The mechanism of the electropolymerization of aniline in 0.5 mol/L sulfuric acid was studied in detail by in situ UV-Vis spectrometry.Spectroelectrochemical experiments were done in a three electrode cell built with a quartz cuvette of 1cm path length.The work electrode was an ITO (indiumtin oxide) conductive glass perpendicular to light path

and the counter electrode was a platinum wire.An Ag/AgCl electrode with saturated KCl served as reference electrode.All potential values in the article were against to the reference.The acquired in situUV-Vis spectra showed that polyanilines could be electropolymerized at aniline concentrations 0.01

0.05 and 0.2 mol/L in sulfuric acid by cyclic voltammetry.Based on in situ UV-Vis spectra corresponding to cylic potential sweep at three different concentration of aniline above

the plots of the relationship between absorbance at 350 nm and 750 nm and elctrolysis time was made

which showed that the obvious inductive period in electropolymerization of aniline by cyclic voltammetry was seen for 0.01 mol/L aniline in 0.5 mol/L sulfuric acid water solution.In order to study how the concerntration of aniline in 0.05 mol/L sulfuric acid and the potential applied on ITO conductive glass electrodes effected the polymerization of aniline

in situUV-Vis spectra was recorded during electrolysis of solution by potentiostatic method at different concentrations of aniline in 0.5 mol/L sulfuric acid.These in situ UV-Vis spectra indicated that the polymerization of aniline occurred by electrolysis of aniline at potentials 0.8

1.0 and 1.3 V when the concentration of aniline was greater than 0.05 mol/L

however at potential 0.8 V

the polymerization of aniline did not happen in 0.01 mol/L solution of aniline.in situ UV-Vis spectra at the earlier phase of aniline electropolymerization by potentiostatic way showed that the 350 nm absorbance band appeared before the 750 nm absorbance band.This fact proposed that lower molecular weight oligomer intermediates during electrochemical polymerization of aniline might exist and that the intermediate was brought out prior to the production of polyaniline on ITO electrode.When the ITO conductive glass electrode was placed parallel to the light path

no absorbance bands were observed during electrolyzing 0.05 mol/L of aniline at potential 0.8 V

which showed that the intermediate and polymer mainly were produced on the ITO conductive glass electrode.These phenomena was not reported up to now.When the aniline concentration was 0.01 mol/L

and the potential applied on the ITO glass conductive electrode was 0.8 V

there were only an absorbance band at 350 nm in corresponding in situ UV-Vis spectra

which showed that the intermediates such as low molecular oligomers could be produced and exist on the ITO electrode

but did not lead to the formation of polyaniliane because of the low concentration of intermediates.After aniline of 0.05 mol/L in 0.5 mol/L sulfuric acid was electropolymerized by potentiostatic electrolysis at a potential 0.8 V for 70 min

the electrolysis was stopped

but in situ UV-Vis spectra were recorded continually.The red shift of absorbance band in spectra was seen

which indicated that polyaniline produced on the ITO electrode was of oxidized state and could react with aniline monomer in solution to form polyaniline at the reduced state.