Semi‐Confinement Effect Enhances CH4 and C2H4 Production in CO2 Electrocatalytic Reduction

Abstract Achieving fast conversion and precise regulation of product selectivity in electrochemical CO 2 reduction reaction (CO 2 RR) remains a challenge. The space confinement effect provides a theoretical basis for the design of catalysts of different morphology and sizes and reveals the physical phenomena caused by the confinement of electrons and other particles at the nanoscale. In this work, a semi‐confinement concept is introduced and a mesoporous silica nanosphere supported Cu catalyst (Cu‐MSN) is prepared as a typical example to realize CO 2 RR enhancement and product selectivity regulation (methane vs ethylene). The semi‐confined structure partially solves the mass transfer problem of classical confined catalysis. Cu‐MSN allows flexible controls aggregation form of Cu species by loading amount, which achieves a free switch from methane Faraday efficiency of 71.1% to ethylene Faraday efficiency of 66.4%. Various characterizations confirm that the fast adsorption behavior and local coordination structure transformation of Cu (from Cu─O─Si to Cu─O─Cu), which can stabilize key intermediates * CHO and * CO * COH for generating respective methane and ethylene.