Beschreibung:
<jats:p> An important degradation mechanism in solid oxide fuel cells (SOFCs) is the microstructural evolution of Ni-YSZ anodes caused by diffusional transport of nickel under operating conditions. In this work, we carry out 3D analysis on several data sets from FIB-SEM reconstructions of a full-ceramic co-sintered SOFC as well as from large-scale phase-field simulations, in order to obtain a quantitative understanding of the different microstructure evolution effects and their impact on anode degradation. </jats:p>
<jats:p>The experimental data stem from FIB-SEM reconstructions of both newly fabricated anodes and anodes aged for ca. 1000h under operating conditions. The simulated data stem from large-scale phase field simulations that have been initialized with a reconstructed microstructure. The underlying phase-field model incorporates both volume diffusion of nickel and interface diffusion along the Ni surfaces, grain boundaries, and Ni-YSZ interfaces. The required material parameters (interface energies and diffusivities) are determined partly by ab-initio simulations and partly by thermal grooving experiments on bicrystalline and polycrystalline nickel. </jats:p>
<jats:p>For the 3D analysis, we calculate standard microstructural features such as volume fractions, active and inactive three-phase-boundary (3PB) length, and tortuosity, and we use the transmission line model to calculate the expected anode performance. Comparison with the measured anode performance shows that the observed decrease of 3PB length explains the measured degradation only partly, while the main degradation factor is loss of connectivity of the nickel phase. To understand the connectivity loss in more detail, we carry out a bottleneck analysis to quantify the gradual tightening of the bottlenecks. In addition, we statistically assess the spatial homogeneity, and we calculate several shape descriptors such as interface areas and local structure size, which allows us to show that nickel relocates over considerable distances from small pores to larger pores within the YSZ skeleton. </jats:p>