Effect of fumed silica nanoparticles on the proton conductivity of polyimide–phosphoric anhydride membranes

Abstract

A series of aromatic polyimide–phosphoric anhydride composite membranes loaded with fumed silica (FS) nanoparticles were prepared from polyamic acid (PAA). First, the influence of the percentage loading of phosphoric anhydride (PA) on the proton conductivity of polyimide (PI) membranes was studied. The PA-PI film containing 45% of PA showed proton conductivity of 1.31 × 10⁻⁴ S/cm at 80°C, whereas the conductivity of neat PI films was 1.80 × 10⁻⁶ S/cm at room temperature. Next, the effects of the FS nanoparticles on the proton conductivity, the mechanical and thermal properties of the formulated PA-PI membranes were studied. Forty-five percent of the PA-PI membrane loaded with 1% FS (45% PA-PI/1% FS) showed an enhanced conductivity of 2.78 × 10⁻⁴ S/cm at 80°C when compared to the neat 45% PA-PI membrane. The tensile strength of the 45% PA-PI/1% FS nanocomposite membrane was comparable to the Nafion proton conductive membranes. The thermal analysis of 45% PA-PI/1% FS nanocomposite membranes showed that these membranes were thermally stable and suitable for high-temperature applications.