The electrochemistry of platinum phthalocyanine microcrystals. IV. Temperature dependence of the electrochemical behaviour in non-aqueous solution

Abstract

The effect of temperature on the electrochemical behaviour of platinum phthalocyanine microcrystals was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in acetonitrile containing 0.1 mol dm −3 of the tetrabutylammonium salt of either ClO 4 −, BF 4 − or PF 6 −. Varying the temperature leads to a shift in the peak potential and a change in the magnitude of the peak current, accompanied by the formation of new peaks and a change in peak shape. The temperature dependence of the electrochemical behaviour is controlled by the identity of the doping anions. The shift in peak potentials is explained using an electrochemically stimulated conformational relaxation model. The changes in peak current depend on the kinetics of the redox processes. For lightly doped film, the peak current is decreased on increasing the temperature. For the highly doped films, a nucleation–growth-like phase transformation is the rate-determining process during oxidation. The phase transformation rate is controlled by both ionic charge transport in the film and the nucleation–growth kinetics. The nucleation–growth rate decreases with increasing temperature, whereas the ionic transport rate increases with temperature. A kinetics model of crystallisation developed by Keith and Padden is used to describe the effect of temperature on the rate of phase transformation.