LAUSR

In electrochemical decomposition of water, the slow kinetics of the anodic oxygen evolution reaction (OER) is a challenge for efficient hydrogen production. Heterointerface engineering is a desirable way to rationally design electrocatalysts for the OER. Herein, we designed and fabricated a nanoparticle flower-like NiCoFe(oxy)hydroxide catalyst in situ grown on the surface of Ni3S2/NF to construct a heterojunction via combining hydrothermal and electrodeposition methods. The heterostructure exhibits a smaller overpotential of 254 mV at a large current density of 100 mA cm-2 in 1 M KOH than that of pristine NiCoFeOxHy/NF (356 mV) and Ni3S2/NF (471 mV). Tafel and electrochemical impedance spectroscopy further showed a favorable kinetics during electrolysis. The role of the substrate Ni3S2 was explored via density functional theory calculations. Our calculations found that SOx on the Ni3S2 surface is a strong nucleophilic group and the synergy effect between Fe and SOx could break *OOH to reduce the Gibbs energy. We also found that the contribution of SOx in sulfates to the OER activity could be negligible. Furthermore, a series of comparative samples were prepared to test this synergy effect. Our experiments indicated that the introduction of Ni3S2 is beneficial. The present contribution provides an important helpful insight into the design and fabrication of novel and highly efficient heterostructure electrocatalysts by introducing nucleophilic groups at the interface.