TPR–TPD–TPO studies on CGO/NiO and CGO/CuO ceramics obtained from freeze-dried precursors

Abstract

Nanocrystalline powders of Ce0.99Gd0.01O2−δ have been obtained at a very low temperature (400°C) by a freeze-drying precursor method. Afterwards, ethanol solution of Ni or Cu nitrates were added to gadolinia doped ceria (CGO) by incipient wetness impregnation and then calcined in air at 650°C in order to obtain CGO/NiO and CGO/CuO series of SOFC anode materials. The resulting materials were characterized by X-ray Diffraction, N2 adsorption–desorption (BET), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD) and Temperature Programmed Oxidation (TPO) techniques. TPR showed wide overlapped peaks which are associated to the different reduction stages; firstly the reduction of highly dispersed metal oxide species took place and then the metal oxide bulk reduction process. After reduction of the CGO-metal powders, the metallic oxides were no longer present (as indicated by the presence of Ni or Cu), and the fluorite CGO solid solution remained stable. He-TPD tests showed that the series CGO/NiO adsorbed CO species on the material surface while CGO/CuO did not. O2-TPO analysis showed that C deposition occurred during the CO-TPR on CGO/NiO samples but this did not occur for the CGO/CuO series.