# The Evolution of Solid Oxide Fuel Cell Materials
## 3 Materials Systems
### Advanced Concepts
Using a yttria-stabilized zirconia (YSZ) electrolyte as support, this nanostructure is compatible as a functional oxide nanomaterial for high-temperature electrochemical devices (i.e., as a SOC functional electrode layer given the high stability against cation migration and accelerated ORR kinetics) [132]. Importantly, the introduction of nano-engineered composite oxides can lead to further ways for the development of new functional materials with improved electrochemical properties [25]. Interestingly, the [PERSON] et al. study [25] employed DFT calculations to study the effects of local high entropy on lattice stabilization. In particular, they used spin-polarized DFT on a confined cubic perovskite supercell (refer to Figure 4), aiming to gain insights into the thermal stability of the LSM-SDC VAN. This is not trivial; however, the study focused on the high degree of cation (Sm and Ce) intermixing. The ability of DFT to decouple between the different contributions and to quantify energy and strain differences is valuable to gain insights that are not feasible via experiment. The study by [PERSON] et al. [25] showed that the determined isotropic compressive strain of LSM in the VAN structure is due to the introduction of Sm from the SDC layers. Importantly, spontaneous cation interdiffusion leads to Sr segregation suppression, whereas LSM can be considered a six-element high-entropy oxide [25]. This is also consistent with the results by [PERSON] et al. [133], who have determined entropy-induced stabilization for bulk LSM. Figure 4 illustrates the DFT-derived results, showing the lattice strain due to doping, the mean and distribution of site volumes around the La and Sr sites and the bond valence mismatch of the ionic positions for the different cation dopants [25]. In La\({}_{0.875}\)Sr\({}_{0.125}\)MnO\({}_{3}\), it is predicted that the Sr ion is significantly overbonded (i.e., the surrounding oxygen ions are closer), whereas La ions are slightly underbonded [25]. This valence mismatch in conjunction with electrostatic effects can be key for the exchange of overbonded Sr ions with underbonded La ions on the surface [25]. This incoherency is balanced by cationic intermixing (refer to Figure 4c,d) [25]. The incorporation of Ce will effectively increase the Sr-O site volume and reduce the Sr-O overbonding compared to the La-O polyhedral [25]. This will result in a decrease in the elastic driving force for Sr surface segregation. That is, the configurational entropy increase leads to more stable LSM via local lattice distortion, consistent with theoretical studies [25; 134]. VAN structures are (a) self-assembled and therefore their composition and interfaces at a growth temperature are thermodynamically stable, and (b) they can accommodate Ce contents beyond the solubility limit [25; 135]. In essence, the whole approach is based on using VANs for the combination of the very good oxygen exchange properties of LSM and the fast oxygen diffusion of SDC to form an advanced designed electrode functional layer for SOCs. The heavily codoped manganite phase in the VAN is a high-entropy oxide which is stable and obstructs Sr segregation from the surface. The consequence is very long-term durability. The study by [PERSON] et al. [25] determined (via isotopic exchange depth profiling based on APT) that there is a fast oxygen diffusion pathway along the SDC phase. This is a paradigm of the use of VAN nanocomposites as a tool to fix current kinetic limitations of existing electrodes. The VAN architecture is relatively easy to form and leads to prolonged thermal stability and fast oxygen reduction kinetics [25; 136; 137; 138]. the long-term durability of solid oxide electrochemical cells. It is determined that VAN nanocomposites can solve kinetic limitations of electrodes and, in general, can be an efficient strategy for oxide electrochemistry (combining fast oxygen reduction kinetics with long-term thermal stability).