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Thursday 27 July 2017

New triple-layered catalyst to split water into hydrogen, oxygen




Splitting water into hydrogen and oxygen to produce clean energy can be simplified with a single catalyst developed by scientists at Rice University and the University of Houston.
The electrolytic film produced at Rice and tested at Houston is a three-layer structure of nickel, graphene and a compound of iron, manganese and phosphorus. The foamy nickel gives the film a large surface, the conductive graphene protects the nickel from degrading and the metal phosphide carries out the reaction.
The research is published in the journal Nano Energy.
Rice chemist Kenton Whitmire and Houston electrical and computer engineer Jiming Bao and their labs developed the film to overcome barriers that usually make a catalyst good for producing either oxygen or hydrogen, but not both simultaneously.
“Regular metals sometimes oxidize during catalysis,” Whitmire said. “Normally, a hydrogen evolution reaction is done in acid and an oxygen evolution reaction is done in base. We have one material that is stable whether it’s in an acidic or basic solution.”
The discovery builds upon the researchers’ creation of a simple oxygen-evolution catalyst revealed earlier this year. In that work, the team grew a catalyst directly on a semiconducting nanorod array that turned sunlight into energy for solar water splitting.
Electrocatalysis requires two catalysts, a cathode and an anode. When placed in water and charged, hydrogen will form at one electrode and oxygen at the other, and these gases are captured. But the process generally requires costly metals to operate as efficiently as the Rice team’s catalyst.
The new catalyst also requires less energy, Whitmire said. “If you want to make hydrogen and oxygen, you have to put in energy, and the more you put in, the less commercially viable it is,” he said. “You want to do it at the minimum amount of energy possible. That’s a benefit of our material: The overpotential (the amount of energy required to trigger electrocatalysis) is small and quite competitive with other materials. The lower you can get it, the closer you come to making it as efficient as possible for water splitting.”

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