Electrochemical sensors were originally used to monitor oxygen concentrations. With the development of science and technology, electrochemical sensors for monitoring and detecting a variety of different toxic gases in the LEL range began to appear, and electrochemical sensors also showed 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 many static and mobile occasions, and play a crucial role in the monitoring of various gases in the occasion. Electrochemical sensor working principle Most electrochemical gas sensors are used in diffusion mode, in which a gas sample from the surrounding environment enters the sensor (through the natural flow of gas molecules) through small holes in the front of the sensor. Some devices use an air pump to draw the air/gas sample into the sensor. A breathable membrane is installed at the air hole to block 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 intake can improve the sensitivity and resolution of the device, while a smaller air intake reduces sensitivity and resolution, but increases the measurement range. Electrochemical sensor composition 1. Breathable membrane (also known as hydrophobic membrane) Gas permeable membranes are used to cover sensing (catalytic) electrodes and in some cases to control the molecular weight of gases reaching the electrode surface. Such barriers are typically made from low-porosity Teflon films. This type of sensor is called a coated sensor. Alternatively, it is also possible to cover with a high porosity Teflon membrane while capillary tubes are used to control the molecular weight of the gas reaching the electrode surface. Such sensors are called capillary sensors. In addition to providing mechanical protection to the sensor, the membrane also has the function of filtering out unwanted particles. To deliver positive gas molecular weights, the correct membrane and capillary pore size needs to be selected. 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. Electrodes The choice of electrode material is important. The electrode material should be a catalytic material capable of performing semi-electrolytic reactions for a long time. Typically, electrodes are fabricated from noble metals, such as platinum or gold, which, after catalysis, react efficiently with gas molecules. Depending on the design of the sensor, the three electrodes can be made of different materials to complete the electrolysis reaction. 3. Electrolyte The electrolyte must be able to carry out the electrolytic reaction and efficiently transport the ionic charge to the electrodes. It must also have a stable reference potential with the reference electrode and be compatible with the materials used within 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 remove unwanted gases. There is a limited selection of filters, each with a different degree of efficiency. The commonly used filter material is activated carbon. Activated carbon can filter out most chemicals, but not carbon monoxide. By choosing the right filter media, electrochemical sensors can have higher selectivity to their target gas. How electrochemical sensors work The electrochemical sensor working method is mainly works by producing a chemical reaction 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 reacts with the sensor through tiny capillary-type openings and then passes through the hydrophobic barrier to the electrode surface. Taking this approach allows the right amount of gas to react with the sensing electrode to create a sufficient electrical signal, while preventing electrolytes from leaking out of the sensor.