In situ dilatometric and impedance spectroscopic study of core-shell like structures: insights into the exceptional catalytic activity of nanocrystalline Cu-doped CeO2

TitleIn situ dilatometric and impedance spectroscopic study of core-shell like structures: insights into the exceptional catalytic activity of nanocrystalline Cu-doped CeO2
Publication TypeJournal Article
Year of Publication2015
AuthorsKnauth, P, Saltsburg, H, Engel, J, Tuller, HL
JournalJournal of Materials Chemistry A
Volume3
Issue16
Pagination8369 - 8379
Date Published2015///
Abstract

Cu-doped CeO2 (8 mol% Cu) nanoparticles were investigated by combined in situ dilatometry and impedance spectroscopy as a means of exploring the impact of temperature and pO(2) driven dopant redistribution and phase separation on both thermo-mechanical and electrical properties of the CuOx-CeO2 system. Dilatometry was used to track the thermal expansion of the CeO2 nanoparticles as well as the reduction of segregated copper oxide into metallic copper when exposed to reducing conditions. The electrical properties of the nanoparticle array, extracted from impedance spectroscopy studies, point to proton conduction at low temperatures, with a transition to n-type electronic conductivity of CeO2 at higher temperatures. After segregation of percolating interfacial layers, induced by exposure to reducing atmosphere, the electrical properties become dominated by p-type Cu2O at intermediate pO(2) and metallic copper at low pO(2). The temperature and pO(2) dependent electrical properties of both the Cu2O shell and the underlying ceria core were examined in light of defect chemical models. Based on these models, the standard formation enthalpy of copper vacancies and holes in Cu2O and the standard formation enthalpy of oxygen vacancies and electrons in CeO2 were found to be equal to Delta H-ox,Cu2O(0) = (2.4 +/- 0.4) eV and Delta H-red,CeO2(0) = (1.5 +/- 0.3) eV, respectively. These findings are discussed in relation to the exceptional catalytic activity of copper-ceria for various oxidation-reduction reactions, focusing on the roles of both nano-dimensions and the influence of Cu on the redox properties of CeO2.