An understanding of degradation mechanisms of SOFC cathodes under operating conditions is essential for the development of commercial, intermediate temperature (<700°C) SOFCs. Literature shows that the presence of H2O in the cathode impacts the performance of SOFCs. In this study, we attempt to determine the degradation mechanisms of the composite cathode, (La0.8Sr0.2)0.95MnO3±δ - (Y2O3)0.8(ZrO2)0.92 (LSM-YSZ) in an H2O environment based on a multi-faceted approach. LSM-YSZ/YSZ/LSM-YSZ symmetric cells were examined in the presence of the contaminant (H2O) under different cycling, polarization and working conditions. Symmetric cell performance was measured by in-situ electrochemical impedance spectrometry (EIS), and directly compared to quantitative microstructural parameters obtained from FIB-SEM 3D reconstructions. FIB-SEM is a powerful technique to quantify important performance characteristics such as triple phase boundary (TPB) length and surface to volume ratio. EIS and FIB-SEM results were compared to kinetic rate data, extracted from isotope exchange experiments, to determine mechanistic relationships.