Investigation of performance losses in microbial fuel cells with low platinum loadings on air-cathodes

Abstract

The effect of platinum (Pt) loadings of air-cathodes in the 0-0.5 mg cm-2 range on single chamber microbial fuel cell (MFC) performance and cathode impedance was evaluated. In MFC tests, reducing benchmarking Pt loading of 0.5 mg cm-2 to 0.1-0 mg cm-2 decreased maximum power density by between 38% and 84%. The decrease in cathode open circuit potential with reduced loadings was small down to a catalyst loading of 0.03 mg cm-2, but was significant when the loading was further reduced to 0.01 or 0 mg cm-2. Impedance measurements of cathodes revealed that both charge-transfer and diffusion resistance increase with decreasing catalyst loadings on cathodes. Charge-transfer resistance of benchmarking cathode increased to a small extent when loadings were reduced to 0.1-0.03 mg cm-2. Below 0.03 mg cm-2, dramatic increase of charge-transfer resistance suggested that 0.03 mg cm-2 can be considered as the minimum Pt loading for which kinetic limitations are not of great concern and can be overcome to a large extent compared to lower loadings. In comparison to charge-transfer resistance, diffusion resistance differed more significantly between the loadings of 0.03 and 0.5 mg cm-2; and it was therefore the main component that changed the internal resistance of these cathodes.