"This experiment allowed us to watch charge accumulate in the catalyst and change the catalyst's voltage," Boettcher said. It turns out, Lin said, that a thin layer of ion-porous electrocatalyst material works best, because the properties of the interface with the semiconductor adapt during operation as the charges excited by sunlight flow from the semiconductor onto the catalyst.
The research was designed to understand how maximum energy might be extracted from excited electrons in a semiconductor when the electrons enter the catalyst, where a chemical reaction separates oxygen and hydrogen. To date, Lin said, researchers have been experimenting with materials for creating efficient and cost-effective devices, but minimizing the energy loss associated with the catalyst-semiconductor interface has been a major hurdle.
In the study, Lin compared the movement of electrons between semiconductors coated with porous nickel oxyhydroxide -- a film previously shown by Boettcher's lab to yield excellent electrocatalytic efficiency for separating oxygen from water -- with semiconductors modified with non-permeable films of iridium oxide.
"The ion porous material allows water and ions to permeate the catalyst material," Lin said. "When these catalysts are in solution the catalyst's energy can move up and down as its oxidation state changes."
Catalysts with non-porous structures in semiconductor-catalytic junctions don't show this behavior and typically don't work as well, said Boettcher, who also is a member of Oregon BEST (Oregon Built Environment & Sustainable Technologies Center), a state signature initiative.
Converting sunlight into energy and storing it for later use in an economically viable way is a major challenge in the quest to replace fossil fuels with renewable ener
|Contact: Jim Barlow|
University of Oregon