Nanowires give 'solar fuel cell' efficiency a tenfold boost

Nanowires give ‘solar fuel cell’ efficiency a tenfold boost
Array of nanowires gallium phosphide made with an electron microscope. Credit: Eindhoven University of Technology.

A solar cell that produces fuel rather than electricity. Researchers at Eindhoven University of Technology (TU/e) and FOM Foundation today present a very promising prototype of this in the journal Nature Communications. The material gallium phosphide enables their solar cell to produce the clean fuel hydrogen gas from liquid water. Processing the gallium phosphide in the form of very small nanowires is novel and helps to boost the yield by a factor of ten. And does so using ten thousand times less precious material.

The electricity produced by a solar cell can be used to set off chemical reactions. If this generates a fuel, then one speaks of solar fuels – a hugely promising replacement for polluting fuels. One of the possibilities is to split using the electricity that is generated (electrolysis). Among oxygen, this produces hydrogen gas that can be used as a clean fuel in the chemical industry or combusted in fuel cells – in cars for example – to drive engines.

Solar fuel cell

To connect an existing to a battery that splits the water may well be an efficient solution now but it is a very expensive one. Many researchers are therefore targeting their search at a semiconductor material that is able to both convert sunlight into an electrical charge and split the water, all in one; a kind of 'solar '. Researchers at TU/e and FOM see their dream candidate in gallium phosphide (GaP), a compound of gallium and phosphide that also serves as the basis for specific colored leds.

A tenfold boost

GaP has good electrical properties but the drawback that it cannot easily absorb light when it is a large flat surface as used in GaP . The researchers have overcome this problem by making a grid of very small GaP nanowires, measuring five hundred nanometers (a millionth of a millimeter) long and ninety nanometers thick. This immediately boosted the yield of hydrogen by a factor of ten to 2.9 percent. A record for GaP cells, even though this is still some way off the fifteen percent achieved by silicon cells coupled to a battery.

Ten thousand times less material

According to research leader and TU/e professor Erik Bakkers, it's not simply about the yield – where there is still a lot of scope for improvement he points out: "For the nanowires we needed ten thousand less precious GaP material than in cells with a flat surface. That makes these kinds of potentially a great deal cheaper," Bakkers says. "In addition, GaP is also able to extract oxygen from the water – so you then actually have a cell in which you can temporarily store your solar energy. In short, for a solar fuels future we cannot ignore gallium phosphide any longer."


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Nanowire-based design incorporates two semiconductors to enhance absorption of light

More information: "Efficient water reduction with gallium phosphide nanowires," Nature Communications (17 July 2015) DOI: 10.1038/nscomms8824
Journal information: Nature Communications

Citation: Nanowires give 'solar fuel cell' efficiency a tenfold boost (2015, July 17) retrieved 19 June 2019 from https://phys.org/news/2015-07-nanowires-solar-fuel-cell-efficiency.html
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Jul 18, 2015
If one increases area available to a reaction, then that reaction will be more intense and productive. One learns that in physical chemistry in colleges since the 1970's Course we were blissfully unaware of nanomaterials back then.

Jul 18, 2015
Storing your fuel at home with your solar panels, then refueling your car and....well, driving.
Though, would it be better to drive with an electric car? Or both will be good? I wonder which version will be the most efficient one, and the first to be mass available.

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