In electrolysis and gas discharge tubes, the positive electrode from which electrons leave the cell or tube. In a battery, the anode is the negative terminal by which electrons leave the battery. An anion is a negative ion that moves towards the positive anode in electrolysis.
An anode (from the Greek άνοδος = 'going up') is the electrode in a device that electrons flow out of to return to the circuit.
Flow of electrons
The flow of electrons is always from anode–to–cathode outside of the cell or device, and from cathode–to–anode inside the cell or device, regardless of the cell or device type. Inside a chemical cell, ions are carrying the electrons but the flow is still from cathode–to–anode inside the cell.
Inside chemical cells, there are two currents: negative ions (anions) flowing from cathode to anode, and positive ions (cations) flowing from anode to cathode, resulting in a net movement of electrons from cathode to anode. Inside solid state or transistor type cells the flow of electrons is also from cathode to anode within the cell.
Electrolytic anode
In electrochemistry, the anode is where oxidation occurs, and is the positive polarity contact in an electrolytic cell. At the anode, anions are forced by the electrical potential to react chemically and give off electrons (oxidation) which then flow up and into the driving circuit.
Battery or galvanic cell anode
In a battery or galvanic cell, the anode is the negative contact from which electrons flow towards the circuit.
Vacuum tube anode
In electronic vacuum devices such as a cathode ray tube, the anode is the positively charged electron collector. In a tube, the anode is a charged positive plate that collects the electrons emitted by the cathode through electric attraction.
Diode anode
In a semiconductor diode, the anode is the P-doped layer which initially supplies electrons to the junction. When a positive voltage is applied to anode of the diode from the circuit, more electrons are able to be transferred to the depleted region, and this causes the diode to become conductive, allowing current to flow through the circuit. The terms anode and cathode should not be applied to a zener diode, since it allows flow in either direction, depending on the polarity of the applied potential (i.e.
Sacrificial anode
In cathodic protection, a metal anode that is more reactive to the corrosive environment of the system to be protected is electrically linked to the protected system, and partially corrodes or dissolves, which protects the metal of the system it is connected to. When the charge on the system is reversed, the electrodes switch functions, so anode becomes cathode, while cathode becomes anode, as long as the reversed charge is applied.
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