EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Ionomers are ion-conducting polymers with a nanophase separated morphology, including hydrophobic polymer domains and hydrophilic ionic clusters. Ionomers present a high ionic conductivity and negligible electronic conductivity and are used as separators in various electrochemical energy technologies, such as polymer membrane fuel cells or redox flow batteries.
The ionic groups are grafted on the macromolecular chains, whereas the respective counter-ions are free to migrate through the ionic domains (typically hydrated nanometric channels extending across the ionomer). Proton and cation-conducting ionomers typically contain anchored sulfonic acid groups and hydroxide and anion-conducting ionomers grafted quaternary ammonium ions.
In order to design improved ionomers with excellent performance, the ion mobility is a relevant parameter, which is related to the nanophase separation and the hydration of the ionomer. The effective ion mobility is a complex parameter, which depends on the complicated situation encountered by the mobile ions during their migration in the restricted area of ion conduction channels surrounded by a solvent with high dielectric constant and fixed counter-ions grafted on the channel walls. This complexity can be described by several phenomenological parameters, such as porosity, tortuosity, or percolation threshold.
In our work, we derive and discuss relations between the ion mobility, determined from measurements of the ionic conductivity, the ion exchange capacity and the water uptake, and the tortuosity and percolation of ion-conducting nanometric channels in various cation- and anion-conducting ionomers [1].

[1] P. Knauth, L. Pasquini, R. Narducci, E. Sgreccia, R.-A. Becerra-Arciniegas, M. L. Di Vona, Effective ion mobility in anion exchange ionomers: relations with hydration, porosity, tortuosity, and percolation, J. Membrane Sci., 617, 118622 (2021).