Weakening Mo–H Bond of Mo2C MXene Cocatalyst by Increased Antibonding-Orbital Occupancy State for Superior Photocatalytic Hydrogen Production

The 2D molybdenum carbide MXene (Mo2CTx) is a promising non-noble cocatalyst for photocatalytic H2 evolution due to its excellent metallic conductivity and Mo active sites with a Pt-like d-band structure. However, the basal plane of Mo2CTx contains numerous inactive F-terminal groups that spontaneously coordinate with exposed Mo atoms by F-containing etchants, which results in the strong Mo–Hads bonds and the weak desorption of produced H2 from their surface so that the Mo2CTx cocatalyst exhibits very limited hydrogen-evolution activity. Considering that the antibonding-orbital occupancy state of Mo can predominately optimize Mo–Hads bonds by free-electron transfer, in this work, an electron-reversal strategy of constructing a MoS2–Mo2C MXene heterophase by increasing the occupancy state of the antibonding orbital to weaken Mo–Hads bonds is first realized for the boosted H2-evolution activity. The MoS2–Mo2CTx/CdS photocatalysts were synthesized by a dual-functional l-Cys-assisted one-step hydrothermal method. Experimental results showed a superior H2-production activity of MoS2–Mo2CTx/CdS (2.35 mmol h–1 g–1, AQE = 3.64%), which was 20 and 2.6 times over those of CdS and Mo2CTx/CdS, respectively. Theoretical calculations corroborate that the weakened Mo–Hads bonds in the MoS2–Mo2CTx heterostructure are realized through the increasing antibonding-orbital occupancy state of Mo sites and the electron transfer from MoS2 to Mo2CTx for the enhanced photocatalytic hydrogen-production performance of CdS. This research determines the dominant role of antibonding-orbital occupancy states in the H-adsorption regulation of active sites in Mo2C MXene cocatalysts for photocatalytic hydrogen production.