ANSYS FLUENT 12.0 Fuel Cell Modules Manual - 3.5.1 Modeling Electrochemical Reactions

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3.5.1 Modeling Electrochemical Reactions

The rate of species production and destruction is:

$S = - \frac{a i}{nF} (g-mole/{m^2}/sec)$

(3.5-1)

where is the source or sink of the species (molar flux), is the stoichiometric coefficient, is the current density ( $A/{m^2}$ ), is the number of electrons per mole of fuel, and is the Faraday constant.

Using the local current information, the ANSYS FLUENT SOFC With Unresolved Electrolyte Model applies species fluxes to the electrode boundaries. By convention [ 6], the current density is positive when it flows from the electrode into the electrolyte solution. The current densities are positive at the anodes and negative at the cathodes.

The reaction at the cathode electrode is:

$\frac{1}{2}O_{\rm 2, cathode} + 2e^{-} \Leftrightarrow O^{2-}$

(3.5-2)

or

$S_{\rm O_{\rm 2}} = - \frac{-(\frac{1}{2})(-i)}{2F} = - \frac{i}{4F}$

(3.5-3)

$S_{\rm O}^{2-} = - \frac{(-i)}{2F} = - \frac{i}{2F}$

(3.5-4)

The reaction at the anode electrode is:

$H_{\rm 2} + O^{2-} \Leftrightarrow H_{\rm 2}O + 2e^{-}$

(3.5-5)

$S_{\rm H_{\rm 2}} = - \frac{i}{2F}$

(3.5-6)

$S_{\rm O}^{2-} = - \frac{i}{2F}$

(3.5-7)

$S_{{\rm H_{\rm 2}}O} = - \frac{-(1)(i)}{2F} = \frac{i}{2F}$

(3.5-8)

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Release 12.0 © ANSYS, Inc. 2009-01-23