Comparative study of two carbon fiber cathodes and theoretical analysis in microbial fuel cells on ocean floor

Abstract

Cathode activity plays an important role in the improvement of the microbial fuel cells on ocean floor (BMFCs). A comparison study between Rayon-based (CF-R) and PAN-based carbon fiber (CF-P) cathodes is conducted in the paper. The two carbon fibers were heat treated to improve cell performance (CF-R-H & CF-P-H), and were used to build a new BMFCs structure with a foamy carbon anode. The maximum power density was 112.4 mW m−2 for CF-R-H, followed by 66.6 mW m−2 for CF-R, 49.7 mW m−2 for CF-P-H and 21.6 mW m−2 for CF-P respectively. The higher specific area and deep groove make CF-R have a better power output than with CF-P. Meanwhile, heat treatment of carbon fiber can improve cell power, nearly two-fold higher than heat treatment of plain fiber. This improvement may be due to the quinones group formation to accelerate the reduction of oxygen and electron transfer on the fiber surface in the three phase boundary after heat treatment. Compared to PAN-based carbon fiber, Rayon-based carbon fiber would be preferentially selected as cathode in novel BMFCs design due to its high surface area, low cost and higher power. The comparison research is significant for cathode material selection and cell design.