Well-ordered sulfonated silica electrolyte with high proton conductivity and enhanced selectivity at elevated temperature for DMFC

Periodic ordered sulphonated-silica nanoelectrolytes with 2D hexagonal (2D-H), 3D body-centered cubic (3D-BC) and 3D cubic bicontinuous (3D-CB) structures were synthesized through multiphase hydrogen bonds self-assembly between the charged silica, 3-mercaptopropyltrimethoxysilane and triblock copolymer. Small-angle XRD and high resolution TEM results exhibit uniform nanoarrays with long-range order of the electrolytes. The well-ordered structure demonstrated a facile proton transport pathway of the electrolyte. At elevated temperature of 200 °C, the conductivity of the sulphonated-2D-H, sulphonated-3D-BC and sulphonated-3D-CB electrolytes reach to 0.270 S cm−1, 0.188 S cm−1 and 0.242 S cm−1, respectively. The low swelling and phase transformation of methanol at the elevated temperature also make low fuel crossover through the sulphonated-silica electrolyte. In the elevated temperature range of 120–200 °C, the limiting methanol permeation current densities decreased dramatically to 0.1–0.5 mA/cm2, resulting in an improved relative selectivity to 66.02–91.74. Thus, the sulphonated-silica electrolyte is promising as high-temperature electrolyte membranes for direct methanol fuel cells.