Continuum-Level Electrochemistry Model

CeU-level macroscale models consider the heat transfer, species transport, chemical reactions, and electrochemistry within the SOFC cell [27, 31, 51, 52]. In cell-level models, the detailed transport of gas in the fuel and air channels and in the porous electrodes are simulated on a macroscale. This requires a rigorous CFD simulation and commercial codes, such as FLUENT, COMSOL, and Star-CD, are used for cell-level models. Cell-level models consider the electrodes and electrolyte on a continuum scale, which means that the models do not explicitly resolve... 

Cell-level models solve the species [Eq. (26.1)], momentum [Eq. (26.5)], and energy [Eq. (26.7)] conservation equations using the effective properties of the electrodes and can include the electrochemistry using a continuum-scale (Section 26.2.4.1) or a mesoscale (Section 26.2.4.2) approach. Traditionally, cell-level models use a continuum-scale electrochemistry approach, which includes the electrochemistry as a boundary condition at the electrode-electrolyte interface [17, 51, 54] or over a specified reaction zone near the interface. The electrochemistry is modeled via the Nernst equation [Eq. (26.12)] using a prescribed current density and assumptions for the polarizations in the cell. The continuum-scale electrochemistry is then coupled to the species conservation equation [Eq. (26.1)] using Faraday s law ... 

Macroscale cell-level models are able to provide a great amount of insight into the operation and performance of SOFCs. With the newer mesoscale electrochemistry models, information about the conditions within the SOFC electrodes and electrolytes can even be resolved. However, due to the continuum-scale treatment of the SOFC, these models stiU rely on effective parameters, which need to be determined through smaller scale modehng or by fitting the models to experimental data. 

In SOFC modeling, the electrochemistry of the fuel cell can be included in the model at various levels of detail. In a continuum-scale approach, empirical current-potential (f-V) relations are typically used to model the electrochemistry of the SOFC. In a mesoscale approach, the electrochemical reactions and the transport of electrons and ions in the SOFC can be modeled explicitly. The continuum-scale approach allows for a quick evaluation of the I-V performance of the SOFC by assuming that the electrochemistry occurs only at the interface of the electrode and electrolyte. In the mesoscale approach, the electrochemistry of the SOFC is resolved through the thickness of the electrodes based on the local conditions in the cell. In this section, we discuss the details of both approaches. 

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