Fluorine-Induced Dual Defects in Cobalt Phosphide Nanosheets Enhance Hydrogen Evolution Reaction Activity

Introduction of defects in a controllable way is important to modulate the electronic structure of catalysts toward enhancement of electrocatalytic activity. Herein we report that incorporation of fluorine into a cobalt phosphide alloy has a unique effect: it creates both F- anion doping and P vacancies, resulting in a nearly 15-fold enhancement of the catalytic activity for the hydrogen evolution reaction (HER) in neutral solution. The existence of dual defects in CoP was confirmed by extended X-ray absorption fine structure (EXAFS) curve fitting results and density functional theory calculations. We show that the dual-defect feature is beneficial for increasing the active-site exposure, tuning the surface wettability, and optimizing the electronic configuration of CoP for the HER. Our fluorine-based modulation protocol may be applicable to other metal alloy electrocatalysts toward more efficient energy conversion reactions.