Heavily Sn-doped barium cerates BaCe_0.8-xSnxYb_0.2O3-: Correlations between composition and ionic transport

The design of new functional materials for solid oxide fuel cells (SOFCs) is of paramount importance in terms of achieving a trade-off between their performance, efficiency and long-term stability. In the present work, synthesised Sn-substituted BaCeO3 materials are characterised as new proton-conducting electrolyte derivatives. BaCe0.8-xSnxYb0.2O3-8 compositions (x = 0.3, 0.4 and 0.5) are formed by heavily doping a barium cerate ceramic with tin for increased chemical stability and ytterbium to provide proton transport. The transport properties of these compositions are comprehensively studied across a wide range of temperatures (200-900 degrees C), oxygen partial pressures (10- 18-0.21 atm) and water vapour partial pressures (from 0.001 to 0.1 atm). Sn-doping is observed to result in a deterioration of both bulk and grain boundary conductivities of the corresponding ceramic materials due to crystallochemical and microstructural factors. At the same time, stability with respect to chemical interaction with H2O and CO2 is improved compared with Sn-free cerates. The obtained results suggest that the co-doping of BaCeO3 with tin and ytterbium is a promising approach to the design of proton-conducting electrolytes having good ionic conductivity coupled with high chemical stability.