Green machine is our weekly column on the latest advances in environmental technologies.

Sea power

Silicon solar cells are so, well, dead. Dollops of green goo made of living cells – from jellyfish to algae – are now being recruited to produce cheaper solar power.

Zackary Chiragwandi at Chalmers University of Technology in Gothenburg, Sweden, and colleagues are developing a photovoltaic device based on green fluorescent protein (GFP) from the jellyfish Aequorea victoria.

The team deposit two aluminium electrodes with a tiny gap between them onto a silicon dioxide substrate. A droplet of green fluorescent protein is then added on top, whereupon the protein assembles itself into strands between the electrodes.


When exposed to ultraviolet light, the GFP absorbs photons and emits electrons, which travel around a circuit to produce electricity.

Cheap goo

The green goo acts like the dye used in current “dye-sensitised” solar cells, called Grätzel cells.

However, unlike such cells, the GFP does not require the addition of expensive materials, such as titanium dioxide particles. Instead, the GFP can be placed directly on top of the electrode, simplifying the design and reducing overall cost.

The team have also used the proteins to create a biological fuel cell that generates electricity without the need for an external source of light.

Instead, they used light emitted from a mixture of chemicals such as magnesium and the luciferase enzymes found in fireflies (Lampyridae) and sea pansies (Renilla reniformis) to generate electricity from the jellyfish biophotovoltaic device.

Such a fuel cell could be used to power nano-devices embedded in living organisms, says Chiragwandi, for example to diagnose disease.

Algaelectricity

Jellyfish are not the only sea creatures that can be exploited to generate energy: algae could power floating devices on the ocean wave. Adrian Fisher and Paolo Bombelli at the University of Cambridge and colleagues are developing biophotovoltaic devices based on algae and photosynthetic bacteria.

The team deposit a film of photosynthetic cells on top of a transparent conductive electrode, which faces a carbon cathode seeded with platinum nanoparticles.

When exposed to sunlight the algal cells begin splitting water and producing oxygen, electrons and protons. These would usually be used by the algae to convert carbon dioxide into organic compounds, but instead the device siphons them off to generate electricity, says Fisher. “The algal cells produce electrons very generously,” he says.

The team has so far used a proof-of-concept device to power a clock. The sunlight-to-electricity efficiency of the device is only 0.1 per cent at present, compared with between 10 and 15 per cent for existing dye-sensitised solar cells, however. Screening different algae species to find the most productive electron donor might be one way to produce more juice.

Eventually, algal cells could float out at sea, generating electricity from sunlight and seawater. “We might end up with less efficiency than [conventional] photovoltaics, but we think we can win on cost, and we don’t require space where people want to live,” says Bombelli.

Journal reference: Energy and Environmental Science, in press

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