The role of lithium, perchlorate and water during electrochemical processes in poly(3,4-ethylenedioxythiophene) films in $\mathit{LiCl}{O}_4$ aqueous solutions

Abstract

Thin films of poly(3,4-ethylendioxythiophene) (PEDOT) were electrochemically deposited on gold electrodes in aqueous media. The role of perchlorate, lithium, and water during the charge/discharge of PEDOT films was investigated by cyclic voltammetry together with EQCM, vis − NIR spectroscopy, and acoustic impedance, also by means of ac-electrogravimetry in a 0.1 M $\mathit{LiCl}{O}_4$ aqueous solutions. In this way, it has been possible to correlate the electrical, mass, color and electromechanical properties changes during the electrochemical reactions of this polymer. Both, hydrated lithium cations and perchlorate anions can act as counterions during the electrochemical reactions, however, at the more positive potentials anions are the preferred ions while at the more negative potentials the relative participation of cations increases. A secondary electrochemical reaction appears in aqueous solutions at potentials near −0.38 V against the Ag|AgCl|KCl(sat) reference electrode and it is neither associated with mass changes nor with spectroscopic changes of the PEDOT. Viscoelastic properties of the film change also with the applied potential and this change is mainly observed at the more negative potentials due to the exchange of highly hydrated $L{i}^{+}$ cations.