Sol-gel-derived ceria nanoarchitectures: Synthesis, characterization, and electrical properties

Nanocrystalline ceria is under study to improve performance in high-temperature catalysis and fuel cells. We synthesize porous ceria monolithic nanoarchitectures by reacting Ce(III) salts and epoxide-based proton scavengers. Varying the means of pore-fluid removal yields nanoarchitectures with different pore-solid structures: aerogels, ambigels, and xerogels. The dried ceria gels are initially X-ray amorphous, high-surface-area materials, with the aerogel exhibiting 225 m(2) g(-1). Calcination produces nanocrystalline materials that, although moderately densified, still retain the desirable characteristics of high surface area, through-connected porosity in the mesopore size range and nanoscale particle sizes (similar to 10 nm). The electrical properties of calcined ceria ambigels are evaluated from 300 to 600 degrees C and compared to those of commercially available nanoscale CeO2. The pressed pellets of both ceria samples exhibit comparable surface areas and void volumes. The conductivity of the ceria ambigel is 5 times greater than the commercial sample and both materials exhibit an increase in conductivity in argon relative to oxygen at 600 degrees C, suggesting an electronic contribution to conductivity at low oxygen partial pressures. The ceria ambigel nanoarchitecture responds to changes in atmosphere at 600 degrees C faster than does the nanocrystalline, non-networked ceria. We attribute the higher relative conductivity of CeO2 ambigels to the bonded pathways inherent to the bicontinuous pore-solid networks of these nanoarchitectures.