Effect of oxygen partial pressure on the electrochemical impedance of La0.8Sr0.2MnO3−δ/Zr0.92Y0.08O2 porous composite anodes in solid oxide electrolysis cell

Abstract

The electrochemical behavior of the La0.8Sr0.2MnO3−δ/Zr0.92Y0.08O2 (LSM/YSZ) porous composite anodes in solid oxide electrolysis cell is investigated by impedance spectroscopy over an oxygen partial pressure (pO2) range from 0 to 0.6×105Pa. The differential analysis of impedance spectra (DIS) shows three separate arcs which correspond to three different electrode processes at high, intermediate and low frequencies, respectively. Three different electrode processes can be attributed to the migration of oxygen ions from the electrolyte to the triple-phase boundary, concentration impedance associated with dissociative desorption of O2− along the LSM surface and diffusion of oxygen, respectively. Interestingly, under low pO2 (≈0Pa), the impedance arcs become clearly separated at different frequencies, especially for the anodes with higher porosity. Meanwhile, the results demonstrate that the electrode process associated with the low-frequency arc is strongly affected by pO2. Furthermore, the porosity plays an important role in dissociative adsorption and diffusion of oxygen.