Search

Pt and intermixed Pt1-xNix (0.65 < x < 0.75) catalysts were sputtered-deposited onto both bare and nanostructured thin film (NSTF)-coated glassy carbon disks. The oxygen reduction reaction (ORR) activities of the disks were determined from Rotating Disk Electrode (RDE) measurements. Experiments on the NTSF-coated disks examined both catalytic activities and the effects of high surface area supports in a single measurement. The RDE measurement protocols were designed to examine changes in catalyst properties and performance during de-alloying and thus did not include the typical "electrochemical cleaning" procedure at the beginning. Instead, a continuous CV-ORR measurement protocol was used to monitor the electrochemical performance indicators such as active surface area (SEF) and ORR kinetic current density of the catalysts over the course of 9 h. As an example, the SEF of Pt25Ni75 on the NSTF-support was initially 20 cm/cm and the SEF increased rapidly at the beginning of the experiment, then stabilized near ∼50 cm²/cm² as Ni de-alloyed. This is compared with sputtered Pt on NSTF support that showed SEF ∼15 cm²/cm². De-alloying is an effective way to create Pt-transition metal catalysts on NSTF with extremely high active surface area. [ABSTRACT FROM AUTHOR]

Nanostructured thin film catalysts (NSTF) with widely varying compositions of PtxMy and PtxMyNz (M, N = Ni, Co, Zr, Hf, Fe, Mn) have been evaluated for 0 x, y, z < 1. The catalysts' activity for oxygen reduction (ORR) was measured in 50 cm² fuel cell membrane electrode assemblies. Pt1-xNix was found to be unique in showing an extraordinarily sharp peak in ORR activity as a function of the as-made composition around x = 0.69 ± 0.02 determined gravimetrically. This composition gave a corresponding fcc lattice parameter of 3.71 Angstroms and a grain size of 7.5 nm. Both surface area and specific activity increases contribute to the increased mass activity of the resultant dealloyed films. The ORR mass activity of the Pt3Ni7 is 60% higher than for the NSTF standard Pt68Co29Mn3 alloy. Rotating disk electrode measurements of a Pt1-xNix series on NSTF coated glassy carbon disks show a similar large and sharp peak in activity. In contrast, PtCo shows a diminished but still sharply peaked mass activity in 50 cm² tests near x = 0.62 by electron microprobe over the 0 < x < 0.7 range examined. [ABSTRACT FROM AUTHOR]

Three Pt1-xNix catalyst compositions, with high Ni content, were sputter deposited onto 3M Company's Nano-Structured Thin Film catalyst support to determine whether the high oxygen reduction reaction (ORR) activities recently reported are a surface phenomenon or require bulk Ni dissolution. The electrodes with Pt0.27Ni0.73 throughout had the highest mass specific ORR activity of the samples tested. When some of the Pt0.27Ni0.73 was replaced with either Pt or Pt0.75Ni0.25, the mass activity dropped. These results confirmed that continuous high Ni content is required to obtain high mass activity. [ABSTRACT FROM AUTHOR]

The oxygen reduction activity of a series of Pt1-xCox catalysts (with high Co content) sputter-deposited onto 3M's nano-structured thin film support was measured with Rotating Disk electrode techniques. The oxygen reduction reaction (ORR) activity was found to be much higher than that measured on pure Pt (3-4 times higher absolute activity at 1000 mV for the same Pt loading). The ORR activity was only weakly dependent on the Co content (as-sputtered). With repeated potential cycling it was, however, somewhat unstable, likely primarily as a result of poisoning of the catalyst surface with electrolyte impurities during the long term test protocol. Ex-situ x-ray diffraction measurements of the disks during testing showed loss of bulk Co from the lattice, resulting in loss of a large fraction of the initial Co content. [ABSTRACT FROM AUTHOR]

Layered Pt1-xIrx (0 1-xIrx film was prepared by depositing alternating layers of Pt (constant thickness) and Jr (gradient), finished with a 5 nm Pt top layer. The NSTP-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 SEP increased (reaching a maximum of 22 at x = 0.2 in Pt1-xIrx) as the Jr content increased for the Pt1-xIrxsamples on NSTF. The kinetic ORR current density also increased with increasing Jr content. A similar trend was not observed for the same cataJyst coated onto bare GC disks. All of the cataJystlsupport combinations had identical Tafel slopes and area-specific current densities, suggesting that Pt is the active catalytic ingredient. Catalysts coated on NSTFcoated GC disks can be used to accurately examine both catalytic activities and the effects of high surface area supports in a single measurement. [ABSTRACT FROM AUTHOR]