Use the Source to add a volume current source.

Select an option from the Specify source using list — Current source (the default) or Reaction rate.

When Current source is selected enter a value or expression for the Current source S (SI unit: A/m3). When Reaction rate is selected enter a value or expression for the Reaction rate R (SI unit: mol/(m3.s)). The actual current source is then computed by multiplying the reaction rate by the elementary charge and the Avogadro’s Number.