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

Abstract Mo ₂ C MXene (Mo ₂ CT _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 Mo ₂ CT _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 H ₂ from Mo sites. To weaken the Mo─H _ads bond, a strategy of oriented electron transfer from Cu to Mo ₂ CT _x to increase the antibonding orbital occupancy of Mo─H _ads hybrid orbitals is implemented by introducing Cu into Mo ₂ CT _x interlayers to form Cu‐Mo ₂ CT _x . The Cu‐Mo ₂ CT _x is synthesized from Mo ₂ Ga ₂ C and CuCl ₂ via a one‐step molten salt method and combined with TiO ₂ to form Cu‐Mo ₂ CT _x /TiO ₂ photocatalyst through an ultrasound‐assisted approach. Hydrogen production tests reveal that an exceptional performance of Cu‐Mo ₂ CT _x /TiO ₂ (6446 µmol h ⁻¹ g ⁻¹ , AQE = 18.3%) is 8.4 fold higher than that of Mo ₂ CF ₂ /TiO ₂ (Mo ₂ CF ₂ by the conventional etchant NH ₄ F+HCl). Density functional theory (DFT) calculations and characterization results corroborate that the oriented electron transfer from Cu to Mo ₂ CT _x increases the Mo─H _ads antibonding occupancy in Cu‐Mo ₂ CT _x , thereby weakening Mo─H _ads bonds and accelerating the hydrogen evolution rate of TiO ₂ . This research offers valuable insights into optimizing H‐adsorption capabilities at active sites on MXene materials.