Unlocking synergistic electron reservoir and hole sink in a Zn0.5Cd0.5S/RuO2 heterojunction for superior photocatalytic hydrogen production.

The practical application of photocatalytic water splitting is primarily hindered by rapid charge recombination and photocorrosion. Herein, we construct a Zn0.5Cd0.5S/RuO2 (ZCSRuO) heterojunction via mechanochemical ball-milling that effectively tackles these challenges. The optimized ZCSRuO-4 (mZCS: mRuO2 = 100: 4 mg) catalyst achieves a remarkable hydrogen evolution rate of 26.37 mmol/(g·h), which is 6.5 times higher than that of pristine Zn0.5Cd0.5S (ZCS), coupled with exceptional stability (98.8 % activity retention over 20 h). A combination of in situ XPS and Kelvin probe force microscopy (KPFM) directly visualizes light-induced electron transfer from ZCS to RuO₂, driven by a 0.54 eV built-in electric field. This facilitates a unique spatially decoupled redox mechanism: RuO₂ acts as an electron reservoir via the Ru4+/Ru3+ redox couple and a dedicated hole sink for efficient lactic acid oxidation, while ZCS exclusively hosts the proton reduction reaction. This synergy not only triples the charge separation efficiency but also significantly suppresses the photocorrosion of ZCS, as evidenced by a significantly shortened charge lifetime (1.61 ns) and distinct photothermal behavior. First-principles calculations further corroborate the interfacial charge redistribution and band alignment. This work provides deep insights and a effective strategy for designing robust photocatalytic systems through spatial decoupling of redox sites mediated by a multifunctional cocatalyst.