Solid oxide cells degradation by Nickel oxidation: A phase field study of oxide growth and its mechanical impact

Résumé fourni par la source

Solid Oxide Cells are highly efficient energy conversion devices that can be damaged by various system failures. Specifically, the porous hydrogen electrode, which is a cermet consisting of Nickel and Yttria Stabilized Zirconia (Ni-YSZ), can deteriorate when exposed to oxidizing atmosphere at high temperature. Ni oxidation induces volumetric expansion which is partially accommodated in the pores of the cermet. This constrained swelling imposes mechanical strain on the YSZ backbone that can compromise its integrity. In this study, a conventional cermet was oxidized under air at 700 °C for different times to characterize the kinetics and features of Ni oxidation and the fracture of YSZ. A novel three-material phase field model, incorporating oxidation-induced strains, was developed to simulate Ni oxidation within the complex electrode microstructure. The model was validated on different cermet microstructures to reproduce the kinetics of oxidation in the different electrode layers and the YSZ mechanical loading after oxidation. The material parameters governing oxidation (Ni diffusion in NiO) and stress state (oxide growth strain) were identified through the model calibration. A correlation between oxidation and microstructural features was identified, revealing that Ni coarsening slows oxidation kinetics, and enabling DoO estimation prior to simulation with a microstructure descriptor. Simulations revealed localized high tensile stresses at several YSZ necks, matching experimental crack initiation timescales and validating a first step towards oxidation-induced damage prediction.

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