Microbial Fuel Cells for the near and distant future

John Greenman1* and Ioannis Ieropoulos2

1Faculty of Health & Applied Sciences, University of the West of England, Bristol BS16 1QY, UK

2Bristol BioEnergy Centre, BRL, University of the West of England, Bristol BS16 1QY, UK

Microbial Fuel Cells

1911 M.C. Potter (University of Durham); first “discovery”

1985: Picked up again by P. Bennetto in King’s College

1991: Habermann and Pommer; sulphide-mediated MFC, operated over 5-years

2004: Lovley et al.: Electron transport out of the bacterial cell via conductance (“anodophiles”)

2008: Ieropoulos, Greenman, Melhuish: Stacks of small MFC.

[Microbial fuel cells based on carbon veil electrodes: Stack configuration and scalability. International Journal of Energy Research, 32(13): 1228-1240].

• Organic waste IN electrical energy OUT –

a truly green technology

• Biochemical energy in waste turned directly into electricity by bacteria resident in the anode

• Now a rapidly expanding international research field

What are microbial fuel cells and how do they work

• Microbial Fuel Cells (MFCs) consist of two compartments (anode and cathode): each containing an electrode with battery-like terminals

• In the MFC, bacteria form a living community (called a biofilm) around the anode (biofilm-electrode)(This is ecologically and physiologically stable and self-sustainable giving steady state conditions)

• The biofilm-electrode is fed waste organic matter as biofuel and the microbes metabolise the fuel into electrons, H+ (protons), CO2 and new cell progeny.

(It is the new cell progeny that “fixes” the soluble elements into new biomass material, highly suitable for fertilizer)

MFC structure

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How do they work

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ANODE CATHODE

In May 2007, the University of Queensland, Australia completed its prototype MFC as a cooperative effort with Foster's Brewing.

The project failed

(now used as a system to produce caustic soda)

Sizes and shapes of MFC

Miniaturisation• Increases surface area to volume ratio• Minimises proton path distance• Increases power density

Our strategy is therefore:

• Miniaturisation and multiplication

Like batteries, they can be joined in series or parallelin order to step up voltage or current

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Substrate type

Microbial Fuel CellsSubstrate diversity: refined organic compounds

Microbial Fuel Cells

Substrate diversity: non-refined organic mixtures

• Urine• Sewage wastewater• Waste products from the food, fermentation and biotech-industries

Low grade organic substrates (biomass)

CO2

NaturalDecompositione.g. compost heap,e.g. anaerobic digester

MFC

e-

Immediate carbon cycle

BiofuelsCombustion

Power outputs:

The first MFC invented by Potter in 1911 produced a few nanoWatts(nW) of power

Our early nafion-based MFC produced units of (1-2) microWatts (mW)

Our best ceramic based MFC now produce milliWatts (mW),

So a stack of 1000 should produce over 1 Watt of power

MFC-technology combined with new systems for energy storage such as:

Batteries, capacitors, supercapacitors and ultracapacitors

Graphine-basedNanotube-basedAluminium-ion based

What are the Key challenges:

Economic costs of material fabrication and mass manufacture

Carbon veil electrodes – essential but low cost (pence)

Stainless steel net and wires – could be made redundant since relatively expensive

Plastic end bits and tubes – certainly redundant since very expensive

Proton exchange – essential process which now is conducive with economies of scale, due to ceramic materials, which have replaced theexpensive and prone-to-fouling plastic polymer (Nafion)

The current high costs are only because of the prototype stage; oncethe process goes into mass manufacturing, then unit costs are expected to be significantly reduced

The main components of an MFC are:

EcoBot-III

Present state of technology:

EcoBot-IV

Soft wearable MFCs

Origami-MFC (Biodegradable)

In summary• Electrical energy produced• Treatment of waste• Re-cycling of essential elements (e.g. phosphate)• Production of clean water• Working without adverse environmental effects

• Near future: Stacks distributed widely to enable humans to charge phones, laptops, LEDs, small pumps, robots & gadgets • Distant future: charging batteries for Electric vehicles?

MFC stacks embodied in households, factories and farms encourage humans to see the advantages of sludge over oil

CogSysCognitive Systems

The Thriplow Trust

Acknowledgements