Performance analysis of cathode materials SSC-xYWO (x = 0–30 wt. %) based on thermal expansion complementarity for SOFCs

Integrating negative thermal expansion (NTE) materials into high TEC cathodes minimizes thermal expansion mismatches in SOFCs. This also boosts their electrochemical performance. Therefore, we chose to prepare the composite cathode material with the negative thermal expansion material Y₂W₃O₁₂ (YWO) and Sm_0.5Sr_0.5CoO_3-δ (SSC). XRD tests show no elemental segregation or adverse reactions between SSC, YWO, and SDC. This indicates excellent chemical compatibility, meeting SOFCs material requirements. TEC tests show that higher YWO content improves thermal matching and increases the effective contact area between the composite cathode and SDC electrolyte. At 20 wt. % YWO, the TEC value is 10.05 × 10^–6 K^-1, closely matching SDC. The minimum polarization resistance (Rp) of 0.092 Ω cm² is achieved for SSC-20YWO at an operating temperature of 800 °C. Oxygen partial pressure tests demonstrate a gradual decrease in Rp as oxygen content increased. Moreover, it is observed that the change in the arc is more pronounced at low-frequency, indicating that the oxygen content has a significant impact on the low-frequency process. For the SSC sample, surface oxygen adsorption is rate-limiting step below 0.05 atm, while the further ionization process of oxygen ion is rate-limiting step above this threshold. For SSC-20YWO, the further ionization process of oxygen ion is consistently rate-limiting step across the entire O₂ partial pressure range (0.01 atm to 1 atm), indicating accelerated surface oxygen adsorption. This is due to the increased length of the triple phase boundary results in a greater number of oxygen active sites, which further enhances the electrochemical performance. These results show that adding YWO to the SOFCs cathode effectively improves both performance and compatibility.