INSITU INFRARED INVESTIGATIONS OF THE ELECTROCHEMISTRY OF HETEROPOLYACIDS AT N-GE ELECTRODES

The electrochemical modification of n-Ge electrodes has been carried out using 10(-3) M heteropolyacid solutions (HPA, here alpha-SiW12O404- and alpha-PW12O403-) in 1 M acidic electrolyte. First, cyclic voltammograms containing the various reduction waves of HPA ions were obtained. The infrared vibrational spectra of the various reduced species were obtained by using Fourier-transform electro-modulated infrared spectroscopy (FTEMIRS), with potential modulation in the ranges corresponding to the reversible reduction waves. After subsequent negative polarization, the irreversibly modified surfaces exhibit a considerable shift of the hydrogen evolution potential in the positive direction. The in-situ infrared vibrational spectra show that a heavily hydrated compound, retaining locally the overall structure of the initial ions, is formed on the Ge surface during the cathodic reduction of the HPA. The electromodulated infrared spectra provide direct evidence for the catalytic activity of the silicotungstate deposit in improving the H-2-evolution kinetics. The hydrogen evolution reaction is shown to be associated with a process involving an increased interaction between water and H3O+ ions and the W-O bonds; a corresponding mechanism is suggested.