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

Abstract

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.