In this blog post, we will take a closer look at the structure and operating principle of electrochemical gas sensors to understand how gas leaks are detected as electrical signals in a simple and detailed manner.
An electrochemical gas sensor is a device that detects specific gases by utilizing the current generated through chemical reactions. This sensor measures the amount of current generated during the oxidation-reduction reaction between the incoming gas and the sensor electrodes to detect gas leaks and measure their concentration.
Electrochemical gas sensors generally consist of an inlet, a detection section, and a rear section. First, the inlet filters out impurities other than the target gas when gas enters the sensor. It consists of a dust filter, an interference gas filter, and a separation membrane. When gas leaks into the air and enters the inlet of the sensor, non-gaseous impurities such as dust and water are filtered out by the dust filter, and only gaseous substances are sent to the interference gas filter. In the interference gas filter, gases that interfere with the detection of the target gas are adsorbed by the filter, and only the target gas is allowed to pass through to the separation membrane. The separation membrane is a device that separates the inlet section from the detection section, and the gas sent from the interference gas filter is directed to the detection section through the separation membrane for accurate measurement.
The detection section generates a current through oxidation-reduction reactions when gas enters, and it consists of an active electrode, a counter electrode, and a reference electrode. In normal conditions, a constant current flows from the reference electrode, and the electrodes of the detection section are immersed in water containing an electrolyte. The electrolyte acts as a medium that enables the movement of electrons when dissolved in water, thereby generating a current. Gases that pass through the separator membrane and reach the sensing section first undergo an oxidation reaction at the working electrode, reacting with water to produce hydrogen ions and electrons. To actively induce this oxidation reaction, the working electrode is structured as a porous membrane with multiple holes and is coated with a catalyst such as platinum to increase the reaction rate. The hydrogen ions and electrons generated through the oxidation reaction move to the counter electrode via the electrolyte, where they undergo a reduction reaction with oxygen supplied from the oxygen inlet at the rear, forming water. During this process, a current is generated proportional to the amount of electron movement between the working electrode and the counter electrode, and the amount of current generated is directly proportional to the concentration of the incoming gas.
Finally, the rear section primarily functions to detect gas leaks and measure the concentration of leaked gas by utilizing the current generated in the detection section. It consists of a current collector, a sensor pin, and an oxygen inlet. The newly generated current in the detection section is collected at one point via the current collector and moves to the sensor pin. At the sensor pin, the amount of newly generated current is compared to the amount of current flowing under normal conditions. If the amount of newly generated current is greater, a gas leak is detected, and the concentration of the gas is measured. To enhance the accuracy of gas concentration measurement, the sensor undergoes a self-calibration process at regular intervals. During this process, the sensor checks the status of the reference electrode and the corresponding electrode inside the sensor, and performs cleaning or replacement of the electrodes as needed.
Meanwhile, when the gas detected by the gas sensor exceeds the reference concentration, the alarm connected to the sensor sounds an alarm to indicate this. There are two types of alarm methods: immediate alarm and delayed alarm. The immediate alarm type sounds an alarm immediately when the gas concentration exceeds the alarm threshold set on the sensor. This method is primarily used in cases where the gas itself is hazardous, such as toxic gases. Delayed alarm type does not trigger an alarm immediately even if the detected gas concentration exceeds the alarm threshold, but instead triggers an alarm after a set delay time if the gas concentration remains above the alarm threshold for the specified duration. This feature is useful in situations such as temporary gas leaks, where a high gas concentration is detected momentarily, such as in the case of a malfunction in a gas stove ignition.
In addition, electrochemical gas sensors can be manufactured in various forms and sizes depending on the type of gas. For example, there are sensors optimized for detecting specific gases such as carbon monoxide (CO), hydrogen sulfide (H₂S), and ammonia (NH₃), which use different electrode materials and electrolytes to achieve maximum efficiency. Furthermore, sensors have been developed in compact or large sizes to suit portable devices or industrial equipment, enabling their use in various environments.
Electrochemical gas sensors play an important role in various fields, such as industrial sites, indoor air quality management, and home safety devices, thanks to these advantages. With the advancement of gas sensors, more sophisticated and reliable detection technologies are being developed, enabling us to enjoy safer and more comfortable living environments.
