Nanopore ceramic membranes as novel electrolytes for proton exchange membranes

Silica, titania, and alumina monolithic ceramic chips were prepared via sol-gel processes. All chips were mesoporous, with average pore sizes of 3.5, 7.7, and 2.9 nm for SiO2, TiO2, and Al2O3, respectively. Proton conductivity varied linearly with relative humidity in Al2O3, whereas a steep increase was observed for TiO2 and SiO2 between 58 and 81% relative humidity. The variation was linear with temperature for SiO2, and exponential for TiO2 and Al2O3. At high relative humidity and temperature, conductivities of 3.9 x 10(-3) and 4.0 x 10(-3) Omega cm(-1) were measured for TiO2 and SiO2, respectively. These values are less than one order of magnitude lower than that of Nafion, a polymeric material, and because our membranes can be prepared 100 times thinner than Nafion, they are possible candidates for application as electrolytes in fuel cells. (C) 1999 The Electrochemical Society. S1099-0062(99)02-048-9. All rights reserved.