Characterization of a cation-exchange/polyaniline composite membrane

A composite membrane was prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of high oxidant concentration on a single face of a sulfonated cation-exchange membrane (Neosepta CMX from Tokuyama Soda Inc.). The CMX−PANI composite membrane was characterized as a function of the polymerization time by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and ion-exchange capacity (IEC) measurements. CV and XPS results demonstrate that, under our experimental conditions, the maximum PANI loading is attained after 1 h of polymerization. This is accompanied by a decrease in membrane ion-exchange capacity due to the presence of the cationic PANI acting as counterions for the sulfonate groups of the membrane. The optimal membrane permselectivity for protons against bivalent metallic cations (Zn2+ and Cu2+) was also found at a polymerization time of 1 h. In fact, at longer polymerization times, XPS data indicate the occurrence of PANI degradation. UV−visible spectros...