Device and method for evaluating separation performance of ion exchange membrane based on electrochemical impedance spectroscopy

Abstract

The invention discloses a device and a method for evaluating the separation performance of an ion exchange membrane based on an electrochemical impedance spectroscopy, and belongs to the technical field of ion exchange membranes. The device comprises an electrochemical workstation and an electrolytic tank, a first output end of the electrochemical workstation is connected with an induction electrode and a reference electrode, and a second output end of the electrochemical workstation is connected with a working electrode and a counter electrode; the electrolytic tank comprises a first electrolytic tank and a second electrolytic tank which are separated by a to-be-detected ion exchange membrane; the sensing electrode and the working electrode extend into the first electrolytic tank, and the reference electrode and the counter electrode extend into the second electrolytic tank. According to the invention, quantitative characterization of migration and diffusion resistance of different ions passing through the membrane is realized, and the separation performance of the ion exchange membrane on ions of different valence states is preliminarily evaluated according to the microscopic mass transfer process of the ions passing through the membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ion exchange membrane, and particularly relates to a device and method for evaluating separation performance of ion exchange membrane based on electrochemical impedance spectroscopy. BACKGROUND

[0002] Electrodialysis is a mature technology in membrane separation process, and ion exchange membrane is the core component of electrodialysis. By using the selective permeability of ion exchange membrane to anions and cations, under the action of a direct current electric field, the anions and cations in the system move directionally, so as to realize the separation, purification and concentration of electrolytes. With the increasing demand for material separation and purification, the selective separation of different valence ions has attracted more and more attention in recent years, thereby promoting the continuous improvement of separation and purification technology. Ion exchange membranes with different valence ion selectivity have become a research hotspot. With the development of new ion exchange membrane materials and ion exchange membrane processes, the application in the fields of resource recovery, environmental protection and industrial production is more and more widely. At present, there are commercial products of ion exchange membranes with different valence ion selectivity, such as cation exchange membranes CIMS, CSO and anion exchange membranes ACS, ASV. There are also a large number of literatures about the preparation of ion exchange membranes with different valence ion selectivity. Therefore, the separation performance is an important performance index of ion exchange membranes with different valence ion selectivity. Therefore, it is necessary to evaluate the separation performance of ion exchange membranes in the application or research of membrane products.

[0003] At present, there is no relevant standard for testing and evaluating the separation performance of ion exchange membrane products. The separation performance of ion exchange membranes is usually evaluated by calculating ion separation selectivity and ion flux through electrodialysis experiment. However, the test methods (experimental device, experimental conditions, etc.) and calculation methods (adopted calculation method, etc.) are different when different researchers evaluate the separation performance of ion exchange membranes, which leads to significant differences in ion separation selectivity and ion flux obtained by different researchers. Therefore, it is difficult to evaluate the separation performance of different ion exchange membranes. SUMMARY

[0004] The present application aims to provide a device and method for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy, so as to solve the technical problem that the lack of uniform evaluation standard for the separation performance of ion exchange membranes in the prior art leads to significant differences in ion selectivity and flux data obtained by different researchers, and the performance of membranes cannot be compared horizontally.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] In a first aspect, the application provides a device for evaluating the separation performance of an ion exchange membrane based on electrochemical impedance spectroscopy, comprising an electrochemical workstation and an electrolytic cell; a first output end of the electrochemical workstation is connected to a sensing electrode and a reference electrode, and a second output end of the electrochemical workstation is connected to a working electrode and a counter electrode; the electrolytic cell comprises a first electrolytic cell and a second electrolytic cell, which are separated by the ion exchange membrane to be tested; the sensing electrode and the working electrode extend into the first electrolytic cell, and the reference electrode and the counter electrode extend into the second electrolytic cell.

[0007] Further, the sensing electrode and the reference electrode are located on the side close to the ion exchange membrane to be tested, and are close to the surface of the ion exchange membrane to be tested through a Luggin capillary, the end of the Luggin capillary being 1-2 mm away from the ion exchange membrane to be tested.

[0008] Further, the electrolytic cell is an H-type electrolytic cell, and the electrolyte solutions in the first electrolytic cell and the second electrolytic cell are the same.

[0009] Further, the sensing electrode and the reference electrode are both saturated Ag / AgCl electrodes, and the working electrode and the counter electrode are both platinum sheets.

[0010] In a second aspect, the application provides a method for evaluating the separation performance of an ion exchange membrane based on electrochemical impedance spectroscopy, comprising the following steps:

[0011] S1, sample preparation: preparing an electrolyte solution, rinsing the surface of the ion exchange membrane to be tested with pure water, and soaking in the test electrolyte solution for 24 hours;

[0012] S2, assembling a four-electrode system: placing the treated ion exchange membrane to be tested in the middle of the electrolytic cell, ensuring good sealing, adding the same volume of electrolyte solution to the two side electrolytic cells, and removing air bubbles; placing two platinum sheet electrodes as the working electrode and the counter electrode in the two side electrolytic cells, respectively, and placing two saturated Ag / AgCl electrodes in the Luggin capillary as the reference electrode and the sensing electrode, respectively, adjusting the position of the Luggin capillary to be 1-2 mm away from the two sides of the membrane; connecting the electrode clamps of the electrochemical workstation to the electrodes already installed in the electrolytic cell;

[0013] S3, parameter setting and data collection: setting the frequency range to 1 kHz to 1 mHz, the AC perturbation amplitude to 10 mV, starting the AC impedance test program, testing at the open circuit potential to obtain the AC impedance spectrum of the ion exchange membrane to be tested, and changing the test conditions to obtain the AC impedance spectrum under different conditions;

[0014] S4, data processing and analysis: constructing an impedance equivalent circuit of the ion exchange membrane, fitting the impedance experimental data through the electrochemical workstation, and obtaining the values of each element of the equivalent circuit.

[0015] Further, the impedance equivalent circuit of the ion exchange membrane includes solution resistance, membrane resistance, double layer resistance of membrane / solution interface, and diffusion boundary layer resistance of membrane surface; if there is a modification layer on the surface of the ion exchange membrane, the impedance equivalent circuit of the modified membrane further includes modification layer resistance, and the migration diffusion resistance of ions through the membrane is the sum of the double layer resistance of membrane / solution interface, the diffusion boundary layer resistance of membrane surface, and the modification layer resistance.

[0016] Further, the separation performance of the ion exchange membrane to be tested, i.e., the separation coefficient, is evaluated according to the ratio of the migration diffusion resistances of different ions through the membrane, and the formula is as follows:

[0017]

[0018] wherein R A and R B are the migration diffusion resistances of A ions and B ions through the ion exchange membrane, respectively.

[0019] Based on the above technical solution, the embodiments of the present application can at least produce the following technical effects:

[0020] The present application can realize quantitative characterization of the migration diffusion resistances of different ions through the membrane, preliminarily evaluate the separation performance of the ion exchange membrane to different valence ions according to the micro mass transfer process of ions through the membrane, objectively evaluate the selectivity of the membrane to different valence ions through the resistance ratio, and the larger the separation coefficient is, the better the separation performance of the ion exchange membrane is, thereby avoiding the complex process of traditional electrodialysis test and realizing performance evaluation only through impedance spectrum test, and the present application has wide applicability. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings shown.

[0022] Figure 1 is a structural schematic diagram of the first embodiment of the present application;

[0023] Figure 2 is an equivalent circuit diagram of the second embodiment of the present application, (a) is an electrochemical impedance equivalent circuit diagram of a standard ion exchange membrane, and (b) is an electrochemical impedance equivalent circuit diagram of an ion exchange membrane with a modification layer;

[0024] Figure 3The following are electrochemical impedance spectra and their fitting curves for Example 3 of the present invention: (a) is the electrochemical impedance spectrum and its fitting curve in a 0.2 g / L LiCl electrolyte solution, and (b) is the electrochemical impedance spectrum and its fitting curve in an 8 g / L MgCl2 electrolyte solution.

[0025] In the figure: 1. Electrochemical workstation; 2. Electrolytic cell; 201. First electrolytic cell; 202. Second electrolytic cell; 3. Ion exchange membrane to be tested; 4. Induction electrode; 5. Reference electrode; 6. Working electrode; 7. Counter electrode; 8. Luggin capillary. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0027] The objective of this invention is achieved through the following technical solution:

[0028] Example 1

[0029] like Figure 1 As shown, this embodiment provides an apparatus for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy, including an electrochemical workstation 1 and an electrolytic cell 2. The first output terminal of the electrochemical workstation 1 is connected to a sensing electrode 4 and a reference electrode 5, and the second output terminal is connected to a working electrode 6 and a counter electrode 7. The electrolytic cell 2 includes a first electrolytic cell 201 and a second electrolytic cell 202, separated by the ion exchange membrane 3 to be tested. The sensing electrode 4 and the working electrode 6 extend into the first electrolytic cell 201, and the reference electrode 5 and the counter electrode 7 extend into the second electrolytic cell 202. The sensing electrode 4 and the reference electrode 5 are located near the ion exchange membrane 3 to be tested and are close to the surface of the ion exchange membrane 3 through a Luggin capillary 8. The distance between the end of the Luggin capillary 8 and the ion exchange membrane 3 to be tested is 1-2 mm. The electrolytic cell 2 is an H-type electrolytic cell, and the electrolyte solutions in the first electrolytic cell 201 and the second electrolytic cell 202 are the same. The sensing electrode 4 and the reference electrode 5 are both saturated Ag / AgCl electrodes, and the working electrode 6 and the counter electrode 7 are both platinum sheets.

[0030] Example 2

[0031] This embodiment provides a method for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy, including the following steps:

[0032] S1. Sample preparation: Prepare electrolyte solutions (such as NaCl, LiCl, MgCl2, CaCl2, etc.), rinse the surface of the ion exchange membrane to be tested with pure water to remove impurities, and then soak it in the test electrolyte solution for 24 hours.

[0033] S2. Assemble the four-electrode system: Place the prepared ion exchange membrane to be tested in the middle of the electrolytic cell, ensuring a good seal. Add the same volume of electrolyte solution to both electrolytic cells and remove air bubbles. Place two platinum sheet electrodes as working electrodes and counter electrodes in the two electrolytic cells respectively. Place two saturated Ag / AgCl electrodes in Luggin capillaries as reference electrodes and sensing electrodes respectively. Adjust the position of the Luggin capillaries so that they are 1-2 mm away from both sides of the membrane. Connect the electrode clamps of the electrochemical workstation to the electrodes already installed in the electrolytic cell.

[0034] S3. Parameter setting and data acquisition: Set the frequency range to 1kHz to 1mHz, the AC disturbance amplitude to 10mV, start the AC impedance test program, and obtain the AC impedance spectrum of the ion exchange membrane under test at the open circuit potential. Change the test conditions to obtain AC impedance spectra under different conditions.

[0035] S4. Data Processing and Analysis: Constructing the equivalent circuit of ion exchange membrane impedance (e.g., ...) Figure 2 As shown, the equivalent impedance circuit of an ion exchange membrane includes the solution resistance, membrane resistance, double-layer resistance at the membrane / solution interface, and diffusion boundary layer resistance at the membrane surface. If there is a modification layer on the surface of the ion exchange membrane, the equivalent impedance circuit of the modified membrane includes the solution resistance, membrane resistance, modification layer resistance, double-layer resistance at the membrane / solution interface, and diffusion boundary layer resistance at the membrane surface. Impedance experimental data are fitted using the software provided with the electrochemical workstation or software such as Zview to obtain the values ​​of each component in the equivalent circuit. The resistance to ion migration and diffusion through the membrane is the double-layer resistance at the membrane / solution interface (R0). P ), membrane surface diffusion boundary layer resistance (R) P ') and the resistance of the modification layer (R) P The sum of the resistances to migration and diffusion of different ions through the membrane. The separation performance of the ion exchange membrane under test is evaluated based on the ratio of the migration and diffusion resistances of different ions through the membrane, i.e., the separation coefficient, which is calculated using the formula:

[0036]

[0037] Among them, R A R B These represent the migration and diffusion resistance of A ions and B ions through the ion exchange membrane, respectively.

[0038] Example 3

[0039] 1. Test the magnesium-lithium separation performance of the cation exchange membrane M1:

[0040] Electrochemical impedance spectroscopy test of the cation exchange membrane M1 in LiCl solution: rinse the surface of the cation exchange membrane M1 with pure water, cut it into a 1 cm x 1 cm membrane piece, immerse it in a 0.2 g / L LiCl solution for 24 hours, take out the membrane piece, place it in the middle of an H-type electrolytic cell, ensure good sealing, add 100 mL of 0.2 g / L LiCl solution to each side of the electrolytic cell, remove air bubbles, place two platinum electrodes in the two electrolytic cells, respectively, place two saturated Ag / AgCl electrodes in Luggin capillaries, adjust the position of the Luggin capillaries to be 1-2 mm away from both sides of the membrane, connect the working electrode and the counter electrode of the electrochemical workstation to the two platinum electrodes, respectively, connect the reference electrode and the sensing electrode to the two saturated Ag / AgCl electrodes, respectively, set the frequency range to 1 kHz to 1 mHz, the AC perturbation amplitude to 10 mV, start the AC impedance test program, and test the AC impedance spectrum of the cation exchange membrane M1 at the open circuit potential, as shown in Figure 3 (a).

[0041] Electrochemical impedance spectroscopy test of the cation exchange membrane M1 in MgCl2 solution: rinse the surface of the cation exchange membrane M1 with pure water, cut it into a 1 cm x 1 cm membrane piece, immerse it in a 8 g / L MgCl2 solution for 24 hours, take out the membrane piece, place it in the middle of an H-type electrolytic cell, ensure good sealing, add 100 mL of 8 g / L MgCl2 solution to each side of the electrolytic cell, remove air bubbles, place two platinum electrodes in the two electrolytic cells, respectively, place two saturated Ag / AgCl electrodes in Luggin capillaries, adjust the position of the Luggin capillaries to be 1-2 mm away from both sides of the membrane, connect the working electrode and the counter electrode of the electrochemical workstation to the two platinum electrodes, respectively, connect the reference electrode and the sensing electrode to the two saturated Ag / AgCl electrodes, respectively, set the frequency range to 1 kHz to 1 mHz, the AC perturbation amplitude to 10 mV, start the AC impedance test program, and test the AC impedance spectrum of the cation exchange membrane M1 at the open circuit potential, as shown in Figure 3 (b).

[0042] Equivalent circuit fitting: the cation exchange membrane M1 is a standard membrane without a modification layer, so its AC impedance spectrum is fitted according to Figure 2 (a), and the software nova of the electrochemical workstation is used for fitting to obtain the values of each element, as shown in Table 1. It can be seen that the Li + The migration diffusion resistance of the ion exchange membrane M1 is 312 Ω, and the Mg 2+The migration diffusion resistance through the ion exchange membrane M1 is 2.87Ω, and the magnesium-lithium separation coefficient of the ion exchange membrane M1 is 0.00920.

[0043] 2. Magnesium-lithium separation performance of the selective cation exchange membrane M2:

[0044] Electrochemical impedance spectrum test of the selective cation exchange membrane M2 in a LiCl solution: The surface of the cation exchange membrane M2 is washed with pure water, and a 1cm×1cm membrane piece is cut and soaked in a 0.2g / L LiCl solution for 24 hours, and then the membrane piece is taken out. The test is carried out in the same way as the M1 electrochemical impedance test, and the M2 electrochemical impedance spectrum is obtained, as shown in Figure 3 (a).

[0045] Electrochemical impedance spectrum test of the selective cation exchange membrane M2 in a MgCl2 solution: The surface of the cation exchange membrane M2 is washed with pure water, and a 1cm×1cm membrane piece is cut and soaked in a 8g / L MgCl2 solution for 24 hours, and then the membrane piece is taken out. The test is carried out in the same way as the M1 electrochemical impedance test, and the M2 electrochemical impedance spectrum is obtained, as shown in Figure 3 (b).

[0046] Equivalent circuit fitting: The monovalent selective cation exchange membrane M2 has a modification layer, so the equivalent circuit fitting of its electrochemical impedance spectrum is carried out according to Figure 2 (b), and the software nova of the electrochemical workstation is used for fitting to obtain the values of each element, as shown in Table 1. It can be seen that the Li + The migration diffusion resistance through the ion exchange membrane M1 is 229Ω, and the Mg 2+ The migration diffusion resistance through the ion exchange membrane M1 is 98Ω, and the magnesium-lithium separation coefficient of the ion exchange membrane M1 is 0.428.

[0047] Table 1: Migration resistance values and ion exchange membrane separation coefficients obtained by equivalent circuit fitting of electrochemical impedance spectrum

[0048]

[0049] 3. Comparison of the separation performance of the cation exchange membranes M1 and M2:

[0050] According to the analysis of the electrochemical impedance spectrum test, the separation coefficient of M1 is 0.00920, and the separation coefficient of M2 is 0.428. Therefore, under the test conditions, the magnesium-lithium separation performance of M2 is significantly better than that of M1.

[0051] The application tests the electrochemical impedance spectrum of the ion exchange membrane through a four-electrode system, quantitatively characterizes the migration diffusion resistance value of different ions through the membrane, and evaluates the separation performance of the ion exchange membrane, so that the method is simple and more applicable, and other membrane products can also use the method to evaluate the separation performance.

[0052] The above shows and describes the basic principles and main features of the application and the advantages of the application. Those skilled in the art should understand that the application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the application. Without departing from the spirit and scope of the application, various changes and improvements can be made to the application, and these changes and improvements all fall within the scope of the claimed application. The scope of the application claimed is defined by the appended claims and their equivalents.

Claims

1. A device for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy, characterized in that, It includes an electrochemical workstation (1) and an electrolytic cell (2); the first output terminal of the electrochemical workstation (1) is connected to the sensing electrode (4) and the reference electrode (5), and the second output terminal of the electrochemical workstation (1) is connected to the working electrode (6) and the counter electrode (7); the electrolytic cell (2) includes a first electrolytic cell (201) and a second electrolytic cell (202), which are separated by the ion exchange membrane (3) to be tested; the sensing electrode (4) and the working electrode (6) extend into the first electrolytic cell (201), and the reference electrode (5) and the counter electrode (7) extend into the second electrolytic cell (202).

2. The apparatus for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy according to claim 1, characterized in that, The sensing electrode (4) and the reference electrode (5) are located on the side close to the ion exchange membrane (3) to be tested, and are close to the surface of the ion exchange membrane (3) to be tested through the Lugin capillary (8). The distance between the end of the Lugin capillary (8) and the ion exchange membrane (3) to be tested is 1-2 mm.

3. The apparatus for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy according to claim 1, characterized in that, The electrolytic cell (2) is an H-type electrolytic cell, and the electrolyte solutions in the first electrolytic cell (201) and the second electrolytic cell (202) are the same.

4. The apparatus for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy according to claim 1, characterized in that, The sensing electrode (4) and the reference electrode (5) are both saturated Ag / AgCl electrodes, and the working electrode (6) and the counter electrode (7) are both platinum sheets.

5. A method for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy, characterized in that, Includes the following steps: S1. Sample preparation: Prepare electrolyte solution, rinse the surface of the ion exchange membrane to be tested with pure water, and soak it in the test electrolyte solution for 24 hours. S2. Assemble the four-electrode system: Place the prepared ion exchange membrane to be tested in the middle of the electrolytic cell, ensuring a good seal. Add the same volume of electrolyte solution to both electrolytic cells and remove air bubbles. Place two platinum sheet electrodes as working electrodes and counter electrodes in the two electrolytic cells respectively. Place two saturated Ag / AgCl electrodes in Luggin capillaries as reference electrodes and sensing electrodes respectively. Adjust the position of the Luggin capillaries so that they are 1-2 mm away from both sides of the membrane. Connect the electrode clamps of the electrochemical workstation to the electrodes already installed in the electrolytic cell. S3. Parameter setting and data acquisition: Set the frequency range to 1kHz to 1mHz, the AC disturbance amplitude to 10mV, start the AC impedance test program, and obtain the AC impedance spectrum of the ion exchange membrane under test at the open circuit potential. Change the test conditions to obtain AC impedance spectra under different conditions. S4. Data Processing and Analysis: Construct an equivalent circuit of ion exchange membrane impedance, and obtain the values ​​of each component of the equivalent circuit by fitting the impedance experimental data through an electrochemical workstation.

6. The method for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy according to claim 5, characterized in that, The equivalent impedance circuit of the ion exchange membrane includes the solution resistance, the membrane resistance, the double layer resistance at the membrane / solution interface, and the diffusion boundary layer resistance at the membrane surface. If there is a modification layer on the surface of the ion exchange membrane, the equivalent impedance circuit of the modified membrane also includes the modification layer resistance. The migration and diffusion resistance of ions through the membrane is the sum of the double layer resistance at the membrane / solution interface, the diffusion boundary layer resistance at the membrane surface, and the modification layer resistance.

7. The method for evaluating the separation performance of ion exchange membranes based on electrochemical impedance spectroscopy according to claim 6, characterized in that, The separation performance of an ion exchange membrane is evaluated based on the ratio of the migration and diffusion resistance of different ions through the membrane, i.e., the separation coefficient, which is calculated using the following formula: Among them, R A R B These represent the migration and diffusion resistance of A ions and B ions through the ion exchange membrane, respectively.

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