Simulation of the electric double layers on Pt(111)

The coadsorption of water and sulfur trioxide (SO3) molecules on Pt(111) was studied by thermal desorption spectroscopy, in situ and ultra-high vacuum (UHV)-infrared reflection absorption spectroscopy with the intention of producing a double layer structure on a Pt(111) electrode surface in a 0.5 M H2SO4 acid solution. The vibrational frequencies of water, bisulfate and sulfuric acid molecules adsorbed on UHV model surfaces at temperatures ranging between 110 and 300 K were compared with those from an actual double layer in a 0.5 M H2SO4 acid solution under active potentials. Model structures on Pt(111) under UHV obtained from surfaces after 190 and 260 K annealing coincided well with those from electrode surfaces at a negative and a positive electrode potential, respectively. Sulfuric acid molecules on a Pt(111) electrode observed at 750-1100 mV were reproduced by dehydration from the coadsorbates of H3O4 and HSO4- at 200-300 K. (C) 1997 Elsevier Science B.V.