Leveraging Intermediates for Selective Acidic CO ₂ ‐to‐CH ₄ Electroreduction via Synergistic Cu‐Based Single Atoms and Subnanoparticles

Electrochemical CO₂ reduction reaction (CO₂RR) to value-added hydrocarbon fuels, such as CH₄, is desirable for a carbon-neutral future but suffers from low selectivity, especially in acidic electrolytes with the competing hydrogen evolution reaction. Leveraging the hydrogenation of *CO intermediate with *H species, while avoiding its desorption or dimerization, is indispensable for selective CO₂-to-CH₄ electroreduction, which also remains challenging. Here, we report a synergistic Cu-based catalyst (Cu_1+SNs) with dual-functional sites on mesoporous silica (SBA-15), comprising isolated Cu single atoms (Cu₁-SAs) and ensembled CuO_x sub-nanoparticles (CuO_x-SNs), enables acidic CO₂RR toward CH₄ production with high performance. The CuO_x-SNs are responsible for CO₂ activation, and their elongated Cu─O─Cu bonds inhibit conventional C─C coupling process of *CO intermediates; while the adjacent Cu₁-SAs play a pivotal role in water dissociation, providing abundant *H species for *CO hydrogenation to *CHO intermediate. Consequently, the synergistic Cu_1+SNs catalyst exhibits outstanding CO₂RR-to-CH₄ performance in acidic electrolyte, reaching a Faradaic efficiency of 70.4%. Remarkably, the robust Cu_1+SNs catalyst also displays high selectivity (> 70%) in pH-universal (acidic, neutral, and alkaline) electrolytes. This work paves a new pathway for designing optimal catalysts with structural heterogeneity toward selective product generation in multistep reactions.