Sunlight + water = hydrogen gas, in a new technique that can convert 60 per cent of sunlight energy absorbed by an electrode into the inflammable fuel.
To generate the gas Thomas Nann and colleagues at the University of East Anglia in Norwich, UK, dip a gold electrode with a special coating into water and expose it to light. clusters of indium phosphide 5 nanometres wide on its surface absorb incoming photons and pass electrons bearing their energy on to clusters of a sulphurous iron compound.
This material combines those electrons with protons from the water to form gaseous hydrogen. A second electrode – plain platinum this time – is needed to complete the circuit electrochemically.
New benchmark
Organic molecules have been used before to perform the same feat. But they are quickly bleached by the sunlight they are collecting, rendering them inefficient after a few weeks.
The inorganic materials used in the University of East Anglia's system are more resilient. Their first generation proof of concept is "a major breakthrough" in the field, they say, thanks to its efficiency of over 60 per cent and ability to survive sunlight for two weeks without any degradation of performance.
"In fact the 60 per cent figure is probably a worst-case scenario," says Nann. "This is still a preliminary study."
Bigger net
That high efficiency is largely thanks to the indium phosphide clusters being better at grabbing photons than organic molecules. "Think of them as a butterfly net for catching photons," says Nann.
By the standard measure of the probability that a material will absorb a photon that hits it, each cluster is 400 times better at netting photons than organic molecules used in previous systems. "That's why it works so well," says Nann.
He and colleagues now plan to refine the system, including lowering the cost by making it with less expensive materials. "There is no major reason for using gold or platinum," he says: those materials were used simply because they are common in the laboratory.
Welcome result
The Nann team's experiment has been welcomed by others in the field. "It's a significant result," says Vincent Artero at the Joseph Fourier University in Grenoble, France. There is still room to improve efficiency and reduce materials costs, but "my overall appreciation of this work is highly positive, both regarding the scientific level and the promises that are held by the new result", he says
Licheng Sun at the Royal Institute of Technology in Stockholm, Sweden, agrees. "It will certainly [provide] future research topics for water splitting," he says.
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