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The Global Energy Prize annually honors outstanding achievements in energy research and technology from around the world that are helping address the world’s various and pressing energy challenges.

Fuel from the air: Why we need artificial photosynthesis

Photosynthesis is one of the most important processes on Earth. And this is recognised by everyone, from biologists to energy specialists. And everyone knows that nearly all the energy we use, we owe to the Sun. Oil, gas and coal all came into being thanks to the ability of organisms to secure solar energy and use it to create organic molecules by means of photosynthesis. Photosynthesis allows plants to transform energy from the sun into fuel.

But, sooner or later, hydrocarbon mineral reserves will run out and significant changes will have to be made to technologies of commercial production of hydrogen on the basis of photosynthesis.

Enter artificial photosynthesis, which can produce a real revolution in the sector of renewable energy sources. It allows sunlight to split water to produce hydrogen and oxygen which create an effective and environmentally clean fuel. All you have to do – in theory – is to halt the process before its conclusion, at its first stage, where water molecules are divided into oxygen and hydrogen atoms through the action of light and some help from catalysts.

For the moment, synthetic photosynthesis remains an experimental project requiring serious scientific research and analysis for practical application. It was first modeled specifically for production of energy from renewable resources several years ago.

Synthetic photosynthesis is in fact a complex process involving costly and toxic catalysts. Academics are endeavouring to use materials that are more easily available or to create a sort of “combined” photosynthesis using naturally occurring enzymes.

And in Cambridge, scientists are using enzymes called hydrogenases – found in water plants – that, in combination with synthetic pigments, act on sunlight to split water into hydrogen and oxygen.

Assortment of fuels

Artificial photosynthesis can solve two problems at once – transforming carbonic gas from the atmosphere, and therefore tackling global warming, and creating hydrogen from water, to be used later as fuel.
Unlike most methods of producing alternative energy, artificial photosynthesis can result in several types of fuel. Liquid hydrogen can be use used as fuel for transport and can also be used in a system of fuel cells to generate electricity through a chemical reaction from mixing hydrogen and oxygen in water.

Methanol can also be produced – a photoelectric cell can generate the methanol fuel, to be added to petrol or used separately for vehicles and small heating systems.
The ability to produce clean fuel without any harmful by-products makes artificial synthesis an ideal source of energy for the environment. It requires no extraction, cultivation or drilling and can serve as a limitless source of energy.
Getting back 100 trees

Forests are the lungs of the planet. They are being cut down the world over and academics are engaged in a search for alternative sources of oxygen to meet the needs of mankind.

Natural photosynthesis is not especially effective: plants need it in order to grow and develop without worrying about climate. Natural photosynthesis provides only 1-2 % of the energy that could potentially be produced. Leaves and solar energy transform carbon dioxide which, when combined with water, forms a plant biomass. And carbon dioxide and water are turned into glucose and oxygen.

English scientists have worked out how to produce artificial leaves able to perform the function of photosynthesis. Leaves use chloroplasts from ordinary plants turned into protein. These “leaves” allow for the creation of hydrogen in normal day-to-day conditions.

Two years ago, Imperial College in London announced it had cultivated the first artificial “leaf” – a BioSolar leaf – a project of the Arborea start-up. The project involves the creation – on buildings or in the open – of structures similar to solar panels containing microscopic plants. The plants, through the process of photosynthesis absorb light and carbon dioxide and cleanse the air of greenhouse gases.

The space for such a process is similar to that of a single tree, but removes an amount of carbon dioxide equivalent to 100 trees. The panels can be mounted on buildings.

Scientists at Cambridge University created a prototype of “photosheets” working on the basis of artificial photosynthesis. The device uses CO2, water and sunlight to produce oxygen and formic acid which can be used on its own or transformed into hydrogen.

The reaction and oxidation in the “photosheet” occurs when sunlight acts on the leaf in water along with a catalyst created on the basis of cobalt. The leaf acts independently and produces practically no by-products. The prototypes are no larger than 20 sq. cm. but the inventors hope to produce it to scale and believe this can be done without undue expense. The sheets can be produced to roughly the same scale as is now the case with solar panels.

Fuel from sunlight

Scientists from the National Laboratory at Berkley in the United States have invented a system of artificial photosynthesis using nano-sized tubes to produce fuel.

“Solar fuel tiles” contain billions of nano-sized tubes, each of which contains a layer of cobalt oxide on the inside, a middle layer of silicon dioxide and an outer layer of titanium dioxide. The energy from sunlight splits water molecules and creates free protons and oxygen. The protons join carbon dioxide and form carbon monoxide – which can be used for fuel. The system essentially imitates live photosynthetic cells inside chloroplasts.

Peydong Yang, professor of energy and chemistry at the University of California Berkeley, was awarded the annual Global Energy Prize for his work inventing solar cells on the basis of nano particles and artificial photosynthesis. The technology created by the scientists allows them to create oxygen and organic compounds from sunlight, carbon dioxide and water.

The device contains a hybrid system – a “forest” from nano wires made from silicon and bacteria which traps solar photons, splits molecules of carbon dioxide and produces nutrients.

The bacteria can multiply, helping to solve problems for future inter-planetary explorers. The atmosphere on Mars, for instance, is made up to a great extent of carbon dioxide and having a biogenerator – an energy storage solution – will be vital in travel to the “red planet”.

But Peydong Yang says it will also be useful on Earth – providing people with both oxygen and fuel.

NASA has plans for prototypes of such devices by 2023 capable of producing 40 kilowatts to provide power for manned exploration of space.

And if energy produced by solar panels has to be stored, artificial photosynthesis can provide a solution by transforming solar energy into chemical energy and storing it in chemical bonds.

There can be no doubt – artificial photosynthesis is of tremendous importance in boosting the energy security of any country.

For example, one of the alternatives to natural photosynthesis is a special “tarpaulin” with solar cells which can be installed just about anywhere. After water and light are absorbed, it can be placed in a reservoir with catalysts to transform CO2 into chemical fuel to be stored or used immediately.

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