Synergistic regulation of directional electron transfer by built-in electric field and selenium vacancies in a MnCdS-CoSe(V) Schottky junction toward efficient photocatalytic hydrogen evolution.

Photocatalytic performance frequently encounters limitations due to slow water activation kinetics and a low density of active sites. Here, a MnCdS-CoSe (MCS-CoSe) composite catalyst with a Schottky junction was constructed via Se-vacancy engineering, thereby enhancing charge-transfer efficiency. Owing to the rational distribution of active sites and the efficient electron-hole separation induced by the Schottky junction, MnCdS-CoSe exhibits enhanced redox capability. The MCS-CoSe photocatalyst achieves a hydrogen production rate of 46.11 mmol/g/h, approximately three times higher than that of pristine MnCdS (MCS). It exhibits an apparent quantum efficiency of 15.41% under 420 nm irradiation. Moreover, the optimized sample exhibits direct photoreduction of polyethylene terephthalate (PET), with formic acid and acetic acid production rates of 0.64 and 0.32 mmol/g/h, respectively. Experimental characterizations and Density Functional Theory (DFT) reveal that the Schottky junction establishes an interfacial electric field that directs charge carrier migration. Meanwhile, adjusting the surface charge distribution disrupts the hydrogen-bond interactions between interfacial water molecules, leading to facilitated water activation. Se vacancy incorporation effectively modulates the adsorption-desorption equilibrium of hydrogen intermediates. Overall, this work provides mechanistic insights that can guide the rational construction of efficient defect-engineered Schottky heterostructures for the hydrogen evolution reaction (HER).