New Nb-doped SrCo1-xNbxO3-delta perovskites performing as cathodes in solid-oxide fuel cells

作者：Cascos V; Martinez Coronado R; Alonso J A^*

来源：International Journal of Hydrogen Energy, 2014, 39(26): 14349-14354.

DOI：10.1016/j.ijhydene.2014.03.100

• Solid oxide fuel cell
• Cathode
• Hydrogen
• SrCoO3-delta
• Neutron diffraction
• Perovskite superstructure

The high-temperature cubic phase of SrCoO3-delta is a promising cathode material for solid oxide fuel cells (SOFC) due to its high electrical conductivity and oxygen permeation flux. However, this phase is not stable below 900 degrees C where a 3C-cubic to 2H-hexagonal phase transition takes place when the sample is slowly cooled down. In this work we have stabilized a 3C-tetragonal P4/mmm structure for SrCo1-xNbxO3-delta with x = 0.05. We have followed the strategy consisting of introducing a highly-charged cation at the Co sublattice, in order to avoid the stabilization of the unwanted 2H structure containing face-sharing octahedra. The characterization of this oxide included X-ray (XRD) and neutron powder diffraction (NPD) experiments. SrCo0.95Nb0.05O3-delta adopts a tetragonal superstructure of perovskite with a = a(0), c = 2a(0) (a(0) approximate to 3.9 angstrom) defined in the P4/mmm space group containing two inequivalent Co positions. Flattened and elongated (Co,Nb)O-6 octahedra alternate along the c axis sharing corners in a three-dimensional array (3C-like structure). In the test cell, the electrodes were supported on a 300-mu m-thick pellet of the electrolyte La0.8Sr0.2Ga0.83Mg0.O-17(3-delta) (LSGM). The test cells gave a maximum power density of 0.4 and 0.6 W/cm(2) for temperatures of 800 and 850 degrees C, respectively, with pure H-2 as fuel and air as oxidant. The good performance of this material as a cathode is related to its mixed electronic-ionic conduction (MIEC) properties, which can be correlated to the investigated structural features: the Co3+/Co4+ redox energy at the top of the O-2p bands accounts for the excellent electronic conductivity, which is favored by the corner-linked perovski te network. The considerable number of oxygen vacancies, with the oxygen atoms showing high displacement factors suggests a significant ionic mobility.

• 出版日期2014-9-3