Development of La_1.7Ca_0.3Ni_1-yCu_yO_4+δ Materials for Oxygen Permeation Membranes and Cathodes for...

The La_1.7Ca_0.3Ni_1-yCu_yO_4+δ (y = 0.0-0.4) nickelates, synthesized via a solid-state reaction method, are investigated as prospective materials for oxygen permeation membranes and IT-SOFC cathodes. The obtained oxides are single-phase and possess a tetragonal structure (I4/mmm sp. gr.). The unit cell parameter c and the cell volume increase with Cu-substitution. The interstitial oxygen content and total conductivity decrease with Cu-substitution. The low concentration of mobile interstitial oxygen ions results in a limited oxygen permeability of Cu-substituted La_1.7Ca_0.3NiO_4+δ ceramic membranes. However, increasing the Cu content over y = 0.2 induces two beneficial effects: enhancement of the electrochemical activity of the La_1.7Ca_0.3Ni_1-yCu_yO_4+δ (y = 0.0; 0.2; 0.4) electrodes and decreasing the sintering temperature from 1200 °C to 900 °C. Enhanced electrode activity is due to better sintering properties of the developed materials ensuring excellent adhesion and facilitating the charge transfer at the electrode/electrolyte interface and, probably, faster oxygen exchange in Cu-rich materials. The polarization resistance of the La_1.7Ca_0.3Ni_1.6Cu_0.4O_4+δ electrode on the Ce_0.8Sm_0.2O_1.9 electrolyte is as low as 0.15 Ω cm² and 1.95 Ω cm² at 850 °C and 700 °C in air, respectively. The results of the present work demonstrate that the developed La_1.7Ca_0.3Ni_0.6Cu_0.4O_4+δ-based electrode can be considered as a potential cathode for intermediate-temperature solid oxide fuel cells.