Matching Diethyl Terephthalate with n-Doped Conducting Polymers

The combination of small, high charge capacity molecules as pendant groups with a conducting polymer backbone having good electronic conductivity upon doping, gives the possibility to design a high capacity conducting redox polymer material for electric energy storage applications. The desired synergetic effect of the two components requires energy matching as well as chemical compatibility of the pendant group and the polymer backbone. Here we investigate the matching of diethyl terephthalate (DeT) with the thiophene-based conducting polymers polythiophene (PT), poly(3,4-ethylenedioxythiophene) (PEDOT), and polyphenylthiophene. We show that a stable and well-defined electrochemical response of DeT is achieved, together with all conducting polymers except for PT in tetrabutylammonium hexafluorophosphate electrolyte, indicating good energy match as well as chemical compatibility between DeT and polymers. By varying the size of ammonium cations in the electrolytes, we further show how this size affects the conductivity and the cycling stability of the polymers and also that the n-doping performance of all conducting polymers can be improved by the use of smaller alkyl ammonium cations. On the basis of these results, we suggest that PEDOT and PT are suitable candidates for a polymer backbone in conducting redox polymers with DeT pendant groups.