Evaluation of Methods for Measuring Internal Resistances of Discharging Microbial Fuel Cells

Microbial fuel cells (MFCs) can generate electricity from organic compounds present in wastewater; however, the resulting small electric power is insufficient for practical applications. This issue occurs because of the high internal resistance of MFCs, which can be addressed by first precisely measuring these internal resistances. However, a standard method for measuring the internal resistance, which depends on the conditions of the MFCs, does not exist. Therefore, five measurement methods in the open-circuit (OC) mode were evaluated in this study. In addition, the internal resistances in the closed-circuit (CC) mode were measured using a one-resistance method and electrochemical impedance spectroscopy (EIS). The values obtained by the linear sweep intensity of current potentiometry (LSIP) method were different from those measured by the other four methods. This was presumably because LSIP involved forcibly flowing electric current in the MFCs. The one-resistance method yielded similar internal resistances to those of the other methods in the OC mode. In addition, this method was applicable in the CC mode. Therefore, the one-resistance method can be used during discharging and for developing MFCs based on discharging.