Electrode preparation method of electrochemical ammonia gas sensor and ammonia gas detection method
By preparing hierarchical porous electrodes and combining them with frequency domain correction technology, the problem of low sensitivity of traditional electrodes was solved, and high-sensitivity ammonia detection was achieved, which can effectively detect trace amounts of ammonia.
Patent Information
- Application Number
- CN202510974320.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-15
- Publication Date
- 2025-10-17
AI Technical Summary
Traditional screen-printed electrodes have low activity at the gas-liquid-solid three-phase interface and poor catalyst utilization, resulting in ammonia gas reacting only on the electrode surface, making it difficult to detect trace amounts of ammonia and causing low sensitivity.
A hierarchical porous electrode, comprising a surface nanopore and a bottom micropore structure, was prepared using a gradient coating process. Ruthenium-based nanoparticles were used as a catalyst, and the catalytic activity was enhanced by plasma activation and electrostatic spray deposition techniques. Ammonia detection was performed by combining frequency domain correction and baseline drift compensation techniques.
The sensitivity of ammonia detection has been improved, with a current drift of less than 3%/month at 100ppm NH3 and a detection limit of 0.05ppm, thus extending the detection limit of electrochemical ammonia sensors.
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Figure CN120801455A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of electrochemical sensor, in particular to an electrode preparation method of electrochemical ammonia sensor and an ammonia detection method. BACKGROUND
[0002] An electrochemical sensor is an instrument for measuring various chemical components. The electrochemical sensor works by reacting with the measured gas and generating an electric signal proportional to the gas concentration. A typical electrochemical sensor is composed of a sensing electrode (or working electrode) and a counter electrode, and is separated by a thin electrolyte layer. Electrochemical gas sensors are widely used in industrial safety, environmental monitoring and other fields due to their high sensitivity, selectivity and real-time monitoring capability.
[0003] Ammonia (NH3) is a highly toxic gas. In the scenarios of breeding and chemical industry, the concentration of ammonia often exceeds the safety threshold (such as 50 ppm in poultry house), and high-precision real-time monitoring is urgently needed. The core component of electrochemical ammonia detector is ammonia sensor, and the core component of ammonia sensor is electrode. The traditional screen-printed electrode has the defect of low sensitivity because the activity of gas-liquid-solid three-phase interface is low, the utilization rate of catalyst is poor, and ammonia gas only reacts on the surface of the electrode, which is difficult to diffuse to the inside to form a high-activity gas-liquid-solid three-phase interface, so it cannot detect trace ammonia. SUMMARY
[0004] Therefore, in order to improve the detection sensitivity of the electrochemical ammonia sensor, the present application provides an electrode preparation method of electrochemical ammonia sensor and an ammonia detection method, and the specific technical scheme is as follows:
[0005] An electrode preparation method of electrochemical ammonia sensor, comprising the following steps:
[0006] A composite slurry containing a catalyst, a pore-forming agent, a binder and a dispersant is prepared;
[0007] The surface of the conductive substrate is activated;
[0008] The composite slurry is deposited on the surface of the conductive substrate by gradient coating process to form a hierarchical porous structure with surface nanometer pores and bottom micrometer pores;
[0009] The coated conductive substrate is subjected to step drying and curing to obtain a hierarchical porous electrode.
[0010] The electrode preparation method of the electrochemical ammonia sensor can improve the interface reaction kinetics and the sensitivity of ammonia detection by preparing a multi-stage porous electrode, and solves the problems of low gas-liquid-solid three-phase interface activity and poor catalyst utilization of traditional screen-printed electrodes, ammonia gas only reacts on the surface of the electrode, it is difficult to diffuse to the inside to form a high-activity gas-liquid-solid three-phase interface, thereby resulting in low detection sensitivity and inability to detect trace amounts of ammonia.
[0011] Preferably, in the composite slurry, the catalyst is ruthenium-based nanoparticles with a mass ratio of 6%-10%; the pore-forming agent is a composite of ammonium oxalate and polyethylene glycol with a mass ratio of 3%-5%; the binder is polyvinylidene fluoride emulsion with a mass ratio of 1%-3%; and the dispersing agent is a mixed solvent of azomethine pyrrolidone and propanol with a volume ratio of 4:1-6:1.
[0012] Preferably, the step of drying and curing in stages comprises:
[0013] drying at 40-60℃ for 30-90 minutes;
[0014] drying at 70-90℃ for 60-150 minutes.
[0015] Preferably, the surface activation treatment is plasma activation, an argon atmosphere is used, the power is 40-60W, and the treatment time is 3-7 minutes.
[0016] Preferably, the gradient coating process is electrostatic spray deposition, the voltage is 10-20kV, the flow rate is 0.3-0.8mL / h, the pore size of the surface layer of nanopores is 30-80nm, and the pore size of the bottom layer of micropores is 0.5-2μm.
[0017] Preferably, the catalyst is distributed in the form of island-shaped nanoclusters in the composite slurry, with a diameter of 5-30nm and a coverage of 15%-40%, and is modified on the surface of the electrode by a sputtering process.
[0018] An ammonia detection method of an electrochemical ammonia sensor, which is based on the electrochemical ammonia sensor for ammonia detection, wherein the electrochemical ammonia sensor comprises the electrode prepared by the electrode preparation method.
[0019] Preferably, the ammonia detection method further comprises:
[0020] obtaining a direct current basic deviation, an alternating current disturbance amplitude, and a scanning frequency;
[0021] obtaining an electrode excitation signal function according to the direct current basic deviation, the alternating current disturbance amplitude, and the scanning frequency.
[0022] Preferably, the ammonia detection method further comprises:
[0023] an initial current amplitude is obtained, and a frequency domain correction term for separating high frequency electrochemical noise and a target signal is obtained according to the initial current amplitude and a scanning frequency;
[0024] a pore distribution factor, a desorption decay coefficient, a concentration correction index for simulating nonlinear response caused by competition of adsorption sites in a catalytic reaction, and a catalytic enhancement coefficient representing electron transfer efficiency of a ruthenium nano-catalytic site are obtained;
[0025] a fast response term for realizing fast signal capture and dynamic balance control in an initial stage of gas adsorption is obtained according to the pore distribution factor, the desorption decay coefficient, the concentration correction index, and the catalytic enhancement coefficient;
[0026] a baseline drift compensation term for dynamically offsetting baseline shift caused by historical exposure accumulation is obtained;
[0027] a current-concentration-time response equation is constructed according to the fast response term, the frequency domain correction term, and the baseline drift compensation term, and a relationship between output current, time, and ammonia concentration of the electrochemical ammonia sensor is obtained according to the current-concentration-time response equation. BRIEF DESCRIPTION OF DRAWINGS
[0028] The present application can be further understood from the following description in conjunction with the drawings. The components in the drawings are not necessarily drawn to scale, but emphasis is instead placed upon illustrating the principles of the embodiments. In different views, the same reference numerals designate corresponding parts.
[0029] Figure 1 is a schematic diagram of the overall process of an electrode preparation method of an electrochemical ammonia sensor according to an embodiment of the present application;
[0030] Figure 2 is a schematic diagram of the overall process of an ammonia detection method of an electrochemical ammonia sensor according to an embodiment of the present application;
[0031] Figure 3 is a schematic diagram of the overall process of an ammonia detection method of an electrochemical ammonia sensor according to another embodiment of the present application. DETAILED DESCRIPTION
[0032] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application is further described in detail below in conjunction with embodiments thereof. It should be understood that the specific embodiments described herein are merely used to explain the present application, and do not limit the protection scope of the present application.
[0033] It should be understood that when an element as a layer, region or plate is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In addition, it should be understood that when an element is referred to as being "connected" to or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements can be present. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.
[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.
[0035] The "first", "second" in the present application do not represent the specific number and order, but only for the name of the distinction.
[0036] As shown in the electrode preparation method of an electrochemical ammonia sensor in an embodiment of the present application includes the following steps: Figure 1 S10, a composite slurry containing a catalyst, a pore-forming agent, a binder and a dispersant is prepared.
[0037] Specifically, the catalyst can be selected as RuOx / Ru nanoparticles. The pore-forming agent can be selected as a composite system of soluble salt and high molecular polymer, and a hierarchical pore structure is formed by selective dissolution to remove the pore-forming agent. The binder can be selected as a thermoplastic elastomer or a water-based resin, which has a glass transition temperature lower than the curing temperature, so as to improve the flexibility of the electrode. The dispersant contains a surfactant, such as sodium dodecyl sulfate, and the concentration is 0.1wt%-0.5wt% to optimize the rheological property of the slurry.
[0038] As a preferred technical solution, in the composite slurry, the catalyst is ruthenium-based nanoparticles, the mass ratio is 6%-10%; the pore-forming agent is a composite of ammonium oxalate and polyethylene glycol, the mass ratio is 3%-5%; the binder is polyvinylidene fluoride emulsion, the mass ratio is 1%-3%; and the dispersant is a mixed solvent of azomethine pyrrolidine and propanol, the volume ratio is 4:1-6:1, preferably 5:1.
[0039] The viscosity η of the composite slurry is calculated by the formula
[0040] The viscosity determines the leveling property and permeability of the slurry during coating, and directly affects the uniformity of the electrode microstructure.
[0041] where k is a process constant, an empirical constant related to the properties of slurry components, affected by factors such as particle morphology and solvent polarity, which integrates the intrinsic properties of materials and is used to calibrate the deviation between actual viscosity and theoretical value. Generally, it can be pre-set according to experience.
[0042] E a represents the activation energy, which can be understood as the energy threshold required for slurry flow (unit: kJ / mol), reflecting the strength of intermolecular forces, which is used to measure temperature sensitivity. The higher the activation energy, the greater the influence of temperature on viscosity.
[0043] φ represents the solid content, which refers to the mass fraction of solid substances in the slurry (0<φ<1), and is the core variable that dominates the change in viscosity. φ 2.5 represents the 2.5th power of the solid content, which has an amplification effect. The solid content of electrode slurry is usually between 0.3 and 0.45, and too high will cause coating cracking, and too low will reduce electrode density. It should be noted that the power of the solid content can be adjusted according to actual conditions, and is not limited to 2.5. R is the gas constant, generally taking the value of 8.314 J / mol·K, and T is the environmental temperature of the slurry.
[0044] The viscosity function can predict the trend of viscosity change. Specifically: 1. The influence of solid content is quantified through the φ 2.5 term, which indicates that when φ>0.4, the hydration layers between particles overlap, and the viscosity increases exponentially. For example, when φ increases from 0.4 to 0.45, η increases by about 34%; 2. The temperature sensitivity is quantified through the term: if E a =30kJ / mol, and the temperature rises from 25℃ to 35℃, η decreases by about 30%. Low-temperature solidification steps (50℃→80℃) can avoid the dramatic fluctuation of the term, preventing the generation of bubbles.
[0045] In general, the viscosity function provides a quantifiable process control method for electrode slurry by combining the temperature effect of activation energy and the power-law relationship of solid content.
[0046] S11, surface activation treatment is performed on the conductive substrate.
[0047] The conductive substrate is carbon cloth, flexible PET or graphene film, with a thickness of 50-200μm to adapt to different application scenarios.
[0048] As a preferred technical solution, the conductive substrate is carbon cloth, and the surface activation treatment is plasma activation in an argon atmosphere with a power of 40W-60W and a treatment time of 3-7 minutes to enhance the adhesion between the substrate and the slurry. Further, the power is set to 50W and the treatment time is set to 5 minutes.
[0049] S12, depositing the composite slurry on the surface of the conductive substrate by a gradient coating process to form a hierarchical porous structure with surface nanoholes and bottom micropores.
[0050] As a preferred technical solution, the gradient coating process is electrostatic spray deposition, the voltage is 10-20 kV, the flow rate is 0.3-0.8 mL / h, the pore size of the surface nanoholes is 30-80 nm, and the pore size of the bottom micropores is 0.5-2 μm, so as to enhance the catalytic activity.
[0051] Further, the voltage is set to 15 V, the flow rate is set to 0.5 mL / h, the surface nanohole size is set to 50 nm, and the bottom micropore size is set to 1 μm.
[0052] S13, performing stepwise drying and curing on the coated conductive substrate to obtain a hierarchical porous electrode.
[0053] As a preferred technical solution, the stepwise drying and curing includes: drying at 40-60 °C for 30-90 min; increasing the temperature to 70-90 °C and drying for 60-150 min. One of the effects of stepwise drying and curing is to avoid damage to the flexible substrate at high temperature.
[0054] Further, drying at 50 °C for 60 min; increasing the temperature to 80 °C and drying for 120 min.
[0055] As a preferred technical solution, the catalyst is distributed in the form of island-like nanoclusters in the composite slurry, with a diameter of 5-30 nm and a coverage of 15-40%, and is modified on the surface of the electrode by a sputtering process. The mechanism is that Ru catalyzes the decomposition of NH3 into H atoms, which penetrate the dielectric layer to regulate the channel carrier.
[0056] For the output current I d after regulating the channel carrier concentration based on the electrochemical reaction, the formula is used, where μ n represents the electron mobility, C ox represents the gate oxide capacitance, W and L represent the channel width and channel length, respectively, V g , V th , and V d represent the gate voltage, threshold voltage, and drain voltage, respectively, ΔH represents the adsorption enthalpy change, and β' represents the sensitivity coefficient. The formula is based on the MOSFET current equation to simulate the regulation of the carrier concentration by the electrochemical reaction.
[0057] e -β'ΔHThe hydrogen adsorption enthalpy change is exponentially modulated by the current. When NH3 is decomposed into H atoms and adsorbed, the change of ΔH is amplified by the β' coefficient, resulting in a sudden change in carrier concentration, which is ultimately reflected in the current signal. Ru nanoclusters accelerate the decomposition of NH3 into H atoms, directly affecting the size of ΔH, while the hierarchical porous electrode can increase the effective reaction area by increasing the W / L (reflecting the restriction of the electrode geometry on the current) ratio, thereby enhancing the current signal.
[0058] Based on the prepared hierarchical porous electrode, an electrochemical ammonia sensor is prepared and subjected to accelerated aging test. The current drift is less than 3% per month at 100 ppm NH3, and the detection limit is 0.05 ppm.
[0059] The island-like Ru nanoclusters provide high active sites, which reduce ΔH in the response current formula, thereby increasing the value of the exponential term e -β'ΔH , significantly improving the current output and increasing the sensitivity of the prepared electrochemical ammonia sensor.
[0060] In addition, the hierarchical porous electrode can enhance the weak signal capture capability to a certain extent by improving the gas adsorption efficiency, combined with the low-temperature decomposition ability of the Ru island catalyst layer for NH3, thereby expanding the lower limit of the detection of the electrochemical ammonia sensor.
[0061] In summary, the electrode preparation method of the electrochemical ammonia sensor can improve the interface reaction kinetics and increase the sensitivity of ammonia detection by preparing a hierarchical porous electrode, thereby solving the problem of low detection sensitivity and inability to detect trace ammonia in traditional screen-printed electrodes due to low activity of the gas-liquid-solid three-phase interface and poor catalyst utilization rate. Ammonia gas only reacts on the surface of the electrode, and it is difficult to diffuse to the inside to form a highly active gas-liquid-solid three-phase interface, resulting in low detection sensitivity and inability to detect trace ammonia.
[0062] An ammonia detection method of an electrochemical ammonia sensor according to an embodiment of the present application, which is based on the electrochemical ammonia sensor for ammonia detection, wherein the electrochemical ammonia sensor comprises the electrode prepared by the electrode preparation method.
[0063] As shown in Figure 2 , the ammonia detection method further comprises:
[0064] S20, obtaining a direct current basic deviation V dc , an alternating current disturbance amplitude V ac and a scanning frequency f;
[0065] S21, obtaining an electrode excitation signal function V(t) = V dc + V ac ·sin(2πft) according to the direct current basic deviation, the alternating current disturbance amplitude and the scanning frequency; wherein V(t) represents the electrode excitation voltage.
[0066] Generally, the direct current base bias can be selected as 0.3V, which provides the base potential of the electrode reaction, ensuring the ammonia oxidation reaction. The alternating current disturbance amplitude is 50mV, which is applied to the small amplitude sinusoidal disturbance to avoid electrode polarization and stimulate the interface charge transfer process. The scanning frequency is between 0.1Hz-100Hz, and different kinetic processes are separated by frequency domain scanning: low frequency (<1Hz) reflects diffusion control, and high frequency (>10Hz) reflects the interface reaction.
[0067] In the electrode excitation signal function V(t) = V dc + V ac ·sin(2πft), the low frequency band is used to capture the mass transfer process of ammonia diffusion to the electrode surface, and the response current is related to the concentration gradient; the high frequency band is used to analyze the charge transfer resistance of the electrode surface catalytic reaction (Ru nanocluster catalytic decomposition of NH3).
[0068] The alternating current disturbance amplitude can be dynamically adjusted according to the electrode aging state. When the electrode is new, the alternating current disturbance amplitude is set to 50mV, and after 30 days of use, the alternating current disturbance amplitude is increased to 80mV to compensate for the loss of activity.
[0069] Specifically, the charge transfer resistance formula is expressed as It can be understood that the charge transfer resistance formula is an equivalent circuit model of electrochemical impedance spectroscopy, which is used to analyze the kinetic process of the electrode surface catalytic reaction (such as Ru nanocluster catalytic decomposition of NH3), which can separate the following three key processes through frequency domain analysis:
[0070] 1. Solution resistance R s , reflecting the ohmic resistance of the electrolyte solution and the electrode contact resistance, which dominates the impedance in the high frequency region, generally ranging from 0.1 ohm to 10 ohm.
[0071] 2. Double-layer capacitance C dl , which characterizes the charge storage capacity of the electrode / solution interface, which behaves as a capacitive reactance at high frequencies, generally ranging from 1μF / cm 2 -100μF / cm 2 .
[0072] 3. Charge transfer resistance R ct and adsorption capacitance C φ : describe the interface kinetics of the electrode surface catalytic reaction, the charge transfer resistance determines the resistance of the charge passing through the interface in the electrode reaction, a low value indicates fast electron transfer, generally ranging from 0.1 ohm to 10 ohm, and the adsorption capacitance is caused by the adsorbed species on the electrode surface, which forms a time constant with the charge transfer resistance in the medium frequency region, generally ranging from 0.01μF / cm 2 -1μF / cm 2 .
[0073] Generally, the relationship between ammonia concentration and charge transfer resistance needs to be calibrated with standard gas, and the specific function is where C NH3 represents the ammonia concentration, k is the sensitivity coefficient determined by the electrode catalytic activity (such as Ru nanoclusters) and the double-layer structure, which is related to the concentration and conductance change, b represents the baseline offset, which is used to compensate for the zero drift (such as electrode aging, environmental temperature and humidity interference, etc.), and the index 0.8 is a non-linear mass transfer correction factor, which represents the effect of the diffusion process deviating from the ideal linear model.
[0074] In this formula , the ammonia concentration is directly inverted by measuring the charge transfer resistance, and the concentration quantitative output is realized. The index 0.8 corrects the deviation of the ideal Fick diffusion law, and is more consistent with the actual mass transfer process. The b term dynamically compensates the baseline drift, which has the effect of resisting environmental interference.
[0075] Fick's law predicts that the mass transfer rate is proportional to the concentration gradient (i.e. C 1.0 ), but in fact there are nonlinear factors such as porous electrode boundary layer effect and surface adsorption saturation. Through frequency domain impedance spectrum analysis, it is found that the diffusion impedance in the low frequency band (0.1Hz-1Hz) is proportional to C 0.8 , which verifies the nonlinearity of mass transfer, while the charge transfer resistance in the high frequency band (>10Hz) is dominant but modulated by the diffusion process.
[0076] For the sensitivity coefficient and the baseline offset, the LSTM network can be dynamically updated to reduce the frequency of manual calibration.
[0077] As a preferred technical solution, as shown in Figure 3 , the ammonia detection method further comprises:
[0078] S30, obtaining an initial current amplitude, and obtaining a frequency domain correction term for separating high-frequency electrochemical noise and target signal according to the initial current amplitude and the scanning frequency.
[0079] S31, obtaining a pore size distribution factor, a desorption decay coefficient, a concentration correction index for simulating the nonlinear response caused by adsorption site competition in the catalytic reaction, and a catalytic enhancement coefficient representing the electron transfer efficiency of the ruthenium nanocatalytic site.
[0080] S32, obtaining a fast response term for realizing fast signal capture and dynamic balance control in the initial stage of gas adsorption according to the pore size distribution factor, the desorption decay coefficient, the concentration correction index, and the catalytic enhancement coefficient.
[0081] S33, obtaining a baseline drift compensation term for dynamically offsetting the baseline offset accumulated by historical exposure.
[0082] S34, constructing a current-concentration-time response equation according to the fast response term, the frequency domain correction term and the baseline drift compensation term, and obtaining a relationship between the output current I, time t and ammonia concentration C of the electrochemical ammonia sensor according to the current-concentration-time response equation.
[0083] Specifically, the current-concentration-time response equation is expressed as wherein I(t, C) represents the relationship between the output current I, time t and ammonia concentration C of the electrochemical ammonia sensor, κ·λ·C μ ·tanh(βt)·e -γ t, I0·e -α t·cos(2πft+φ), respectively represent the fast response term, the frequency domain correction term and the baseline drift compensation term, κ represents a catalytic enhancement coefficient, λ represents a pore size distribution factor, C μ represents a concentration correction index, μ represents a correction factor, e represents a natural constant, β represents a diffusion rate constant, γ represents a desorption decay coefficient, I0 represents an initial current amplitude, α represents a relaxation rate of a double-layer capacitance, φ represents a phase angle, ζ represents a drift compensation coefficient, represents an integral term of ammonia concentration C.
[0084] More specifically, the catalytic enhancement coefficient is defined as the electron transfer efficiency per unit area of the catalytic active site of the ruthenium island, that is, μ n represents a carrier mobility, A eff represents an effective surface area of the hierarchical porous electrode, ΔG + represents an activation energy of ammonia decomposition reaction. The pore size distribution factor is dimensionless, which represents the diffusion delay effect of ammonia in the gradient porous structure (50 nm of surface layer / 1 μm of bottom layer), and the gas permeability is ensured by the 1 μm large pores of the bottom layer to avoid diffusion bottleneck. D eff represents an effective diffusion coefficient, and δ is an average pore size.
[0085] The correction factor μ can generally be set to 0.8, and the concentration correction index C 0.8 breaks through the traditional linear model and reflects the catalytic site competition mechanism: the higher the ammonia concentration, the fewer the idle active sites, and the current growth rate decreases. e -γ t is used to suppress residual adsorption interference and offset the accumulation of ammonia molecules that are not completely desorbed. tanh(βt) simulates the transition process of gas diffusion from linear growth to saturation, and the surface layer 50 nm of microporous structure preferentially adsorbs ammonia molecules, which reflects the transition of diffusion rate from linearity to saturation, and β can be set to 0.25 s -1 . The desorption decay coefficient has a unit of s -1 , and γ=k d ·[1+θres (t)], k d denotes the intrinsic desorption rate, θ res is the residual adsorbed molecule coverage. The desorption decay coefficient quantifies the current decay caused by the incomplete desorption of adsorbed molecules, which can be set as 0.008 s -1 , and can be set as 0.012 s -1 after the degradation of flexible substrate such as 1000 times of bending.
[0086] The cos(2πft+φ) term can be understood as an AC modulation term, which filters noise by scanning frequency, suppresses the low-frequency response of H2O / SO2 at f>50Hz, has a frequency domain separation effect, and the ζ term makes the baseline recovery speed after 100 ppm ammonia test increase by 60%, which can realize dynamic baseline compensation. The phase angle is determined by the charge transfer resistance and the double-layer capacitance, and reflects the ion recombination speed at the interface. -αt The double-layer relaxation decay avoids the capacitance effect from masking the real gas response. The integral term of ammonia concentration C is used to quantify the total amount of ammonia that the sensor has historically contacted in real time, which is related to the sustained interference of residual molecules on the current.
[0087] Drift compensation coefficient I drift denotes the drift current, dI drift denotes the differential change of baseline drift current, i.e. the current offset caused by the continuous accumulation of undesorbed ammonia molecules due to long-term exposure of the sensor to ammonia environment. d(∫C(τ)dτ) represents the differential change of historical cumulative ammonia concentration.
[0088] The drift compensation coefficient is proportional to the accumulation of undesorbed ammonia molecules, specifically, the undesorbed ammonia molecules continuously interfere with the electrode interface due to chemical adsorption or physical retention, resulting in a baseline current I drift unidirectional shift, and the drift compensation coefficient directly characterizes the intensity of this interference.
[0089] Diffusion rate constant which quantifies the transition speed of ammonia diffusion rate in the gradient porous electrode from linear to saturation. The diffusion rate constant is mainly determined by the microstructure of the electrode material. The gradient porous structure (50 nm in the surface layer / 1 μm in the bottom layer) leads to a layered average pore size, and the diffusion rate constant differs significantly in different regions, while the effective diffusion coefficient is affected by temperature, humidity and catalyst coverage, which can be measured by experiment or calculated by molecular dynamics simulation. For the calibration of the diffusion rate constant, the tanh(βt) curve can be fitted by concentration step experiment (such as 20→100 ppm), and the charge transfer process can be analyzed by electrochemical impedance spectroscopy to finally determine the value of the diffusion rate constant.
[0090] The current-concentration-time response equation jointly describes three-stage kinetics of gas diffusion in porous layer (i.e., λ), surface catalytic reaction (i.e., κ), and carrier migration (i.e., μ n ) with the synergistic effect of diffusion-reaction-electron transfer. In general, the current-concentration-time response equation breaks through the limitations of the traditional first-order linear model, integrates three mechanisms of porous diffusion non-ideality (i.e., fast response term), catalytic interface quantum effect (i.e., frequency domain correction term), and dynamic memory effect (i.e., baseline drift compensation term) for the first time, and provides core algorithm support for high-precision flexible ammonia gas sensors.
[0091] Finally, it should be pointed out that for the function formula involved in the present application, the variables therein can be dimensionless for convenient calculation and processing.
[0092] The technical features of the above-described embodiments can be combined arbitrarily, and to make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present application.
[0093] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.
Claims
1. A method for preparing an electrode for an electrochemical ammonia sensor, characterized in that: The electrode preparation method comprises the following steps: preparing a composite slurry comprising a catalyst, a pore former, a binder and a dispersant; Performing surface activation treatment on the conductive substrate; Depositing the composite slurry on the surface of the conductive substrate through a gradient coating process to form a hierarchical porous structure with surface nanopores and bottom micropores; The coated conductive substrate is subjected to stepwise drying and curing to obtain a graded porous electrode.
2. The method for preparing an electrode for an electrochemical ammonia sensor according to claim 1, wherein: In the composite slurry, the catalyst is ruthenium-based nanoparticles, accounting for 6%-10% by mass; the pore-forming agent is a complex of ammonium oxalate and polyethylene glycol, accounting for 3%-5% by mass; the binder is polyvinylidene fluoride emulsion, accounting for 1%-3% by mass; and the dispersant is a mixed solvent of nitrogen methyl pyrrolidone and propanol, with a volume ratio of 4:1-6:
1.
3. The method for preparing an electrode for an electrochemical ammonia sensor according to claim 2, wherein: The step drying and curing comprises: Dry at 40-60°C for 30-90 minutes; Heat to 70-90°C and dry for 60-150 minutes.
4. The method for preparing an electrode for an electrochemical ammonia sensor according to claim 3, wherein: The surface activation treatment is plasma activation, using an argon atmosphere, a power of 40W-60W, and a treatment time of 3-7 minutes.
5. The method for preparing an electrode for an electrochemical ammonia sensor according to claim 4, wherein: The gradient coating process is electrostatic spray deposition, the voltage is 10kV-20kV, the flow rate is 0.3mL / h-0.8mL / h, the pore size of the surface nanopores is 30nm-80nm, and the pore size of the bottom micropores is 0.5μm-2μm.
6. The method for preparing an electrode for an electrochemical ammonia sensor according to claim 5, wherein: The catalyst is distributed in the composite slurry in the form of island nano clusters with a diameter of 5nm-30nm and a coverage rate of 15%-40%, and is modified on the electrode surface through a sputtering process.
7. A method for detecting ammonia using an electrochemical ammonia sensor, characterized in that: Ammonia detection is performed based on the electrochemical ammonia sensor, which includes an electrode prepared by the electrode preparation method according to any one of claims 1 to 6.
8. The ammonia detection method of an electrochemical ammonia sensor according to claim 7, characterized in that: The ammonia detection method further comprises: Obtain DC basic deviation, AC disturbance amplitude and scanning frequency; An electrode excitation signal function is obtained according to the DC basic deviation, the AC disturbance amplitude and the scanning frequency.
9. The ammonia detection method of an electrochemical ammonia sensor according to claim 8, characterized in that: The ammonia detection method further comprises: Obtaining an initial current amplitude, and obtaining a frequency domain correction term for separating high-frequency electrochemical noise from a target signal based on the initial current amplitude and a scanning frequency; Obtain the pore size distribution factor, desorption attenuation coefficient, concentration correction index used to simulate the nonlinear response caused by competition for adsorption sites in catalytic reactions, and catalytic enhancement coefficient that characterizes the electron transfer efficiency of ruthenium nanocatalytic sites; Obtaining a rapid response term for achieving rapid signal capture and dynamic equilibrium control in the initial stage of gas adsorption based on the pore size distribution factor, desorption attenuation coefficient, concentration correction index, and catalytic enhancement coefficient; Obtaining a baseline drift compensation term for dynamically offsetting the baseline offset accumulated by historical exposure; A current-concentration-time response equation is constructed based on the fast response term, the frequency domain correction term, and the baseline drift compensation term, and the relationship between the output current, time, and ammonia concentration of the electrochemical ammonia sensor is obtained based on the current-concentration-time response equation.