Hydration and Mobility of Alkaline Metal Cations in Sulfonic Cation Exchange Membranes

• Published in: Membranes (Basel) Vol. 13; no. 5; p. 518
• Main Authors: Volkov, Vitaly I, Slesarenko, Nikita A, Chernyak, Alexander V, Avilova, Irina A, Tarasov, Victor P
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 16-05-2023; MDPI
• Subjects: Bond energy; Cation exchange; Cation exchanging; Cations; Cesium; Cesium 133; Cesium isotopes; Chemical equilibrium; Diffusion coefficient; Einstein equations; Electric properties; Heterogeneity; Humidity; Hydration; hydration number; Hydrogen bonds; Investigations; Ion motion; Ions; Lithium; Lithium isotopes; Mass transfer; Mathematical analysis; Membranes; Metal ions; Mobility; Moisture content; Molecular dynamics; NMR; NMR relaxation; Nuclear magnetic resonance; Nuclear magnetic resonance spectroscopy; Polyethylene; Polystyrene; Polystyrene resins; pulsed field gradient NMR; Self diffusion; Sodium; Spectrum analysis; sulfonated polystyrene; Sulfonates; sulfonic cation-exchange membrane; Temperature; Water chemistry; sulfonic cation-exchange membrane; hydration number; ionic conductivity; selectivity mechanism; correlation time; pulsed field gradient NMR; sulfonated polystyrene; mass transfer; NMR relaxation; diffusion coefficient
• ISSN: 2077-0375; 2077-0375
• DOI: 10.3390/membranes13050518

The interconnection of ionogenic channel structure, cation hydration, water and ionic translational mobility was revealed in Nafion and MSC membranes based on polyethylene and grafted sulfonated polystyrene. A local mobility of Li
, Na
and Cs
cations and water molecules was estimated via the
H,
Li,
Na and
Cs spin relaxation technique. The calculated cation and water molecule self-diffusion coefficients were compared with experimental values measured using pulsed field gradient NMR. It was shown that macroscopic mass transfer is controlled by molecule and ion motion near sulfonate groups. Lithium and sodium cations whose hydrated energy is higher than water hydrogen bond energy move together with water molecules. Cesium cations in possession of low hydrated energy are directly jumping between neighboring sulfonate groups. Cation Li
, Na
and Cs
hydration numbers (
) in membranes were calculated from
H chemical shift water molecule temperature dependences. The values calculated from the Nernst-Einstein equation and the experimental conductivity values were close to each other in Nafion membranes. In MSC membranes, calculated conductivities were one order of magnitude more compared to the experimental ones, which is explained by the heterogeneity of the membrane pore and channel system.