Cathode

The cathode is an electrode in electrical devices and chemical cells that plays a key role in electron transfer. In electrochemistry, the cathode is defined as the electrode where reduction occurs. In a galvanic (voltaic) cell, the cathode is the positive terminal because reduction takes place there and electrons flow toward it. In an electrolytic cell, the cathode is the negative terminal, since an external power source drives electrons into that electrode to force reduction.

In electroplating and electrolysis, the cathode is the object or surface that is reduced and gains material or a chemical species. For example, in plating, metal ions in solution are reduced and deposited onto the cathode.

In electronics and vacuum devices, the cathode refers to the electrode that emits electrons. In thermionic devices such as vacuum tubes and cathode-ray tubes, the cathode is heated (hot cathode) to emit electrons. Some devices use field emission or other mechanisms for electron release. In semiconductor diodes, the term is used to describe the terminal from which conventional current leaves the device during forward bias; the anode is the terminal through which current enters.

Cathodes are made from various materials, including coated tungsten or other metals, chosen for efficient electron emission. The term cathode comes from the Greek kathodos, meaning “the way down,” in contrast to anodos, meaning “the way up.”