Electrochemical studies of Ruddlesden-Popper layered perovskite-type La_0.6Sr_1.4Co_0.2Fe_0.8O_4+δ cathode for solid oxide fuel cells and associated electrical loss phenomena

The electrochemical performance of solid oxide fuel cell (SOFC) depends on functional properties of the anode, the cathode and the electrolyte that are being employed. There is a need for better cathode catalyst to decrease operating temperature of SOFCs. Here, we report a layered perovskite-type Ruddlesden-Popper structure La_0.6Sr_1.4Co_0.2Fe_0.8O_4+δ (RP-LSCF) as cathode for SOFCs. The structural stability, thermal expansion, electrical, and fundamental electrochemical properties of RP-LSCF were investigated. The O₂ reduction reaction (ORR) and O₂ surface exchange properties of RP-LSCF and Gd-doped CeO₂ (GDC)-RP-LSCF composite were studied using symmetrical cells. Area normalized resistances for charge transfer (R_i) and surface exchange processes (R_s), and total polarization are found to be 0.14, 0.28 and 0.42 Ω cm² at 800 °C, respectively. The exchange current density and oxygen surface exchange co-efficient for RP-LSCF are 54.53 mA cm⁻² and 1.15 × 10⁻⁶ cm s⁻¹ at 800 °C, respectively. Addition of nano-GDC with RP-LSCF leads to increase of polarization resistances, while the activation energies for charge transfer and surface exchange processes are reduced significantly. For the first time, we report a dielectric loss tangent analysis corresponding to the electrode phenomena in RP-LSCF and GDC-RP-LSCF to understand the electrical losses associated with SOFC cathode (ORR) processes.