Solar cells used to produce electricity are now commonplace. But a solar cell used to produce fuel? Researchers have developed a new prototype “solar fuel cell”, using gallium phosphide nanowires, that turns sunlight into an electrical charge and splits water to produce hydrogen all in one. They say that the novel use of the nanowires increases the efficiency of gallium phosphide cells by up to ten times, while at the same time using ten thousand times less of the precious metal.
This is a record for gallium phosphide cells, but you might want to hold on before you rush out to make your own. The new configuration might be ten times more efficient, but this still only pulls it up to 2.9% efficiency, showing that there is clearly still a long way to go.
“For the nanowires we needed ten thousand [times] less precious [gallium phosphide] material than in cells with a flat surface. That makes these kinds of cells potentially a great deal cheaper,” explained Erik Bakkers, one of the authors of the paper, published in Nature Communications. “In short, for a solar fuels future we cannot ignore gallium phosphide any longer.”
The electricity produced by regular solar cells can already be used for electrolysis to split water and produce hydrogen. According to the researchers though, while it might be very efficient at around 15%, it is also very expensive. It is for this reason that they’ve turned instead to looking at using semiconductors, such as gallium phosphide, which will both produce an electrical charge and split water at the same time.
Gallium phosphide has good electrical properties, but there are problems with using it in large, thin sheets. In this arrangement, the metal is very poor at absorbing light and so the researchers, from Eindhoven University of Technology in the Netherlands, decided to make a grid out of the metal, using nanowires that measured just 90 nanometers thick and 500 nanometers long. It was this simple act that created the immediate effect of increasing efficiency.
A lot of work still needs to be done, however, before it could compete in any meaningful way with the current silicon solar cells already in mass use. There are already many companies working to increase the efficiency of using regular solar cells for electrolysis, and with those already at 15%, the researchers looking at the gallium phosphide cells are already on the back foot.