Researchers at the Eindhoven University of Technology (TU/e) and FOM Foundation have demonstrated a prototype for a solar cell that separates hydrogen from water using GaP nanowires. The work is described in the journal Nature Communications. Solar electricity can be employed to set off chemical reactions. If such reactions create a fuel, then the fuel is called a solar fuel. Electrolysis, which separates liquid water into hydrogen and oxygen, is one chemical reaction that promises to create an abundant clean burning fuel, hydrogen.
Researchers have previously attempted to connect silicon solar cells to a battery. Then, they have used the battery for electrolysis. This method of producing hydrogen is expensive. Some have begun to look for material that can act both as a solar cell and can split liquid water into hydrogen and oxygen when electricity is applied. Researchers at TU/e and FOM have made a solar cell and electrolysis inducing material of GaP nanowires. Others have attempted to use GaP as a solar cell material with little success. The flat surface of GaP does not readily absorb the light in large area GaP solar cells.
The researchers have made a grid of GaP nanowires that can overcome this issue. The grid of nanowires measures 500nm long and 90nm thick. In addition to boosting the solar cell efficiency, the GaP nanowires boosted the hydrogen yield from liquid water by a factor of ten to 2.9 percent. However, the technology still trails the 15 percent achieved with silicon solar cells and a battery.
According to head researcher and TU/e professor Erik Bakkers, the yield was not the entire picture. Bakkers stated, “For the nanowires we needed ten thousand times less precious GaP material than in cells with a flat surface. That makes these kinds of cells potentially a great deal cheaper,” he 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 GaP any longer.”
‘Efficient water reduction with gallium phosphide nanowires’, by Anthony Standing et al, Nature Communications (17 July 2015) DOI: 10.1038/nscomms8824