Thermal Stability of an in Situ Exsolved Metallic Nanoparticle Structured Perovskite Type Hydrogen Electrode for Solid Oxide Cells

Abstract

In this work, thermal stability of an in situ exsolved Ni–Fe nanoparticle structured Sr2Fe1.4Ni0.1Mo0.5O6 (SFMNi) perovskite type hydrogen electrode is studied by examining the evolution of electrode polarization resistance and material morphology. During the 745-h durability testing, the polarization resistance measured at 800 °C dramatically decreases from 0.68 to 0.31 Ω cm2 with an activation rate of 22.92%/100 h in the initial 200 h, then undergoes a stable period in the following 200 h, and subsequently rises to 0.40 Ω cm2 with a degradation rate of 6.20%/100 h in the last 345 h. Variation of electrode electrochemical performance could be explained by the morphology evolution of the exsolved nanoparticles, which are well-fitted by the self-limiting growth model. Distribution of relaxation time analysis results indicate that gas conversion is the primary rate-limiting step during the electrode reaction and can be effectively accelerated by the gradually exsolved Ni–Fe nanoparticles during the durability testing. Additionally, higher temperature results in a shorter equilibrium time, which can be explained by the accelerated thermodynamic and kinetic properties of the in situ exsolution process because of the lowered Gibbs free energy at higher temperature. The approach developed in this study could be used to predict the lifetime of the in situ metallic nanoparticle structured electrode and provide a significant insight into the development of other ceramic materials with high activity and robust stability for solid oxide cell application.