In microbial fuel cells, the surface areas of electrodes play a key role in power generation. Conventionally, the surface area ratio of 1 is considered; but it is neither electrochemically optimized nor economically justified. This study seeks the optimized ratio of Aan/Aca in a double chamber air cathode pure culture microbial fuel cell. Four different anode electrode surface areas were considered in four pure-culture air-cathode MFCs with the Aan/Aca ratios of 0.4, 0.6, 0.8, and 1. Electrochemical impedance spectroscopy (EIS) indicates that as the Aan/Aca ratio increases, total internal resistance decreases from 117.54 Ω to 42.03 Ω in which the share of substrate oxidation resistance ranges from 98% at the ratio of 0.4 to 86% at the ratio of 1. Tafel plot also indicates that exchange current increases from 3.76 mA to 19.27 mA as the anode surface increase suggesting higher reaction rates at higher ratios. The polarization test demonstrates that power output does not follow total resistance pattern and that maximum power density (based on the cathode surface) of 41.67±2.08 mW.m-2 occurs at the Aan/Aca ratio of 0.6. Also, the highest operating current of 1.17 mA is recorded at the Aan/Aca ratio of 0.6 after 90 days of operation. These observations suggest that there is an optimum Aan/Aca ratio of 0.6 in which the charge transfer rate is maximum and substrate oxidation rate is minimum. The results also suggest that there is a correlation between power output and Aan/Aca ratio that predicts the optimum ratio of 0.68 where power output is maximum.

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