Artificial photosynthesis moves a step closer to reality

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    "Ke Sun’s reflection onto a sample coating with the nickel oxide film his team developed. (Credit: Lance Hayashida, Caltech Marcomm)"
    A team led by Ke Sun, the George L. Argyros professor and Nate Lewis, the professor of chemistry at Caltech, devised a new film coating that facilitated catalysis and electron transfer in a solar powered system that split water into hydrogen and oxygen, which can be used as fuels. Such a system is also called an artificial leaf or solar-fuel generator because in many ways it mimics the process which plants use to convert sunlight and CO2 into oxygen and fuel (sugars, carbohydrates). Their study was published online in the Proceedings of the National Academy of Sciences. The artificial leaf developed at the Caltech Joint Center for Artificial Photosynthesis (JCAP) consists of three main components: two electrodes — a photoanode and a photocathode — and a membrane. The photoanode uses sunlight to oxidize water molecules to generate oxygen gas, protons, and electrons, while the photocathode recombines the protons and electrons to form hydrogen gas. The coating is a nickel oxide film that prevents rusts building- up on the semiconductor electrodes (silicon or gallium arsenide), while also acting as a highly reactive catalysis. The membrane, which is typically made of plastic, keeps the two gases separate in order to eliminate any possibility of an explosion, and allows the gas to collect under pressure to safely push it into a pipeline.The membrane for their artificial leaf only allows hydrogen protons to pass through, like an ion sieve, while hydrogen and oxygen gases are safely and separately expelled to use as fuels or oxidants. They developed a technique for creating the nickel oxide film that involved smashing atoms of argon into a pellet of nickel atoms at high speeds, in an oxygen rich environment. The film works well in conjunction with the membrane that separates the photoanode from the photocathode and staggers the production of hydrogen and oxygen gases.