Predicted superior hydrogen evolution activities of MoC via surface dopant

Molybdenum carbides (MoC) are regarded as promising candidates for electrocatalytic hydrogen evolution reaction (HER) as their stabilities, high conductivities. Non-metallic doping is a robust way to enhance the HER activity of MoC in experiments, yet the systematic theoretical study is still lacking. In this work, we investigate the surface doping effect on HER activity of C-terminated γ-MoC(100) by density functional theory (DFT). The thermodynamical stability and realistic catalytic surface of doped surfaces, including mono- and co-doping by three elements (N, P and S) with various doping ratios, are verified by formation energies and surface Pourbaix diagrams, respectively. According to the hydrogen adsorption ability on different coverage and the calculated exchange current densities (i0) of the doped surfaces, the surfaces doping in range of (P% > 60% and N% > 5%), (60% < N% <85% and P% < 25%), and (60% < N% < 85% and S% < 25%), show larger i0 (i0 > 4 mA/cm2). Especially the N/P co-doping γ-MoC(100), their larger i0 in greater range enables their promising excellent performance in hydrogen evolution in experiments. The improved HER activities of doped MoC(100) are ascribed to suitable hydrogen adsorption abilities tuned by suitable pz-band centers and the charge redistribution. Our DFT simulations provide more insight and guidance for improving the HER performance of electrode catalysts using non-metallic doping effects.