RDE Measurements of ORR Activity of Pt1-xIrx (0<x<0.3) on High Surface Area NSTF-Coated Glassy Carbon Disks

Layered Pt1-xIrx (0 < x < 0.3) and Pt films were sputtered onto 0.05 mu m mirror-polished and nanostructured thin film (NSTF)-coated glassy carbon (GC) disks. Rotating disk electrode (RDE) studies of oxygen reduction reaction (ORR) activity were completed for all prepared disks. The Pt1-xIrx film was prepared by depositing alternating layers of Pt (constant thickness) and Ir (gradient), finished with a 5 nm Pt top layer. The NSTF-supported catalysts had much higher active surface areas and reached the diffusion-limited current at higher potentials than the bare GC 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 Pt1-xIrx) as the Ir content increased for the Pt1-xIrx samples on NSTF. The kinetic ORR current density also increased with increasing Ir content. A similar trend was not observed for the same catalyst coated onto bare GC disks. All of the catalyst/support combinations had identical Tafel slopes and area-specific current densities, suggesting that Pt is the active catalytic ingredient. Catalysts coated on NSTF-coated GC disks can be used to accurately examine both catalytic activities and the effects of high surface area supports in a single measurement.