West, Keld5; Bay, Lasse6; Nielsen, Martin Meedom2; Velmurugu, Y.7; Skaarup, Steen3
1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Department of Physics, Technical University of Denmark3 Department of Chemistry, Technical University of Denmark4 Physical and Biophysical Chemistry, Department of Chemistry, Technical University of Denmark5 Department of Chemical and Biochemical Engineering, Technical University of Denmark6 Department of Chemistry, Technical University of Denmark7 Technical University of Denmark
The electronic conductivity of the electroactive polymer polypyrrole-dodecyl benzene sulfonate (PPy-DBS) has been characterized as function of the redox level. The polymer was synthesized with different isomers of the dopant anions: the common mixed DBS tenside and three well-defined synthetic dodecyl isomers (with the benzene group at positions 1, 2 and 6). The conductivity was measured both by van der Pauw measurements on PPy-DBS in the oxidized, dry state as function of temperature, and by electrochemical impedance spectroscopy as function of potential in 0.1 M NaCl aqueous electrolyte. These investigations demonstrate that even minor differences in the dopant anion can cause significant changes in the physical properties of the electroactive polymer. The highest conductivities ($sigma$-25$/ = 39 Scm$+-1$/) are obtained by the (6D)BS isomer, perhaps because the branching leads to denser packing and therefore smaller hopping distances. This was supported by X-ray measurements. Synthesis at lower temperatures generally leads to higher conductivity. The conductivity is strongly dependent on the potential, being more than four magnitudes smaller for the reduced state where the number of electronic carriers is at a minimum. The conductivity is further reduced because of the uptake of water at low potentials, creating electrolytic domains that separate the electronic domains and inhibit hopping. There is a pronounced hysteresis in the conductivity as a function of potential. However, the major part of this hysteresis can be accounted for by the composition hysteresis implying that that the conductivity mainly depends on the number of charge carriers, but not on the history of the sample.
Journal of Physical Chemistry B, 2004, Vol 108, Issue 39, p. 15001-15008