Poly(vinylidene fluoride-co-hexafluoropropylene) phase inversion coating as a diffusion layer to enhance the cathode performance in microbial fuel cells

A low cost poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) phase inversion coating was developed as a cathode diffusion layer to enhance the performance of microbial fuel cells (MFCs). A maximum power density of 1430 ± 90 mW m^-2 was achieved at a PVDF-HFP loading of 4.4 mg cm^-2 (4:1 polymer:carbon black), with activated carbon as the oxygen reduction cathode catalyst. This power density was 31% higher than that obtained with a more conventional platinum (Pt) catalyst on carbon cloth (Pt/C) cathode with a poly(tetrafluoroethylene) (PTFE) diffusion layer (1090 ± 30 mW m^-2). The improved performance was due in part to a larger oxygen mass transfer coefficient of 3 × 10^-3 cm s^-1 for the PVDF-HFP coated cathode, compared to 1.7 × 10^-3 cm s ^-1 for the carbon cloth/PTFE-based cathode. The diffusion layer was resistant to electrolyte leakage up to water column heights of 41 ± 0.5 cm (4.4 mg cm^-2 loading of 4:1 polymer:carbon black) to 70 ± 5 cm (8.8 mg cm^-2 loading of 4:1 polymer:carbon black). This new type of PVDF-HFP/carbon black diffusion layer could reduce the cost of manufacturing cathodes for MFCs.