Studies of pyrrole black electrodes as possible battery positive electrodes

It is shown that a polypyrrole, pyrrole black, may be formed anodically in several aqueous acids. The polypyrrole film shows a redox couple at less positive potentials than that required to form the film and the charge associated with these reduction and oxidation processes together with their stability to cycling varies with the anion in solution and the potential where the polypyrrole is formed; overoxidation of the film caused by taking its potential too positive has a particularly disadvantageous affect. In the acids HBr and HI, the polypyrrole films can act as a storage medium for Br2 or I2 so that they may be used as a substrate for a X2/X- electrode. Such electrodes may be charge/discharge cycled and the pyrrole/Br2 electrode shows promise as a battery positive electrode.