Abstract
In this study, graphite–metal oxide (Gr–MO) composites were produced and explored as potential anodic catalysts for microbial fuel cells. Fe2O3, Fe3O4, or Mn3O4 were used as a catalyst precursor. The morphology and structure of the fabricated materials were analyzed by scanning electron microscopy and X-ray diffraction, respectively, and their corrosion resistance was examined by linear voltammetry. The manufactured Gr–MO electrodes were tested at applied constant potential +0.2 V (vs. Ag/AgCl) in the presence of pure culture Pseudomonas putida 1046 used as a model biocatalyst. The obtained data showed that the applied poising resulted in a generation of anodic currents, which gradually increased during the long-term experiments, indicating a formation of electroactive biofilms on the electrode surfaces. All composite electrodes exhibited higher electrocatalytic activity compared to the non-modified graphite. The highest current density (ca. 100 mA.m−2), exceeding over eight-fold that with graphite, was achieved with Gr–Mn3O4. The additional analyses performed by cyclic voltammetry and electrochemical impedance spectroscopy supported the changes in the electrochemical activity and revealed substantial differences in the mechanism of current generation processes with the use of different catalysts.
Highlights
Bioelectrochemical systems (BESs), utilizing whole living microorganisms, are considered as emerging technologies for numerous applications—as power sources for environmental sensors and electronic devices, for wastewater treatment, desalination, bioremediation, electrosynthesis of valuable products, etc. [1]
After 10 days of operation, the achieved current density with the modified electrodes was 2.5 to 10-times higher than the values achieved with P. putida entrapped in alginate redox-active polymer and carbon felt electrodes, independently of the improved redox conditions [26]. These findings suggest that the utilized metal oxides are appropriate anodic catalysts for the enhancement of the microbial fuel cells (MFCs) electric characteristics
The inclusion of the metal oxides in the graphite matrix was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD)
Summary
Bioelectrochemical systems (BESs), utilizing whole living microorganisms, are considered as emerging technologies for numerous applications—as power sources for environmental sensors and electronic devices, for wastewater treatment, desalination, bioremediation, electrosynthesis of valuable products, etc. [1]. The use of living microorganisms restricts the BES electrical current and power outputs to values determined by the rate of the extracellularly transferred electrons from the microbial cells to the anode, which in turn is limited by the intensity of the cell metabolism. Catalysts 2020, 10, 796 and other constructive components as well as the cultivation conditions for a certain exoelectrogenic strain, have been applied [2,3,4,5,6] to enhance the extracellular electron transfer (EET) and the MFC electrical outputs. To reduce the electron transport limitations from the microorganisms to the anode and to improve the MFC performance, different electrode modifications made by electrodeposition of metallic nanostructures (Ni, NiFe, NiFeP), pyrolysis of polyacrylonitrile (activated carbon nanofiber), doping with metallic salts, etc., have been accomplished [8,9,10,11]
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