A team from Cornell University and Brookhaven National Laboratory has devised a new class of core-shell electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, consisting of a platinum (Pt) monolayer shell and ordered intermetallic compound cores.
These electrocatalysts comprise a Pt monolayer shell and ordered intermetallic compounds cores and have enhanced activity and stability compared with conventional ones. These advantages, the researchers said, are derived from combining the unique properties of Pt monolayer catalysts (high activity, low metal content) and of the intermetallic compounds (high stability and, possibly, low price). A paper on their work was published online 29 December in the Journal of the American Chemical Society.
The insufficient catalytic activity and stability of Pt for the oxygen reduction reaction (ORR) at fuel cell cathodes and its high content in catalysts remain major obstacles to the widespread commercialization of this technology. We describe one promising way of resolving these impediments with a class of electrocatalysts comprising a Pt monolayer deposited on intermetallic compound nanoparticles. The enhanced activity and stability of this class of electrocatalysts are derived from the combination of the unique properties of Pt monolayer catalysts and of the intermetallic compounds. Pt monolayers (PtML) deposited on late-transition metals or their alloys exhibit high activity at ultralow Pt content. Some intermetallic compound nanoparticles are stable and highly active catalysts for small organic molecule oxidation. By combining these materials we obtain electrocatalysts that can overcome the above-named obstacles.
—Ghosh et al.
In the JACS paper, the researchers reported on the electrocatalytic properties of PtML deposited on PtPb, PdPb, and PdFe intermetallic compound nanoparticles. The intermetallics with Pd afford an excellent support for a PtML, while PdFe alloys have the advantage of being Pt-free, in addition to having high activity.
The team found that the Pt/PtPb catalysts produced currents at 0.9 V as high as 2.7 mA/cm-2 (geometric surface area). They also found that the PdFe samples investigated showed interesting morphologies and excellent activity, and concluded that the possible presence of additional functionalities warrant further studies.
Our data indicate strategies suitable for selecting the types of intermetallic compounds as the support for a Pt monolayer. We consider that this fabrication method holds excellent potential for creating efficient fuel cell electrocatalysts.
—Ghosh et al.
Tanushree Ghosh, Miomir B. Vukmirovic, Francis J. DiSalvo and Radoslav R. Adzic (2009) Intermetallics as Novel Supports for Pt Monolayer O2 Reduction Electrocatalysts: Potential for Significantly Improving Properties. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja905850c