Nano‐Antenna Reactors With Spatially Coordinated Microenvironments Enable Atmospheric CO ₂ Photoreduction to C ₂ H ₆

Photocatalytic CO 2 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 C 2 H 6 formation, even under low CO 2 concentration. An AuCu‐CeO 2 nano‐antenna‐reactor photocatalyst is constructed where CeO 2 nanosheets serve as oxide antenna supports and Au nanoparticles act as CO 2 reduction reactors. Notably, Cu sites incorporated within Au nanoparticles function as localized water‐activation centers, creating a proton‐rich microenvironment adjacent to CO 2 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‐CeO 2 achieves a ∼3‐fold enhancement in C 2 H 6 production under pure CO 2 compared with Au‐CeO 2 , while maintaining appreciable rates of 3.3 and 1.67 µmol g −1 h −1 at flue‐gas (15%) and atmospheric (0.03%) CO 2 levels, respectively. This work establishes a general principle for regulating proton‐coupled multi‐electron transformations on catalytic surfaces.