What is a microbial fuel cell?
A device in which bacteria digest organic matter and generate (some) power.
Dr. Ioannis Ieropoulos and Prof. John Greenman, Bristol Robotics Laboratory
A microbial fuel cell (MFC) or biological fuel cell is a bio-electrochemical system that drives a current by mimicking bacterial interactions found in nature.
In more detail
Bacteria oxidise (remove electrons from) organic molecules in waste water. When they have finished with the electrons they need to get rid of them.
The problems with this method are that you need to add ‘fuel’ and the process generates CO2.
Photo-microbial fuel cell
Microbial solar cells and photomicrobial fuel cells exploit the energy of light and the activity of phototrophic microorganisms to produce electricity. Whereas microbial solar cells use light as the sole energy source, photomicrobial fuel cells degrade organic matter in the presence of light.
Do they work – Chlorella vulgaris?
Photo-microbial fuel cells
A microbial fuel cell (MFC) converts chemical energy, available in a bio-convertible substrate, directly into electricity. To achieve this, bacteria or algae are used as a catalyst to convert substrate into electrons.
Questions and Problems!
What should we use for the anode material? Carbon felt? TCO?
What is the mechanism of electron transfer?
Is there a need for a redox mediator?
What is the role of oxygen in the anodic chamber?
We need to understand the algal interactions better and work out how to improve the device.
We need the electrode to be transparent and have a high surface area for algae to grow on.
The lower left picture is carbon felt, the lower middle picture is TCO glass and the lower right picture show algae growing on limestone.
Transparent conducting films (TCFs) are optically transparent and electrically conductive in thin layers.
Porous Mineral Electrodes
Slip cast method:
1) Mix up slip – titania particles in water and various organic compounds for binding and dispersal;
2) Leave to ball mill for 24 hours;
3) Coat foam with slip;
4) Put in furnace and start sintering cycle – cycle peak at 1200 oC for 4 hours;
5) Coat the ceramic in FTO (fluorine doped tin oxide).
Once the structure is made it has to be coated with a transparent conducting layer
How well cells grow on the surface of the new material is tested
The algae attach themselves directly to the electrode surface
The above left graph shows the ferricyanide conditions for cell growth. The above right graph shows the maximum current produced over time.
-small and directly corresponds to O2 production
Illumination: 652nm, with a power per unit area (flux density) of 5 x E-4 Wcm^-2
Relationship between Fe and O2
Control shows that 5 mM Fe3+ is not toxic to algae on this timescale – for a fixed Fe3+ concentration, oxygen evolution remains the same for hours.
We can use algae and cyanobacteria to produce power – not very much, but we are learning how to improve the cells all the time.
We are starting to understand the different redox processes in the cell and how the algae interact with the electrodes.
We are learning lots of physics, biology, engineering, physics and chemistry.
Pictures courtesy of the Algal Biotechnology Consortium