Interactions between the Keggin-type lacunary polyoxometalate, α-SiW11O398-, and electrode surfaces

Cyclic voltammetry, scanning tunneling microscopy (STM), and surface-enhanced Raman spectroscopy (SERS) are used to investigate the interactions between lacunary polyoxometalate, alpha-SiW11O398-, and glassy carbon, Au(111), and Ag(111) electrode surfaces. The cyclic voltammetry and STM measurements show that alpha-SiW11O398- anions adsorb strongly only on Ag(111). alpha-SiW11O398- species adsorbed on Ag(111) retains its redox activity on the Ag surface. STM images reveal the formation of monolayers on Ag(111), which have hexagonal adlattice structures with spacings between 1.22 and 1.37 run, somewhat larger than the 1.0-mn spacing observed for the complete Keggin ion. SERS measurements show that alpha-SiW11O398- is present on the Ag surface at potentials between 0.0 and -0.9 V. A model rationalizing the larger spacing is proposed.