Abstract:

The conversion of solar energy into hydrogen represents a promising and sustainable approach to addressing the global energy crisis and mitigating environmental pollution. However, achieving the industrial benchmark of solar-to-hydrogen efficiency remains challenging due to the inherently insufficient spatial separation of charge carriers and sluggish interfacial kinetics. Engineering redox-active sites has emerged as an effective approach to enhance photocatalytic hydrogen evolution performance. Herein, a dual-mode copper-modified titanium dioxide photocatalyst (Cu/TiO₂), comprising isolated Cu atoms and CuO nanoclusters, was successfully synthesized via a facile molten salt method. The optimized Cu/TiO₂ exhibited a remarkable hydrogen evolution rate of 37.6 mmol g^-1 h^-1 with methanol as a sacrificial agent, representing a 96-fold enhancement compared to pristine TiO₂. Mechanistic studies revealed that isolated Cu atoms incorporated into the TiO₂ lattice substantially lower the free energy of hydrogen adsorption (*H), thereby promoting the proton reduction half-reaction. Simultaneously, the surface-dispersed CuO nanoclusters were found to reduce the overpotential for methanol oxidation, thereby accelerating the oxidation half-reaction and facilitating overall charge balance during photocatalysis. Furthermore, photocatalytic hydrogen production coupled with the oxidation of various organic molecules was evaluated under a low sacrificial agent concentration (0.1%) over the Cu/TiO₂ photocatalyst, offering a more sustainable and practically relevant assessment of catalyst performance for green energy applications.

Key words: Isolated Cu Atoms, CuO nanoclusters, Engineering redox-active sites, Photocatalytic hydrogen evolution reaction, Organic molecule oxidation