EVALUATION OF THE 1ST DISCHARGE REDOX PROCESS OF DOPED POLYPYRROLE

The first potentiodynamic discharge of thick (4-10 mum) polypyrrole (ppy) layers in 0.11 M LiClO4 in MeCN leads to a very flat profile at positive potentials with a superimposed sharp peak, beginning at -0.5 V vs. SCE. The latter is totally absent for 0.1 M NBu4BF4. It disappears in the course of subsequent cycling. This effect is discussed in terms of selective cathodic insertion of Li+ ions, which leads to Li+ClO4- in the solid, either directly or indirectly, via the equilibration of an initially formed donor type ppy-Li+ with residual ppy+ClO4- in the solid. The influence of thickness, reorganization of the polymer structure after first discharge and solvent (water) is discussed in detail. It was also found that relatively high redox capacities, which may be derived from the first discharge curve, decay to about 50% in the steady state cycles in some cases at the same low-voltage scan rate. As a practical consequence, this is suggested as a method to evaluate the steady state cycles for the determination of the intrinsic redox capacity of the conducting polymer.