Enhanced electron transfer on microbial electrosynthesis biocathode by polypyrrole-coated acetogens

Area of Science:

• Microbial Electrosynthesis
• Bioelectrochemistry
• Sustainable Chemistry

Background:

• Extracellular electron transfer (EET) is crucial for microbial electrosynthesis systems (MESs).
• Enhancing EET is key to improving the efficiency of MES applications.
• Polypyrrole (PPy) is a high-conductivity polymer with potential for bioelectrochemical applications.

Purpose of the Study:

• To investigate the effect of in situ polypyrrole (PPy) coating on acetogenic bacteria for enhanced EET in MESs.
• To evaluate the impact of PPy coating on biocathode performance, including charge transfer resistance and acetate production.
• To elucidate the electron transfer pathways involved and the role of PPy in stimulating these pathways.

Main Methods:

• In situ coating of mixed culture acetogens with polypyrrole (PPy).
• Fabrication and inoculation of PPy-coated bacteria onto the cathode of MES.
• Electrochemical impedance spectroscopy to measure charge transfer resistance.
• Analysis of acetate production rate and Faradaic efficiency.
• Microbial community analysis and gene expression studies.

Main Results:

• PPy-coated biocathodes exhibited significantly reduced charge transfer resistance (33%-70% of uncoated).
• Acetate production rate and Faradaic efficiency increased by 3 to 6 times with PPy coating.
• Microbial communities on coated and uncoated biocathodes were dominated by Acetobacterium, Desulfovibrio, and Acinetobacter after 960 hours.
• PPy coating stimulated electron transfer pathways involving the quinone loop and NADH dehydrogenase to ubiquinone.
• Low expression of C-type cytochromes suggests a minor role in inward EET.

Conclusions:

• In situ PPy coating is an effective strategy to enhance EET and improve biocathode performance in MESs.
• PPy coating facilitates electron transfer by stimulating specific microbial pathways.
• The findings provide valuable information for the application of conductive polymers in microbial electrosynthesis.