Electrochemical and impedance characterization of Microbial Fuel Cells based on 2D and 3D anodic electrodes working with seawater microorganisms under continuous operation

• Comparison of the performances of two MFCs based on planar and 3D-packed anodes.
• A mixed seawater-based microbial population used as biofilm grown on the anodes.
• Electrochemical impedance spectroscopy as a tool for energy losses comprehension.
• Carbon-coated saddles satisfy electrical requirements and promote bacterial adhesion.
• Main contribution of internal R is mass-transport between biofilm and electrolyte.

A mixed microbial population naturally presents in seawater was used as active anodic biofilm of two Microbial Fuel Cells (MFCs), employing either a 2D commercial carbon felt or 3D carbon-coated Berl saddles as anode electrodes, with the aim to compare their electrochemical behavior under continuous operation. After an initial increase of the maximum power density, the felt-based cell reduced its performance at 5 months (from 7 to 4 μW cm−2), while the saddle-based MFC exceeds 9 μW cm−2 (after 2 months) and maintained such performance for all the tests. Electrochemical impedance spectroscopy was used to identify the MFCs controlling losses and indicates that the mass-transport limitations at the biofilm-electrolyte interface have the main contribution (>95%) to their internal resistance. The activation resistance was one order of magnitude lower with the Berl saddles than with carbon felt, suggesting an enhanced charge-transfer in the high surface-area 3D electrode, due to an increase in bacteria population growth.

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