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April 11, 2011

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Scientists claim first practical “artificial leaf”

March 28, 2011
Courtesy of the American Chemical Society
and World Science staff

Sci­en­tists have claimed a mile­stone in the drive for sus­tain­a­ble en­er­gy: de­vel­op­ment of the first prac­ti­cal ar­ti­fi­cial leaf.

Speak­ing at the an­nu­al of the Amer­i­can Chem­i­cal So­ci­e­ty in An­a­heim, Calif., on March 27, re­search­ers de­scribed an ad­vanced so­lar cell the size of a play­ing card that mim­ics the pro­cess, called pho­to­syn­the­sis, that green plants use to con­vert sun­light and wa­ter in­to en­er­gy.

“A prac­ti­cal ar­ti­fi­cial leaf has been one of the Holy Grails of sci­ence for dec­ades,” said chem­ist Dan­iel No­cera, who led the proj­ect. “We be­lieve we have done it. The ar­ti­fi­cial leaf shows par­tic­u­lar prom­ise as an in­ex­pen­sive source of elec­tri­city for homes of the poor in de­vel­op­ing coun­tries. Our goal is to make each home its own pow­er sta­t­ion,” he said. “One can en­vi­sion vil­lages in In­dia and Af­ri­ca not long from now pur­chas­ing an af­ford­a­ble bas­ic pow­er sys­tem based on this tech­nol­o­gy.”

The de­vice is made from sil­i­con, elec­tron­ics and cat­a­lysts—sub­stances that ac­cel­er­ate or en­a­ble spe­cif­ic chem­i­cal re­ac­tions. Placed in a gal­lon of wa­ter in bright sun­light, the de­vice could pro­duce enough elec­tri­city to supply a house in a de­vel­op­ing coun­try with elec­tri­city for a day, No­cera said. It does so by split­ting wa­ter in­to its two com­po­nents, hy­dro­gen and ox­y­gen. The hy­dro­gen and ox­y­gen gas­es would be stored in a fu­el cell, which uses those two ma­te­ri­als to pro­duce elec­tri­city.

Ar­ti­fi­cial leaves are­n’t a new con­cept, not­ed No­cera, who is with the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy. The first one was de­vel­oped over a dec­ade ago by John Turn­er of the U.S. Na­t­ional Re­new­able En­er­gy Lab­o­r­a­to­ry in Boul­der, Colo. Al­though it car­ried out pho­to­syn­the­sis well, Turn­er’s de­vice was imprac­ti­cal, as it was made of rare, costly met­als and stopped work­ing af­ter a day.

No­cera’s new leaf pur­portedly overcomes these prob­lems. It con­sists of widely avail­a­ble, af­ford­a­ble ma­te­ri­als, works un­der sim­ple con­di­tions and is sta­ble. In lab­o­r­a­to­ry stud­ies, he showed that an pro­to­type could oper­ate con­tin­u­ously for at least 45 hours with­out a drop in ac­ti­vity.

The key, he said, was his disco­very of sev­er­al pow­erful new, in­ex­pen­sive cat­a­lysts, made of nick­el and co­balt, ca­pa­ble of ef­fi­ciently split­ting wa­ter un­der sim­ple con­di­tions. No­cera said his leaf is about 10 times more ef­fi­cient at pho­to­syn­the­sis than a real leaf, and will be­come even more ef­fi­cient in the fu­ture.

“Na­ture is pow­ered by pho­to­syn­the­sis, and I think that the fu­ture world will be pow­ered by pho­to­syn­the­sis as well in the form of this ar­ti­fi­cial leaf,” said No­cera.

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Scientists have claimed a milestone in the drive for sustainable energy: development of the first practical artificial leaf. Speaking at the annual of the American Chemical Society in Anaheim, Calif., on March 27, researchers described an advanced solar cell the size of a playing card that mimics the process, called photosynthesis, that green plants use to convert sunlight and water into energy. “A practical artificial leaf has been one of the Holy Grails of science for decades,” said chemist Daniel Nocera, who led the project. “We believe we have done it. The artificial leaf shows particular promise as an inexpensive source of electricity for homes of the poor in developing countries. Our goal is to make each home its own power station,” he said. “One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology.” The device is made from silicon, electronics and catalysts—substances that accelerate or enable specific chemical reactions. Placed in a gallon of water in a bright sunlight, the device could produce enough electricity to supply a house in a developing country with electricity for a day, Nocera said. It does so by splitting water into its two components, hydrogen and oxygen. The hydrogen and oxygen gases would be stored in a fuel cell, which uses those two materials to produce electricity. The “artificial leaf” isn’t a new concept, noted Nocera, who is with the Massachusetts Institute of Technology. The first was developed over a decade ago by John Turner of the U.S. National Renewable Energy Laboratory in Boulder, Colo. Altthough it carried out photosynthesis well, Turner’s device was impractical, as it was made of rare, costly metals and stopped working after a day. Nocera’s new leaf purportedly overcomes these problems. It consists of widely available, affordable materials, works under simple conditions and is stable. In laboratory studies, he showed that an prototype could operate continuously for at least 45 hours without a drop in activity. The key to was Nocera’s discovery of several powerful new, inexpensive catalysts, made of nickel and cobalt, capable of efficiently splitting water into its two components, hydrogen and oxygen, under simple conditions. Nocera said his leaf is about 10 times more efficient at photosynthesis than a natural leaf, and will become even more efficient in the future. “Nature is powered by photosynthesis, and I think that the future world will be powered by photosynthesis as well in the form of this artificial leaf,” said Nocera.