Immobilization of imidazole moieties in polymer electrolyte composite membrane for elevated temperature fuel cells

• Reinforced imidazole-g-SiO2/Nafion/ePTFE composite membranes were developed.
• Mechanical properties of the formed membranes is greatly improved.
• Anhydrous proton conductivity reaches 1.8 × 10−2 S cm−1 at 180 °C.
• Assembled cell is continuously operated at 110 °C for 20 h without performance loss.

Development of membrane electrolyte with reasonable proton conductivity at elevated temperature without external humidification is essential for practical applications of elevated temperature proton exchange membrane fuel cells. Herein, a novel polymer electrolyte composite membrane using imidazole as anhydrous proton carriers for elevated temperature fuel cells is investigated. The imidazole moieties are immobilized inside the Nafion/poly(tetrafluoroethylene) (PTFE) composite membrane through in situ formation of imidazole functionalized silica nanoparticles in Nafion dispersion. The thus-formed membrane exhibits strong Coulombic interaction between negatively charged sulfonic acid groups of Nafion and protonated imidazole moieties, leading to an anhydrous proton conductivity of 0.018 S cm−1 at 180 °C. With the introduction of PTFE matrix, the mechanical strength of the membrane is greatly improved. The peak power density of a single cell assembled from the hybrid membrane is observed to be 130 mW cm−2 under 350 mA cm−2 at 110 °C without external humidification and it remains stable for 20 h continuous operation. The obtained results demonstrate that the developed composite membranes could be utilized as promising membrane electrolytes for elevated temperature fuel cells.