Mar
25
Competition for Platinum Catalysts in Fuel Cells
March 25, 2011 | 3 Comments
Liming Dai, a professor of chemical engineering and research associates Shuangyin Wang and Dingshan Yu at Case Western Reserve University 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.
Carbon Nanotube Doped to Act as a Catalyst. Click image for the largest view. Image Credit: The Dai Lab, Case Western Reserve University.
The team believes their activated carbon nanotubes cost about $100 per kilogram to make. In contrast, platinum, which represents at least a quarter of the cost of fuel cells, currently sells for about $65,000 per kilogram. Much of the research in fuel cells has been delayed or stopped by those costs. If the coated nanotube production can scale up, fuel cells could have a whole new kind of future.
The abstract offers a more technical, but understandable view, “Having a strong electron-withdrawing ability, poly (diallyldimethylammonium chloride) (PDDA) was used to create net positive charge for carbon atoms in the nanotube carbon plane via intermolecular charge transfer. The resultant PDDA functionalized/adsorbed carbon nanotubes (CNTs), either in an aligned or nonaligned form, were demonstrated to act as metal-free catalysts for oxygen reduction reaction (ORR) in fuel cells with similar performance as Pt (platinum) catalysts. The adsorption-induced intermolecular charge-transfer should provide a general approach to various carbon-based efficient metal-free ORR catalysts for oxygen reduction in fuel cells, and even new catalytic materials for applications beyond fuel cells.”
In the lab the team 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.
In testing, the fuel cell produced as much power as an identical cell using a platinum catalyst.
Dai and his team 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.
There are other advantages already easy to see. 1. The activated nanotubes last longer and are more stable. 2. Unlike platinum, the carbon-based catalyst: doesn’t lose catalytic activity and, therefore, efficiency, over time; isn’t fouled by carbon monoxide poisoning; 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.
No CO poisoning is very, very encouraging news. Added to longer service life prospects the team is sure to get lots of enquiries and the paper at the ACS journal will gets closely reviewed.
The beginning is not over yet, 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 electrons partially from the carbon to create a charge.
Testing showed the nitrogen-doped carbon nanotubes tripled the energy output of platinum.
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.”
Its looking like the threshold for practical affordable fuels cell is getting close. With product demonstrators from portable electronics and small vehicles up to full sized farm tractors powered by fuel cells – the engineering is pretty far along. Even more encouraging is the Dai Lab team’s work can effectively use methanol, a liquid that would solve the notorious gaseous hydrogen storage problem.
Should the doping research equal the already known nitrogen doped results, fuel cells would be reduced in size by about 2/3rds cutting even more cost from production units.
This is one technological breakthrough that will get intense attention. And “breakthrough” might turn out to be a lightweight choice in terms. Cheap fuel cells with low cost light alcohol fuels could give the electron drive guys a real run for the market.
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I’m not sure that increasing the output of the catalyst would decrease the size of the stack by 2/3rds. Anyone?
Checking further the platinum catalyst is used in the anode, and so only that element would be reduced in size, it would appear:
http://en.wikipedia.org/wiki/File:PEM_fuelcell.svg
“isn’t fouled by carbon monoxide poisoning”
Not only will using carbon nanotubes reduce the cost of manufacture – but it won’t require the costly step of super-refining the Hydrogen inputs to remove carbon monoxide. This is a huge advantage and will significantly reduce the fuel costs.