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Sunlight shines on silver technology
Scientists have taken a promising step toward the goal of generating a new source of clean energy, using little more than sunlight and water.

Dr Zhiguo Yi from the Australian National University (ANU) and collaborators in Australia, China and Japan have proven that a simple chemical based on silver, called silver orthophosphate, can produce gaseous oxygen from water when exposed to visible light.

This breakthrough, published in the journal Nature Materials, raises the possibility that the silver compound could be used to 'split water' into oxygen and hydrogen, allowing the hydrogen to be used as a clean fuel.

Researchers have long hoped that splitting water could be a way to produce clean energy, but so far all the methods they have tried have required large amounts of electricity.

The new technology helps overcomes that problem by allowing sunlight to be used as the energy source.

"With increasing world-wide interest in alternative renewable sources of energy, developing materials that can be used to efficiently convert solar energy to clean energy is a vitally important task," says study co-author Professor Ray Withers of the ANU.
Overcoming instability

Yi came up with the idea of using the silver compound after thinking about the silver halide chemicals that are used to develop photographs. Photographic developing has to be done in the dark because these chemicals break down in sunlight.

"It is well known that compounds such as the silver halides, used for photographic applications, are not stable under light illumination. The silver orthophosphate we use is no exception," says Yi, who first discovered the new property while working in Japan.

Although the instability of this silver orthophosphate compound is what makes the water splitting possible, it was also a potential drawback as stability is important for long time usage.

But the ANU scientists and their colleagues have overcome this problem by developing a technique for regenerating the silver orthophosphate in an energy-efficient way.

"On the laboratory scale it seems to work well. We think this is a very important and encouraging first step," say Withers. "But of course if you are going to use it on a large scale there are many questions to answer."

Meanwhile, the researchers also found that silver orthophosphate can be used as a means of cleaning chemical contaminants out of water, again only using sunlight.

"Under visible light illumination, this material shows an amazing ability to oxidize water to release oxygen as well as to decompose organic contaminants such as methylene blue and Rhodamine B," says Yi.

"We believe it has got good potential for industrial applications," adds Withers. The research team says they are hoping to work with industrial partners to develop these applications in the near future.

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