Immobilization of a Series of Dawson Type Heteropolyanions

Abstract

Attempts to immobilize a series of Dawson type heteropolyanions (HPAs) by anodization and the use of polymeric, polyvinylpyridine (PVP), and conducting pyrrole and N-methylpyrrole, films has been undertaken. A stable film of the Dawson Parent, [P2W18O62]6–, HPA was obtained on an anodized carbon electrode, the film exhibited thin layer behavior and was stable up to a pH value of 2.00. The same HPA was successfully immobilized in a protonated PVP film with the resultant modified electrode being stable between pH values of 1.00 and 8.00, with the redox activity of the immobilized HPA exhibiting the same pH dependence as shown by the solution phase species. It was shown that a stable polypyrrole film doped with the Dawson parent HPA was obtained when the cycling of the film was restricted to the first two tungsten-oxo based redox processes in buffer solutions more alkaline than 2.00. The CuII Dawson HPA was successfully immobilized in a polypyrrole matrix exhibiting good stability and clear redox activity for the CuII HPA. Poly(N-methylpyrrole) was found to be the most suitable conducting polymer film for the immobilization of the FeIII Dawson HPA. The film was found to be extremely stable to electrochemical cycling in a buffer solution of pH 4.50. The redox activity of the immobilized HPA was clearly observed and well behaved. In addition to this the electrocatalytic properties of the FeIII HPA towards the reduction of nitrite, as observed in solution, was preserved in the immobilized state.