Power densities using different cathode catalysts (Pt and CoTMPP) and polymer binders (nafion and PTFE) in single chamber microbial fuel cells.

Cathode catalysts and binders were examined for their effect on power densities in single chamber, air-cathode, microbial fuel cells (MFCs). Chronopotentiometry tests indicated thatthe cathode potential was only slightly reduced (20-40 mV) when Pt loadings were decreased from 2 to 0.1 mg cm(-2), and that Nafion performed better as a Pt binder than poly(tetrafluoroethylene) (PTFE). Replacing the precious-metal Pt catalyst (0.5 mg cm(-2); Nafion binder) with a cobalt material (cobalt tetramethylphenylporphyrin, CoTMPP) produced slightly improved cathode performance above 0.6 mA cm(-2), but reduced performance (<40 mV) at lower current densities. MFC fed batch tests conducted for 35 cycles (31 days) using glucose showed that replacement of the Nafion binder used for the cathode catalyst (0.5 mg of Pt cm(-2)) with PTFE reduced the maximum power densities (from 400 +/- 10 to 480 +/- 20 mW m(-2) to 331 +/- 3 to 360 +/- 10 mW m(-2)). When the Pt loading on cathode was reduced to 0.1 mg cm(-2), the maximum power density of MFC was reduced on average by 19% (379 +/- 5 to 301 +/- 15 mW m(-2); Nafion binder). Power densities with CoTMPP were only 12% (369 +/- 8 mW m(-2)) lower over 25 cycles than those obtained with Pt (0.5 mg cm(-2); Nafion binder). Power densities obtained using with catalysts on the cathodes were approximately 4 times more than those obtained using a plain carbon electrode. These results demonstrate that cathodes used in MFCs can contain very little Pt, and that the Pt can even be replaced with a non-precious metal catalyst such as a CoTMPP with only slightly reduced performance.