F, N neutralizing effect induced Co-P-O cleaving endows CoP nanosheets with superior HER and OER performances

Electrochemical water splitting, the most direct and clean method used for the production of hydrogen, requires highly efficient bifunctional electrocatalysts that can accelerate hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) by overcoming their kinetics barriers. Herein, self-supported F, N codoping CoP nanosheets (denoted as FN-CoP NS) are prepared as efficient and stable bifunctional electrocatalysts. Codoping of F and N neutralizes the electronegativity of surface P-O by cleaving the Co-P-O of non-metallic P sites on the surface (O derived from the surface oxidation). This contributes to an increased Co²⁺ content with considerable adjustable electronegativity and also optimizes HER and OER processes. As a result, FN-CoP NS requires 66 and 241 mV overpotentials to deliver the current density of 10 mA cm^-2 during HER and OER, respectively. A full water electrolyzer equipped FN-CoP NS as both cathode and anode only require 1.57 V to drive the current density of 10 mA cm^-2 and to sustain 50 mA cm^-2 for 48 h. This work adjusts the electronic structure of metal phosphides by a double anion codoping strategy, which provides a reference value for the rational design of efficient bifunctional electrocatalysts.