Chloride Ion Catalysis of the Copper Deposition Reaction

The accelerating effect of anions for electrode reactions has been known for a long time, but it is much less appreciated that these effects can sometimes be caused by traces of anions. We have demonstrated that the Cu ++ /Cu + reaction is strongly catalyzed by trace amounts of chloride ions in the solution. The Cu + /Cu + reaction was found to be unaffected by chloride ions. These experimental results were also substantiated by theoretical calculations. We have investigated the electronic coupling for homogeneous electron‐transfer reactions that are approximate models for electron transfer in the copper deposition: ( i ) outer‐sphere reaction (water‐water bridge), and ( ii ) inner‐ sphere reaction (chloride bridge). For Cu ++ /Cu + electron transfer we found increased coupling for the chloride bridge, which we attribute to the closer approach found for this complex compared to the water bridge, while for Cu + /Cu + electron transfer, coupling was not increased for the chloride bridge reaction.