Understanding the influence of carbon vacancy-doped 3d transition metals on the adsorption ability and hydrogen evolution activity of the β-Mo2C(100) surface: A holistic computational analysis

HER plays a crucial role in renewable energy storage and conversion, making the development of efficient electrocatalysts to replace traditional precious metals essential for improving HER performance. β-Mo 2 C has garnered significant attention due to its favorable physicochemical properties, yet its catalytic activity requires further optimization. In this study, DFT was used to investigate the effect of carbon vacancy on HER properties of β-Mo 2 C(100) doped with 3 d -TM (3 d -TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). The geometric configuration and electronic structure of the β-Mo 2 C(100) surface before and after doping were analyzed in detail by varying the 3 d -TM doping concentration, revealing its regulatory effect on the local electronic environment of active sites. The results indicate that among 63 3 d -TM-β-Mo 2 C(100) catalyst models, 16 exhibit ideal catalytic performance, with the absolute Δ G H* of hydrogen intermediates being less than 0.2 eV. Notably, 2/4-c ML Co-β-Mo 2 C (Δ G H* = −0.08 eV) outperforms Pt, indicating potentially superior intrinsic HER activity under idealized theoretical conditions. Structure stability analysis reveals that early 3 d -TM-β-Mo 2 C, despite possessing good electrical conductivity, suffers from structure instability. Additionally, electronic structure analysis shows that for intermediate transition metals from Cr to Co, the d -band center shifts upward with increasing doping concentration, strengthening the adsorption interaction between hydrogen intermediates and the 3 d -TM-β-Mo 2 C surface. Moreover, 26 catalysts maintain excellent hydrogen evolution activity across a wide pH range (pH = 0∼14). This work provides a doping-concentration-dependent descriptor landscape for Mo 2 C-based HER catalysts, highlighting the synergetic role of d -band center shifting and orbital hybridization.