Chemical stability enhancement of doped BaCe0.9Y0.1O3-δ as an electrolyte for proton conducting SOFCs

Abstract

BaCe0.9-xNbxY0.1O3-δ and BaCe0.9-xTaxY0.1O3-δ (where x = 0.01, 0.03 and 0.05) powders were synthesized by solid-state reaction method to investigate the influence of dopant and concentration on chemical stability and electrical properties of the sintered samples. The dense electrolyte pellets were formed from the powders after being uniaxially pressed and sintered at 1550ºC for 5h. The electrical conductivities determined by impedance measurements in temperature range of 550-750 ºC in wet hydrogen atmosphere showed a decreasing trend with increase of Nb and Ta content. On the other hand, stability of the sintered samples treated in 100% CO2 at 700 ºC for 5h determined by X-ray analysis was enhanced with increased concentrations of Nb and Ta. It was found that BaCe0.87Nb0.3Y0.1O3-δ is the optimal composition that satisfies the opposite demands for electrical conductivity and chemical stability, reaching 8.0. 10-3 Sm. cm -1 in wet hydrogen at 650 ºC compared to 1.0. 10-2 Sm. cm -1 for undoped electrolyte. Similar results obtained by doping with Nb and Ta can be explained by almost equal size and same valence of Nb and Ta cations, as well as their similar electronegativities. The electrolyte characteristics are strongly dependent on these properties, whereas doping with Nb showed slightly higher conductivities for each dopant concentration.