Synthesis of Novel Proton Conducting Mesoporous Silica (ms) Films for High Temperature Pem Fuel Cells

Transparent free-standing mesoporous silica (MS) films were synthesized from a system of TMOS-Brij-Acid-H2O. The non-ionic surfactants used included Brij 22 (C12EO10OH), Brij 56 (C16EO10OH), and Brij 76 (C18EO10OH). The acids used include HCl, H3PO4, and CF3SO3H. The effect of synthesis parameters on the synthesis and the proton conductivity of mesoporous silica were investigated. The Brij 56/CF3SO3H based product showed the highest conductivity of 6.5 x 10 S/cm at room temperature. INTRODUCTION Proton conducting mesoporous materials offer several important features, such as uniform pore size (in the range of 20 – 500 Å), high specific surface area (≥ 1000 m/g), large dimensional open channels, and high thermal stability. There have been studies of the proton conductivity of mesoporous silica [1-3]. To make mesoporous silica proton conductive, postsynthesis or co-condensation method can be used to graft acid groups like SO3H. Margolese et al. [1] reported the direct synthesis of SBA-15 with sulfonic acid groups. Later, Mikhailenko et al. [2] reported sulfonated SBA-15 showed a proton conductivity of 10 S/cm at room temperature. Halla et al. [3] also reported that the synthesis of a novel proton-conducting solid electrolyte, meso-SiO2-C12E10OH-CF3SO3H, and found that the ionic conductivity (at room temperature) varied from 1 x 10 S/cm at low humidity to 1 x 10 S/cm at high humidity. However, the influence of the synthesis parameters on the synthesis and the proton conductivity were not reported in detail. In this paper, we report the effects of various parameters on the synthesis and the proton conductivity of transparent free-standing mesoporous silica films. The non-ionic surfactants that were used include Brij 22 (C12EO10OH), Brij 56 (C16EO10OH), and Brij 76 (C18EO10OH). The acids employed in this study were HCl, H3PO4, and CF3SO3H.