Effect of humidification on the grain boundary conductivity and space-charge effects in yttrium-doped barium cerate

Abstract

Yttrium-doped barium cerate (BCY) exhibits proton conductivity in the nominal absence of water (pH2O ≤ 10−4 atm) below 450 °C (J. Mater. Chem. A 7 (2019) 18,135–18142). Under these conditions, the well-known instability of this material against carbon dioxide and humidity can be minimized, potentially allowing its application even in hydrocarbon-based atmospheres. Nonetheless, electrochemical transport properties of grain boundaries of BCY are still not well understood. Hence, we compare specific grain boundary conductivity and space-charge properties of BaCe0·9Y0·1O3-δ (BCY10) in both wet and low humidity by means of impedance spectroscopy in the temperature range 100–300 °C. In H2, specific grain boundary conductivity increases in nominally dry conditions, while the bulk remains practically humidity independent. Conversely, in O2, both bulk and specific grain boundary conductivities are higher in wet. The space-charge properties highlight that low levels of humidity, pH2O ~10−4 atm, are sufficient to maintain functional performance, while providing enough stability. This work offers a significant advance to the knowledge of the transport properties of this family of materials at low temperatures, with special emphasis to conditions of low humidity, for potential future applications in proton-conducting electrolyte membranes.