Fluorine-triggered surface reconstruction of Ni3S2 electrocatalysts towards enhanced water oxidation

Developing efficient electrocatalysts to accelerate the rate-determining step of oxygen evolution reaction (OER) is a tough challenge to water electrolysis. Herein, we report a fluorinated Ni3S2 nanoarray electrocatalyst with Ni-F bonds enriched and low-crystalline ultrathin nanosheets on the surface, which are responsible for the rapid and deep electrochemical-transformation of active phase during OER process. Electrochemical characterizations indicate that the fluorinated Ni3S2 (F-Ni3S2) possesses a larger electrochemical active surface area, better conductivity and higher intrinsic OER activity (TOF) than the pristine Ni3S2. Consequently, the optimized F-Ni3S2 electrocatalyst shows a small overpotential of 239 mV at 10 mA cm(-2) with a low Tafel slope of 36 mV dec(-1), superior to most of reported Ni3S2-based electrocatalysts to date. Ex-situ structural analysis further reveals the NiF bonds can be easily activated with F loss under OER process, thus generating more highly active Ni-OOH species for accelerating rate-determining step (*O -> *OOH). This work expands fluorine chemistry applications in designing high-activity electrocatalysts for energy-conversion.

Automated summary

In this study, a novel fluorinated Ni3S2 nanoarray electrocatalyst was reported, exhibiting excellent electrochemical performance during the OER process. The electrocatalyst showed a larger electrochemical active surface area, better conductivity, and higher OER activity, resulting in lower overpotential and Tafel slope compared to most reported Ni3S2-based electrocatalysts. The activation of NiF bonds under OER process generated highly active Ni-OOH species, contributing to the acceleration of rate-determining step.