Enhanced visible light photocatalytic H2 production on ZnMn2O4

This work highlights the development of nanocrystalline ZnMn₂O₄, synthesized via a sol–gel route, as a visible-light-active photocatalyst for hydrogen production. Structural characterization through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and FT-IR spectroscopy confirmed the formation of a single-phase cubic spinel structure. Scanning electron microscopy (SEM) revealed grains with uniform morphology, while the BET analysis showed a specific surface area of 27.75 m²/g and a pore volume of 0.2 cm³/g. The material exhibits an optical bandgap of 1.33 eV, attributed to Mn³⁺ 3d orbital splitting, and displays p-type behavior, with a flat band potential (E_fb) of 0.18 V vs. SCE, as determined from capacitance-potential measurements. The current–potential profile resembles a chemical diode, supporting a redox potential near − 0.7 V vs. SCE and low hydrogen overvoltage. Under optimal conditions (pH ~ 12, 50 °C, light flux of 28 mW/cm²), ZnMn₂O₄ achieved a hydrogen evolution rate of 0.32 μmol min⁻¹ g⁻¹ and a quantum efficiency of 0.79% using S₂O₃²⁻ as a reducing agent. ZnMn₂O₄ demonstrated excellent stability and reusability over successive runs. These findings highlight the catalyst's potential as an affordable material for solar-powered hydrogen production, paving the way for efficient renewable energy systems.