UNUSUALLY STRONG ADSORPTION OF HIGHLY-CHARGED HETEROPOLYTUNGSTATE ANIONS ON MERCURY-ELECTRODE SURFACES

The adsorption of multiply charged, heteropolytungstate anions on merc ury electrodes is extraordinarily strong. For the chromium(III)-substi tuted anion, alpha(2)-[P2W17O61Cr(OH2)](7-), the mercury surface is ha lf-saturated at concentration of the heteropolyanion of only 5 X 10(-9 ) M. In the presence of the adsorbed anions, the rate of reduction of the unadsorbed heteropolytungstates in solution is greatly diminished. The decreased reduction rates appear to result from increases in the negative diffuse layer potentials produced by the anion adsorption. Th e spontaneous adsorption of heteropolytungstates on mercury may prove useful in their electroanalysis at very low levels and in electrocatal ytic applications.