Katodien

Katodien are the electrodes that serve as the site of reduction in electrochemical systems, and, in vacuum electronic devices, the electron-emitting electrode of a diode or similar tube. In electrochemistry, the katode is the electrode at which reduction occurs: cations in the electrolyte gain electrons and are deposited or reduced. The katode acts as the sink for electrons supplied by the external circuit. Materials for katoden can be inert, such as platinum or graphite, or active metals like copper or nickel, depending on the chemical reaction. In applications such as electroplating and electrorefining, the object to be plated or refined is often connected as the katode, where metal deposition occurs.

In vacuum tubes and related devices, the katode is the source of electrons. It is typically heated in a thermionic cathode to emit electrons, or uses field emission in a cold cathode design. The emitted electrons are drawn toward the anode, producing an electric current through the evacuated tube. Common cathode materials include tungsten filaments and oxide-coated tungsten, sometimes with coatings designed to enhance emission and lifetime.

Across contexts, the katode is contrasted with the anode: the katode is where reduction or electron emission occurs, while the anode is where oxidation or electron collection takes place. The concept derives from the Greek katodos, meaning “the way down,” reflecting the historical perspective on the direction of current flow relative to the electrode.