A comparative study on the electrochemical properties of ring-substituted polyanilines

The redox behavior of polyanilines with ring-substituted groups synthesized by chemical polymerization, poly-2,5-dimethoxyaniline (PDMAn), poly-m-chloroaniline (PmClAn) and poly-o-toluidine (POT), was studied and the morphology and crystal orientation of platinum particles deposited on these polymer membranes was compared. The oxidation of isopropanol on platinized polyaniline-modified electrodes as a model reaction was also investigated to examine the electrocatalytic properties of the polymers. The results show that the first oxidation potential of the polymers increases in the following sequence: PDMAn, POT and then PmClAn, which can be explained in terms of the electronic and steric effects of ring-substituted groups. The growth of Pt particles electrodeposited on doping-state POT and PDMAn polymer membranes takes place by a 'progressive nucleation mechanism', but by an 'instantaneous nucleation mechanism' on PmClAn. Platinum crystallites trend towards preferred-orientation and Pt (200) is the preferred face, but the degree of preferred orientation depends on the polymer. The oxidation potentials of isopropanol are located near 0.3 V, and the oxidation currents increase on platinized polymer-modified electrodes, indicating that the interaction of polymer with Pt particles might improve the catalytic activity of Pt. Polyanilines act not only as dispersion media but also change the electronic properties of Pt crystalline grains. (c) 2005 Society of Chemical Industry.