Supercritical CO2-induced partial oxidation of Cu enabling tailored Cu2O {111}/{110} facets for enhanced electrochemical CO2 reduction

Supercritical CO 2 works as a soft oxidant to adjust the oxidation states and crystal facets of Cu-based materials. • In the supercritical state, CO 2 dissociates to generate active *O on the Cu surface with water assistance. • Spontaneously reconstructed hydrogen bond network stabilizes the dissociated *O species for Cu oxidation to Cu 2 O {111}. • Ethanol induces thermodynamic selectivity towards Cu 2 O {110} facets via an interfacial adsorption coupling mechanism. • Facet-engineered Cu 2 O-Cu achieves over 73% Faradaic efficiency for CO 2 RR-to-syngas and a tunable CO/H 2 ratio of 0.25−0.94. Catalytic versatility of copper-based catalysts has been demonstrated to arise from synergistic effect between Cu and Cu 2 O with controlled crystal facets, though precise synthesis of crystal facet-tailored Cu-based catalysts remains challenging. Herein, we develop a novel strategy to partially convert Cu nanoparticles into crystallographically defined Cu 2 O with supercritical CO 2 (scCO 2 ) as soft oxidant. Under supercritical fluid state, CO 2 dissociation on Cu surface generates reactive ⁎ O species with assistance of water. The spontaneously reconstructed hydrogen bond network with surrounding water molecules stabilizes these dissociated ⁎ O species for Cu oxidation to Cu 2 O with exposure of {111} crystal facet. While, ethanol introduction induces the formation of Cu 2 O {110} rather than Cu 2 O {111} facet from a thermodynamic perspective through interfacial adsorption coupling. The resulting facet-engineered Cu 2 O-Cu catalysts exhibit excellent electrochemical CO 2 reduction reaction (CO 2 RR) for syngas production with a high Faradaic efficiency of >73% and a tunable CO/H 2 ratio of 0.25–0.94. The enhanced performance is attributed to the interfacial synergy between Cu and Cu 2 O with distinct crystal facets, which facilitates significantly improved electron transfer to the key ⁎ COOH intermediate and thus lowers the energy barrier for CO formation. This interfacial effect is particularly pronounced in Cu/Cu 2 O {110}. This scalable platform enables solvent-directed synthesis of surface-customized metal oxides for functional nanomaterials using scCO 2 as mild oxidant. Supercritical CO 2 dissociates to active ⁎ O species for Cu oxidation to Cu 2 O {111} with assistance of water, while ethanol introduction induces Cu 2 O {110} formation. The face-engineered Cu 2 O-Cu demonstrated enhanced CO 2 RR-to-syngas performance. Download: Download high-res image (92KB) Download: Download full-size image