoretical investigations demonstrate the dual effect of SO42− on improving OER performances. SO42− leaching is favorable for the electrochemical reconstruction to form active NiFeOOH under OER condition. Simultaneously, the residual SO42− adsorbed on surface can stabilize the intermediate of OOH*, and thus enhance the OER performances. As expected, NF‐S0.15 delivers an ultralow overpotential of 234 mV to reach the current density of 50 mA cm−2, a fast OER kinetics (27.7 mV dec−1), and a high stability for more than 100 h. This unique insights into anionic modification could inspire the development of advanced electrocatalysts for efficient OER. This work demonstrates the vital effect of SO42− in NF‐S0.15 during oxygen evolution reaction (OER) process. The leaching of SO42− can accelerate the electrochemical reconstruction to form the active NiFeOOH. In addition, a part of SO42− remains and is adsorbed on the surface of NF‐S0.15, which can stabilize the reaction intermediate of OOH* to further improve the OER activity of catalyst.