Cutting off the upstream and downstream costs for CO2 electroreduction by upcycling fermentation emissions into ethanol

Electrochemical reduction of CO2 (CO2RR), when powered by renewables, opens up a new avenue to mitigate the greenhouse gas while producing value sustainably. Nevertheless, this technology has been largely limited by the high costs of the upstream CO2 feed and downstream product separation. Here we report a hybrid bio-electrochemical system, integrating yeast fermentation with CO2RR in one single cell, that upcycles the fermentation-emitted CO2 into ethanol. We engineer a CuO–Ag tandem electrocatalyst with rationally designed CuO–Ag interfaces that pose minimal impact on the yeast, while efficiently converting CO2 into ethanol against side reactions, such as hydrogen evolution and glucose reduction. We showcase the win–win model enabled by this hybrid system—the CO2RR cost can be cut by 17.8% because the fermentation process provides a free, high-purity CO2 source and free ethanol distillation and in return, the CO2RR reduces the CO2 emissions of fermentation and increases the final ethanol product concentration. This proof-of-concept procedure sheds light on a tempting possibility for a cost-effective CO2 value chain.