Titanium Dioxide Key to Producing Hydrogen Fuel from Sunlight
Published on August 26, 2004 at 11:46 PM
A team of Australian scientists predicts that a revolutionary new way to harness the power of the sun to extract clean and almost unlimited energy supplies from water will be a reality within seven years.
Using special titanium oxide ceramics that harvest sunlight and split water to produce hydrogen fuel, the researchers say it will then be a simple engineering exercise to make an energy-harvesting device with no moving parts and emitting no greenhouse gases or pollutants.
It would be the cheapest, cleanest and most abundant energy source ever developed: the main by-products would be oxygen and water. Rooftop panels placed on 1.6 million houses, for example, could supply Australia's entire energy needs.
"This is potentially huge, with a market the size of all the existing markets for coal, oil and gas combined," says Professor Janusz Nowotny, who with Professor Chris Sorrell is leading a solar hydrogen research project at the University of NSW Centre for Materials and Energy Conversion. The team is thought to be the most advanced in developing the cheap, light-sensitive materials that will be the basis of the technology.
"Based on our research results, we know we are on the right track and with the right support we now estimate that we can deliver a new material within seven years," says Nowotny.
Sorrell says Australia is ideally placed to take advantage of the enormous potential of this new technology: "We have abundant sunlight, huge reserves of titanium and we're close to the burgeoning energy markets of the Asia-Pacific region. But this technology could be used anywhere in the world. It's been the dream of many people for a long time to develop it and it's exciting to know that it is now within such close reach."
The results of the team's work will be presented this week at an international conference.
Eminent delegates from Japan, Germany, the United States and Australia will be in Sydney on August 27 for a one-day International Conference on Materials for Hydrogen Energy at UNSW.
Among them will be the inventors of the solar hydrogen process, Professors Akira Fujishima and Kenichi Honda. Both are frontrunners for the Nobel Prize in chemistry and are the laureates of the 2004 Japan Prize.
Since their 1971 discovery that allowed the splitting of water into hydrogen and oxygen, researchers have made huge advances in achieving one of the ultimate goals of science and technology - the design of materials required to split water using solar light.
The UNSW team opted to use titania ceramic photoelectrodes because they have the right semiconducting properties and the highest resistance to water corrosion.
Professors Nowotny and Sorrell say that with appropriate government support and financial backing, their technology could help Australia become part an OPEC of the future.
"We have a solar energy empire in Australia and have a moral obligation to utilise this," says Nowotny. "The very same sentiments were shared by David Sukuzi when he visited Sydney recently. He said he hoped Australia would serve as an example to the rest of the world."
Solar hydrogen, Professor Sorrell argues, is not incompatible with coal. It can be used to produce solar methanol, which produces less carbon dioxide than conventional methods. "As a mid-term energy carrier it has a lot to say for it," he says.
At present, the UNSW work is backed by Rio Tinto, Sialon Ceramics and Austral Bricks A major producer of titania slag, Rio Tinto hopes that an early outcome will be a more environmentally friendly and economically attractive local source of fuel for its remote mining operations while Sialon Ceramics is interesting in production and marketing of a solar-hydrogen production device.
Isolation: titanium is readily available from commercial sources so preparation in the laboratory is not normally required. In industry, reduction of ores with carbon is not a useful option as intractable carbides are produced. The Kroll method is used on large scales and involves the action of chlorine and carbon upon ilmenite (TiFeO3) or rutile (TiO2). The resultant titanium tetrachloride, TiCl4, is separated from the iron trichloride, FeCl3, by fractional distillation. Finally TiCl4 is reduced to metallic titanium by reduction with magnesium, Mg. Air is excluded so as to prevent contamination of the product with oxygen or nitrogen.
Hydrogen production under sunlight with an electrochemical photocell
Fujishima, A.; Kohayakawa, K.; Honda, K.
Electrochemical Society, Journal, vol. 122, Nov. 1975, p. 1487-1489.
Three methods of forming oxide film on metal, electrochemical formation, thermal formation in an electric furnace, and thermal formation by simple heating, were studied as possible means of producing titanium dioxide electrodes. The maximum photocurrents produced by potentiostatically or galvanically formed oxide film electrodes under anodic polarization were 1/10 that of single crystal rutile electrodes, and similar results were obtained using electrodes formed in an electric furnace to which oxygen was supplied. Those produced in a reducing atmosphere produced slightly greater photocurrents. The oxide film layers formed by heating in a gas burner were thicker than those obtained by other methods, and produce anodic photocurrents comparable to those produced by a single crystal rutile electrode. A photocell containing titanium dioxide film anodes was developed on the basis of these results and collected hydrogen at the rate of 6.6l of H2/sq mm of titanium dioxide.
Keywords: ELECTROCHEMICAL OXIDATION, ELECTRODES, HYDROGEN, OXIDE FILMS, PHOTOELECTRIC CELLS, TITANIUM OXIDES, ANODIZING, CRYSTAL STRUCTURE, ELECTROCHEMICAL CELLS, FILM THICKNESS, FURNACES, HEAT OF COMBUSTION, HEAT TREATMENT, SUNLIGHT