Selective Electroreduction of CO2 to Ethanol via Cobalt-Copper Tandem Catalysts

The selective electrocatalytic conversion of CO2 into multicarbon products, such as ethanol, is a major technological challenge. Currently, this reactivity is limited by the sluggish formation of C-C bonds inherent to many single-site catalysts. Here, we report a new tandem electrocatalyst based on earth-abundant elements, which facilitates the selective CO2-to-ethanol conversion. The composite catalyst consists of neighboring cobalt and copper atoms anchored to electrically conductive nitrogen-doped carbon. At low overpotentials (E = -0.8 V vs reversible hydrogen electrode), the system shows high selectivity for ethanol production (faradaic efficiencies >70%), while retaining its reactivity and stability for 18 h. A CO spillover mechanism is proposed as the basis for the observed selectivity, where efficient CO generation at Co sites leads to high local CO concentrations at neighboring Cu sites, thereby favoring C-C coupling and ethanol formation. Operando X-ray absorption spectroscopy reveals a dynamic transformation of the single-site Cu into Cu clusters as actual active sites. In situ infrared spectroscopy reveals the formation of intermediate CO at Co sites, which undergo subsequent spillover and C-C coupling on the Cu clusters. This design concept offers new avenues for noble metal-free tandem electrocatalysts for the conversion of CO2-to-multicarbon products.