Carbon dioxide sensor based on equilibrium potential type of lglzo thin film and wc-li2co3 auxiliary phase and preparation method thereof

Abstract

A kind of carbon dioxide sensor based on LGLZO film and WC-Li2CO3 auxiliary phase balanced potential type and preparation method, belong to gas sensor technical field.It is composed of alumina substrate with platinum heater, LGLZO film, sensitive electrode and reference electrode.The present application includes the steps of preparing LGLZO plating solution, preparing LGLZO film by spin coating method, WC-Li2CO3 auxiliary phase material preparation, etc.The gold electrode under the auxiliary phase and the sensitive electrode are composed of the sensitive electrode.The LGLZO film prepared by the present application has high conductivity and low temperature working characteristics, WC has high hardness, high conductivity and high stability, which improves the structural stability of auxiliary phase material and forms electron transport channel, the combination of the two significantly reduces the working temperature of the sensor, improves its stability, realizes the low-power, long-time rapid detection of CO2 concentration, and provides a research basis for the miniaturization and integration of balanced potential CO2 sensor.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, specifically relating to an equilibrium potential type carbon dioxide (CO2) sensor based on gallium-doped lithium lanthanum zirconium oxide (LGLZO) thin film and tungsten carbide-lithium carbonate (WC-Li2CO3) auxiliary phase, and its preparation method. Background Technology

[0002] Equilibrium potential-type CO2 sensors stand out from numerous low-cost CO2 sensors due to their advantages such as small size, good stability, and long lifespan, making them a promising option for gridded, long-term online monitoring needs. The electrolyte provides the ion transport pathway for the electrochemical reaction, and a high-conductivity, low-operating-temperature electrolyte is the design basis for low-temperature, low-power sensors. Furthermore, the sensitive electrode auxiliary phase, characterized by high electrochemical activity, high specific surface area, and high conductivity, can effectively promote the electrochemical reaction of CO2 on the sensitive electrode.

[0003] However, the electrolytes commonly used in these sensors operate at high temperatures and are large in size, affecting stability and increasing sensor power, thus adding challenges to integrated applications. While using pure carbonate as an auxiliary phase offers high ion transport efficiency at high temperatures, the lack of electron transport pathways for the reaction limits the electrochemical reaction to the metal electrode surface, resulting in a small active area for the sensitive electrode. Pure carbonate also exhibits significant grain growth, especially at high operating temperatures where small grains rapidly aggregate, reducing the auxiliary phase surface area and further shrinking the electrochemical active area. Therefore, equilibrium potential-type CO2 sensors generally suffer from high operating temperatures (300~500℃), large size, high power consumption, and baseline drift, representing significant challenges that must be overcome to move from laboratory applications to production.

[0004] To address the issues of high operating temperature and high power consumption in sensors, some research has attempted to use lithium-ion conductive solid electrolytes to reduce their operating temperature. Studies have explored the use of sheet-type lithium lanthanum zirconium oxide (LLZO) solid electrolytes in gas sensor fabrication, achieving both lower operating temperature and fast response. However, the sheet-type sensor structure results in high power consumption and hinders array-based applications. Garnet-type LLZO solid electrolytes have been extensively studied in lithium metal batteries and are considered one of the most promising candidate materials, not only due to their high conductivity but also their excellent thermal stability, electrochemical stability, and high mechanical strength. Furthermore, with the increasing demands for battery energy density, the fabrication process of LLZO solid electrolyte films is becoming increasingly mature. This aligns with the main development direction of gas sensors—microelectromechanical systems (MEMS) technology—providing a research foundation for low-power and integrated equilibrium potential CO2 sensors. The stability, conductivity, and electrochemical activity of the auxiliary phase of the sensitive electrode directly affect the key performance characteristics of CO2 sensors. Li2CO3, with its significantly better moisture resistance than other carbonates, is typically chosen for sensor development. However, at temperatures above 300℃, small Li2CO3 crystals gradually dissolve and large crystals gradually grow, leading to a decrease in the active area, severe baseline drift, and difficulty in electron transfer, which also restricts the electrochemical reaction to the interface between the electrolyte and the auxiliary phase. Summary of the Invention

[0005] This invention aims to overcome the technical bottlenecks of high operating temperature and poor stability in existing equilibrium potential type CO2 sensors, and provides an equilibrium potential type carbon dioxide sensor based on a gallium-doped lithium lanthanum zirconium oxide solid electrolyte film and a tungsten carbide-lithium carbonate auxiliary phase, as well as its preparation method. In the following content of this invention, the gallium-doped lithium lanthanum zirconium oxide solid electrolyte film is abbreviated as LGLZO film, and the tungsten carbide-lithium carbonate auxiliary phase is abbreviated as WC-Li2CO3 auxiliary phase.

[0006] This invention, on the one hand, prepares amorphous LGLZO thin films with good density and integrity through spin coating and low-temperature sintering, effectively avoiding lithium loss under high-temperature environments; on the other hand, the development of thin-film devices helps reduce device power consumption and provides a material basis for device integration and arraying. Simultaneously, by doping nano-tungsten carbide into the lithium carbonate auxiliary phase, a WC-Li2CO3 auxiliary phase is obtained. Utilizing its conductor-like properties and high hardness, the electronic conductivity of the auxiliary phase is improved, and a "pinning effect" is formed to enhance stability. The combination of the LGLZO thin film and the WC-Li2CO3 auxiliary phase significantly reduces the operating temperature of the device described in this invention and improves its sensitivity, stability, and response speed.

[0007] The method for fabricating an equilibrium potential type carbon dioxide sensor based on LGLZO thin film and WC-Li2CO3 auxiliary phase according to the present invention comprises the following steps:

[0008] (1) Lithium tert-butoxide and zirconium n-propoxide are dissolved in ethylene glycol monomethyl ether and stirred for 0.5 to 1 hour; then lanthanum nitrate hexahydrate and gallium nitrate are added and stirred for 4 to 8 hours for aging to obtain LGLZO coating solution;

[0009] (2) The LGLZO coating solution obtained in step (1) is spin-coated and dried on the upper surface of a clean alumina substrate with a platinum heater at the bottom, and then calcined and heat-treated to obtain an LGLZO thin film.

[0010] (3) Apply gold paste to one side of the upper surface of the LGLZO film to form two interconnected double gold strips; apply gold paste to the other side of the upper surface of the LGLZO film to form a single gold strip; and then sinter at 550~650℃ for 10~20 minutes.

[0011] (4) Mix and grind lithium carbonate and nano-tungsten carbide in a mass ratio of 100:5~20 for 20~40 minutes. Mix the ground material with terpineol and coat it on the double gold strip. After sintering, a WC-Li2CO3 auxiliary phase is formed. The WC-Li2CO3 auxiliary phase and the double gold strip below together form the sensitive electrode, and the single gold strip forms the reference electrode.

[0012] (5) The sensitive electrode, the reference electrode and the platinum heater are soldered to the hexagonal base pins through platinum wire leads to complete the fabrication of the sensor.

[0013] Furthermore, in step (1), the molar ratio of lithium tert-butoxide, gallium nitrate, lanthanum nitrate hexahydrate, and zirconium propoxide is 6.5~7.5:0.1~0.3:2~4:1.5~2.5.

[0014] In step (2), the alumina substrate with a platinum heater at the bottom is ultrasonically treated in deionized water, acetone and anhydrous ethanol for 3 to 6 minutes respectively to obtain a clean alumina substrate.

[0015] In step (2), the LGLZO coating solution obtained in step (1) is spin-coated onto the surface of a clean alumina substrate at a speed of 2500~3500 rpm for 1~3 minutes, followed by drying at room temperature for 5~10 minutes; the above "spin-coating-drying" process is repeated 3~5 times; the dried alumina substrate is calcined at 300~500℃ for 1~5 minutes; finally, the calcined alumina substrate is heat-treated at 500~700℃ for 5~10 minutes, thereby obtaining an LGLZO film with a thickness of 600~1000nm on the surface of the alumina substrate.

[0016] In step (3), the thickness of the double gold strip and the single gold strip is 1~2µm.

[0017] In step (4), the ground material is mixed with terpineol at a mass ratio of 1:10~20 and then coated onto the double gold strip.

[0018] In step (4), sintering is carried out at 400~500℃ for 60~120 minutes to form a WC-Li2CO3 auxiliary phase with a thickness of 1~5µm.

[0019] The equilibrium potential type carbon dioxide sensor based on LGLZO thin film and WC-Li2CO3 auxiliary phase described in this invention is prepared by the above-mentioned preparation method.

[0020] The equilibrium potential type carbon dioxide sensor based on LGLZO thin film and WC-Li2CO3 auxiliary phase described in this invention has the following advantages:

[0021] (1) This invention uses LGLZO thin film as ion transport layer. The doping of Ga element helps to form high-quality thin film at a lower temperature. It has high electrical conductivity and good chemical and thermal stability, which significantly reduces the operating temperature of the sensor. At the same time, the spin coating process of LGLZO thin film is low cost and simple process, which is consistent with the main development direction of gas sensors - microelectromechanical systems process, and provides a research basis for the low power consumption and integration of balanced potential type CO2 sensor.

[0022] (2) This invention utilizes the high electronic conductivity, high hardness and high stability of tungsten carbide to dope it into the lithium carbonate auxiliary phase to form a “pinning effect”, which can effectively limit the grain growth of lithium carbonate at high temperature and form an electron transport path, extending the active sites from a two-dimensional interface to a three-dimensional network structure, significantly improving the sensor sensitivity and stability, and realizing long-term monitoring of environmental CO2 concentration.

[0023] The sensor response test process is as follows: The platinum wire lead of the platinum heater is connected to a DC linear power supply through the hexagonal socket pins. The operating temperature of the sensor is adjusted by regulating the current intensity. A digital multimeter is used to measure and record the potential difference between the sensitive electrode and the reference electrode in real time through the hexagonal socket pins. This multimeter is connected to a computer. This potential difference is the sensor output voltage, and the difference between the output voltage after the gas concentration change and the output voltage before the change is the response value. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the fabrication process and device structure of the equilibrium potential type carbon dioxide sensor of the present invention;

[0025] Figure 2 Scanning electron microscope (SEM) images, energy dispersive X-ray spectroscopy (EDS) images, and atomic force microscope (AFM) images of the LGLZO thin film provided in Embodiment 1 of the present invention;

[0026] Figure 3 The polarization curves of the WC-Li2CO3 auxiliary phase with different tungsten carbide doping ratios provided in Examples 1-4 and Comparative Example 1, and the sensor performance test curves based on them;

[0027] Figure 4 The response curve of the equilibrium potential CO2 sensor based on LGLZO thin film and 10wt% WC-Li2CO3 auxiliary phase provided in Example 1 to 4000ppm CO2 at an operating temperature of 235~310℃;

[0028] Figure 5 Selectivity test results for different gases for the equilibrium potential CO2 sensor based on LGLZO thin film and 10wt% WC-Li2CO3 auxiliary phase provided in Example 1;

[0029] Figure 6 The adsorption and desorption concentration gradient test curves and sensitivity curves of the equilibrium potential CO2 sensor based on LGLZO thin film and 10wt% WC-Li2CO3 auxiliary phase provided in Example 1 are shown.

[0030] Figure 7 The long-term stability test curve of the equilibrium potential type CO2 sensor based on LGLZO thin film and 10wt% WC-Li2CO3 auxiliary phase provided in Example 1 within 60 days. Detailed Implementation

[0031] Example 1: Fabrication of an equilibrium potential CO2 sensor based on LGLZO thin film and 10wt% WC-Li2CO3 auxiliary phase

[0032] (1) Preparation of Ga-doped LGLZO coating solution: 40 mL of ethylene glycol monomethyl ether (Aladdin, M102853) was measured with a graduated cylinder, and 0.123 g of lithium tert-butoxide (Aladdin, L118703) and 0.187 g of zirconium propoxide (Aladdin, Z106340) were weighed and dissolved in ethylene glycol monomethyl ether and stirred for 0.5 hours; then 0.26 g of lanthanum nitrate hexahydrate (Aladdin, L106046) and 0.01 g of gallium nitrate (Aladdin, G109501) were added and stirred for 6 hours for aging to obtain LGLZO coating solution; the molar ratio of lithium tert-butoxide, gallium nitrate, lanthanum nitrate hexahydrate and zirconium propoxide was 7.04:0.2:3:2.

[0033] (2) Preparation of Ga-doped LGLZO thin film: Take a 2×2 mm alumina substrate (Suzhou Insite Sensing Technology Co., Ltd.) with a platinum heater at the bottom, and sonicate it in deionized water, acetone (Merck, 179124) and anhydrous ethanol (Aladdin, E111964) for 5 minutes to ensure the substrate surface is clean. Place the alumina substrate on a spin coater and set the spin coating process to accelerate from 300 rpm to 3000 rpm, and spin coat at a constant speed for 3 minutes. During the acceleration process, use a 100µL pipette to drop 1 drop of the coating solution prepared in step (1) onto the surface of the alumina substrate. After spin coating, place the alumina substrate in clean air to dry for 5 minutes; repeat the above "spin coating-drying" process 4 times. Then place the alumina substrate in a rapid heat treatment furnace and calcine it at 400℃ for 2 minutes. Finally, a heat treatment was performed at 600°C for 5 minutes to obtain an LGLZO thin film with a thickness of 800 nm on the surface of the alumina substrate.

[0034] (3) Fabrication of gold electrodes: The LGLZO thin film prepared in step (2) was ultrasonically cleaned in anhydrous ethanol for 5 minutes; gold paste (Saiqin Electronics Technology Co., Ltd., 54H-1803) was coated on one side of the upper surface of the LGLZO thin film to form two interconnected double gold strips, and platinum wire (Boyan Technology Co., Ltd., 0.05 mm) was attached to the double gold strips with gold paste; a single gold strip was coated on the other side of the upper surface of the LGLZO thin film with gold paste, and platinum wire was attached to the single gold strip with gold paste; then sintered at 600℃ for 10 minutes, the double gold strips formed the gold electrode used for the sensitive electrode, and the single gold strip formed the gold electrode used for the reference electrode; the thickness of the gold strips was 1.5µm.

[0035] (4) Preparation of 10wt% WC-Li2CO3 auxiliary phase: Take 1g of lithium carbonate (Aladdin, L1455823) and grind it in a mortar for 20 minutes. Then take 0.1g of tungsten carbide (Aladdin, T431585) and mix it with the ground lithium carbonate. Grind and mix for another 10 minutes. Use terpineol (Aladdin, T103776) to make it into a slurry (the mass ratio of auxiliary phase material to terpineol is 1:15). Use a fine brush to dip the slurry and coat it on the gold electrode used for the sensitive electrode in step (3). Sinter at 450℃ for 90 minutes to form WC-Li2CO3 auxiliary phase. WC-Li2CO3 auxiliary phase and the gold electrode below together form sensitive electrode. The thickness of WC-Li2CO3 auxiliary phase is 3µm.

[0036] (5) Sensor element pin soldering: The sensor’s sensitive electrode, reference electrode and platinum heater are soldered to the pins of the hexagonal base (Zhengzhou Weisheng Electronic Technology Co., Ltd.) by platinum wire, thus completing the sensor fabrication.

[0037] Example 2: Fabrication of an equilibrium potential CO2 sensor based on LGLZO thin film and 5wt% WC-Li2CO3 auxiliary phase

[0038] The preparation process of this embodiment is basically the same as that of Example 1. The only difference is that in step (4) preparation of the sensitive electrode auxiliary phase, the ground lithium carbonate is mixed with 0.05g of tungsten carbide and then coated with terpineol to form a slurry. The rest of the preparation of the coating solution, thin film preparation, gold electrode preparation and pin welding are the same as those in Example 1.

[0039] Example 3: Fabrication of an equilibrium potential CO2 sensor based on LGLZO thin film and 15wt% WC-Li2CO3 auxiliary phase

[0040] The preparation process of this embodiment is basically the same as that of Example 1. The only difference is that in step (4) preparation of the sensitive electrode auxiliary phase, the ground lithium carbonate is mixed with 0.15g of tungsten carbide and then coated with terpineol to form a slurry. The rest of the preparation of the coating solution, thin film preparation, gold electrode preparation and pin welding are the same as those in Example 1.

[0041] Example 4: Fabrication of an equilibrium potential CO2 sensor based on LGLZO thin film and 20wt% WC-Li2CO3 auxiliary phase

[0042] The preparation process of this embodiment is basically the same as that of Example 1. The only difference is that in step (4) preparation of the sensitive electrode auxiliary phase, the ground lithium carbonate is mixed with 0.2g of tungsten carbide and then coated with terpineol to form a slurry. The rest of the preparation of the coating solution, thin film preparation, gold electrode preparation and pin welding are the same as those in Example 1.

[0043] Comparative Example 1: Fabrication of an equilibrium potential CO2 sensor based on LGLZO thin film and pure lithium carbonate auxiliary phase

[0044] The preparation process of this comparative example is basically the same as that of Example 1. The only difference is that in step (4) preparation of the sensitive electrode auxiliary phase, the ground lithium carbonate is directly coated with terpineol to form a slurry without adding nano tungsten carbide. The rest of the coating solution preparation, thin film preparation, gold electrode preparation and pin welding are the same as those in Example 1.

[0045] like Figure 1 As shown, the names of each part are: LGLZO coating solution 1, platinum heater 2, LGLZO thin film 3, gold electrode 4, sensitive electrode 5, and reference electrode 6.

[0046] like Figure 2As shown, (a) is a planar SEM image of the LGLZO thin film, (b) is an EDS image of Zr in the LGLZO thin film, (c) is an EDS image of La in the LGLZO thin film, (d) is an EDS image of Ga in the LGLZO thin film, (e) is a cross-sectional SEM image of the LGLZO thin film, (f) is an EDS image of Zr in the cross-section of the LGLZO thin film, (g) is an EDS image of La in the cross-section of the LGLZO thin film, (h) is an EDS image of Ga in the cross-section of the LGLZO thin film, (i) is an AFM image of a 5×5µm LGLZO thin film, and (j) is an AFM image of a 1×1µm LGLZO thin film. Figure 2 As can be seen, the LGLZO film is complete and dense, with uniform element distribution, a film thickness of about 800 nm, and low surface roughness.

[0047] like Figure 3 As shown, (a) is the polarization current curve of auxiliary phase materials with different doping ratios, and curves 1 to 5 correspond to Comparative Example 1 and Examples 1 to 4, respectively. It can be seen that the electronic conductivity of the WC-Li2CO3 auxiliary phase increases significantly with the increase of tungsten carbide ratio. (b) is the performance test curve of CO2 sensor based on auxiliary phase materials with different doping ratios. The sensor baseline voltage was measured in 400ppm CO2, and the sensor response voltage was measured in 4000ppm CO2. The response value is the difference between the baseline voltage and the response voltage. The response values ​​of the sensors corresponding to Examples 1 to 4 and Comparative Example 1 are -23mV, -13mV, -16.5mV, -8mV and -6mV, respectively, indicating that the 10wt% WC-Li2CO3 described in Example 1 is the best auxiliary phase material.

[0048] like Figure 4 As shown, the response time (the time required for the response voltage to reach 90% of its stable value) is the shortest after the operating temperature reaches 265℃. At the same time, the response value only increases slightly with the increase of temperature. Therefore, 265℃ is the optimal operating temperature for the sensor.

[0049] like Figure 5 As shown, CO2 is a gas present in large quantities in the air, while other interfering gases are mostly toxic and harmful, with concentrations varying greatly in different application scenarios. Therefore, in our testing, we selected gases of different concentrations that met the specific application scenarios for testing. Figure 5 To compare the sensor's response values ​​to 4000ppm CO2 and 100ppm common interfering gases, the response value calculation method is the same as... Figure 3 The results are identical (only the test gas is changed to the interfering gas), indicating that the sensor prepared in this invention has significantly better selectivity for CO2 than other interfering gases.

[0050] like Figure 6As shown, (a) is the adsorption and desorption concentration gradient test curve, where the upper curve is the sensor's output voltage for adsorption / desorption of CO2 from 400 to 100,000 ppm, and the lower curve is the CO2 concentration corresponding to each segment of the concentration gradient test. The vertical axis represents the CO2 concentration value provided during ventilation, indicating that the sensor's adsorption and desorption responses are highly consistent. (b) is the sensitivity linear fitting curve, which is obtained by linearly fitting the output voltage obtained in (a) with the corresponding logarithm of the concentration. The sensitivity is the slope of the fitted line, and the adsorption curve equation is Y = -18.87X + 93.20, R 2 =0.9938; the desorption curve equation is Y = -18.16X + 90.35, R 2 =0.9967; the adsorption and desorption sensitivities are -18.87 mV / decade and -18.16 mV / decade, respectively.

[0051] like Figure 7 As shown, the sensor was used to perform three repeated tests on 4000ppm CO2 every three days, and the average response value was taken to obtain the curve. As can be seen from the figure, the response value stabilized at around -21.7mV within 60 days, with a fluctuation error of less than 10%, and the response value did not decay over time, indicating that the sensor has good long-term stability.

Claims

1. A method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase, characterized in that: The steps are as follows: (1) Lithium tert-butoxide and zirconium n-propoxide are dissolved in ethylene glycol monomethyl ether and stirred for 0.5 to 1 hour; then lanthanum nitrate hexahydrate and gallium nitrate are added and stirred for 4 to 8 hours for aging to obtain LGLZO coating solution; (2) The LGLZO coating solution obtained in step (1) is spin-coated and dried on the upper surface of a clean alumina substrate with a platinum heater at the bottom, and then calcined and heat-treated to obtain an LGLZO thin film. (3) Apply gold paste to one side of the upper surface of the LGLZO film obtained in step (2) to form two interconnected double gold strips; apply gold paste to the other side of the upper surface of the LGLZO film to form a single gold strip; and then sinter at 550~650℃ for 10~20 minutes. (4) Mix lithium carbonate and nano tungsten carbide in a mass ratio of 100:5~20 and grind for 20~40 minutes. Mix the ground material with terpineol and coat it on the double gold strip. After sintering, a WC-Li2CO3 auxiliary phase is formed. The WC-Li2CO3 auxiliary phase and the double gold strip below together form the sensitive electrode, and the single gold strip forms the reference electrode. (5) The sensitive electrode, the reference electrode and the platinum heater are soldered to the hexagonal base pins through platinum wire leads to complete the fabrication of the sensor.

2. The method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase as described in claim 1, characterized in that: In step (1), the molar ratio of lithium tert-butoxide, gallium nitrate, lanthanum nitrate hexahydrate, and zirconium propoxide is 6.5~7.5:0.1~0.3:2~4:1.5~2.

5.

3. The method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase as described in claim 1, characterized in that: In step (2), the alumina substrate with a platinum heater at the bottom is ultrasonically treated in deionized water, acetone and anhydrous ethanol for 3 to 6 minutes respectively to obtain a clean alumina substrate.

4. The method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase as described in claim 1, characterized in that: In step (2), the LGLZO coating solution obtained in step (1) is spin-coated onto the surface of a clean alumina substrate at a speed of 2500~3500 rpm for 1~3 minutes, followed by drying at room temperature for 5~10 minutes; the above "spin-coating-drying" process is repeated 3~5 times; the dried alumina substrate is calcined at 300~500℃ for 1~5 minutes; finally, the calcined alumina substrate is heat-treated at 500~700℃ for 5~10 minutes, thereby obtaining an LGLZO film with a thickness of 600~1000nm on the surface of the alumina substrate.

5. The method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase as described in claim 1, characterized in that: In step (3), the thickness of the double gold strip and the single gold strip is 1~2µm.

6. The method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase as described in claim 1, characterized in that: In step (4), the ground material is mixed with terpineol at a mass ratio of 1:10~20 and then coated onto the double gold strip.

7. The method for fabricating an equilibrium potential type carbon dioxide sensor based on an LGLZO thin film and a WC-Li2CO3 auxiliary phase as described in claim 1, characterized in that: In step (4), sintering is carried out at 400~500℃ for 60~120 minutes to form a WC-Li2CO3 auxiliary phase with a thickness of 1~5µm.

8. A equilibrium potential type carbon dioxide sensor based on LGLZO thin film and WC-Li2CO3 auxiliary phase, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 7.

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