Four Main Types of Electrochemical Gas Detectors
A considerable number of flammable, toxic and hazardous gases possess electrochemical activity and can be electrochemically oxidized or reduced. These reactions are utilized to identify gas components and measure gas concentrations. Electrochemical gas sensors are divided into multiple subcategories:
① Galvanic Cell Gas Sensor (also named Voltaic Cell Gas Sensor, Fuel Cell Gas Sensor or Spontaneous Cell Gas Sensor) Its working principle is similar to that of ordinary dry batteries, except that the carbon-manganese electrodes of dry batteries are replaced with gas-sensitive electrodes. Taking an oxygen detector as an example, oxygen is reduced at the cathode, electrons flow through an ammeter to the anode, where lead metal undergoes oxidation. The magnitude of the generated current is directly proportional to the oxygen concentration. This type of sensor can effectively detect oxygen, sulfur dioxide, chlorine and other gases.
② Potentiostatic Electrolytic Cell Gas Sensor This sensor performs excellently in detecting reducing gases. Different from galvanic cell sensors, its electrochemical reactions are driven by applied external current, making it a genuine coulometric analysis sensor. It has been widely and successfully applied to the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine and other gases, and serves as the mainstream sensing element for current toxic and hazardous gas detectors.
③ Concentration Cell Gas Sensor Electrochemically active gases spontaneously generate a concentration-gradient electromotive force on two sides of the electrochemical cell, and the value of electromotive force correlates with gas concentration. Typical mature applications include automotive oxygen sensors and solid electrolyte carbon dioxide detectors.
④ Limiting Current Gas Sensor A type of oxygen concentration sensor is developed based on the principle that the limiting current in an electrochemical cell is proportional to carrier concentration. It is applied for oxygen measurement in automobile exhaust and dissolved oxygen detection in molten steel.
