ORALS

A semi-interpenetrating network of PEDOT and PEO was used as a highly effective supercapacitor electrode. Wang and co-authors in 2017[1] detailed a process in which an semi-interpenetrating polyethylenedioxythiophene/polyethylene oxide (PEDOT/PEO) network with mixed ionic and electronic conductivity could be synthesized in a simultaneous fashion[1]. The ionically conducting PEO was phase separated with the electronically conductive PEDOT, leading to a larger triple phase boundary and thus a higher capacity[1,2]. The phase separation of PEDOT and PEO also allowed for mechanical robustness and increased cycling ability[1]. While these films represent a significant step forward for flexible electronics, solution casting, the current fabrication process, is not suitable for large scale production. In this work, films of this interpenetrating polymer network were made through inkjet printing[3]. The viscosity of the polymer precursor is 31 cP, at the upper limit of what a typical inkjet printhead can handle (~20 cP)[3,4]. The raw prepolymer also displays shear thinning behavior, dropping linearly to 21 cP between shear rates of 130 and 210 s-1. To make a more suitable precursor for inkjet printing, ethanol was added to decrease the viscosity of the precursor. Ethanol is a commonly used solvent for inkjet printing as is has an optimal viscosity (1.1 cP at STP), low vapor pressure, and good wetting properties. Additionally, ethanol is not known to polymerize via free-radical polymerization[5] and will not compromise the chemical integrity of the interpenetrating network [5]. Ethanol is a relatively safe organic solvent and is soluble in the precursor. It is also soluble in methanol, which is used in the initial polymer processing to clear away excess unpolymerized precursor. Cyclic voltammograms of both neat and inkjet printed films in an aqueous LiClO4 electrolyte with a platinum counter electrode and an Ag/AgCl reference electrode were taken. The results of the two cyclic voltammograms were comparable and showed a similar capacitance.

References:
1. Fong, K. D., Wang, T., Kim, H.-K., Kumar, R. V. & Smoukov, S. K. Semi-Interpenetrating Polymer Networks for Enhanced Supercapacitor Electrodes. ACS Energy Lett. 2014–2020 (2017). doi:10.1021/acsenergylett.7b00466.
2. Ghosh, S. & Inganäs, O. Networks of Electron-Conducting Polymer in Matrices of Ion-Conducting Polymers Applications to Fast Electrodes. Electrochem. Solid-State Lett. 3, 213 (1999).
3. Magdassi, S. et al. The Chemistry of Inkjet Inks. (World Scientific Publishing Co. Pte. Ltd., 2009). doi:10.1142/6869
4. Magdassi, S. Ink Requirements and Formulations Guidelines. in The Chemistry of Inkjet Inks 19–41 doi:10.1142/9789812818225_0002.
5. Hazrati, H. D., Whittle, J. D. & Vasilev, K. A Mechanistic Study of the Plasma Polymerization of Ethanol. doi:10.1002/ppap.201300110