Electroless deposition of gold into poly-3,4-ethylenedioxythiophene films and their characterization performed in chloride-containing solutions

Au-containing polymer films were obtained by electroless deposition of gold from diluted solutions of HAuCl₄ into preliminarily reduced poly-3,4-ethylenedioxythiophene (PEDOT) films. Structural peculiarities of such pristine and composite films were characterized by scanning and transmission electron microscopy methods. It was established that the gold clusters forming under such deposition appear on the outer surface of polymer films and their pores. The clusters’ sizes ranged between 30 and 100 nm depending on the time of exposition of a PEDOT film in solutions of Au(III) ions and the concentration of these ions. It was also observed that in contrast to pristine PEDOT films, cyclic voltammograms (CVs) of composite films in the presence of chloride ions show additional redox peaks resulting from oxidation of gold with formation of an insoluble product and followed by the product reduction under reversal of the potential scan direction. As a result of parallel electrochemical quartz crystal microbalance (EQCM) and CV measurements, it was also established that the number of chloride ions per one transferring electron in the gold oxidation process is near to unity. To elucidate the oxidation degree of gold in the presence of chloride ions, a special procedure of changing the electrode potential was used. It consisted of clamping the high anodic potential in the region of gold oxidation (0.97 V, Ag/AgCl) and subsequent gradual decrease of the electrode potential with a constant scan rate. Under these conditions, it was possible to completely oxidize all the gold particles containing in a composite film and find out the maximum amount of electricity consumed for the product particles’ reduction. A comparison between such data and the results obtained in EQCM determinations of the gold content in the same film led to the conclusion that the oxidation state of gold in the complexes formed is Au(III). The effects of chloride ion concentration and scan rate of the electrode potential on current responses of PEDOT–Au films were investigated. Some primary conclusions on the kinetics of the studied processes are made.