The Cathode Compartment The electrons that are released at the anode travel through the external circuit and are now used at the cathode to reduce Cu2+(aq) ions at the surface of the copper electrode. The product is solid copper which adheres to the copper electrode and consequently the electrode "grows" in size. Because Cu2+(aq) ions are removed from the solution, K+(aq) ions are released from the salt bridge (or sulfate ions migrate to the salt bridge) to balance the charge. In this animation potassium ions are released from the salt bridge to maintain electrical neutrality. To see what happens in the anode compartment, click on anode. To return to the beginning of this animation, click on electrochemical cells.