Carbon-based cathodes influence biofilm composition and performance in soil microbial fuel cells

May 14, 2023

(Nanowerk News) The cathode material plays an important role in the performance of microbial fuel cells. In this study, the researchers compared the performance of membrane-free air cathode soil microbial fuel cells (SMFCs) using four different cathodes: carbon cloth, Pt-doped carbon cloth, graphite cloth, and Fe-doped carbon nanofibers electrodes. The researchers performed prolonged electrochemical tests, along with microbial taxonomic analysis, to assess the effect of the electrode material on biofilm formation and electrochemical performance.

In a study published in the journal Environmental Science and Ecotechnology (“Effect of carbon-based cathodes on biofilm composition and electrochemical performance in soil microbial fuel cells”), researchers from the University of Bath revealed that Fe-doped carbon nanofibers and Pt-doped carbon cloth cathodes produced stable performance, with peak power densities of 25.5 and 30.4 mW m-−2, each. The graphite felt cathode showed the best electrochemical performance, with a peak power density of 87.3 mW m−2. However, they also show the greatest instability. a, Design and electrode materials of the four SMFCs tested in this study. b, Cathode assembly. c, Experimental setup.

Examination of the microbial community found differences between the anodic and cathodic communities. The anodes are mostly fortified with Geobacter And Pseudomonas species, while the cathodic community is dominated by hydrogen-producing and hydrogenotropic bacteria. This suggests that the hydrogen cycle could be a possible electron transfer mechanism. In addition, the presence of nitrate-reducing bacteria in combination with the cyclic voltammogram results indicated that microbial nitrate reduction occurred at the graphite-compressed cathode.

The use of an innovative Fe-doped carbon nanofiber cathode provides electrochemical performance comparable to Pt-doped carbon cloth, offering a low-cost alternative. However, graphite noticeably outperformed all other electrodes tested but exhibited lower reproducibility and higher bulk transport losses. Microbial taxonomic profiles of cathode biofilms reveal the presence of taxa associated with reduction of oxygen or involvement in the utilization of alternative electron acceptors, such as nitrates.

The results of this study can guide future research on low-cost, high-performance SMFCs for practical applications in energy harvesting and bioremediation. By understanding how electrode materials affect microbial community and electrochemical performance, researchers can accelerate the translation of SMFCs into real-world implementations.

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