Development and evaluation of carbon and binder loading in low-cost activated carbon cathodes for air-cathode microbial fuel cells{

Activated carbon (AC) air cathodes were constructed using variable amounts of carbon (43–171 mg cm) and an inexpensive binder (10 wt% polytetrafluoroethylene, PTFE), and with or without a porous cloth wipe-based diffusion layer (DL) that was sealed with PDMS. The cathodes with the highest AC loading of 171 mg cm, and no diffusion layer, produced 1255 ¡ 75 mW m and did not appreciably vary in performance after 1.5 months of operation. Slightly higher power densities were initially obtained using 100 mg cm of AC (1310 ¡ 70 mW m) and a PDMS/wipe diffusion layer, although the performance of this cathode decreased to 1050 ¡ 70 mW m after 1.5 months, and 1010 ¡ 190 mW m after 5 months. AC loadings of 43 mg cm and 100 mg cm did not appreciably affect performance (with diffusion layers). MFCs with the Pt catalyst and Nafion binder initially produced 1295 ¡ 13 mW m, but the performance decreased to 930 ¡ 50 mW m after 1.5 months, and then to 890 ¡ 20 mW m after 5 months. Cathode performance was optimized for all cathodes by using the least amount of PTFE binder (10%, in tests using up to 40%). These results provide a method to construct cathodes for MFCs that use only inexpensive AC and a PTFE, while producing power densities similar to those of Pt/C cathodes. The methods used here to make these cathodes will enable further tests on carbon materials in order to optimize and extend the lifetime of AC cathodes in MFCs.