Design, synthesis, and characterization of fuel cell electrocatalysts for the direct oxidation of organic fuels.

摘要

This thesis examines the fundamental surface structures and reactions involved in the direct electro-oxidation of carbonaceous fuels. We have accomplished this through an integrated approach that probes the electrocatalytic interface using particle characterization techniques, voltammetry, and nuclear magnetic resonance (NMR).;Electrochemical characterization is accomplished primarily through voltammetry. The electrocatalytic activities of CePt2 and PrPt2 alloys toward CH3OH oxidation are determined to be less than that of commercial PtRu catalysts. For Pt and PtRu electrocatalysts, COads stripping experiments are analyzed using a modified Butler-Volmer equation developed in previous work. The behavior of the surface species derived from CO(g) and CH3OH is discussed.;The electronic and geometric structure of metal catalysts are probed using 195Pt NMR because of its sensitivity to the electron band structure which varies spatially through nanoparticles. The 195 Pt NMR spectra of CePt2 and PrPt2 alloys at room temperature are found to be very broad and exhibit a positive Knight shift. Particle characterization techniques (XRD, BET, TEM) are also presented to aid in the analysis of these data. 195Pt NMR is shown on electrode stack samples containing PtRu and Pt black electrocatalysts at room temperature. Application of this scheme for acquiring electrochemically relevant 195Pt NMR data on novel alloy material is discussed.;Finally, 13C NMR of adsorbates on pure platinum in our electrode stack setup is used to probe the dynamics of COads . A model for COads motion based on two types of platinum surface sites is proposed; surface species experience a fast motion within each type of site and a slower motion involving two-site exchange between our proposed WB and SB sites. We find that CPMG experiments and lineshape analysis support our model for two-site exchange. The results from the CPMG data analysis and 13C NMR lineshape modeling yield kex and Deltanu values on the same order of magnitude. These results are discussed in the context of previous work done in our lab and work from literature.