RRDE Measurements of ORR Activity of Pt 1-x Ir x (0 < x < 0.3) on High Surface Area NSTF-coated GC Disks Gary Chih-Kang Liu a , R.J. Sanderson a , George Verndstrom b , D.A. Stevens a , R.T. Atanasoski b , M.K. Debe b and J. R. Dahn a, * a: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS Canada B3H 3J5 b: 3M Fuel Cell Components Program, 3M Co., St. Paul, MN 55144-1000, USA Layered Pt 1-x Ir x (0 < x < 0.3) and Pt films were sputtered onto mirror-polished and nano-structured thin film (NSTF)-coated GC disks. Rotating ring disk electrode studies of oxygen reduction reaction activity (ORR) were completed for all disks prepared. The NSTF-supported catalysts had much higher active surface area and reached the diffusion-limited current at a higher potential than the mirror-polished supported catalysts. The surface enhancement factor (SEF) of Pt on NSTF-coated disks was approximately 14. The SEF increased, (reaching a maximum of 22 at x = 0.2 in Pt 1-x Ir x ) as the Ir content increased. The kinetic ORR current density also increased with increasing Ir content. A similar trend was not observed for catalyst coated, mirror- polished disks. All of the catalyst/support combinations had identical Tafel slopes and area specific current densities suggesting that the Pt is the active catalytic ingredient. Introduction Rotating (Ring) Disk Electrode (R(R)DE) experiments are commonly used to examine the kinetic activities of fuel cell catalysts with well-defined mass-transport properties (1). RRDE has been used as part of the screening process for potential catalyst candidates deposited by combinatorial sputtering techniques (2, 3). In order to screen sputter- deposited catalysts more effectively, the trends observed in the RRDE experiments should reflect those observed in Proton Exchange Membrane Fuel Cell (PEMFC) measurements of the same materials. Although the samples for RRDE testing and PEMFC testing are prepared in the same sputtering run, the samples for RRDE are prepared on polished glassy carbon (GC) discs, while the samples for PEMFC are prepared on 3M's nanostructured thin-film support (NSTF) (4, 5). The resulting grain size and surface area of the materials differ greatly. To overcome this difficulty, glassy carbon discs, pre-coated with a layer of NSTF whiskers are proposed as the ideal support for comparative RRDE experiments. In this paper, Pt and Pt-Ir alloys were sputter- deposited on both mirror-polished GC disks and NSTF-coated GC disks. The ORR activity of the disks was determined by RRDE. The results were then compared to examine the contribution of the high surface area NSTF support to the overall catalytic performance of different catalyst/support combinations. The aim is to allow RRDE techniques to be used to screen catalysts sputter-deposited on high-surface area supports more effectively. ECS Transactions, 25 (1) 625-634 (2009) 10.1149/1.3210614 ©The Electrochemical Society 625 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 219.246.65.61 Downloaded on 2014-10-13 to IP