Tuning the Spatial Arrangement of Sol-Gel Based Polymer Electrolyte Membranes

Polymer electrolyte membranes (PEMs) are an integral part of many of the next generation’s clean and sustainable energy sources. The spatial arrangement of PEMs plays a key role in deciding the final properties of these membranes. Altering the morphology of PEMs via functional inorganic nanoparticles has been of great interest among researchers due to their synergistic interactions between the organic and inorganic phases in the PEM matrix. In this study, five different molar ratios of inorganic nanoparticles were synthesized using tetraethylorthosilicate (TEOS): titanium isopropoxide (TIP) via sol-gel chemistry in THF. The inorganic phase was introduced into a Penta block copolymer (PBC (1.0), commercially known as Nexar, with an ion exchange capacity (IEC) of 1.0 to form 2 wt% homogenous nanocomposite PBC membranes. To elucidate the interrelationships between the interactions of the sol-gel network with the PBC ionomer and their microstructure, TEOS-TIP was added to the PBC 1.0 domain in two different forms, solid and liquid. It was postulated that the addition of TEOS-TIP in its powder form could probe the domain spacing in the PBC (1.0) ionomer and push them farther away compared to the addition of TEOS-TIP in its liquid state. FTIR shows the successful integration of TEOS-TIP in the PBC (1.0) matrix. The changes in the intensity of the peak at 910 cm^-1 corresponded to the molar ratio of TEOS-TIP in the system. TGA showed that the decomposition temperature for the PEM decreased when the ratio of sol-gel was increased. However, PBC (1.0) liquid nanocomposites exhibited a greater reduction in thermal stability at high TIP concentrations compared to the PBC (1.0) powder nanocomposite membranes. It was also observed at high ratios of TIP, the proton conductivity of PBC (1.0) is greatly reduced when exchanged with powder form compared to the liquid form. These changes in the properties at a high TIP ratio suggest the disruption in the domain spacing of the PBC (1.0) matrix due to changes in the interaction strength of TIP with the sulfonate groups in the PBC (1.0). Hence this can be a potential route to systematically alter the phase separation of the ionomers and design the membranes for fuel cells and gas separation applications. Future studies will incorporate SAXS to investigate the changes in the microstructure of these PEM nanocomposites, as well as TEM studies to explore the changes in domain size and spacing.