ELECTROCATALYTIC REDUCTION OF CR(VI) BY POLYPYRROLE-MODIFIED GLASSY-CARBON ELECTRODES

The reduction of Cr(VI) to Cr(III) on polypyrrole-modified glassy carb on electrodes in 0.1M H2SO4 was studied by rotating disk electrode vol tammetry. The Cr(VI) substrate concentration and the polypyrrole film thickness were used as the process variables for these experiments. Th e data were analyzed within the framework of the theory of Andrieux, S aveant and coworker for polymer-modified electrodes. However, the perm eation of Cr(VI) into the microporous polypyrrole matrix was facile, s uch that direct reduction of Cr(VI) at the support electrode/polymer f ilm boundary was also taken into account. At electrode potentials at w hich the polypyrrole matrix was catalytically active, the cross-reacti on between the reduced polymer sites and Cr(VI) was shown to be the ra te-limiting step. At more negative potentials, the electronic conducti vity of polypyrrole was degraded such that charge percolation through the polymer matrix limited the catalytic reaction rate.