Three-dimensional porous carbon nanotube sponges for high-performance anodes of microbial fuel cells

• Fabricating 3D sponge anode composed of interconnected CNTs without base materials.
• MFCs with CNT sponge generated 170 W m−3, 40% higher than that from carbon felt.
• Charge transfer resistance of the CNT sponge was 13 times lower than carbon felt.
• Materials cost of producing the CNT sponge was estimated to be ∼$0.1/gcnt.
• 3D CNT sponge synthesis process is scalable.

Highly-porous, light-weight, and inexpensive three-dimensional (3D) sponges consisting of interconnected carbon nanotubes (CNTs) without base materials are synthesized with a facile and scalable one-step chemical vapor deposition process as anode of microbial fuel cells (MFCs). The MFCs generates higher power densities of 2150 W m−3 (per anode volume) or 170 W m−3 (per anode chamber volume), comparable to those of commercial 3D carbon felt electrodes under the same conditions. The high performances are due to excellent charge transfer between CNTs and microbes owing to 13 times lower charge transfer resistance compared to that of carbon felt. The material cost of producing these CNT sponge estimates to be ∼$0.1/gcnt, significantly lower than that of other methods. In addition, the high production rate of about 3.6 g h−1 compared to typical production rate of 0.02 g h−1 of other CNT-based materials makes this process economically viable. The one-step synthesis method allowing self-assembly of 3D CNT sponges as they grow is low cost and scalable, making this a promising method for manufacturing high-performance anodes of MFCs, with broad applicability to microbial electrochemical systems in general.