Array of nanowires gallium phosphide made with an electron microscope.
Credit: Eindhoven University of Technology
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 liquid water 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 silicon solar cell 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 fuel
cell'. 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 solar
cells. 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 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 cells 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 fuel cell
in which you can temporarily store your solar energy. In short, for a
solar fuels future we cannot ignore gallium phosphide any longer."
Story Source:
The above post is reprinted from
materials provided by
Eindhoven University of Technology.
Note: Materials may be edited for content and length.
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