Electrochemical and kinetic analysis for electrode overpotential of LaGaO₃-based cells in reversible operation

A single cell with the configuration of LSCF/GDC/LSGM/Ni-SDC was fabricated and kinetic analysis of the electrochemical performance of electrodes under steam electrolysis and fuel cell operation was performed at 550-800 °C. Electrochemical impedance spectroscopy revealed that the polarization resistance of the LSCF/GDC air electrode (0.12 Ω cm²) was lower than that of the Ni-SDC fuel electrode (0.25 Ω cm²) at 800 °C, while both values became comparable at lower temperatures, indicating temperature dependence changes in electrode polarization behaviour. Tafel analysis based on the Butler-Volmer equation was performed separately for each electrode by using two reference electrodes. The Ni-SDC fuel electrode showed asymmetric kinetic behaviour, with activation energies of 0.94 and 1.25 eV in SOFC and SOEC modes, respectively, suggesting different reaction pathways under anodic and cathodic polarization. In contrast, the LSCF/GDC air electrode exhibited nearly identical exchange current density values at 800 °C in both modes, indicating highly reversible kinetic. The reconstructed Butler-Volmer curves showed good agreement with experimental data, confirming the reasonable values of the kinetic parameters of electrodes.