Anode Anode Akio Morita Category="Electricity"Category="Electrochemistry"[image]

An anode (from the Greek άνοδος = 'going up') is the Electrode in a device that electrons flow out of to return to the circuit. Literally, the path through which the electrons ascend out of an Electrolyte solution. The other charged electrode in the same cell or device is the Cathode. For electrons to flow through the anode a positive charge is applied to the anode (attracting electrons).

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. (note that in most electronic circuit diagrams current is shown to flow from positive to negative but that the actual electrons in the circuit are flowing OPPOSITE to the electrical current diagram).

Electrolytic anode

In Electrochemistry, the anode is where oxidation occurs and is also the negative polarity contact in an Electrolytic cell. At the anode anions are forced by the electrical voltage potential to chemically react 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 that electrons flow from through the circuit. Internally the anions are flowing to the anodic material inside the cell which is connected to the negative contact of the cell; but, external to the cell in the circuit electrons are being pushed out through the negative contact and thus through the circuit by the voltage potential of the cell.

Vacuum tube anode

In electronic vacuum devices circuits 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. In the junction region the electrons supplied by the anode combine with holes supplied from the N-doped region creating a depleted zone. As the P-doped layer supplies electrons to the depleted region, positive dope ions are left behind in the P-doped layer ('P' for positive charge carrier ions). This creates a base charge of positive on the anode. 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 based on potential applied to the zener diode.

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 sytem it is connected to. As an example an Iron or Steel ship's hull may be protected by a zinc sacrificial anode which will dissolve into the seawater and prevent the hull from being corroded. Sacrificial anodes are particularly needed for systems where a static charge is generated by the action of flowing liquids, such as pipelines and watercraft.

Related antonym

The opposite of an anode is a Cathode. When the charge on the sytem is reversed the Electrodes switch functions and anode becomes Cathode, while Cathode becomes anode as long as the reversed charge is applied.