(Invited) A New Frontier in Hybrid Inorganic-Organic Membranes for Redox Flow Batteries: The Polyketone-Based Membranes

Abstract

Zinc iodide flow batteries (ZIFBs) are amongst the most promising chemistries to substitute the expensive and less energy intensive Vanadium Flow Batteries (VFBs). One of main problems related to this technology is the crossover of water due to the transport of Zn2+. One possible approach is the development of new ion-exchange membranes (IEMs). For practical applications they are required to possess high ionic conductivity, high thermal stability, long lifetime, and electrical insulation. The preparation of polymeric materials with such high-performance properties is still challenging and can lead to high prices, hindering their widespread use in energy conversion technologies. This is even more difficult when considering anion conducting membranes [1-3].Polyketones (PK) are known to be high performance thermoplastic polymers with applications ranging from fire-retardants film coatings, packaging, and fibers, resulting from their high thermal and chemical stability. They can be obtained in high yields by copolymerization of inexpensive and readily available feedstocks such as ethylene and carbon monoxide. Our group proved that PK with alternating 1,4-dicarbonyl repeating units constitute an ideal starting point to access a wide class of modified polymers by simple Paal-Knorr cyclization, to gain pyrrole-N-bound functional groups stemming from the aliphatic backbone [4-5].Different ion-conducting membranes have been developed and the effect of reaction conditions on their thermal properties, chemical stability, and their conductivity in a wide range of frequencies have been assessed by broadband electric spectroscopy to shed light on the conduction mechanisms [4, 6]. The more promising material developed has been tested in a single cell redox flow battery obtaining promising results.The proposed conducting polymers combine the thermal stability of the aliphatic PK structure with the chemical flexibility given by the groups derived from functionalized amines branching out, proving to be highly tailorable, with possible applications in current energy conversion technologies. Acknowledgements: The authors wish to thank the Research Projects of Relevant National Interest (PRIN 2017) of the Italian Ministry of Education, University and Research “Novel Multilayered and Micro-Machined Electrode Nano-Architectures for Electrocatalytic Applications (Fuel Cells and Electrolyzers)” (Prot. 2017YH9MRK) and SID2020 Project of Department of Industrial Engineering, University of Padova “A New frontier in Hybrid Inorganic-Organic Membranes for Energy Conversion and Storage Devices” (Prot. BIRD201244) for funding.