Enhancing performance of microbial electrosynthesis process via nano zero valent iron/graphitic carbon nitride photoelectrocatalyst on carbon felt electrode

The increase in atmospheric carbon dioxide (CO₂) concentrations is the key factor in raising the issues of global warming and climate change. Globally, nations have tried to mitigate the high levels of atmospheric CO₂ through the application of carbon capture and utilization (CCU) strategies. The microbial electrosynthesis (MES) cell is a promising and sustainable integration of CCU towards decarbonization and biofuel production. However, the cathodic reactions in MES are being limited by the loss of applied voltage created by cathodic overpotentials, lowering the production of biochemicals (e.g., acetate). To overcome the limitations, this study synthesized nano zero-valent iron photoelectrocatalysts/graphitic carbon nitride (nZVI/g-C₃N₄) as a composite catalyst in-situ coating a carbon felt electrode to simultaneously enhance photo-induced charge separation and stimulate in situ hydrogen evolution for microbial carbon conversion into acetate. The results exhibited the promising performance of nZVI/ g-C₃N₄ during 14 days of operation under light exposure. nZVI/g-C₃N₄ revealed higher acetate concentrations (59.9 mg/L), higher HCO₃⁻ consumption (67.9 mg/L), 73.7 % of coulombic efficiency, and carbon conversion efficiency of 27.4 %. These outcomes suggest that the conductive properties of nZVI lowered the activation barrier for photogenerated electrons to flow in situ hydrogen evaluation reaction (HER), mediating the carbon reduction to acetate. However, due to the possible metabolism shift created by product accumulation, the effective nZVI/g-C₃N₄ may be associated with improved HER, aiding acetate consumption for further possible microbial growth. Thus, future studies should focus on modifying MES considering product extraction and optimal acclimation period to direct electron flow towards carbon reduction, along with HER to mediate acetate synthesis.