Alkaline Polymer Electrolytes based on Polyketone for Application in Electrochemical Energy Conversion and Storage Devices

The objective of this work is to explore new functionalities for the development of anion exchange membranes possessing a unique combination of properties, including high level of ionic conductivity, long term chemical stability, and low cost. For this purpose, aliphatic polyketones (derived from ethylene/CO copolymerization or ethylene/propylene/CO terpolymerization) have been chosen as starting materials owing to their excellent properties in terms of high mechanical and chemical resistance, and wear resistance over a broad range of temperatures. The functionalization of aliphatic polyketones with a suitable primary amines via Paal-Knorr cyclization allows to incorporate a variety of N-functional groups and to modulate the physicochemical and conductivity properties of the final polypyrrole-co-polyketone polymer. It is crucial to understand the interactions at molecular level of both the backbone and the side chains to tailor the properties of the polymer for its application in anion exchange membranes. For this purpose, the functionalization of the aliphatic polyketones has been studied systematically with four different primary amines, i.e. N,N-dimethyl ethylenediamine, 2-(2-aminoethylamino)ethanol, 1-(2-aminoethylpiperazine), and n-butylamine. The obtained functionalized polyketones possess chemically stable backbones, offering the possibility to prepare membranes by solvent casting or hot pressing, and easily convert their amine functionalities to the corresponding quaternary ammonium groups by simple methylation. Furthermore, the electrical and thermal properties can be tuned by carefully optimizing the synthetic conditions, i.e. the amount of amine added relative to 1,4-diketonic groups in the polyketone, or by adding suitable inorganic fillers to obtain composite membranes. Derivatives with high ion conductivity coupled with good chemical stability in alkaline media have been obtained, opening the way to further improvement and possible application in electrochemical energy storage devices e.g. poly[N-(N-(4,4’ dimethyl piperaziniumethyl)-ethylenepyrrole(X)/(ethylene ketone)/(propylene ketone)] membrane in hydroxide form exhibits an ion conductivity of 11.7 mS/cm at 80oC while maintaining its structural integrity for 336 hours in alkaline conditions). The results from Broadband Electrical Spectroscopy studies allow to suggest the long-range charge migration mechanism, revealing the effect of the polymer host matrix on the ion conduction in these systems.