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

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 (NixSy-NSCs) with different chemical valences of Ni, Ni9S8-NSCs, Ni9S8-NiS1.03-NSCs, and NiS1.03-NSCs are successfully fabricated, and their electrocatalytic performances as oxygen evolution reaction electrocatalysts are systematically investigated. The NixSy-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 NixSy-NSCs, Ni9S8-NSCs, Ni9S8-NiS1.03-NSCs, and NiS1.03-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 NiS1.03-NSCs show an exceptional low overpotential of approximate to 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 IrO2, RuO2, and Ni-based electrocatalysts.