By using O, water-vapor and H concentration cells, with Ba3Ca1.18Nb1.82O9 as a solid-state electrolyte, Nernst voltages were measured at high temperatures. Proton transport numbers that were near to unity were observed for O partial pressures of less than 10-5bar. At higher pressures, electron hole transport predominated over ionic transport. At an O partial pressure of 0.2bar, the proton transport number reached a value of only 0.15. Under fuel-cell conditions, for O partial pressures ranging over 23 orders of magnitude, an ionic transport number of 0.9 was attained at 700C.

The High-Temperature Proton Conductor Ba3(Ca,Nb)3O9: Electrochemical Cell Measurements and TEM. T.Schober, H.G.Bohn, T.Mono, W.Schilling: Solid State Ionics, 1999, 118[3-4], 173-8