XPS studies of nitrogen-containing conjugated polymers–palladium systems

Polyaniline (PANI) and polypyrrole doped with chloride ions (PPyCl) have been treated with PdCl2 solutions in HCl of various concentrations. Basing on the results of XPS studies it is shown that the differences in the redox and basic properties of both polymers lead to different mechanisms of their interactions with palladium ions present in the PdCl2 solutions studied. Thus, in the PdCl2 solutions of low acidity in which [PdCl2(H2O)2] predominates, both polymers are oxidized with simultaneous reduction of a part of Pd2+ to Pd0. In the PdCl2 solutions of high acidity in which [PdCl4]2− is the major complex, reduction of Pd2+ does not occur. Owing to stronger basic properties of PANI than those of PPyCl, palladium is incorporated into the former polymer as anionic chlorocomplexes via protonation reaction. In the case of PPyCl the situation is more complex. Detailed analysis of the possible surface reactions taking place in the PPyCl–Pd systems studied is given in the paper.