SSITKA investigation of CO and H 2 competitive adsorption at PEM fuel cell anode catalysts

Abstract

Steady-state isotopic transient kinetic analysis (SSITKA) experiments have been performed using the isotopic exchange between 13CO and 12CO to investigate the competitive adsorption of hydrogen and CO on commercial Pt and PtRu catalysts. PtRu alloys are known to be more tolerant fuel cell anode catalysts than platinum, in the instance where the hydrogen fuel contains ppm levels of CO. It has been recently demonstrated that there is a dynamic equilibrium between CO adsorbed on platinum or platinum/ruthenium nano-particles and CO in the gas phase. In this paper, the effect of the competitive adsorption between hydrogen and CO on this equilibrium has been demonstrated. For 1400 ppm CO in hydrogen little difference was observed in the measured exchange rates for Pt and PtRu at room temperature, 9.91 × 10 −4 for Pt compared to 1.15 × 10 −3 for PtRu, however there is a significant effect observed at 100 ppm CO in hydrogen, where the rates on PtRu are considerably smaller than on Pt (3.61 × 10 −4 desorption rate constant for PtRu and 5.49 × 10 −4 for Pt). The presented methodology using the SSITKA technique has demonstrated a novel way to measure these rate constants, and the implications of these measurements on the mechanistic understanding of the anode reaction are presented.