Impact of Humic Acid on Bioanode Electrochemistry and Horizontal Diffusion Kinetics of Dissolved Organic Carbon in Marine Sediment Microbial Fuel Cells

Abstract The long-term utilisation of marine sediment microbial fuel cells (MSMFCs) faces the challenges of diminished power output and the ambiguous diffusion mechanism of dissolved organic carbon (DOC). Here, a regulation strategy for enhancing MSMFCs performance by adding humic acid (HA) is proposed. Through HA addition, the proportion and abundance of electroactive microbial communities were increased, thus leading to the excellent electrochemical activity of the bioanode. The results demonstrate that HA significantly improves the power generation and DOC horizontal diffusion of MSMFCs, with 1.0 g/L HA showing the optimal enhancement. After a 120-d of operation, the output voltage stabilised at 650 mV, the power density reached 65.32 mW/m 2 , and the coulombic efficiency was 86.8%. These results confirm that HA addition effectively enhances the operating time and energy generation capacity of MSMFCs. Moreover, an innovative DOC transport model incorporating a quantitative relationship among HA concentration, system lifespan, and distance to the anode is established, which provides theoretical support for future siting and long-term application of MSMFCs.