The working life and long-term stability of electrochemical formaldehyde sensors are the main obstacles restricting the popularization and application of formaldehyde sensors in the field of home appliances. The key problem is how to improve the long-term working stability of the internal core components of the sensor. This is to solving the current formaldehyde sensor’s short service life and poor resistance to external harsh environments. In this study, we develop a formaldehyde sensor based on a new electrolyte and anti-interference catalyst formulation.
We carry out the anti-alcohol interference experiment and the life experiment in a targeted manner. It is in the air-conditioning mode and the simulated scenario experiment. The results show that the new electrolyte and anti-interference catalyst formulation optimized and designed can effectively improve two aspects. 1. The long-term working stability and working life of the sensor. 2. The anti-interference ability of the formaldehyde sensor to deal with external environmental gas pollution sources. This research plays an important role in broadening the application of electrochemical formaldehyde sensors in the field of home appliances.
In recent years, the Internet is developing and people pay more attention to air. The demand for sensors in smart homes, vehicle equipment, smart mobile terminals and other fields is increasing day by day. However, the working life and long-term stability of electrochemical formaldehyde sensors are the main obstacles that restrict their popularization and application in the field of home appliances. The sensor has a short life and long-term response to external environmental performance degradation. This often results in inaccurate detection results and false alarms in the detection system. And it further restricts the wide application of sensors in various fields. The long-term stability of electrolyte materials and catalysts is one of the bottlenecks restricting the application of formaldehyde sensors.
Therefore, we develop a long-term formaldehyde sensor. And we further carry out simulated scene experimental analysis and long-term work stability research. They are based on the optimized design of the new electrolyte and anti-interference catalyst formulation. The experimental results show that the new electrolyte and anti-interference catalyst formulation can effectively improve two aspects. 1. The sensor’s resistance to damage and interference caused by high temperatures, high humidity, high concentration etc. 2. The long-term working stability of the formaldehyde sensor. This research has a positive effect on broadening the application of formaldehyde sensors in the field of home appliances.
The formaldehyde sensor used in this experiment is an electrochemical sensor element. First, the acid-base electrolyte commonly used in the industry replaces the self-developed new electrolyte . At the same time, we spray the self-developed anti-poisoning catalyst formula slurry on the surface of the new electrolyte membrane. This is to make the sensor electrode. And then assemble the cover body, support sheet, electrode, dust-proof breathable film, signal lead-out PCB board and metal leads. After that, the fabricated sensor gets older for 1 month under specific working conditions. Among them, the anti-interference catalyst slurry formulation mainly includes four kinds. 1. Platinum powder. 2.Nano-carbon. 3.An appropriate amount of doped multi-system precious metals 4. Other active ingredients. The performance of the sensor is tested by using the static test method.
First, the sensor element was put into a sealed test chamber.And a specific concentration of test gas was added and mixed uniformly. Then, a spectrophotometer was used to sample and test. And further comparative analysis was carried out between the homemade and commercial electrochemical formaldehyde sensors. Among them, 1# is the formaldehyde sensor based on the new electrolyte and anti-interference catalyst slurry formulation in this study; 2#, 3#, 4# are commercial electrochemical formaldehyde sensors produced by Company A, Company B and Company C. The above electrochemical formaldehyde sensors are based on the working principle of fuel cells.
The test scheme of each simulated scene experiment is as follows:
(1) Simulated high-temperature experiment: We place the sensor in a test box with a temperature of 70°C for 168 hours.
(2) Simulated low-temperature experiment: We place the sensor in a test box with a temperature of -20℃ for 168 hours.
(3) Simulated high-temperature and high humidity experiment: We place the sensor in a test box with a temperature of 60°C and a humidity of 93% for 168 hours.
(4) Life-acceleration experiment: We place the sensor in a sealed chamber with a high concentration of 10 mg/m3 formaldehyde for 500 hours.
(5) Simulated alcohol interference experiment: Plan 1: Test the sensor in a test chamber with 30m3 and an alcohol concentration of 10 ppm. Plan 2: we place A certain brand of liquor with 53 vol%, and four glasses of 180 mL wine in a home restaurant of 70m2 for 4 hours. The air conditioner is refrigerating with a high wind speed, and the doors of each room are in the same open and closed state as usual; we install the sensor in the side area of the hanging air conditioner.
Therefore, for the formaldehyde sensor in this study, the influence of high temperatures on the sensor is a little. In the actual transportation, storage or working process of the air conditioner, the sensor can ensure the reliability of continuous operation and storage under extremely high temperatures. For the current commercial formaldehyde sensors 2#, 3#, and 4#, traditional liquid acid-base electrolytes are used as proton conduction media. Under high temperatures, the water in the electrolyte is easily lost, which leads to an increase in the system concentration. As a result, the ability of the electrolyte system to conduct protons gradually deteriorates, or even loses its ability to conduct protons. At the same time, at a long-term high temperature, it may seriously damage the reactivity of the internal catalyst material.
The above problems will eventually cause sensors 2#, 3# and 4# to be unable to resist the destructive effect of the external high-temperature environment. The sensor 1# in this study adopts a new type of electrolyte system, which is different from the current traditional electrolyte system. It has excellent thermal stability and chemical stability, and moisture can be effectively and stably confined in the electrolyte system. After treatment at a high temperature, the ability of the electrolyte system to conduct protons will not be destroyed. Therefore, compared with the current commercial sensors 2#, 3#, and 4#, the formaldehyde sensor 1# in this study has the characteristics of high-temperature resistance at 70°C, which lays the foundation for ensuring its application in the air conditioner.
1.Figure 1 High-temperature decay curve of sensors
Anti-alcohol interference tests
In order to verify that the sensor can resist the false detection and false alarm caused by family life, we reflect the anti-interference ability of the sensor to continuously work under the environmental conditions with interference sources by simulating the scene of drinking in a family gathering for a long time. It shows the formaldehyde concentration output result of the sensor in Figure 2; People carried out the anti-alcohol interference experiment in a user’s home with an area of 70m2, and it shows its distributions of internal layout and test point in Figure 3.
2.Figure 2 The formaldehyde concentration output of the sensor in the anti-alcohol interference experiment
3.Figure 3 The distribution of home interior layouts and test points
Figure 2a is the output of the sensor’s anti-alcohol interference performance in an experimental chamber with an area of 30m3 by creating an environment with 10 ppm alcohol to simulate a drinking scene. Through comparison, we find that in the atmosphere of 10 ppm alcohol, the commercial formaldehyde sensor 2# is seriously bursting, and the displayed formaldehyde concentration is 4 to 5 mg/m3, far exceeding the national standard safety line of 0.1 mg/m3.
The formaldehyde concentration output by commercial formaldehyde sensors 3# and 4# also reaches 0.1 to 0.2 mg/m3, which exceeds the national standard safety line, that is to say, under a certain alcohol concentration environment, the currently commercialized formaldehyde sensors 2#, 3#, and 4# are weak in resisting alcohol interference. When we apply them to air conditioners, there will be obvious false detections and false alarms. For the formaldehyde sensor 1# based on the new electrolyte and anti-interference catalyst slurry formulation in this study, under the atmosphere of 10 ppm alcohol, the formaldehyde concentration of the formaldehyde sensor is less than 0.1 mg/m3, which is lower than the national standard safety line, and the anti-alcohol interference is less than 1%.
At the same time, we further simulate the scenario of drinking for 4 hours in the user’s home to verify the anti-interference ability of each sensor, as shown in Figure 2b. The formaldehyde sensor 2# is still seriously bursting, and the formaldehyde concentration output by formaldehyde sensors 3# and 4# also reaches 0.15 to 0.35 mg/m3, which exceeds the national standard safety line. However, the concentration output of the formaldehyde sensor 1# in this study is less than 0.05 mg/m3 in the long-term range, which is significantly lower than the national standard safety line.
It has good resistance to alcohol interference. We can apply it to air conditioners, which will effectively reduce the probability of false detection and false alarms and improve the user experience. The highly selective active composition of the multi-precious metal system in the catalyst slurry formulation designed in this study may mainly causes the above differences in anti-interference ability. This can significantly reduce the adsorption and chemical action of alcohol molecules, thereby showing excellent anti-alcohol interference ability.
3.3 Simulation scene experiment
|Before the experiment
|After the experiment
|Before the experiment
|After the experiment
|Before the experiment
|After the experiment
|Before the experiment
|After the experiment
|High and low temperature impact
|High-temperature and high humidity
Before and after the experiment, the sensor was tested by liquid formalin in an experimental chamber with an area of 30m3 to create a formaldehyde concentration of 0.1mg/m3. Among them, after the experiment, the sensor needs to be continuously powered on for 24 hours in an indoor environment before testing.It can be seen from Table 1 that for the sensors 1# to 4#, the detection accuracy of the sensor before and after the experiment remains unchanged after the drop and scanning vibration experiments, indicating that when they are applied to products such as air conditioners in the later stage, the sensor may be subjected to physical vibration or falling due to the installation, transportation or operation process, and it won’t affect the normal use of the sensor. They all show low sensitivity to external physical vibration and other behaviors.
At the same time, for the low-temperature experiment, the output characteristics of the sensor can be recovered before and after the experiment, which shows that in the low-temperature environment, both the traditional electrolyte system and the new electrolyte and catalyst formulation system of this study can resist the damage due to low temperatures, thus ensuring the resistance to transport or storage at low temperatures for the sensor. For the high and low temperature impact test, there are different degrees of attenuation for the detection accuracy of commercial sensors 2#, 3# at low temperatures of -20°C and high temperatures of 60°C reaching -52%, -55%, -52% and -36%.
This may be caused by the gradual loss of water in the electrolyte inside the sensor during the high-temperature experiment at 60°C and the increase of the electrolyte concentration, which leads to the gradual deterioration of the electrolyte’s ability to conduct protons, which in turn leads to irreversible degradation of the detection accuracy of the sensor.
For the sensor 1# of this study, the frequent impact of high and low temperature has a limited impact on the new electrolyte system and catalyst formulation system inside the sensor, which also shows that the sensor has good safety performance and reliability at the high and low temperature transient environment. For high-temperature and high-humidity experiments with a temperature of 60°C and humidity of 93%), commercial sensors 2#, 3#, and 4# all show varying degrees of attenuation of detection accuracy, reaching -50%, -59% and -47%. This may be caused by the fact that the sensor is prone to leakages in a high temperature and high humidity environment, resulting in irreversible degradation of the detection accuracy of the sensor.
However, the sensor 1# in this study adopts a new electrolyte system, and the high temperature and high humidity environment will not cause the sensor to leak so as to avoid the damage to the proton conductivity caused by high temperatures. Therefore, compared with the current commercial sensors, the formaldehyde sensor in this study can effectively resist the damage of the sensor element caused by the external harsh environment, which plays an important role in improving the long-term working stability and service life of the sensor.
Figure 4 The accelerated aging model of the sensor
3.4 Lifetime acceleration experiment
In order to verify that the sensor element can continue to work normally in an environment with a certain degree of pollution for a long time, an accelerated life experiment is carried out in a high-concentration formaldehyde environment to simulate the accelerated aging of the sensor device, as shown in Figure 4. An environment with a formaldehyde concentration of 10mg/m3 is created in the experimental chamber. After the test time t, when natural attenuation is reduced to 1mg/m3, the formaldehyde concentration is quantitatively supplemented to 10mg/m3, and repeat this process. During the period, the attenuation concentration data is monitored in real time, and the attenuation curve f(t) equals to at2 plus bt plus c; then the accumulated formaldehyde mass data A (mg/m3•h) in the test process simulated by the accelerated life experiment is calculated, as shown in the formula ( 1):
(1) Therefore, compared with the formaldehyde mass concentration (0.1 mg/m3) in the normal experiment, the working life N of the simulated accelerated experiment in this research, as shown in formula (2):
(2) The experimental verified that, under the specific test environment and conditions, the attenuation trend of each cycle is the same, as shown in Figure 4, and the calculated decay curve is: f(t)=0.0016t 2 -0.3286t+8.8202. As shown in Figure 5, the accumulated formaldehyde quality data for 21 days is: A=5544 mg/m3 •h; the detection accuracy attenuation is 26%, and the working life of the sensor in the calculation simulation acceleration experiment is: N=55440 h≈6.33 years.
For commercial sensors 2#, 3#, and 4#, after 21 days of accumulative experiments, the detection accuracy attenuation was 55%, 63%, and 36%, all exceeding the reasonable attenuation range of 30%. Therefore, the simulated accelerated working life of the formaldehyde sensor in this study is greater than and equal to 6 years. Compared with the commercial sensors 2#, 3#, and 4#, the sensor in this study can more effectively meet the normal use of the air conditioner during the warranty period.
Figure 5 Accelerated aging test curve of the sensor for 21 days
In this article, high-temperature experiments, simulated scene experiments, and anti-interference experiments were carried out based on the formaldehyde sensor element and commercial sensor based on the new electrolyte and anti-interference catalyst formulation. The experimental results show that the new electrolyte and anti-interference catalyst formulation optimized and designed in this experiment can effectively improve its resistance to damage and interference caused by external high temperatures, high humidity, high concentration and other harsh environmental changes, and effectively improve the long-term stability of formaldehyde sensor elements. This has important promotion and significance for the subsequent development of formaldehyde sensors with long service life and good anti-interference ability, and broadening their application in the field of home appliances.
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