Surface chemistry of five-membered heteroaromatics at Pt(III) electrodes studied by EELS, LEED, Auger spectroscopy and electrochemistry: furan, pyrrole and thiophene

Abstract

Reported here are studies of the chemisorption, surface vibrational spectroscopy, elemental and molecular packing densities, and electrochemical reactivity of three related five-membered heterocycles at Pt(III): pyrrole (PRR), furan (FRN), and thiophene (TPE). Packing density and stoichiometry were investigated by the use of Auger spectroscopy. None of the adsorbed layers exhibited long-range order detectable by LEED. Vibrational spectra of the chemisorbed species were obtained by means of electron energy-loss spectroscopy (EELS), and were compared with infrared spectra of the unadsorbed compounds. Electrochemical oxidation of the adsorbed molecules was explored by the use of cyclic voltammetry (CV). The results reveal that PRR adsorbs at Pt(III) mainly in a horizontal orientation with the ring intact; electrochemical oxidation of adsorbed PRR proceeds completely to NO 2 and CO 2. However, FRN is converted by hydrolytic, ring-opening isomerization to adsorbed pi-bonded butenoic acid (BTA); electrochemical oxidation of adsorbed BTA proceeds to CO 2. TPE forms a mixed layer consisting of S atoms and adsorbed TPE molecules S-bonded and near-vertically oriented; adsorbed TPE is oxidized to CO 2 and SO 4 2−.