Cathodic Polarization Study on Doped Lanthanum Gallate Electrolyte Using Impedance Spectroscopy

The perovskite electrolyte La_{1 – x}Sr_xGa_{1 – y}Mg_yO₃ (LSGM) has received a lot of interest in recent years after it was first reported to have significantly higher oxygen-ion conductivity than conventional YSZ. A very large fraction of the total polarization losses in SOFC is known to occur at the electrode-electrolyte interfaces manifesting itself as the kinetic barrier to charge-transfer reactions. AC complex impedance spectroscopy studies were conducted on symmetrical cells of the type air, electrode/LSGM electrolyte/electrode, air] to measure the charge-transfer polarization at the cathode-electrolyte interfaces. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The cathode materials investigated in this study include La_{1 – x}Sr_xMnO₃(LSM), LSCF (La_{1 – x}Sr_xCo_yFe_{1 – y}O₃) and a two-phase particulate composite consisting of LSM +doped-lanthanum gallate (LSGM). Symmetrical cell studies were also performed on SOFC anode materials. The principal anode material investigated in this study is a porous composite of Ni-gadolinium doped ceria (GDC). It is well known that Ni reacts with the state-of-the-art LSGM anode material. Thus our approach is to use a barrier layer of GDC between the Ni-GDC anode and the LSGM electrolyte. This paper will focus on the influence of microstructure, electrode composition, electrode thickness, interfacial compatibility and electrode processing conditions on cathode and anode polarization.