CFD & AMP Center
Department of Mechanical & Aerospace Engineering
West Virginia University

Dynamic 3D multi-physics cathode/anode model

Dynamic 3D multi-physics cathode/anode model
National Energy Technology Laboratory (NETL)
Dr. Ismail B. Celik
Dr. Tao Yang
Dr. Suryanarayana Raju Pakalapati
Hayri Sezer

Executive Summary

The dynamic 3D multi-physics cathode/anode model is developed to describe the local dynamic state in terms of temperature, species concentrations (including solid state species), and overpotential. The high-fidelity, dynamic and efficient model possesses complete oxygen reduction reactions in cathode and complete oxidation reactions in anode. Parametric studies are performed for further understanding of the processes occurring in SOFCs. Different mechanisms of oxidation and reduction on electrodes are analyzed, and the optimal mechanism was determined through the comparison with experimental results.

To be more realistic, the microstructures of porous electrodes were reconstructed based on microstructural data from experimental observations, and the realistic properties, e.g. tortuosity, specific area, and distribution of porosity, on the performance of solid oxide fuel cells are investigated. In our study, a more physically accurate tortuosity (hence diffusion coefficient) is calculated through path line integrations of the velocity field from a numerical simulation of flow passing through the reconstructed porous media.

The optimal solver for stiff systems of differential equations is investigated to improve the efficiency of SOFC simulation which is limited by stiff ODEs arising from species transport equations. A semi-implicit scheme is developed by only calculating the diagonal elements in Jacobian matrix to improve the efficiency of solver with acceptable accuracy. This scheme is also further improved by transforming the stiff ODEs to space where the equations are less stiff than the original ones. Various transformations were derived and another investigated on cases with different stiffness (e.g. Nitrogen case and Propane case), and their performances were compared to obtain the optimal one with both high efficiency and accuracy.

Figure 1. Comparison of simulation polarization curve (A), simulation Nyquist plot (B), and simulation Bode plot (C) to the data from the anode-supported cell at 800◦C and normal flow.

Figure 2. Schematic representation of the composite cathode and the reaction mechanisms for 2PB and 3PB pathways of oxygen reduction on LSM-YSZ

Figure 3. Reconstruction of porous cathode based on microstructural data from experimental observations

Figure 4. Results of 3D simulations using real microstructure data.

Figure 5. Effects of different properties on fuel cell impedance behavior: (a) specific interface area between phases, (b) particle size, (c) equilibrium concentration of surface oxygen ion, (d) oxygen partial pressure.