Conducting polymers are considered to suffer metal–insulator transitions during reduction. After a deep electrochemical reduction, freestanding films of polypyrrole retain a conductivity as high as 0.05 S cm−1. Used as cathodes, they allow the flow of high cathodic currents from aqueous solutions, the hydrogen release being inhibited up to −3.0 V. Fast copper electrodeposition was obtained at −0.6, −1.5 and −2.1 V using freestanding films reduced for a long time. The electrochemically stimulated conformational relaxation (ESCR) model can explain the high conductivity of these “reduced” materials by the trapping of counterions when the structure shrinks and closes. Conductivity in the range of semiconductors and the inhibition of hydrogen release open new possibilities for the use of reduced conducting polymers as electronic conductors and cathodes for electrochemical studies in aqueous solutions.
