Transport Properties of Ions
There are three modes of transport of ions in solution: diffusion, migration and convection. The factors that encourage ions to move in these modes are, in the case of diffusion, a concentration gradient; in the case of migration, a potential gradient; in the case of convection, either a temperature gradient or mechanical stirring or flow.
The electrical potential of species i is defined as
Spontaneous movement of i will take
place from regions of higher to lower electrochemical potential. The rate of such movement
is proportional to the gradient 
where x
is the distance of i from a reference plane so that
where ki is a proportionality constant. Thus the rate of movement is given by
The flux is defined as
the units normally being mol s-1 cm-2. So the flux is given by
This is a function of both concentration and potential gradients.