Vibrational spectroscopy of a Keggin polyoxometalate on metal electrode surfaces

Polarization modulation infrared reflection-absorption spectroscopy and surface-enhanced Raman spectroscopy are used to interrogate the behavior of the Keggin-type polyoxometalate alpha-[SiW12O40](4-) on Ag and An electrode surfaces. Assignment of specific vibrational modes and their behavior as a function of potential show that alpha-[SiW12O40](4-) adsorbs strongly on Ag but not on Au. On Ag, analysis of the potential-dependent spectroscopy provides insight into the behavior of this species on the electrode surface, especially at cathodic potentials. In particular, the spectroscopy shows that the molecule reorients on the Ag electrode surface at the potential where a voltammetric wave is found in the solution-based voltammetry. This reorientation inhibits the oxidation of the Ag surface-confined species.