Posted: Jun 7th, 2012 New twist on old chemical process could boost energy efficiency ( Nanowerk News ) Chemical reactions on the surface of metal oxides, such astitanium dioxide and zinc oxide, are important for applicationssuch as solar cells that convert the sun’s energy to electricity.Now University of Washington scientists have found that apreviously unappreciated aspect of those reactions could be key indeveloping more efficient energy systems. Such systems could include, for example, solar cells that wouldproduce more electricity from the sun’s rays, or hydrogen fuelcells efficient enough for use in automobiles, said James Mayer, aUW chemistry professor. “As we think about building a better energy future, we have todevelop more efficient ways to convert chemical energy intoelectrical energy and vice versa,” said Mayer, the correspondingauthor of a paper about the discovery in the June 8 edition of Science ( “Titanium and Zinc Oxide Nanoparticles Are Proton-CoupledElectron Transfer Agents” ). This image from an electron microscope shows a coated titaniumdioxide nanocrystal. (Image: Joel Schrauben/James Mayer) Chemical reactions that change the oxidation state of molecules onthe surface of metal oxides historically have been seen as atransfer solely of electrons.
The new research shows that, at leastin some reactions, the transfer process includes coupled electronsand protons. “Research and manufacturing have grown up around models in whichelectrons moved but not atoms,” Mayer said. The new paper proposesa different model for certain kinds of processes, a perspectivethat could lead to new avenues of investigation, he said. “In principle this is a path toward more efficient energyutilization.” Coupling the transfer of electrons with the transfer of protonscould help reduce the energy barriers to chemical reactionsimportant in many technologies. For example, using solar energy tomake fuels such as hydrogen requires that electrons and protons becoupled. d.
The new perspective also could be important for photocatalyticchemical processes, including those designed for wastewaterremediation or to create self-cleaning surfaces, such as theoutside of buildings in areas with heavy industrial air pollution. The research focused specifically on nanoparticles, measured inbillionths of a meter, of titanium dioxide and zinc oxide. Titaniumdioxide is the most common white pigment, used in paints, coatings,plastics, sunscreen and other materials. Zinc oxide also is used inpigments, coatings and sunscreens, as well as white athletic tape,and also is used in the manufacture of rubber, concrete and othermaterials.
Nanocrystals were used to closely examine chemicalprocesses at the material’s surface. Mayer said the goal of the work is to get those working in varioustechnological areas involving metal oxides to think in differentways about how those technologies work and how to make them moreefficient. The work also could prove important in finding more efficient waysto fuel vehicles of the future, he said. Fuel cells, for example,transform atmospheric oxygen into water by adding both electronsand protons. Coupling those added electrons and protons could makefuel cells more efficient and allow replacement of costly materialssuch as platinum.
“Chemical fuels are very useful, and they’re not going away,” Mayersaid. “But how do we utilize them better in a non-fossil-fuelworld?”.
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