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Application of electrochemical sensor in gas sensor

by:Rika Sensors     2021-11-23
Application of electrochemical sensor in gas sensor
With the development of science and technology, the application of gas sensors has become more and more extensive. Driven by ubiquitous applications such as the Internet of Things, the development direction of gas sensors has begun to develop in the direction of miniaturization, integration, modularization, and intelligence. Among them, electrochemical sensors are popular in the field of gas detection due to their linear output, low power consumption, and better resolution. In addition, electrochemical gas sensors have better measurement repeatability and accuracy than other sensors. After decades of technological development, electrochemical gas sensors have very good selectivity for specific gas monitoring.

In the beginning, electrochemical sensors were used to monitor oxygen concentration. With the evolution of technology, electrochemical sensors for monitoring and detecting a variety of different toxic gases in the LEL range began to appear, and electrochemical sensors It also shows good sensitivity and selectivity in practical applications, so until now, electrochemical sensors are still the main sensors for monitoring gas concentration. At present, electrochemical sensors have been widely used in many static and mobile applications, and have played a vital role in the monitoring of multiple gases in the occasion. The following editor briefly introduces the relevant knowledge of electrochemical gas sensors:

1. Principles of electrochemical sensors

Most electrochemical gas sensors are used in diffusion mode. In this mode, the surrounding environment The gas sample in the sensor enters the sensor through the small hole on the front of the sensor (through the natural flow of gas molecules). Some devices draw air/gas samples into the sensor through a suction pump. A breathable membrane is installed at the air hole to prevent water or oil from entering the sensor. The measuring range and sensitivity of the sensor can be changed by adjusting the size of the air inlet during design. A larger air inlet can increase the sensitivity and resolution of the device, while a smaller air inlet reduces the sensitivity and resolution, but can increase the measurement range.

Second, the composition of the electrochemical sensor

1. The breathable membrane (also called hydrophobic membrane)

The breathable membrane is used to cover the sensing (catalytic) electrode, and in some cases it is used to control the arrival The molecular weight of the gas on the electrode surface. Such barriers are usually made of low-porosity Teflon films. This type of sensor is called a coated sensor. Alternatively, it can also be covered with a high-porosity Teflon film, and the molecular weight of the gas reaching the electrode surface can be controlled with a capillary. This type of sensor is called a capillary sensor. In addition to providing mechanical protection for the sensor, the membrane also has the function of filtering out unwanted particles. In order to transmit positive gas molecular weight, it is necessary to select the correct pore size of the membrane and capillary. The pore size should be able to allow a sufficient amount of gas molecules to reach the sensing electrode. The pore size should also prevent leakage or rapid drying of the liquid electrolyte.

2. Electrode

The choice of electrode material is very important. The electrode material should be a catalytic material that can perform a semi-electrolytic reaction for a long time. Generally, electrodes are made of precious metals, such as platinum or gold, which react effectively with gas molecules after being catalyzed. Depending on the design of the sensor, in order to complete the electrolysis reaction, the three electrodes can be made of different materials.

3. Electrolyte

The electrolyte must be able to carry out the electrolysis reaction and effectively transfer the ionic charge to the electrode. It must also form a stable reference potential with the reference electrode and be compatible with the materials used in the sensor. If the electrolyte evaporates too quickly, the sensor signal will be weakened.

4. Filter

Sometimes a scrubber filter is installed in front of the sensor to filter out unwanted gas. The selection of filters is limited, and each filter has a different degree of efficiency. The commonly used filter material is activated carbon. Activated carbon can filter out most chemical substances, but it cannot filter out carbon monoxide. By choosing the right filter material, the electrochemical sensor can have higher selectivity for its target gas.

3. The working method of the electrochemical sensor

The working method of the electrochemical sensor is mainly to work by chemically reacting with the measured gas and producing an electrical signal proportional to the gas concentration. A typical electrochemical sensor consists of a sensing electrode and a counter electrode, separated by a thin electrolytic layer. The gas will react with the sensor through tiny capillary-shaped openings, and then reach the electrode surface through the hydrophobic barrier layer. Using this method can allow an appropriate amount of gas to react with the sensing electrode to form a sufficient electrical signal, while preventing the electrolyte from leaking out of the sensor.

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