Selective and efficient catalytic conversion of carbon dioxide (CO 2 ) into value-added fuels and feedstocks provides an ideal avenue to high-density renewable energy storage. An impediment to enabling deep CO 2 reduction to oxygenates and hydrocarbons (e.g., C 2+ compounds) is the difficulty of coupling carbon−carbon bonds efficiently. Copper in the +1 oxidation state has been thought to be active for catalyzing C 2+ 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 C 2+ Faradaic efficiency of 75.2 ± 2.7% at a C 2+ partial current density of 267 ± 13 mA cm −2 and a large C 2+ -to-C 1 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 CO 2 reduction, which leads to the marked C 2+ selectivity at a large conversion rate.

Copper is currently the material with the most promise as catalyst to drive carbon dioxide (CO 2 ) electroreduction to produce value-added multicarbon (C 2+ ) compounds. However, a copper catalyst on a carbon-based gas diffusion layer electrode often has poor stabilityespecially when performing at high current densitiesowing to electrolyte flooding caused by the hydrophobicity decrease of the gas diffusion layer during operation. Here, we report a bioinspired copper catalyst on a gas diffusion layer that mimics the unique hierarchical structuring of Setaria's hydrophobic leaves. This hierarchical copper structure endows the CO 2 reduction electrode with sufficient hydrophobicity to build a robust gas−liquid−solid triple-phase boundary, which can not only trap more CO 2 close to the active copper surface but also effectively resist electrolyte flooding even under high-rate operation. We consequently achieved a high C 2+ production rate of 255 ± 5.7 mA cm −2 with a 64 ± 1.4% faradaic efficiency, as well as outstanding operational stability at 300 mA cm −2 over 45 h in a flow reactor, largely outperforming its wettable copper counterparts.

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