The effect of internal capacitance on power quality and energy efficiency in a tubular microbial fuel cell

Abstract

The pseudo-capacitive behaviour of a high surface area carbon veil electrode in a tubular microbial fuel cell (MFC) was investigated as a mechanism to enhance power quality and energy efficiency. Accumulated charge and energy from the anodic biofilm after prolonged open circuit times (1–120min) were compared against equivalent periods of steady state loading (R=100–3000Ω). A significant difference in the amount of accumulated charge with different loads was observed, resulting in 1.051C (R=100Ω) compared to 0.006C (R=3kΩ). The automated application of short open and closed circuit (0.5–10s) cycles resulted in an increase of power/current production (closed circuit alone), but presented lower efficiency considering entire open and closed period. The cumulative charge on the carbon veil electrode with biofilm was 39,807Cm−2 at 100Ω. Electrochemical Impedance Spectroscopy (EIS) showed that the Helmholtz layer presented a double layer capacitance of more than ten times the biofilm on electrode. The results indicate that the capacitive behaviour could be utilized to increase the power quality, i.e. its availability/applicability with respect to the operation of low power consuming devices.