The prototype mechanism developed by a team comprised of researchers from the California Institute of Technology in the US, and the Eidgenössische Technische Hochschule and Paul Scherrer Institute I Switzerland, captures the Sun's rays and concentrates it with a quartz window, focusing it onto a metal oxide known as cerium oxide, or ceria.
Ceria exhales oxygen when it gets hot and inhale it as it cools, and in the device, that property is harnessed by pumping in carbon dioxide and/or water, which will then have its oxygen stripped from it by the cooling ceria and produce hydrogen for fuel cells, or a hydrogen/carbon monoxide blend known as "syngas" fuel.
In an interview with the London Guardian newspaper, research leader Sossina Haile of the California Institute of Technology, said simply, “We have a big energy problem and we have to think big”.
In the abstract for their Science piece, the researchers suggest that “because solar energy is available in large excess relative to current rates of energy consumption, effective conversion of this renewable yet intermittent resource into a transportable and dispatchable chemical fuel may ensure the goal of a sustainable energy future.”
The problem they said is that “low conversion efficiencies, particularly with CO2 reduction, as well as utilization of precious materials have limited the practical generation of solar fuels.”
Their solution uses a standard parabolic mirror to focus the sun's rays into a reaction chamber where the cerium oxide catalyst breaks down water and carbon dioxide. It does this because heating cerium oxide drives oxygen atoms out of its crystal lattice.
When cooled the lattice strips oxygen from surrounding chemicals, including water and CO2 in the reactor. That produces hydrogen and carbon monoxide, which can be converted to a liquid fuel.
Haile told the Guardian that she believes a rooftop reactor could produce about three gallons of fuel a day. She also thinks transport fuels would be the first application of the reactor, if it goes on to commercial use.
But she said an equally important use for the renewable fuels would be to store solar energy so it is available at times of peak demand, and overnight.
She says the first improvements that will be made to the existing reactor will be to improve the insulation to help stop heat loss, a simple move that she expects to treble the current efficiency.
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