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Honolulu, Hawaii, United States, 2006/10/06 - Researchers demonstrate a new class of low cost (non-precious metal/heteroatomic polymer) nanocomposite catalysts for the PEFC cathode, capable of combining high oxygen-reduction activity with good performance durability.
Fuel cells are electrochemical energy conversion devices for the direct conversion of the chemical energy of a fuel into electricity. They are among the key enabling technologies for the transition to a hydrogen-based economy. Of several different types of fuel cells under development today, polymer electrolyte fuel cells (PEFCs) have been recognized as a potential future power source for zero emission vehicles. However, to become commercially viable, PEFCs have to overcome the barrier of high catalyst cost caused by the exclusive use of platinum and platinum-based catalysts in the fuel-cell electrodes. Researchers at Los Alamos National Laboratory now demonstrate a new class of low cost (non-precious metal/heteroatomic polymer) nanocomposite catalysts for the PEFC cathode, capable of combining high oxygen-reduction activity with good performance durability. The results of their study show that heteroatomic polymers can be used not only to stabilize the nonprecious metal in the acidic environment of the PEFC cathode but also to generate active sites for oxygen reduction reaction.
Two approaches are at present gaining momentum to replace platinum, which is scarce and expensive. One approach uses non-platinum catalysts that nonetheless contain precious metals with limited abundance and/or limited world distribution. Such catalysts are typically based on palladium or ruthenium. Although platinum is thus avoided, the result is the replacement of one precious metal with another that is on the whole less active than platinum.
An alternative approach is to replace platinum with abundant, nonprecious materials that are not susceptible to price inflation under high-demand circumstances.
The class of non-precious cathode catalysts that has attracted the most attention over the years is pyrolized metal porphyrins, with cobalt and iron porphyrins viewed as the most promising precursors.
"The search for practically viable non-precious metal oxygen reduction reaction (ORR) catalysts for the polymer electrolyte fuel cell (PEFC) cathode is by no means new, dating back to 1960's or even before that" Dr. Piotr Zelenay, a Project Leader in the Materials Science and Technology Division of Los Alamos National Laboratory, points out to Nanowerk. "Several different classes of non-precious metal catalysts have been investigated over the years, including pyrolized transition-metal porphyrins. Some of these materials have shown respectable oxygen-reduction activity - still far lower than that of platinum, which is the state-of-the-art ORR (oxygen reduction reaction) catalyst - but not a good stability. Typically, catalyst performance degradation begins as soon as the catalyst is introduced into a fuel cell and continues until it is no longer active."
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By Michael Berger, Copyright 2006 Nanowerk LLC