IMPROVED PROPERTIES OF SULFONATED OCTAPHENYL POLYHEDDRAL SILSEQUIOXANE CROSSLINK WITH HIGHLY SULFONATED POLYPHENYLSULFONE AS PROTON EXCHANGE MEMBRANE

Nor Azureen Mohamad Nor; Juhana Jaafar; Je-Deok Kim

doi:10.1007/s10008-020-04594-2

Article IMPROVED PROPERTIES OF SULFONATED OCTAPHENYL POLYHEDDRAL SILSEQUIOXANE CROSSLINK WITH HIGHLY SULFONATED POLYPHENYLSULFONE AS PROTON EXCHANGE MEMBRANE

Nor Azureen Mohamad Nor ; Juhana Jaafar ; Je-Deok Kim (National Institute for Materials Science)

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Nor Azureen Mohamad Nor, Juhana Jaafar, Je-Deok Kim. IMPROVED PROPERTIES OF SULFONATED OCTAPHENYL POLYHEDDRAL SILSEQUIOXANE CROSSLINK WITH HIGHLY SULFONATED POLYPHENYLSULFONE AS PROTON EXCHANGE MEMBRANE. JOURNAL OF SOLID STATE ELECTROCHEMISTRY. 2020, 24 (5), 1185-1195. https://doi.org/10.1007/s10008-020-04594-2

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This study explored the concept of improving the properties of the crosslinked membrane using a 1.5 nm closed cage octaphenyl polyhedral oligosilsesquioxane (POSS) form of nanosilica carrying the sulfonic acid group. POSS functioned with SO3H groups (SPOSS) at 0, 1, 2, and 5 wt. % were crosslinked with water-soluble sulfonated polyphenylsulfone (SPPSU) polymer. The crosslinking between SPPSU and SPOSS was accomplished through the interchain condensation of sulfonic acid functionalities initiated by thermal curing treatment. In this study, a covalently crosslinked membrane was obtained under stepwise thermal curing from 80°C to 180°C. Upon curing at 180°C, the SPPSU-SPOSS showed considerable improvement on the membrane proton conductivity under low and high RH (%) conditions compared to the pristine SPPSU membrane. The membrane proton conductivity shows similar patterns with the membrane water uptake as the presence of water greatly influences the crosslinked membrane. The proton conductivity of the SPPSU crosslinked with 1 wt. % SPOSS that conducted under low RH (%) and at elevated temperature exhibited about six times higher of proton conductivity as compared to pristine SPPSU membrane. However, increasing the loading of SPOSS beyond 1 wt. % significantly dropped the membrane water uptake and proton conductivity due to SPOSS aggregation that blocking the hydrophilic domains in the polymer matrix. The results indicated that the incorporation of SPOSS in the SPPSU membrane by curing at 180°C exhibit improvement on membrane water management and proton conductivity as compared to the pristine SPPSU membrane.

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