Harnessing Schottky Barrier in ZnO-AuCu to Enhance Charge Separation for Selective CO₂ Methanation

The photocatalytic conversion of CO₂ into valuable solar fuels presents a promising strategy for addressing both greenhouse gas emissions and energy sustainability. In this study, uniform and highly dispersed AuCu alloy nanoparticles were deposited on ZnO nanoparticles through an in situ photoreduction method for photocatalytic CO₂ reduction to CH₄. The optimized ZnO-AuCu catalyst achieved a CH₄ yield of 45.2 µmol g^-1 h^-1 (12.22 times higher than that of pure ZnO), with a remarkable selectivity of 98.7%. The enhanced activity originates from the synergistic effects of AuCu alloying and the ZnO/AuCu heterointerface. Specifically, the AuCu alloy extends visible light harvesting through surface plasmon resonance, while the intimate ZnO-AuCu contact forms a Schottky junction that drives photogenerated electron separation and enriches electrons at Cu sites. CO₂-TPD and DFT adsorption calculations indicate that the ZnO/AuCu interface favors CO₂ capture and activation, whereas the AuCu surface facilitates subsequent hydrogenation steps. In situ DRIFTS further reveals the accumulation of key CH_x* intermediates, and Gibbs free energy calculations confirm that AuCu alloying lowers the energetic barriers for CO₂ activation and deep hydrogenation. This work provides insight into regulating interfacial charge transfer and surface reaction pathways through alloy engineering for efficient and selective CO₂ methanation.