Study of poly(3,4-ethylenedioxythiophene) films prepared in propylene carbonate solutions containing different lithium salts

Poly(3,4-ethylenedioxythiophene) [PEDOT] was obtained from organic electrolytes containing the monomer in a solution of propylene carbonate (PC). Different lithium salts (LiBF4, LiClO4, LiPF6 or LiN(SO2C2F5)2 [LiBETI]) were used as supporting electrolytes. The electrosynthesis was conducted under galvanostatic conditions on to a platinum–quartz microelectrode up to a charge density of 200 mC cm−2. Scanning electron microscopy (SEM) performed on the deposited polymers reveals that they are obtained as granular films whose porosity is dependent on the supporting electrolyte. When LiBETI is used, the polymer is more compact and the porosity hardly visible by SEM observation. Cycling experiments, using triangular wave or square wave signals, were carried out on PEDOT films immersed in the same electrolyte as used for the electrosynthesis. All polymers exhibit reversible behaviour: the mass, charge and particles exchanges are very reproducible from one cycle to the next. The best results in term of current density and time of discharge are obtained in the presence of anions of intermediate size (PF6−, ClO4−) for which the polymer exhibits a mean pore size of 0.12–0.15 μm.