A new way to split water molecules into hydrogen and oxygen by using just the sun and ultrathin films of iron oxide (rust) has been developed by researchers from the Technion-Israel Institute of Technology. This technological breakthrough will almost undoubtedly lead to more efficient, and less expensive, ways to store solar energy.
By using the sun to split water molecules and create hydrogen-based fuels, the energy of the sun can then be used at any time and in any place, rather than just those that are conducive to direct solar power. The researchers think that this could be a major factor in the replacing of fossil fuels.
“Our approach is the first of its kind,” says lead researcher Associate Prof. Avner Rothschild, of the Department of Materials Science and Engineering. “We have found a way to trap light in ultrathin films of iron oxide that are 5,000 times thinner than typical office paper. This is the enabling key to achieving high efficiency and low cost.”
Iron oxide, also known as rust, has many clear benefits as a semiconductor material; it is very common, very inexpensive to produce, stable in water, and, in contrast to other semiconductors, it “can oxidize water without itself being oxidated, corroded, or decomposed,” a news release from American Technion Society notes. There are challenges to working with it, though, the largest of which is its poor electrical transport properties. “Researchers have struggled for years with the tradeoff between light absorption and the separation and collection of photogenerated charge carriers before they die out by recombination.”
“Our light-trapping scheme overcomes this tradeoff, enabling efficient absorption in ultrathin films wherein the photogenerated charge carriers are collected efficiently,” says Prof. Rothschild. “The light is trapped in quarter-wave or even deeper sub-wavelength films on mirror-like back reflector substrates. Interference between forward- and backward-propagating waves enhances the light absorption close to the surface, and the photogenerated charge carriers are collected before they die off.”
This creates the potential of making inexpensive solar cells that can combine both ultrathin iron oxide photoelectrodes and conventional photovoltaic cells. Simultaneously producing electricity and hydrogen, these solar cells would be able to efficiently store energy for use anytime, 24 hours per day, which is a significant advantage compared to conventional photovoltaic cells. One of the primary criticisms of solar power is its inability to produce electricity when it is very cloudy, but this new technology could remedy that.
And since the new technology uses only very common materials, it could go a long way towards reducing the use of expensive rare earth elements in solar panels, most of which is imported from geopolitical competitors, reducing the use of rare elements like Tellurium and Indium by up to 90%, with no loss of performance.
The new research was just published in the journal Nature Materials.
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