Preparation and characterization of carbon-supported polyaniline-palladium composite electrodes

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Gawron, Erin L.
Janata, Jiří
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Polyaniline (PANI) is an electronically conducting polymer whose redox state can be precisely controlled. The nitrogen groups in the polymer are weak bases, which can be protonated and because of the redox and acid –base properties, it can be used as a matrix for insertion of various metal complexes. The preparation for this work uses the conducting form of PANI with precisely controlled potentials and solution conditions in order to insert and reduce Pd into the polymer matrix. The goals of this thesis were to identify which carbon substrate provides the best support for the deposition of PANI, to find the palladium species in aqueous acidic solution that results in the most favorable interactions with the polymer, and to elucidate the nature of these interactions in a controlled and systematic way, in order to create C/PANI-Pd composite materials. Characterization of the materials was achieved through the use of X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, cyclic voltammetry (CV), and scanning electron microscopy (SEM). Characterization results of PANI were correlated across the techniques to provide information regarding the oxidation state of the polymer. Results showed that a synthetic graphite fabricated from petroleum coke displayed the optimal properties for use as a PANI support due to the greater level of sp2 character and less presence of surface oxygen groups. Using this carbon to create C/Pt-PANI composites, the catalytic activity of this composite electrode was tested using the oxidation of n-propanol in KOH. Recorded CVs confirmed that the activity was dependent upon the Pt loading in the composite and the presence of PANI had no effect on the oxidation products, deeming this composite suitable for palladium metal insertion. Due to the speciation of tetrachloropalladate in acidic aqueous solutions, the optimal species for the insertion of palladium metal had to be determined. Each species, PdCl2(H2O)2, PdCl3(H2O)-, and PdCl4-, was evaluated for the strongest interaction with PANI and results show that the PdCl3(H2O)- complex interacts most fully with PANI giving the greatest amount of Pd insertion. Finally, the nature of the interaction between PANI and Pd was studied in more detail by considering the effects of conditioning of the polymer and the amount of Pd inserted. Results showed a lesser extent of Pd reduction on conditioned PANI samples and more Pd in the matrix did not result in more reduction. The final hypothesis is that the Pd(II) chlorocomplex is “bridging” two PANI fibrils and forming an irreducible structure.
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