Nano-Antenna Reactors With Spatially Coordinated Microenvironments Enable Atmospheric CO₂ Photoreduction to C₂H₆

Photocatalytic CO₂ reduction to multicarbon products is often limited by inefficient proton delivery to metal nanoparticle surfaces, restricting proton-coupled C─C coupling to a small fraction of metal-oxide interfacial sites. Here, we report a spatially coordinated microenvironment engineering strategy to activate underutilized metal surface atoms for efficient C₂H₆ formation, even under low CO₂ concentration. An AuCu-CeO₂ nano-antenna-reactor photocatalyst is constructed where CeO₂ nanosheets serve as oxide antenna supports and Au nanoparticles act as CO₂ reduction reactors. Notably, Cu sites incorporated within Au nanoparticles function as localized water-activation centers, creating a proton-rich microenvironment adjacent to CO₂ reduction sites. In situ spectroscopy combined with density functional theory calculations reveals that this proton-rich microenvironment lowers the rate-determining *CO to *COH protonation barrier from 1.23 to 0.54 eV, promoting C─C coupling via a *CO─*COH pathway. As a result, AuCu-CeO₂ achieves a ∼3-fold enhancement in C₂H₆ production under pure CO₂ compared with Au-CeO₂, while maintaining appreciable rates of 3.3 and 1.67 µmol g^-1 h^-1 at flue-gas (15%) and atmospheric (0.03%) CO₂ levels, respectively. This work establishes a general principle for regulating proton-coupled multi-electron transformations on catalytic surfaces.