Artificial Photosynthesis

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by Anastasia Eleftheriou
Imperial College London

Energy production is always a research field that interests people, and nowadays their attempts aremore focused on renewable and effective sources of energy. Recently, Professor Micheal Gratzel,the inventor of the third generation dye-sensitized solar cells, was awarded the MilleniumTechnology Prize, in recognition of his great work in the field of artificial photosynthesis.

Artificial Photosynthesis is a renewable source of energy that is still under development, whichmimics the natural every-day behaviour of the plants that convert water,sunlight and carbon dioxideinto oxygen and carbohydrates.

But how does the process of the photosynthesis in plants produce energy? Photosynthesis occurs intwo stages, namely the light reactions and the dark reactions. During the light reactions, plants usethe sunlight to break the water into oxygen and hydrogen (a process called photoelectrolysis), whilstduring the dark reactions, where no light is needed for the process, plants convert carbon dioxideinto molecules of glucose and fructose. These two molecules make sugar, and they provide energyfor the plant growth and repair.

Hydrogen produced by the first stage of photosynthesis, can be used directly as a fuel or stored forfuture consumption. Using Hydrogen to cover our energy demands is environmentally friendly,considered as one of the best alternative renewable sources of energy. The second stage ofphotosynthesis also has a great benefit which is that it reduces the amount of carbon dioxide in theatmosphere. CO2 is a gas with the ability to absorb infra-red radiation emitted from the Earth, trapit near Earth's surface, causing the greenhouse effect and consequently many environmentalproblems.

Although artificial photosynthesis has all the advantages of the renewable energy sources, such asthat they don't consume petrol, they are cheaper in the long term etc.,it has also a benefit whichdistinguishes it from the other energy sources of its kind. That is its potential to become one of thevery useful mechanisms of the carbon dioxide elimination, providing a solution to the minimizationof the global warming effects. Those artificial systems will use metals such as ruthenium and iron tocapture light and the water splitting core will be based on manganese.

Gratzel has developed the Dye-Sensitised Solar Cell which is a device composed of a porous layerof titanium dioxide nano-particles, that uses special dyes to capture the energy in light at differentwavelengths, like the chlorophyll in plants does. It only converts around 11 per cent of the lightenergy into electricity, but it's still under development.

Artificial Photosynthesis promises to be a very elegant, efficient and carbon-neutral source ofenergy, however, its cells don't last more than a few years and the cost of alteration at the momentis not advantageous enough to compete with fossil fuels. At least, the future energy production canhave something to be based on.

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