Polymer brush functionalized SiO2 nanoparticle based Nafion nanocomposites: a novel avenue to low-humidity proton conducting membranes

Polyelectrolyte membranes showing proton conductivity at moderate levels of relative humidity and temperatures are essential for the development of polyelectrolyte membrane fuel cells (PEMFCs). Herein, monomethoxy oligoethylene glycol methacrylate derived polymer brush functionalized silica nanoparticles (SiO2 NPs) are presented as humidifying-nanoadditives for the fabrication of Nafion nanocomposite membranes, exhibiting improved proton conductivities at moderate levels of relative humidity and temperatures. Polymer brush functionalized SiO2 NPs (SiO2-polymer-brush), fabricated via surface initiated atom transfer radical polymerization (SI-ATRP), are dispersed in the Nafion resin solution, and nanocomposite membranes (Nafion/SiO2-polymer-brush) are fabricated via solution casting. For comparison, composite membranes of Nafion are also prepared with bare SiO2 NPs. Spectroscopic measurements confirm the presence of polymer brushes in the final membranes and demonstrate increased water uptake in membranes with polymer brush-functionalized nanocomposite membranes. Electrochemical impedance analyses reveal that 1 wt% of functionalized SiO2 NPs is sufficient to achieve Nafion nanocomposite membranes with superior proton conductivities at ambient and moderately high temperatures over the entire range of relative humidity (RH). This study presents a facile avenue to membranes with superior proton conductivities under moderate levels of RH and temperature, and provides important insights into the scope of nanocomposite PEMs for fuel cell applications.