Surface oxygen-doping induced atom migration of iron-nickel sulfides with tailored d-band center for enhanced oxygen evolution

The rational design of tailored surface properties by surface doping is an efficient yet challenging method for enhanced OER performance. Herein, we propose atom migration effect, induced by surface O-doping to precisely control surface compositions of FeNiS 2 (FNS). The FNS undergoes a surface sulfur/oxygen exchange to form FeNiS 2-x O x (FNSO) structure after surface O-doping, while the bulk phases remain unchanged. In contrast, the surface Ni/Fe ratio is significantly increased due to the accelerated atom migration of nickel during surface O-doping. At elevated temperatures, the bulk phase is prone to transition into complex phases of FeNiS and FeNiO, leading to the decreased surface Ni/Fe ratio. The optimized FNSO demonstrates superior OER performance with a low overpotential of 256 mV at 100 mA cm −2 , and the assembled anion exchange membrane water electrolyzer requires only 1.83 V at 1 A cm −2 with robust durability. Theoretical calculations reveal that this surface atom migration adjusts the d-band center level, optimizes surface adsorption/desorption behaviors, and expedites the OER kinetics. This work contributes to a deeper comprehension of surface modulation with desired surface properties of sulfides and other compounds for enhanced OER performance.