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Table 2-1: Common Potential Variables
Variable	Description	Defined at
phil	Electrolyte phase potential	Electrolyte and Porous Electrode domains
phis	Electrode phase potential	Electrode and Porous Electrode domains
xxx.phisext	Electrode phase potential	Electrode Reaction boundaries to Electrolyte domains
xxx.Eeq_yy	Equilibrium potential	Electrode Reaction boundaries and Porous Electrode Reaction domains
xxx.eta_yy	Overpotential	Electrode Reaction boundaries

Table 2-1: Common Potential Variables

Variable

Description

Defined at

phil

Electrolyte phase potential

Electrolyte and Porous Electrode domains

phis

Electrode phase potential

Electrode and Porous Electrode domains

xxx.phisext

Electrode phase potential

Electrode Reaction boundaries to Electrolyte domains

xxx.Eeq_yy

Equilibrium potential

Electrode Reaction boundaries and Porous Electrode Reaction domains

xxx.eta_yy

Overpotential

Electrode Reaction boundaries

xxx denotes the tag of the physics interface. For instance, cd for the Secondary Current Distribution interface.

yy denotes the tag of the (Porous) Electrode Reaction node, for instance, er1 for an Electrode Reaction node.

The current density may vary between locations on an electrode surface. This effect is very important to understand through modeling because it cannot be directly measured. Experimental measurement can only return the total current drawn at an electrode, although the variation in current density can be inferred by other means.

To calculate the total current in COMSOL Multiphysics, it is necessary to integrate the total drawn current density along the boundary or over the domain of the electrode. Some common current density variables are shown in Table 2-2.

Table 2-2: Common current density variables.
Variable	Unit	Description	Defined at
xxx.nIl	A/m2	Electrolyte current density in normal direction	Boundaries to Electrolyte and Porous Electrode domains
xxx.nIs	A/m2	Electrode current density in normal direction	Boundaries to Electrolyte and Porous Electrode domains
xxx.iloc_yy	A/m2	Local current density of electrode reaction	Electrode Reaction boundaries
xxx.itot	A/m2	Total interface current density (local sum of all xxx.iloc_yy)	Electrode Reaction boundaries
xxx.iv_yy	A/m3	Volumetric current density of a Porous Electrode Reaction	Porous Electrode domains
xxx.ivtot	A/m3	Total volumetric current densities (local sum of all xxx.iv_yy)	Porous Electrode domains
xxx.IlMag	A/m2	Electrolyte current density magnitude (L2 norm)	Electrolyte domains
xxx.IsMag	A/m2	Electrode current density magnitude (L2 norm)	Electrode domains

Table 2-2: Common current density variables.

A/m2

Electrolyte current density in normal direction

Boundaries to Electrolyte and Porous Electrode domains

xxx.nIs

A/m2

Electrode current density in normal direction

Boundaries to Electrolyte and Porous Electrode domains

xxx.iloc_yy

A/m2

Local current density of electrode reaction

Electrode Reaction boundaries

xxx.itot

A/m2

Total interface current density (local sum of all xxx.iloc_yy)

Electrode Reaction boundaries

xxx.iv_yy

A/m3

Volumetric current density of a Porous Electrode Reaction

Porous Electrode domains

xxx.ivtot

A/m3

Total volumetric current densities (local sum of all xxx.iv_yy)

Porous Electrode domains

xxx.IlMag

A/m2

Electrolyte current density magnitude (L2 norm)

Electrolyte domains

xxx.IsMag

A/m2

Electrode current density magnitude (L2 norm)

Electrode domains

xxx denotes the tag of the physics interface. For instance cd for the Secondary Current Distribution interface.

yy denotes the tag of the (Porous) Electrode Reaction node, For instance er1 for an Electrode Reaction node.

In 1D or 1D axisymmetric, the electrode is implicitly uniform so you can just multiply by the area of the electrode. In 2D or 2D axisymmetric, compute the appropriate line integral. In 3D, compute the surface integral.

You can also define your own total current variable by using an nonlocal coupling across the electroactive boundaries. This variable can also be used during the computation. In 1D axisymmetric and 2D axisymmetric components, make sure to select the check box.