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

ABSTRACT Electrochemical CO ₂ reduction reaction (CO ₂ RR) to value‐added hydrocarbon fuels, such as CH ₄ , 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 CO ₂ ‐to‐CH ₄ 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 (Cu ₁ ‐SAs) and ensembled CuO _x sub‐nanoparticles (CuO _x ‐SNs), enables acidic CO ₂ RR toward CH ₄ production with high performance. The CuO _x ‐SNs are responsible for CO ₂ activation, and their elongated Cu─O─Cu bonds inhibit conventional C─C coupling process of *CO intermediates; while the adjacent Cu ₁ ‐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 CO ₂ RR‐to‐CH ₄ 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.