Gradient‐Driven Spatial Relay in Titanium Oxynitride for Photocatalytic CO 2 ‐to‐C 2 H 4 Conversion

Photocatalytic CO 2 reduction to C 2 H 4 demands simultaneous management of light harvesting, proton supply, and C−C coupling, functions that are difficult to integrate on a single surface site. Here, we present a “surface‐subsurface spatial relay” strategy to overcome this limitation using a gradient titanium oxynitride (G−TiNO) architecture that spatially partitions these steps, realizing CO 2 ‐to‐C 2 H 4 conversion without noble metal on Ti‐based catalysts. Operando spectroscopy and DFT reveal that the surface Ti−O layer captures CO 2 and dissociates water to supply *H, while a built‐in electric field drives linear intermediates into a subsurface N−Ti−O domain, where the barrier for *OCCO formation is markedly lowered. Crucially, operando XAFS spectroscopy unveils a reversible “breathing‐mode” adsorption of CO 2 within the gradient architecture, wherein the N−Ti−O lattice dynamically expands and contracts in response to interfacial charge accumulation, stabilizing key intermediates. The optimized G−TiNO−425 achieves a C 2 H 4 evolution rate of 73.34 µmol g −1 h −1 with 76.46% product selectivity and 93.14% electron selectivity. Comparative control experiments show that progressive removal of the TiNO interlayer shifts selectivity from C 2 H 4 to CO, establishing a causal link between the gradient interface and C−C coupling. This work provides a design principle for buried interfaces that exploit dynamic structural flexibility to direct complex multi‐electron photocatalysts.