PYRIDINE ADSORPTION ON POLYCRYSTALLINE PLATINUM STUDIED BY THE RADIOACTIVE-LABELING METHOD

The adsorption of pyridine on a polycrystalline platinum electrode was measured by using a radioactive-labeling technique. The potential dependence and concentration dependence of adsorption were measured in 0.1 M HC1O4, and two exchange experiments were performed. The potential dependence revealed behavior typical for a strongly adsorbed organic species; a broad plateau of maximum adsorption occurs in the double-layer region with decreased adsorption toward potential extremes. No exchange of surface species with added unlabeled solution pyridine occurred at 0.2 V (vs Ag/AgCl, 1 M Cl-), but slow exchange was observed at -0.2 V over about 2 h; slow hydrogenation is the most likely cause of the loss of adsorbate at this potential. Two different concentration dependence profiles were observed depending on the treatment of the platinum electrode surface; a clean surface gave consistently higher packing densities as a function of pyridine concentration than one that had been pretreated at 10-6 M. The observed packing densities correspond to horizontally oriented pyridine, formed at low concentrations, and vertically oriented pyridine, formed at high concentrations. © 1990, American Chemical Society. All rights reserved.