A carbon monoxide gas sensor based on ysz substrate and its preparation method and detection application

Abstract

This invention discloses a carbon monoxide sensor based on a YSZ substrate, its preparation method, and its detection application. The sensor comprises a yttrium-stabilized zirconia solid electrolyte substrate, a counter electrode, a reference electrode, and a first sensitive electrode disposed on the same surface of the solid electrolyte substrate. The thickness of the first sensitive electrode is greater than that of the counter electrode, and the reference electrode is a manganese dioxide sintered body. The preparation method includes printing or coating a manganese dioxide paste onto the surface of the solid electrolyte substrate and sintering it at 1300-1450℃ to form the reference electrode; and printing or coating a mixed paste composed of platinum or platinum alloy particles and solid electrolyte particles onto the surface of the solid electrolyte substrate and sintering it at 1200-1400℃ to form the counter electrode and the first sensitive electrode, respectively. The advantages are simple structure, low cost, convenient preparation process, and effective suppression of oxygen interference, achieving low sensitivity, high selectivity, and high stability.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, specifically relating to a carbon monoxide gas sensor based on a YSZ substrate, its preparation method, and its detection application. Background Technology

[0002] Carbon monoxide (CO) is a colorless, odorless, and non-irritating highly toxic gas, primarily originating from the incomplete combustion of fossil fuels. Rapid and accurate detection of CO concentrations has significant social and economic value in fields such as industrial production, vehicle exhaust monitoring, boiler combustion efficiency optimization, and real-time ambient air quality monitoring.

[0003] Existing carbon monoxide (CO) sensors are mainly classified into semiconductor, electrochemical, and solid-state electrolyte types. Among them, solid-state electrolyte CO gas sensors, based on the electromotive force measurement principle of concentration gradient batteries, consist of stable zirconium oxide (ZrO2) with oxygen ion transport characteristics and metal electrodes. They possess excellent heat resistance, impact resistance, and resistance to poisoning, making them suitable for harsh high-temperature environments. However, existing YSZ-based CO sensors still have several shortcomings in practical applications and industrialization. First, since sensors using stable ZrO2 are themselves oxygen sensors, it is difficult to selectively measure CO concentration in oxygen-containing gas mixtures. Especially in commonly used platinum electrode sensors, when the temperature reaches 600 to 900°C, CO rapidly oxidizes on the platinum electrode surface, making it difficult to distinguish the measurement signals caused by oxygen and CO respectively.

[0004] Secondly, existing YSZ-based CO sensors have complex structures. To achieve a stable oxygen reference environment, a sealed reference cavity or a complex multi-electrode circuit system is generally required. This not only leads to complex processes and high costs, but also makes sealing the sealed cavity difficult, easily resulting in problems such as incomplete sealing and gas leakage, directly causing sensor failure, low yield, and difficulty in large-scale production. Some solutions also require additional treatments such as electrode doping and surface modification, further increasing the fabrication difficulty. Therefore, there is an urgent need to provide a carbon monoxide sensor that is simple in structure, low in cost, easy to fabricate, and can effectively suppress oxygen interference, achieving high selectivity and high stability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a carbon monoxide gas sensor based on YSZ substrate, which is simple in structure, low in cost, convenient in preparation process, and can effectively suppress oxygen interference, achieve low sensitivity, high selectivity and high stability, as well as its preparation method and detection application.

[0006] The technical innovation of this invention lies in achieving stable CO signal output under a wide concentration range (2 vol.% - 40 vol.%) of O2 coexistence by adjusting the film thickness of the first sensitive electrode SE and the counter electrode CE. The key technical approach is to precisely control the thickness of the sensor's sensitive electrode SE and counter electrode CE, thereby regulating the gas-phase reaction activity at the CO interface, suppressing the concentration of other gases participating in the interface reaction, and ultimately enabling the sensor to respond with high selectivity and high sensitivity to CO.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a carbon monoxide sensor based on YSZ substrate, comprising a solid electrolyte substrate: the solid electrolyte substrate is yttrium-stabilized zirconium oxide (YSZ), specifically it can be zirconium oxide doped with 3-8 mol% yttrium oxide, which has good oxygen ion conductivity at high temperature, and realizes cation conduction between the counter electrode and the first sensitive electrode; Three-electrode system: a counter electrode, a reference electrode, and a first sensitive electrode are disposed on the same surface of the solid electrolyte substrate, with the counter electrode forming a current loop and the first sensitive electrode undergoing an electrode reaction. Both the counter electrode and the first sensitive electrode are sintered bodies composed of platinum (Pt) or platinum alloy particles and solid electrolyte particles. Crucially, the film thickness of the first sensitive electrode is greater than that of the counter electrode. This thickness difference design, combined with a specific operating bias voltage, effectively suppresses the interference of oxygen on the CO measurement signal. Reference electrode: It is a manganese dioxide (MnO2) sintered body. Using MnO2 to replace the traditional Pt / air reference electrode eliminates the need for a complex reference cavity, simplifies the structure, and provides a stable reference potential.

[0008] Preferably, the thickness of the first sensitive electrode is 9-80 μm (more preferably 20-40 μm), and the thickness of the counter electrode is 1-20 μm (more preferably 14-18 μm).

[0009] Preferably, the area ratio of the counter electrode to the first sensitive electrode is 1:2.

[0010] Preferably, the reference electrode is made of manganese dioxide powder with a purity of 85%-99.95%, with a thickness of 1-30μm (more preferably 5μm) and a diameter of 0.2-1mm (more preferably 0.5mm).

[0011] As a further improvement, the sensor may also include: Heater: Located on or near the back of the solid electrolyte substrate, used to heat the sensor to its operating temperature (e.g., 600-900°C).

[0012] The second sensitive electrode, integrated on the same substrate, is used to measure oxygen concentration and compensate for CO measurement by using oxygen measurement value to achieve dual-parameter detection and more accurate calibration.

[0013] Furthermore, the second sensitive electrode is sintered at a temperature of 1200-1350℃, has a film thickness of 9-80μm, and operates at a bias voltage of 0.01-1V. The surface area where the solid electrolyte substrate connects to the counter electrode, the first sensitive electrode, and the second sensitive electrode is a roughened surface formed by sandblasting. After sandblasting, the surface roughness of the solid electrolyte is significantly increased, forming a uniform micro-uneven structure. This effectively increases the contact interface area between the gas phase (the gas being measured), the metal electrode, and the solid electrolyte, accelerating the adsorption, diffusion, and electrochemical reaction rate of CO gas at the interface, reducing reaction resistance, and thus further improving the CO gas detection sensitivity. This enables the sensor to accurately respond to low concentrations of CO gas and expand the detection range.

[0014] This invention also provides a method for fabricating a carbon monoxide sensor based on a YSZ substrate, comprising the steps of fabricating or providing a YSZ substrate, and forming a reference electrode, a counter electrode, and a first sensitive electrode through printing and high-temperature sintering processes, respectively. Specifically: Step 1: Print or coat manganese dioxide paste onto the surface of a solid electrolyte substrate and sinter at 1300-1450℃ to form a reference electrode; Step 2: A mixed slurry consisting of platinum or platinum alloy particles and solid electrolyte particles is printed or coated onto the surface of the solid electrolyte substrate, and then sintered at 1200-1400℃ to form a counter electrode and a first sensitive electrode, respectively; wherein the printing thickness of the first sensitive electrode is greater than that of the counter electrode, so that the film thickness of the first sensitive electrode after sintering is greater than that of the counter electrode. The present invention also provides a method for detecting carbon monoxide concentration using the above-mentioned sensor, comprising: heating the sensor to its operating temperature (≥500℃, preferably 600-900℃), applying a bias voltage (-1V to -0.05V, preferably -0.1V) between the first sensitive electrode and the reference electrode, introducing the gas to be measured at a flow rate of not less than 200mL / min to the surface of the first sensitive electrode, measuring the current or electromotive force signal between the first sensitive electrode and the counter electrode, and determining the concentration of carbon monoxide based on the signal value.

[0015] Compared with the prior art, the advantages of the present invention are as follows: 1. Simplified structure and reduced cost: The use of MnO2 reference electrode eliminates the need to construct a complex Pt / air reference cavity, simplifying the sensor structure, reducing the difficulty and cost of the fabrication process, improving the product yield, and facilitating miniaturization and integration.

[0016] 2. High selectivity and anti-interference capability: By adopting a differentiated film thickness design between the first sensitive electrode and the counter electrode, and combined with an optimized bias voltage, the cross-response of oxygen and other coexisting gases (such as methane, hydrogen sulfide, ammonia, etc.) is effectively suppressed, achieving specific and high-precision monitoring of CO gas.

[0017] 3. Excellent environmental resistance: The inherent heat resistance of the YSZ substrate, combined with the alumina protective layer and the encapsulation shell, enables the sensor to work stably for a long time under harsh conditions such as high temperature, high humidity and corrosion at 600-900℃.

[0018] 4. Stable quantitative detection capability: Experimental data demonstrates that under different oxygen concentrations (2 vol.% - 40 vol.%), the sensor of this invention maintains a essentially constant sensitivity to CO, and the detection linearity (R0) remains consistent. 2 All values ​​are greater than 0.95, enabling accurate quantitative detection of CO concentration in a complex oxygen-containing atmosphere.

[0019] In summary, this invention provides a carbon monoxide gas sensor based on a YSZ substrate, its preparation method, and its detection application. By designing the differential thickness of the Pt-YSZ composite electrode and introducing a MnO2 reference electrode, a YSZ-based carbon monoxide sensor with simple structure, low cost, easy preparation, and high selectivity, high sensitivity, and high stability over a wide oxygen concentration range has been successfully constructed. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the sensor structure of the present invention; Figure 2 for Figure 1 Right side view of the sensor shown; Figure 3 The response step curve for testing a carbon monoxide mixture using a sensor with unoptimized film thickness; Figure 4 The response step curve of the sensor with optimized film thickness according to the present invention for testing carbon monoxide mixed gas; Figure 5 This is a graph showing the linear relationship between the current signal of the sensor of the present invention and the carbon monoxide concentration under different oxygen concentrations. Figure 6 This is the response step curve of the sensor of the present invention when testing a carbon monoxide mixture in the extremely low concentration range of 0.2~5 ppm. Figure 7 This is a graph showing the selective test results of the sensor of the present invention for carbon monoxide and various interfering gases; Figure 8 shows the long-term stability test curve of the sensor of the present invention over 80 days. Figure 9 The response and recovery time curves of the sensor of the present invention when placed in CO gas with a concentration of 500 ppm are shown. Figure 10 The T90 response recovery time of the sensor of the present invention in CO atmospheres of different concentrations; Figure 11 The response step curve of the comparative sensor for testing carbon monoxide mixture; Figure 12 Circuit diagram for integrating the second sensitive electrode O2 sensor; Figure 13 The curve of open-circuit voltage between the second electrode SE-2 and RE as a function of O2 concentration and the linear relationship; In the figure: 1-YSZ solid electrolyte layer, 2-counter electrode, 3-reference electrode, 4-first sensitive electrode, 5-second sensitive electrode. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that the specific embodiments of this invention are only for explaining the invention and are not intended to limit the scope of protection of this invention.

[0022] Specific Implementation Example 1: Carbon monoxide sensor based on YSZ substrate.

[0023] Its structure is as follows Figure 1 As shown, it includes a solid electrolyte substrate 1, which is yttrium-stabilized zirconium oxide; a counter electrode 2, a reference electrode 3, and a first sensitive electrode 4 disposed on the same surface of the solid electrolyte substrate 1; the counter electrode 2 and the first sensitive electrode 4 are both sintered bodies composed of platinum or platinum alloy particles and solid electrolyte particles, and the film thickness of the first sensitive electrode 4 is greater than the film thickness of the counter electrode 2; the reference electrode 3 is a manganese dioxide sintered body.

[0024] The sensor of this invention operates based on the principle of electrochemical limiting current. For example... Figure 2 As shown, in operation, the sensor as a whole is heated to above 500°C, preferably 600-900°C, by a built-in heater. At this high temperature, the YSZ solid electrolyte substrate 1 becomes oxygen ions (O2). 2- It is an excellent conductor.

[0025] A specific negative bias voltage (e.g., -0.1V) is applied between the first sensitive electrode 4 (SE) and the reference electrode 3 (RE). The reference electrode 3 is MnO2, which provides a stable and constant electrode potential at high temperatures, does not participate in electrochemical reactions, and provides a reliable potential reference for the system.

[0026] Under this bias voltage, the potential of the first sensitive electrode 4 is forcibly reduced, making it a highly efficient catalytic oxidation anode. When the analyte gas containing CO and O2 diffuses to the surface of the first sensitive electrode 4, CO molecules are preferentially and rapidly electrochemically oxidized. The reaction equation is as follows: Anode reaction (first sensitive electrode 4): CO(g) + O 2- (YSZ) → CO2(g) + 2e - (Equation 1) CO oxidation releases electrons, and this reaction consumes oxygen ions (O2) in the YSZ electrolyte. 2- ) and release electrons (e - The released electrons flow through the external circuit to the counter electrode 2 (CE). The consumed O 2- Then the O migrated from the counter electrode side 2- Replenish.

[0027] At electrode 2, since the circuit is closed, the arriving electrons combine with oxygen molecules in the atmosphere, undergoing a reduction reaction to regenerate O. 2- It is then injected into the YSZ electrolyte. The reaction equation is as follows: Cathode reaction (counter electrode 2): ½ O2(g) + 2e - → O 2- (YSZ) (Equation 2), O2 reduction, generating O 2- .

[0028] Analysis of the above electrode reaction process shows that: The principle of O2 interference suppression: Within the preferred bias range of this invention (-1V to -0.05V, especially -0.1V), the CO oxidation reaction rate on the surface of the first sensitive electrode 4 is extremely fast. Once CO reaches the electrode surface, it is immediately consumed, causing its surface concentration to approach zero. At this point, the CO diffusion rate becomes the controlling step of the entire reaction. According to Faraday's law, the limiting current output by the sensor (I...) lim It is directly proportional to the concentration of CO: Where z is the number of electrons in the reaction (z=2), F is the Faraday constant, D is the diffusion coefficient of CO, A is the diffusion area, L is the diffusion path length, and C is the diffusion coefficient. CO The formula does not include an oxygen concentration term. Therefore, as long as the catalytic activity of the first sensitive electrode 4 is ensured to be sufficiently high (achieved through the thick-film porous structure of the present invention), within the above-mentioned bias range, changes in the external oxygen concentration have almost no effect on the CO diffusion process, thereby fundamentally suppressing the interference of coexisting O2 on the CO measurement value.

[0029] The principle of high selectivity: By designing the film thickness of the first sensitive electrode 4 to be significantly greater than that of the counter electrode 2 (e.g., 9-80 μm vs. 1-20 μm), a three-phase reaction interface with high specific surface area and strong catalytic activity is constructed. Combined with a precisely set bias voltage, the electrochemical oxidation reaction of CO by the first sensitive electrode 4 achieves excellent kinetic advantages. Compared to other reducing gases such as methane, hydrogen sulfide, and ammonia, CO is more easily oxidized under this specific electrode structure and bias voltage conditions, thus achieving a specific response to CO.

[0030] The principle of precise measurement: By combining a stable MnO2 reference electrode 3, the system obtains a reference potential unaffected by atmospheric fluctuations. When the reaction is in diffusion-controlled mode, the output current signal exhibits a perfect linear relationship with the CO concentration (experimentally measured R...). 2 >0.95). This enables accurate quantitative detection of CO concentration over a wide oxygen concentration range of 2-40 vol.% using a simple current-concentration calibration curve.

[0031] Specific embodiment two: A method for preparing a carbon monoxide sensor, comprising the following steps: Step 1, Solid electrolyte substrate 1: Select a zirconium oxide (YSZ) ceramic substrate doped with 8 mol% yttrium oxide, with dimensions of 10 mm × 10 mm × 0.5 mm; The shape of the solid electrolyte substrate 1 is not particularly limited; as long as it can achieve ion conductivity connection between the first carbon monoxide sensitive electrode 4 and the counter electrode 2. Step 2, Preparation of Reference Electrode 3: 99.9% pure MnO2 powder was mixed with an organic carrier (ethyl cellulose dissolved in terpineol) at a mass ratio of 6:4 and ground uniformly to prepare a MnO2 slurry. The MnO2 slurry was then screen-printed onto the center of the front side of the YSZ substrate 1, forming a rectangular (0.4mm × 0.6mm) wet film with a thickness of approximately 15μm. Subsequently, the temperature was increased to 1400℃ at 5℃ / min in air, held for 2 hours, and then decreased at 5℃ / min to form a reference electrode 3 with a thickness of approximately 5μm.

[0032] Step 3: Preparation of counter electrode 2 and first sensitive electrode 4: Platinum powder (Pt, average particle size 0.5 μm) and YSZ powder (average particle size 0.3 μm) were mixed at a mass ratio of 7:3, an organic carrier was added, and the mixture was ground uniformly to prepare a Pt-YSZ composite slurry. Counter electrode 2 and first sensitive electrode 4 were printed on the front side of the YSZ substrate 1 and on both sides of the reference electrode 3 via screen printing. The printing process was controlled so that the wet film thickness of the first sensitive electrode 4 was approximately 2-3 times that of the counter electrode 2. The printed pattern was square, and the area ratio of counter electrode 2 to first sensitive electrode 4 was designed to be 1:2. The temperature was increased to 1300℃ in air at 5℃ / min, held for 1 hour, and then decreased at 5℃ / min to form a porous sintered electrode. After sintering, the film thickness of counter electrode 2 was measured to be approximately 15 μm, and the film thickness of first sensitive electrode 4 was approximately 30 μm. The distance between counter electrode 2, first sensitive electrode 4, and reference electrode 3 was not less than 1 mm.

[0033] Step 4: Lead wire formation: Apply platinum paste to the edge of the electrode and sinter to form a platinum lead wire with a diameter of 0.2 mm.

[0034] Step 5: Encapsulation (optional): Print an alumina protective layer paste on the electrode surface, dry at 120°C, sinter at 1000°C for 1 hour, and then install the chip into a ceramic package and fix it with ceramic sealant.

[0035] Performance testing and analysis of the carbon monoxide sensor prepared in specific embodiment three and specific embodiment two.

[0036] Test System and Detection Method: The prepared sensor was placed in the test bench and connected to the electrochemical workstation. The sensor was heated to and stabilized at 650°C using the built-in heater. A constant bias voltage of -0.1V was applied between the first sensitive electrode 4 and the reference electrode 3. Standard gases of different concentrations were introduced onto the sensor surface at a flow rate of 200 mL / min. The current signal (unit: µA) between the first sensitive electrode 4 and the counter electrode 2 was measured.

[0037] 1. Resistance to oxygen interference and linear response test The sensor was tested under the following conditions: ambient temperature of 650°C, oxygen concentrations of 2 vol.%, 10 vol.%, 21 vol.%, and 40 vol.%, carbon monoxide concentration varying stepwise (100, 200, 500, 1000, 1500 ppm), and the remainder being nitrogen. The control sensor differs from the sensor in this embodiment in that the control sensor has the same film thickness for both the counter electrode and the first sensitive electrode, which is 35 μm.

[0038] Test results are as follows Figure 3 As shown, for the control sensor without optimized film thickness, almost no significant response current step was observed at different CO concentrations. Conversely, as... Figure 4 As shown, the sensor in this embodiment (with a film thickness of much greater than that of the counter electrode) exhibits a stable, clear, and reversible negative current step when the CO concentration changes in a stepwise manner. Under different oxygen concentrations, the sensor's response signal amplitude to the same CO concentration remains essentially consistent.

[0039] Further analysis Figure 4 The data in the figure shows that the stable current value at each fixed oxygen concentration is linearly fitted to the CO concentration, and the results are as follows: Figure 5 As shown, the coefficients of determination (R²) of all fitted curves are greater than 0.95, demonstrating excellent electrochemical response characteristics and a superb linear relationship between different current signals and different CO concentrations at a fixed O₂ concentration. More importantly, the fitted curves at different oxygen concentrations almost overlap, indicating that the sensor of this invention maintains essentially constant detection sensitivity for CO in complex atmospheres with varying oxygen contents (2 vol.%–40 vol.%), successfully overcoming the severe interference of oxygen on CO measurement.

[0040] Based on the fitting of the CO gradient response curve from 100 to 1500 ppm, the sensitivity in the high concentration range was found to be 0.050–0.065 μA / ppm. Combined with the 3x baseline noise method, the equivalent theoretical detection limit for this range was calculated to be 3–10 ppm.

[0041] like Figure 6 As shown, at an ambient temperature of 650℃, an O2 concentration of 21 vol.%, and carbon monoxide concentrations of 0.2, 0.5, 1.0, 3.0, and 5.0 ppm, the response signals were -0.6, -4.2, -9.1, -14.8, and -18.9 μA, respectively. The CO sensor response curve exhibits piecewise linearity: in the extremely low concentration range of 0.2–5 ppm, the device can stably resolve CO concentrations at the 0.2 ppm level.

[0042] 2. Selective Testing In a background atmosphere of 650℃ and 21 vol.% O2+ N2, 1500 ppm CO and several common interfering gases were introduced. The equivalent current response of the sensor was measured and converted into CO readings. The results are shown in Table 1 and... Figure 7 As shown.

[0043] Test Results: The sensor responds accurately to 1500 ppm CO. For various gases such as 1000 ppm methane, 1 ppm n-heptane, 1 ppm hydrogen sulfide, and 5000 ppm carbon dioxide, the sensor's response is almost zero. For gases such as 16 ppm isooctane and 8 ppm ammonia, its equivalent CO reading is also far below 40 ppm, demonstrating extremely high selectivity.

[0044] Table 1. Test results of sensor selectivity for mixed gases

[0045] 3. Stability Analysis Figure 8 shows the long-term stability test curve of the sensor over 80 days. Figure 8 The error bar represents the standard deviation of the response current from three parallel tests at each time point. During the intermittent cyclic testing from 0 to 80 days, the sensor's response current to 1500 ppm CO remained consistently at a similar level, without significant sustained attenuation or baseline drift. The small amplitude of the error bar at each test point indicates good repeatability of the sensor in a single detection. After an 80-day aging test, the device maintained a stable sensing output with signal fluctuations ≤10%, demonstrating that the CO sensor possesses excellent long-term operational stability and reliable long-term detection capability.

[0046] 4. Response recovery test analysis T90 time refers to the time required for a concentration sensor to reach 90% of its steady-state response from its initial state; it is a key indicator for measuring the sensor's dynamic performance. For example... Figure 9 The figure shows the sensor's response and recovery curves. When the sensor is placed in CO gas with a concentration of 500 ppm, its T90 response time is 9 s and its T90 recovery time is 18 s. Figure 10 As shown, the sensor's response recovery time in CO atmospheres of different concentrations is less than 30 s, demonstrating rapid response and rapid desorption recovery kinetic characteristics. Figure 4 After the CO concentration tests at each gradient were completed, the sensor output signal could completely fall back to the initial baseline, indicating that the electrode material has good signal reversibility, no obvious baseline drift, irreversible adsorption poisoning problems, and excellent device cycle stability.

[0047] 5. Comparative analysis with different reference electrodes The CO sensor in the comparative example is the same as in specific embodiment 1, except that the reference electrode is replaced with a Pt electrode.

[0048] Figure 11 With Pt as the reference electrode (the same material as the counter electrode and the first sensitive electrode, meaning all three electrodes are Pt), under the same testing conditions (ambient temperature 650℃, O2 concentration 21 vol.%, carbon monoxide concentration 1500 ppm, and a mixture of other gases including nitrogen), the sensor with Pt as the reference electrode showed a response of -6 μA to 1500 ppm CO, significantly lower than the -79.8 μA response of the system using MnO2 as the reference electrode. Figure 4At an ambient temperature of 650℃ and an O2 concentration of 21 vol.%, with carbon monoxide concentrations of 100, 200, 500, 1000, and 1500 ppm, the response signals were -8.8, -15.6, -32.3, -56.5, and -79.8 μA, respectively. The Pt reference structure exhibits a weak response, making it difficult to effectively identify low-concentration CO.

[0049] Specific Embodiment 4: A carbon monoxide sensor with oxygen partial pressure self-compensation function.

[0050] The carbon monoxide sensor in Specific Embodiment 1 is based on the electrochemical oxidation reaction of carbon monoxide at the three-phase interface of the electrode. In practical applications, such sensors commonly suffer from oxygen cross-interference. Specifically, fluctuations in the oxygen concentration in the sensor's environment cause oxygen and carbon monoxide to compete for adsorption and consumption of oxygen ions on the electrode surface, resulting in a nonlinear shift in the limiting current signal of carbon monoxide related to the oxygen partial pressure. Single-cell structure sensors cannot synchronously acquire accurate real-time oxygen partial pressure data, and single-point calibration of carbon monoxide alone is insufficient to eliminate this interference. Under high-oxygen or variable-oxygen conditions, the indication deviation can reach over 30%, severely limiting the sensor's measurement accuracy and environmental adaptability. Therefore, this paper further provides a carbon monoxide sensor with oxygen partial pressure self-compensation function and its compensation and correction method. By integrating a second sensitive electrode to monitor the oxygen partial pressure in real time and combining it with a nonlinear compensation model to correct the original carbon monoxide signal, the measurement accuracy of carbon monoxide under wide oxygen conditions is significantly improved.

[0051] This embodiment further adds a second sensitive electrode 5 based on specific embodiment one. The specific structure is as follows: Figure 12 As shown, the first sensitive electrode 4 is prepared using platinum-YSZ composite slurry, which is used to detect the concentration of carbon monoxide in the environment and output the original limiting current signal of carbon monoxide.

[0052] The second sensitive electrode 5 is prepared using a platinum-YSZ composite slurry, which is made of the same material as the first sensitive electrode 4, but the preparation process parameters differ from those of the first sensitive electrode. Specifically, in this embodiment, the sintering temperature of the second sensitive electrode 5 is set to 1300℃, and the film thickness after sintering is controlled to 35μm, so that the electrode produces a specific electrochemical response to oxygen, while having virtually no response to carbon monoxide.

[0053] The second sensitive electrode 5 and the counter electrode 2 constitute an oxygen concentration detection unit. The measurement of the open circuit potential between them is independent of the carbon monoxide detection circuit, does not introduce additional polarization, and does not affect the acquisition of the carbon monoxide limiting current.

[0054] The second sensitive electrode 5 is used to measure the oxygen partial pressure in the environment in real time and outputs an open-circuit potential signal related to the oxygen partial pressure. The second sensitive electrode 5 and the first sensitive electrode 4 can be disposed on the same surface of the solid electrolyte substrate 1, or they can be disposed on different surfaces. The surface areas of the solid electrolyte substrate 1 that are connected to the counter electrode 2, the first sensitive electrode 4, and the second sensitive electrode 5 are all roughened surfaces formed by sandblasting to increase electrode adhesion strength and interfacial reactivity.

[0055] The carbon monoxide sensor in this embodiment, its working principle, measurement, and compensation calibration method include the following steps: Real-time monitoring of oxygen partial pressure: An oxygen concentration detection unit is constructed using the second sensitive electrode 5 and the counter electrode 2, and the open-circuit potential between the second sensitive electrode 5 and the counter electrode 2 is measured. This open-circuit potential is determined by the ratio of the oxygen partial pressures on both sides and strictly follows the Nernst equation: (1), Where E is the electromotive force, R is the gas constant, T is the absolute temperature, F is the Faraday constant, PO₂ is the partial pressure of oxygen, and n is the number of electrons participating in the oxygen equilibrium electrochemical reaction. Figure 13 As shown in the figure, experimental measurements indicate that at an operating temperature of 650℃, with an oxygen concentration ranging from 2 to 40 vol.%, the electromotive force exhibits a good linear relationship with the logarithm of the oxygen concentration, with a slope of 48.2 mV per ten times the concentration range. This corresponds to an electron number n of approximately 3.9, consistent with the theoretical value. Based on this relationship, the measured open-circuit potential can be converted into the real-time dimensionless oxygen partial pressure of the current environment.

[0056] Acquisition of raw carbon monoxide signal: A carbon monoxide detection unit is constructed by using the first sensitive electrode 4 and the counter electrode 2. The gas is controlled to reach the electrode by Knudsen diffusion through a porous diffusion barrier, thereby obtaining the original limiting current signal of carbon monoxide that is interfered with by oxygen.

[0057] Nonlinear compensation correction for oxygen interference: An oxygen interference compensation model was constructed. Studies have shown that gaseous oxygen and carbon monoxide exhibit a competitive reaction at the electrode three-phase interface, and the offset of the original limiting current of carbon monoxide caused by oxygen is linearly positively correlated with the square root of the ambient oxygen partial pressure. Therefore, a compensation model was constructed using the square root term of the oxygen partial pressure. The real-time dimensionless oxygen partial pressure obtained in step (1) was substituted into the following formula to correct the original limiting current of carbon monoxide obtained in step (2): (2) Where ICOraw is the original limiting current value for carbon monoxide, and ICOcorr is the compensated and corrected current value for carbon monoxide. This is the real-time dimensionless oxygen partial pressure. This is the oxygen cross-interference coefficient obtained from two-dimensional standard gas calibration.

[0058] After calibration, the maximum relative deviation of CO measurement in the full oxygen range of 2 vol% to 40 vol% was reduced to less than 3.0%, effectively suppressing the coupling interference of O2 on the CO detection signal and significantly improving the accuracy of carbon monoxide measurement under wide oxygen conditions.

[0059] Table 2. CO detection error data and comparison results before calibration compensation

[0060] Table 3. CO detection error data and comparison results after calibration compensation

[0061] In this embodiment, the ambient oxygen partial pressure is acquired in real time through the second sensitive electrode 5, and the original limiting current of carbon monoxide is compensated and corrected according to equation (2). Tables 2 and 3 respectively show the comparison data of detection error before and after compensation under the same oxygen partial pressure and carbon monoxide concentration conditions. The results show that after compensation and correction in this embodiment, the measurement error of carbon monoxide in the whole oxygen range is significantly reduced, proving the effectiveness of the proposed solution.

[0062] In summary, by integrating a second sensitive electrode 5 into the existing sensor structure, and ensuring that this electrode operates in open-circuit potential mode without external polarization, real-time, non-destructive monitoring of the oxygen partial pressure in the environment is achieved without affecting the normal operation of the original carbon monoxide detection circuit. The structure is compact and easy to implement. Based on the Nernst equation, the oxygen partial pressure is accurately measured, and a nonlinear compensation model is constructed using the square root term of the oxygen partial pressure, eliminating the cross-coupling interference of oxygen on the carbon monoxide signal at the mechanistic level. Experimental verification shows that within the full oxygen range of 2 vol.% to 40 vol.%, the maximum relative deviation of carbon monoxide measurement is significantly reduced from 244.6% before compensation to less than 3.0%, greatly improving the sensor's measurement accuracy and environmental adaptability under wide oxygen conditions.

[0063] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A carbon monoxide sensor based on a YSZ substrate, characterized in that, The device includes a solid electrolyte substrate (1), which is yttrium-stabilized zirconium oxide; a counter electrode (2), a reference electrode (3), and a first sensitive electrode (4) disposed on the same surface of the solid electrolyte substrate (1); the counter electrode (2) and the first sensitive electrode (4) are both sintered bodies composed of platinum or platinum alloy particles and solid electrolyte particles, and the film thickness of the first sensitive electrode (4) is greater than the film thickness of the counter electrode (2); the reference electrode (3) is a manganese dioxide sintered body, the film thickness of the first sensitive electrode (4) is 20-40 μm, the film thickness of the counter electrode (2) is 14-18 μm, the area ratio of the counter electrode (2) to the first sensitive electrode (4) is 1:2, and also includes a heater, which is disposed on the surface of the solid electrolyte substrate (1) opposite to the surface on which the counter electrode (2), the reference electrode (3), and the first sensitive electrode (4) are disposed, or disposed near the solid electrolyte substrate (1).

2. The carbon monoxide sensor based on a YSZ substrate according to claim 1, characterized in that, The reference electrode (3) is made of manganese dioxide powder with a purity of 85%-99.95%, with a thickness of 1-30μm and a diameter of 0.2-1mm.

3. The carbon monoxide sensor based on a YSZ substrate according to claim 1, characterized in that, It also includes a second sensitive electrode, which is disposed on the solid electrolyte substrate (1) for measuring oxygen concentration and compensating for carbon monoxide concentration measurement value by means of oxygen concentration measurement value.

4. The carbon monoxide sensor based on a YSZ substrate according to claim 3, characterized in that, The second sensitive electrode has a sintering temperature of 1200-1350℃, a film thickness of 9-80μm, and an operating bias voltage of 0.01-1V.

5. The carbon monoxide sensor based on a YSZ substrate according to claim 3, characterized in that, The surface area where the solid electrolyte substrate (1) connects with the counter electrode (2), the first sensitive electrode (4) and the second sensitive electrode is a rough surface formed by sandblasting.

6. A method for fabricating a carbon monoxide sensor based on a YSZ substrate as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Print or coat manganese dioxide paste onto the surface of a solid electrolyte substrate (1) and sinter it at 1300-1450℃ to form a reference electrode (3). Step 2: Print or coat a mixed slurry composed of platinum or platinum alloy particles and solid electrolyte particles on the surface of the solid electrolyte substrate (1), and sinter it at 1200-1400℃ to form a counter electrode (2) and a first sensitive electrode (4); wherein the printing thickness of the first sensitive electrode (4) is greater than the printing thickness of the counter electrode (2), so that the film thickness of the first sensitive electrode (4) after sintering is greater than the film thickness of the counter electrode (2).

7. A method for detecting carbon monoxide concentration using the sensor according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Place the sensor in an environment of 600-900℃; Step 2: Apply a bias voltage between the first sensitive electrode (4) and the reference electrode (3), wherein the bias voltage is -1V to -0.05V; Step 3: Deliver the gas to be tested to the surface of the first sensitive electrode (4); Step 4: Measure the current signal value or electromotive force signal value in the circuit between the first sensitive electrode (4) and the counter electrode (2), and determine the concentration of carbon monoxide based on the signal value.

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