The overshoot phenomenon as a function of internal resistance in microbial fuel

Abstract

A method for assessing the performance of microbial fuel cells (MFCs) is the polarisation sweep where different external resistances are applied at set intervals (sample rates). The resulting power curves often exhibit an overshoot where both power and current decrease concomitantly. To investigate these phenomena, small-scale (1 mL volume) MFCs operated in continuous flow were subjected to polarisation sweeps under various conditions. At shorter sample rates the overshoot was more exaggerated and power generation was overestimated; sampling at 30 s produced 23% higher maximum power than at 3 min. MFCs with an immature anodic biofilm (5 days) exhibited a double overshoot effect, which disappeared after a sufficient adjustment period (5 weeks). Mature MFCs were subject to overshoot when the anode was fed weak (1mM acetate) feedstock with low conductivity (<100 μS) but not when fed with a higher concentration (20 mM acetate) feedstock with high conductivity (>1500 μS). MFCs developed in a pH neutral environment produced overshoot after the anode had been exposed to acidic (pH 3) conditions for 24 h. In contrast, changes to the cathode both in terms of pH and varying catholyte conductivity, although affecting power output did not result in overshoot, suggesting that this is an anodic phenomenon.

Key findings

• ▸Overshoots are more pronounced at shorter sample rates, with 23% higher maximum power at 30s compared to 3min.
• ▸Immature anodic biofilms exhibit a double overshoot effect, which resolves after a sufficient adjustment period.
• ▸Mature MFCs with low-conductivity feedstock exhibit overshoot, while those with high-conductivity feedstock do not.
• ▸Changes to the anode's pH environment can induce overshoot in MFCs developed in a pH-neutral environment.

Keywords

Identifiers

DOI

10.1007/s00449-010-0491-x.

Journal

Unknown journal

Year

2010