Mechanical-Electrochemical Coupling in Materials for Solid Oxide Fuel Cells: Insights from Computer Simulations

The coupling between the electrical, chemical and mechanical properties of materials, usually referred to as Electro-Chemo-Mechanics [1], has very important implications for energy related materials and devices. Indeed, this coupling can be beneficial, e.g. the ion conductivity enhancement observed in ceria and zirconia when these materials are strained [2], or detrimental, e.g. the lattice parameter expansion observed in ceria upon reduction [3]. For this reason a better understanding of this coupling is necessary in order to tailor the properties of these materials.

Atomistic computer simulations represent a powerful tool to study the mechanical-electrochemical coupling, as they can provide information that is complementary to experiments. In this presentation, I will review some recent computational work in this field. First I will talk about chemical expansion in ceria, an example of chemo-mechanical coupling. I will show how, by combining Density Functional Theory and Molecular Dynamics Calculations with experimental data, we concluded that chemical expansion is caused by two competing processes, the formation of a vacancy (leading to a lattice contraction) and the cation radius change (leading to a lattice expansion). This information was then condensed in a simple analytical model, which was then used to predict materials compositions that minimize chemical expansion. Then I will present two more examples from my work: the first one on the study of co-doping strategies in ceria as a means to enhance its ionic conductivity (electro-chemical coupling) and the second one on the effects of dislocations in SrTiO₃ on the defect chemistry and mobility of this material (electro-chemo-mechanical) coupling.

References

[1] Tuller and Bishop, Annu. Rev. Mater. Res. 41 369 (2011)

[2] Kushima and Yildiz, J. Mat. Chem. 20 4809 (2011)

[3] Marrocchelli et al. Adv. Fun. Mat. 22 1958 (2012)