Co2P/CoP heterostructures with significantly enhanced performance in electrocatalytic hydrogen evolution reaction: Synthesis and electron redistribution mechanism

Heterostructures are often constructed to modulate the electronic states of the two catalysts, achieving high-performance in alkaline hydrogen evolution reaction (HER). Various mechanisms have been proposed for the heterostructural catalysts, which however awaits further approvement. Herein, a heterostructure composed of Co2P and CoP was successfully prepared with significantly enhanced HER catalytic activity relative to the endmembers. The ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) revealed the effective promotion of the self-driven transferring of electrons from CoP to Co2P and the accumulation of electrons on the P sites in Co2P due to the strong electronic coupling of built-in electric field in the Co2P/CoP interface. In situ electrochemical impedance spectroscopy (EIS) and poison experiments confirmed the Heyrovsky step of H* intermediate depleting on electronegative P sites and contributions of both metal and P to the reactivity in the Co2P/CoP. Density functional theory (DFT) calculations clarify that the electronic structure at interface of the heterojunction significantly weakens the hydrogen adsorption free energy (Delta G(H* ads)) of P site in Co2P/CoP to near zero. We also propose an electronic redistribution strategy for heterostructures that activates the multiple routes mechanism and production of more active sites. The working mechanism is expected to be further extended to other transition metal compounds for efficient HER activity.