The electrochemical activity of sulfonic acid ring-substituted polyaniline in the wide pH range

Polyaniline (PAn) film can directly react with the concentrated sulfuric acid to form sulfonic acid ring-substituted polyaniline (SPAn). Based on the cyclic voltammograms, the electrochemical behavior of SPAn is the same as that of PAn in the acid solution at pH <1, but is quite different from that of PAn in the basic solution. The cyclic voltammograms of SPAn in 0.3 M Na2SO4 solution with various pH values indicate that there are an anodic peak and two cathodic peaks at pH 10.6 when the scan rate was set at 60 mV s−1. The electrochemical behavior of SPAn is affected by the potential scan rate. At the scan rate of 6 mV s−1, two pairs of redox peaks occur on the cyclic voltammogram of SPAn in the solution of pH 10.6. In this case, its usable potential range is between 0.0 and 0.65 V (versus SCE). Based on the area of the cyclic voltammogram, a 44.8% of the electrochemical activity of SPAn is still retained when the SPAn electrode moved from pH 5.0 to 10.6. SPAn has a conductivity of 4.3 S cm−1, which is slightly dependent on pH when equilibrated with water. SPAn can react with alcohol to form the ester followed by hydrolization, which gives a straightforward evidence for the sulfonation of polyaniline. The FTIR spectra reveal a fact that polyaniline immersed in the concentrated sulfuric acid can be sulfonated, and the sulfonic acid group can be removed from SPAn by the reaction of SPAn with alcohol.