Semiconducting Single Wall Carbon Nanotubes as Artificial Pili for Enhanced CO 2 Clostridium ljungdahlii Biofilms

Abstract

Bio-electrochemical systems have been applied successfully for electroreduction of waste carbon dioxide to chemicals. Despite the recent advances in biocathode design and performance, a fundamental understanding of how support electrode materials affect growth, organization and electroactivity of biofilms, and electron transfer across the electrode/bacterium interface is still lacking. Our study demonstrates that surface nanostructuring with semiconducting single-walled carbon nanotubes (SWCNTs) is beneficial for interfacial charge transfer and CO2 reducing activities of Clostridium ljungdahlii biofilms by mimicking the biological functions of conductive bio-wires, not by the commonly suggested mechanism of simply increasing biofilm coverage. We also show that applying a negative potential during biofilm growth is essential for production of electroactive biofilms. 13C isotope labeling experiments conclusively demonstrate that biocathodes can simultaneously utilize ethanol while reducing CO2. Deuterium isotope labeling experiments confirmed that the availability of electrochemically produced H2 as a redox mediator does not limit the efficiency of extracellular electron transfer (EET) and CO2 electro-reduction. These results provide important mechanistic information about EET across the bacterium/material interface in a model biohybrid system.