Ni/GDC Fuel Electrode for Low-Temperature SOFC and its Aging Behavior Under Accelerated Stress

Abstract

The microstructural integrity of Ni-based fuel electrodes is important for long-term solid oxide fuel cell (SOFC) operation. Degradation due to microstructural changes such as Ni-agglomeration, coarsening, and densification must be prevented by an appropriate microstructure. Here, the performance of four types of nickel-ceria-based fuel electrodes, which differ concerning layer sequence and manufacturing processes, was evaluated by electrochemical impedance spectroscopy at the nominal operating temperature of 600 °C. Electrodes produced through screen-printed GDC exhibited an acceptable polarization resistance (0.260 Ωcm2), whereas electrodes with an additional printed Ni/GDC layer demonstrated inferior performance (0.550 Ωcm2). Electrodes formed through infiltration of GDC into the printed GDC-layer displayed unreproducible performance values ranging from 0.16 to 1.20 Ωcm2 despite similar processing. Conversely, electrodes with an extra layer of GDC infiltrated into the Ni-backbone exhibited good performance (0.195 Ωcm2) and stability. Accelerated degradation tests under OCV at increased operating temperatures of 700 and 900 °C were performed on the sample based on a GDC infiltrated Ni-backbone that performed best among reproducible samples. The polarization resistance at 600 °C recorded at the beginning and the end of life increased by up to 100%. Microstructural analysis of the electrodes at different aging states revealed strong microstructural changes of fine-infiltrated GDC structures and Ni agglomeration at higher operating temperature.