Eco-friendly robot powered by organic waste

Researchers at the University of the West of England (UWE) in Bristol have developed a microbial fuel cell about the size of a mobile phone that could be powered by organic household waste. The cell is being used to run a small light-sensitive robot.

The bacteria-driven cell directly converts biochemical energy into electricity. It uses Escherichia coli bacteria to break down carbohydrates and release hydrogen atoms.

The cell also contains chemicals that drive a series of redox, reduction and oxidation reactions, stripping electrons from the hydrogen atoms and delivering them to the fuel cell’s anode. This creates a voltage that can be used to power a circuit.

UWE’s Chris Melhuish said the organic battery can produce eight times as much energy as other microbial fuel cells. Power is produced by use of a microbial cell permeable chemical mediator, which in its oxidised form intercepts a proportion of NADH (nicotinamide adenine dinucleotide) within the microbial cell and oxidises it to NAD+.

The now reduced form of the mediator is also cell-permeable and diffuses from the microbial cell to the anode where the reduced redox mediator is then electro-catalytically re-oxidised.

In addition, cell metabolism produces protons in the anodic chamber, which may migrate through a proton selective membrane to the cathodic chamber where they are consumed by ferricyanide (Fe3-(CN)6) and incoming electrons (via the external circuit) reducing it to ferrocyanide (Fe4-(CN)6).

The oxidised mediator is then free to repeat the cycle. This cycling continually drains off metabolic reducing power from the microbial cells to give electrical power at the electrodes.

In many ways the system mimics real digestion (in the use of micro-organisms within a tubular membrane to break down the food components and produce reducing power) and respiration (by using air to provide oxygen to an electrochemical half-cell to create useful energy).

The battery does not use fossil fuels and involves no net CO2 production other than that which occurs naturally in vegetable decomposition.

There are plans to develop industrial applications for the robot project, such as pollution monitoring.

UWE (0117) 965 6261

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