Carbon-based cathodes influence the composition and performance of biofilms in soil

In the context of increasing energy demand and environmental concerns, renewable energy solutions are critical to achieving net-zero emissions by 2050. Microbial electrochemical technologies, such as SMFC, are cost-effective and environmentally friendly, making them attractive options for green energy systems. SMFC utilizes endogenous microorganisms present in soil to convert organic matter into electricity, offering a sustainable energy source and self-sustaining in situ bioremediation strategy for contaminated soil.

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 SMFCs using four different cathodes: carbon cloth, Pt-doped carbon cloth, graphite cloth, and Fe-doped carbon nanofiber 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 Volume 16 of the journal Environmental Science and Ecotechnology in April 2023, researchers from the University of Bath revealed that Fe-doped carbon nanofibers and Pt-doped carbon cloth cathodes delivered 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.

Examination of the microbial community found differences between the anodic and cathodic communities. The anode is dominated by 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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Reference

Writer

Arpita Nandy ^ADaniel Farkas ^BBelén Pepio-Tárrega ^CSandra Martinez-Crepiera ^CEduard Borras ^CClaudius Avignon-Rossa ^BMirella DiLorenzo ^A

Affiliate

^A Department of Chemical Engineering and Center for Biosensors, Bioelectronics & Biodevices (C3Bio), University of Bath, Claverton Down, BA2 7AY, UK

^B Department of Microbial Sciences, University of Surrey, Guildford, GU2 7XH, UK

^C LEITAT Technology Center, C/ de la Innovación, 2, 08225, Terrassa, Barcelona,​​Spain