Proton conductivity in yttrium-doped barium cerate under nominally dry reducing conditions for application in chemical synthesis

Abstract

Electrochemical membrane reactors using proton-conducting ceramics are promising and efficient technologies for the production of valuable chemical products by the promotion of hydrogenation/dehydrogenation reactions. Due to a very high equilibrium constant for hydration, yttrium-doped barium cerate, BaCe_0.9Y_0.1O_3−δ (BCY10), presents one of the highest proton conductivities at low temperatures among known proton-conducting ceramic oxides (e.g. ∼10⁻³ S cm⁻¹ at 400 °C under humidified atmospheres, p_H2O ∼ 10⁻² atm). Nonetheless, BCY10 is commonly discarded for such applications due to its poor chemical stability towards hydroxide or carbonate formation. Moreover, the use of humidified atmospheres may not be feasible for many chemical syntheses, due to undesired side reactions. The current work, therefore, combines impedance spectroscopy, thermogravimetric analysis, coulometric titration and defect chemistry modelling to assess the limits for pure protonic conductivity in BCY10 in nominally dry atmospheres (p_H2O ∼ 10⁻⁴ to 10⁻⁵ atm, at low temperatures <600 °C), conditions where its stability and applicability to industrially relevant chemical synthesis reactions may be maintained, whilst still being hydrated. This work, thereby, unlocks a new application area for proton-conducting ceramics in a wide range of hydrogenation/de-hydrogenation reactions in the nominal absence of water.