Preparation and properties of Nafion/SiO2 composite membrane derived via in situ sol-gel reaction: size controlling and size effects of SiO2 nano-particles

A novel technique in controlling the size of SiO2 nano-particles in the preparation of Nafion/SiO2 composite membranes via in situ solgel method, as well as the effects of nano-particle size on membrane properties and cell performance, is reported in this paper. Nafion/SiO2 composite membranes containing SiO2 nano-particles with four different diameters (5 +/- 0.5, 7 +/- 0.5, 10 +/- 1, and 15 +/- 2nm) are fabricated by altering the reactant concentrations during in situ solgel reaction. Sequentially, size effects of SiO2 nano-particles on membrane properties and cell performance are investigated by SEM/EDAX, TEM, TGA, mechanical tensile, and single cell tests, etc. The results suggest that 10nm is a critical diameter for SiO2 incorporated into Nafion matrix, exhibiting desirable physico-chemical properties for operation at elevated temperature and low humidity. At 110 degrees C and 59% RH, the output voltage of the cell equipped with Nafion/SiO2 (10nm) obtains an output voltage of 0.625V at 600mA/cm2, which is 50mV higher than that of unmodified Nafion. Copyright (C) 2010 John Wiley & Sons, Ltd.