The influence of microstructural evolution on performance degradation in solid oxide fuel cells

The microstructure evolution effects performance degradation of solid oxide fuel cells (SOFCs) under elevated temperatures. The microstructural evolution, including elemental diffusion, phase changes, and Ni agglomeration, is studied via X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) techniques. The ohmic resistance and polarization impedance, including activation polarization impedance and concentration resistance, causing the performance degradation, are estimated using electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) techniques. The voltage gradually decreases from 0.9  V, at the beginning of the load, to 0.75  V after 240  h of service. The formation of pores at the (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ) LSCF/(Gd_0.1Ce_0.9O_2-δ) GDC interface and cracks at the (8 mol% Y₂O₃-stabilized ZrO₂) YSZ/NiO-YSZ interface induce the increase in ohmic resistance. The increase in activation polarization resistance is attributed to the formation of the SrZrO₃ phase and Gd₂(Zr_1-xCe_x)₂O₇, at the YSZ/GDC interface, and the redistribution and coarsening of Ni. The formation of Co– or Fe-based oxides in the LSCF layer slightly increases the concentration polarization impedance.