We have studied the pattern formation in a planar reaction-diffusion front driven by an inhomogeneous electric field to maintain a constant current density parallel to the direction of propagation. Our experiments and modeling calculations show that in the selected reaction lateral instability is favored for field orientation where the mixing of the reactants and the autocatalyst is enhanced by ionic migration. Cellular fronts develop when the drift velocity of reactant anions ahead of the front sufficiently exceeds that of the autocatalyst cation behind the front. which is achieved by the differential acceleration of the reactants. (C) 2004 Published by Elsevier B.V.