An electrochemical humidity sensor with high power generation and a preparation method thereof

Abstract

The application discloses an electrochemical humidity sensor with high power generation and a preparation method thereof, and belongs to the technical field of humidity-sensitive elements and humidity sensors. The electrochemical humidity sensor comprises a substrate, a pair of electrodes and a humidity-sensitive layer on the surface of the substrate, a positive electrode of the electrode is manganese dioxide, a negative electrode is aluminum, and the material of the humidity-sensitive layer is composed of metal salt and carbon nanotubes. The manganese dioxide-aluminum electrode has a high voltage window, which is used for improving the response voltage of the humidity sensor; the carbon nanotube has a large specific surface area, good hydrophilicity and conductive characteristics, promotes the adsorption of the humidity-sensitive layer to water molecules, and reduces the internal resistance of the sensor; and the electrode and the humidity-sensitive layer jointly improve the power generation of the electrochemical humidity sensor. The electrochemical humidity sensor has a wide humidity detection range, high output voltage and high power generation, and has a wide application prospect in self-powered humidity detection.

Description

Technical Field

[0001] This invention belongs to the technical field of humidity-sensitive elements and humidity sensors, specifically relating to a high-power electrochemical humidity sensor and its preparation method. Background Technology

[0002] With the continuous development of the Internet of Things and information technology, humidity measurement is becoming increasingly intertwined with people's daily lives, playing a vital role in industrial production, agricultural planting, climate monitoring, and even health management. For example, humidity sensors can be used to monitor human respiratory rate and assess skin moisture. Existing humidity sensors are mainly capacitive and resistive, and cannot operate independently of an external power source, resulting in typically large detection devices. Furthermore, in distributed humidity detection, powering and maintaining multiple sensors presents a challenge. Generating humidity sensors not only enable ultra-low power humidity detection but also promise to power the entire detection system with the electricity generated by humidity, thus solving the aforementioned problems. Therefore, the development of generating humidity sensors is of great significance.

[0003] Currently, power-generating humidity sensors can be categorized based on their working principles into triboelectric / piezoelectric nanogenerator type, ion diffusion type, and electrochemical type humidity sensors. Chinese patent application CN 109655492 A discloses a humidity sensor and method based on a triboelectric nanogenerator. This device belongs to the power-generating humidity sensor category, capable of generating different response voltages under different humidity stimuli. It is connected to a light-emitting diode (LED) and utilizes the LED's luminous intensity to indicate humidity levels. However, its operation requires spontaneous external mechanical energy to drive the triboelectric nanogenerator, which significantly limits its application scenarios. Chinese patent application CN 114350545 A discloses a flexible moisture-generating device based on ion diffusion and its application, belonging to the category of power-generating humidity sensors. This device consists of a microbial thin film, a bottom electrode, and a top porous electrode. The microbial thin film is obtained by drying electroactive bacteria (such as E. coli) and serves as the hygroscopic material. Although the device can spontaneously generate voltage, its open-circuit voltage and short-circuit current under high humidity conditions (80% RH) are only 0.28V and 3.4μA, respectively, making it difficult to achieve high power generation. Furthermore, the device exhibits poor humidity sensitivity. Chinese patent application CN 111879838A discloses a flexible paper-based voltage-type humidity sensor and its fabrication method. The sensor is fabricated by attaching copper and aluminum electrodes to both sides of paper soaked in an electrolyte solution. This belongs to the category of electrochemical humidity sensors. This device has a wide humidity response range (0%-91.5% RH) and a relatively large response voltage (~640mV).

[0004] In recent years, electrochemical humidity sensors have attracted widespread attention from researchers due to their inherent coupling of humidity sensing and power generation characteristics. Existing technology, "Self-Powered Graphene Oxide Humidity Sensor Based on Potentiometric Humidity Transduction Mechanism," discloses an electrochemical humidity sensor with a "sandwich" structure consisting of a reduced graphene oxide (rGO) positive electrode, a graphene oxide (GO) humidity-sensitive electrolyte, and a porous foamed nickel negative electrode, achieving a wide humidity detection range (20-90% RH) and a high output voltage (0.77V). Another existing technology, "Facile primary battery-based humidity sensor for multifunctional application," discloses a planar electrochemical humidity sensor consisting of a copper foil positive electrode, a lithium chloride humidity-sensitive electrolyte, and an aluminum foil negative electrode, achieving a wide humidity detection range (10.9-91.5% RH). However, the aforementioned electrochemical humidity sensors suffer from low low-humidity response (<25mV) and low output power (<1μW), limiting the realization of self-powered humidity detection. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical problems of low low humidity response and low power generation of existing power-generating humidity sensors, and to provide an electrochemical humidity sensor with high power generation and its preparation method.

[0006] The technical problem addressed by this invention is solved as follows:

[0007] A high-power electrochemical humidity sensor includes a substrate 1, a humidity-sensitive layer 2, a positive electrode 3, a negative electrode 4, and test leads 5. The positive electrode 3 and the negative electrode 4 are disposed on both sides of the upper surface of the substrate 1, with a channel in the middle. The humidity-sensitive layer 2 is located at the channel of the positive electrode 3 and the negative electrode 4 on the upper surface of the substrate 1, and its two ends are connected to the positive electrode 3 and the negative electrode 4, respectively. Test leads 5 are led out from the positive electrode 3 and the negative electrode 4, respectively. The positive electrode 3 is made of manganese dioxide, the negative electrode 4 is made of aluminum, and the humidity-sensitive layer 2 is composed of metal salts and carbon nanotubes.

[0008] More specifically, the metal salt is sodium chloride, lithium chloride, or potassium chloride; the carbon nanotubes are hydroxylated carbon nanotubes or carboxylated carbon nanotubes; the mass ratio of metal salt to carbon nanotubes is 1 to 15:1.

[0009] More specifically, the positive electrode 3 is composed of manganese dioxide, carbon black and sodium alginate; the mass ratio of manganese dioxide, carbon black and sodium alginate is 2 to 8:1:1; among which, carbon black is used to improve the conductivity of the electrode and sodium alginate is used as a binder.

[0010] More specifically, the distance between the positive electrode 3 and the negative electrode 4 is 0.1mm-2mm.

[0011] A method for fabricating a high-power electrochemical humidity sensor includes the following steps:

[0012] Step 1: Deposit the material of the positive electrode 3 on one side of the substrate 1 and dry it;

[0013] Step 2: Prepare a negative electrode 4 on the other side of the substrate surface where the positive electrode has been deposited;

[0014] Step 3: Deposit the metal salt and carbon nanotube mixture between the positive electrode 3 and the negative electrode 4 and dry it to form a humidity-sensitive layer 2;

[0015] Step 4: Lead out test leads 5 from the positive electrode 3 and the negative electrode 4 respectively to complete the preparation of the electrochemical humidity sensor.

[0016] Furthermore, the positive electrode 3 and the humidity-sensitive layer 2 in steps 1 and 3 are prepared by brushing, spraying, dipping or screen printing.

[0017] The beneficial effects of this invention are:

[0018] In the high-power electrochemical humidity sensor of the present invention, the manganese dioxide-aluminum electrode has a high voltage window, which can improve the response voltage of the electrochemical humidity sensor.

[0019] In the high-power electrochemical humidity sensor of the present invention, carbon nanotubes have a large specific surface area, good hydrophilicity and conductivity, which promote the adsorption of water molecules by the humidity sensitive layer and reduce the internal resistance of the sensor.

[0020] In the high-power electrochemical humidity sensor described in this invention, the output power of the electrochemical humidity sensor is improved by the combined action of the electrodes and the composite humidity-sensitive layer.

[0021] In the high-power electrochemical humidity sensor of the present invention, thanks to the improved output power of the sensor, the electrochemical humidity sensor can directly drive a microamplitude meter, thus constructing a simple passive visual humidity detection device. Attached Figure Description

[0022] Figure 1 This is a schematic cross-sectional view of the high-power electrochemical humidity sensor described in this invention.

[0023] Figure 2 The above is a dynamic response / recovery curve of the electrochemical humidity sensor described in the example.

[0024] Figure 3 The above are the response fitting curves of the electrochemical humidity sensor described in the example under different humidity levels.

[0025] Figure 4 The image shows the response of the electrochemical humidity sensor described in the example for 20 cycles switching between 0% RH and 91.5% RH.

[0026] Figure 5 The graph shows the output power versus load resistance of the electrochemical humidity sensor described in the example under different humidity levels.

[0027] Figure 6 This is a physical image of the electrochemical humidity sensor directly driving the microammeter as described in the embodiment. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] This embodiment provides a high-power electrochemical humidity sensor, the cross-sectional structure of which is shown in the figure below. Figure 1 As shown, the device includes a substrate 1, a humidity-sensitive layer 2, a positive electrode 3, a negative electrode 4, and test leads 5. The positive electrode 3 and the negative electrode 4 are disposed on both sides of the upper surface of the substrate 1, with a channel in the middle. The humidity-sensitive layer 2 is located at the channel between the positive electrode 3 and the negative electrode 4 on the upper surface of the substrate 1, and its two ends are connected to the positive electrode 3 and the negative electrode 4, respectively. Test leads 5 are led out from the positive electrode 3 and the negative electrode 4, respectively. The positive electrode 3 is made of manganese dioxide, the negative electrode 4 is made of aluminum, and the humidity-sensitive layer 2 is composed of metal salts and carbon nanotubes.

[0030] More specifically, the metal salt is sodium chloride, lithium chloride, or potassium chloride; the carbon nanotubes are hydroxylated carbon nanotubes or carboxylated carbon nanotubes; the mass ratio of metal salt to carbon nanotubes is 1 to 15:1.

[0031] More specifically, the positive electrode 3 is composed of manganese dioxide, carbon black and sodium alginate; the mass ratio of manganese dioxide, carbon black and sodium alginate is 2 to 8:1:1; among which, carbon black is used to improve the conductivity of the electrode and sodium alginate is used as a binder.

[0032] More specifically, the distance between the positive electrode 3 and the negative electrode 4 is 0.1mm-2mm.

[0033] In this embodiment, substrate 1 is an alumina ceramic sheet with dimensions of 10mm × 10mm × 0.5mm; humidity-sensitive layer 2 is prepared by brush coating of a mixed aqueous solution of sodium chloride and hydroxylated carbon nanotubes (mass ratio of 4:1), and the width of humidity-sensitive layer 2 (i.e., the distance between the positive and negative electrodes) is 0.5mm; positive electrode 3 is prepared by brush coating of an aqueous solution of a composite material of manganese dioxide, carbon black and sodium alginate (mass ratio of 4:1:1); negative electrode 4 is an aluminum foil, which is bonded to substrate 1 by a bonding process.

[0034] The working mechanism of the high-power electrochemical humidity sensor described in this embodiment can be explained by the adsorption / dissociation of water molecules and electrochemical reactions. The humidity-sensitive layer 2 can spontaneously absorb water molecules from the air, and some of the absorbed water molecules dissociate into H+. + and OH - (H2O=H + +OH - Simultaneously, the adsorbed water molecules can promote the dissociation of metal salts, forming cations and anions; on the other hand, they can also accelerate the redox reaction rate on the electrodes of the electrochemical humidity sensor. Specifically, a reduction reaction occurs on the manganese dioxide positive electrode, and the chemical reaction equation is as follows:

[0035] 2MnO2+2H + +2e - =Mn2O3 + H2O

[0036] An oxidation reaction occurs on the negative electrode of the aluminum foil. The chemical reaction equation is as follows:

[0037] Al-3e - =Al 3+

[0038] Therefore, the overall reaction equation for the high-power electrochemical humidity sensor described in this embodiment can be derived as follows:

[0039] 6MnO2+6H + +2Al=3Mn2O3+2Al 3+ +3H2O

[0040] During redox reactions, cations and anions migrate towards the positive and negative electrodes, respectively, and the rate of ion migration is affected by the number of ion transport pathways. The water film formed by absorbed water molecules can serve as a channel for ion transport, influencing the total number of ion transport pathways in the humidity-sensitive layer. Therefore, the output voltage and current of an electrochemical humidity sensor are correlated with humidity.

[0041] According to the power calculation formula (P=U) 2The output power of an electrochemical humidity sensor can be increased by improving its output voltage and reducing its internal resistance. In the high-power electrochemical humidity sensor described in this embodiment, the manganese dioxide-aluminum electrode has a high voltage window, which improves the response voltage of the humidity sensor. The large specific surface area, good hydrophilicity, and conductivity of carbon nanotubes promote the adsorption of water molecules by the humidity-sensitive layer, reduce the sensor's internal resistance, and increase the sensor's output power. Compared to humidity-sensitive electrolytes constructed from single metal salts, the humidity-sensitive layer prepared from the composite material of metal salts and carbon nanotubes can absorb more water molecules under low humidity conditions and has more ion transport pathways. Therefore, the combined effect of the electrode and the humidity-sensitive layer improves the output voltage and output power of the electrochemical humidity sensor.

[0042] The performance of the high-power electrochemical humidity sensor described in this embodiment was tested according to methods disclosed in the art. Specifically, the method was as follows: (a) The response voltage of the prepared electrochemical humidity sensor was tested using a KEITHLEY 6500 multimeter. Different relative humidity environments were obtained by the bubbling method and calibrated by a high-precision humidity sensor. The relative humidity (RH) included 0%, 10.9%, 18.7%, 28.8%, 41.1%, 51.9%, 60.8%, 72%, 79.3%, and 91.5%; (b) To verify the application of the electrochemical humidity sensor in a self-powered scenario, the prepared electrochemical humidity sensor was connected in series with a microammeter, and the sensor was placed in different humidity environments.

[0043] The dynamic response / recovery curve of the electrochemical humidity sensor described in this embodiment is as follows: Figure 2 As shown, it has a wide humidity detection range (10.1-91.5% RH), high output voltage (1.32V, 91.5% RH) and high output power (20.52μW, 91.5% RH).

[0044] The response fitting curves of the electrochemical humidity sensor described in this embodiment under different humidity levels are as follows: Figure 3 As shown in the figure, it can be seen that the voltage of the electrochemical humidity sensor described in this embodiment exhibits a quadratic response relationship with changes in relative humidity (R0). 2 >0.9).

[0045] The response graph of the electrochemical humidity sensor described in this embodiment for 20 cycles switching between 0% RH and 91.5% RH is shown below. Figure 4 As shown in the figure, the electrochemical humidity sensor described in this embodiment has good repeatability.

[0046] The output power versus load resistance curves of the electrochemical humidity sensor described in this embodiment under different humidity levels are shown in the following figures. Figure 5As shown, the electrochemical humidity sensor described in this embodiment has a high output power (20.52 μW) at 91.5% RH and still has an output power of 475 nW at 28.8% RH.

[0047] The physical diagram of the electrochemical humidity sensor directly driving the microammeter described in this embodiment is shown below. Figure 6 As shown in the figure, it can be seen that the electrochemical humidity sensor described in this embodiment can cause the pointer of the microammeter to deflect significantly under different humidity levels, and has great application potential in self-powered systems.

[0048] This embodiment also provides a method for preparing a high-power electrochemical humidity sensor, including the following steps:

[0049] Step 1: Apply the aqueous solution of manganese dioxide, carbon black and sodium alginate composite material to one side of the ceramic sheet with a fine brush and place it in a drying oven for 15 minutes (60℃) to complete the preparation of positive electrode 3.

[0050] Step 2: Cut the aluminum foil into a rectangle of 4.8mm*10mm, attach it to the other side of the surface of the ceramic sheet where the positive electrode 3 is located, and form a channel with a spacing of 0.5mm between it and the positive electrode 3 to complete the preparation of the negative electrode 4.

[0051] Step 3: Apply the mixed aqueous solution of sodium chloride and hydroxylated carbon nanotubes evenly to the grooves with a fine brush and place it in a drying oven for 15 minutes (60°C) to remove excess water, thus completing the preparation of the humidity-sensitive layer 2.

[0052] Step 4: Lead out test leads 5 from the positive electrode 3 and the negative electrode 4 respectively to complete the preparation of the electrochemical humidity sensor.

[0053] Furthermore, the positive electrode 3 and the humidity-sensitive layer 2 in steps 1 and 3 are prepared by brushing, spraying, dipping or screen printing.

[0054] Based on the above embodiments, the following designs can also be made:

[0055] (1) The humidity-sensitive layer 2 is a mixed aqueous solution of sodium chloride and hydroxylated multi-walled carbon nanotubes with a mass ratio of 6:1. The distance between the positive electrode 3 and the negative electrode 4 is 1 mm, and other parameters remain unchanged.

[0056] (2) Humidity-sensitive layer 2 is an aqueous solution of lithium chloride and carboxylated multi-walled carbon nanotubes in a mass ratio of 2:1, with other parameters remaining unchanged.

[0057] (3) The positive electrode 3 is composed of manganese dioxide, carbon black and sodium alginate in an aqueous solution with a mass ratio of 8:1:1, and other components remain unchanged.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-power electrochemical humidity sensor, characterized in that, The device includes a substrate (1), a humidity-sensitive layer (2), a positive electrode (3), a negative electrode (4), and test leads (5). The positive electrode (3) and the negative electrode (4) are disposed on both sides of the upper surface of the substrate (1), with a channel in the middle. The humidity-sensitive layer (2) is located at the channel of the positive electrode (3) and the negative electrode (4) on the upper surface of the substrate (1), and its two ends are connected to the positive electrode (3) and the negative electrode (4) respectively. Test leads (5) are led out from the positive electrode (3) and the negative electrode (4) respectively. The material of the positive electrode (3) includes manganese dioxide, the material of the negative electrode (4) is aluminum, and the material of the humidity-sensitive layer (2) is composed of metal salt and carbon nanotubes. The metal salt is sodium chloride, lithium chloride, or potassium chloride; the carbon nanotubes are hydroxylated carbon nanotubes or carboxylated carbon nanotubes; the mass ratio of metal salt to carbon nanotubes is 1~15:

1. The positive electrode (3) is composed of manganese dioxide, carbon black and sodium alginate; the mass ratio of manganese dioxide, carbon black and sodium alginate is 2~8:1:

1.

2. The high-power electrochemical humidity sensor according to claim 1, characterized in that, The distance between the positive electrode (3) and the negative electrode (4) is 0.1 mm to 2 mm.

3. A method for preparing a high-power electrochemical humidity sensor, characterized in that, The method for preparing the high-power electrochemical humidity sensor of claim 1 includes the following steps: Step 1: Deposit the material of the positive electrode (3) on one side of the substrate (1) and dry it; Step 2: Prepare a negative electrode (4) on the other side of the substrate on which the positive electrode has been deposited; Step 3: Deposit the metal salt and carbon nanotube mixture between the positive electrode (3) and the negative electrode (4) and dry it to form a humidity-sensitive layer (2); Step 4: Lead out test leads (5) from the positive electrode (3) and the negative electrode (4) respectively to complete the preparation of the electrochemical humidity sensor.

4. The method for preparing a high-power electrochemical humidity sensor according to claim 3, characterized in that, The positive electrode (3) and the humidity-sensitive layer (2) in steps 1 and 3 are prepared by brushing, spraying, dipping or screen printing.

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