Selective photocatalytic hydrogen peroxide production in pure water through interfacial charge-flow engineering and oxygen adsorption control in an S-scheme Mn0.2Cd0.8S/ZnIn2S4 heterojunction.

Photocatalytic hydrogen peroxide (H2O2) synthesis in pure water (H2O) is challenging because it requires simultaneous efficient charge separation and selective two-electron oxygen reduction. Herein, we report an S-scheme Mn0.2Cd0.8S/ZnIn2S4 (MZ) heterojunction that synergistically regulates interfacial charge flow and surface oxygen (O2) adsorption configuration. The optimized MZ-15 achieves a H2O2 production rate of 3917.3 μmol g-1 h-1 in pure water without sacrificial agents. The S-scheme pathway promotes charge separation while preserving strong redox capability. More importantly, the pronounced ionic-radius mismatch between Mn2+ and Cd2+ in Mn0.2Cd0.8S induces an asymmetric electronic environment that shifts O2 adsorption from side-on to end-on (Pauling-type) configuration, thereby favoring OO bond retention and two-electron oxygen reduction reaction (2e- ORR). This work highlights that simultaneous engineering of interfacial charge dynamics and O2 adsorption geometry is a powerful strategy for highly selective photocatalytic H2O2 production.