How do electrochemical gas sensors work, and what is the process of measuring the concentration of an incoming gas?

Electrochemical gas sensors detect the concentration of a gas by measuring the amount of current generated when a specific gas reacts with the electrodes inside the sensor. After filtering out impurities at the inlet, the gas undergoes a redox reaction at the sensing element to generate a current, which is then measured at the outlet to determine the gas concentration.

 

An electrochemical gas sensor is a device that detects a specific gas using a current generated through a chemical reaction. They detect gas leaks and measure concentration by measuring the amount of current generated as the incoming gas interacts with the sensor’s electrodes in a redox reaction.
Electrochemical gas sensors typically consist of an inlet, a sensing, and a backing section. The inlet part is responsible for filtering out impurities other than the gas to be detected when gas enters the sensor and consists of a dust filter, an interference gas filter, and a separator. When gas leaks into the air and enters the inlet of the sensor, non-gaseous impurities such as dust and water are first filtered out by the dust filter, and only gaseous gas is sent to the interference gas filter. Then, the interference gas filter adsorbs gases that interfere with the detection of a specific gas, and only the gas to be detected passes through the filter and is sent to the separator. The separator is a device that separates the inlet and detection parts, and the gas sent from the interference gas filter enters the detection part through the separator for accurate measurement.
The detection part is responsible for generating a current through a redox reaction when gas enters and consists of an action electrode, a response electrode, and a reference electrode. The current generated by the reference electrode is constantly flowing in the sensing part, and the electrodes of the sensing part are immersed in water with electrolyte dissolved in it. When dissolved in water, the electrolyte acts as a medium that enables the movement of electrons, generating a current. After passing through the separator and reaching the sensing part, the gas first reacts with the water at the working electrode, where it undergoes an oxidation reaction to produce hydrogen ions and electrons. To actively induce this oxidation reaction, the working electrode takes the form of a porous membrane with multiple pores and is coated with a catalyst, such as platinum, to increase the rate of the oxidation reaction. The hydrogen ions and electrons generated by the oxidation reaction are transferred to the counter electrode using the electrolyte as a medium, where the hydrogen ions and electrons combine with oxygen supplied from the oxygen inlet at the rear of the electrode and undergo a reduction reaction to become water. In this process, a current is generated as much as the amount of electron movement between the acting electrode and the counter electrode, and the amount of current generated is proportional to the concentration of the gas introduced.
Finally, the rear part is mainly responsible for checking gas leakage and measuring the concentration of leaked gas through the current generated by the detection part, and consists of a capacitor, a sensor pin, and an oxygen inlet. The newly generated current from the detection section is collected through the capacitor and moved to the sensor pin. The sensor pin compares the amount of newly generated current with the amount of normal current, and if the amount of newly generated current is higher, it detects a gas leak and measures the concentration of gas. To improve the accuracy of gas concentration measurements, the sensor also calibrates itself at regular intervals. During this process, the condition of the reference electrode and the counter electrode inside the sensor is checked, and the electrodes are cleaned or replaced as needed.
Meanwhile, if the gas detected by the gas sensor is above the reference concentration, the alarm connected to the sensor will sound an alarm to notify you. There are two types of alarms: immediate and delayed alarms. Immediate alarms are alarms that sound as soon as the gas concentration reaches the alarm threshold set on the sensor. This method is mainly used in cases where the gas itself is dangerous, such as toxic gases. The delayed alarm type does not alarm immediately when the concentration of the detected gas exceeds the alarm setting, but rather alarms when the concentration of the gas remains above the alarm setting for a set period of time. This is characterized by the fact that it does not alarm in temporary gas leakage situations, such as when a high concentration of gas is detected momentarily, such as a gas stove ignition malfunction.
In addition to this, electrochemical gas sensors can be made in different shapes and sizes depending on the type of gas. For example, there are sensors optimized for detecting specific gases, such as carbon monoxide (CO) sensors, hydrogen sulfide (H2S) sensors, and ammonia (NH3) sensors, which use different electrode materials and electrolytes to achieve maximum efficiency. In addition, sensors have been developed that are miniaturized or oversized for portable devices or industrial installations, and are used in a variety of environments.
Because of these advantages, electrochemical gas sensors play an important role in a variety of applications, including industrial applications, indoor air quality management, and home safety devices. With the advancement of gas sensors, more sophisticated and reliable detection technologies are being developed, enabling us to enjoy a safer and more comfortable living environment.