Journal of Membrane Science, Vol.397, 92-101, 2012
Correlation between proton conductivity, thermal stability and structural symmetries in novel HPW-meso-silica nanocomposite membranes and their performance in direct methanol fuel cells
The intrinsic relationship between proton conductivity, thermal stability and structural symmetries of phosphotungstic acid (HPW)-functionalized mesoporous silica (HPW-meso-silica) membrane was investigated with mesoporous silica from 2D hexagonal p6mm, 3D face-centered cubic (Fm (3) over barm), body-centered Im (3) over barm, to cubic bicontinuous Ia (3) over bard symmetries. HPW-meso-silica nanocomposites with 3D mesostructures display a significantly higher proton conductivity and higher stability as a function of relative humidity in comparison to 2D mesostructures. The best result was obtained with body-centered cubic (Im (3) over barm)-HPW-meso-silica, showing proton conductivities of 0.061 S cm(-1) at 25 degrees C and 0.14 S cm(-1) at 150 degrees C, respectively, and an activation energy of 10.0 kJ mol(-1). At 150 degrees C, the cell employing a HPW-meso-silica membrane produced a maximum power output of 237 mW cm(-2) in a methanol fuel without external humidification. The high proton conductivity and excellent performance of the new methanol fuel cells demonstrate the promise of HPW-meso-silica nanocomposites with 3D mesostructures as a new class of inorganic proton exchange membranes for use in direct methanol fuel cells (DMFCs). (C) 2012 Elsevier B.V. All rights reserved.
Keywords:Direct methanol fuel cells;Mesoporous silica;Structural symmetries;Heteropolyacid;High temperature proton exchange membranes