ION CONDUCTIVITY: THE KEY PARAMETER FOR ELECTROCHEMICAL DEVICES

In this energy transition period, hydrogen is progressively used to produce electrical power in the stationary (domestic and industrial), portable and automotive sectors. The main advantages of using hydrogen are the highly efficient conversion into electricity and vice versa. The clean combustion of hydrogen offers a solution for grid balancing service to convert the surplus of renewable energy. Fuel cells-based devices are considered the most attractive power source for their high efficiency and low emissions [1-3] while, among the several methods for "green" hydrogen production, water electrolysis remains the most reliable and efficient [4]. All these technologies require a core component based on an ion exchange polymeric membrane (IEMs), and ion conduction is considered the fundamental parameter for the good performance of the devices. It is a water-assisted process. The water acts as a vehicle from one functional group to another. It is mainly associated with two distinct mechanisms: the vehicular and Grotthuss one. Generally, these mechanisms differ in the water contained in the ion clusters; in particular, the vehicular mechanism occurs when high humidity and low temperature conditions are combined. The water molecules confined into the electrolyte membrane form a cluster in which ion migration is possible. Depending on the type of ionic groups, IEMs are broadly classified into PEMs for PEMFC and AEMs for AEMFC. IEMs are typically composed of hydrophobic substrates, immobilized ion-functionalized groups, and movable counter-ions. The main transport phenomena that occur within an IEM are the transport of water and ions, and the two phenomena are strictly related. The maintenance of an optimal level of water is a critical issue in the membrane because sufficient water is needed to maintain high conductivity. The ions transport depends on the amount of water contained within the membrane, and those phenomena directly control the performance of the fuel cell. In this work, an overview of recent advancements in ion exchange membranes is carried out considering different polymer backbone and functional groups and a relation between the ion conductivity and fuel cell performance [1]A. Carbone, M. Castriciano, L. Monsù, I. Gatto, "Novel Polymeric Composite TPPS/s-PEEK Membranes for Low Relative Humidity PEFC", Polymers, 12, 2020, 1431-1444 [2]I. Gatto, A. Carbone, A. Saccà, E. Passalacqua, C. Oldani, L. Merlo, D. Sebastian, A. S. Aricò, V. Baglio, Increasing the stability of membrane-electrode assemblies based on Aquivion® membranes under automotive fuel cell conditions by using proper catalysts and ionomers, J. Electroanal Chemistry 842, 59-65, 2019 [3]A. Carbone, R. Pedicini, I. Gatto, A. Saccà, A. Patti, G. Bella, M Cordaro, "Development of Polymeric Membranes Based on Quaternized Polysulfones for AMFC Applications ", Polymers, 12, 2020, 283-298 [4]A Carbone, S. Campagna Zignani, I. Gatto, S. Trocino, A.S. Aricò, "Assessment of the FAA3-50 polymer electrolyte in combination with a NiMn2O4 anode catalyst for anion exchange membrane water electrolysis", International Journal of Hydrogen Energy, 45, 2020, 9285-9292.