Electrocatalytic reaction monitoring method based on electrostrictive effect

Abstract

The invention discloses an electrocatalytic reaction monitoring method based on an electrostrictive effect. The principle of the method provided by the invention is as follows: (1) alternating voltage is applied to an upper electrode and a lower electrode of an electrostrictive material, and the electrostrictive material generates electrostrictive strain, electrostrictive stress and electrostrictive displacement under the excitation of the voltage, so that an electric signal is converted into a mechanical signal; (2) measuring mechanical signal response by adopting laser interference or an atomic force microscope; (3) decoupling a second-order electrostriction response in the mechanical response through Fourier series or fast Fourier transform; (4) because the electrostrictive material has certain catalytic activity, the electrostrictive material can generate electrochemical reaction under voltage excitation; and (5) the strength of the electrochemical reaction is related to the electrostrictive strain, the stronger the electrochemical reaction is, the larger the electrostrictive strain is, and the weaker the electrochemical reaction is, the smaller the electrostrictive strain is. Therefore, the electrocatalytic reaction process can be monitored according to the magnitude of mechanical signals such as electrostrictive strain, stress or displacement. The electrochemical reaction process involved in the method disclosed by the invention is not limited to a specific electro-catalytic reaction, and more universal electro-catalytic reaction monitoring can be realized.

Description

Technical Field

[0001] The present invention belongs to the fields of microelectromechanical systems and catalytic technologies, and particularly relates to an electrocatalytic reaction monitoring method based on the electrostrictive effect. Background Art

[0002] Catalytic reactions are widely applied in the fields of chemical engineering, energy, and environment. Traditional monitoring methods mainly rely on off-line analysis, such as gas chromatography, liquid chromatography, etc. Although these methods are accurate, they are cumbersome to operate and time-consuming. There are also some monitoring means, such as spectroscopy, which mainly analyze through indirect information and may be restricted by various factors such as sample properties and reaction conditions, making it difficult to achieve rapid and effective monitoring of catalytic reactions. Although the catalytic combustion detection method can monitor the concentration of combustible gases in real time, it is mainly applicable to the monitoring of specific types of gases such as combustible gases and cannot effectively monitor other types of catalytic reactions. Therefore, there is an urgent need to explore an efficient and universal catalytic reaction monitoring method.

[0003] Electrostrictive materials can be used as high-precision displacement sensors and have been widely applied in the field of micro / nanoelectromechanical systems. However, traditional commercial electrostrictive materials are mainly relaxor ferroelectric materials based on PMN and PZN, and their electrostrictive coefficients are much smaller than those of non-classical electrostrictive materials such as ionic conductors. Therefore, the electrostrictive strain is small. Non-classical electrostrictive materials, such as rare-earth-doped ceria materials, rare-earth-doped zirconia materials, and δ-Bi2O3 ionic conductor materials, not only have a giant electrostrictive effect and can generate large electrostrictive strain and stress, but also have good catalytic activity and are expected to replace traditional commercial electrostrictive materials. However, there is currently no report on the relationship between the catalytic reactions and the electrostrictive effect of non-classical electrostrictive materials. Summary of the Invention

[0004] Aiming at the limitations in catalytic reaction monitoring mentioned in the above technical background, the purpose of this application is to provide an electrocatalytic reaction monitoring method based on the electrostrictive effect, which directly monitors the progress of electrocatalytic reactions based on the electrostrictive effect of electrostrictive materials. This method utilizes the internal relationship between the magnitude of the electrostrictive effect of electrostrictive materials and the strength of the electrocatalytic reactions of electrostrictive materials, and finally monitors the progress of electrocatalytic reactions by monitoring mechanical signals.

[0005] To this end, the present invention proposes an electrocatalytic reaction monitoring method based on the electrostrictive effect, comprising the following steps: ① Applying an alternating voltage to the upper and lower electrodes of the electrostrictive material. The electrostrictive material generates mechanical response signals such as strain, stress, and displacement under the excitation of the alternating voltage. At the same time, an electrocatalytic reaction occurs in the electrostrictive material; ② Measuring the mechanical response signals generated in step ①; ③ Analyzing the mechanical response signals generated in step ① to isolate the second-order electrostrictive resonance signal; ④ Recording in real time the mechanical response signals generated by the electrostrictive material to monitor the strength of the electrocatalytic reaction.

[0006] When the electrostrictive material undergoes electrostrictive deformation under voltage excitation, since the magnitude of its displacement response signal is in the nanometer range, it is very difficult to measure this tiny deformation by ordinary macroscopic displacement or strain measurement methods. Therefore, it is necessary to use measurement methods with high spatio-temporal resolution such as optical interferometry and atomic force microscopy to measure the tiny mechanical response signals generated by the electrostrictive material under the excitation of the alternating voltage. At the same time, since the displacement, strain, and displacement of the electrostrictive material satisfy the constitutive relationship and geometric relationship of continuous medium mechanics, the response signals of other physical quantities can be obtained through the mechanical intrinsic relationship by testing the response signal of one of the physical quantities.

[0007] When measuring the electrostrictive mechanical signals of the electrostrictive material by methods such as optical interferometry and atomic force microscopy under the excitation of the alternating voltage, the test process is often affected by thermal vibration and other factors, and there is a background noise signal. Therefore, a lock-in amplifier can be used to improve the signal-to-noise ratio of the mechanical response signal to obtain a clearer electrostrictive mechanical signal.

[0008] When the electrostrictive material is under the excitation of the alternating voltage, there are not only second-order electrostrictive signals, but also first-order Vegard signals, induced piezoelectric signals, and higher-order mechanical response signals. The mechanical signals measured by methods such as optical interferometry and atomic force microscopy include mechanical response signals of all orders. If only the second-order electrostrictive signal is required, the measured mechanical response signals must be further analyzed. Therefore, the above mechanical response signals are analyzed by Fourier series or fast Fourier transform to isolate the second-order electrostrictive resonance signal.

[0009] By applying an alternating voltage, the defect migration energy is reduced, the electrochemical potential is increased, and an electrochemical reaction is induced in the electrostrictive material to achieve electrocatalysis. There is an inherent correlation between the electrostrictive mechanical response and electrocatalysis of the electrostrictive material, mainly because both the electrostrictive effect and electrocatalysis are closely related to the electric migration of vacancies or ions in the electrostrictive material. When the electrostrictive material is excited by an alternating voltage, vacancies or ions will undergo electric migration under the action of the external voltage, and the degree of this electric migration is further closely related to the catalytic process. The relationship between the degree of electric migration and the catalytic process mainly includes two aspects: on the one hand, electric migration will affect the distribution of positive and negative carriers in the electrostrictive material, thus affecting the built-in electric field in the electrostrictive material, and then affecting the electrochemical potential of its electrocatalytic reaction; on the other hand, electric migration will affect the distribution of vacancies or ions on the surface of the electrostrictive material, thus affecting the concentration of reactants or products, and further affecting the electrocatalytic reaction process.

[0010] The intensity of the electrocatalytic reaction will affect the electrostrictive coefficient of the electrostrictive material, thus affecting the mechanical response signals such as strain, stress, and displacement of the electrostrictive material. The more intense the electrocatalytic reaction, the stronger the mechanical response signals such as strain, stress, and displacement generated by the electrostrictive material; conversely, the more gentle the electrocatalytic reaction, the weaker the mechanical signals such as strain, stress, and displacement of the electrostrictive material.

[0011] A low-frequency alternating voltage is applied between the upper and lower electrodes of the electrostrictive material. The electrostrictive material generates mechanical response signals such as electrostrictive strain, electrostrictive stress, and electrostrictive displacement under the excitation of the alternating voltage. Since the strength of the electrostrictive effect is related to the migration of vacancies or ions in the electrostrictive material, and the kinetic process of the migration of vacancies or ions is related to the frequency of the excitation voltage, the electrostrictive effect has a strong frequency dependence. Usually, the smaller the excitation voltage frequency, the more sufficient the ion migration, making the electrostrictive effect more obvious, and thus the electrostrictive material has a larger electrostrictive strain; conversely, when the excitation frequency is very high, vacancies or ions do not have time to migrate, so the electrostrictive effect is often smaller. Therefore, the alternating voltage frequency used in the present invention is less than 1 kHz, preferably 100 Hz, more preferably less than 1 Hz, and still more preferably less than 0.1 Hz.

[0012] The electrostrictive material used in the present invention is a non-classical electrostrictive material and an ionic conductor material with good catalytic activity. The electrostrictive material can be selected from fluorite structure oxide materials such as Gd-doped ceria, Sm-doped ceria, Y-doped zirconia, δ-Bi2O3, or non-fluorite structure oxide materials such as LaMo2O9, LaMoWO9, MAPbI3. The electrode material is a metal material with high conductivity such as Au, Pt, Cu, Ag.

[0013] The electrocatalytic reactions in the present invention include all electrochemical reactions related to the redox reaction of electrostrictive materials, and are not limited to a specific reaction atmosphere.

[0014] The electrocatalytic reactions related to the redox reaction of electrostrictive materials in the present invention are not limited to a specific reaction temperature.

[0015] Compared with the prior art, the present invention has the following beneficial effects: A method for monitoring electrocatalytic reactions based on the electrostrictive effect of the present invention can directly monitor the progress of electrocatalytic reactions by measuring the magnitude of the mechanical signals of electrostrictive materials, providing a new method for measuring the progress of electrocatalytic reactions; the present invention measures electrocatalytic reactions through mechanical signals, not limited to a certain or certain specific electrocatalysis, and can monitor all electrocatalytic reactions related to the redox of electrostrictive materials, with good universality; due to the good temperature stability of the selected electrostrictive materials, it has good monitoring effects in a wide temperature range. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the relationship between electrocatalytic reactions and electrostrictive strain magnitudes in a specific embodiment of the present invention; Figure 2 It is the measurement of electrostrictive strain of 20% Sm-doped CeO2 ceramics under different voltage amplitudes in a specific embodiment of the present invention; Figure 3 It is the measurement of electrostrictive coefficients of 20% Sm-doped CeO2 ceramics at different frequencies in a specific embodiment of the present invention; Figure 4 It is the measurement of electrostrictive coefficients of CeO2 ceramics with different Sm doping concentrations in the present invention; Detailed Embodiments

[0017] To make the objectives, technical solutions, and advantages of the implementation of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the drawings in the present invention. Example 1

[0018] Measurement of electrostrictive strain of 20% Sm-doped CeO2 ceramics under different voltage amplitudes: (1) Sample preparation 24.3286 grams of cerium nitrate (Ce(NO3)3·6H2O) and 6.2232 grams of samarium nitrate (Sm(NO3)3·6H2O) were dissolved in 350 milliliters of deionized water (H2O) and stirred to prepare a 0.2 mol / L solution. An ammonia water solution was selected to precipitate metal ions. At room temperature, the ammonia water solution was slowly and evenly added dropwise to the solution containing Ce 4+ and Sm 3+in a solution, and strictly control the pH value to be stably maintained at about 10. After the titration process is completed, continue to stir on a magnetic stirrer until the precipitation is complete, and then the hydroxide precipitation of the corresponding metal ions can be generated. The color of the precipitate is light yellowish-white. Collect the obtained precipitate, and alternately centrifuge and wash the precipitate several times with ionized water and absolute ethanol using a centrifuge. After drying with the help of a constant temperature drying oven, a yellowish-white precursor can be obtained. Calcinate the obtained precursor in a muffle furnace at 700 °C for 2 hours to convert the hydroxide into the corresponding oxide, and then fully grind the calcined powder. After drying, the Sm-doped CeO2 powder is obtained.

[0019] Fully grind the calcined powder, and then add an appropriate amount of 5 wt% PVA solution to start granulation. After granulation is completed, sieve the powder with uniform particle size through a sieve. After leaving it overnight, use a powder press to press it into a green compact disk with a diameter of 13 mm, and the pressure is fixed at about 240 MPa. The thickness of the circular green compact is about 0.9 mm. First, put the disk into a high-temperature furnace for debinding, and the condition is to hold at 650 °C for 3 hours to fully remove the binder therein. Then, perform the high-temperature densification step of SDC ceramics. The temperature condition is to hold at 1500 °C for 6 hours, and the heating rate is maintained at 2 °C / min. Finally, a dense Sm-doped CeO2 ceramic disk (SDC ceramic disk) is obtained.

[0020] (2) Electrostrictive strain measurement Apply AC voltages with different amplitudes and a frequency of 1 Hz to the bottom electrode of the 20SDC ceramic through the high-voltage Holder of an atomic force microscope (AFM). During the test, ensure that the top electrode is grounded, and at the same time, select a hard probe to avoid the influence of electrostatic force as much as possible. Use the AFM probe to record the strain generated at multiple points in a small area of the ceramic sample in real time. Fit the strain response measured by AFM using Fourier series, and the strain response as shown in Figure 2 can be obtained. It is found that under the excitation of AC voltages with different amplitudes, when obvious electrochemical reactions occur in the SDC ceramic, that is, a large amount of Ce 4+ is reduced to Ce 3+ , and at the same time, there is a large slope between the 20SDC ceramic and the square of the electric field, indicating that the 20SDC ceramic has a large electrostrictive coefficient at this time. When the electrochemical reaction of the SDC ceramic weakens, only a small amount of Ce 4+ is reduced to Ce 3+ , and the slope between the strain of the 20SDC ceramic and the square of the electric field will decrease significantly, indicating that the electrostrictive coefficient of the 20SDC ceramic becomes smaller at this time. It can be seen from this that under the excitation of voltages with different amplitudes, when strong electrocatalytic reactions occur in the 20SDC ceramic, the electrostrictive strain is large; when the electrocatalytic reaction of the 20SDC ceramic weakens, the electrostrictive strain will become smaller.

[0021] Example 2 Measurement of electrostrictive coefficient of 20% Sm-doped CeO2 ceramics at different frequencies: Apply an AC voltage of 140 V at different frequencies to the bottom electrode of the 20SDC ceramic through the high-voltage holder of the atomic force microscope (AFM). During the test, ensure that the top electrode is grounded, and at the same time, select a hard probe to avoid the influence of electrostatic force as much as possible. Use the AFM probe to record the strain generated at multiple points in a small area of the ceramic sample in real time. Fit the strain response measured by AFM with Fourier series, extract the second-order electrostrictive strain, and then use the quadratic relationship between strain and the square of the electric field to analyze the electrostrictive coefficient at different frequencies as shown in Figure 3 the electrostrictive coefficient at different frequencies M 33 . It is found that when obvious electrochemical reactions occur in the SDC ceramic, that is, a large amount of Ce 4+ is reduced to Ce 3+ , the electrostrictive coefficient of the 20SDC ceramic has obvious frequency dependence. Moreover, the electrostrictive coefficient is larger when the frequency is less than 100 Hz. When the electrochemical reaction of the SDC ceramic weakens, at this time only a small amount of Ce 4+ is reduced to Ce 3+ , the electrostrictive coefficient of the 20SDC ceramic does not have frequency dependence, and at this time the electrostrictive coefficient of the 20SDC ceramic is smaller. It can be seen from this that under the excitation of voltage at different frequencies, when strong electrocatalytic reactions occur in the 20SDC ceramic, the electrostrictive coefficient is larger; when the electrocatalytic reaction of the 20SDC ceramic weakens, the electrostrictive coefficient becomes smaller. The change of the electrostrictive coefficient indicates that the strength of the electrostrictive effect of the 20SDC ceramic is related to the strength of the electrocatalytic reaction. Example 3

[0022] Measurement of electrostrictive coefficient of CeO2 ceramics with different Sm doping concentrations: (1) Sample preparation Prepare CeO2 ceramics with different Sm doping concentrations by the co-precipitation method. Configure a 0.2 mol / L rare earth metal ion solution according to the stoichiometry of the final product to obtain CeO2 with different Sm doping concentrations. Select ammonia water solution to precipitate metal ions. At room temperature, slowly and evenly drip the ammonia water solution into the solution containing Ce 4+ and Sm 3+The solution is placed in a solution and the pH value is strictly controlled to be maintained at about 10. After the titration process is completed, continue stirring on a magnetic stirrer until the precipitation is complete, and then the hydroxide precipitate of the corresponding metal ion can be generated, and the color of the precipitate is light yellow-white. Collect the obtained precipitate, wash the precipitate alternately with deionized water and anhydrous ethanol through a centrifuge for several times, and then dry it in a constant temperature drying oven to obtain a yellow-white precursor. The obtained precursor is calcined at 700°C in a muffle furnace for 2 hours to convert the hydroxide into the corresponding oxide, and then the calcined powder is fully ground and dried to obtain Sm-doped CeO2 powder.

[0023] The calcined powder was fully ground, and then an appropriate amount of 5wt% PVA solution was added to it to start granulation. After granulation, the powder with uniform particle size was screened through a sieve, and it was placed overnight and then pressed into a green embryo sheet with a diameter of 13 mm using a powder tablet press. The pressure was fixed at about 240MPa, and the thickness of the circular green embryo was about 0.9mm. First, the disc was placed in a high-temperature furnace for debinding, and the condition was kept at 650℃ for 3 hours in order to fully remove the binder. Then, the SDC ceramic high-temperature densification step was carried out, and the temperature condition was kept at 1500℃ for 6 hours, and the heating rate was kept at 2℃ / min, and finally a dense Sm-doped CeO2 ceramic sheet (SDC ceramic sheet) was obtained.

[0024] (2) Electrostrictive displacement measurement In order to obtain the electrostrictive displacement response of SDC ceramics (20SDC) with a Sm doping concentration of 20%, an AC voltage of 140V with frequencies of 0.01, 0.1, 1, 10 and 100 Hz was applied from the bottom electrode of the ceramic through the high-voltage holder of an atomic force microscope (AFM). The top electrode was grounded, and a hard probe was used to avoid the influence of electrostatic force as much as possible. The displacement response generated at multiple points in a small area of the ceramic sample was recorded in real time using the AFM probe. Since the bottom electrode of the SDC ceramic sample is larger than the ceramic sample and the top electrode is also close to the size of the ceramic, even the strain recorded by the probe is actually the electrostrictive strain response of the entire ceramic. Under AC voltage excitation, SDC ceramics with different concentrations all undergo obvious electrochemical reactions, that is, a large amount of Ce 4+ Reduced to Ce 3+ , then SDC ceramics will have the following characteristics Figure 4 The electrostrictive coefficients of SDC ceramics with Sm doping concentrations of 10% and 20% are relatively large. When the electrochemical reaction of SDC ceramics is weak, the electrostrictive coefficients of SDC ceramics with different concentrations are reduced, and the reduction of SDC ceramics with Sm doping concentrations of 10% and 20% is the most obvious.

Claims

1. An electrocatalytic reaction monitoring method based on the electrostrictive effect, comprising the following steps: ① Applying an alternating voltage to the upper and lower electrodes of the electrostrictive material. The electrostrictive material generates mechanical response signals such as strain, stress, and displacement under the excitation of the alternating voltage. At the same time, an electrocatalytic reaction occurs in the electrostrictive material; ② Measuring the mechanical response signals generated in step ①; ③ Analyzing the mechanical response signals generated in step ① to isolate the second-order electrostrictive resonance signal; ④ Real-time recording the mechanical response signals generated by the electrostrictive material to monitor the strength of the electrocatalytic reaction.

2. The electrocatalytic reaction monitoring method according to claim 1, wherein the mechanical response signals generated by the electrostrictive material under the excitation of the alternating voltage can be measured by methods such as optical interferometry and atomic force microscopy techniques.

3. The electrocatalytic reaction monitoring method according to claim 1 or 2, wherein the mechanical response signals generated in step ① can be analyzed by Fourier series or fast Fourier transform to isolate the second-order electrostrictive resonance signal.

4. The electrocatalytic reaction monitoring method according to any one of claims 1-3, and the signal-to-noise ratio of the mechanical response signals described in step ① can also be improved by a lock-in amplifier.

5. The electrocatalytic reaction monitoring method according to claim 4, wherein the electrostrictive material is a non-classical electrostrictive material.

6. The electrocatalytic reaction monitoring method according to claim 5, wherein the non-classical electrostrictive material can be fluorite structure oxide materials such as Gd-doped ceria, Sm-doped ceria, Y-doped zirconia, δ-Bi2O3, or non-fluorite structure oxide materials such as LaMo2O9, LaMoWO9, MAPbI3.

7. The electrocatalytic reaction monitoring method according to any one of claims 1-5, wherein the frequency of the alternating voltage is less than 1 kHz.

8. The electrocatalytic reaction monitoring method according to claim 7, wherein the frequency of the alternating voltage is less than 100 Hz.

9. The electrocatalytic reaction monitoring method according to claim 8, wherein the frequency of the alternating voltage is less than 1 Hz.

10. The electrocatalytic reaction monitoring method according to claim 9, wherein the frequency of the alternating voltage is less than 0.1 Hz.

Images