Abstract
Microbial fuel cells (MFCs), which convert organic waste to electricity, could be used to make the wastewater infrastructure more energy efficient and sustainable. However, platinum and other non-platinum chemical catalysts used for the oxygen reduction reaction (ORR) at the cathode of MFCs are unsustainable due to their high cost and long-term degradation. Aerobic biocathodes, which use microorganisms as the biocatalysts for cathode ORR, are a good alternative to chemical catalysts. In the current work, high-performing aerobic biocathodes with an onset potential for the ORR of +0.4 V vs. Ag/AgCl were enriched from activated sludge in electrochemical half-cells poised at −0.1 and + 0.2 V vs. Ag/AgCl. Gammaproteobacteria, distantly related to any known cultivated gammaproteobacterial lineage, were identified as dominant in these working electrode biofilms (23.3–44.3% of reads in 16S rRNA gene Ion Torrent libraries), and were in very low abundance in non-polarised control working electrode biofilms (0.5–0.7%). These Gammaproteobacteria were therefore most likely responsible for the high activity of biologically catalysed ORR. In MFC tests, a high-performing aerobic biocathode increased peak power 9-fold from 7 to 62 μW cm−2 in comparison to an unmodified carbon cathode, which was similar to peak power with a platinum-doped cathode at 70 μW cm−2.
Highlights
Microbial Fuel Cells (MFCs) are a sustainable energy technology in which biodegradable organic chemicals are converted into electricity using bacteria, and provide a route for the efficient conversion of organic substrates present in wastewater directly into electricity
This resulted from the appearance of an oxygen reduction reaction (ORR) wave with an onset potential value of þ0.4 V, which is considerably more positive than the abiotic ORR wave at t 1⁄4 0 days with an onset potential of approximately À0.1 V
Aerobic biocathode with an onset potential for the ORR of þ0.4 V for ORR have been successfully developed
Summary
Microbial Fuel Cells (MFCs) are a sustainable energy technology in which biodegradable organic chemicals are converted into electricity using bacteria, and provide a route for the efficient conversion of organic substrates present in wastewater directly into electricity. MFCs work by coupling the anaerobic oxidation of organic matter by bacteria at the anode with the reduction of oxygen (most commonly) at the cathode, with electrons flowing through the external circuit and protons moving through solution or across a membrane separator, generating electrical power [2,3]. If MFC technology is to be adopted, capital and operational costs must be lowered. Many of the biggest capital costs in the MFC system arise from the membrane and cathode. The oxygen reduction reaction (ORR) occurs; O2 þ 4Hþ þ 4eÀ / 2H2O
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