Lateral CO diffusion on micropatterned Ag/CuO arrays enables efficient CO₂-to-C₂₊ electroreduction

Multi-carbon (C₂₊) products from the electrocatalytic CO₂ reduction reaction (CO₂RR) hold significant industrial value. Tandem Cu-based catalytic systems can markedly improve C₂₊ selectivity, but their performance is often limited by suboptimal spatial configurations. In this study, we fabricate layer-stacked Ag/CuO and array-patterned Ag/CuO catalysts with tunable array spacings (200, 400, and 800 μm) to decouple CO generation and consumption, thereby enabling precise regulation of *CO flux. The array-patterned Ag/CuO systems markedly outperform layer-stacked designs, indicating that lateral CO diffusion is more effective than longitudinal diffusion. Moreover, C₂₊ selectivity strongly depends on array spacing, with the best performance achieved at 400 μm (Ag-CuO-400), reaching a faradaic efficiency (FE) of 63% for ethylene at 300 mA cm^-2 in a neutral electrolyte. Through operando infrared microscopy, we visualize the *CO coverage distribution in real time, revealing an effective lateral CO diffusion length of approximately 200 μm. This corresponds to an optimal balance between *CO supply and C-C coupling activity on the Ag-CuO-400 catalyst. This work underscores the significance of anisotropic *CO transport and provides a design strategy for spatially structured tandem catalysts.