TiO₂ nanoparticle enhanced high temperature proton conductivity in hyperbranched sulfonated polyarylene aliphatic ketones for proton exchange membrane fuel cell applications

Abstract A new hyperbranched sulfonated poly(arylene aliphatic ketones) (HB‐SPAAK) has been synthesized and loaded with titania nanoparticles to obtain HB‐SPAAK/TiO 2 nanocomposites for thermally stable proton‐conducting electrolyte membrane fuel cell (PEMFC) applications. The synthesis of HB‐SPAAKs was carried out through the polycondensation reaction of different aliphatic and aromatic acids with simultaneous loss of H 2 O, trifluromethane sulfonic acid used as catalyst. The long chain hyperbranched polymers and TiO 2 ‐loaded nanocomposites were characterized by FT‐IR, 1 H‐NMR, SEM and HR‐TEM. Proton conductivity (PC), swelling ratio, water uptake and oxidative stability. The SEM image of TiO 2 NPs and HB‐SPAAKs/TiO 2 nanocomposites membrane clearly showed the spherical of TiO 2 and porous structure of HB‐SPAAKs with a pore diameter of 2–50 μm. TEM image reveals the uniform particle size distribution of TiO 2 nanoparticles having a nanosize of 100 nm. TiO 2 loaded polymer nanocomposites showed lower values of W/U and S/R when compared to the unmodified HB‐SPAAK, while 3% TiO 2 loaded HB‐SPAAKs exhibited a threefold increment of proton conductivity of 1.439 × 10 −2 S cm −1 compared to HB‐SPAAKs (0.41 x 10 −2 S cm −1 ) and lower than that of Nafion 117 (0.1003 S cm −1 at 80°C). The 5% TiO 2 NPs‐embedded with HB‐SPAAKs nanocomposites membranes also presented admirable oxidative stability with a degradation value of 13.8% during immersion in Fenton reagent for 8 h at 70°C.