Extracellular electron transfer across bio-nano interfaces for CO₂ electroreduction

Area of Science:

• Bioelectrochemistry
• Microbial Electrosynthesis
• Carbon Nanomaterials

Background:

• Acetogenic bacteria convert CO2 and reducing equivalents into valuable chemicals.
• Materials-based bio-electrochemical systems offer direct electron supply for CO2 conversion.
• Carbon nanotube (CNT)-modified biocathodes show promise for microbial electrosynthesis but lack mechanistic understanding of electron transfer.

Purpose of the Study:

• To investigate the mechanism of extracellular charge transfer at the interface between semiconducting single-walled carbon nanotubes (s-SWCNT) and acetogenic bacteria.
• To elucidate the role of direct electron transfer versus H2 mediation in CO2 electro-reduction by bacteria on s-SWCNT biocathodes.
• To determine the efficiency of CO2 electro-reduction at the CNT-bacterium interface.

Main Methods:

• Utilized transistor-based devices to study bacteria/s-SWCNT interactions.
• Employed deuterium isotope labeling to assess the role of electrochemically produced H2 as a redox mediator.
• Quantified CO2 electro-reduction efficiency using isotope labeling studies.

Main Results:

• Evidence suggests direct extracellular electron transfer (EET) occurs at the bacteria/s-SWCNT interface.
• Deuterium labeling indicates that H2 availability does not limit EET and CO2 electro-reduction efficiency for Clostridium ljungdahlii biofilms.
• High Faradaic efficiency for CO2 electro-reduction was observed at the SWCNT/bacterium interface.

Conclusions:

• Direct electron transfer is a key mechanism at the bio-nano interface in microbial electrosynthesis.
• Electrons delivered directly across the electrode/bacterium interface are likely the primary reducing equivalents for CO2 conversion.
• These findings advance the fundamental understanding of extracellular charge transfer in biocathodes for sustainable chemical production.