IN-SITU SPECTROSCOPY OF CYANIDE VIBRATIONS ON PT(111) AND PT(110) ELECTRODE SURFACES - POTENTIAL DEPENDENCIES AND THE INFLUENCE OF SURFACE DISORDER

The stretching vibrations of cyanide (CN-) ions adsorbed on single-cry stalline Pt electrodes in aqueous electrolytes were measured in-situ b y optical sum-frequency generation (SFG). Adsorption of CN- on well-or dered Pt(111) and Pt(110) surfaces is characterized by a stretching vi bration with a strongly potential-dependent frequency, ranging from ab out 2090 cm(-1) near the potential of hydrogen evolution to values of about 2150 cm(-1) (Pt(111)) and 2130 cm(-1) (Pt(110)) for potentials c lose to Pt oxidation. At negative potentials, a second band with a fre quency around 2090 cm(-1) is resolved on Pt(111). A vibrational band a round 2147 cm(-1) with very small potential dependence is related to c yanide on microscopically disordered surfaces. This band, previously o bserved on polycrystalline Pt electrodes as well as on Pt(110) and Pt( 100), appears after application of oxidation-reduction cycles to singl e-crystalline electrode surfaces and is assigned to a surface intermed iate state of [Pt(CN)(4)](2-) complex formation.