Introduction to Electrochemical Probes for Gas Detectors
A considerable portion of its flammable, toxic and harmful gases have electrochemical activity and can be electrochemically oxidized or reduced. By utilizing these reactions, gas composition can be distinguished and gas concentration can be detected. There are many subcategories of electrochemical gas sensors:
(1) The principle of primary cell type gas sensors (also known as Gavoni cell type gas sensors, fuel cell type gas sensors, and spontaneous cell type gas sensors) is similar to that of dry batteries we use, except that the carbon manganese electrode of the battery is replaced by a gas electrode. For example, in an oxygen sensor, oxygen is reduced at the cathode, and electrons flow through the ammeter to the anode, where the lead metal is oxidized. The magnitude of the current is directly related to the concentration of oxygen. This type of sensor can effectively detect oxygen, sulfur dioxide, chlorine gas, etc.
(2) The constant potential electrolytic cell type gas sensor is very effective in detecting reducing gases. Its principle is different from that of original battery type sensors. Its electrochemical reaction occurs under the force of current, making it a true sensor for Coulomb analysis. This type of sensor has been successfully used in the detection of gases such as carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, etc. It is currently the mainstream sensor for detecting toxic and harmful gases.
(3) Concentration battery type gas sensors, with electrochemically active gases on both sides of the electrochemical cell, will spontaneously form concentration electromotive force. The magnitude of the electromotive force is related to the concentration of the gas. Successful examples of such sensors are oxygen sensors for automobiles and solid electrolyte type carbon dioxide sensors.
(4) A limit current gas sensor is a type of sensor that measures oxygen concentration. It utilizes the principle that the limit current in an electrochemical cell is related to the carrier concentration to prepare an oxygen (gas) concentration sensor, which is used for oxygen detection in automobiles and for detecting oxygen concentration in molten steel.
