Chemical Valence‐Dependent Electrocatalytic Activity for Oxygen Evolution Reaction: A Case of Nickel Sulfides Hybridized with N and S Co‐Doped Carbon Nanoparticles

Abstract Exploration of the relationship between electrocatalytic activities and their chemical valence is very important in rational design of high‐efficient electrocatalysts. A series of porous nickel sulfides hybridized with N and S co‐doped carbon nanoparticles (Ni x S y ‐NSCs) with different chemical valences of Ni, Ni 9 S 8 ‐NSCs, Ni 9 S 8 ‐NiS 1.03 ‐NSCs, and NiS 1.03 ‐NSCs are successfully fabricated, and their electrocatalytic performances as oxygen evolution reaction electrocatalysts are systematically investigated. The Ni x S y ‐NSCs are obtained via a two‐step reaction including a low‐temperature synthesis of Ni‐Cys precursor followed by thermal decomposing of the precursor in Ar atmosphere. By controlling the sulfidation process during the formation of Ni x S y ‐NSCs, Ni 9 S 8 ‐NSCs, Ni 9 S 8 ‐NiS 1.03 ‐NSCs, and NiS 1.03 ‐NSCs are obtained, respectively, giving rise to the increase of high‐valence Ni component, and resulting in gradually enhanced oxygen evolution reaction electrocatalytic activities. In particular, the NiS 1.03 ‐NSCs show an exceptional low overpotential of ≈270 mV versus reversible hydrogen electrode at a current density of 10 mA cm −2 and a small Tafel slope of 68.9 mV dec −1 with mass loading of 0.25 mg cm −2 in 1 m KOH and their catalytic activities remained for at least 10 h, which surpass the state‐of‐the‐art IrO 2 , RuO 2 , and Ni‐based electrocatalysts.