STUDIES OF ADSORBED SATURATED ALCOHOLS AT PT(111) ELECTRODES BY VIBRATIONAL SPECTROSCOPY (EELS), AUGER-SPECTROSCOPY, AND ELECTROCHEMISTRY

Adsorption of a representative series of saturated alcohols from aqueous fluoride solutions at a Pt(111) electrode surface has been studied by means of Auger spectroscopy, electron energy-loss spectroscopy (EELS), and cyclic voltammetry (CV). Alcohols studied are as follows: methanol (MeOH); ethanol (EtOH); propanol (PrOH); 2-propanol (2PrOH); 1-butanol (BuOH); racemic 2-butanol (2BuOH); (R)-(-)-2-butanol (R2BuOH); (S)-(+)-2-butanol (S2BuOH); 2-methyl-2-propanol (tert-butyl alcohol, tBuOH); 1-hexanol (HxOH); cyclohexanol (CyOH); 1-heptanol (HpOH); 1,4-butanediol [Bu(OH)2]; 1,6-hexanediol [Hx(OH)2]. Each alcohol studied chemisorbs at Pt(111) from aqueous fluoride electrolyte solution (pH = 4; electrode potential typically -0.1 V vs Ag/AgCl reference; alcohol concentration 0.1 M or saturated) to form a layer that is stable under vacuum and in solution. Surface attachment of saturated alcohols is through the oxygen atom and possibly the adjoining carbon atom. The aliphatic moieties of EtOH, PrOH, 2BuOH, R2BuOH, S2BuOH, 2PtOH, BuOH, 2BuOH, R2BuOH, S2BuOH, HxOH, HpOH, CyOH, and Bu(OH)2 are in contact with the Pt(111) surface. However, the alkyl chain and one OH group of Hx(OH)2 are pendant; tBuOH likewise has a pendant alkyl moiety in the adsorpted state. "Short-chain" alcohols such as MeOH, EtOH, PrOH, 2PrOH, BUOH, and Bu(OH)2 undergo partial decomposition as a result of adsorption from aqueous solution at Pt(111) to form a mixed adsorbed layer consisting of CO and the appropriate alkoxide. Electrochemical oxidation of the adsorbed intermediate is limited primarily to the carbon atom adjacent to the attached oxygen atoms.