Unusually Strong Adsorption of Highly Charged Heteropolytungstate Anions on Mercury Electrode Surfaces

The adsorption of multiply chrged, heteropolytungstate anions on mercury electrodes is extraordinarily strong. For the chromium(III)-substituted anion, α 2 -[P 2 W 17 O 61 Cr(OH 2 )] 7- , the mercury surface is half-saturated at concentration of the heteropolyanion of only 5×10 -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. The spontaneous adsorption of heteropolytungstates on mercury may prove useful in their electroanalysis at very low levels and in electrocatalytic applications