The oxygen probes currently on the market mainly use two technologies, namely electrochemical fuel cell and zirconia sensor technology. The working principles of these two technologies are quite different.

1) Electrochemical fuel cell technology:

The working principle of an electrochemical fuel cell is based on oxygen as the positive electrode and metallic lead as the negative electrode, and the electrolyte is potassium hydroxide. The electrolyte and metallic lead are contained in a small solvent-resistant cylindrical container, and the opening is sealed with a polytetrafluoroethylene film. The use of a completely sealed fuel oxygen sensor is one of the most advanced oxygen measurement methods in the world. Oxygen diffuses into the battery through the PTFE membrane. When the oxygen gets electrons on the positive electrode and the metal lead loses electrons on the negative electrode, a current is generated. The magnitude of the current is proportional to the oxygen concentration.

The negative electrode reaction formula is: 2Pb -4e-== 2Pb2+ The positive electrode is: O2 + 2H2O + 4e-== 4OH-

Total reaction: O2 + 2H2O+2Pb==2Pb2+4OH

2. Analysis of the advantages and disadvantages of the two oxygen probes.

1. Electrochemical fuel cell

Advantages: 1) The zero point is accurate, not easy to drift, and only needs a single point calibration; from the chemical reaction formula, it can be seen that when there is no oxygen, there is no current, so the zero point of the electrochemical fuel cell is accurate, and only a single point is required for calibration.

 2) Strong resistance to the influence of organic solvents. Electrochemical fuel cell detection of oxygen is a redox chemical process at room temperature, so it is less affected by a small amount of common organic solvents.

 3) The replacement cost is low, only the fuel cell needs to be replaced. When the fuel cell fails and the oxygen analyzer fails, the user only needs to replace the chemical fuel cell in the oxygen probe, and the replacement cost is less than one-third of the price of the entire probe.

    Disadvantages: 1) Prolonged contact of the oxygen probe with high-concentration oxygen will affect its life. The battery needs to be stored in a high-purity inert gas. This is when the glove box continues to operate normally and there is no misoperation, the probe life will be longer, up to more than 1 year. If there is a mistake in the glove box operation and more oxygen enters, the loss of the probe will be faster. Moreover, when the probe fuel cell is damaged, the oxygen value is generally zero, which is not easy to find.

2) Cannot be used to detect high temperature gas

2. Zirconia sensor

Advantages: 1) The reaction time is fast, and the oxygen concentration can be measured at high temperature, high pressure, and low pressure, such as boiler tail gas;

2) It can be in contact with the air when it is not detected, and can be stored in the air for a long time because the physical properties of the zirconia sensor are stable.

3) The zero point is not easy to deviate. It is usually calibrated with standard gas when measuring PPM gas; the probe measurement value is very accurate, the offset is small, and the detection repeatability is high. When detecting 1PPM gas, the concentration difference is more than 200,000 times. It is difficult to accurately detect and needs to be calibrated frequently. It is best to use a standard gas before each detection.

    Disadvantages: 1) Zirconia sensors need to work at high temperatures. When the detection gas contains an organic solvent, the organic solvent will chemically react on the electrode, and the oxygen will react with the organic matter and be consumed, making the measured oxygen value higher than the actual value.

   2) The zirconia probe has a long service life. Generally, it can be used normally for 3 to 5 years in an environment containing organic solvents. The service life of a solvent-free environment can generally reach more than 5 years. The sensor can be replaced when the sensor is damaged. But the cost is higher.