With the development of science and technology, electrochemical sensors are used more and more widely. Electrochemical sensors have the advantages of low power consumption and high resolution, so they are more popular in the field of gas detection. The development direction of gas sensors begins to be miniaturized, integrated, modular and intelligent. In addition, compared with other sensors, electrochemical gas sensors have better measurement repeatability and accuracy. After decades of technological development, electrochemical gas sensors have very good selectivity for specific gas monitoring.
Electrochemical sensors were initially used to monitor oxygen concentrations. With the evolution of science and technology, electrochemical sensors for detecting various toxic gases in the LEL range begin to appear, and the electrochemical sensors also show good sensitivity and selectivity in practical applications. So until now, electrochemical sensors have been the main sensors for monitoring gas concentrations. At present, electrochemical sensors have been widely used in a number of static and mobile applications, plays a crucial role in the field of a variety of gas monitoring.
Principles of electrochemical sensors
Most electrochemical gas sensors are applied in diffusion mode, in which a sample of gas from the surrounding environment enters the sensor through small holes on the front of the sensor (natural flow of gas molecules). Some devices use a pump to pump air/gas samples into the sensor. A breathable membrane is installed in the stoma area to prevent water or oil from entering the sensor. The measuring range and sensitivity of the sensor can be changed by adjusting the inlet size at design time. A larger intake can improve the sensitivity and resolution of the device, while a smaller intake can reduce the sensitivity and resolution but increase the measurement range.
Working methods of electrochemical sensors
The working method is mainly through the chemical reaction with the measured gas and the output of electrical signals proportional to the concentration of the gas. A typical electrochemical sensor consists of a sensing electrode and a reverse electrode separated by a thin electrolytic layer. The gas reacts with the sensor through tiny capillary holes and then passes through a hydrophobic barrier to the electrode surface. This method allows the appropriate amount of gas to react with the sensor electrode to form a sufficient electrical signal while preventing electrolyte leakage from the sensor.
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Breathable membrane
The breathable film is used to cover the sensing (catalytic) electrode and in some cases to control the molecular weight of the gas reaching the electrode surface. Such barriers are usually made of Teflon films with low porosity.
Electrode
The choice of electrode material is very important. The electrode material should be a catalytic material capable of performing semi-electrolytic reactions for a long time. Typically, electrodes made of precious metals, such as platinum or gold, react effectively with gas molecules when catalyzed.
Electrolyte
The electrolyte must be able to perform electrolysis and efficiently transfer ionic charges to the electrode. It must also form a stable reference potential with reference to the electrode and be compatible with the material used in the sensor. If the electrolyte evaporates too quickly, the sensor signal will weaken.
Filters
The selection of filters is limited, each filter has a different degree of efficiency. The common filter material is activated carbon. Activated carbon can filter out most chemicals, but not carbon monoxide. By selecting the right filter material, the electrochemical sensor can be more selective to its target gas.
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