Prussian blue analogue electrode and preparation method and application thereof

Abstract

The invention discloses a Prussian blue analogue electrode and a preparation method and application thereof.The preparation method comprises the following steps that a manganese salt solution, a nickel salt solution and a potassium ferricyanide solution are prepared and added into water at the same time, a mixture with the molar ratio of manganese to nickel being larger than or equal to 0.1: 1 is obtained, aging, washing and drying are conducted, and the Prussian blue analogue electrode is obtained. And mixing the manganese-doped Prussian blue analogue with a binder, a conductive agent and a solvent, carrying out ultrasonic treatment to obtain an electrode slurry liquid, covering the surface of a current collector with the electrode slurry liquid, and drying to obtain the Prussian blue analogue electrode. The Prussian blue analogue electrode prepared by the method has the advantages of low energy consumption, high salt adsorption capacity, high salt adsorption rate and the like, can be used for desalting treatment as a capacitive deionization cathode, has the salt adsorption rate and the salt adsorption capacity which are more than two times of those of a conventional electrode, and is high in use value, good in application prospect and wide in application prospect. The method is of great significance in promoting wide application of the capacitive deionization technology.

Description

Technical Field

[0001] The invention belongs to the technical field of capacitive deionization and relates to a Prussian blue analog electrode and a preparation method and application thereof. Background Art

[0002] Capacitive deionization (CDI) technology is an efficient, environmentally friendly, and low-energy water treatment technology that is widely used in desalination, deionization, and removal of specific pollutants. In recent years, CDI has shown great potential in achieving high energy efficiency and zero secondary pollution. Its core principle is to purify water by adsorbing ions in the solution to the electrode surface through the electrosorption of electrode materials under an external electric field. At present, the commonly used CDI electrode materials are mainly porous carbon materials, such as activated carbon, carbon aerogels, carbon nanotubes, and graphene. These materials have high specific surface area and good electrical conductivity, and can provide sufficient adsorption sites for ions. However, traditional carbon-based CDI is limited by the inherent low desalination capacity of the electric double layer (EDL) (10-15 mg·g -1 The practical application of CDI is greatly limited by the problems of low charge utilization efficiency caused by common ion discharge and severe anode corrosion. Therefore, the development of high-performance electrode materials has always been the focus and difficulty of research in this field.

[0003] Compared with the traditional CDI system, the hybrid capacitive deionization (HCDI) system constructed by introducing faradaic intercalation materials as electrodes has greater advantages in desalination capacity and charging efficiency, among which the electrode material determines the performance of the HCDI system. Prussian blue analogs (PBAs) have great advantages for commercial applications due to their low cost, non-toxicity, and easy preparation, and are considered to be the new generation of faradaic materials for CDI electrodes. The existing research on HCDI of Prussian blue analogs mainly focuses on designing three-dimensional frameworks and enhancing electrochemical properties. However, researchers have not paid attention to the effect of the particle size of Prussian blue analogs on material properties. In addition, the Prussian blue analogues prepared in the existing preparation methods still have deficiencies such as uneven morphology and large particle size, which leads to insufficient contact between the Prussian blue analogues and the electrolyte, which is not conducive to improving the ion transmission capacity of the electrode. At the same time, the Prussian blue analogues with large particle size are also not conducive to increasing the specific surface area and the number of active sites of the material, so it is difficult to enhance the redox active sites of the material and to improve the ion storage capacity of the electrode. The final result is that the Prussian blue analogue electrode still has defects such as low adsorption amount and slow ion adsorption rate. Therefore, obtaining a Prussian blue analogue electrode with large salt adsorption capacity and fast salt adsorption rate is of great significance for promoting the widespread application of capacitive deionization technology. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a Prussian blue analog electrode with large salt adsorption capacity and fast salt adsorption rate and a preparation method and application thereof.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for preparing a Prussian blue analog electrode comprises the following steps:

[0007] S1, respectively mixing a manganese salt, a nickel salt, and potassium ferrocyanide with water to obtain a manganese salt solution, a nickel salt solution, and a potassium ferrocyanide solution;

[0008] S2, adding the manganese salt solution, nickel salt solution and potassium ferrocyanide solution obtained in step S1 into water simultaneously to obtain a mixture; the molar ratio of manganese to nickel in the mixture is ≥0.1:1;

[0009] S3, aging, washing, and drying the mixture obtained in step S2 to obtain a manganese-doped Prussian blue analogue;

[0010] S4, mixing the manganese-doped Prussian blue analogue obtained in step S3, a binder, a conductive agent and a solvent, and ultrasonicating to obtain an electrode slurry liquid;

[0011] S5. Apply the electrode slurry obtained in step S4 to the surface of the current collector and dry it to obtain a Prussian blue analog electrode.

[0012] The above preparation method is further improved, in step S2, the molar ratio of manganese to nickel in the mixture is 0.1-2:1.

[0013] The above preparation method is further improved, in step S2, the molar ratio of manganese to nickel in the mixture is 0.25 to 1:1.

[0014] The above preparation method is further improved, in step S2, the molar ratio of manganese to nickel in the mixture is 0.3-0.6:1.

[0015] The above preparation method is further improved, in step S1, the manganese salt is manganese chloride; the nickel salt is nickel chloride.

[0016] The above preparation method is further improved, in step S3, the aging is carried out at a stirring speed of 300 rpm; the aging time is 6 hours.

[0017] The above preparation method is further improved. In step S4, the mass ratio of the manganese-doped Prussian blue analogue, the binder, and the conductive agent is 8-9:0.8-1:0.8-1, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol and polypropylene, and the conductive agent is conductive carbon black; the solvent is at least one of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, and deionized water; and the ultrasonic time is 60 minutes.

[0018] The above preparation method is further improved, in step S5, the current collector is one of graphite paper, nickel foam, copper foil, aluminum foil, and titanium mesh.

[0019] As a general technical concept, the present invention also provides a Prussian blue analog electrode, which is prepared by the above-mentioned preparation method.

[0020] The above-mentioned Prussian blue analogue electrode is further improved, wherein the Prussian blue analogue electrode comprises a manganese-doped Prussian blue analogue; the peak position of the particle size distribution of the manganese-doped Prussian blue analogue is located at 270 nm.

[0021] As a general technical concept, the present invention also provides an application of the above-mentioned Prussian blue analog electrode in solution desalination.

[0022] The above application, further improved, comprises the following steps:

[0023] (1) A capacitive deionization device constructed with a Prussian blue analog electrode as the cathode and an activated carbon electrode as the anode;

[0024] (2) Desalination of saline solution using a capacitive deionization device.

[0025] The above application is further improved, in step (2), the saline solution is brackish water or seawater; the salt concentration in the saline solution is ≤500 mg·L -1 ; The control voltage during the desalination process is 1.2V; The circulation rate of the saline solution during the desalination process is 8mL·min -1 .

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] (1) In view of the shortcomings of existing Prussian blue analog electrodes, such as small specific surface area, few active sites, poor stacking density, and the resulting defects of small salt adsorption capacity, slow salt adsorption rate, and difficulty in effectively treating pollutants of different concentrations, the present invention proposes a method for preparing a Prussian blue analog electrode, firstly preparing a manganese-doped Prussian blue analog with manganese salt, nickel salt, and potassium ferrocyanide as raw materials, and then mixing the manganese-doped Prussian blue analog with a binder, a conductive agent, and a solvent to form an electrode slurry and coating it on the surface of the current collector to obtain a Prussian blue analog electrode. Compared with conventional Prussian blue analogs (such as Cu 3 [Fe(CN) 6 ] 2 ), the manganese-doped Prussian blue analogue prepared by the present invention has the advantages of uniform morphology and small particle size, which is conducive to promoting the full contact between the manganese-doped Prussian blue analogue and the electrolyte, thereby improving the ion transmission capacity of the electrode. At the same time, the manganese-doped Prussian blue analogue with a smaller particle size is also conducive to increasing the specific surface area and the number of active sites of the material, thereby enhancing the redox active sites of the material and improving the ion storage capacity of the electrode. More importantly, the manganese-doped Prussian blue analogue prepared by the present invention has a higher specific capacity and a lower operating voltage, and is a very promising cathode material. Moreover, the addition of Mn can enhance the activation effect of the redox active center of the Prussian blue analogue. At the same time, manganese doping can also change the particle size of the material and improve The electrochemical properties of the material, on this basis, the present invention optimizes the molar ratio of manganese to nickel ≥ 0.1: 1, under this condition, by adjusting the ratio of manganese doping, the particle size of the manganese-doped Prussian blue analogue can be gradually reduced, and the particle size becomes more and more uniform, which can enhance the redox active sites of the material and improve its ion storage capacity, especially, the manganese-doped Prussian blue analogue with a smaller particle size is more fully in contact with the electrolyte, thus being more conducive to rapid ion transmission, and finally the Prussian blue analogue electrode prepared with the manganese-doped Prussian blue analogue as the active material has a higher salt adsorption capacity, a faster salt adsorption rate, and can effectively adsorb low-concentration target pollutants under lower voltage conditions, has lower energy consumption, and has better adaptability to pollutants of different concentrations. The Prussian blue analogue electrode prepared by the present invention has the advantages of low energy consumption, high salt adsorption capacity, fast salt adsorption rate, etc., can effectively treat pollutants of different concentrations, has high use value, good application prospects, and is of great significance for promoting the wide application of capacitive deionization technology.

[0028] (2) In the preparation method of the Prussian blue analog electrode of the present invention, the molar ratio of manganese to nickel in the mixture is further optimized to be 0.1 to 1:1. In particular, when the molar ratio of manganese to nickel in the mixture is 0.3 to 0.6:1, on the one hand, the particle size of the Prussian blue analog can be effectively reduced to form smaller and more uniform particles, increase the active sites of the electrode material, and improve the efficiency of CDI. On the other hand, by optimizing the doping amount of manganese, agglomeration due to too small particles can be effectively avoided, thereby making the prepared particles Manganese-doped Prussian blue analog particles with smaller diameters can also effectively improve the charge transfer efficiency and obtain a larger specific surface area, thereby ensuring a higher adsorption capacity and a faster salt adsorption efficiency. The ion storage of the Prussian blue analog electrode prepared when the molar ratio of manganese to nickel in the mixture is 3:7 involves Faraday reaction and intercalation, and compared with the nickel-based Prussian blue analog electrode, the salt adsorption rate and salt adsorption capacity of the Prussian blue analog electrode prepared based on manganese-doped Prussian blue analog are both increased by about two times. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

[0030] Figure 1 These are SEM images of the manganese-doped Prussian blue analogues (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) prepared in Comparative Example 1.

[0031] Figure 2 1 is a particle size distribution diagram of the manganese-doped Prussian blue analogues (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) prepared in Comparative Example 1.

[0032] Figure 3 The manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) electrode prepared in Comparative Example 1 were tested at 20 mV·s -1 CV curves at a scan rate of .

[0033] Figure 4 The manganese-doped Prussian blue analog (MNP-3) electrode prepared in Example 1 of the present invention is 1V·s -1 , 2V·s -1 , 5V·s -1 , 10V·s -1 and 20mV·s-1 CV curves at a scan rate of .

[0034] Figure 5 GCD diagrams of the manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) electrode prepared in Comparative Example 1.

[0035] Figure 6 It is an EIS curve diagram of the manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) electrode prepared in Comparative Example 1.

[0036] Figure 7 This is a diagram showing the desalination effect of the manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes and the nickel-based Prussian blue analogue (NP) electrode in Example 2 of the present invention.

[0037] Figure 8 This is a diagram showing the cyclic desalination effect of the manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes and the nickel-based Prussian blue analogue (NP) electrode in Example 2 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0039] In the following examples of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0040] Example 1

[0041] A method for preparing a Prussian blue analog electrode, characterized in that it comprises the following steps:

[0042] S1, respectively, manganese salt (specifically MnCl 2 , 99.0%), nickel salts (specifically NiCl 2 , 99.0%), potassium ferrocyanide (K 3 Fe(CN) 6 , 99.0%) was mixed with 30 mL of deionized water to obtain a manganese salt solution, a nickel salt solution, and a potassium ferrocyanide solution.

[0043] In this step, NiCl 2The concentration of potassium ferrocyanide solution is 5mM. 3 Fe(CN) 6 The concentration is 2.5 mM.

[0044] S2. The manganese salt solution, nickel salt solution and potassium ferrocyanide solution obtained in step S1 are slowly added into 15 mL of deionized water at the same time to obtain a mixture.

[0045] In step S2, the molar ratios of manganese to nickel in the prepared mixture are 1:9, 1:4, 3:7, 2:3, and 1:1, respectively.

[0046] S3. Aging the mixture obtained in step S2, using a magnetic stirrer and stirring at a rotation speed of 300 rpm for 6 hours during the aging process. After the aging is completed, washing with deionized water, placing in a vacuum drying oven and drying for 24 hours to obtain a manganese-doped Prussian blue analogue, recorded as MNP-x.

[0047] In this step, when the molar ratio of manganese to nickel in the mixture is 1:9, 1:4, 3:7, 2:3, and 1:1, the corresponding manganese-doped Prussian blue analogues (MNP-x) are respectively recorded as MNP-1, MNP-2, MNP-3, MNP-4, and MNP-5.

[0048] S4. According to the mass ratio of manganese-doped Prussian blue analogue, binder and conductive agent of 8:1:1, the manganese-doped Prussian blue analogue, binder (specifically polyvinylidene fluoride, PVDF), conductive agent (specifically conductive carbon black) and solvent (specifically N-methyl-2-pyrrolidone, NMP) obtained in step S3 are mixed respectively, and ultrasonicated for 60 minutes to obtain electrode slurry liquid.

[0049] S5. Apply the electrode slurry obtained in step S4 to the surface of the current collector (specifically graphite paper with a size of 1 cm×1 cm) respectively, and dry to obtain a Prussian blue analog electrode, that is, a manganese-doped Prussian blue analog (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrode.

[0050] Comparative Example 1

[0051] A method for preparing a nickel-based Prussian blue analog (NP) electrode is substantially the same as that of Example 1, except that no manganese salt is added in Comparative Example 1.

[0052] The nickel-based Prussian blue analogue prepared in Comparative Example 1 is denoted as NP.

[0053] The morphology and structural properties of manganese-doped Prussian blue analogs (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) and nickel-based Prussian blue analogs (NPs) were determined by scanning electron microscopy (SEM, Zeiss Genimi 500). The particle size distribution of manganese-doped Prussian blue analogs (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) and nickel-based Prussian blue analogs (NPs) was determined using a nanoparticle sizer and a zeta potential meter (Zetasizer Nano ZS, Malvern, UK).

[0054] Figure 1 These are SEM images of the manganese-doped Prussian blue analogues (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) prepared in Comparative Example 1. Figure 1 The microstructure of the material was observed using a scanning electron microscope (SEM). Figure 1 In the above equation, a,b,c are NP, MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5, respectively. Figure 1 As shown in the figure, when the manganese ions are not doped, the particle size of NP is 1-3 μm. When the manganese / nickel doping ratio is 1:9, the particle size of MNP-1 decreases sharply to 692nm-741nm. When the manganese / nickel doping ratio is 1:4, the particle size of MNP-2 further decreases to 390nm-637nm. When the manganese / nickel doping ratio is 3:7, the particle size of MNP-3 decreases sharply to 35nm-72nm. When the manganese / nickel doping ratio is 2:3, the particle size of MNP-4 is 52nm-74nm. When the manganese / nickel doping ratio is 1:1, the particle size of MNP-5 is 53nm-68nm. It can be seen that the particle size of the material usually decreases with the increase of the doping ratio, and when the manganese / nickel doping ratio is greater than 3:7, the particle size of the material is already less than 100nm. Therefore, the comparison of the surface images of NP and MNP-x shows that as the Mn in the material increases, the particle size of the material decreases. 2+ With the increase of content, their particle size gradually decreases, the particle size becomes more and more uniform, and the stacking between particles becomes denser and denser.

[0055] Figure 2 1 is a particle size distribution diagram of the manganese-doped Prussian blue analogs (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) prepared in Example 1 of the present invention and the nickel-based Prussian blue analog (NP) prepared in Comparative Example 1. Figure 2As shown in the figure, the first peak in the NP size distribution is located at around 1170 nm, while the larger particle size peak is attributed to the agglomeration phenomenon. When the Mn / Ni doping ratio is 1:9, 1:4, 3:7, 2:3, and 1:1, the peaks of the particle size distribution of MNP-1, MNP-2, MNP-3, MNP-4, and MNP-5 are around 380 nm, 410 nm, 270 nm, 240 nm, and 230 nm, respectively. It can be seen that the particle size of the manganese-doped Prussian blue analogue (MNP-x) gradually decreases with the increase of the Mn / Ni doping ratio.

[0056] The electrochemical properties of Prussian blue analog electrodes prepared from manganese-doped Prussian blue analogs (MNP-1, MNP-2, MNP-3, MNP-4, and MNP-5) and nickel-based Prussian blue analogs (NPs) were investigated using an electrochemical workstation (CHI 760E, Shanghai, China). Cyclic voltammetry (CV) and constant current charge-discharge (GCD) tests were performed using a three-electrode system with 1 M NaCl as the electrolyte. Pt sheets were used as counter electrodes, and Ag / AgCl was used as reference electrodes. 0.05 M Na 2 SO 4 Electrochemical impedance spectroscopy (EIS) curves were performed as electrolytes.

[0057] GCD and CV tests: The potential window was -0.4 V to 1.2 V at different scan rates (1, 2, 5, 10 and 20 mVs -1 CV curves were performed at different current densities (0.5, 1, 2, 3 and 4 A·g -1 ) to measure GCD test. Specific capacitance (C, F·g -1 ) were obtained from the GCD and CV curves and calculated according to Equation 1 and Equation 2, respectively.

[0058]

[0059] Where C is the capacitance (F·g -1 ), I is the discharge current response (A), Δt is the discharge time (s), m is the mass of active material (g), and ΔV is the applied voltage window in the GCD test.

[0060]

[0061] Where ∫IdV represents the integrated area of ​​the CV curve, and v is the scan rate in the CV test (V · s -1 ) 。

[0062] Figure 3The manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes prepared in Example 1 of the present invention and the nickel-based Prussian blue analogue (NP) electrode prepared in Comparative Example 1 were tested at 20 mV·s -1 CV curve at a scan rate of Figure 3 As shown in Figure 5, several redox peaks were found on the CV curves of the NP and MNP-x composites, showing typical pseudocapacitive behavior corresponding to the reversible redox of Prussian blue analogs. It is worth noting that the combination of EDL charge storage and Faraday charge storage significantly improves the overall electrochemical performance. The Na + The insertion / dissociation forms redox pairs, which are clearly visible in all samples, thus revealing the reversible Faradaic reaction at these electrodes. In addition, the CV curve of MNP-3 encloses the largest area, indicating that MNP-3 has better ion storage capacity. The specific capacitances of NP, MNP-1, MNP-2, MNP-3, MNP-4, and MNP-5 were calculated from the CV curves to be 65 F·g -1 、70F·g -1 ,82F·g -1 ,87F·g -1 , 80F·g -1 and 83F·g -1 . The modified electrode materials exhibited different CV curves compared to NPs. The specific capacitance of MNP-x was greater than that of NPs, which may be due to the smaller particle size of the nanoparticles. The smaller particle size of MNP-x increased the specific surface area available for reaction and provided more active sites for the insertion and extraction of ions during the redox process. In contrast, NPs had a larger particle size, resulting in looser packing between particles, a smaller specific surface area involved in the reaction, and a lower ion storage capacity during the redox process.

[0063] To further understand the electrochemical behavior, CV experiments were performed on MNP-3 with a scan rate range of 1 V s -1 , 2V·s -1 , 5V·s -1 , 10V·s -1 and 20mV·s -1 , the results are as follows Figure 4 shown.

[0064] Figure 4 The manganese-doped Prussian blue analog (MNP-3) electrode prepared in Example 1 of the present invention is 1V·s -1 , 2V·s -1 , 5V·s -1 , 10V·s -1 and 20mV·s-1 CV curve at a scan rate of Figure 4 As shown in Figure 2, a faster current response is observed with increasing scan rate because ions can migrate to the electrode more easily and be stored in the active sites. In addition, the properties of the CV curves do not change with the voltage scan rate, which reflects the good electrochemical reversibility of the MNP-3 electrode. The small peak at low scan rate is consistent with the Na + Related to the interaction with MNP-3.

[0065] Figure 5 The GCD diagrams are of the manganese-doped Prussian blue analog (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes prepared in Example 1 of the present invention and the nickel-based Prussian blue analog (NP) electrode prepared in Comparative Example 1. Figure 5 As shown in Figure 3, the MNP-3 electrode exhibits obvious charge-discharge platform during the charge and discharge process, indicating typical pseudocapacitive behavior. The NP and MNP-3 composite electrodes have two voltage platforms between 0.2 and 0.5 V, which correspond to the redox peaks observed in the CV curves. -1 At a high current density, the discharge time of MNP-3 is 204.0s ( Figure 5 a), the discharge time of MNP-3 is not much different from that of NP, and as the Mn / Ni doping ratio continues to increase, the discharge time of the material decreases significantly. -1 , 1A·g -1 , 2A·g -1 , 3A g -1 and 4A·g -1 The specific capacitances are 156.2 F·g -1 , 129.9F·g -1 、89.0F·g -1 、86.5F·g -1 and 81.0F·g -1 , indicating good multiplication performance ( Figure 5 b).

[0066] Figure 6 The EIS curves of the manganese-doped Prussian blue analog (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes prepared in Example 1 of the present invention and the nickel-based Prussian blue analog (NP) electrode prepared in Comparative Example 1 are shown in FIG. Figure 6As shown in Figure 1, the EIS curves of NP and MNP-x have typical circular curves and straight lines. The quasi-semicircle in the high-frequency region is related to the interfacial resistance between the electrode and the electrolyte, while the oblique line in the low-frequency region is related to the ion diffusion rate at the electrode surface. A larger semicircle means a higher charge transfer resistance, while a steeper slope means a faster ion diffusion rate. Figure 6 R ct (NP)=6.5Ω,R ct (MNP-3) = 5.6Ω, MNP-3 has a smaller interface charge transfer resistance. The slope of the low-frequency region decreases with the increase of manganese doping amount, and its surface ion diffusion energy decreases slightly.

[0067] Example 2

[0068] A Prussian blue analog electrode is used in solution desalination, specifically: using the Prussian blue analog electrode to desalinate a saline solution, specifically comprising the following steps:

[0069] (1) A Prussian blue analog electrode was prepared according to the method in Example 1, except that in Example 2, the size of the graphite paper used was 3 cm×3 cm.

[0070] (2) A capacitive deionization device is constructed using the Prussian blue analog electrode prepared in step (1) as the cathode (negative electrode) and the activated carbon electrode as the anode (positive electrode).

[0071] (3) Desalting the salt solution using the capacitive deionization device constructed in step (2), specifically: using a peristaltic pump at 8 mL min -1 The rate will be 100 ml 500 mg·L -1 The NaCl solution is circulated into the capacitive deionization device, and the sodium chloride in the solution is removed by adsorption using a Prussian blue analog electrode, thereby completing the desalination treatment of the saline solution.

[0072] During the desalination process, the conductivity of the NaCl solution leaving the CDI unit was measured using a conductivity meter. Throughout the test, a constant voltage charge was applied. During the adsorption phase, the NP / MNP-x electrode served as the negative electrode and the AC electrode served as the positive electrode for constant voltage charging. During the desorption phase, the voltage was reversed to release the ions.

[0073] Control group: The nickel-based Prussian blue analogue (NP) prepared in Comparative Example 1 was used instead of the manganese-doped Prussian blue analogue, and other conditions were the same.

[0074] The salt adsorption capacity (SAC, mg g) in batch mode operation was calculated according to Eq. -1 ), Equation 3:

[0075]

[0076] Among them C 0 and C t (mg L -1 ) are the initial NaCl concentration before charging and the NaCl concentration at time t, V T is the total solution volume (L), m T is the total active material mass of the anode and cathode (g).

[0077] Figure 7 The figure is a diagram showing the desalination effect of the manganese-doped Prussian blue analog (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrode and the nickel-based Prussian blue analog (NP) electrode in Example 2 of the present invention. Figure 7 As shown in the figure, for the comparison of NP and MNP-x at five different doping ratios, MNP-3 (58.82 mg·g -1 ) has the largest SAC in batch mode, which is NP (30.15 mg·g -1 ) was 1.95 times that of MNP-1 and MNP-2. -1 , 41.67mg·g -1 ) is relatively lower than that of MNP-3, which may be because their particle size is larger than that of MNP-3, resulting in insufficient mass transfer efficiency. NMP-4 and NMP-5 (51.47 mg·g -1 , 33.60mg·g -1 ) is also inferior to MNP-3 in desalination performance, because excessive Mn doping reduces the particle size, while too small a particle size increases the possibility of particle accumulation, which is detrimental to the capacitive deionization process. In addition, excessive Mn doping leads to a decrease in the electrochemical performance of the electrode: the specific capacitance decreases, the charge and discharge time of the GCD curve becomes shorter, and the slope of the EIS curve decreases.

[0078] Figure 8 This is a diagram showing the cyclic desalination effect of the manganese-doped Prussian blue analogue (MNP-1, MNP-2, MNP-3, MNP-4 and MNP-5) electrodes and the nickel-based Prussian blue analogue (NP) electrode in Example 2 of the present invention. Figure 8 The graphs showing the conductivity and SAC of NP and MNP-3 electrodes during the cycling test. Figure 8 It can be seen that from the 1st to the 30th cycle, the SAC of NP increased from 31.25 mg·g -1 Reduced to 25 mg g -1 The capacity retention rate was 80%, and the SAC of MNP-3 decreased from 47.0 to 33.83 mg·g after 30 cycles. -1 , the capacity retention rate is 72%, indicating that the cycle stability has decreased. One of the main reasons for the decrease in cycle stability is that Mn3+ The Jahn-Teller distortion of NP is reduced, while it still shows better SAC compared with NP.

[0079] It can be seen from the above results that, compared with conventional Prussian blue analogue electrodes, the Prussian blue analogue electrode prepared with manganese-doped Prussian blue analogue as active material in the present invention has higher salt adsorption capacity, faster salt adsorption rate, and can effectively adsorb low concentrations of target pollutants under lower voltage conditions, has lower energy consumption, and has better adaptability to pollutants of different concentrations. It has the advantages of low energy consumption, high salt adsorption capacity, and fast salt adsorption rate. It can effectively treat pollutants of different concentrations, has high use value, and good application prospects. It is of great significance for promoting the widespread application of capacitive deionization technology.

[0080] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a Prussian blue analog electrode, characterized in that: The following steps are involved: S1, respectively mixing a manganese salt, a nickel salt, and potassium ferrocyanide with water to obtain a manganese salt solution, a nickel salt solution, and a potassium ferrocyanide solution; S2, adding the manganese salt solution, nickel salt solution and potassium ferrocyanide solution obtained in step S1 into water simultaneously to obtain a mixture; the molar ratio of manganese to nickel in the mixture is ≥0.1:1; S3, aging, washing, and drying the mixture obtained in step S2 to obtain a manganese-doped Prussian blue analogue; S4, mixing the manganese-doped Prussian blue analogue obtained in step S3, a binder, a conductive agent and a solvent, and ultrasonicating to obtain an electrode slurry liquid; S5. Apply the electrode slurry obtained in step S4 to the surface of the current collector and dry it to obtain a Prussian blue analog electrode.

2. The preparation method according to claim 1, characterized in that: In step S2, the molar ratio of manganese to nickel in the mixture is 0.1-2:

1.

3. The preparation method according to claim 2, characterized in that: In step S2, the molar ratio of manganese to nickel in the mixture is 0.25 to 1:

1.

4. The preparation method according to claim 3, characterized in that: In step S2, the molar ratio of manganese to nickel in the mixture is 0.3-0.6:

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step S1, the manganese salt is manganese chloride; the nickel salt is nickel chloride; In step S3, the aging is carried out at a stirring speed of 300 rpm; the aging time is 6 hours; In step S4, the mass ratio of the manganese-doped Prussian blue analogue, the binder, and the conductive agent is 8-9:0.8-1:0.8-1, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol and polypropylene, and the conductive agent is conductive carbon black; the solvent is at least one of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, and deionized water; the ultrasonic time is 60 minutes; In step S5, the current collector is one of graphite paper, nickel foam, copper foil, aluminum foil, and titanium mesh.

6. A Prussian blue analog electrode, characterized in that The Prussian blue analog electrode is prepared by the preparation method according to any one of claims 1 to 5.

7. The Prussian blue analog electrode according to claim 6, characterized in that The Prussian blue analogue electrode comprises a manganese-doped Prussian blue analogue; the peak position of the particle size distribution of the manganese-doped Prussian blue analogue is located at 270 nm.

8. Use of the Prussian blue analog electrode as claimed in claim 7 in solution desalination.

9. The use according to claim 8, characterized in that: The following steps are involved: (1) A capacitive deionization device constructed with a Prussian blue analog electrode as the cathode and an activated carbon electrode as the anode; (2) Desalination of saline solution using a capacitive deionization device.

10. The use according to claim 9, characterized in that: In step (2), the saline solution is brackish water or seawater; the salt concentration in the saline solution is ≤500 mg·L -1 ; The control voltage during the desalination process is 1.2V; The circulation rate of the saline solution during the desalination process is 8mL·min -1 .

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