Work-function-engineered Mo 4d electronic structure modulation in Mo2C MXene cocatalyst for efficient photocatalytic H2 evolution

Abstract

Mo₂C MXene (Mo₂CT_x) exhibits exceptional hydrogen-evolution potential in photocatalysis due to the Pt-like electronic structure of surface Mo active sites. However, the Mo sites in Mo₂CT_x usually show excessively strong H-adsorption during HER, significantly limiting the intrinsic catalytic activity of Mo₂CT_x. To weaken the H-adsorption capacity of Mo active sites, a strategy of modulating d-orbital electron is implemented via in-situ constructing MoC-Mo₂C MXene heterojunction by a work-function-induced effect. The MoC-Mo₂CT_x heterojunction was synthesized by in-situ conversion of Mo₂C MXene into MoC via a Co-induced molten salt method, followed by coupling with TiO₂ through a simple ultrasonication-assisted method to prepare the MoC-Mo₂CT_x/TiO₂ photocatalyst. Photocatalytic tests showed that the optimal MoC-Mo₂CT_x/TiO₂ sample achieves an excellent hydrogen production rate of 1886 μmol h⁻¹ g⁻¹, representing 117.9 and 3.9 fold enhancements over TiO₂ and Mo₂CF_x/TiO₂ (Mo₂CF_x prepared by a conventional etchant NH₄F + HCl), respectively. Experimental and theoretical calculations substantiate that the work-function gradient between MoC and Mo₂C MXene induces electron transfer from MoC to Mo₂C MXene to weaken the H-adsorption of Mo active sites in Mo₂CT_x cocatalyst, thereby enhancing its HER activity. This research provides a new strategy of in-situ constructing Mo₂C MXene-based heterojunction for adjusting the H-adsorption capacity of Mo active sites.