US scientists report bimetallic PEM fuel cell catalyst

Materials scientists at Washington University in St Louis, Missouri (WUSTL) have developed a technique for producing a bimetallic fuel cell catalyst that they say is efficient, robust, and between two and five times more effective than commercial catalysts. The palladium-platinum bimetallic nanodendritic structure offers high activity for oxygen reduction on PEM fuel cell cathodes.

Professor Younan Xia led a team of scientists at WUSTL and at Brookhaven National Laboratory in New York in developing a bimetallic catalyst comprised of a palladium core or ‘seed’ that supports dendritic platinum branches, that are fixed on the nanostructure, consisting of a 9 nm core and 7 nm platinum arms. The study was published online recently in Science.

The team synthesized the catalysts by sequentially reducing precursor compounds to palladium and platinum with L-ascorbic acid (i.e. vitamin C) in an aqueous solution. The catalysts have a high surface area, which is invaluable for a number of applications besides fuel cells, and are robust and stable.

Xia and his team tested how the catalysts performed in the oxygen reduction reaction process in a fuel cell, which determines how large a current will be generated in an electrochemical system similar to the cathode of a PEM fuel cell.

They found that their bimetallic nanodendrites, at room temperature, were two-and-a-half times more effective per platinum mass for this process than a state-of-the-art commercial platinum catalyst, and five times more active than another leading commercial catalyst. At an operating temperature of 60°C, the performance almost meets the Department of Energy targets set.

Xia and his collaborators are exploring the possibility of adding other noble metals, such as gold, to the bimetallic catalysts, making them trimetallic. Gold has been shown to oxidize CO, making for even more robust catalysts that can resist CO poisoning.

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