Self-driving CO₂-to-formate electro-conversion on Bi film electrode in novel microbial reverse-electrodialysis CO₂ reduction cell

Sustainable energy recovery from microbial electrochemical system provided a promising way for the electrochemical reduction of CO₂ into value-added products, which potentially tackled the problems regarding to the higher electrical energy input. Herein, a microbial reverse-electrodialysis CO₂ reduction cell (MRECC) was developed to achieve self-driving CO₂-to-formate conversion by extracting the energy from salinity gradient and wastewater simultaneously. Results confirmed that assembling 11 cell pairs in reverse electrodialysis (RED) stack of MERCC could meet the potential requirement of Bi film cathode for driving CO₂ reduction. The cell pairs, flow rate of the salt solution (sodium chloride) and the external resistance showed obvious effects on the MRECC performance. Under the optimal condition, the maximum formate concentration of 185.4 ± 6.1 mg L⁻¹ and faradaic efficiency of 88.9 ± 3.2% were yielded with anodic COD removal up to 87.0 ± 4.3%. Energy efficiency indicated nearly 5.8% of extracted energy from salinity gradient and wastewater had been utilized for CO₂-to-formate conversion. Overall, MRECC exhibited a promising platform for CO₂ reduction and value-added chemicals production by using sustainable energy from wastewater.