Abstract
Nanocomposite anion exchange membranes were synthesized based on poly(sulfone trimethylammonium) chloride. A hybrid semi-interpenetrating silica network containing a large amount of quaternary ammonium groups was prepared by two sol–gel routes, in situ with a single precursor, N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMSP), or ex situ mixing two precursors, TMSP and 3-(2-aminoethylamino)propyldimethoxy-methylsilane (AEAPS). The properties of these hybrid composites and their degradation after immersion in 1 M KOH at 60 °C were studied. The degradation is reduced in the composite materials with a lower decrease in the ion exchange capacity. FTIR spectra showed that a main degradation mechanism with a single precursor TMSP is the dissolution of the hybrid silica network in KOH, whereas it is stable with the mixture of TMSP/AEASP. This conclusion is in agreement with the thermogravimetric analysis. The mechanical properties show a better ductility with a single precursor and higher stiffness and strength, but less ductility, by the ex situ route. The activation energy was between 0.25 and 0.14 eV for Cl and OH ion conduction, respectively, consistent with the migration mechanism.
Highlights
Published: 4 April 2021Anion exchange membranes (AEM) are extensively investigated for their well-known advantages when used in electrochemical devices, including the absence of noble metal catalysts for the oxygen reduction reaction in fuel cells [1,2,3,4,5,6]
The main April 2021Anion exchange membranes (AEM) weaknesses are the degradation of the ionomeric groups, essentially ammonium moieties, and the scission of the backbone induced by the polarization of the matrix [9,10,11,12,13]
The reactivity of organically modified alkoxides is related to the steric hindrance of the organic substituent groups; the bulky propylammonium moiety most likely decreases the rate of hydrolysis
Summary
Anion exchange membranes (AEM) are extensively investigated for their well-known advantages when used in electrochemical devices, including the absence of noble metal catalysts for the oxygen reduction reaction in fuel cells [1,2,3,4,5,6]. One of the most promising approaches to improve the properties of ion exchange polymers is the formation of organic-inorganic composite membranes [14,15,16,17,18,19] These hybrid materials show a consistent stabilization due to the interactions between the polymer backbone and the inorganic component, including van der Waals forces and ionic interactions, e.g., between quaternary ammonium groups in the polymer or in the organosilica part with sulfone groups or ether oxygens. One of the strong points of the sol–gel method is its flexibility that allows the use of a large range of precursors, such as inorganic molecules (alkoxides) or hybrid molecules (ormosils) The latter can be functionalized in various ways, for example, with ionic groups. The nanocomposites were analysed in terms of hydration, thermal stability, mechanical properties, ionic conductivity and degradation in alkaline conditions
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