Regulating Complex Transition Metal Oxyhydroxides Using Ni 3 S 2 : 3D NiCoFe(oxy)hydroxide/Ni 3 S 2 /Ni Foam for an Efficient Alkaline Oxygen Evolution Reaction.

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 Ni 3 S 2 /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 NiCoFeO x H y /NF (356 mV) and Ni 3 S 2 /NF (471 mV). Tafel and electrochemical impedance spectroscopy further showed a favorable kinetics during electrolysis. The role of the substrate Ni 3 S 2 was explored via density functional theory calculations. Our calculations found that SO x on the Ni 3 S 2 surface is a strong nucleophilic group and the synergy effect between Fe and SO x could break *OOH to reduce the Gibbs energy. We also found that the contribution of SO x 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 Ni 3 S 2 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.