Counterions in Electrochemically Polymerized PEDOT

The electrochemical polymerization of PEDOT allows the introduction of a wide range of counterions since the latter can be added in the form of salts to the reaction mixture. The choice of counterions is limited only by their solubility and stability under the reaction conditions. A list of selected counterions used in the electrochemical polymerization is shown in Table 7.1 together with the methods used and the conductivities obtained. Different polymerization methods such as potentiostatic, galvanostatic, and repetitive multisweep result in different PEDOT films with differing properties. The in situ photoelectropolymerization uses light as well as a constant potential. Brief descriptions of polymerization methods can be found in the description of Table 7.1. 

The highest conductivities are obtained in the presence of perchlorate, using acetonitrile as solvent (method C and F with 650 and 780 S/cm, respectively). The results obtained by El Moustafid et al. show that water as a solvent leads to lower conductivities than organic solvents such as propylene carbonate or acetonitrile for the same counterions. Using water as solvent, the highest conductivity was found in the presence of nitrate. 

The series of measurements using bis(perfluorosulfonyl)imides or perfluo-rosulfonates with different chain lengths performed by Xia et al. using in situ photoelectropolymerization indicates that long perfluoroalkyl chains decrease the conductivity of the resulting films.  

Several groups performed the electrochemical polymerization of EDOT in the presence of polymeric counterions. Yamato et al. were the first to report 

Notes Method A—polymerization in propylene carbonate (PC) at -30°C with 1 = 0.04 tnA/cm method B— polymerization in PC at -30°C with 1 = 0.01 - O.ObmA/cm method C— polymerization in acetonitrile at RT with E=0.85 -1.1 eV method D— polymerization in water with tenside at RT with sweeps between -1 and +1 V method E—in situ photoelectropolymerization in acetonitrile with a series of potentials above the half-wave oxidation potential method F— polymerization in microfiltration membranes in acetonitrile at 1.3 V method G— polymerization at 0.8 V in acetonitrile (in the case of PSS in acetonitrile and water). 

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