Electrode

Common batteries have two electrodes.

An electrode is an electrical conductor used to make contact with a non-metallic part of a circuit, for example a semiconductor, an electrolyte, the group vacuum (in a thermoionic valve), a gas (in a neon lamp, or argon), etc. The word was coined by the scientist Michael Faraday as a composition of the Greek words elektron, which means amber and from which the word electricity comes; and hodos, which means way.

Anode and cathode in electrochemical cells

An electrode in an electrochemical cell. It refers to any of the two concepts, be it anode or cathode, which were also coined by Faraday. The anode is defined as the electrode at which electrons leave the cell and the oxidation process occurs, and the cathode is defined as the electrode at which electrons enter the cell and reduction occurs. Each electrode can become an anode or a cathode depending on the voltage applied to the cell. A bipolar electrode is an electrode that functions as the anode in one cell and the cathode in another.

Primary cell

A primary cell is a special type of electrochemical cell in which the reaction cannot be reversed, and the identities of the anode and cathode are therefore fixed. The anode is always the negative electrode. The cell can be discharged but not recharged.

Secondary cell

A secondary cell, a rechargeable battery for example, is a cell in which the reaction is reversible. When the cell is being loaded, the cathode becomes the negative electrode (-) and the positive (+) anode. This also applies to electrolytic cell. When the cell is being discharged, it behaves like a primary or voltaic cell, with the cathode as a positive electrode and the anode as negative.

Other anodes and cathodes

In a vacuum tube or a polarized semiconductor (diodes, electrolytic capacitors) the anode is the positive electrode (+) and the cathode the negative (-). The electrons enter the device through the cathode and leave the anode.

In a three electrodes cell, an auxiliary electrode is used only to connect with the electrolyte so that a current can be applied to the current electrode. The auxiliary electrode is normally made of an inert material, such as a noble metal or graphite.

Welding electrodes

In arc welding, an electrode is used as the pole of the circuit and the electric arc is generated at its end. In some cases, it also serves as a flux material. The electrode or metal rod is usually covered by a combination of different materials depending on its use. The functions of the coatings can be: electrical to achieve good ionization, physical to facilitate good weld bead formation, and metallurgical to achieve anti-oxidation properties and other characteristics.

Alternating current electrodes

For electrical systems that use alternating current, the electrodes are connections of the circuit to the object that will act under the electric current, but anode or cathode are not designated because the direction of the flow of electrons changes periodically, numerous times per second. An exception to this are systems in which the alternating current applied is of low amplitude (for example 10 mV) in such a way that the properties as anode or cathode are not altered, since the system is maintained in a state pseudo-stationary.

The electrodes are also considered metal rods covered with substances suitable for the type of welding. The most commonly used electrode sizes are 32.50 x 350 and 3.25 x 350 mm. The first number indicates the diameter of the electrode (1.5-2.5, etc.) and the second number the total length of the electrode.

Types of electrodes

• Electrodes for medical purposes, such as EEG, EKG, ECT, defibrillator;
• Electrodes for Electrophysiology techniques in biomedical research;
• Electrodes for electric chair execution;
• Electrodes for galvanoplasty;
• Welding electrodes;
• Chodic protection electrodes;
• Inert electrodes for hydrolysis (platin)
• Electrodes for grounding, also known as pica or jabalina;
• Ultramicroelectrode;
• Rotary ring-disco electrode;
• Calomel electrode;
• Electrode of work;
• Reference electrode;
• Pararrayos.