IT'S NOT AS IF PLANTS WORK...:

Plants are excellent at absorbing sunlight and using its energy to split water. Scientists have been trying to mimic photosynthesis to make hydrogen fuel from water using different techniques. One relies on special semiconductor materials that absorb sunlight and produce electricity to split water in a battery-like electrochemical cell. But those need corrosive electrolytes that are not environmentally benign.

A more direct approach is to use semiconductor catalysts that trigger a water-splitting reaction when they are energized by the sun. But the solar-to-hydrogen efficiencies of such photocatalytic systems have been pretty low so far, with the best reaching just below 3 percent.

Mi and his colleagues found a way to boost this efficiency via two pathways. One was to use concentrated sunlight. The other was to harness higher-wavelength visible light and heat-producing infrared light that is usually wasted by conventional catalysts.

The key advance that lets them harvest more sunlight is the catalyst they use: nanowires of indium gallium nitride grown on a silicon wafer. Unlike traditional catalysts, which break down under concentrated sunlight, the nanowires are self-healing and in fact become more efficient at producing hydrogen over time. The nanowires can also absorb a very wide spectrum of sunlight. They harvest higher wavelengths of visible light to trigger the water-splitting reaction. The infrared heat they absorb, meanwhile, accelerates the reactions and keeps the hydrogen and oxygen separate, boosting efficiency.

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