(705f) Copper Templated Platinum Nanotubes as Oxygen Reducing Electrocatalysts

Platinum supported on carbon (Pt/C) is commonly utilized in proton exchange membrane fuel cells (PEMFCs) as an oxygen reducing electrocatalyst. 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]

Previous PtNT catalysts were synthesized by galvanic replacement with silver nanowires, which were formed by the ethylene glycol reduction of silver nitrate. Current studies have investigated the effect of the template material on PtNT activity. PtNTs have been synthesized by galvanic replacement with copper nanowires, which were formed by the sodium hydroxide and hydrazine reduction of copper nitrate. While the PtNTs have been synthesized under similar conditions, differences are observed in surface area and ORR activity. An alteration in ORR specific activity, or the ORR capability per unit area of available platinum, is of particular concern in this study. Improvement to ORR specific activity has been observed in catalysts templated from copper nanowires, principally due to changes in the coordination number and crystal planes of surface platinum and a decrease in atomic spacing created during the templating process. From these findings, optimization of the template material can be utilized to further increase the ORR activity of electrocatalysts synthesized by the galvanic replacement method.

Optimal ORR activity has been explored with the synthesis of platinum thin-coated copper nanowires and platinum thin-coated palladium nanotubes, synthesized in subsequent galvanic replacement reactions to create a surface layer of platinum instead of alloys. Catalysts have been characterized for ORR activity and durability to demonstrate the benefit of PtNTs to conventional PEMFC catalysts.

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