Hitachi Maxell Develops New Gold-Platinum Catalyst Enabling Higher Performance Fuel Cells
01 April 2008
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| An electron microscope photograph of a gold-platinum (AuPt) catalyst deposited on a conductive carbon support. The dark grey or black areas are the gold-platinum catalysts, and the light grey areas are the carbon support. Click to enlarge |
Hitachi Maxell, Ltd. has developed a new gold-platinum (AuPt) nanoparticle catalyst 2 to 3 nanometers in size for polymer electrolyte fuel cells. Used in the oxygen reduction reaction at the cathode, the new AuPt catalyst generates approximately 4.8 times more oxygen reduction current per unit area than current commercial platinum catalysts.
Fuel cell developers are seeking to reduce the material cost of the devices by minimizing the utilization of platinum—generally used as a catalyst for the oxygen reduction reaction—while further improving catalytic activity. Increasing surface area by reducing the size of the catalyst particles is one approach.
Adding base metals such as iron (Fe), cobalt (Co) and nickel (Ni) to Pt also improves the oxygen reduction reaction activity. However, these kinds of base metals are easy to dissolve in acidic media where the catalyst works in fuel cells.
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| The oxygen reduction reaction activity of commercial platinum (Pt) and gold-platinum (AuPt) catalysts deposited on the same conductive carbon support (specific surface area: 800 m2/g). The oxygen reduction currents were normalized by unit surface area of the catalysts. NHE = normalized hydrogen electrode. Click to enlarge. |
Maxell’s new catalyst is composed of Pt and Au that is resistant to acidic media. However, it is difficult to synthesize Au particles with size less than 5 nanometer due to its relatively low melting point. Maxell developed a process to produce a new catalyst with a high-activity structure in which Au and Pt are not fully alloyed. Using citric acid as a reducing agent, Maxell synthesized the AuPt catalyst, 2 to 3 nanometers in size, at 373 K. Maxell suggests that the structure, in which Au and Pt are not fully alloyed, as evaluated by X-ray diffraction analysis, improves the oxygen reduction reaction activity.
Maxell presented this new technology for synthesizing the highly active AuPt catalyst at a catalysis conference in Tokyo on 29 March. The company will continue research and development on the catalyst and the technology with a view to practical application in polymer electrolyte fuel cells and direct methanol fuel cells.
This looks encouraging. Gold is less expensive than platinum and an increase in performance helps as well. It would be nice if they could use less expensive catalysts, but this is a good step. I do not know how much gold and platinum they use in a fuel cell per KW, I am hoping that his is not what makes them so expensive.
Posted by: sjc | 01 April 2008 at 09:07 AM
However, these kinds of base metals are easy to dissolve in acidic media where the catalyst works in fuel cells.
So why not alkaline fuel cells? The carbonate precipitation problem is likely easier to solve than that of reducing the Pt loading.
Posted by: Paul Dietz | 01 April 2008 at 02:09 PM
I just hope that one day they find a way to use lead or something like that has no value b/c as soon as i read this article i think of someone going in and trying to steal the catalyst for the material. Then again i am probably overreacting.
Posted by: JJSpawn | 02 April 2008 at 06:48 AM
"..4.8 times more oxygen reduction current per unit area than current commercial platinum catalysts."
That is really significant and if they can use very little precious metal by using nano particles that is even better. The contamination may be an issue though.
Posted by: sjc | 02 April 2008 at 09:43 AM
It is misleading. What they measured is diffusion limited current, not kinetic current of ORR. The diffusion limited current is controlled by the hydrodynamic layer which is related to the morphology of electrode. My 2 cents.
Posted by: TH | 04 April 2008 at 12:45 PM
Thanks for the clarification. It sounds like when combining metals with platinum, you not only save platinum but get a better catalytic reaction. Other metals degrade, so they used gold. Gold is cheaper than platinum, so that is a plus. This seems like an advance, but it remains to be see if it is enough of an advance to make a difference.
Posted by: sjc | 05 April 2008 at 09:47 AM