Facilitating Oriented Electron Transfer from Cu to Mo ₂ C MXene for Weakened Mo─H Bond Toward Enhanced Photocatalytic H ₂ Generation

Mo₂C MXene (Mo₂CT_x) is recognized as an excellent cocatalyst due to unique physicochemical properties and platinum-like d-band of Mo active sites. However, Mo sites of Mo₂CT_x with high-density empty d-orbitals exhibit strong Mo─H_ads bonds during photocatalytic hydrogen evolution, leading to easy adsorption of hydrogen ions from solution and unfavorable desorption of H₂ from Mo sites. To weaken the Mo─H_ads bond, a strategy of oriented electron transfer from Cu to Mo₂CT_x to increase the antibonding orbital occupancy of Mo─H_ads hybrid orbitals is implemented by introducing Cu into Mo₂CT_x interlayers to form Cu-Mo₂CT_x. The Cu-Mo₂CT_x is synthesized from Mo₂Ga₂C and CuCl₂ via a one-step molten salt method and combined with TiO₂ to form Cu-Mo₂CT_x/TiO₂ photocatalyst through an ultrasound-assisted approach. Hydrogen production tests reveal that an exceptional performance of Cu-Mo₂CT_x/TiO₂ (6446 µmol h^-1 g^-1, AQE = 18.3%) is 8.4 fold higher than that of Mo₂CF₂/TiO₂ (Mo₂CF₂ by the conventional etchant NH₄F+HCl). Density functional theory (DFT) calculations and characterization results corroborate that the oriented electron transfer from Cu to Mo₂CT_x increases the Mo─H_ads antibonding occupancy in Cu-Mo₂CT_x, thereby weakening Mo─H_ads bonds and accelerating the hydrogen evolution rate of TiO₂. This research offers valuable insights into optimizing H-adsorption capabilities at active sites on MXene materials.