Analysis of polarization methods for elimination of power overshoot in microbial fuel cells

a r t i c l e i n f o Polarization curves from microbial fuel cells (MFCs) often show an unexpectedly large drop in voltage with increased current densities, leading to a phenomenon in the power density curve referred to as " power overshoot ". Linear sweep voltammetry (LSV, 1 mV s − 1) and variable external resistances (at fixed intervals of 20 min) over a single fed-batch cycle in an MFC both resulted in power overshoot in power density curves due to anode potentials. Increasing the anode enrichment time from 30 days to 100 days did not eliminate overshoot, suggesting that insufficient enrichment of the anode biofilm was not the primary cause. Running the reactor at a fixed resistance for a full fed-batch cycle (~ 1 to 2 days), however, completely eliminated the overshoot in the power density curve. These results show that long times at a fixed resistance are needed to stabilize current generation by bacteria in MFCs, and that even relatively slow LSV scan rates and long times between switching circuit loads during a fed-batch cycle may produce inaccurate polarization and power density results for these biological systems. Much of the research involving the use of microbial fuel cells (MFC) for combined electricity production and wastewater treatment is focused on producing the most power through improved reactor designs [1]. However, estimates of the amount of power that can be produced in an MFC are a function of the technique used to obtain polarization data. Linear sweep voltammetry (LSV) is commonly used in MFC studies to obtain polarization data, but high scan rates can overestimate power production [2]. An alternate approach is to vary the circuit resistance at fixed time intervals, ranging from 10 s to 24 h [3,4]. There have been few studies comparing the different techniques , but in one study it was found that power production with scan rates higher than 0.1 mV s − 1 produced higher power densities than those where the circuit resistance was varied [2]. A common problem often encountered when evaluating polarization curves is " power overshoot " [2,5–7]. Power overshoot refers to the response of the system at high current densities (past the maximum power) in a power density curve where the cell voltage and current drop very quickly resulting in a doubling back of the power density curve, producing lower power than previously measured for the lower …