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New methodology could reduce cost of catalytic material
January 07, 2010
One of the most pressing concerns in PEMFC development is the high cost of the catalytic material. There is thus a large effort underway to reduce the content of expensive precious metal (i.e., Pt) in the catalyst. The team of Prof. John Van Zee and John Monnier from the Department of Chemical Engineering have been working on a new methodology based on electroless deposition to prepare controlled structure core-shell nanoparticles that can address this issue. The following is taken from the abstract of their published paper.
Cobalt core/platinum shell nanoparticles were prepared by the electroless deposition (ED) of Pt on carbon-supported cobalt catalyst (Co/C) and verified by HRTEM images. For a 2.0 wt % Co/C core, the ED technique permitted the Pt loading to be adjusted to obtain a series of bimetallic compositions with varying numbers of monolayers (ML). The tendency for corrosion of Co and the electrochemical (i.e., oxygen reduction reaction (ORR)) activity of the structures were measured. The results from temperature-programmed reduction (TPR) analysis suggest that a single Pt ML coverage is formed at a Pt weight loading between 0.5 and 0.7% on the 2.0% Co/C. HRTEM analysis indicates that the continuity of the Pt shell on the Co core depends on the precursor Co particle size, where “large” Co particles (>10 nm) favor noncontinuous, three-dimensional Pt structures and “small” Co particles (<6 nm) favor layer-by-layer growth. For these larger core-shell particles, Co was observed to quickly corrode in 0.3 M H2SO4. Surface area specific ORR activity, measured by chemisorption techniques, revealed that the Pt-Co/C catalysts performed better than a commercial Pt/C catalyst; however, on a Pt mass basis, only the lower Pt:Co atomic ratio Pt-Co/C catalysts outperformed the Pt/C catalyst.
The article was recently published in ACS Nano (Beard, K. D.; Borrelli, David; Cramer, Alison M.; Blom, D.; Van Zee, J. W.; Monnier, John R. “Preparation and Structural Analysis of Carbon-Supported Co Core/Pt Shell Electrocatalysts Using Electroless Deposition Methods,” ACS Nano 2009, 3(9), 2841-2853) and the full details can be found online here.