Functionalised graphite felt anodes for enhanced power generation in membrane-less soil microbial fuel cells

There is a global need for sustainable and clean technologies that can actively contribute to reach the net-zero carbon goal by 2050. Soil microbial fuel cell (SMFC) technology has a huge potential as affordable and green energy harvesting source and as a carbon-neutral bioremediation strategy for the treatment of pollutant lands. In this work, for the first time the use of cobalt oxide modified graphite felt (GF) electrodes is explored as the anode material in SMFCs, with the aim of promoting the development of a high-performing electroactive biofilm and, therefore, boosting the electrocatalytic processes. Cobalt oxide (Co3O4) nanoflowers, obtained by calcinating cobalt hydroxide salt hydrothermally deposited onto graphite felt, decreased the hydrophobicity, the conductivity and consequently the electrochemical activity of carbon-based electrodes. Physiochemical characterisation studies revealed that the cobalt nanostructures were uniformly deposited and anchored onto the GF electrode. Nonetheless, when Co3O4-GF anodes were tested in a membrane-less, air-cathode SMFC device, after an initial boost in power performance, the activity decayed with time, probably due to Co3O4 leaching. Interweaving of Co3O4 functionalised GF electrodes with polyaniline (PANI) (PANI-Co3O4-GF anode), led to a highly performing SMFC system that generated a peak power density of 70 mW m-2, corresponding to a current density of 143 mA m-2. This value of power density was nearly three times greater than the power generated by the same SMFC system but with a plain GF anode. The interweaving of PANI onto the Co3O4-GF electrode led to a porous structure that, while favouring microbial attachment, provides stability to the electrode over prolonged periods of operation. Overall, these results provide exciting perspectives on the development of composite carbon-based anode materials for highly performing soil microbial fuel cells, thus inspiring future trends in the field