Mar 22, 2011 |
Cheap catalyst made easy with carbon nanotubes
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(Nanowerk News) Catalysts made of carbon nanotubes dipped in a polymer solution equal the energy output and otherwise outperform platinum catalysts in fuel cells, a team of Case Western Reserve University engineers has found.
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(Also see our Nanowerk Spotlight on this research: "Role of intermolecular charge transfer promises efficient metal-free catalysts").
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The researchers are certain that they'll be able to boost the power output and maintain the other advantages by matching the best nanotube layout and type of polymer.
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But already they've proved the simple technique can knock down one of the major roadblocks to fuel cell use: cost.
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Platinum, which represents at least a quarter of the cost of fuel cells, currently sells for about $65,000 per kilogram. These researchers say their activated carbon nanotubes cost about $100 per kilogram.
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Their work is published in the online edition of Journal of the American Chemical Society ("Polyelectrolyte Functionalized Carbon Nanotubes as Efficient Metal-free Electrocatalysts for Oxygen Reduction").
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"This is a breakthrough," said Liming Dai, a professor of chemical engineering and the research team leader.
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Dai and research associates Shuangyin Wang and Dingshan Yu found that by simply soaking carbon nanotubes in a water solution of the polymer polydiallyldimethylammoniumn chloride for a couple of hours, the polymer coats the nanotube surface and pulls an electron partially from the carbon, creating a net positive charge.
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They placed the nanotubes on the cathode of an alkaline fuel cell. There, the charged material acts as a catalyst for the oxygen-reduction reaction that produces electricity while electrochemically combining hydrogen and oxygen.
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In testing, the fuel cell produced as much power as an identical cell using a platinum catalyst.
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But the activated nanotubes last longer and are more stable, the researchers said. Unlike platinum, the carbon-based catalyst: doesn't lose catalytic activity and, therefore, efficiency, over time; isn't fouled by carbon monooxide poising; and is free from the crossover effect with methanol. Methanol, a liquid fuel that's easier to store and transport than hydrogen, reduces activity of a platinum catalyst when the fuel crosses over from the anode to the cathode in a fuel cell.
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The new process builds on the Dai lab's earlier work using nitrogen-doped carbon nanotubes as a catalyst. In that process, nitrogen, which was chemically bonded to the carbon, pulled electron partially from the carbon to create a charge. Testing showed the doped tubes tripled the energy output of platinum.
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Dai said the new process is far simpler and cheaper than using nitrogen-doped carbon nanotubes and he's confident his lab will increase the energy output as well. "We have not optimized the system yet."
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