The microbial fuel cell: electricity from yeast
Submitted by rau on 30 April 2010
For decades, microbes that produce electricity were a biological curiosity. Now, however, researchers foresee a use for them in watches and cameras, as power sources and for bioreactors to generate electricity from organic waste. The microbial fuel cell described here generates an electrical current by diverting electrons from the electron transport chain of yeast. It uses a ‘mediator’ (in this case, methylene blue) to pick up the electrons and transfer them to an external circuit. This process is not very efficient, and this demonstration fuel cell will generate only a very small current. In the classroom, this can provide a stimulating introduction to the study of respiration and permit the study of some of the factors that influence microbial respiration. More recently, mediator-less fuel cells of greater efficiency have been developed, in which the micro-organisms donate electrons directly to the fuel-cell electrodes.
Equipment and materials
Needed by each student or working group
Important: All of the solutions listed below must be made up in 0.1 M phosphate buffer, pH 7.0, not in water.
Image courtesy of Dean Madden
Microbial fuel cells of this type typically generate 0.4–0.6 V and 3–50 mA. If the cell is topped up with solutions as necessary, it will continue to generate electricity for several days.
How the microbial fuel cell works:
In one chamber of the cell, yeast cells are fed on glucose solution. A mediator, methylene blue, enters the yeast cells and takes electrons from the yeast’s electron transport chain. The electrons are then passed to an electrode (anode). The electrons pass through the external circuit and are accepted by potassium hexacyanoferrate (III) in the second chamber of the cell. Hydrogen ions pass through a cation exchange membrane, which separates the two chambers.
Microbial fuel cells of this type typically generate 0.4-0.6 V and 3-50 mA. This is sufficient to power a very low-current motor. If several such cells are joined in series, it is possible to light a light-emitting diode (LED)
Image courtesy of Dean Madden
Potassium hexacyanoferrate (III) is poisonous. Eye protection should be worn when handling this material. If the solution comes into contact with the eyes, flood them with water and seek medical attention. If swallowed, give plenty of water to drink and seek medical attention. If spilled on the skin, the solution should be washed off promptly with water. Local regulations should be observed when disposing of used solution.
To make 0.1 M phosphate buffer, pH 7.0, dissolve 4.08 g Na2HPO4 and 3.29 g
Preparation and timing
It takes about 30 min from the assembly of the fuel cell to the generation of electricity.
Scope for open-ended investigations
Several fuel cells may be joined together in series to give a greater voltage; the current produced will remain the same, however. Conversely, increasing the size of the cell (or the electrode area) will increase the current generated, but not the voltage.
Different mediators and/or types of yeast, such as wine-makers’ or bakers’ yeast, may be used. Note that for safety reasons, the use of this fuel cell with other micro-organisms is not recommended.
Investigate the effect of temperature on the action of the fuel cell (remember to consider what ‘controls’ are necessary when making comparisons of this type).
Microbial fuel cells suitable for school investigations as described here are available from the National Centre for Biotechnology Education (NCBE) at the University of Reading, UKw1.
For those who prefer to build their own fuel cells, following the instructions in this article, the cation exchange membrane and carbon-fibre tissue electrodes are also available from the NCBE. The cation exchange membrane can also be purchased from VWRw2.
Low-current motors suitable for use with a fuel cell such as the one described here are expensive and difficult to find.
Disposal of waste and recycling of materials
Potassium hexacyanoferrate (III) solution is poisonous. Local regulations should be observed when disposing of used solution.
Storage of materials
The microbial fuel cell was developed by Dr Peter Bennetto, formerly of the Department of Chemistry, King’s College, London, UK. It has been adapted for school use by John Schollar and Dean Madden.
w1 – To learn more about the National Centre for Biotechnology Education (NCBE) and to order their fuel cells, see: www.ncbe.reading.ac.uk
w2 – To contact VWR, the supplier of the cation exchange membrane, see: www.vwr.com
Bennetto P (1987) Microbes come to power. New Scientist 114: 36–40
Bennetto HP (1990) Electricity generation by micro-organisms. BIO/technology Education 1: 163–168. This article can be downloaded from the NCBE website: www.ncbe.reading.ac.uk or here: http://tinyurl.com/ncf6ql
Lovley DR (2006) Bug juice: harvesting electricity with micro-organisms. Nature Reviews Microbiology 4: 497–508. doi: 10.1038/nrmicro1442
Sell D (2001) Bioelectrochemical fuel cells. In: Biotechnology. Volume 10: Special Processes (Second edition). Rehm H-J and Reed G (Eds). Frankfurt am Main, Germany: Wiley-VCH. ISBN: 9783527620937
For a complete list of all teaching activities published in Science in School, see: www.scienceinschool.org/teaching
Dr Dean Madden is a biologist working for the National Centre for Biotechnology Education (NCBE)w1 at the University of Reading, UK. The NCBE was established in 1984 and has since gained an international reputation for the development of innovative educational resources. Its materials have been translated into many languages including German, Swedish, French, Dutch and Danish.
This article describes a laboratory practical for demonstrating the electron transport chain. The practical is highly relevant for biology lessons on microbial respiration. It seems obvious to use this practical as an extension of fermentation exercises.
The practical can be used interdisciplinarily at the interface of biotechnology and physics, demonstrating the use of micro-organisms for energy production. It could also be related to the production of bioethanol, as an example of an alternative biotechnological way of producing energy.
Niels Bonderup Dohn, Denmark