Classification of Electrochemical Gas Detection Instruments
A considerable portion of flammable, toxic and harmful gases have electrochemical activity and can be electrochemically oxidized or reduced. By utilizing these reactions, the gas components can be distinguished and the gas concentration can be detected. Electrochemical gas sensors are divided into many subcategories:
(1) Primary battery type gas sensors (also known as: galvanic battery type gas sensors, some are also called fuel cell type gas sensors, and some are called spontaneous battery type gas sensors). Their principle is similar to that of the dry batteries we use. However, the carbon-manganese electrodes of the battery are replaced by gas electrodes. Taking an oxygen detector as an example, 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, etc.
(2) Constant potential electrolytic cell type gas sensors. This type of sensor is very effective for detecting reducing gases. Its principle is different from that of the primary battery type sensor. Its electrochemical reaction occurs under the coercion of current, and it is a true coulometric analysis sensor. This type of sensor has been successfully used in the detection of gases such as carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, etc., and is currently the mainstream sensor in toxic and harmful gas detectors.
(3) Concentration cell type gas sensors. Gases with electrochemical activity on both sides of the electrochemical cell will spontaneously form a concentration difference electromotive force, and the magnitude of the electromotive force is related to the concentration of the gas. A successful example of this type of sensor is the oxygen sensor used in automobiles and the solid electrolyte type carbon dioxide detector.
(4) Limiting current type gas sensors. There is a type of sensor for measuring oxygen concentration that uses the principle that the limiting current in the electrochemical cell is related to the carrier concentration to prepare an oxygen (gas) concentration sensor, which is used for the detection of oxygen in automobiles and the detection of oxygen concentration in molten steel.
