Bacteria and yeasts as catalysts in microbial fuel cells: electron transfer from micro-organisms to electrodes for green electricity

TLDR

Microbial fuel cells generate clean electricity and treat water by harnessing electron transfer from bacteria and yeasts, whose diverse metabolic pathways enable direct or mediated contact with electrodes. This review examines the role of microorganisms as catalysts at MFC electrodes. It surveys direct, nanowire, mediated, and metabolite‑based electron transfer mechanisms, highlights key bacterial and emerging yeast species, and discusses electrode functionalization strategies to enhance MFC performance.

Abstract

This article reviews the use of micro-organisms as catalysts at the electrodes of microbial fuel cells (MFCs). The principle of MFCs and their intended use for water treatment and clean electricity production is discussed. We address the different microbial structure and metabolic pathways found in prokaryote (bacteria) and eukaryote (yeasts) that allow the understanding of why electron transfer is possible between a microbe and an electrode. The different mechanisms of microbe–electrode electron transfer are discussed: direct electron transfer or through natural nanowires (pili), mediated electron transfer by natural or artificial redox mediator and finally direct redox transformation of excreted metabolites at the electrodes. This is followed by a review of the different bacteria that have been found and studied in MFCs mainly in the anodic compartment but also more recently in the cathodic side of the fuel cells. A perspective on the possible advantages and challenges of the use of yeasts in MFCs is provided, as this aspect has not been thoroughly studied so far. The fourth section of the review focuses on how to improve the performance and sustainability of MFCs through the functionalisation of the electrode surface, for instance with the covalent grafting of redox mediators and/or enzymes.