The features of concentration polarization by an electric current passing through the boundary of two conducting media are considered. A bulk charge appears inside the concentration polarization zone under the action of a strong electric current. In the case of a curved surface, its appearance is connected with the normal component of the electric field. The action of the tangential field on this bulk charge leads to liquid movement along the surface which is similar to electroosmotic slip. The possible application of electroosmotic slip of the second kind for the intensification of electrodialysis is discussed.