10 Unsolved Mysteries -> How Do We Tap More Solar Energy?

With every sunrise comes a reminder that we currently tap only a pitiful fraction of the vast clean-energy resource that is the sun. The main problem is cost: the expense of conventional photovoltaic panels made of silicon still restricts their use. Yet life on Earth, almost all of which is ultimately solar-powered by photosynthesis, shows that solar cells do not have to be terribly efficient if, like leaves, they can be made abundantly and cheaply enough.

“One of the holy grails of solar-energy research is using sunlight to produce fuels,”

says Devens Gust of Arizona State University. The easiest way to make fuel from solar energy is to split water to produce hydrogen and oxygen gas. Nathan S. Lewis and his collaborators at Caltech are developing an artificial leaf that would do just that [see illustration on opposite page] using silicon nanowires.

Earlier this year Daniel Nocera of the Massachusetts Institute of Technology and his co-workers unveiled a siliconbased siliconbased membrane in which a cobaltbased photocatalyst does the water splitting. Nocera estimates that a gallon of water would provide enough fuel to power a home in developing countries for a day. “Our goal is to make each home its own power station,” he says.

Splitting water with catalysts is still tough. “Cobalt catalysts such as the one that Nocera uses and newly discovered catalysts based on other common metals are promising,” Gust says, but no one has yet found an ideal inexpensive catalyst. “We don’t know how the natural photosynthetic catalyst, which is based on four manganese atoms and a calcium atom, works,” Gust adds.

Gust and his colleagues have been looking into making molecular assemblies for artificial photosynthesis that more closely mimic their biological inspiration, and his team has managed to synthesize some of the elements that could go into such an assembly. Still, a lot more work is needed on this front. Organic molecules such as the ones nature uses tend to break down quickly. Whereas plants continually produce new proteins to replace broken ones, artificial leaves do not (yet) have the full chemicalsynthesis machinery of a living cell at their disposal.

Source of Information : Scientific American Magazine