  We study the effects of an external electric field on both the motion of the
reaction zone and the spatial distribution of the reaction product, $C$, in an
irreversible $A^- +B^+ \to C$ reaction-diffusion process. The electrolytes
$A\equiv (A^+,A^-)$ and $B\equiv (B^+,B^-)$ are initially separated in space
and the ion-dynamics is described by reaction-diffusion equations obeying local
electroneutrality. Without an electric field, the reaction zone moves
diffusively leaving behind a constant concentration of $C$-s. In the presence
of an electric field which drives the reagents towards the reaction zone, we
find that the reaction zone still moves diffusively but with a diffusion
coefficient which slightly decreases with increasing field. The important
electric field effect is that the concentration of $C$-s is no longer constant
but increases linearly in the direction of the motion of the front. The case of
an electric field of reversed polarity is also discussed and it is found that
the motion of the front has a diffusive, as well as a drift component. The
concentration of $C$-s decreases in the direction of the motion of the front,
up to the complete extinction of the reaction. Possible applications of the
above results to the understanding of the formation of Liesegang patterns in an
electric field is briefly outlined.
