Electrogeneration and electrochemical properties of hybrid materials:: polypyrrole doped with polyoxometalates PW12-xMoxO403-(x=0, 3, 6, 12)

Hybrid materials such as polypyrrole doped with polyoxometalates PW12-xMoxO403- (x = 0, 3, 6, 12) were electrogenerated from organic solution. The effects of the Mo-substitution on the electrogeneration and electrochemical properties of the hybrid materials were studied by potential step and cyclic voltammetry. It was found that Mo-substituted polyoxometalates could stimulate the oxidation-polymerization of pyrrole. The oxidation-polymerization potential of pyrrole decreases as the Mo content increases, correlating the redox properties of the polyoxometalates. During the initial cathodic sweep, a great cathodic peak (altogether a blue cloud of material release) with a shoulder is shown by all the studied materials. A substantial loss of weight was always observed during this reduction process. Polyoxometalates and polypyrrole oligomers determined by FT-IR [J. Chem. Phys. B 104 (2000) 10528] and UV-VIS contributed to the weight loss giving rise to a partial electrochemically stimulated dissolution of the material. After this initial cycle, the consecutive voltammograms present two redox processes. Charges and current densities involved in those two cathodic processes show a linear variation, in opposite directions, at almost the same rate upon cycling. Those shifts of the cathodic processes are related to a continuous change of the counter-ion involved in the redox process from Li+ to ClO4-, altogether the subsequent release of polyoxometalate (that required the Li+ counter-ion) from the hybrid. (C) 2002 Elsevier Science B.V. All rights reserved.