Calcium manganite as oxygen electrode materials for reversible solid oxide fuel cell

摘要

For an efficient high-temperature reversible solid oxide fuel cell (RSOFC), the oxygen electrode should be highly active for the conversion between oxygen anions and oxygen gas. CaMnO3-delta (CM) is a perovskite that can be readily reduced with the formation of Mn3+ giving rise to oxygen defective phases. CM is examined here as the oxygen electrode for a RSOFC. CaMn0.9Nb0.1O3-delta (CMN) with Nb doping shows superior electric conductivity (125 S cm(-1) at 700 degrees C) compared with CM (1-5 S cm(-1) at 700 degrees C) in air which is also examined for comparison. X-ray diffraction (XRD) data show that CM and CMN are compatible with the widely used yttria-stabilized zirconia (YSZ) electrolyte up to 950 degrees C. Both materials show a thermal expansion coefficient (TEC) close to 10.8-10.9 ppm K-1 in the temperature range between 100-750 degrees C, compatible with that of YSZ. Polarization curves and electrochemical impedance spectra for both fuel cell and steam electrolysis modes were investigated at 700 degrees C, showing that CM presented a polarization resistance of 0.059 Omega cm(2) under a cathodic bias of -0.4 V while CMN gave a polarization resistance of 0.081 Omega cm(2) under an anodic bias of 0.4 V. The phase stability up to 900 degrees C of these materials was investigated with thermogravimetric analysis (TGA) and variable temperature XRD.