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Buvat, G., Sellemi, H., Ravella, U. K., Barre, M., Coste, S., Corbel, G. & Lacorre, P. (2016) Reduction Kinetics of La2Mo2O9 and Phase Evolution during Reduction and Reoxidation. Inorg. Chem. 55 2522–2533.
Added by: Richard Baschera (2016-04-19 07:39:44) |
| Type de référence: Article DOI: 10.1021/acs.inorgchem.5b02876 Numéro d'identification (ISBN etc.): 0020-1669 Clé BibTeX: Buvat2016a Voir tous les détails bibliographiques  |
Catégories: INTERNATIONAL, ST2E Mots-clés: diffusion, ionic-conductivity, nanoparticles, oxide fuel-cell, performance, reducibility, sofc, sulfur-tolerant anode, thermodynamic stability, transition Créateurs: Barre, Buvat, Corbel, Coste, Lacorre, Ravella, Sellemi Collection: Inorg. Chem. |
Consultations : 1/602
Indice de consultation : 4% Indice de popularité : 1% |
| Résumé |
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An amorphous reduced form of oxide ion conductor La2Mo2O9 had been proposed as sulfur-tolerant anode material for solid oxide fuel cell, but its oxygen content was not known. In this paper, we investigate the reduction kinetics by diluted hydrogen of La2Mo2O9 to amorphous, and the oxygen range of the amorphous form. The reduction kinetics is studied as a function of the powder specific surface area and of the temperature, on powders synthesized by solid state reaction and by polyol process using two different solvents. The reduction process was carried out by TGA under 10% H-2 diluted in argon, and its kinetics is analyzed and modeled. As expected, small particles and high temperature lead to higher reduction rates. Several reduction steps were identified by XRD during the process. At 700 degrees C La2Mo2O9 is directly reduced into the amorphous phase La2Mo2O7-y, whereas at 760 degrees C reduction occurs through an intermediate crystallized La7Mo7O30 congruent to La2Mo2O8.57) phase before amorphization. In both cases, further reduction of La2Mo2O62 amorphous phase leads to an exsolution of metallic molybdenum and a molybdenum deficiency in the amorphous phase. Reoxidation of amorphous La2Mo2O7-y was studied by TGA, DTA and XRD. At low temperature in air, the reduced compounds are reoxidized while remaining amorphous. The annealing for 60 h at 350 degrees C in air of reduced La2Mo2O6.66, obtained beforehand by solid state reaction, gives an amorphous phase with composition La2Mo2O8.85. The existence domain of the reduced amorphous phase in terms of oxygen content therefore ranges at least from O-6.2 to O-8.85, thus including the composition La2Mo2O8.50 of the amorphous surface layer at the origin of a huge increase of ionic conductivity recently reported in nanowires of La2Mo2O9.
Added by: Richard Baschera |