Cavity-confined Au@Cu₂O yolk-shell nanoreactors enable switchable CH₄/C₂H₄ selectivity

The regulation of product selectivity in electrochemical CO₂ reduction (ECO₂R) remains fundamentally constrained by the dynamic equilibrium between intermediate transport and surface coverage. In this study, we report a progress in catalytic architecture through precision-engineered Au@Cu₂O yolk-shell tandem nanoreactors featuring dual-tunable parameters: cavity confinement dimensions and shell thickness gradients. This structural modulation enables dynamic control over both *CO intermediate enrichment and reaction pathway bifurcation. ECO₂R performance evaluations demonstrate significant product selectivity switching at −1.31 V (vs. reversible hydrogen electrode (RHE)). The Faradaic efficiency (FE) for CH₄ exhibits significant architectural dependence, increasing from 43.02% (thick-shell/large-cavity) to 65.54% (medium-dimension) and then decreasing to 23.26% (thin-shell/small-cavity). Conversely, the FE for C₂H₄ demonstrates an inverse structural correlation, improving from 6.68% (medium-dimension) to 38.73% (thin-shell/small-cavity). The spatial domain-limiting mechanism of the yolk-shell structure directly controls the transition between protonation-dominated CH₄ formation and coupling-driven C₂H₄ production. This work establishes a pioneering paradigm for dynamically steering catalytic selectivity through purely geometrical modulation, bypassing traditional compositional tuning limitations, thereby opening avenues for precision design of advanced electrocatalytic systems.