CO2 Electroreduction to Multicarbon Products Over Cu2O@Mesoporous SiO2 Confined Catalyst: Relevance of the Shell Thickness

Abstract Despite the advantage of high carbon utilization, CO 2 electroreduction (CO 2 ER) in acid is challenged by the competitive hydrogen evolution reaction (HER). Designing confined catalysts is a promising strategy to suppress HER and boost CO 2 ER, yet the relationship between the confined structure and catalytic performance remains unclear, limiting rational design. Herein, using Cu 2 O@mesoporous SiO 2 core‐shell catalysts as a well‐defined platform, a volcano‐shaped relationship is found between the thickness of mesoporous SiO 2 layer and productivity of multicarbon (C 2+ ) products in CO 2 electroreduction. The optimal shell thickness of 15 nm is identified, with in situ spectroscopies and theoretical simulations attributing this to the trade‐off between the local alkalinity and CO 2 concentration, arising from the nanoconfinement effect. At this optimal thickness, the Cu 2 O@ mesoporous SiO 2 catalyst achieves a C 2+ Faradaic efficiency of 83.1% ± 2.5% and partial current density of 687.8 mA cm −2 in acidic electrolytes, exceeding most reported catalysts. This work provides valuable insights for the rational design of confined catalysts for electrocatalysis.