Researchers at the US Department of Energy ’s Pacific Northwest National Laboratory used iron-based catalysts to split hydrogen quickly and efficiently for the first time, greatly reducing the cost of fuel cells. The research results were published in the latest online edition of Nature & Chemistry.
R. Morris Bullock, the head of the laboratory's molecular electrocatalysis center and chemist, said that the current fuel cell uses platinum as a catalyst, and its disadvantage is that the price is more than 1,000 times higher than iron. And his research team has developed the use of cheaper metals, such as nickel and iron as catalysts, which can quickly split hydrogen up to two molecules per second, close to the efficiency of commercial catalysts.
Fuel cells use hydrogen to generate electrons in chemical fuels: a large piece of metal platinum acts as a catalyst, bursting a hydrogen molecule as if blasting an egg, and white electrons like egg white "flow" out to form a current. Because of the special chemical properties of platinum, chemists cannot simply replace this expensive metal with cheaper iron or nickel. However, a molecule called "hydrogenase" that exists in nature can split iron from hydrogen.
Inspired by hydrogenase's use of iron as a catalyst, Bullock and his colleagues first created several potential molecules for testing; and then determined the shape of the best performing molecules and adjusted the power of internal electrons to achieve more improvements.
To do this, it is necessary to separate hydrogen molecules unevenly in the early process. In view of the fact that a hydrogen molecule is composed of two protons and two electrons, a proton needs to be dragged and sent by a catalyst first, and then it will be captured by a molecule called a proton acceptor. In actual fuel cells, this receptor will be oxidized. Once the pulling force between the initial proton and its electron is dissipated, the electrode will easily pull off the first electron. Then, another proton and electron will also be removed, so that the two electrons will shuttle between the electrodes.
Through the design of the experiment, the research team measured the rate at which the catalyst splits hydrogen molecules. The highest value is about two molecules per second. In addition, the researchers also determined its overvoltage to measure the efficiency of the catalyst. The results show that overvoltages of 160-220 millivolts clearly have the efficiency of commercial catalysts. The research team is currently trying to slow down these reaction steps so that it can also be accelerated, and to determine the performance of the catalyst under optimal conditions.
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