Effect of functionalized SiO₂ toward proton conductivity of composite membranes for PEMFC application

Organic-inorganic composite membranes were prepared by introducing silicon dioxide (SiO₂) or functionalized SiO₂ (ƒ-SiO₂) with various particle sizes into sulfonated poly (arylene ether ketone) (SPAEK) containing pendant groups, and the membrane was manufactured via directly casting which is a cost-competitive method. The structure and morphology of the composite membranes were confirmed by ¹H NMR, FT-IR, XRD, and FE-SEM analysis which demonstrated that inorganic nanofillers were successfully introduced. The FE-SEM surface images showed that SiO₂ and ƒ-SiO₂ particles were very well dispersed within the membrane sheets. The water uptake and swelling ratio of the composite membranes including SiO₂ or ƒ-SiO₂ almost did not change when compared with the pristine SPAEK membrane. All fabricated membranes demonstrated good thermal/dimensional stabilities, robust mechanical behavior, and excellent proton conductivity. In particular, the SPAEK/ƒ-SiO₂ composite membranes exhibited improved ionic conductivity compared with the pristine membrane at 70% relative humidity (RH) due to hydrogen bonding between ─SO₃H groups of functionalized inorganic filler and polymer backbone. Furthermore, the maximum power density of SPAEK/ƒ-SiO₂ reached as high as 273.11 mW cm⁻² at 60°C under 70% RH. Therefore, the composite membranes with ƒ-SiO₂ testify to great potential as polymer electrolyte membrane.