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Researchers have demonstrated that fuels such as butane and diesel can be used to produce electricity in newly designed fuel cells without first converting hydrocarbons to hydrogen. The study moves fuel cells closer to commercial viability by providing users with fuel options that are more convenient, less expensive, and potentially safer than the commonly used fuel—hydrogen.
Attractive because of their energy-efficient and nonpolluting nature, fuel cells employ catalyzed electrochemical reactions (not combustion) to convert fuels to electric power. Many substances, including methane and methanol, have been examined as candidate fuels for these power sources but with limited success.
Now, Authors have developed electrode materials that enable common hydrocarbons like butane to liberate their stored electrochemical energy without quickly gunking up fuel cells, which is a problem that commonly plagues researchers in this area.
The key to the improved performance in the Org. solid-oxide fuel cells (so called because they include a solid-phase oxide electrolyte) is using anodes made of a composite of copper and ceria—or samaria-doped ceria—in place of the ceramic-metal composite conventionally used: nickel and yttria-stabilized zirconia.
Author explains that nickel is commonly used in solid-oxide fuel cells because it is a good electronic conductor and a good steam-reforming catalyst. That is, used with water, it can convert methane to hydrogen to feed a fuel cell. But nickel also turns hydrocarbons into graphite. And that reaction eventually kills fuel-cell performance.
"We replaced nickel with copper because it is rather inert to C-H bond breaking—and therefore avoids carbon formation—yet it is an excellent electronic conductor," Author asserts. The Org. group was familiar with ceria s properties from its earlier automobile emissions catalysis work. The researchers selected that material because of its high activity for hydrocarbon oxidation and its high ionic conductivity. Excellent ion mobility is needed to ensure efficient reaction between hydrocarbons and O2-.
Using their redesigned anode materials, the researchers tested fuel cells on a variety of hydrocarbons, including alkanes, alkenes, and aromatic compounds. The results are very promising.
"We have demonstrated that we can build a fuel cell that runs on hydrocarbons—even synthetic diesel fuel," Author says. "It provided reasonable power densities and ran up to four days with no evidence of coking or deterioration." By contrast, conventional solid-oxide fuel cells would have failed quickly as a result of carbon fouling.
Although Author acknowledges that there is more work to do to further boost power densities and improve the device s response to temperature cycling, this study may help retire the old tongue-in-cheek adage that states, "Fuel cells can run on any fuel—so long as it is hydrogen."
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