When carbon monoxide gas diffuses through the air holes on the shell and the gas-permeable membrane to the surface of the working electrode, it undergoes oxidation on the working electrode under the catalytic action of the electrode. The chemical reaction formula is as follows:CO+H2O→CO2+2H++2e−
The H+ ions and electrons generated by the oxidation reaction on the working electrode are transferred through the electrolyte to the counter electrode, which is spaced a certain distance from the working electrode, where they react with oxygen in water in a reduction reaction. The chemical reaction formula is:
21O2+2H++2e−→H2O
Therefore, a reversible redox reaction occurs inside the sensor, with the overall chemical reaction formula:
2CO+O2→2CO2
This reversible redox reaction takes place continuously between the working electrode and the counter electrode, generating a potential difference between the two electrodes.
However, the reactions occurring on both electrodes will cause electrode polarization, which makes it difficult to maintain a constant potential between the electrodes and thus limits the detectable range of carbon monoxide concentrations.
To maintain a constant potential between the electrodes, a reference electrode is added. In a three-electrode electrochemical gas sensor, the output signal reflects the potential change between the reference electrode and the working electrode. Since the reference electrode does not participate in oxidation or reduction reactions, it can maintain a constant potential between the electrodes (i.e., potentiostatic condition). Under this condition, the potential change is directly related to the change in carbon monoxide concentration. When the gas sensor generates an output current, its magnitude is proportional to the gas concentration. By measuring the output current of the sensor through an external circuit connected via electrode leads, the concentration of carbon monoxide can be detected with a wide linear measurement range. In this way, by connecting a signal acquisition circuit and corresponding conversion and output circuits to the gas sensor, the detection and monitoring of carbon monoxide gas can be achieved.
Carbon monoxide sensors are widely used in air quality
detection scenarios such as mines, automobiles, and households.
