Bi/S Co‐Doping of CeVO ₄ for Enhanced Photocatalytic Hydrogen Evolution: Insights into Multivalent Ce/V States and Oxygen Vacancies

Herein, a simple and environmentally benign synthetic strategy is developed to construct a hydrazine‐regulated Bi/S co‐doped CeVO 4 trimetallic sulfur‐oxide photocatalyst (Bi/S‐CeVO 4 ). The resulting material features abundant oxygen vacancy (Vo) defects and stabilized multivalent Ce 3+ /Ce 4+ and V 4+ /V 5+ states, which synergistically enhance photocatalytic hydrogen evolution reaction (PHER) performance under visible light irradiation. Band structure analyses indicate that Bi/S co‐doping effectively modulates the electronic structure of CeVO 4 , leading to improved photocatalytic performance toward PHER. The coexistence of multivalent Ce 3+ /Ce 4+ and V 4+ /V 5+ species provides efficient electron‐hopping pathways, facilitating photogenerated charge separation and transfer while prolonging carrier lifetime. In addition, Vo defects served as catalytic sites for water‐molecule adsorption and activation, further accelerating surface reaction kinetics. Benefiting from these synergistic effects, the optimized Bi/S‐CeVO 4 ‐3, featuring the highest electrochemically active surface area of 0.0015 cm 2 and Vo concentration of 24.5%, and suitable ratio of Ce 4+ /(Ce 3+ +Ce 4+ ) (41.8%) and V 4+ /(V 4+ +V 5+ ) (38.5%), delivers the highest PHER rate of 1514.7 μmol·h –1 , with an apparent quantum efficiency (AQE) x‐ray diffraction of 15.28% at 420 nm. Moreover, the catalyst demonstrates excellent stability and durability. This work presents a feasible and effective strategy for electronic structure and defect engineering of CeVO 4 ‐based photocatalysts to achieve efficient solar‐driven hydrogen evolution.