The Effect of Ru or Ir Addition on Nano-Structured-Thin-Film Supported Pt Fuel Cell Catalysts under Rotating Disk Electrode Simulated Start-up Shut-down

Abstract

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 ).

Screening Bifunctional Pt Based NSTF Catalysts for Durability with the Rotating Disk Electrode: The Effect of Ir and Ru

“…Using the RDE test protocol and catalyst synthesis techniques developed by Crowtz et al, 20 the effect of Ru or Ir, or both Ir and Ru have on the ORR and OER durability of a base layer of 85 μg cm −2 Pt sputtered on 3M's NSTF fuel cell catalyst support has been determined. Ir loading linearly increases OER durability ( Figure 6B).…”

“…Electrochemically active Pt based surface area corrections were not applied due to the inaccuracies caused by Ru and Ir pseudocapacitance, as explained in Crowtz et al 20 The numerical technique used for ORR ohmic drop correction is summarized in the Supplemental Material. Electrochemical evaluation: electrolyte and electrodes.-Samples were tested with a rotating disk electrode (RDE).…”

“…C: Eight percent above the initial start-up end-potential of two pure Pt samples was greater than 1.8 V RHE (the highest allowable start-up end potential). A legend for the symbols can be found in Figure 2. in Crowtz et al 20 Binninger et al 41 present experimental techniques which solve this problem, but unfortunately laboratory circumstances did not allow their method to be applied in this study. Figure 8A shows the general trend is for initial ORR activity to decrease with increasing molar coverage of OER catalyst.…”

“…The rotating disk electrode (RDE) data contained herein compliments existing PEMFC studies 15,18,19 many of which are summarized in the final report to the U.S. Department of Energy (DOE) Hydrogen Fuel Cell Program) 16 about Ir and Ru on NSTF supported Pt. In particular, this study is a follow up study to Crowtz et al 20 which was a preliminary RDE exploration of the OER and ORR activities and durabilities of overlayered and intermixed NSTF supported Ir or Ru plus Pt. The OER catalysts in this study are always overlayered on the Pt because an overlayer deposition scheme is preferable for the roll-to-roll process proposed for the manufacture of NSTF catalysts.…”

Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions

“…Therefore, in this work an approach has been adapted which is known to work for Pt/C ORR catalysts. Crowtz et al 27 showed that the addition of Ir or Ru OER catalysts led to improved stability of a Pt/C catalyst during 1400 SSC/load/idle pulses in form of subsequent constant current (0.942 mA cm À2 ) and potential (0.65 and 0.95 V RHE ) holds in rotating disc electrode (RDE) experiments. The stabilization during 1.6 V potential holds for 30 min in PEM-FC was observed by Oh et al 28 for Pt/C catalysts with 1-5 wt% IrO 2 added.…”