SIMULATION OF THE ELECTRIC DOUBLE-LAYERS ON PT(111)

The coadsorption of water and sulfur trioxide (SO3) molecules on Pt(11 1) was studied by thermal desorption spectroscopy, in situ and ultra-h igh 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 o f water, bisulfate and sulfuric acid molecules adsorbed on UHV model s urfaces at temperatures ranging between 110 and 300 K were compared wi th those from an actual double layer in a 0.5 M H2SO4 acid solution un der 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 potenti al, respectively. Sulfuric acid molecules on a Pt(111) electrode obser ved at 750-1100 mV were reproduced by dehydration from the coadsorbate s of H3O4 and HSO4- at 200-300 K. (C) 1997 Elsevier Science B.V.