Pt-195 NMR of platinum electrocatalysts: Friedel-Heine invariance and correlations between platinum knight shifts, healing length, and adsorbate electronegativity

The influence of a series of different ligands (H, O, S, CN-, CO, and Ru), electrochemically adsorbed onto carbon-supported nanoscale Pt particles, ha s been investigated by Pt-195 NMR, in an electrochemical environment. The N MR Knight shifts from atoms in the;interior of the particles are invariant to surface ligand adsorption, as expected by the Friedel-Heine invariance t heorem. However, the shifts of the surface and subsurface atoms vary over a similar to 11000 ppm range for the adsorbates investigated. The Knight shi fts of the surface and subsurface platinum atoms, obtained by using an NMR layer-model simulation, linearly map the electronegativity of the adsorbate . These observations permit the derivation of a correlation between the "he aling length" of the Pt metal, a parameter indicating how fast the bulk met al properties are recovered when moving in from the surface, and the electr onegativity of the adsorbate, providing a new probe of electrocatalyst and heterogeneous catalyst surface electronic structure.