Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g., a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential components in electrochemical cells, such as batteries, fuel cells, and electrolysis setups, where they serve as the interface between the electrical and ionic conduction pathways.

More specifically, an electrode can be defined as a point or surface at which electrical current enters or leaves an electrochemical cell or device. The direction of current flow defines the electrode's polarity.

There are two main types of electrodes within an electrochemical cell:

• Anode: The anode is the electrode where oxidation occurs. Oxidation involves the loss of electrons by a chemical species. Conventionally, in a galvanic cell (a cell that produces electricity), the anode is negatively charged. However, in an electrolytic cell (a cell that uses electricity to drive a non-spontaneous reaction), the anode is positively charged. The confusion arises from the differing frames of reference (electron flow vs. conventional current flow).

• Cathode: The cathode is the electrode where reduction occurs. Reduction involves the gain of electrons by a chemical species. Conventionally, in a galvanic cell, the cathode is positively charged. Conversely, in an electrolytic cell, the cathode is negatively charged.

The material used for an electrode is often chosen based on its conductivity, chemical inertness (resistance to corrosion or reaction within the electrochemical cell), and compatibility with the electrolyte and the chemical reactions occurring. Common electrode materials include metals (e.g., platinum, gold, copper, silver), carbon (e.g., graphite, glassy carbon), and semiconductors.

Electrodes are also used in various other applications, including:

• Welding: An electrode provides the electrical current to create an arc and melt the metals being joined.

• Medical devices: Electrodes are used in electrocardiograms (ECGs) to measure heart activity and in electroencephalograms (EEGs) to measure brain activity. They are also used in therapeutic applications, such as transcutaneous electrical nerve stimulation (TENS).

• Electronics manufacturing: Electrodes are used in processes such as electroplating and etching.

The performance and functionality of an electrode are crucial to the overall efficiency and effectiveness of the device or process in which it is employed.