Electrochemical performance and stability of nano-structured Co/PdO-co-impregnated Y₂O₃ stabilized ZrO₂ cathode for intermediate temperature solid oxide fuel cells

Palladium (Pd) is an attractive cathode catalyst component for solid oxide fuel cells (SOFCs) that has high tendency to agglomerate during operation at around 800 °C. This work shows that such agglomeration can be inhibited by alloying Co into Pd. PdO, Pd_0.95Co_0.05O, Pd_0.90Co_0.10O, and Pd_0.80Co_0.20O were synthesized and characterized. Powder X-ray diffraction patterns at 750 and 900 °C confirmed that PdO decomposition to Pd which normally occurred at 840 °C was suppressed for Co containing Pd alloys while thermal gravimetric analyses indicated improved redox reversibility of PdO ↔ Pd conversion for alloys during the thermal cycling between 600 and 900 °C. Scanning electron microscopy images supported these arguments. Pd_0.90Co_0.10+yttria stabilized zirconia (YSZ) electrode (i.e., 10 mol % Co containing PdO-impregnated YSZ electrode) displayed the highest oxygen reduction reaction (ORR) performance and stability. The polarization resistance for ORR on Pd_0.90Co_0.10+YSZ cathode is only 0.088 Ω cm² at 750 °C. During polarization test at 750 °C, Pd_0.90Co_0.10+YSZ cathode showed stable performance for 30 h while the performance of Pd+YSZ cathode degraded after 10 h.