A study of the polymerisation and electrochemical cycling of Pd methoxy-Salen derivatives using fast ellipsometry and FT-infrared spectroscopy

Abstract

A new fast electrochemical ellipsometer has been constructed using a Stokesmeter configuration, and applied to the study of poly[Pd(MeOSalen)] films during growth from acetonitrile solutions and subsequent electrochemical cycling. Growth of the films does not take place until a critical potential is reached, after which nucleation on the electrode surface takes place. Earlier work has emphasised the importance of metal–metal interactions in these systems, and it is suggested that initial formation of stacked oligomers may take place in solution, and these then nucleate on the surface to give a film of approximately 40 nm initial thickness. As growth continues through cycling, the nature of the film changes, becoming relatively close packed near the electrode surface, but less close packed at the film/electrolyte interface. Even when growth is complete, the resultant films remain inhomogeneous, and show substantial swelling on anodic cycling. Evidence for this swelling is also provided by insitu FTIR studies, and it is suggested that the morphology of the films is dominated at low potentials by stacking interactions, and that inter-chain repulsions at high potentials disrupt these interactions, giving rise to substantial ingress of solvent and counter-ions.