Chemical synthesis and characterization of polypyrrole coated on porous membranes and its electrochemical stability

Microporous membranes coated with polypyrrole (PPy) are developed for electrodes in electrokinetic membrane separation processes. The fabrication method is based upon the oxidative chemical polymerization of pyrrole associated with the phase inversion principle, using an optional dopant (2-naphthalenesulfonic acid, NSA or p-toluenesulfonic acid, TSA) and FeCl3 as an oxidant. The electrochemical properties of PPy films formed on various substrates such as a porous nylon filter, a silanized alumina membrane, a filter paper, and a track-etched polycarbonate membrane are characterized. For applications as membrane electrodes, the electrochemical stability of PPy-coated membranes is investigated under a potentiostat condition. The cyclic voltammograms (CV) in conjunction with conductivity measurements reveal the conductivity decay of PPy due to an anomalously high current density. A simple treatment with aq. 0.5 M H2SO4 at an elevated temperature improves the stability against aging time and electrochemical oxidation, showing an increase in the half life of conductivity during the aging experiments.