Characterization of anodically formed polypyrrole/tungsten trioxide composites

Abstract

Composite PPy/WO₃ materials were synthesized anodically under various conditions. The cyclovoltammetric switching curves are very close to the blank polypyrrole. The redox behaviour of the filler is only detected through electrochromism, leading to a yellow grey colour at +0.4 V vs SCE and to a green surface at −0.6 V. For overoxidation of the composite, a degree of overoxidation Y = 5 is found, the same as for the matrix alone. Photoelectrochemical response is due to the conducting polymer at negative potentials and even at 0 V vs SCE. A strong effect at positive potentials is due to the WO₃ pigment. From this, a flat band potential of +0.15 V vs SCE is determined for aqueous 0.1 m LiClO₄. Some non-electrochemical properties are also reported. Surface roughness increases with increasing WO₃ concentration, but for thicker layers, from MeCN, it decreases. SEM micrographs reveal homogeneous distribution of WO₃. Large secondary particles are observed in NBu₄BF₄ electrolyte. True and nominal thicknesses differ by up to a factor 1.65 due to the porous structure and this explains differences between densities measured by the flotation and the jump method. X-ray diffraction analysis exhibits unchanged WO₃-lines, but no PPy-lines due to the amorphous character. The conductivity of the composite from MeCN is much lower than expected by the volume filling of the WO₃.