Construction of an S-scheme ZnMn2O4/CdO heterojunction for enhanced photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution represents a promising strategy for sustainable energy conversion, yet its efficiency is often limited by the rapid recombination of photogenerated carriers and insufficient redox capabilities. In this work, an S-scheme ZnMn 2 O 4 /CdO (ZMO/CdO) heterojunction was successfully fabricated via a simple solvothermal method to address these challenges. Based on band structure analysis, the composite satisfies the thermodynamic prerequisites for photocatalytic hydrogen evolution. The establishment of an S-scheme charge transfer pathway, driven by the combined effect of an internal electric field (IEF) and band bending, enables photogenerated electrons (e − ) to accumulate in the conduction band (CB) of ZnMn 2 O 4 (ZMO), while holes (h + ) are retained in the valence band (VB) of CdO. This mechanism not only promotes the spatial separation of photogenerated electron–hole pairs (PEHP) but also preserves the strongest redox ability of the system. Under optimized conditions (pH = 8 with triethanolamine (TEOA)), the ZMO/CdO composite achieves an outstanding hydrogen evolution rate of 2237 μmol∙g −1 ∙h −1 , which is approximately 4.38 and 2.84 times higher than that of pure CdO and ZMO, respectively. Moreover, the photocatalyst maintains high hydrogen production activity and structural stability in diverse real water samples, including municipal water, natural surface water, and even wastewater, highlighting its strong potential for practical solar-driven hydrogen production in complex environments.