Balancing surface area and electrical conductivity in carbon nanotube composite networks to enhance thermophilic microbial fuel cell performance

Microbial fuel cells (MFCs) enable simultaneous energy generation and organic waste treatment; however, their performance is often limited by inefficient electron transfer at the microbe–electrode interface. Carbon nanotubes (CNTs) have been widely investigated as anode materials owing to their high electrical conductivity and large specific surface area, yet how surface area and electrical conductivity jointly influence anode performance under thermophilic conditions remain unclear. In this study, two types of single-walled CNTs, super-growth CNTs (SG-CNTs), which possess high surface area, and enhanced direct injection pyrolytic synthesis CNTs (eDIPS-CNTs), which possess high electrical conductivity, were used to fabricate anodes individually and in controlled mixtures on stainless-steel mesh substrates. The anodes were evaluated in thermophilic MFCs inoculated with compost-derived microbial communities at 55 °C. All CNT-based anodes exhibited enhanced redox activity relative to CNT-free controls, with distinct redox features observed at −0.55 to −0.60 V vs Ag/AgCl. Notably, the SG-CNT/eDIPS-CNT anode prepared at a 1:1 (w/w) ratio delivered the highest current response and achieved approximately one order of magnitude higher relative electrical output than the CNT-free control. Gas evolution and microbial community analyses further suggest that CNT composition influences anaerobic microbial electron utilization without markedly inhibiting microbial activity. These findings highlight the importance of the nanoscale CNT-network architecture in optimizing electron transfer in thermophilic MFCs.