30 May 2012
If only solar energy could be continuous and portable… In what could turn out to be a giant leap toward the creation of solar fuels, researchers at the University of Wisconsin-Madison (US) now have developed a high-speed screening method for new electrocatalysts. Efficient, earth-abundant electrocatalysts that facilitate the oxidation of water are critical to the production of solar fuels.
To store solar energy efficiently, two catalysts are needed, one of which will be involved in forming the oxygen that is released. “This oxygen-forming reaction is one of the biggest challenges. It is where there are the greatest potential gains in efficiency if we can find better, economically viable catalysts,” says UW-Madison staff scientist James Gerken, Ph.D., a member of the University's Stahl Group, who conducted the research project. However, the researcher notes, “The number of potentially catalytic mixtures of readily available elements is vast, far too vast to search through sequentially.” Up until now, researchers depended on the luck of the draw in finding promising electrocatalytic materials that are inexpensive and readily available. Water oxidation provides electrons and protons needed for hydrogen production, and, says Stahl.
To begin this new and extremely efficient high-throughput screening method, mixtures that could be candidates for catalysts are put in a grid on an electrode. During electrolysis, the better catalysts make oxygen faster. The researchers identify the spots where oxygen is formed the fastest by devising a mesh coated with fluorescent paint to detect the oxygen. It changes color under ultraviolet light depending on the concentration of oxygen in the electrolysis bath. “This way, we can take pictures of the fluorescence and tell how well all the different mixtures are working instead of testing them one-by-one,” Dr. Gerken explains. “We can put hundreds of potential catalysts on the same electrode and find out which ones are winners or losers in the time that it would take to do conventional measurements on just one possible catalyst,” Gerken says. “Then we do rigorous experiments on the interesting mixtures without wasting time on materials that show no activity in the screening technique.”
The Wisconsin team anticipates that this method will enable them to discover new catalyst mixtures that display unexpected levels of activity. “In our initial testing, we have already seen some highly active mixtures that we wouldn't have otherwise tested,” Dr. Gerken says. Some of the new metal-oxide catalysts the researchers have identified so far as holding promise for solar energy storage are composed of such inexpensive materials iron, nickel and aluminum.
Photo: View of the fluorescent mesh being illuminated in the electrochemical cell (credit: Jamie Y. C. Chen, UW Madison)
Written by Sandra Henderson, Research Editor, Solar Novus Today