A novel structure of scalable air-cathode without Nafion and Pt by rolling activated carbon and PTFE as catalyst layer in microbial fuel cells

Single chambered air-cathode microbial fuel cells (MFCs) are promising to be scaled up as sustainable wastewater treatment systems. However, the current air-cathode made by brushing noble metal catalyst and Nafion binder onto carbon matrix becomes one of the biggest bottlenecks for the further development of MFCs due to its high cost, huge labor-consuming and less accuracy. A novel structure of air-cathode was constructed here by rolling activated carbon (AC) and polytetrafluoroethylene (PTFE) as catalyst layer to enhance the reproducibility and improve the performance by an optimized three-phase interface (TPI). Air-cathodes with AC/PTFE ratios of 3, 5, 6, 8 and 11 in the catalyst layer were prepared, and the physical and electrochemical techniques were employed to investigate their surface microstructure and electrochemical characteristics. Uniform cross-linked ropiness networks were observed from the catalyst layer of all the cathodes and increased as the AC/PTFE ratio decreased, while the exchange currents were positively related to this ratio. Maximum power densities (MPDs) decreased as follows: AC/PTFE = 6 (802 mW m−2 at 3.4 A m−2), 5 (704 mW m−2 at 2.2 mA m−2), 8 (647 mW m−2 at 2.2 A m−2), 3 (597 mW m−2 at 2.1 A m−2) and 11 (584 mW m−2 at 2.0 mA m−2), which was due to the changes of both the capacitance characteristics and conductivities according to the electrochemical impedance spectrum (EIS) analysis. This study demonstrated that inexpensive, highly reproducible, high performance and scalable air-cathode can be produced by rolling method without using noble metal and expensive binder.

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► A novel air-cathode was made by rolling activated carbon/PTFE as catalyst layer.
► This air-cathode was scalable without using noble metal and expensive binder.
► A maximum power density of 802 mW m−2 was obtained at 3.4 A m−2.
► The three-phase interface was optimized as AC/PTFE ratio of 6.
► The rolling method exhibited a better reproducibility compared to brushing method.