A NEW WAY TO SPLIT WATER RENEWABLE ENERGY: Thermal technique that holds temperature steady could raise productivity
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O MEET FUTURE ENERGY NEEDS, scientists
would like to find sustainable ways to generate hydrogen for use in fuel cells and to make liquid fuels. As an alternative to other H2 sources, such as processing of biomass and electrolysis of water, scientists are developing a thermal water-splitting method that would use heat from solar arrays and metal oxide catalysts. But the classic thermal approach has required repetitive heating and cooling, which wastes energy. Charles B. Musgrave, Alan W. Weimer, and coworkers at the University of Colorado, Boulder, have now sidestepped the temperature-cycling problem by demonstrating the first constant-temperature version of the technique (Science 2013, DOI: 10.1126/science.1239454). The work “offers the potential for reaching higher solar-to-fuel energy conversion efficiencies” to make solar-based fuels at large scale and competitive costs, says solar technology expert Aldo Steinfeld of ETH Zurich. In temperature-swing catalytic water splitting, a metal oxide catalyst is reduced at high temperature, 1,200 to 1,500 °C, releasing O2; the reduced metal oxide is then oxidized in the presence of water at a temperature about 400 °C cooler, yielding H2 and regenerating the original catalyst. The cycle is then repeated. In the new isothermal approach, metal oxide catalysts are reduced at 1,350 °C, releasing O2; the system is then oxidized in the presence of water at the same temperature, producing H2 and regenerating the catalysts. The process is repeated. Isothermal was more efficient than temperature-swing splitting in the new study, but further studies are needed.
The new technique “has a good chance to outperform” temperature-swing splitting in practice, says solar hydrogen-generation expert Martin Roeb of the Institute of Solar Research, in Cologne, Germany. Materials science and chemical engineering professor Sossina M. Haile of Caltech says potential advantages SPLITTING IMAGE Solar-powered of isothermal cycling temperature-swing (top) and isothermal include “design (bottom) water splitting. simplification and reduced mechanical Oxidized metal oxide stresses. What is remarkable in this work H2 Heat is that there is a draOxidation, Reduction, matic enhancement 800–1,000 °C 1,200–1,500 °C in hydrogen producH2O O2 tion” compared with temperature-swing Reduced metal oxide splitting. Zhaolin Wang, a MFe2O4 + 3 Al2O3 hydrogen-generation expert at the UniHeat H2 versity of Ontario, Oxidation, Reduction, says eliminating 1,350 °C 1,350 °C temperature swings H O O2 could lead to longer 2 catalyst life, simpler MAl2O4 + 2 FeAl2O4 operation, and inM = other metal creased H2 production. Wang notes a possible explosion hazard from simultaneous H2 and O2 formation caused by inadvertent catalyst mixing, but Weimer believes this can be prevented. Liquid fuels made with H2 from solar water splitting would be more expensive than today’s fossil fuels, so the thermal approaches anticipate different fuel economics. But the new study is “ground-breaking and of fundamental significance,” Steinfeld says, “because it experimentally demonstrates the feasibility of operating thermochemical redox cycles under isothermal conditions.”—STU BORMAN
PURDUE U
NATIONAL SCIENCE FOUNDATION Astrophysicist France Córdova tapped as new leader President Barack Obama has Board of Regents and a memnominated astrophysicist ber of the National Science France A. Córdova, president Board, NSF’s governing body. emerita of Purdue University, to She led Purdue from 2007 to serve as the next NSF director. 2012. Prior to that, she served Cora B. Marrett has been actfor five years as chancellor of ing director at NSF since March the University of California, Rivwhen Subra Suresh left to erside, where she was a profesbecome president of Carnegie sor of physics and astronomy. Mellon University. Córdova She was vice chancellor for Córdova, 66, has significant research and a professor of administrative experience. At present, physics at UC Santa Barbara from 1996 she is chair of the Smithsonian Institution to 2002 and head of the astronomy
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and astrophysics department at the University of Pennsylvania from 1989 to 1993. Córdova also has government experience. She was NASA’s chief scientist from 1993 to 1996 and on staff at Los Alamos National Laboratory from 1979 to 1989, the last two years as deputy group leader in the Earth & Space Science Division. Córdova holds a B.A. from Stanford University and a Ph.D. from Caltech. Nominees for the NSF director position must be confirmed by the Senate, which Córdova now awaits.—SUSAN MORRISSEY
COURTESY OF C. B. MUSGRAVE & A. W. WEIMER
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