The high temperature proton conductor Ba3Ca1.18Nb1.82O9-δ. Part II : electrochemical cell measurements and TEM

Abstract Using oxygen, water-vapor and hydrogen concentration cells and Ba 3 Ca 1.12 Nb 1.82 O 9− δ (BCN18) as a solid state electrolyte the Nernstian voltages were measured at elevated temperatures. Proton transport numbers near unity were observed for p O2 −5 bar. In the domain of p O2 >10 −5 bar the electron hole transport prevailed over the ionic one, e.g. at p O2 ≈0.2 bar the proton transport number reached only values of 0.15. Under fuel cell conditions spanning the whole range of p O2 over 23 orders of magnitude an ionic transport number of 0.9 was achieved at 700°C. Treatment of BCN18 in hydrogen atmospheres was found to produce a high density of grain boundary cavities leading to pronounced mechanical weakness.