Improved H-adsorption ability and conductivity of a Co-doped Mo2N cocatalyst for efficient photocatalytic H2 generation of g-C3N4

Abstract

Cocatalysts are usually applied in the photocatalytic water splitting process to accelerate the kinetics of the hydrogen evolution reaction (HER). Specifically, the transition metal nitride (Mo₂N) featuring a unique local surface plasmon resonance (LSPR) effect has exhibited great potential to function as a HER cocatalyst. However, the low metallicity of Mo₂N hampers its ability to improve charge separation. To address this issue, transition metal atom doping (Co and Cu) engineering was used to modulate the electronic structure of Mo₂N nanosheets to achieve a higher electrical conductivity and a lower hydrogen adsorption free energy (|ΔG_H*|), thereby favoring the HER kinetics. Density functional theory (DFT) calculations and experimental results showed that Co-doping and Cu-doping mainly take place at Mo sites in the crystal structure of Mo₂N to form stable structures of Co doped Mo₂N (Co–Mo₂N) and Cu doped Mo₂N (Cu–Mo₂N). Compared with pristine Mo₂N, both Cu–Mo₂N and Co–Mo₂N demonstrated a much improved cocatalytic effect over g-C₃N₄ in promoting charge separation, accelerating HER kinetics and enhancing light absorption. The Co–Mo₂N with the highest conductivity and lowest |ΔG_H*| illustrated the best cocatalytic effect, and the H₂ production performance (367.8 μmol g⁻¹ h⁻¹) of Co–Mo₂N/g-C₃N₄ achieved was 10 and 5 times higher than those of Mo₂N/g-C₃N₄ and Cu–Mo₂N/g-C₃N₄. This paper provides significant guidance in the design and development of efficient cocatalysts for the HER application.