THIN-FILM POLYANILINE POLYANILINE ELECTROCHEMICAL-CELLS

Electrodeposited polyaniline (PANi) in the emeraldine oxidation state was used as the electrodes of open rechargeable cells containing 1 M HClO4 as the electrolyte. The cells could be charged at very high hourly rates to 85% of the redox charge in the leucoemeraldine-emeraldine transition of the polymer. Contrary to normal behaviour of rechargeable cells, the coulombic efficiency improved with increasing rates of charge injection and withdrawal. This is attributed to less charge being dissipated by self-discharge at high rates of discharge. The poor charge retention was caused by reactions between the charged electrodes and their environment. The decrease in cell voltage on standing may also be induced by internal redox reactions of PANi of different oxidation states present at the electrodes as a result of incomplete oxidation or reduction during cell operation. Ultraviolet (u.v.) spectroscopy of the charged electrodes identified mostly protonated leucoemeraldine at the negative electrode and pernigraniline at the positive electrode. The irreversibility in the oxidation from the emeraldine state to the pernigraniline state accounts mostly for the degeneration of cell performance after prolonged cycling.