[Structure of Electrochemical Gas Sensors] 

    Electrochemical gas sensors mainly use the chemical potential difference between two electrodes, one to measure the gas concentration in the gas, and the other is a fixed reference electrode. Electrochemical sensors work in constant potential electrolysis and galvanic cell mode. There are liquid electrolytes and solid electrolytes, and liquid electrolytes are divided into potential type and current type. The potential type uses the relationship between electrode potential and gas concentration for measurement; the current type uses the limiting current principle, using the diffusion of gas through a thin layer of breathable membrane or capillary pores as a current limiting measure to obtain stable mass transfer conditions and generate a limiting diffusion current proportional to the gas concentration or partial pressure.

    Electrochemical sensors have two-electrode and three-electrode structures, the main difference is whether there is a reference electrode. The two-electrode CO sensor has no reference electrode, has a simple structure, is easy to design and manufacture, and has a low cost. It is suitable for the detection and alarm of low-concentration CO. The three-electrode CO sensor introduces a reference electrode, which gives the sensor a larger range and good accuracy, but the introduction of the reference electrode increases the manufacturing process and material costs, so the price of the three-electrode CO sensor is higher than that of the two-electrode CO sensor, and is mainly used in the industrial field. The two-electrode electrochemical CO sensor is mainly composed of electrodes, electrolytes, electrolyte retention materials, filter materials for removing interfering gases, pins and other components.

[Working principle of electrochemical gas sensor] 

    Electrochemical gas sensor is a chemical sensor, which is generally divided into the following according to the working principle: 

    a. When the interface between the electrode and the electrolyte solution is kept at a constant potential, the gas is directly oxidized or reduced, and the current flowing through the external circuit is used as the output of the sensor; 

    b. The ions of the gaseous substance dissolved in the electrolyte solution and ionized react with the ion electrode, and the electromotive force generated thereby is used as the sensor output; 

    c. The electrolysis current generated by the reaction of the gas and the electrolyte solution is used as the sensor output; 

    d. Instead of using electrolyte solution, the sensor is made of organic electrolytes, organic gel electrolytes, solid electrolytes, solid polymer electrolytes and other materials.

[Detection of electrochemical gas sensor]

    Electrochemical gas sensors can be divided into four types: galvanic cell type, controllable potential electrolysis type, coulometric type and ion electrode type. 

    a. Galvanic cell gas sensor detects the volume fraction of gas by detecting current. Almost all commercially available instruments for detecting hypoxia are equipped with this sensor. 

    b. The controllable electrolytic sensor detects the volume fraction of the gas by detecting the current flowing during electrolysis. Unlike the primary cell type, it requires a specific voltage to be applied from the outside. In addition to detecting gases such as CO, NO, NO2, O2, SO2, it can also detect the volume fraction of oxygen in the blood.

    c. The coulometric gas sensor detects the volume fraction of the gas by the current generated by the reaction between the measured gas and the electrolyte.

    d. The ion electrode gas sensor appeared earlier and detects the volume fraction of the gas by detecting the ion polarization current. The main advantages of the electrochemical gas sensor are high sensitivity and good selectivity in detecting gas. 

    In summary, different types of gas sensors are suitable for different gas detection and control needs. With the development of modern industry, especially the continuous strengthening of the concept of green environmental protection, the development and application of gas sensor technology will surely have a very broad development prospect. The two-electrode electrochemical CO sensor has been a hot topic of research in recent years and is an internationally advanced sensor technology. Through experimental research, many technical difficulties that affect the life of the sensor have been overcome in the selection of materials and structural design of electrodes, filter layers, electrolytes, etc., and a new CO sensor with practical significance has been successfully developed. It will definitely play a positive role in the field of CO gas detection.