Electrochemical analysis for anode-supported microtubular solid oxide fuel cells in partial reducing and oxidizing conditions

Microtubular solid oxide fuel cells (SOFCs) with a diameter on the millimeter scale are suitable for small-scale applications such as micro combined heat/power systems and portable power sources. However, the use in reducing purge gas is not practical during start-up and shutdown in the small-scale applications. In this study, the redox tolerance was evaluated for nickel gadolinia-doped ceria (Ni-GDC) anode-supported microtubular SOFCs with an open-end at fuel outlet, when the hydrogen fuel supply was stopped 8 times for 10 min/cycle at 615 °C. The open circuit voltage was unchanged, and the degradation of less than 3% was confirmed after 8 redox cycles. The Ni-GDC anode-supported microtubular SOFCs have redox tolerance at 615 °C. Each electrode polarization resistance can be separated by the distribution of relaxation times (DRT) analysis from the measurement of AC impedance between the anode and the cathode. While the anode activation polarization (10-100 Hz) was clarified to increase because of the decrease in the TPB length, the anode concentration polarization (< 1 Hz) decreased by the change in pore distribution after redox cycles. The DRT analysis is one of the most effective methods to investigate the mechanism of electrode degradation for microtubular SOFCs.