Diego Larrain

Co-casting and co-sintering of porous MgO support plates with thin dense perovskite layers of LaSrFeCoO3

A tape casting co-sintering route is described in which thin dense layers of LaSrFeCoO3 (LSFC) have been formed on planar, porous MgO substrates 100- 200 micron thick. SEM analysis of the sintered structure showed that it was possible to eliminate most of the residual porosity in the LSFC layer, but maintain a porosity between 25 and 45% in the MgO support layer. The LSFC layer dit not reveal many cracks. The overall shrinkage of the co-sintered structure was about 25%. The LSFC layer topography was smooth and uniform with a metallic-like lustre. A good correlation was obtained between the observed microstructure and the gas permeability measurements made at room temperature.

Fuel Cell Modeling and Simulations

Abstract: Fundamental and phenomenological models for cells, stacks, and complete systems of PEFC and SOFC are reviewed and their predictive power is assessed by comparing model simulations against experiments. Computationally efficient models suited for engineering design include the (1+1) dimensionality approach, which decouples the membrane in-plane and through-plane processes, and the volume-averaged-method (VAM) that considers only the lumped effect of pre-selected system components. The former model was shown to capture the measured lateral current density inhomogeneities in a PEFC and the latter was used for the optimization of commercial SOFC systems. State Space Modeling (SSM) was used to identify the main reaction pathways in SOFC and, in conjunction with the implementation of geometrically well- defined electrodes, has opened a new direction for the understanding of electrochemical reactions. Furthermore, SSM has advanced the understanding of the COpoisoning- induced anode impedance in PEFC. Detailed numerical models such as the Lattice Boltzmann (LB) method for transport in porous media and the full 3-D Computational Fluid Dynamics (CFD) Navier-Stokes simulations are addressed. These models contain all components of the relevant physics and they can improve the understanding of the related phenomena, a necessary condition for the development of both appropriate simplified models as well as reliable technologies. Within the LB framework, a technique for the characterization and computer- reconstruction of the porous electrode structure was developed using advanced pattern recognition algorithms. In CFD modeling, 3-D simulations were used to investigate SOFC with internal methane steam reforming and have exemplified the significance of porous and novel fractal channel distributors for the fuel and oxidant delivery, as well as for the cooling of PEFC. As importantly, the novel concept has been put forth of functionally designed, fractal-shaped fuel cells, showing promise of significant performance improvements over the conventional rectangular shaped units. Thermo-economic modeling for the optimization of PEFC is finally addressed. Keywords: Multidimensional simulations of fuel cells · Porous electrode structure characterization · State-space modeling of electrochemical reactions · Thermo-economic optimization

Multi-scale modeling methodology for computer aided design of a Solid Oxide fuel cell stack

This paper presents the modeling strategy developed for the design of a planar solid oxide fuel cell repeat element. Design goal are to reach good performance (power density) and reliability (ie. limit risk of failure and degradation). This challenging problem, involving multiple physical phenomena, different scales (from the pores of the catalyst to the interaction of the fuel cell with the system), is addressed with a multi-scale modeling approach. Handling the complexity of the problem (including kinetics, mass, species and energy balances for fluids and solid parts) and the complete geometry may lead to unmanageable models in terms of complexity and CPU time. Therefore, simplified models are needed to understand the behavior and give the trade-off between the conflictive design objectives. The general methodology is presented as well as the different models features. A model for the routine electrochemical experiment allows to identified parameters for the kinetics (which is a key parameter for behavior and performance prediction). A simplified 2D model for the repeat element allows to easily explore and compare different configurations, make sensitivity studies and optimize some key design parameters. Finally a more complete CFD-based model is used to validate the decisions and options identified with the simplified model. This approach makes possible to explore different configuration and use optimization tools for the design of a repeat element. As mesh generation is the main bottleneck in CFD modeling, this method uses this tool only at the end of the process to validate the previous models used and decisions, therefore only a couple of mesh have to be generated. One of the key problem is here to make sure the simplified model and CFD model give the same trends and comparable results. This approach can be extended to the interaction of the system with the stack.