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 CHx* 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.