Asymmetric reactors as an innovative approach for optimum microbial fuel cells performance

Abstract

Microbial fuel cells (MFCs) exhibit asymmetric overpotentials and redox potentials/rates at the cathode and anode. However, the impact of this asymmetric on power density and anode microbial community remains poorly understood. In this study, asymmetric reactors were designed for H-type MFCs to investigate this configuration. Contrary to the initial expectation of increased MFC power output with larger cathode volumes, it was unexpectedly found that the small-cathode reactor outperformed the large-cathode reactor, achieving a 61 % increase in maximum power density. Electrochemical characterization revealed a slightly lower charge transfer resistance (29.34 Ω) in the small-cathode reactor with carbon-felt anode biofilm in PBS. Moreover, 16S rRNA sequence analysis showed that the small-cathode reactor harbored a higher proportion of anaerobic bacteria (83 %), lower species diversity, and a higher abundance of exoelectrogens. Additionally, higher abundances of key gene modules (top eight), such as quinone oxidoreductase and citrate cycle, were observed in the small-cathode reactor. The anode biofilms in both reactors also synthesized some vitamins, such as menaquinone and thiamine. Furthermore, compared to the large-cathode reactor, each set of the small-cathode reactor saved ¥ 20, 23 g of borosilicate, and 55 mL of cathode electrolytes. This study sheds light on the interplay between reactor conformation and performance, contributing to the development of low-cost, high-performance MFCs for real field conditions.