Protic ionic liquid-functionalized mesoporous silica-based hybrid membranes for proton exchange membrane fuel cells

Abstract

Mesoporous silica with an average particle size of 90 nm and pore diameter of 3.4 nm was successfully prepared and functionalized with ionic liquid (IL) end capped with alkoxy silane. Two varieties of silica, unmodified silica (US) and IL-functionalized silica (ILS), were incorporated into the Nafion matrix. The physical properties and proton conductivity of the resulting nanocomposites were analyzed. The thermo-mechanical stability and water uptake of the nanocomposites are higher than the virgin Nafion (VN). The mechanical and thermal stabilities of the US-based nanocomposites are higher than those of the ILS-based nanocomposites, but the water uptake and proton conductivities are lower due to the high hydrophilicity and high conductivity of IL. The maximum proton conductivity of 375.0 mS cm⁻¹ has been attained at 90 °C and 100% relative humidity (RH) for the nanocomposite containing merely 3 wt% of ILS. The conductivity of the same nanocomposite has been noted to be 54.6 mS cm⁻¹ at 90 °C and 30% RH, which is close to the room temperature conductivity of the virgin Nafion at 100% RH. Hence, these ILS-based Nafion composite membranes can be a potential candidate for application to proton exchange membrane fuel cells (PEMFCs) under low hydration conditions.