In-situ surface exafs at chemically modified electrodes

Abstract

The surface EXAFS and near edge structure of electropolymerized films of [M(v-bpy) 3] 2+ (v-bpy is 4-vinyl-4'-methyl-2,2'-bipyridine and M = Ru, Os) and [Os(phen)(v-bpy) 2] 2+ (phen is 4-methyl-l,10-phenanthroline) on platinum electrodes have been studied as a function of surface coverage and applied potential by measuring the characteristic RuK α or OsL fluorescence intensities. For [Ru(v-bpy) 3] 2+ spectra for electrodes modified with 1, 5, 12, 25 and 50 monolayers were obtained. Analysis and comparison of EXAFS and XANES features for these films showed similar morphological and electronic characteristics in agreement with previous electrochemical studies showing that solution redox properties of monomer complexes can be transferred to electrode surfaces by electrodeposition as polymer films of varying thickness. Electrochemical oxidation of the films resulted in a shift of 2 eV in the edge position towards higher energy, consistent with the higher charge on the ruthenium centers. Other spectral features, however, remained essentially unchanged. Similar studies were performed on the osmium complexes but in addition, changes in the edge position and near edge features could be correlated with the coordination environment. The applicability of these studies to the in-situ investigation of electrocatalytic systems is discussed.