Effect of morphology of mesoporous silica on characterization of protic ionic liquid-based composite membranes

Effects caused by the morphology of mesoporous silica on the characterization of protic ionic liquid-based composite membranes for anhydrous proton exchange membrane applications are investigated. Two types of SBA15 materials with platelet and fiberlike morphologies are synthesized and incorporated into a mixture of polymerizable monomers together with an ionic liquid (IL) [1-butyl-3-methylimidazolium bis(trifluoromethane sulfone)imide (BMIm-TFSI)] to form new conducting membranes using an in situ photo crosslinking process. Incorporation of a defined amount of fiber-shaped SBA 15 and platelet 15 significantly increases the ionic conductivity to between two and three times that of a plain poly(methyl methacrylate) (PMMA)/IL membrane (2.3 mS cm−1) at 160 °C. The protic ionic liquid (PIL) retention ability of the membranes is increased by the capillary forces introduced by the mesoporous silica materials, while ionic conductivity loss after leaching test is retarded. The highest ionic conductivity (5.3 mS cm−1) is obtained by incorporating 5 wt% of P-SBA 15 in the membrane to about six times that of plain PMMA/IL membrane (0.9 mS cm−1) at 160 °C after leaching test.

Incorporation of a defined amount of fiber-shaped SBA 15 and platelet 15 significantly improved the ionic conductivity of IL-based membrane due to the formation of continuous and interconnected ion transport channels, formed at the interface between the polymer and mesoporous silica in the membrane.Figure optionsDownload as PowerPoint slideHighlights
► Prepared composite membranes are semitransparent, flexible, and have good thermal stabilities.
► Incorporation of a defined amount of fiber-shaped SBA 15 and platelet 15 significantly increased the ionic conductivity.
► The highest ionic conductivity was obtained by incorporating 5 wt% of P-SBA 15 in the membrane at 160 °C after leaching test.
► The morphology of the mesoporous materials in the composite membrane is a crucial factor in controlling the diffusion properties of the PIL and the resulting conductivities of membranes.