In this study, small amounts of either Ir or Ru (up to 22 μg cm −2 ) were added to 85 μg cm −2 Pt by either co-sputtering or over-layer sputtering onto 3M Company's NSTF catalyst support, which was grown on glassy carbon electrodes for the purpose of simulating fuel cell start-up and shut-down with rotating disk electrode techniques. The transient cathode potentials caused by fuel cell start-up, shut-down and operating conditions were simulated with a combination of potentiostatic and galvanostatic holds. Constant potential was used to simulate fuel cell run, rest and idle, and constant current was used to simulate the start-up and shut-down events. Over the course of an experiment, the catalyst would experience potential as low as 0.650 V RHE (run) and as high as 1.53-1.8 V RHE (dependent on the behavior of the composition) under the galvanostatic holds. All compositions including either Ir or Ru lasted significantly longer than for pure Pt under repeated start-up/shut-down. The stability of the over-layer Ir-Pt compositions was significantly higher than for the co-sputtered deposition. The compositions containing 9 and 22 μg cm −2 Ir over-layer on Pt showed no ORR activity decrease over the course of 1400 SU/SD simulations (2800 potential peaks >1.5 V RHE ).

Various amounts of Ir (<20 μg cm −2 ) and Ru (up to 12 μg cm −2 ) on a consistent base Pt loading of 85 μg cm −2 , were sputter deposited on a nanostructured thin film catalyst support to mimic a hydrogen fuel cell's cathode catalyst. The nanostructured support was grown on glassy carbon disks designed for a rotating disk electrode, which was used to simulate what happens to a fuel cell cathode during repeated start-up, operation, and shut-down. The testing protocol subjected the catalyst to a minimum potential of 0.65 V RHE and a maximum between 1.53 and 1.8 V RHE . The upper potential was achieved with a galvanostatic hold which is an alternative way to simulate potential transients on the cathode caused by start-up and shut-down. Increasing Ir loading improved the durability of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. When combined with Ir, Ru provided no benefit to OER durability except at an Ir loading of 10 μg cm −2 . Ru addition (no Ir present) improved the ORR durability compared to pure Pt. ORR durability was not influenced by Ru addition to Ir-containing samples. In general, ORR durability showed no dependence on Ru loading for all the Ru containing samples and ORR activity was decreased by OER catalyst addition, though more so for Ir than Ru.

A Ru 1-x Ir x binary over-layer was deposited on Pt-coated nanostructured thin film from 3M Company. XPS measurements were used to confirm the composition of the over-layer. Rotating disk electrode measurements were used to assess oxygen evolution activity of the catalysts. The results showed that a low Ir/high Ru over-layer had a higher activity but lower stability than high Ir/low Ru samples.

The catalytic performance under simulated transient start-up and shut-down conditions is evaluated for five potential cathode-side catalyst compositions containing Pt, Ir and Ru. Experiments using the rotating disk electrode technique showed that samples containing a solid solution of Ir and Ru on top of a Pt base layer were the most active and the most durable over 1000 simulated start-stop events.

not Available.