Tuesday, October 25, 2011

10 Unsolved Science Mysteries (part 7) : 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 (treasure knowledge) 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 using silicon nanowires.
     Earlier this year , scientist, Daniel Nocera of the  Massachusetts Institute of Technology and his co-workers unveiled a silicon-based membrane in which a cobalt-based photocatalyst does the water splitting. Nocera estimates that a gallon of  water would provide enough fuel to pow-er 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 photo-synthetic 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. Where-as plants continually produce new proteins to replace broken ones, artificial  leaves do not (yet) have the full chemical-synthesis machinery of a living cell at  their disposal.



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