Compared with conventional cermet solid oxide cell fuel electrodes, perovskite electrodes have the advantages of redox stability, coking resistance and sulfur resistance. Moreover, cation exsolution, where metal nanoparticles exsolve from the parent perovskite oxide under reducing conditions, has been shown to significantly enhance the electrochemical performance of the perovskite fuel electrodes due to the surface decoration of highly dispersed, catalytically active metal nanoparticles. Unfortunately, the phase transition of perovskite electrodes with time under different fuel conditions and its effect on their durability have not been fully understood. Furthermore, the phase and microstructure transformation of these exsolved perovskite electrodes under redox cycles still need more investigation.

Here durability test of Ni-doped strontium iron titanate (STFN) was conducted at 850^oC under different fuel conditions and redox cycles were introduced during these life-tests. Degradation in both ohmic resistance (R₀) and polarization resistance (Rp) was observed during aging in 97% H₂ + 3% H₂O, and the introduction of wet Ar after 240-hour aging successfully recovered some of the electrochemical performance of STFN. In-situ X-ray diffraction shows the formation of Ruddlesden-Popper phase together with Ni-Fe alloy exsolution upon exposing to 97% H₂ + 3% H₂O and the change in composition over time was also observed. Scanning electron microscopy also shows coarsening of exsolved nanoparticles and microstructural change of perovskite electrodes. Moreover, life tests of STFN were also conducted in 50% H₂ + 50% H₂O and 50% H₂ + 50% H₂O at 850^oC. Despite the more Ni-rich exsolved nanoparticles due to the higher oxygen partial pressure, the durability was worse than that of 97% H₂ + 3% H₂O. The increased degradation rate was attributed to the microstructural change of the parent perovskite phase.