Geometric Modulation of Local CO Flux in Ag@Cu₂O Nanoreactors for Steering the CO₂RR Pathway toward High‐Efficacy Methane Production

The electroreduction of carbon dioxide (CO₂ RR) to CH₄ stands as one of the promising paths for resourceful CO₂ utilization in meeting the imminent "carbon-neutral" goal of the near future. Yet, limited success has been witnessed in the development of high-efficiency catalysts imparting satisfactory methane selectivity at a commercially viable current density. Herein, a unique category of CO₂ RR catalysts is fabricated with the yolk-shell nanocell structure, comprising an Ag core and a Cu₂ O shell that resembles the tandem nanoreactor. By fixing the Ag core and tuning the Cu₂ O envelope size, the CO flux arriving at the oxide-derived Cu shell can be regulated, which further modulates the *CO coverage and *H adsorption at the Cu surface, consequently steering the CO₂ RR pathway. Density functional theory simulations show that lower CO coverage favors methane formation via stabilizing the intermediate *CHO. As a result, the best catalyst in the flow cell shows a high CH₄ Faraday efficiency of 74 ± 2% and partial current density of 178 ± 5 mA cm⁻ ² at -1.2 VRHE , ranking above the state-of-the-art catalysts reported today for methane production. These findings mark the significance of precision synthesis in tailoring the catalyst geometry for achieving desired CO₂ RR performance.