Effects of Br doping on the structure, stability and electrical properties of proton-conducting BaCe0.8Y0.2O3-d

Doped barium cerates such as BaCe(Y)O3-δ (BCY) exhibit fast proton transport for use in high-temperature ceramic electrochemical devices such as protonic ceramic fuel cells; however, poor stability in acidic environments,... [ view full abstract ]

Doped barium cerates such as BaCe(Y)O_3-δ

(BCY) exhibit fast proton transport for use in high-temperature ceramic electrochemical devices such as protonic ceramic fuel cells; however, poor stability in acidic environments, principally CO₂, has inhibited their widespread application. One recently adopted but little explored strategy [1,2] is to dope the oxide sublattice with halogen anions in order to lower the basicity of the anion network, thereby offering enhanced stability in acidic gases and high water-vapour partial pressures. Here, we report the synthesis by a modified Pechini method of a wide solid-solution range of Br-doped BCY (nominal composition BaCe_0.8Y_0.2O_2.9-(x/2)±dBr_y, 0 ≤ y ≤ 0.2). The Br-containing samples exhibit greater distortion of the perovskite lattice in comparison to BCY, as indicated by Rietveld refinement of X-ray diffraction data. Prolonged impedance measurements (up to 10 days) at 700 °C were employed in O₂ then CO₂ in order to assess the stability towards interchange of Br with atmospheric O₂ and carbonation, respectively. Whereas negligible degradation of the impedance response was observed in O₂, the stability in CO₂ was poorer than that reported previously for halogen-doped proton-conducting perovskites, as confirmed by thermogravimetry in CO₂. Impedance-spectroscopy measurements in the temperature range 300-900 °C reveal higher conductivity in wet in comparison to dry O₂ consistent with a protonic contribution to transport. The highest conductivity is registered for the Br-rich composition, y = 0.2, suggesting a novel strategy for enhancing mixed-conducting properties in BCY (Fig. 1.).

References

[1] Y. Wang, H. Wang, T. Liu, F. Chen, C. Xia, Electrochem. Comm. 28 (2013) 87-90.

[2] H. Zhou, L. Dai, J. Zhu, Y. Li, L. Wang, Int. J. Hydr. Energy. 40 (2015) 8980-8988.