Nature Catalysis, Published online: 17 August 2026; doi:10.1038/s41929-026-01601-z Achieving a high selectivity for multicarbon alcohols via electrocatalytic CO2 reduction on copper has proved challenging. Here a nanoconfined catalytic reactor strategy integrates localized CO2 supersaturation, leading to the stabilization of ethoxy intermediates and a 70.3% Faradaic efficiency for ethanol at practical current densities.