Modeling and Study of the Influence of Sealing on a Solid Oxide Fuel Cell

Abstract

The properties of sealing materials are important for the performance and reliability of solid oxide fuel cells (SOFCs). Even if the properties of a sealing material can be studied separately, it remains difficult to quantify the effect of an imperfect seal on the repeat-element behavior. In this study, simulation is used to investigate the effects of an imperfect seal behavior on the performance and reliability of SOFCs. Diffusion through the sealing material and inherent local combustion of fuel are added to the computational fluid dynamics (CFD) repeat-element model, which also allows us to compute the flow field, the electrochemical reactions, and the energy equations. The results are in good agreement with experiments. The zones of parasitic combustion and local overheating are well reproduced. Furthermore, the model predicts a risk of reoxidation under polarization that is well observed. The model also shows the necessity to take into account the diffusion transport for the development of compressive seal materials, hence verifying the hypotheses made by other groups. The modeling approach presented here, which includes the imperfections of components, allows us to reproduce experiments with good accuracy and gives a better understanding of degradation processes. With its reasonable computational cost, it is a powerful tool for a design of SOFC based on reliability.

Mechanical reliability and durability of SOFC stacks. Part II: Modelling of mechanical failures during ageing and cycling

“…The aforementioned component failures indirectly affect the integrity of the cells, by modifying the electrochemical performance [29] and by causing localised reoxidation or reduction of the anode and cathode, respectively [2], the sole mechanical interactions between the components can also promote cell cracking. The choice of GDL and sealing solutions determines the mechanical interactions between the components.…”

Modifier-Adaptation Methodology for Real-Time Optimization

“…A lumped model is used in this simulation study, as it captures the fundamental behavior of the SOFC while providing a good trade-off between accuracy and fast computation. The model has been validated from more detailed models developed at the Laboratoire d'Énergétique Industrielle (LENI) at EPFL, and it corresponds to SOFC stacks typically running at LENI's facilities [68,87]. This lumped model considers a homogeneous temperature throughout the whole stack.…”

“…The fuel cell is operated under a number of inequality constraints including bounds on input and output variables (flow rates, cell potential, fuel utilization, stack temperature and current density). Constraints on the potential and fuel utilization are set due to risks of oxidation of the cell's anode, which may degrade or even cause the failure of the cell [19,87]. Operating at high current densities will cause material damage to the cell through excessive heating [51].…”

“…The low airratio limit is set to avoid high thermal gradients, while the high limit is due to system constraints. Current density is constrained to avoid degradation [51,87]. The constraint bounds are given in Table 3.6.…”

Progressive activation of degradation processes in solid oxide fuel cells stacks: Part I: Lifetime extension by optimisation of the operating conditions

“…Herein lies their partial incompatibility, in particular that of (ii), with modelling at the SRU/stack scale. The range of operation is determined by indicators for anode reoxidation [21] or cathode reduction in the case of imperfect sealants [22,23]. The SRU geometry and gas manifold is adjusted to reduce high local current densities to avoid ensuing high localised rates of heat generation and current constriction effects.…”