Synthesis of proton conducting tungstosilicate mesoporous materials and polymer composite membranes

Tungstosilicate mesoporous materials (WMM) were synthesized using the ionic surfactant cetyltrimethylammonium bromide (C16H33N+(CH3)3Br−, CTMABr) and non-ionic surfactants, including C12H25(OCH2CH2)10OH (Brij 22, C12EO10OH), C16H33(OCH2CH2)10OH (Brij 56, C16EO10OH), and C18H37(OCH2CH2)10OH (Brij 76, C18EO10OH). Using CTMABr, the highest W/Si ratio achieved for the molecular sieve product was 0.03. The proton conductivity ranged from 0.5 to 2.2 × 10−2 S/cm, where the highest conductivity was observed with the H3PO4 based preparation. Non-ionic surfactants produced materials with a W/Si ratio as high as 0.05 without any dense WO3 impurities. These samples showed thicker pore walls (39 Å), higher thermal stability, and higher proton conductivity (4.0 × 10−2 S/cm). The WMMs were also employed to make a composite membrane with linear polyethyleneimine (PEI)-3-glycidoxypropyl-trimethoxysilane (GLYMO)-bis(trifluoromethanesulfonyl)imide (HTFSI). At 100 °C and 100% relative humidity, the composite membrane with 30 wt.% calcined (at 500 °C) WMM showed the highest conductivity of 6.1 × 10−2 S/cm. At 130 °C and 20% relative humidity, the highest conductivity of 6.4 × 10−3 S/cm was obtained for the composite membrane with 30 wt.% as-synthesized WMM.