Nickel-iron sulfide has shown attractive activity in electrocatalytic oxygen evolution reaction (OER). However, the effects of low valence sulfur (S²⁻) and metal species on OER in binary nickel-iron sulfide have rarely been systematically studied. Works based on post-catalysis characterization have led to the assumption that the real active species are nickel-iron oxyhydroxide, and that nickel-iron sulfide acts only as a precatalyst. Therefore, to study the role of S, Ni, and Fe for the development of nickel-iron sulfide catalyst is of self-evident importance. Herein, a facile solvothermal method is used to synthesize acetylene black coated with nickel-iron sulfide nanosheets. Electrochemical tests show that the presence of low valence S species makes the catalyst have faster OER kinetics, larger active area, and intermediate active species adsorption area. Therefore, the present study reveals the enhancing effect of low valence sulfur species (S²⁻) on OER in binary nickel-iron sulfide. In situ Raman spectroscopy shows that the generation of γ-NiOOH intermediate is essential and Fe does not directly participate in the oxygen production. Density functional theory (DFT) calculation shows that Ni-OH deprotonation is a rate-determining step for both binary nickel-iron sulfide and nickel sulfide. The addition of Fe into NiS_x lightly increases the charge transfer of Ni atom to O atom, which makes deprotonation easier and thereby improves the OER performance.

镍-铁硫化物在电催化析氧反应 (OER) 中显示出有吸引力的活性。然而，低价硫（S ²⁻) 和二元硫化镍铁中 OER 上的金属物种很少被系统地研究。基于后催化表征的工作导致假设真正的活性物质是镍铁羟基氧化物，并且镍铁硫化物仅作为预催化剂起作用。因此，研究S、Ni、Fe对硫化镍铁催化剂的作用，其重要性不言而喻。在此，采用简便的溶剂热法合成了包覆有镍铁硫化物纳米片的乙炔黑。电化学测试表明，低价S物种的存在使催化剂具有更快的OER动力学、更大的活性面积和中等活性物种吸附面积。因此，本研究揭示了低价硫物质 (S ²⁻) 在二元镍铁硫化物中的 OER。原位拉曼光谱表明，γ-NiOOH 中间体的产生是必不可少的，而 Fe 不直接参与氧气的产生。密度泛函理论 (DFT) 计算表明，Ni-OH 去质子化是二元镍铁硫化物和硫化镍的速率决定步骤。在 NiS _{x 中}加入 Fe略微增加了 Ni 原子向 O 原子的电荷转移，这使得去质子化更容易，从而提高了 OER 性能。