PFeW 11-doped polymer film modified electrodes and their electrocatalytic activity for H 2O 2 reduction

Abstract

A study of electrochemical and electrocatalytic properties, toward H 2O 2 reduction, of the [PFeW 11O 39] −4 polyoxoanion in solution as well as immobilized in partially oxidized polypyrrole (pPy) and in polyvinyl alcohol bearing styrylpyridinium groups (PVA) films is reported. Using cyclic voltammetry at different pH values and scanning rates it was observed that: (i) the two bielectronic waves corresponding to the tungstate-oxo cage are pH-dependent; (ii) the Fe center of the polyoxoanion has an excellent electrocatalytic effect on H 2O 2 reduction, giving a catalytic efficiency and an electrode sensitivity, both higher when dissolved than when immobilized onto electrode surface; and (iii) the one-step method used to obtain the pPy-doped film assures a greater amount of immobilized polyoxoanion than the ionic-exchange method used for PVA films. From rotating-disk electrode (RDE) measurements, the polyoxoanion diffusion coefficient was estimated at 4.1×10 −6 cm 2 s −1, which agrees to that obtained by cyclic voltammetry, 3.9×10 −6 cm 2 s −1, and the heterogeneous rate constant was found to vary between 3.5×10 −3 and 1.9×10 −3 cm s −1 at a variation of the electrode potential from 30 to −30 mV vs. SCE. The best amperometric response observed for the PFeW 11-doped pPy membrane, showed a linear response to H 2O 2 additions up to 9 mM and a sensitivity of 4.8 mA M −1 H 2O 2 in the first day of utilization.