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

The selective formation of C 1 or C 2 products remains a significant challenge in electrochemical carbon dioxide reduction reaction (eCO 2 RR). Attaining large-scale CH 4 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 CH 4 production by encapsulating Cu 2 O nanocubes with polyimine shells serving as diffusion barriers. The simple encapsulation with 50 nm thick shells significantly enhances the CH 4 -to-C 2 H 4 ratio of Cu 2 O nanocatalysts from 0.14 to 8.9, achieving a Faradaic efficiency of 50.2% for CH 4 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 eCO 2 RR, 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 eCO 2 RR mechanisms and product selectivity by tuning local chemical environments and Cu-oxidation states.