Proton Conduction in Grain-Boundary-Free Oxygen-Deficient BaFeO2.5+delta Thin Films

Reduction of the operating temperature to an intermediate temperature range between 350 degrees C and 600 degrees C is a necessity for Solid Oxide Fuel/Electrolysis Cells (SOFC/SOECs). In this respect the application of proton-conducting oxides has become a broad area of research. Materials that can conduct protons and electrons at the same time, to be used as electrode catalysts on the air electrode, are especially rare. In this article we report on the proton conduction in expitaxially grown BaFeO2.5+delta (BFO) thin films deposited by pulsed laser deposition on Nb:SrTiO3 substrates. By using Electrochemical Impedance Spectroscopy (EIS) measurements under different wet and dry atmospheres, the bulk proton conductivity of BFO (between 200 degrees C and 300 degrees C) could be estimated for the first time (3.6 x 10(-6) S cm(-1) at 300 degrees C). The influence of oxidizing measurement atmosphere and hydration revealed a strong dependence of the conductivity, most notably at temperatures above 300 degrees C, which is in good agreement with the hydration behavior of BaFeO2.5 reported previously.