Facet-Engineered Cu ₂ O Catalysts Enable Tunable Cu ⁰ /Cu ⁺ Sites for Selective Electroreduction of Furfural

The electrochemical hydrogenation of furfural (FF) to furfuryl alcohol (FA) represents a sustainable strategy for upgrading biomass-derived feedstocks, where synergistic Cu0/Cu+ sites serve as key active centers. However, elucidating the underlying mechanism and optimizing catalytic performance remain challenging due to the difficulty in precisely tuning the Cu0/Cu+ ratio. Herein, we report a facet-engineering approach to modulate the surface reconstruction of Cu2O, enabling the controlled regulation of Cu oxidation states and enhanced FF-to-FA conversion. Finite element simulations and experimental characterizations reveal that morphological evolution from cubic to cuboctahedral and to octahedral Cu2O nanoparticles progressively intensifies local electric fields, promoting in situ Cu+ reduction and adjusting the Cu0/Cu+ ratio. Among these, the cuboctahedral Cu2O-derived catalyst exhibits the highest FA faradic efficiency (FE) and conversion rate (72.5% and 100.0%), outperforming its cubic (56.5% and 79.0%) and octahedral (59.5% and 85.6%) counterparts. Density functional theory (DFT) calculations corroborated by in situ electrochemical impedance spectroscopy (EIS) reveal that a moderate Cu0/Cu+ ratio optimally lowers the desorption energy of the key intermediate (FCH2OH*) and accelerates interfacial charge transfer, thereby enhancing the overall catalytic performance. This work establishes facet engineering as an effective strategy for tailoring Cu0/Cu+ sites, advancing the rational design of biomass conversion electrocatalysts.