Reducing agents should have the ability to undergo oxidation that implies the property to easily loose electrons. Consequently the coupling element should have a greater tendency to attract the donated electron. As I^- and Br^- already are reduced ions so they cannot further undergo reduction. Between Ag and Br we can find from electrochemical series that the reduction potential of Br₂ is more as compared to Ag.

Thus Cu will reduce Br₂ as follows:

Corresponding [potential for the developed cell is