Confinement‐Driven CO Spillover in CuAg@MSN Tandem Catalysts Boosts C ₂ Selectivity Toward Electrocatalytic CO ₂ Reduction

Tandem catalysts represent a promising paradigm for synergistic electrochemical CO 2 reduction (CO 2 RR) to high‐value multi‐carbon (C 2 ) products, yet coordinate regulation of key intermediates to boost C 2 selectivity remains unclear. Herein, a dual‐phase templating coupled with gas‐phase reduction strategy is exploited to fabricate a series of CuAg@MSN tandem catalysts with tunable Cu/Ag mass ratios. A volcano‐type relationship between catalyst composition and C 2 product selectivity is observed, with CuAg@MSN‐3 (15 wt.% Ag, 40 wt.% Cu) delivering the maximum C 2 Faradaic efficiency (FE) of 75.4% at −1.4 V vs RHE. And a high FE of 63.5% and a large partial current density of 330 mA/cm −2 toward C 2 products on CuAg@MSN‐3 at a cell voltage of 4.5 V in a membrane‐electrode assembly (MEA). In situ infrared spectroscopy and density functional theory (DFT) calculations jointly corroborate that CO generated on Ag sites spontaneously spills over and becomes confined within the mesopores of the MSN framework, markedly promoting CO re‐adsorption on adjacent Cu sites and elevating the * CO surface coverage. This intermediate regulation effectively enhances the reaction rate of C─C coupling and consequently boosts C 2 product selectivity. The present work exemplifies a rational, confinement‐guided design of tandem catalysts for steering reaction intermediates toward desired multicarbon products.