Enhancing anode intrinsic capacitance improves the performance of microbial fuel cells in wastewater treatment

Capacitive anodes hold promise for enhancing microbial fuel cells (MFCs) in wastewater treatment, yet the impact of capacitive anodes with different capacitance type and mass specific capacitance on the performance remains unclear. This study compared electric double layer (EDL) and pseudo-capacitance anodes, evaluating their power generation and pollutant removal in MFCs. Results showed that EDL anode with 2 mg mass loading achieved 5.48-fold higher specific capacitance (27.95 ± 7.39 F/g) than pseudo-capacitance anodes (5.10 ± 1.48 F/g), enabling a higher maximum power density (P_max) of 561.09 ± 109.54 mW/m². Increasing EDL mass loading further amplified capacitive current contributions (39 %), P_max and stored charge. Although there was no obvious effect on sulfamethoxazole (SMX) (a persistent organic pollutant) removal, COD removal was improved in MFCs with capacitive anodes. EDL anode with 6 mg mass loading had satisfactory comprehensive performance of power generation and COD removal (>80 %). Based on Pearson correlation analysis and microbial co-occurrence networks, the mechanism of capacitive anodes to enhance MFCs power generation by increasing capacitive current, electrochemically active bacteria (EAB) abundance, and adenosine triphosphate (ATP) content and dehydrogenase activity (DHA) was revealed. These findings demonstrate that enhancing the anode intrinsic capacitance, particularly EDL capacitance, can significantly improve MFCs performance. This study will not only provide a new direction for the electrode design of MFCs, but also advance the development of MFCs as dual-functional devices integrating power generation and energy storage capabilities in wastewater treatment.