IN-SITU INFRARED-SPECTROSCOPY OF WATER AND ELECTROLYTES ADSORBED ON APT(111) ELECTRODE SURFACE IN ACID-SOLUTION - STRUCTURAL-CHANGES OF ADSORBED WATER-MOLECULES UPON AN ELECTRODE POTENTIAL

At least two different solution species were adsorbed on a Pt(lll) ele ctrode in acid solutions; one is neutral H2O, and the other the hydron ium ion H3O+. The former neutral molecule chemisorbed through an oxyge n lone pair to a hydrogen covered platinum surface. At potentials more positive than 0.4-0.6 V (NKE), the water molecule started to be repla ced by specifically adsorbed anions (ClO4-, HSO4-). The latter hydroni um ion could also be observed in an uppermost layer of a Pt(lll) elect rode at relatively wide potential ranges. The coverages of the surface water molecules were highest at the most negative potential. The rema rkably higher nu(OH) stretching frequencies of the water molecules ind icate that the molecules are isolated from the outer bulk solution.