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

Abstract

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.