Highly dispersed Cu-Cu₂O-CeO_x interfaces on reduced graphene oxide for CO₂ electroreduction to C₂₊ products

The Cu⁰-Cu⁺ interfaces play a key role in the electrochemical CO₂ reduction reaction (CO₂RR) to produce multi-carbon products (C₂₊), however, it is difficult for Cu⁺ to exist stably under reducing conditions. Herein, we construct highly dispersed and stable Cu-Cu₂O-CeO_x interface on reduced graphene oxide (rGO) for CO₂ electroreduction to C₂₊ products. During the synthesis process, utilizing strong electrostatic interactions, the complex ions of Cu²⁺ and Ce³⁺ are uniformly adsorbed on the surface of graphene oxide. Then, under the solvothermal reaction of ethylene glycol and thiourea, the two metal complex ions are converted into highly dispersed and ultrafine Cu₂S-CeO_x nanocomposites on rGO. Interestingly, CeO_x and thiourea synergistically regulate the generation of only Cu⁺. Under the CO₂RR process, the reconstruction of Cu₂S promotes the formation of Cu⁰ and Cu₂O species. CeO_x stabilizes partial Cu⁺ species and promotes the formation of Cu-Cu₂O-CeO_x composite interface. With the help of synergistic effect of Cu⁰, Cu⁺ and CeO_x, the optimized reaction interface achieves the Faradaic efficiency (FE) of 74.5 % for C₂₊ products with the current density of 230 mA cm^-2 at -0.9 V versus the reversible hydrogen electrode. In situ attenuate total reflectance-infrared absorption spectroscopy (ATR-IRAS) spectra show that the composite interfaces promote the adsorption and activation of H₂O and CO₂, improve the surface coverage of CO intermediates (*CO), and thus accelerate the CC coupling process.