AC impedance characteristics for anode-supported microtubular solid oxide fuel cells

The DRT method was applied to analyze the AC impedance spectra for anode-supported microtubular solid oxide fuel cells (SOFCs). The anode microstructure has a more severe effect on the electrochemical properties of the anode-supported microtubular SOFCs because of the small inside diameter and thickness of the anode. For example, the maximum current density and fuel utilization for the cells sintered at 1400 °C were lower than that at 1350 °C due to the low porosity of the anode. However, it is difficult to separate the anode and cathode impedances by the general method of complex non-linear least squares (CNLS) with equivalent circuit models, because several components overlap for the impedance spectra measured between the anode and cathode without a reference electrode. The DRT method can easily separate the impedance spectra into five polarization components for the anode-supported microtubular SOFCs. The activation energy of the anode diffusion resistance was only 24–33 kJ/mol. The walls of the pores in the anode were relatively well-packed with the nickel and YSZ particles for the cells made by the use of acrylic resin as a pore former. The anode diffusion resistance decreased by only a small amount with a rise of operating temperature for the anode-supported microtubular SOFCs.

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► Impedance spectra were separated into 5 polarization components by DRT method.
► Activation and diffusion resistances were large for anode with low porosity.
► Activation energy of anode diffusion resistance was small for microtubular SOFCs.