The reversible hydroxide doping of polypyrrole. Delay of polaron and mobile bipolaron injection in polypyrrole by H bonding of hydroxide anions

The reversible hydroxide-anion doping of polypyrrole (PPy) has been investigated by FT-IR, cyclic voltammetry, in situ conductivity and ESR techniques. FT-IR confirmed that the hydroxide anion substitutes the counteranion reversibly in doped PPy. The dopant hydroxide anion produces a strong negative shift of the oxidation potential of PPy and doubling of the reversible charge. No similar effects are displayed in N-substituted PPys. In situ conductivity shows that the material becomes conducting (up to 2 S cm−1) only after about 50% of the doping charge is passed. Similarly, the ESR signal is absent during the initial stages of charging, developing just before the onset of conductivity. The results indicate that the hydroxide anion stabilizes the positive charges in PPy by NH bonding. The interaction is so strong that fixed bipolarons are formed without the intermediate formation of polarons. Polarons are produced only at higher charges with subsequent injection of mobile bipolarons and setting in of conductivity.