Defect chemistry, electrical properties and evaluation of new oxides Sr2CoNb1-xTixO6-δ (0≤x≤1) as cathode materials for Solid Oxide Fuel Cells

Abstract

The perovskite series Sr2CoNb1-xTixO6-δ (0≤x≤1) is investigated in the full compositional range to assess its potential as cathode material for solid state fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing titanium content from x=0 to x=1 produces both oxidation of Co3+ to Co4+ (from 0% up to 40%) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit) though each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Ti-contents lose a significant amount of oxygen on heating above 600K. Oxygen is partially recovered on cooling since the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating-cooling cycles and atmospheres produce, a complicated behaviour of electrical conductivity. Cathodes containing Sr2CoTiO6-δ display low ASR values, 0,13 Ωcm2 at 973 K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC.