A Homogeneous/Agglomerate Model for Molten Carbonate Fuel Cell Cathodes

Abstract

A molten carbonate fuel cell cathode model was developed which enables the estimation of performance as a function of cathode electrolyte content. This model is neither a thin film nor a conventional agglomerate model, but involves the calculation of the effective agglomerate diameter, porosity, tortuosity, and number based on knowledge of the electrode's pore spectrum and electrolyte content. Calculated electrode performance and experimental results are compared for cathodes of different pore spectra over a range of electrolyte contents.

Characterization of fuel cell electrode processes by AC impedance

“…Under these conditions the main diffusion resistance is associated with transverse diffusion of dissolved gaseous reactants and products into the agglomerate, while the main ohmic resistance is axial, that is, in the thickness dimension of the porous electrode, Fig Thus, concentrations are assumed to vary only in the transverse direction-perpendicular to the electrode thicknesswhile the potential of the electrolyte varies only in the axial (thickness) direction. This assumption has been used extensively in fuel cell electrode modeling (Giner and Hunter, 1969;Wilemski, 1983;Kunz et al, 1984;Yuh and Selman, 1984).…”

Three-dimensional modeling of polarization characteristics in molten carbonate fuel cells using peroxide and superoxide mechanisms

“…By doing so, it introduces average concentrations defined across both phases, represented by Eq. (14). Nevertheless, there is a major apprehension in regards to the diffusive flux terms which is related to the diffusion coefficients.…”

“…In fact, the prediction capability of these mechanisms is rarely discussed in literature. Therefore, the two most common reaction mechanisms, namely the peroxide and superoxide mechanisms [12,14] are employed and compared in this paper. In any event, the general form of the cathode reaction equation reads…”

“…This research shows that none of the available cathode reaction mechanisms can predict the MCFC behaviour at high cathode gas utilizations. This issue is related to the current correlations for cathode reaction rate [12,14] which characterize only apparent values without considering the true kinetics. Perhaps, one way to obtain a good fit to the experimental data at high current densities is to assign a positive exponent to CO 2 in Eq.…”

“…Nevertheless, it oversimplifies pore structure, and requires measured values for film areas and thicknesses, forcing these parameters to be treated empirically. Afterwards, Kunz et al [14] modified the conventional agglomerate model and developed a homogeneous model by calculating the effective agglomerate diameter, porosity and tortuosity based on the electrode's pore spectrum and electrolyte content. Many researchers have used this theory and developed it further.…”