Sunlight shines on clean energy future: Simple inorganic semiconductor - silver orthophosphate - used to oxidize water

June 8, 2010, Australian National University
Dr Zhiguo Yi and Professor Ray Withers have found a simple inorganic compound can efficiently oxidise water to release oxygen.

( -- The production of clean energy and the treatment of waste water are set to become easier thanks to Australian National University researchers.

The scientists - Dr Zhiguo Yi and Professor Ray L Withers of the Research School of Chemistry at ANU, along with colleagues from Japan and China - have demonstrated that a simple inorganic compound, silver orthophosphate, can efficiently be used to oxidise with only the power of light. The oxidisation process can be used to convert solar energy to clean energy or break down contaminants in water. The research is published in .

“With increasing worldwide interest in alternative renewable sources of energy, as well as on the need to clean up environmental pollution, developing materials that can be used to efficiently convert solar energy to or to decompose organic contaminants is a vitally important task,” said Dr Yi.

“The material we have studied is a very simple inorganic semiconductor - silver orthophosphate. Under visible light illumination this material shows an amazing ability to oxidise water to release oxygen, as well as to break down organic contaminants such as methlyene blue, Rhodamine B and other chemicals which may be undesirable in water supplies,” added Professor Withers.

Dr Yi first discovered the new property of silver orthophosphate while working at the National Institute for Materials Science (NIMS) in Japan in 2007, but only after moving to ANU did the research team solve the problem of how to stabilise the compound.

“It’s well known that compounds such as silver halides - such as those used in photographic applications - are not stable under light illumination. The silver orthophosphate we use is no exception,” said Dr Yi.

“Our work here, however, has uncovered that silver orthophosphate can be regenerated in an energy-efficient manner by an electrochemical method,” added Professor Withers.

Dr Yi and Professor Withers worked with colleagues from NIMS and Nanjing University in China to develop the ideas and research. The researchers say that the next step will be to look at the use of electricity to power the process.

“We are optimistic about future uses of silver orthophosphate, although there remain problems to overcome as electrical energy is still required to generate hydrogen and for the material to regenerate itself. However, the results are important and encouraging first step towards solving energy and environmental issues,” said Dr Yi.

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2.3 / 5 (3) Jun 08, 2010
This is good work- maybe even excellent work- but, as too often seems the case, it would have been nice to see some throughput numbers- otherwise, just another hopeful story, at least from this reader's perspective.
5 / 5 (1) Jun 08, 2010
..can efficiently be used to oxidise water with only the power of light.

Under visible light illumination this material shows an amazing ability to oxidise water to release oxygen,...

I am somewhat confused by different parts of this article. My understanding of the words oxidize is that you are combining oxygen with something. such that water would be oxidized Hydrogen. Carbon dioxide is oxidized carbon etc.

But in this article they are oxidizing water and the water is giving off oxygen? This would seem to indicate that instead of oxidizing the water the water is being split apart into Hydrogen and Oxygen.

So I am thinking that maybe the words oxidize are used instead of deoxidize? In any case oxygen is taken out not added.
1 / 5 (3) Jun 08, 2010
It's a catalyzing reaction, but one would assume that it would have roughly the same effect as electrolysis, and therefore produce H or H2, as well, which one would also assume would solve the problem of a power source to electrically regenerate at least some of the spent catalyst through recombination of H and O.

Anyone have any insight to add?
5 / 5 (3) Jun 08, 2010

In chemistry, the terms "oxidize" and "reduce" (which are opposite of each other) hold a special meaning. To oxidize something, means to take away electrons from it. To reduce something, is to give electrons to it.

In this case, to oxidize water means I'll guess they're stealing electrons from the OH- ions, causing them to dissociate into O- and H+. Two O- ions can then spontaneously combine into a happy wholesome O2 molecule with a full valence shell, whilst the "stolen" electrons can be funneled by the catalysts toward the H+ ions, allowing them to combine into H2 molecules.
not rated yet Jun 19, 2010
Is it just me or are they unclear if it's a photo reaction, or if they're using photo-voltaics to electrify the silver orthophosphate, lump, plate, grid? I've long thought that the key to these hydrogen generators we've all seen, is in fining the right anode/cathode material

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