Synthesis of amorphous silica and sulfonic acid functionalized silica used as reinforced phase for polymer electrolyte membrane

Thanh Nhan Tran, Thi Van Anh Pham, My Loan Phung Le, Thi Phuong Thoa Nguyen and Van Man Tran

Abstract

In this work silica (SiO₂) and sulfonic acid-functionalized silica (sul-SiO₂) were synthesized by sol–gel method from tetraethoxysilane (TEOS) and 3-mercatopropyltrimethoxysilane (MPTMS) with various ratios between them. The synthesized materials were characterized by x-ray diffraction (XRD) for crystalline structure, Brunauer–Emmet–Teller (BET) specific surface area analysis, transmission electronic microscopy (TEM) and dynamic light scattering (DLS) for particle size analysis, and ion exchange capacity (IEC) for determining sulfur content in Sul-SiO₂ materials. The initial results showed that the average particle size of amorphous SiO₂ and Sul-SiO₂ at different TEOS: MPTMS ratios are in narrow distribution with average diameter about 20–30 nm. The particle size of Sul-SiO₂ is almost unaffected by the content of MPTMS while IEC depends strongly on it. Composite membranes of 60 μm thickness were successfully prepared from blending of poly(vinylidene fluoride) (PVDF) and synthesized amorphous SiO₂. It was shown that the latter may be used as a reinforced phase for composite membrane electrolytes based on PVDF