Influence of the S:Ni ratio in raw materials on the NixSy electrocatalysts

Nickel sulfides have been considered to be among the most effective oxygen evolution reaction (OER) electrocatalysts. Until now, there are many different nickel sulfides, such as Ni₃S₂, NiS, Ni₃S₄, NiS₂, etc. In this paper, we set out to explore the influence of the S:Ni ratio in raw materials on the different nickel sulfides. With the characterizations of XRD, XPS, SEM, TEM and BET, the relevance between the molar ratio of S:Ni in raw materials and stoichiometric ratio, microscopic structure and OER performance are discussed. According to the results of the experiments, the Ni₃S₄ derived from the 3:1 M ratio of S:Ni in raw material exhibits the smallest overpotential (245 and 314 mV to achieve 10 and 20 mA/cm²) and Tafel slope (81.5 mV/dec). Meanwhile, theoretical calculation of ΔG(H₂O*) indicate that the adsorption energy in Ni₃S₄ is much closer to the IrO₂ than other nickel sulfides, which are in good agreement with the OER performance of electrochemical measurements.