Tuning Electronic and Ionic Conductivities in Composite Materials for Electrochemical Devices

Abstract

Mixed conductors having both high ionic and electronic conductivity are needed in membrane electrode assemblies (MEA) present in electrochemical devices from fuel cells, to supercapacitors and all battery chemistries. Typically, carbon black, binders and redox active materials are combined to make an electrode assembly into which a liquid electrolyte can 2 impregnate. Solid state devices require the ionic conduction built into the MEA. In this case, a material which can provide both electronic and ionic conduction as well as a redox functionality is described based on PEDOT-Cl as both the electronic conductor and the redox active component whilst an organic ionic plastic crystal [C2mpyr][FSI] is present as both binder and ionic conductor. Surprisingly, both the electronic and ionic conductivity of the composite are enhanced relative to the pure components by a factor of ×9 for electronic and ×180 for ionic. The mixed conducting composites are demonstrated to retain their redox activity in aqueous electrolytes, and, in the optimum case, 103 F g-1 and 296 mF cm-2 capacitance values are obtained for low and high mass loading electrodes. These materials demonstrate an innovative approach to prepare electrode assemblies where all three functionalities are incorporated into the materials. ie. electronic, ionic and redox activity for future energy devices.