ELECTROCHEMICAL PREPARATION OF POLYPYRROLE MOLYBDENUM TRISULFIDE TETRATHIOMOLYBDATE ELECTRODE WITH VARIOUS AMOUNTS OF MOLYBDENUM SPECIES

Polypyrrole films doped with molybdenum trisulfide and tetrathiomolybd ate anions have been prepared from an aqueous solution containing pyrr ole and ammonium tetrathiomolybdate in the presence of tiron, (4,5-dih ydroxy-1,3-benzenedisulfonic acid), in the deposition solution. In suc h a solution the electrodeposition of polypyrrole doped with tetrathio molybdate anions is in competition with the electrodeposition of molyb denum trisulfide by oxidation of tetrathiomolybdate anions. Our result s indicate that the relative amounts of polypyrrole and molybdenum spe cies can be varied over larger ratios when tiron is present in the dep osition solution. The variation of the amount of molybdenum species ca n be explained by considering the number of electrons required to gene rate one mole of tetrathiomolybdate as dopant for polypyrrole and one mole of molybdenum trisulfide; 14 electrons are required per mole of t etrathiomolybdate incorporated in the polymer in comparison to 2 elect rons per mole of molybdenum trisulfide generated directly by electroch emical oxidation of tetrathiomolybdate. Tiron acts as a catalyst for t he deposition of polypyrrole and in this case the relative amount of p olypyrrole in the composite film electrode is larger. For higher tetra thiomolybdate concentration, the direct formation of molybdenum trisul fide occurs preferentially and the catalytic effect of tiron is less i mportant. (C) 1997 Elsevier Science S.A.