anode

An anode is the electrode in an electrical device or chemical cell where oxidation occurs. The designation of anode follows the rule that oxidation happens at this electrode, with the sign of the electrode depending on the cell type: in galvanic (voltaic) cells the anode is the negative electrode, whereas in electrolytic cells it is the positive electrode. In both cases, electrons are produced at the anode by oxidation, and the flow of these electrons through an external circuit drives the electrochemical reaction at the opposite electrode, the cathode.

In galvanic cells, the anode is the source of electrons and is consumed as the metal or compound is oxidized. A common example is the zinc anode in a Daniell cell: zinc metal oxidizes to Zn2+ ions, releasing electrons that travel through the external circuit to the copper cathode where reduction occurs. The anode thus acts as the site of oxidation and often dissolves or deposits ions into the electrolyte.

In electrolytic cells, the anode is positive because an external power source drives the oxidation reaction at this electrode. Electrons are drawn away from the anode into the external circuit, while reduction occurs at the cathode. Examples include the electrolysis of water or molten salts, where the anode may be inert (such as platinum or graphite) or active, depending on the process.

Applications of anodes include corrosion protection (sacrificial anodes), electroplating and refining, and various industrial electrolysis processes. In electronics, the term anode is also used to denote the positive electrode in diodes and vacuum tubes, where conventional current flows from the anode to the cathode when forward-biased.