Electrochemical cells generate or use electrical energy through oxidation and reduction reactions. One example is a cell composed of zinc and copper metals in which electrons travel from the zinc to the copper. Each electrochemical cell features a circuit consisting of several components that allow for the flow of electrons.
An electrochemical cell circuit includes an anode, cathode, electrolyte, salt bridge and external circuit. At the anode, oxidation reactions in which electrons are lost occur, while electrons are gained via reduction at the cathode. The anode and cathode are connected via the external circuit.
Scientists are able to create electrochemical cells by inserting metallic electrodes into electrolytes. There are two main classifications of electrochemical cells: voltaic cells, also known as galvanic cells, and electrolytic cells. Voltaic cells are the type of electrochemical cells found in batteries. These cells generate electric currents, and a given battery may contain one or several of these cells. An exothermic reaction involving the release of energy occurs when an electrochemical cell is in voltaic mode.
Unlike voltaic cells, electrolytic cells use rather than generate electric currents. Chemical reactions do not occur spontaneously in electrolytic cells, so an electric current must be externally applied. Energy becomes absorbed inside the cell, classifying the reactions that occur within electrolytic cells as endothermic rather than exothermic.