Thursday, July 31, 2008
Researchers have found a cheap and easy way to store the energy made by solar power.
By Kevin Bullis
Splitting water: Daniel Nocera poses with a device for breaking down water into hydrogen and oxygen. The device uses an inexpensive catalyst that he has developed.
Credit: Donna Coveney, MIT
Watch Daniel Nocera explain how his catalyst can be used to store sunlight.
Researchers have made a major advance in inorganic chemistry that could lead to a cheap way to store energy from the sun. In so doing, they have solved one of the key problems in making solar energy a dominant source of electricity.
Daniel Nocera, a professor of chemistry at MIT, has developed a catalyst that can generate oxygen from a glass of water by splitting water molecules. The reaction frees hydrogen ions to make hydrogen gas. The catalyst, which is easy and cheap to make, could be used to generate vast amounts of hydrogen using sunlight to power the reactions. The hydrogen can then be burned or run through a fuel cell to generate electricity whenever it's needed, including when the sun isn't shining.
Solar power is ultimately limited by the fact that the solar cells only produce their peak output for a few hours each day. The proposed solution of using sunlight to split water, storing solar energy in the form of hydrogen, hasn't been practical because the reaction required too much energy, and suitable catalysts were too expensive or used extremely rare materials. Nocera's catalyst clears the way for cheap and abundant water-splitting technologies.
Nocera's advance represents a key discovery in an effort by many chemical research groups to create artificial photosynthesis--mimicking how plants use sunlight to split water to make usable energy. "This discovery is simply groundbreaking," says Karsten Meyer, a professor of chemistry at Friedrich Alexander University, in Germany. "Nocera has probably put a lot of researchers out of business." For solar power, Meyer says, "this is probably the most important single discovery of the century."
The new catalyst marks a radical departure from earlier attempts. Researchers, including Nocera, have tried to design molecular catalysts in which the location of each atom is precisely known and the catalyst is made to last as long as possible. The new catalyst, however, is amorphous--it doesn't have a regular structure--and it's relatively unstable, breaking down as it does its work. But the catalyst is able to constantly repair itself, so it can continue working.
In his experimental system, Nocera immerses an indium tin oxide electrode in water mixed with cobalt and potassium phosphate. He applies a voltage to the electrode, and cobalt, potassium, and phosphate accumulate on the electrode, forming the catalyst. The catalyst oxidizes the water to form oxygen gas and free hydrogen ions. At another electrode, this one coated with a platinum catalyst, hydrogen ions form hydrogen gas. As it works, the cobalt-based catalyst breaks down, but cobalt and potassium phosphate in the solution soon re-form on the electrode, repairing the catalyst.
MIT researchers have discovered a way to store solar energy that could make solar power in homes a mainstream energy option and might even make power companies obsolete, at least for residential needs.
Daniel Nocera, a professor of chemistry and energy at MIT, and postdoctoral fellow Matthew Kanan have figured out how to split water into hydrogen and oxygen cheaply and efficiently at room temperature. The process can later be reversed, allowing the recombination of hydrogen and oxygen in a fuel cell to create carbon-free electricity.
"This is the nirvana of what we've been talking about for years," Nocera told the MIT News Service. "Solar power has always been a limited, far-off solution. Now we can seriously think about solar power as unlimited and soon."
Nocera's breakthrough could enable the "hydrogen economy," a possibility that many have dismissed as impractical.
Nocera told the MIT News Service that within 10 years, he expects that homeowners will be able to use solar power to provide electricity during the day and to store unused solar energy to power a household fuel cell for evening use. This would eliminate the need for electricity delivered over power lines.
According to the MIT News Service, James Barber, a professor of biochemistry at Imperial College in London, characterized the research by Nocera and Kanan as "a major discovery with enormous implications for the future prosperity of humankind."
Nocera and Kanan's research is described in an academic paper, "In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+," that has just been published in Science magazine. [See below]
Published Online July 31, 2008
Submitted on June 19, 2008
Accepted on July 18, 2008
In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+
1 Department of Chemistry, 6-335, Massachusetts Institute of Technology, Cambridge, MA 02139–4307, USA.
* To whom correspondence should be addressed.
Daniel G. Nocera , E-mail: firstname.lastname@example.org
(Next paper in a few months detailing a full system design with an alternative to Pt catalyst)