Enhancing oxygen reduction reaction of supercapacitor microbial fuel cells with electrospun carbon nanofibers composite cathode

Microbial fuel cells (MFCs) as a novel, environmental-friendly wastewater treatment technology have received increasing attention. One of the major challenges for its large-scale application lies in the sluggish oxygen reduction reaction (ORR) kinetics and high catalyst costs. To address this issue, carbon nanofibers (CNFs) composite electrodes that combine both ORR catalytic activity and electrochemical capacitance behavior were fabricated in this study. Results showed that the interconnectivity of fiber aggregates and thorns-like structure of the as-prepared electrodes exhibited a high ORR catalytic activity with low internal resistance (0.18 Ω·cm⁻²) and high exchange current density (13.68 A·m⁻²). When MFCs were equipped with the carbon nanotubes (CNTs)/CNFs electrode, a maximum power density of 306 ± 14 mW·m⁻² was obtained, which was 140% higher than that with Pt/C. Moreover, the CNTs/CNFs electrode showed stable catalytic activity without decline in voltage for 60 d. Both faradaic and non-faradaic processes were involved during GLV discharge. The high apparent capacitance (0.68 ± 0.11 F·cm⁻²) and prolonged discharge time were achieved by the CNTs/CNFs electrode, which could be attributed to the simultaneous effects of electrochemical double layer capacitance and pseudo-capacitance behavior. Together we demonstrated that the great promise of the CNTs/CNFs electrode for MFCs applications.