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 Cu-0 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-C-1 ratio of similar to 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.