Electrochemical gas sensor

Electrochemical gas sensors are gas detectors that measure the concentration of a target gas by oxidizing or reducing the target gas at an electrode and measuring the resulting current. Beginning his research in 1962, Mr. Naoyoshi Taguchi became the first person in the world to develop a semiconductor device that could detect low concentrations of combustible and reducing gases when used with a simple electrical circuit. Devices based on this technology are often called "TGS" (Taguchi Gas Sensors). The sensors contain two or three electrodes, occasionally four, in contact with an electrolyte. The electrodes are typically fabricated by fixing a high surface area of precious metal onto the porous hydrophobic membrane. The working electrode contacts both the electrolyte and the ambient air to be monitored, usually via a porous membrane. The electrolyte most commonly used is a mineral acid, but organic electrolytes are also used for some sensors. The electrodes and housing are usually in a plastic housing which contains a gas entry hole for the gas and electrical contacts. The gas diffuses into the sensor, through the back of the porous membrane to the working electrode, where it is oxidized or reduced. This electrochemical reaction results in an electric current that passes through the external circuit. In addition to measuring, amplifying, and performing other signal processing functions, the external circuit maintains the voltage across the sensor between the working and counter electrodes for a two-electrode sensor or between the working and reference electrodes for a three-electrode cell. At the counter electrode, an equal and opposite reaction occurs, such that if the working electrode is an oxidation, then the counter electrode is a reduction. The magnitude of the current is controlled by how much of the target gas is oxidized at the working electrode. Sensors are usually designed so that the gas supply is limited by diffusion, and thus the output from the sensor is linearly proportional to the gas concentration.