(91b) Gold Stabilized Platinum and Palladium Nanotubes

Platinum supported on carbon (Pt/C) is commonly the commercial material used as an electrocatalyst in the oxygen reduction reaction (ORR) as a cathode in proton exchange membrane fuel cells (PEMFCs). The small particles are used due to the high surface area and thus high mass activity in the oxygen reduction reaction (ORR). The carbon support provides spacing for the platinum particles and prevents agglomeration. The use of Pt/C, however, creates concerns with respect to catalyst durability and specific activity loss due to alterations in the coordination number and crystal planes of the surface platinum atoms. Platinum nanotubes (PtNTs) with a thickness of 5 nm have previously been synthesized to improve the durability and ORR activity of PEMFC catalysts.[1]

PtNTs have previously demonstrated improved durability to conventional catalysts through the elimination of a carbon support and a reduction in agglomeration and surface area loss due to the use of the one-dimensional nanotube framework. Surface area losses, however, are still observed following the United States Department of Energy guidelines. These losses are exacerbated following the addition of palladium, principally as the lower hydroxide adsorption region allows for a greater degree of agglomeration on the catalyst surface. The addition of gold into pure PtNTs and PtNTs containing palladium has been found to shift the hydroxide adsorption region to a higher value, allowing for a decreased degree of catalyst oxidation and agglomeration during durability testing. Gold in this endeavor is added during bulk synthesis as a substrate material to alter the behavior of the surface platinum. The gold content is varied within pure PtNTs and PtNTs containing palladium in an effort to ensure both increases in stability and ORR activity. Compared to traditional PtNTs and conventional catalysts, gold stabilized platinum and palladium nanotubes will demonstrate an improved PEMFC catalyst stability.

[1] Z. W. Chen, M. Waje, W. Z. Li, Y. S. Yan, Angewandte Chemie-International Edition 2007, 46, 4060.