Weakening Mo–H Bond of Mo<sub>2</sub>C MXene Cocatalyst by Increased Antibonding-Orbital Occupancy State for Superior Photocatalytic Hydrogen Production
Miaomiao Pan, Ping Wang, Xuefei Wang, Feng Chen, Huogen Yu
Abstract
The 2D molybdenum carbide MXene (Mo 2 CT x ) is a promising non-noble cocatalyst for photocatalytic H 2 evolution due to its excellent metallic conductivity and Mo active sites with a Pt-like d-band structure. However, the basal plane of Mo 2 CT x contains numerous inactive F-terminal groups that spontaneously coordinate with exposed Mo atoms by F-containing etchants, which results in the strong Mo–H ads bonds and the weak desorption of produced H 2 from their surface so that the Mo 2 CT x cocatalyst exhibits very limited hydrogen-evolution activity. Considering that the antibonding-orbital occupancy state of Mo can predominately optimize Mo–H ads bonds by free-electron transfer, in this work, an electron-reversal strategy of constructing a MoS 2 –Mo 2 C MXene heterophase by increasing the occupancy state of the antibonding orbital to weaken Mo–H ads bonds is first realized for the boosted H 2 -evolution activity. The MoS 2 –Mo 2 CT x /CdS photocatalysts were synthesized by a dual-functional l -Cys-assisted one-step hydrothermal method. Experimental results showed a superior H 2 -production activity of MoS 2 –Mo 2 CT x /CdS (2.35 mmol h –1 g –1, AQE = 3.64%), which was 20 and 2.6 times over those of CdS and Mo 2 CT x /CdS, respectively. Theoretical calculations corroborate that the weakened Mo–H ads bonds in the MoS 2 –Mo 2 CT x heterostructure are realized through the increasing antibonding-orbital occupancy state of Mo sites and the electron transfer from MoS 2 to Mo 2 CT x 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 Mo 2 C MXene cocatalysts for photocatalytic hydrogen production.