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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