Correlation of Overvoltages and Current Densities to Estimate Optimal Electrode Size for Sediment Microbial Fuel Cells

We propose a method to determine the optimal electrode size of sediment microbial fuel cells (SMFCs). Four SMFCs presented a proportional increase in the current to the electrode size of the MFCs at day16. From the I-V curves of the SMFCs, four plots of current versus electrode size (I-E_size plots) were obtained, which displayed high R² values ranging from 0.980 to 0.994. At day47, however, V-I curves deviated in one of the four MFCs, such that the I-E_size plots obtained from the I-V curves were inappropriate for estimating the electrode size. We found that the curves of overvoltage against the current density (η-j curves) were comparable in the SMFCs, suggesting that the overvoltage is inversely proportional to the electrode size of the MFCs. The I-E_size plots corrected by using the η-j curves had high R² values of over 0.978, indicating that the η-j curves can be used for estimating the electrode size when the working voltage to current density ratio is different in SMFCs. Size does matter: Determining the optimal electrode size for sediment microbial fuel cells (SMFCs) is important to reduce the costs of constructing SMFC systems. We demonstrate that the optimal electrode size for SMFCs can be estimated from the correlation of voltage and current or overvoltage and current using the SMFCs having different electrode size. These findings may contribute to lower costs for installing and maintaining SMFCs.