Steady state isotopic transient kinetic analysis study of PEM fuel cell Anodes (SPA) : exploratory research project

The hydrogen oxidation reaction at Proton Exchange Membrane Fuel Cell anodes is poisoned by part per million levels of carbon monoxide, present even after purification steps following the production of hydrogen by the reformation of hydrocarbons. Whilst platinum is the catalyst of choice for the oxidation of pure hydrogen, platinum/ruthenium alloys are shown to be more tolerant when ppm levels of CO are present. It has recently been demonstrated that there is a dynamic equilibrium between CO adsorbed on platinum or platinum/ruthenium nanoparticles and CO in the gas phase, and that this equilibrium is affected by the competitive adsorption between CO and hydrogen. The purpose of this research to perform Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments using the isotopic exchange between 13CO and 12CO to investigate the competitive adsorption of hydrogen and CO on commercial Pt and PtRu catalysts. For 1400ppm CO in hydrogen little difference was observed in the measured exchange rates for Pt and PtRu at room temperature, however there is a more significant effect observed at 100ppm CO in hydrogen, where the rates on PtRu are considerably slower than on Pt. This can be attributed to increased competition on PtRu for CO and H adsorption, leading to lower equilibrium coverage of CO on the PtRu surface. Preliminary measurements were also made regarding the temperature dependence of this process in the range relevant to the fuel cell (25-90ºC). This work was performed as a joint venture between the Institute for Energy (IE) and the Institute for Reference Materials and Measurements (IRMM), as IE have the experience in the area of PEM fuel cell catalysis whilst IRMM have the pre-existing Isotope Ratio Mass Spectrometry instrumental capabilities with the required resolution to perform measurements at these concentration levels, along with fast switching capabilities for applying the traditional SSITKA technique to this system.