Definition - What does Cathode mean?

A cathode is the electrode through which the negatively charged electrons enter a device or a system from an external circuit in case of electrolytic cell, or it is the source of electrons in an electronic valve. In the case of a primary cell, the terminal can have a positive charge.

The study of cathodes is important because they are the basis of electrical, electronic and electrochemical process studies, which is fundamental to scientific applications, including corrosion prevention.

Corrosionpedia explains Cathode

A cathode has two basic meanings in two different situations:

  • In an electrolytic cell, the cathode terminal is connected to the negative power supply terminal, attracting positively charged particles.
  • In a voltaic cell, the cathode is the terminal receiving a positive charge due to electrochemical reaction, as in the case of a battery.

The corrosion process needs both a cathode and an anode as well as an electrolyte in order to occur. Most types of corrosion, except some forms of high-temperature corrosion, occur because of the formation of electrochemical cells. The corrosion cell has an anode, where a chemical reaction or oxidation and resultant material depletion or deterioration occur, a cathode terminal at which a reduction reaction occurs, and parallel conductive metallic and electrolytic flow paths connecting the anode and cathode through which electrons and ions flow. A potential difference is maintained by the reaction between the cathode and anode to drive the continuity of the cell. The potential generation can be due to the characteristics of the metals, conditions of the surface and the environmental chemical concentrations.

In some corrosion cells, electrons can flow along a conductive metal path from the surface site where anodic chemical reactions are taking place on surfaces, where cathodic reactions are enabled. Charged particles find a path through the electrolyte to ensure a balance to the flow of electrons. Anions flow in the direction of the anode, while cations flow in the direction of the cathode to maintain potential difference. The result is that the anode corrodes due to continued electrochemical reaction, while the cathode does not corrode.

In an electrical circuit, the cathode is differentiated from the anode on the basis of the direction of current. Electric current means the movement of electrical charge. By that convention, the direction of the current is based on how the positive charge moves, and not how a negative charge or electrons move. So, if electrons are flowing in one direction in a cell, then, by convention the current is flowing in the opposite direction. Thus, the cathode is an electrode which is negatively charged, attracting positive charge, and as a source of surplus electrons.

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