Electrochemical preparation of composite electrodes based on organic/organic and organic /inorganic hybrid structure

Abstract

Electrochemical preparations of composite film electrodes compo~:;Of organic/organic and organic/inorganic hybrid structures have been described. Organic film electrode, PANI was prepared electrochemically from an aqueous electrolytic solution by coating its film onto a Pt substrate. The organic/organic electrodes, PANIIMB and PANIIPR were also grown electrochemically as film from the same electrolytic solution that contain either MB or PRo The organic/inorganic film electrode PANI/TiOz was obtained electrochemically by polymerizing aniline in the presence of TiOz suspension in the same electrolytic media. The film electrodes thus grown electrochemically are free- standing and adhere to the substrate even in a deposit of sufficient thickness. The rate of electrochemical polymerization in the presence of MB, PR and TiOz were evaluated from the observed slope of a straight Iine obtained in a plot of anodic peak current vs no. of potential scan. It was observed that, the line for the formation of PANIITiOz film raises sharply compared to that of PAN!, PANIIMB or PANIIPR films. The steeper line suggests that the electrochemical growth rate of PANI/TiOz is faster compared to the other films synthesized under the identical electrolytic and electrochemical condition employed. IR spectral analysis of the film samples yielded useful information on the identification of the components present in the film electrodes of hybrid structure. In each electrode system, the corresponding components, viz., PAN!, MB, PR, TiOz show, characteristics bands confirming the presence of the components in each electrode matrix. UV-Vis optical spectra of the samples were recorded in their DMF solution. Strong absorption maxima in the ultra violet region and another band in the visible region were observed for • the PANI sample. This optical phenomenon is identical to that of PANI and other conducting polymers reported previously suggesting an interband transition and mid-gap states transition occuring in the ultra violet and visible region, respectively. However, the peak responses in the optical spectra seem to be modified when MB or PR was embedded in the PAN! matrix. TiOz was not dissolved in the DMF solution and thus optical .", '.'. characterization of the PANI/TiOz matrix was not attempted. XRD spectra of PANI, PANIIMB, PANIlPR and PANI/TiOz samples showed diffused scattering indicating the amorphous nature of the materials. The electrical conductivity of the film matrices was measured in their compressed solid formed by two point-probe method. The results of conductance measurement clearly provide evidence that the inclusion ofMB, PR or TiOz into the PANI matrix affects the electrical properties of the matrix. The electrical conductivity of the PANI/TiOz was found to be significantly higher while the PANIIMB shows a considerably lower conductance than that of the parent PANI matrix. However, the measured conductance of all the samples indeed shows that their conductivity values still exist in the conductivity range of conventional inorganic semiconductors. The surface morphology of the PANI was observed to be modified when either MB, PR or TiOz was embedded in it. The SEM image shows a granular morphology for the PANI surface. The granular morphology appears to be fibrillar on inclusion of MB in the PANI matrix. The PANIIPR surface seems to be consisted of agglomerates and stacked over the surface as deposit. The PANIITiOz, on the other hand, exhibits deposit of the particles that are aggregated and distributed non-uniformly over the substrate they grown. The film electrodes thus synthesized were found to be electroactive. The voltammetric features of the films show regular oxidation and reduction processes when cycled between -0.3 V and +0.6 V vs SeE in aqueous sulphuric acid. During oxidation and reduction, electrolytic anions are pushed in and out, respectively, of the film with its characteristics color changes. However, the redox reactivities of the films employed are found not to be identical. This may arises due to the inclusion of different chemical entities, viz., MB, PR, and TiOz into the PAN! matrix and thus modifying the electrode surface behavior and hence shows dissimilar redox activity. The stability of the film electrodes, thus synthesized in repeated oxidation/reduction cycles and its degradation at highly positive potentials were examined. The results obtained from the current-voltage response (cyclic voltammogram) indicate that although over oxidation takes place with the composite electrodes (pANIIMB, PANIlPR and PANIITiOz), the extent of degradation is not as 2 drastic as with the PANI, suggesting a better electrochemical stability of the composite electrodes relative to the bulk PANI film electrode.