Mass Fluxes and Sources Due to Electrochemical Reactions
When relating the species fluxes at an electrode surface to the electrical currents, the general electrochemical reaction formula:
is used to define the stoichiometric coefficients, νi, with νi being positive (νred) for products and negative (νox) for the reactants in a reduction reaction. The number of participating electrons, n, is always positive.
The molar species fluxes, Ni (SI unit: mol/(m2·s)), perpendicular to an electrode-electrolyte interface are calculated by summing all the flux contributions from the electrode reactions of index m, according to Faraday’s laws:
where im is the local current density (SI unit: A/m2) of the electrochemical reaction, nm the number of participating electrons and F (SI unit: C/mol) is the Faraday constant.
The molar species flux, Ni, is obtained from the normal component of the molar species flux vector over the electrode-electrolyte interface:
where n is the normal vector of the boundary pointing into the domain.
For a porous electrode, the electrochemical reactions result in species source terms calculated from:
where av,m (SI unit: m2/m3) is the specific surface area.