[Competition between redox mediator and oxygen in the microbial fuel cell]

Area of Science:

• Biotechnology
• Electrochemistry
• Microbiology

Background:

• Bacterial fuel cells (BFCs) offer sustainable energy solutions.
• Understanding electron transfer mechanisms is crucial for optimizing BFC efficiency.
• Gluconobacter oxydans is a relevant bacterium for bioelectrochemical applications.

Purpose of the Study:

• To evaluate the maximal rates and effective constants of 2,6-dichlorphenolindophenol (DCIP) and oxygen reduction by Gluconobacter oxydans in BFCs.
• To investigate electron transfer pathways and potential competition between the redox mediator and oxygen.
• To assess the feasibility of cost reduction in BFCs utilizing G. oxydans.

Main Methods:

• Measurement of DCIP and oxygen reduction rates under open- and closed-circuit conditions.
• Utilizing membrane fractions of G. oxydans for mediator reduction assays.
• Comparative analysis of electron transfer rates in the presence and absence of DCIP.

Main Results:

• DCIP reduction rates varied between 1.0–1.1 μM s–1 g–1 (open-circuit) and 0.4–0.44 μM s–1 g–1 (closed-circuit).
• Mediator reduction rates using membrane fractions were higher in open-circuit (6.3–6.9 μM s–1 g–1) than closed-circuit (2.2–2.4 μM s–1 g–1) modes.
• Oxygen reduction rates were similar with or without DCIP (0.31–0.32 μM s–1 g–1), indicating independent electron transfer.

Conclusions:

• Electron transfer from G. oxydans redox centers to the mediator is independent.
• There is no competition between the redox mediator (DCIP) and oxygen for electron transfer.
• Optimizing G. oxydans activity can lead to cost-effective microbial fuel cells.