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Microbial electrodes

Nature Reviews Methods Primers volume 4, Article number: 60 (2024) Cite this article

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Abstract

Microorganisms interacting with electrodes are at the centre of the evolving research field of microbial electrochemical technologies. The interdisciplinarity of the topic of microbial electrodes, including electrochemistry, microbiology and engineering, provides exciting opportunities and poses challenges. For further consolidation of the field, a solid methodology and approach as well as reporting are required. In this Primer, we provide an overview of the key parameters and main electrochemical methods, and the insights that can be obtained from microbial electrodes. These are exemplified and discussed for two case studies, one related to bioanodes and one related to biocathodes. The main applications of microbial electrodes, as well as challenges and directions for research, are summarized.

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Fig. 1: An electrochemical cell consisting of a microbial electrode coupled to a second (counter) electrode.
Fig. 2: Example results for the bioanode experiment using continuous flow reactors.
Fig. 3: Cyclic voltammograms of an electrode with and without biofilm.
Fig. 4: Analysis of performance through polarization curves and efficiency.
Fig. 5: Methods to determine microbial electrode performance.

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Acknowledgements

The authors thank R. Linssen for creating the initial artwork and J. Pereira for assistance in drafting an initial version of this manuscript.

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Authors and Affiliations

  1. Environmental Technology, Wageningen University & Research, Wageningen, The Netherlands

    Annemiek Ter Heijne

  2. Department Microbial Biotechnology, Helmholtz Centre for Environmental Research GmbH - UFZ, Leipzig, Germany

    Falk Harnisch

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  1. Annemiek Ter Heijne
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  2. Falk Harnisch
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The authors contributed equally to all aspects of the article.

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Correspondence to Annemiek Ter Heijne.

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Nature Reviews Methods Primers thanks John Greenman, Makarand Ghangrekar, Santosh Kumar and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Glossary

Chronoamperometry

An electrochemical method in which a potential is applied to the working electrode (versus the reference electrode), and the resulting current is measured as function of time.

Chronopotentiometry

An electrochemical method in which a current is applied between anode and cathode, and the resulting potential (of the anode or cathode versus the reference electrode) is measured as function of time.

Coulombic efficiency

The part of electrons from a converted substrate that ends up as electric charge (for anodes), or the part of electrons from electric charge that is converted to the (desired) product(s) (for cathodes).

Cyclic voltammetry

(CV). Electrochemical method in which the potential of the working electrode is changed (versus the reference electrode) from an initial value to an end value, and back to the initial value. Such a cycle is typically repeated several times. The resulting current is measured, and information can be gained on the formal potential of electron transfer processes.

Electroactive microorganisms

Microorganisms that can exchange electrons with an electrode. They can either donate electrons to an anode or accept electrons from a cathode.

Energy efficiency

Ratio between the energy harvested in the form of electricity and the energy supplied in the form of substrate (for fuel cell mode), or ratio between the energy in the desired product and the energy supplied in the form of electricity (for electrolysis cell mode).

Extracellular electron transfer

(EET). Electron transfer to solid surfaces that are located outside the microbial cell. EET typically occurs through extracellular charge carriers (for example, cytochromes and flavins) located on the outer cell membrane or via soluble compounds (such as redox shuttles) like phenazines or flavins.

Microbial electrochemical technologies

(METs). Technologies based on the interfacing of microbial and electrochemical conversions. Primary METs are based on the principle that microorganisms perform extracellular electron transfer for which they form biofilms at the anode or cathode.

Microbial electrolysis cell

A type of microbial electrochemical technology that involves coupling a bioanode, which converts organic or inorganic matter, with a thermodynamically unfavourable cathodic reaction, requiring electric power.

Microbial electrosynthesis

The synthesis of a desired product by a microbial electrochemical technology (MET). In a narrower sense, a type of MET in which the reaction of the cathode is the conversion of CO2 to organic products, for example formate or acetate, catalysed by microorganisms performing extracellular electron transfer.

Microbial fuel cell

A type of microbial electrochemical technology that involves coupling a bioanode, which converts organic or inorganic matter, with a thermodynamically favourable cathodic reaction, resulting in the harvesting of electric power.

Polarization curve

A graph in which the potential of the working electrode (versus the reference electrode) is shown as a function of the current. Information can be gained on the losses (overpotentials) that occur at the electrode and how these depend on the rate (current).

Voltage efficiency

Ratio between actual cell voltage and theoretical (equilibrium) cell voltage (for fuel-cell mode), or ratio between theoretical (equilibrium) cell voltage and applied cell voltage (for electrolysis cell mode).

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Ter Heijne, A., Harnisch, F. Microbial electrodes. Nat Rev Methods Primers 4, 60 (2024). https://doi.org/10.1038/s43586-024-00332-4

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