The electrosynthesis of higher-order alcohols from carbon dioxide and carbon monoxide addresses the need for the long-term storage of renewable electricity; unfortunately, the present-day performance remains below what is needed for practical applications. Here we report a catalyst design strategy that promotes C3 formation via the nanoconfinement of C2 intermediates, and thereby promotes C2:C1 coupling inside a reactive nanocavity. We first employed finite-element method simulations to assess the potential for the retention and binding of C2 intermediates as a function of cavity structure. We then developed a method of synthesizing open Cu nanocavity structures with a tunable geometry via the electroreduction of Cu2O cavities formed through acidic etching. The nanocavities showed a morphology-driven shift in selectivity from C2 to C3 products during the carbon monoxide electroreduction, to reach a propanol Faradaic efficiency of 21 ± 1% at a conversion rate of 7.8 ± 0.5 mA cm−2 at −0.56 V versus a reversible hydrogen electrode.