Electrochemistry of PANI/metal composites in basic solutions

Polyaniline (PANI) has been extensively investigated due to its unique conductivity, which is primarily dependent on the oxidation state of the material and the solution pH. PANI is an insulator when it is oxidized, and the solution pH exceeds four. Numerous attempts to extend PANI's conductivity to neutral and alkaline environments have been unsuccessful. However, our previous study has demonstrated that PANI/Pd composite is conductive and catalytically active in a basic solution, pH ∼ 12. Therefore, the conductivity and the electrochemical properties of PANI composites including PANI/Au, PANI/Pd and PANI/Pt were evaluated in basic solutions. The fundamental studies of PANI/metal composites were conducted to determine if the applications for the polymer could be extended to basic solutions that are traditionally precluded.;PANI/metal composites are produced electrochemically through the controlled uptake and reduction of metal anions including PtCl42− , PdCl42−, and AuCl4 − using cyclic voltammetry. The deposition of metals into PANI was confirmed using the acid doping of the polymer, FTIR spectroscopy, and thermal gravimetric analysis (TGA). The acid doping study suggests that the metal species physically block proton-doping sites in the polymer. FT-IR data indicates that a higher oxidation state is obtained for the polymer after the metal reduction. The TGA data also provides the measure of the approximate amount of metal in the polymer. The characterization data suggests that the conductivity should be diminished relative to the pristine polymer. However, all of the PANI/metal composites demonstrate catalytic activity for alcohols oxidation in basic solutions. The data indicate that the electrochemical responses and the conductivity of the composites are maintained at pH values that have typically produced insulating PANI. The results suggest that the metals act as solid-state dopants, which facilitates the continued conductivity of the polymer in basic solutions.