Temperature programmed oxygen desorption of the perovskites series Ln0.65Sr0.3Mn0.8Co0.2O3 (Ln=La-Gd)

Abstract

Temperature programmed O2 desorption (hereafter denoted reduction, TPR) in a high vacuum system equipped with a mass spectrometer was used to investigate the oxygen loss as a function of temperature in perovskites materials of the type Ln0.65Sr0.3Mn0.8Co0.2O3 (Ln=La-Gd), which are important as potential electrode materials for solid oxide fuel cells (SOFC). The materials were prepared either by spray drying as described in [1] or via the Pechini method [2] for the perovskites with Ln=Nd-Gd. The TPR experiments were carried out at temperatures 300–1000 K with various heating rates β in order to determine the onset of reduction and the activation energy of reduction for each perovskite. The experiments were carried out in an ultra high vacuum chamber (base pressure 10−10 mbar after baking) equipped with a quadrupole mass spectrometer [3, 4]. Additional oxygen adsorption was attempted at several adsorption temperatures but no discrete oxygen desorption peaks were observed before the onset of reduction. Pr0.65Sr0.3Mn0.8Co0.2O3 was found to have the lowest reduction activation energy (149±19 kJ/mol) and the lowest temperature, TR, for onset of reduction (750 K). On the other hand Gd0.65Sr0.3Mn0.8Co0.2O3 was found to have the highest reduction activation energy (232±38 kJ/mol) while the TR was about 850 K. The reduction activation energies follow the sequence Pr<Sm<Eu<La<Nd<Gd while the TR values follow the sequence Pr<La<Gd<Eu<Sm<Nd.