CuO/g-C₃N₄/rGO multifunctional photocathode with simultaneous enhancement of electron transfer and substrate mass transfer facilitates microbial electrosynthesis of acetate

Microbial electrosynthesis (MES) is a potential CO₂ fixation technique in which biocatalysts obtain electrons from electrodes as a driving force to reduce CO₂ to more valuable multi-carbon products. In this study, a novel CuO/g-C₃N₄/rGO multifunctional photocatalyst was developed, and an MES system was constructed using mixed culture as a biocatalyst. Compared with CuO/g-C₃N₄, the introduction of rGO into CuO/g-C₃N₄ can enhance light absorption capacity and improve photogenerated electron–hole separation migration efficiency. Under the action of increasing reducing power, CuO/g-C₃N₄/rGO can accelerate electron transport rate to microbes in three ways (indirect via formate, indirect via hydrogen, and direct electron transfer). Furthermore, CuO/g-C₃N₄/rGO was beneficial for enriching electroautotrophic microorganisms and increasing the abundance of Acetobacterium and Arcobacter. In addition, the CO₂ adsorption capacity of the photocatalyst can be improved. At a potential of −0.9 V (versus Ag/AgCl), the acetate production of MES with the CuO/g-C₃N₄/rGO photocathode was 0.27 g/L/d, which was 4.2 times higher than that of the control. This study provides an idea for the design of a multifunctional photocathode for reducing energy consumption and improving MES efficiency by simultaneously enhancing electron transfer and substrate mass transfer.