where ∇T is the tangential gradient operator,
s (SI unit: m) is the electrode layer thickness, and
in (SI unit: A/m
2) are the sum of all currents flowing out from the electrode (in the normal direction to the boundary). Furthermore,
is (SI unit: A/m
2) is the tangential current density vector along the electrode boundary, defined as
where σs is the electric conductivity (SI unit: S/m). The next section discusses
Coupling to Other Physics Interfaces.