Sol−Gel-Derived Ceria Nanoarchitectures:  Synthesis, Characterization, and Electrical Properties

Abstract

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 m2 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 (∼10 nm). The electrical properties of calcined ceria ambigels are evaluated from 300 to 600 °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 °C, suggesting an electronic contribution to conductivity at low oxygen partial pressures. The ceria ambigel nanoarchitecture responds to changes in atmosphere at 600 °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.