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 (beta-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 (Delta G(H)) can be effectively controlled by strain and C-vacancies concentration. Appropriate combinations of strain and C-vacancies concentration can achieve optimal conditions of Delta G(H) approximate to 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 beta-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.