Surface engineering of morphology and electronic structure of CoP by Zn doping for enhanced water splitting performance

Transition metal phosphides are considered as promising alternatives to noble-metal based electrocatalysts for water splitting due to their bifunctional catalytic activity. The modulation of morphology and electronic structure is an efficient strategy to improve the mass transport and electronic conductivity of metal phosphides, but still faces a great challenge to achieve this conjoint regulation. Herein, a facile Zn-doped strategy was developed to synthesize cobalt phosphide (CoP) catalyst with thickness-controlled porous nanosheet structure. At the current density of 10 mA cm⁻², the optimized Zn_0.1-CoP catalyst delivers an overpotentials of 290 mV and 98 mV for OER and HER, respectively. The cell voltage for the overall water splitting is 1.57 V to reach the current density of 10 mA cm⁻², outperforming the counterparts of noble metal-based Pt/C and IrO₂ catalysts. The density functional theory (DFT) calculations reveal that Zn doping can effectively improve the conductivity and regulate the electronic structure of CoP, thus resulting in fast charge transfer transport and reduced energy barrier of the rate-determining step. This work provides a favorable strategy for the rational design of bifunctional catalysts with high-performance for overall water splitting.