A novel nickel-based catalyst also developed recently by Nocera is applied to the other side of the silicon to split hydrogen from water. The nickel catalysts already used in other water splitting devices known as electrolyzers would quickly be rendered useless by phosphate and borate present in the water. The results of initial tests of the device have been submitted for publication. They show that it can operate for at least six days without a drop in efficiency, Nocera says.
John Turner, a research fellow at the National Renewable Energy Laboratory in Golden, Colorado, says the ability to use a virtually transparent cobalt catalyst is a key advance, and the reported efficiency is promising. “He is getting most of the efficiency out of the cell,” Turner says. “If he [starts with] an 11 or 12 percent cell, which is commercially available, he should be able to do much better. But we would need to see what he can do once he gets a better cell.”
However, Turner says, Nocera will have to demonstrate significantly longer run times—tens of thousands of hours. “They may have the durability, but they need to continue to show it,” he says.
Sun Catalytix, a company founded by Nocera, will now work with Indian industrial giant Tata to commercialize the technology for residential use in developing countries. The companies are already working together to develop another artificial photosynthesis device developed previously by Nocera. This initial device will be based on a 100-watt solar panel and will require a separate electrolyzer connected by wires to the panel. It should sell for around $100.
The device would also have to be paired with a fuel cell to convert stored hydrogen to electricity. Nocera says he hopes to deliver this initial solar-powered hydrogen-producing device to Tata by the end of 2011. The new artificial leaf should be less expensive, but it could be another two and a half years before a commercial prototype would be ready, Nocera says.
James Stevens, a research fellow at Dow Chemical, says the technology still has a long way to go. “There is a lot that has to be done before this could be practical,” he says. “The efficiency is low and the capital costs of these things are very high.”
Other practical issues, such as safely storing hydrogen gas and preventing the system from freezing in subzero temperatures, are also significant challenges, Stevens says. “We’re not really interested in the state of the art as it now stands,” he says.