CuO/g-C₃N₄ heterojunction photocathode enhances the microbial electrosynthesis of acetate through CO₂ reduction

Microbial electrosynthesis (MES) is a novel CO₂ utilization technology. Biocatalysts in this process may use electrons obtained from a photovoltaic system to reduce CO₂ to chemicals and realize energy conversion from solar energy to chemical energy. The photoelectric material CuO/g-C₃N₄ was directly introduced into the MES system using mixed culture as biocatalyst in this study. CuO/g-C₃N₄ can effectively absorb light and presents satisfactory electron and hole separation ability. Photogenerated electrons from CuO/g-C₃N₄ enhanced the electron transfer rate and reduced cathodic charge transfer resistance. CuO/g-C₃N₄ mainly improved the electron supply of electroautotrophic microorganisms through direct electron transfer rather than indirect electron transfer via hydrogen. Photogenerated holes can combine electrons from anode and provide extra driving force to improve the MES performance. Furthermore, the CuO/g-C₃N₄ photocathode also improved the biocatalytic activity by increasing the total amount of biocatalyst and regulating cathodic microbial community composition. Acetate production rate in MES with the CuO/g-C₃N₄ photocathode was 2.6 times higher than that of the control group. This study provides a new strategy for semiconductor photocathodes to improve the MES performance with mixed culture.