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

Despite the advantage of high carbon utilization, CO₂ electroreduction (CO₂ER) in acid is challenged by the competitive hydrogen evolution reaction (HER). Designing confined catalysts is a promising strategy to suppress HER and boost CO₂ER, yet the relationship between the confined structure and catalytic performance remains unclear, limiting rational design. Herein, using Cu₂O@mesoporous SiO₂ core-shell catalysts as a well-defined platform, a volcano-shaped relationship is found between the thickness of mesoporous SiO₂ layer and productivity of multicarbon (C₂₊) products in CO₂ 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 CO₂ concentration, arising from the nanoconfinement effect. At this optimal thickness, the Cu₂O@ mesoporous SiO₂ catalyst achieves a C₂₊ 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.