Redox behaviour of polyaniline–palladium catalytic system in the presence of formic acid

Redox behaviour of polyaniline (PANI) films containing chemically incorporated palladium particles in the presence of formic acid was studied. Two types of PANI–Pd hybrids were prepared: PANI-PdHA and PANI-PdLA, depending on the acidity of the PdCl2 solution used for the introduction of palladium into the polymer matrix. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the nature of processes involved upon the decomposition of formic acid on polyaniline–palladium hybrids. In particular, UV–vis changes of both kinds of films were followed in situ (in 1 M aqueous HCOOH solution) as a function of time. Rather unexpectedly, the redox properties of polyaniline films are found to be significantly altered in the presence of palladium particles. Particles of Pd0 promote the reduction of PANI from the most oxidized and semi-oxidized states to the most reduced one with simultaneous decomposition of formic acid.