Fabrication, morphological, structural and electrochemical characterization of sulfonated polyimide/clay-based hybrid nanocomposite membranes for energy application

Abstract

Sulfonated polyimide (SPI) using 1, 4, 5, 8-Naphthalenetetracaboxylic Dianhydride was fabricated by a one-step high-temperature direct imidization method in the presence of organo-modified clay (sepiolite) as reinforcement in the polymer matrix. Different sets of SPI and clay sepiolite (in different content 1–7 wt. %) in the form of thin films were fabricated by the solution casting method. These films were cast at a temperature of 80 °C for 12 h followed by curing at 150 °C and 180 °C for 1 and 6 h, respectively. Several physicochemical parameters and analytical techniques were performed to characterize the newly fabricated nanocomposite membranes. Ion exchange capacity and hydrolytic study results showed the impact of clay content on the hydrolytic stability and morphology of hybrid membranes. Lowering in ion exchange capacity with higher hydrolytic stability was observed by increasing the clay contents in the polymeric matrix. The as-synthesized membranes were tested for its oxidative stability by Fenton reagent and observed that membrane with 5-wt (%) clay presented the maximum oxidative stability. The SPI-clay hybrid membrane with 7 wt.% of clay exhibited a water-uptake of 3.03% at 40 °C and proton conductivity of 2.45 mmol/g at 25 °C, while the pure SPI showed the values of 3.62% and 3.12 mmol/g in the same experimental conditions. FT-IR analysis investigated the structural aspects of neat SPI and all other synthesized nanocomposite membranes. The thermogravimetric analysis examined the presence of inorganic materials in the synthesized membranes along with their thermal stability profile. X-ray diffraction patterns were used to scrutinize the crystalline nature of neat sulfonated polyimide and the SPI-Clay composites membrane. In conclusion, these nanocomposite membranes can be applied as proton exchange films in fuel cells for energy application due to their interesting physicochemical, morphological, structural, and electrochemical properties.