Besides, many of the alternative approaches are being pursued elsewhere. Up the coast in Santa Barbara, California, for example, a start-up firm called HyperSolar is testing a system in which coated nano- or micro-particles combining a photoabsorber and a catalyst are placed in a transparent, water-filled plastic bag. The bag will inflate as it is exposed to sunlight, and hydrogen and oxygen gas form inside. Such units could be deployed in sunny regions such as deserts. A 2009 DOE report5 estimated that, if it uses cheap materials, this 'baggie' approach could produce hydrogen economically with 10% efficiency, stable for 10 years.
But the system is risky, says Turner, because it produces oxygen along with the hydrogen. “If you're talking about 100 square miles of baggies in the desert with this explosive mixture,” he says, “one lightning bolt and you have a disaster.” HyperSolar researchers are exploring several ways to eliminate that danger. One is to use a system that separates the gases into two bags, says Syed Mubeen, a postdoc at the University of California, Santa Barbara, and lead scientist at the company. Another is to run the system using waste water rather than pure water, so that the oxygen reacts with organic impurities and degrades them into valuable chemicals. This approach “completely removes oxygen out of the equation”, says Mubeen. As with JCAP's stable photoanode, HyperSolar's photoabsorber is protected by a coating.
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