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(-2)) 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(-2), and no diffusion layer, produced 1255 +/- 75 mW m(-2) and did not appreciably vary in performance after 1.5 months of operation. Slightly higher power densities were initially obtained using 100 mg cm(-2) of AC (1310 +/- 70 mW m(-2)) and a PDMS/wipe diffusion layer, although the performance of this cathode decreased to 1050 +/- 70 mW m(-2) after 1.5 months, and 1010 +/- 190 mW m(-2) after 5 months. AC loadings of 43 mg cm(-2) and 100 mg cm(-2) did not appreciably affect performance (with diffusion layers). MFCs with the Pt catalyst and Nafion binder initially produced 1295 +/- 13 mW m(-2), but the performance decreased to 930 +/- 50 mW m(-2) after 1.5 months, and then to 890 +/- 20 mW m(-2) 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.