PFeW11-doped polymer film modified electrodes and their electrocatalytic activity for H2O2 reduction

A study of electrochemical and electrocatalytic properties, toward H2O2 red uction, of the [PFeW11O39](-4) polyoxoanion in solution as well as immobili zed in partially oxidized polypyrrole (pPy) and in polyvinyl alcohol bearin g styrylpyridinium groups (PVA) films is reported. Using cyclic voltammetry at different pH values and scanning rates it was observed that: (i) the tw o bielectronic waves corresponding to the tungstate-oxo cage are pH-depende nt: (ii) the Fe center of the polyoxoanion has an excellent electrocatalyti c effect on H2O2 reduction, giving a catalytic efficiency and an electrode sensitivity, both higher when dissolved than when immobilized onto electrod e surface; and (iii) the one-step method used to obtain the pPy-doped film assures a greater amount of immobilized polyoxoanion than the ionic-exchang e method used for PVA films. From rotating-disk electrode (RDE) measurement s, the polyoxoanion diffusion coefficient was estimated at 4.1x10(-6) cm(2) s(-1), which agrees to that obtained by cyclic voltammetry, 3.9x10(-6) cm( 2) s(-1), and the heterogeneous rate constant was found to vary between 35x 10(-3) and 1.9x10(-3) cm s(-1) at a variation of the electrode potential fr om 30 to -30 mV vs. SCE. The best amperometric response observed for the PF eW11-doped pPy membrane, showed a linear response to H2O2 additions up to 9 mM and a sensitivity of 4.8 mA M-1 H2O2 in the first day of utilization. ( C) 1999 Elsevier Science B.V. All rights reserved.