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“Artificial leaves” could help power machines of future

March 26, 2010
Courtesy of the American Chemical Society
and World Science staff

Sci­en­tists are pre­sent­ing a de­sign strat­e­gy for a long-sought ar­ti­fi­cial leaf, which they say could har­ness Moth­er Na­ture’s abil­ity to pro­duce en­er­gy from sun­light and wa­ter. 

The blue­print, based on the chem­is­try and bi­ol­o­gy of leaves, could lead to work­ing pro­to­types of an ar­ti­fi­cial leaf that cap­ture so­lar en­er­gy and use it ef­fi­ciently to change wa­ter in­to hy­dro­gen fu­el, the re­search­ers said.

Part of the recipe for an artificial leaf (Credit: Tongxiang Fan)
Us­ing sun­light to split wa­ter in­to its com­po­nents, hy­dro­gen and ox­y­gen, is one of the most prom­is­ing and sus­tain­a­ble tac­tics to es­cape cur­rent de­pend­ence on coal, oil, and oth­er tra­di­tion­al fu­els, said re­search­er Tong­xi­ang Fan of Shang­hai Jiao­tong Uni­vers­ity in Chi­na. 

When burned, those fu­els re­lease car­bon di­ox­ide, the main “green­house gas” blamed for glob­al warm­ing be­cause of its heat-trapping ef­fects in the at­mos­phere. 

Burn­ing hy­dro­gen, in con­trast, forms just wa­ter va­por. That ap­peal is cen­tral to the much-discussed “hy­dro­gen econ­o­my”; some au­to com­pa­nies have de­vel­oped hy­dro­gen-fu­eled cars. Lack­ing, how­ev­er, is a cost-ef­fec­tive sus­tain­a­ble way to pro­duce hy­dro­gen.

Fan and col­leagues de­cid­ed to take a clos­er look at leaves, which har­vest en­er­gy from light ex­tremely ef­fi­ciently in a pro­cess called pho­to­syn­the­sis. Leaves con­tain struc­tures re­spon­si­ble for fo­cus­ing and guid­ing so­lar en­er­gy in­to their light-har­vesting ar­eas. The sci­en­tists opted to mim­ic that de­sign in a blue­print that in­cor­po­rates the com­pound ti­ta­ni­um di­ox­ide, al­ready rec­og­nized as a “photo-catalyst” for hy­dro­gen—a chem­i­cal stim­u­la­tor of hy­dro­gen pro­duc­tion from light.

In a two-step process, the sci­en­tists in­fil­trat­ed leaves of the Chin­ese plant Anem­o­ne vi­ti­fo­lia with ti­ta­ni­um di­ox­ide to cre­ate a new, ar­ti­fi­cial struc­ture based on that com­pound. They found that the struc­tur­al fea­tures in the leaf fa­vor­a­ble for light har­vesting were rep­li­cat­ed in the new struc­ture, which was meas­ured to be three times as ac­tive for hy­dro­gen pro­duc­tion as com­mer­cial photo-catalysts. 

Next, the in­ves­ti­ga­tors em­bed­ded sub-microscopic par­t­i­cles of plat­i­num in­to the leaf sur­face. This helped boost the ac­ti­vity of the ar­ti­fi­cial leaves by an ad­di­tion­al fac­tor of ten, they said. “Na­ture still has much to teach us, and hu­man in­genu­ity can mod­i­fy the prin­ci­ples of nat­u­ral sys­tems for en­hanced util­ity,” Fan de­clared. The find­ings were pre­sented March 25 at the Na­tional Meet­ing of the Amer­i­can Chem­i­cal So­ci­e­ty in San Fran­cis­co.

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Scientists are presenting a design strategy for a long-sought artificial leaf, which they say could harness Mother Nature’s ability to produce energy from sunlight and water in real leaves. The new recipe, based on the chemistry and biology of leaves, could lead to working prototypes of an artificial leaf that capture solar energy and use it efficiently to change water into hydrogen fuel, the researchers said. Using sunlight to split water into its components, hydrogen and oxygen, is one of the most promising and sustainable tactics to escape current dependence on coal, oil, and other traditional fuels, said researcher Tongxiang Fan of Shanghai Jiaotong University in China. When burned, those fuels release carbon dioxide, the main “greenhouse gas” blamed for global warming because of its heat-trapping effects in the atmosphere. Burning hydrogen, in contrast, forms just water vapor. That appeal is central to the much-discussed “hydrogen economy”; some auto companies have developed hydrogen-fueled cars. Lacking, however, is a cost-effective sustainable way to produce hydrogen. Fan and colleagues decided to take a closer look at leaves, which harvest energy from light extremely efficiently in a process called photosynthesis. Leaves contain structures responsible focusing and guiding of solar energy into the light-harvesting areas. The scientists opted to mimic that design in a blueprint that incorporates the compound titanium dioxide, already recognized as a “photo-catalyst” for hydrogen—a chemical stimulator of hydrogen production from light. The scientists infiltrated leaves of the Chinese plant Anemone vitifolia with titanium dioxide to create a new, artificial structure based on that compound. They found that the structural features in the leaf favorable for light harvesting were replicated in the new structure, which was measured to be three times as active for hydrogen production as commercial photo-catalysts. Next, the investigators embedded sub-microscopic particles of platinum into the leaf surface. This helped boost the activity of the artificial leaves by an additional factor of ten, they said. “Nature still has much to teach us, and human ingenuity can modify the principles of natural systems for enhanced utility,” Fan declared. The findings were presented March 25 at the National Meeting of the American Chemical Society in San Francisco.