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 ϕl = 0.

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.

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:

The Electroanalysis charge conservation model solves Equation 4-10 and Equation 4-11 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:

Equation 4-12 is Fick’s second law of diffusion.