Electrochemical oxidation of adsorbed terminal alkenols as afunction of chain length at Pt (111) electrodes: Studies by cyclic voltanunetry, EELS, and Auger spectroscopy

Abstract

Reported are studies of adsorption and electrochemical oxidation of a series of straight-chain terminal alkenols at a Pt (111) electrode surface. Vibrational spectra of each adsorbed layer were obtained by use of electron energy-loss spectroscopy (EELS). Molecular packing density in the adsorbed layer was measured by means of Auger electron spectroscopy. Substrate surface structure was monitored by use of LEED. Electrochemical oxidation of each adsorbed layer was explored by means of linear potential scan voltammetry in an inert aqueous electrolyte (KF+HF). Compounds studied are: 2-propen-1-ol (PPEOH, allyl alcohol); 3-buten-1-ol (BTEOH); 4-penten-1-ol (PTEOH); 5-hexen-l-ol (HXEOH); and 10-undecen-1-ol (UDEOH). Attachment to the surface is primarily through the CC double bond. Regardless of chain length each chemisorbed aLkenol molecule occupies an area similar to that of PPEOH. EELS spectra indicate that the CC double bond is preserved in the adsorbed state. Evidently, the CC axis is parallel to the Pt (111) surface, and the alphatic chain is pendant. The -OH moiety is in contact with the Pt surface only in the case of PPEOH. An O-H stretching band is present only in the EELS spectrum of BTEOH; intermolecular hydrdogen bonding (PTEOH, HXEOH, UDEOH) and interaction with the Pt surface (PPEOH) eliminate the O-H stretching bands of the other adsorbed terminal alkenols studied. Measurement of the average number of electrons, n ox required for catalytic electrocheroical oxidation of an adsorbed molecule reveals that oxidation takes place primarily at the CC double bond and one adjacent saturated carbon.