Switching Methane Selectivity in Carbon Dioxide Electroreduction via Confining Copper(I) Oxide Nanocubes by Polyimine Shells

The selective formation of C1 or C2 products remains a significant challenge in electrochemical carbon dioxide reduction reaction (eCO2RR). Attaining large-scale CH4 production is significant in advancing a carbon-neutral economy. However, hydrogenation simultaneously competes with C–C coupling and hydrogen evolution reactions, which poses substantial obstacles in steering a single reaction pathway. Herein, we promote CH4 production by encapsulating Cu2O nanocubes with polyimine shells serving as diffusion barriers. The simple encapsulation with 50 nm thick shells significantly enhances the CH4-to-C2H4 ratio of Cu2O nanocatalysts from 0.14 to 8.9, achieving a Faradaic efficiency of 50.2% for CH4 at a partial current density of −201 mA cm–2 in alkaline electrolytes. In situ X-ray absorption and Raman spectroscopy demonstrate that encapsulation promotes the accumulation of surface-adsorbed hydroxide ions and significantly stabilized Cu(I) species throughout eCO2RR, with over 82% Cu(I) retention at −200 mA cm–2 for 2 h. Density functional theory calculations support the high coverage of surface-adsorbed hydroxide ions favored *CO hydrogenation over dimerization. This shell encapsulation strategy provides a straightforward approach to modulating eCO2RR mechanisms and product selectivity by tuning local chemical environments and Cu-oxidation states.