High temperature electrocatalytic properties of the SOFC air electrode La0.8Sr0.2MnO3/YSZ
Abstract The electrocatalytic properties of the air electrode La 0.8 Sr 0.2 MnO 3 in solid oxide fuel cells were examined by using complex impedance spectroscopy under the conditions of oxygen partial pressure, P (O 2 ), between 1 and 10 − 4 atm and temperatures, T , between 800 and 1000°C. The electrodes, O 2 /La 0.8 Sr 0.2 MnO 3 /YSZ, were prepared by co-firing at 1350, 1400, 1435, and 1500°C in air. In the measurements at 800–1000°C, σ E was nearly proportional to P (O 2 ) 1/2 at high P (O 2 )s and was proportional to P (O 2 ) at low P (O 2 )s. In the region where σ E was proportional to P (O 2 ), σ E showed nearly the same value irrespective of the different electrode microstructures, suggesting that the electrode reaction was controlled by O 2 gas diffusion. In the region where σ E ∝ P (O 2 ) 1/2 , the relationship between σ E and P (O 2 ) was interpreted by the model that the electrode reaction was controlled by the surface diffusion of adsorbed oxygen atoms, O ad , from the electrode surface to the electrode/electrolyte boundary. The results obtained in the present work meant that La 2 Zr 2 O 7 , formed on the La 0.8 Sr 0.2 MnO 3 surface, disturbed the surface diffusion of O ad from the La 0.8 Sr 0.2 MnO 3 surface to the three phase boundary of O 2 , La 0.8 Sr 0.2 MnO 3 , and Y 2 O 3 stabilized ZrO 2 (YSZ). Increasing the co-firing temperature, the surface composition of the electrode material changed, and hence the oxygen adsorption process might be changed.