Nanoparticle Surfaces Studied by Electrochemical NMR

Abstract

A review. Nanoparticles of Pt deposited on conducting C substrates were investigated by 195Pt and 13C EC-NMR spectroscopy. A layer model deconvolution is presented describing the surface, subsurface, and structure of these materials. Data obtained with unsupported Pt particle electrodes are also given, and the spatially resolved oscillation of the Fermi level local-d. of states (Ef-LDOS) in a Pt catalyst is discussed. Correlations are drawn between the Pt Knight shift and the electronegativity of the adsorbates. In 13C-NMR, the temp. dependence of the relaxation rates is governed by the Korringa equation implying metallic behavior just as it is found for Al-supported Pt catalysts. In EC-NMR, the spectra can also be obtained under potential control and are sensitive to the applied potentials. Results are presented indicating a linear relationship between the clean-Pt-surface Ef-LDOS and the Knight shift of a 13CO adsorbate. Variations of the Ef-LDOS reflect changes in the Pt-CO chemisorption bond due to both surface modifications, like changes of the particle size, alloying, deposition, and/or chemisorption, and changes of the electrode potential. [on SciFinder(R)]