Metal-free two-dimensional phosphorus carbide as an efficient electrocatalyst for hydrogen evolution reaction comparable to platinum

The development of effective metal-free electrocatalytic for hydrogen evolution reaction (HER) to substitute precious Pt based catalyst has attracted massive research interests. Herein, we report a density functional theory (DFT) investigation on activation and optimization of a new metal-free two-dimensional (2D) material, namely, phosphorus carbide (β-PC) monolayer as efficient HER electrocatalysts by applying reasonable C-vacancies and strain. Our theoretical results show that the C-vacancies introduce in-gap states, thus significantly increase the electrical conductance and hydrogen binding strength, which are favorable for HER process. The hydrogen adsorption free energies (ΔG_H) can be effectively controlled by strain and C-vacancies concentration. Appropriate combinations of strain and C-vacancies concentration can achieve optimal conditions of ΔG_H ≈ 0 and excellent exchange current density, suggesting a superior catalytic activity comparable to Pt. Moreover, the physico-chemical origin of defect and strain on nonmetal-H bonding were rationalized by establishing a linear relationship between hydrogen adsorption strength and the intrinsic electronic structure of β-PC. Our work offers a new promising metal-free catalyst for HER and reveals profound insights into the bonding mechanisms of nonmetal-H bond to guide the atomic design of more efficient metal-free electrocatalysts.