G. Zotti et al., THE REVERSIBLE HYDROXIDE DOPING OF POLYPYRROLE - DELAY OF POLARON ANDMOBILE BIPOLARON INJECTION IN POLYPYRROLE BY H BONDING OF HYDROXIDE ANIONS, Synthetic metals, 80(1), 1996, pp. 35-39
The reversible hydroxide-anion doping of polypyrrole (PPy) has been in
vestigated by FT-IR, cyclic voltammetry, in situ conductivity and ESR
techniques. FT-IR confirmed that the hydroxide anion substitutes the c
ounteranion reversibly in doped PPy. The dopant hydroxide anion produc
es a strong negative shift of the oxidation potential of PPy and doubl
ing of the reversible charge. No similar effects are displayed in N-su
bstituted PPys. In situ conductivity shows that the material becomes c
onducting (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 sta
ges of charging, developing just before the onset of conductivity. The
results indicate that the hydroxide anion stabilizes the positive cha
rges in PPy by NH bonding. The interaction is so strong that fixed bip
olarons are formed without the intermediate formation of polarons. Pol
arons are produced only at higher charges with subsequent injection of
mobile bipolarons and setting in of conductivity.