A novel carbon nanotube modified scaffold creates an efficient biocathode material for improved microbial electrosynthesis

JOURDIN, L.; VICTORIA FLEXER; CHEN, J.; WALLACE, G.G.; FREGUIA, S.; KELLER, J.

Laussane

Conferencia; 65th Annual Meeting of the International Society of Electrochemistry; 2014

International Society of Electrochemistry

Microbial electrosynthesis (MES) is a novel strategy for the renewable production of organic commodities from the microbial reduction of carbon dioxide [1]. Successful optimization of microbial electrosynthesis processes and scale-up to practical applications requires significant performance improvement while maintaining low costs. Here we report on a novel biocompatible, highly conductive three-dimensional cathode synthesized by direct growth of multi-wall carbon nanotubes (CNT) on reticulated vitreous carbon, NanoWeb-RVC [2], for the improvement of MES. The CNT surface appears as a fine roughness on the surface. NanoWeb-RVC allows for an enhanced bacterial attachment and biofilm development within its hierarchical porous structure. Moreover, 1.65 and 2.6 fold higher current density (0.29 mA cm-2) and acetate bioproduction rate (0.103 mM cm-2 day-1) normalized by the total surface area within the porous macrostructure were reached on NanoWeb-RVC versus flat carbon plate control, for the microbial reduction of carbon dioxide by a mixed culture at ‑0.85 V vs. SHE. To the best of our knowledge, this is the first study showing better intrinsic efficiency (normalization by total surface area) for a three-dimensional biocathode versus a flat electrode. Unmodified reticulated vitreous carbon lacking the nanostructure was also tested and found to be far less efficient for MES. However, the combination of the macrostructured RVC with the nanostructured surface modification creates significant advantages. The high surface area to volume ratio of the macroporous RVC maximizes the available biofilm area while ensuring effective mass transfer to and from the biocatalysts. The carbon nanostructure, in turn, enhances the microbe-electrode interaction and microbial extracellular electron transfer. When normalized by projected surface area, very high cathodic current density (3.72 mA cm-2) and acetate production rate (1.325 mM cm-2 day-1) were reached which makes the NanoWeb-RVC an extremely efficient material from an engineering perspective as well. This current density and acetate production rate are the highest reported to date for a cathodic MES.