The use of a fully sealed fuel cell oxygen sensor is currently one of the most advanced oxygen measurement methods in the world. The fuel cell oxygen sensor consists of a highly active oxygen electrode and a lead electrode and is immersed in a KOH solution. At the cathode oxygen is reduced to hydroxide ions, and lead is oxidized at the anode. The O2 2H2O 4e?4OH?2Pb 4OH?2Pb(OH)2 4eKOH solution is separated from the outside by a layer of a polymer film, and the sample gas does not directly enter the sensor, so the solution and the lead electrode do not need to be regularly cleaned or replaced. Oxygen molecules in the sample gas are diffused into the oxygen electrode through the polymer film for electrochemical reaction. The current generated in the electrochemical reaction is determined by the number of oxygen molecules diffused into the oxygen electrode, and the diffusion rate of oxygen is proportional to that of the sample gas. The oxygen content, so that the size of the sensor output signal is only related to the oxygen content of the sample gas, regardless of the total amount of gas passing through the sensor. Through the connection of the external circuit, the charge transfer in the reaction, that is, the magnitude of the current is in direct proportion to the oxygen that participates in the reaction. Oxygen measurement using this method can avoid the influence of the reducing gas in the measured gas, eliminating many sample gas treatment systems. It is faster than the old “Goldnet-Lead†primary battery for oxygen measurement. It does not require a long boot-up purge process. The “Golden-lead†primary battery sample gas enters the solution directly, resulting in a large amount of maintenance of the instrument, and the fuel The battery sample gas does not enter the solution directly, and the sensor can work very stably and reliably for a long time. In fact, the fuel cell oxygen sensor is completely maintenance-free.
The core component of the zirconia sensor is a zirconium oxide solid electrolyte, and the zirconium oxide solid electrolyte is composed of multiple oxides. ZrO2·Y2O3, which is commonly used as such electrolytes, is composed of binary oxides. Among them, ZrO2 is called a matrix and Y2O3 is called a stabilizer. ZrO2 is a monoclinic crystal at room temperature, and it becomes a cubic crystal (fluorite type) at high temperature, but when it cools it becomes a monoclinic crystal, so the pure zirconium oxide crystal form is unstable. Therefore, when a certain amount of stabilizer Y2O3 is doped in ZrO2, because Y replaces the position of Zr, on the one hand an oxygen ion hole is left in the crystal, and on the other hand, the crystal is cooled because of the internal stress of the crystal. The cubic crystal remains afterwards, so it is also called stable zirconia. According to the above analysis, stable zirconia is a good conductor of oxygen ions at high temperatures (above 650°C).
In the above battery, Pt represents two platinum electrodes, which are coated on both sides of the zirconia electrolyte, and two gases having oxygen partial pressures of P''O2 and P'O2 pass through both sides of the electrolyte, respectively. As an oxygen sensor, where P''O2 is a reference gas, such as human air (20.6% O2), P'O2 is the gas to be tested, for example, flue gas. At high temperatures, since the zirconia electrolyte is a good oxygen ion conductor, the above battery is a typical oxygen concentration battery.
At high temperatures (650-850°C), oxygen will diffuse from the P''O2 side with a high partial pressure to the P'O2 side with a low partial pressure. This diffusion is not due to oxygen molecules passing through the zirconia from P. From the 'O2 side to the P'O2 side, the oxygen molecules dissociate into oxygen ions and pass through the zirconia process. At a high temperature of around 750°C, a reduction reaction takes place on the P''O2 side of the cell under the catalytic action of a platinum electrode, and one oxygen molecule takes four electrons from the platinum electrode and becomes two oxygen ions (O2-) into Electrolyte, ie:
The O2(P''O2)4e→2O2-P''O2 platinum electrode is positively charged due to a large amount of electrons, and becomes a positive electrode or an anode of an oxygen concentration cell. After these oxygen ions enter the electrolyte, they move forward through the holes in the crystal and reach the right platinum electrode. An oxidation reaction occurs on the P'O2 side of the battery. Oxygen ions release electrons on the platinum electrode and combine into oxygen molecules to precipitate. :
The platinum electrode on the P′ O 2 side is negatively charged due to a large amount of electrons, and becomes a negative electrode or a cathode of an oxygen concentration cell. In this way, on both electrodes, a potential is formed due to the accumulation of positive and negative charges, which is called an oxygen concentration difference electromotive force. When two electrodes are connected to a circuit by a wire, the electrons on the negative electrode flow through the external circuit to the positive electrode, and then the oxygen molecules are supplied to form ions, and a current flows in the circuit.
Where R is the gas constant, T is the thermodynamic temperature (K) of the cell, and F is the Faraday constant. (1) The formula is derived in an ideal state and must have four conditions: (1) Both sides of the gas are ideal gases; (2) The entire battery is in a constant temperature and constant pressure system; (3) The concentration battery is reversible (4) There is no additional potential in the battery. Therefore, (1) is called the theoretical equation of the zirconia sensor. It can be seen from the formula (1) that since the oxygen content of the reference gas P''O2 is known, the oxygen content P'O2 value of the gas to be measured can be obtained after the E value is measured.
From the above equation, at a temperature of 700°C, when the oxygen partial pressure of the solid dielectric side is air (20.6%), the electromotive force E is output from the concentration cell, and the oxygen partial pressure on the other side of the solid dielectric can be calculated. This is oxidation. Oxygen content analyzer oxygen measuring principle.
Gas industry terminology. It is a physical gas analyzer based on the physical phenomenon that the magnetic susceptibility of oxygen is far greater than the susceptibility of other gases to measure the oxygen content in the mixture. Since the direct measurement of the magnetic susceptibility value is complicated, indirect measurement is often used in industry, that is, the measurement is performed through a bridge circuit according to the thermomagnetic phenomenon in which the magnetic susceptibility decreases with increasing temperature. It is suitable for automatically and continuously measuring the oxygen content of various industrial gases.
The core component of the zirconia sensor is a zirconium oxide solid electrolyte, and the zirconium oxide solid electrolyte is composed of multiple oxides. ZrO2·Y2O3, which is commonly used as such electrolytes, is composed of binary oxides. Among them, ZrO2 is called a matrix and Y2O3 is called a stabilizer. ZrO2 is a monoclinic crystal at room temperature, and it becomes a cubic crystal (fluorite type) at high temperature, but when it cools it becomes a monoclinic crystal, so the pure zirconium oxide crystal form is unstable. Therefore, when a certain amount of stabilizer Y2O3 is doped in ZrO2, because Y replaces the position of Zr, on the one hand an oxygen ion hole is left in the crystal, and on the other hand, the crystal is cooled because of the internal stress of the crystal. The cubic crystal remains afterwards, so it is also called stable zirconia. According to the above analysis, stable zirconia is a good conductor of oxygen ions at high temperatures (above 650°C).
In the above battery, Pt represents two platinum electrodes, which are coated on both sides of the zirconia electrolyte, and two gases having oxygen partial pressures of P''O2 and P'O2 pass through both sides of the electrolyte, respectively. As an oxygen sensor, where P''O2 is a reference gas, such as human air (20.6% O2), P'O2 is the gas to be tested, for example, flue gas. At high temperatures, since the zirconia electrolyte is a good oxygen ion conductor, the above battery is a typical oxygen concentration battery.
At high temperatures (650-850°C), oxygen will diffuse from the P''O2 side with a high partial pressure to the P'O2 side with a low partial pressure. This diffusion is not due to oxygen molecules passing through the zirconia from P. From the 'O2 side to the P'O2 side, the oxygen molecules dissociate into oxygen ions and pass through the zirconia process. At a high temperature of around 750°C, a reduction reaction takes place on the P''O2 side of the cell under the catalytic action of a platinum electrode, and one oxygen molecule takes four electrons from the platinum electrode and becomes two oxygen ions (O2-) into Electrolyte, ie:
The O2(P''O2)4e→2O2-P''O2 platinum electrode is positively charged due to a large amount of electrons, and becomes a positive electrode or an anode of an oxygen concentration cell. After these oxygen ions enter the electrolyte, they move forward through the holes in the crystal and reach the right platinum electrode. An oxidation reaction occurs on the P'O2 side of the battery. Oxygen ions release electrons on the platinum electrode and combine into oxygen molecules to precipitate. :
The platinum electrode on the P′ O 2 side is negatively charged due to a large amount of electrons, and becomes a negative electrode or a cathode of an oxygen concentration cell. In this way, on both electrodes, a potential is formed due to the accumulation of positive and negative charges, which is called an oxygen concentration difference electromotive force. When two electrodes are connected to a circuit by a wire, the electrons on the negative electrode flow through the external circuit to the positive electrode, and then the oxygen molecules are supplied to form ions, and a current flows in the circuit.
Where R is the gas constant, T is the thermodynamic temperature (K) of the cell, and F is the Faraday constant. (1) The formula is derived in an ideal state and must have four conditions: (1) Both sides of the gas are ideal gases; (2) The entire battery is in a constant temperature and constant pressure system; (3) The concentration battery is reversible (4) There is no additional potential in the battery. Therefore, (1) is called the theoretical equation of the zirconia sensor. It can be seen from the formula (1) that since the oxygen content of the reference gas P''O2 is known, the oxygen content P'O2 value of the gas to be measured can be obtained after the E value is measured.
From the above equation, at a temperature of 700°C, when the oxygen partial pressure of the solid dielectric side is air (20.6%), the electromotive force E is output from the concentration cell, and the oxygen partial pressure on the other side of the solid dielectric can be calculated. This is oxidation. Oxygen content analyzer oxygen measuring principle.
Gas industry terminology. It is a physical gas analyzer based on the physical phenomenon that the magnetic susceptibility of oxygen is far greater than the susceptibility of other gases to measure the oxygen content in the mixture. Since the direct measurement of the magnetic susceptibility value is complicated, indirect measurement is often used in industry, that is, the measurement is performed through a bridge circuit according to the thermomagnetic phenomenon in which the magnetic susceptibility decreases with increasing temperature. It is suitable for automatically and continuously measuring the oxygen content of various industrial gases.
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