An electrode is a conductor through which electric current is passed. Found in variable forms, electrodes may be wires, plates, or rods. An electrode may be constructed of metal, such as copper, silver, lead, or zinc. However, an electrode may also be made of a nonmetal substance, such as carbon.

An electrode passes current between a metallic part and a nonmetallic part of an electrical circuit. Most frequently, conductors that are metallic carry electrical current. In other circuits, however, current is passed through a nonmetallic conductor.

In an electrochemical cell, an electrode is called either an anode or a cathode. An anode is an electrode at which current leaves the cell and oxidation takes place. For example, an anode is the positive electrode in a storage battery.

A cathode is described as a negative electrode. Current enters the cell at the cathode and reduction takes place. Electrons are repelled from the cathode.

When it comes to certain electric devices, like electric batteries, the anode may actually be negative and the cathode may be positive. In such cases, a conversion of non-electric energy to electric energy occurs and current flows from the negative electrode to the positive electrode. However, most familiar electronic devices involve current that flows from the positive electrode or anode to the negative electrode or cathode.

Depending on the particular voltage that is applied to a cell, an electrode may become an anode or a cathode. Some electrodes may perform both functions. For instance, a bipolar electrode acts as the anode to one cell, while functioning as the cathode of a different cell.

In a primary cell, the reaction cannot be changed or reversed and the anode and cathode values are fixed. Attempting to change the reaction in a primary cell can be dangerous. For example, attempting to reverse the reaction by recharging could cause a battery to explode. Primary cells are meant to be used just once.

A secondary cell allows for reversing the reaction. During charging the anode takes is place as the positive electrode and the cathode is negative. By contrast, the anode is the negative electrode when the cell is being discharged and the cathode plays the positive role.

In certain types of electrical systems, alternating currents are used. For such systems, electrodes are used as conductors, but are not defined as either anodes or cathodes. This is due to the fact that the direction of current is changed frequently. In fact, the flow direction may be changed multiple times within a mere second.