Thermo-Electro-Chemo-Mechanical Modeling of Solid Oxide Fuel Cell for Stress and Failure Evolution during Duty Cycle

Abstract

A comprehensive three-dimensional model for an assembled button solid oxide fuel cell is developed by coupling thermal-electrochemical and mechanical models. Different mechanical effects including residual strain, thermal strain, accelerated and normal creep, mechanical properties change of anode, as well as chemical expansion are considered. The mechanical response of the button cell subjected to an idealized duty cycle from the as-fabricated state, heating-up stage, reduction stage, to three operation periods of 800 °C, 700 °C, and 600 °C is numerically simulated. Simulations are based on and validated by the experimental polarization curves and residual stress curve. Results show that the sealant is susceptible to fracture at the as-fabricated state, while the cathode is likely to fail during heating-up stage. The accelerated creep effect during reduction significantly eliminates the tensile stress in the anode nevertheless leads to higher stress in the cathode and electrolyte. It indicates that the assumption of zero-stress temperature at the reduction point could cause an underestimation of stress in the cathode and electrolyte in the case of a constrained cell. The chemical expansion effect in the cathode is more prominent at higher operating temperatures. A minimum failure probability of the cell is found at 700 °C with consideration of chemical expansion.

Chemical lattice strain in nonstoichiometric oxides: an overview

“…[32][33][34] As seen, the great multitude of experimental and computational methods does not allow them to be reviewed in this work in detail. Some more applied aspects of chemical expansion, such as the modeling of chemically induced stresses in membranes [35][36][37][38][39][40][41][42] and SOFCs, 43,44 were thought to be beyond the scope of this rather more fundamentally oriented review. However, our leaving them out does not mean that they are somehow unrelatedon the contrary, high quality experimental data on defect equilibria and chemical expansion of materials gure among the necessary parameters of these models.…”

Performance evaluation for Ag and Au nanoparticle containing K2O‐MgO‐B2O3‐Al2O3‐SiO2‐F glass sealants for SOFC application

“…During SOFC operations, the amount, size, morphology as well as arrangement of crystalline phase/s within the microstructure contribute significantly towards the thermal stability of the glass‐ceramics sealants 21–23 . Figure 3 represents the SEM micrographs for the glass‐ceramics after crystallization heat treatment relevant for intermediate temperature SOFC condition.…”

“…During the SOFC operation, the sealant material is also required to form compact bonding with other components in order to avoid the passage/leakage of fuels and oxidants 4 . For this, the glass sealant material should produce sufficient volume shrinkage to achieve a good densification by viscous flow 22 . The highest volume shrinkage of ∼8% between room temperature and SOFC operating temperature (∼900°C) for Au nanoparticle containing NPG‐3 glass sealant therefore makes it a suitable sealing material 4,23 .…”

“…Corresponding microstructure contribute significantly towards the thermal stability of the glass-ceramics sealants. [21][22][23] Figure 3 represents the SEM micrographs for the glass-ceramics after crystallization heat treatment relevant for intermediate temperature SOFC condition. As seen from Figure 3A-A′, plate-like (average width 1.0 ± 0.2 μm) and rod-like (average width 500 ± 50 nm) fluorophlogopite crystals form a compact microstructure for NPG-1 glassceramics.…”

“…4 For this, the glass sealant material should produce sufficient volume shrinkage to achieve a good densification by viscous flow. 22 The highest volume shrinkage of ∼8% between room temperature and SOFC operating temperature (∼900 • C) for Au nanoparticle containing NPG-3 glass sealant therefore makes it a suitable sealing material. 4,23 Relatively larger volume shrinkage in this temperature range also confirms that 900 • C can be safely considered as the sealing temperature for the base glass.…”