Domain Equations for the Electroanalysis Case
The Electroanalysis option assumes that the electric field is zero, and so the electrolyte potential is constant. Since you can arbitrarily choose to ground the electrolyte potential at any point, set it to .
This is equivalent to the assumption of infinite electrolyte conductivity. Therefore the Electroanalysis option does not solve for charge transfer within domains, because current density is not meaningfully defined within the electrolyte.
The transport of chemical species in an electrolyte solution obeys the Nernst–Planck equation for the flux of species i:
Here Ji denotes the molar flux relative to the convective transport.
At zero electric field, this reduces to:
(3-10)
where the only contributions to the flux of a chemical species are from diffusion and convection respectively. In the absence of convection (no fluid flow, u = 0), this is also known as Fick’s first law of diffusion:
A mass balance also applies to each chemical species:
(3-11)
The Electroanalysis charge conservation model solves Equation 3-10 and Equation 3-11 for the unknown concentrations of each chemical species under analysis.
This combination is often written as a single equation for the unknown ci. For zero convection, zero reaction, and a constant diffusion coefficient, the domain equation is:
(3-12)
Equation 3-12 is Fick’s second law of diffusion.
The Electroanalysis charge conservation model is not suitable to explicitly model the transport of the supporting electrolyte, since the migration of the supporting electrolyte is always its dominant mode of mass transport. For a coupled model including the chemical species of all charge-carrying species, use the electroneutrality model in Tertiary Current Distribution, Nernst–Planck interface.
You can also include additional chemical species and reactions that are not involved in the electrochemical reaction.
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Electrode Potentials and Reference Electrodes
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The Tertiary Current Distribution, Nernst-Planck Interface