One-step fabrication of binder-free air cathode for microbial fuel cells by using balsa wood biochar

Efficient cathode performance is crucial for the power generation of microbial fuel cells (MFCs). Therefore, the development of a cost effective and efficient cathode is urgently needed for the wider application of MFCs. In this study, a novel biochar air cathode with naturally porous structure and high oxygen reduction reaction (ORR) activity prepared from the pyrolysis of Balsa Wood chip at 800 °C was proposed. The biochar chips can be installed directly in the MFC as an air cathode without the need to apply expensive catalysts, binders and a gas diffusion layers. In the single chamber MFC tests, the biochar air cathode achieved a maximum power density of 200 mW/m² which was comparable to those of the other biochar based air cathodes. Moreover, when they were used in soil MFCs, our results showed that the chip thickness had effect on the performance of the soil MFCs. The 3.5 mm biochar produced the highest power density of 72 mW/m², which was 45% higher than that of the soil MFC equipped with common carbon felt floating cathode. These findings demonstrate for the first time, that whole biochar chip could be considered as an effective and environmental-friendly material for the production of binder- and catalysis-free air cathode.