Thursday, March 18, 2010

Artificial leaves for hydrogen production

(Nanowerk Spotlight) Artificial photosynthesis, using solar energy to split water generating hydrogen and oxygen, can offer a clean and portable source of energy supply as durable as the sunlight. Natural photosynthesis uses chlorophyll to absorb visible light and many solar hydrogen cells are imitating this process by using light-sensitive organic dye molecules as light absorbers and then transfer the absorbed energy to a catalyst that reduces protons to hydrogen (read: "Another step towards inexpensive hydrogen production from sunlight").

Today, over 130 materials and derivatives are known to facilitate photocatalytic splitting of water to produce hydrogen. Many efforts have been made to design new photocatalysts of different materials such as transition-metal oxides or metal oxynitrides or in nanotechnology research to design photocatalysts with various nanoscale morphologies such as nanoparticles, nanosheets, nanowires, etc for enhanced light-harvesting and catalytic efficiency.
"Using sunlight to split water molecules and form hydrogen fuel is one of the most promising tactics for kicking our carbon habit," Di Zhang tells Nanowerk. "Of the possible methods, nature provides the blueprint for converting solar energy in the form of chemical fuels. A natural leaf is a synergy of the elaborated structures and functional components to produce a highly complex machinery for photosynthesis in which light harvesting, photoinduced charge separation, and catalysis modules combined to capture solar energy and split water into oxygen and hydrogen efficiently."
Zhang, a professor at Shanghai Jiao-Tong University in China and director of the university's State Key Laboratory of Metal Matrix Composites, points out that the design of efficient, cost-effective artificial systems by coupling of leaf-like hierarchical structures and analogous functional modules under the guidance of the key steps of natural photosynthesis into hydrogen would be a major advance in energy conversion.
Many efforts have been made to develop such systems by constructing a variety of analogous molecular systems consisting of electron donors and acceptors to mimic light driven charge separation or by assembling semiconductor photocatalysts into various nanostructures. However, most of them only focused on the functional imitation of photosynthesis, and neglected the structural effect. Read more.

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