Protecting Copper Oxidation State via Intermediate Confinement for Selective CO₂ Electroreduction to C₂₊ Fuels

Selective and efficient catalytic conversion of carbon dioxide (CO₂) into value-added fuels and feedstocks provides an ideal avenue to high-density renewable energy storage. An impediment to enabling deep CO₂ reduction to oxygenates and hydrocarbons (e.g., C₂₊ compounds) is the difficulty of coupling carbon–carbon bonds efficiently. Copper in the +1 oxidation state has been thought to be active for catalyzing C₂₊ formation, whereas it is prone to being reduced to Cu⁰ at cathodic potentials. Here we report that catalysts with nanocavities can confine carbon intermediates formed in situ, which in turn covers the local catalyst surface and thereby stabilizes Cu⁺ species. Experimental measurements on multihollow cuprous oxide catalyst exhibit a C₂₊ Faradaic efficiency of 75.2 ± 2.7% at a C₂₊ partial current density of 267 ± 13 mA cm^–2 and a large C₂₊-to-C₁ ratio of ∼7.2. Operando Raman spectra, in conjunction with X-ray absorption studies, confirm that Cu⁺ species in the as-designed catalyst are well retained during CO₂ reduction, which leads to the marked C₂₊ selectivity at a large conversion rate.