Polyacid-based materials, preparation methods, applications, and electrodes thereof

Abstract

The present invention relates to the field of degradation of N-methyldiethanolamine (MDEA), and discloses a polyacid-based crystalline material, a preparation method thereof, an application thereof, and an electrode thereof. The chemical formula of the polyacid-based material is [Fe2(H6P2W 22 O 78 )]·p(C x H y N z ) r qH2O; wherein p is an integer between 1 and 4; x is an integer between 10 and 13; y is 15 or 16; z is an integer between 2 and 4; r is an integer between 2 and 4; and q is a natural number between 0 and 3. This polyacid-based crystalline material has the effect of electrocatalytically degrading MDEA, achieving an MDEA degradation rate of over 99%.

Description

Technical Field

[0001] The present invention relates to the field of degradation of N-methyldiethanolamine (MDEA), and in particular to a polyacid-based material, a preparation method and application thereof, and an electrode. Background Art

[0002] N-Methyldiethanolamine (MDEA), an alkaline solvent from the alkanolamine family, has been widely used in carbon removal in recent years due to its excellent acid gas absorption properties. However, with the increasing demand for amine solution concentrations, problems such as amine foaming, deterioration, and failure have become more frequent. Many companies have experienced amine foaming leading to tower overflow and amine leakage. Therefore, with the widespread use of amine solutions, it is necessary to recycle high-concentration waste amine solutions and effectively treat any trace amounts of leaked organic amines to prevent them from mixing directly with other wastewater, increasing the difficulty of wastewater treatment, and reducing pollution and harm to organisms and the environment.

[0003] MDEA wastewater is mainly degraded by adsorption, chemical oxidation, and biological methods. Although the above methods have certain effects on the degradation of MDEA, they have disadvantages such as low degradation rate, excessive amount of oxidant, complex operation, and low safety performance. Currently, electrochemical methods are rarely used to degrade MDEA. Electrochemical water treatment technology is a green water treatment technology. Its main principle is to use potential difference to regulate the flow of electrons, so that pollutants can complete the degradation or transformation process at the electrode interface or in the solution to achieve water purification. The core of electrochemical degradation lies in the research of electrocatalysts.

[0004] Polyacids are normally fully oxidized and can exist in either a fully or partially protonated form. The presence of metal ions in polyacids can provide empty orbitals for accepting electrons, resulting in excellent redox properties and potential use as excellent electrocatalysts. However, studies have shown that because classic polyacids are soluble in water and some organic solvents, their use as catalyst materials to modify electrodes is prone to detachment and instability, resulting in a short catalyst life. Furthermore, classic polyacids themselves have a very small specific surface area, with relatively few surface active sites that are prone to aggregation, limiting their inherent catalytic performance. Therefore, in order to address the issue of classic polyacids being prone to detachment when used as catalyst materials to modify electrodes, a polyacid-based material capable of effectively degrading MDEA and its preparation method are needed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems of easy shedding of polyacid-based material modified electrodes and low efficiency in degrading MDEA in the prior art, and to provide a polyacid-based material that can effectively degrade MDEA and a preparation method thereof.

[0006] In order to achieve the above object, the present invention provides a polyacid-based crystalline material in a first aspect, wherein the chemical formula of the polyacid-based material is [Fe2(H6P2W22 O 78 )]·p(C x H y N z ) r qH2O;

[0007] Among them, p is an integer between 1 and 4; x is an integer between 10 and 13; y is 15 or 16; z is an integer between 2 and 4; r is an integer between 2 and 4; and q is a natural number between 0 and 3.

[0008] A second aspect of the present invention provides a method for preparing a polyacid-based crystalline material, the method comprising:

[0009] (1) mixing a polyacid, an iron salt, a ligand, and water to obtain a mixture;

[0010] (2) subjecting the mixture to a chemical reaction and obtaining the polyacid-based crystalline material after post-processing.

[0011] The third aspect of the present invention provides a polyacid-based crystalline material prepared by the method described in the second aspect of the present invention.

[0012] The fourth aspect of the present invention provides an application of the polyacid-based crystalline material described in the first aspect or the third aspect of the present invention in the field of degrading N-methyldiethanolamine.

[0013] The fifth aspect of the present invention provides an electrode, which includes the polyacid-based crystalline material described in the first aspect or the third aspect of the present invention.

[0014] Through the above technical solution, the beneficial effects of the present invention are as follows:

[0015] 1. The present invention adopts a simple hydrothermal synthesis technology and utilizes 4,4′-(1,3-propanediyl)bipyridine ligand or 1,4-bis(imidazol-1-yl)butane ligand, Na9(A-α-PW9O 34 )·7H2O, and metal iron salts were used to successfully prepare polyacid-based supramolecular materials with electrocatalytic degradation performance; Keggin-type vacancy polyacid (PW9O 34 ) 9- First, obtain the WO6 polyhedron (PW 11 ) unit, and then coordinates with the iron atom to form the iron atom monosubstituted type (FePW 11 ) unit, adjacent (FePW 11 The iron atoms in the ) unit are connected to each other by the terminal oxygen atoms to form a novel dimer structure such as Figure 1 As shown, the length of the dimer is 1.9 nm as measured by Diamond software.

[0016] 2. The polyacid-based nanocluster material-modified glassy carbon electrode prepared by the present invention exhibits electrocatalytic performance. Using an electrochemical workstation and a standard three-electrode system, the polyacid-based nanocluster material-coated glassy carbon electrode serves as the working electrode, a platinum wire serves as the counter electrode, and Ag / AgCl serves as the reference electrode. The polyacid-based nanocluster material-modified glassy carbon electrode exhibits an electrocatalytic oxidative degradation efficiency of 99.92% for MDEA in a Na₂SO₄ solution containing 0.05 mol / L MDEA, demonstrating promising application in MDEA degradation.

[0017] 3. The polyacid-based nanocluster material with electrocatalytic performance prepared by the present invention has stable performance when catalyzing the MDEA degradation reaction and can be used continuously for more than 10 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of a polyacid-based crystalline material having a dimer structure for electrocatalytic oxidation degradation of MDEA prepared in Example 1 of the present invention;

[0019] Figure 2 This is a schematic diagram of powder X-ray diffraction of a polyacid-based crystalline material having a dimer structure capable of electrocatalytically oxidatively degrading MDEA, prepared in Example 1 of the present invention;

[0020] Figure 3 This is a schematic diagram of the infrared spectrum of a polyacid-based crystalline material having a dimer structure capable of electrocatalytically oxidatively degrading MDEA, prepared in Example 1 of the present invention;

[0021] Figure 4 This is an X-ray single crystal diffraction pattern of a polyacid-based crystalline material having a dimer structure for electrocatalytic oxidation degradation of MDEA prepared in Example 7 of the present invention;

[0022] Figure 5 This is a thermogravimetric diagram of a polyacid-based crystalline material having a dimer structure capable of electrocatalytically oxidatively degrading MDEA, prepared in Example 1 of the present invention;

[0023] Figure 6 This is a cyclic voltammetry curve of a polyacid-based crystalline material having a dimer structure for electrocatalytic oxidation degradation of MDEA prepared in Example 1 of the present invention;

[0024] Figure 7 This is a chromatogram of MDEA before reaction in a polyacid-based crystalline material having a dimer structure for electrocatalytic oxidation degradation of MDEA prepared in Example 1 of the present invention;

[0025] Figure 8This is a chromatogram after the reaction of MDEA in a polyacid-based crystalline material having a dimer structure capable of electrocatalytically oxidatively degrading MDEA, prepared in Example 1 of the present invention.

[0026] Figure 9 This is the IT curve of the polyacid-based crystal material, which shows that the polyacid-based crystal material remains stable after 10 hours of use. Where i represents the ordinate Current Density. DETAILED DESCRIPTION

[0027] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0028] The first aspect of the present invention provides a polyacid-based crystalline material, wherein the chemical formula of the polyacid-based material is [Fe2(H6P2W 22 O 78 )]·p(C x H y N z ) r qH2O;

[0029] Among them, p is an integer between 1 and 4; x is an integer between 10 and 13; y is 15 or 16; z is an integer between 2 and 4; r is an integer between 2 and 4; and q is a natural number between 0 and 3.

[0030] In some embodiments of the present invention, preferably, the crystal system of the polyacid-based crystal material is triclinic; the space group of the polyacid-based crystal material is P-1; the single package parameters of the polyacid-based crystal material include: a=11.671(12)-12.148(3), b=13.394(2)-13.591(13), c=17.080(3)-18.132(18), α=86.366(3)-101.532(5), β=74.056(2)-95.030(5), γ=67.280(2)-108.957(5), V=2540.0(8)-2547.9(4), Z=1. It can be determined by X-ray diffraction.

[0031] In the present invention, preferably, the polyacid-based crystal material is [Fe2(H6P2W 22 O 78 )]·4(C 13 H 15N2)2 or [Fe2(H6P2W 22 O 78 )]·(C 10 H 16 N4)4·3H2O.

[0032] In the present invention, the polyacid-based crystalline material has a dimer structure and can be Figure 2 The X-ray diffraction pattern shown is characteristic of this structure.

[0033] A second aspect of the present invention provides a method for preparing a polyacid-based crystalline material, the method comprising:

[0034] (1) mixing a polyacid, an iron salt, a ligand, and water to obtain a mixture;

[0035] (2) subjecting the mixture to a chemical reaction and obtaining the polyacid-based crystalline material after post-processing.

[0036] In some embodiments of the present invention, preferably, in step (1), the iron salt is selected from ferrous acetate and ferrous chloride, and is used to provide iron ions in the polyacid-based crystalline material.

[0037] In some embodiments of the present invention, preferably, the polyacid is a Keggin-type vacancy phosphotungstic acid; preferably selected from Na9(A-α-PW9O 34 )·7H2O.

[0038] In some embodiments of the present invention, the ligand is preferably selected from a pyridine- or imidazole-containing compound, preferably 4,4′-(1,3-propanediyl)bipyridine or 1,4-bis(imidazol-1-yl)butane, to provide the ligand component in the polyacid-based crystalline material.

[0039] In some embodiments of the present invention, preferably, in step (1), the molar ratio of the polyacid to the iron salt is 1:3-6.

[0040] In some embodiments of the present invention, preferably, in step (1), the molar ratio of the polyacid to the ligand is 1:2-3.

[0041] In some embodiments of the present invention, preferably, in step (1), the pH value of the mixture is 2.5-4.5, which can enable the chemical reaction to proceed smoothly while minimizing the occurrence of side reactions.

[0042] In some embodiments of the present invention, preferably, in step (2), the temperature of the chemical reaction is 130-140° C. This allows the chemical reaction to proceed fully while minimizing the amount of by-products produced.

[0043] In some embodiments of the present invention, preferably, in step (2), the reaction time of the chemical reaction is 5-7 days, so that the chemical reaction can proceed fully and the yield of the polyacid-based crystalline material can be maximized.

[0044] In the present invention, the post-treatment process includes: cooling to room temperature, dissolving impurities using ultrasound, washing with deionized water and then drying to obtain a dry product, which can purify the polyacid-based crystalline material.

[0045] The third aspect of the present invention provides a polyacid-based crystalline material prepared by the method described in the second aspect of the present invention.

[0046] The polyacid-based crystalline material may have the aforementioned dimer structure, which will not be described in detail here.

[0047] The fourth aspect of the present invention provides an application of the polyacid-based crystalline material described in the first aspect or the third aspect of the present invention in the field of degrading N-methyldiethanolamine.

[0048] The fifth aspect of the present invention provides an electrode, which includes the polyacid-based crystalline material described in the first aspect or the third aspect of the present invention.

[0049] The present invention will be described in detail below through examples. In the following examples, the raw materials sodium tungstate, iron salt, 4,4′-(1,3-propanediyl)bipyridine, phosphoric acid, and 1,4-bis(imidazol-1-yl)butane were purchased from Aladdin Reagent Co., Ltd.

[0050] Polyacid Na9(A-α-PW9O 34 )·7H2O synthesis steps: 120g sodium tungstate is dissolved in 150g water, 4mL phosphoric acid is added, and then 22.5mL glacial acetic acid is added and stirred continuously to obtain a white precipitate, which is filtered and dried. This synthesis step is a commonly used method in the art (see the preparation method disclosed in "Multinuclear transition metal sandwich-type polytungstate derivatives for enhanced electrochemical energy storage and bifunctional electrocatalysis performances" (XY Ma, KYu, J Yuan, et al., Inorg. Chem., 2020, 59(7): 5149-5160) for details).

[0051] Example 1

[0052] Polyacid Na9(A-α-PW9O 34)·7H2O, iron salt Fe(OAc)2, 4,4′-(1,3-propanediyl)bispyridine ligand and 10 mL of deionized water were stirred and mixed for 1.5 hours to obtain a mixture, and the pH value was adjusted to 2.5 using 2 M HCl;

[0053] The molar ratio of the polyacid to the iron salt is 1:3;

[0054] The molar ratio of the polyacid to the 4,4'-(1,3-propanediyl)bipyridine ligand is 1:3;

[0055] The mixture was reacted at 140°C for 7 days and then removed. After cooling to room temperature, impurities were dissolved by ultrasound and washed with deionized water. After washing and drying, the product obtained yellow flaky crystals. X-ray diffraction analysis showed that it was a polyacid-based crystal material with a yield of 53% [based on Na9(A-α-PW9O 34 )].

[0056] Example 2

[0057] High-purity ammonia was prepared in the same manner as in Example 1, except that the iron salt was ferric chloride. The yield of the polyacid-based crystalline material was 37% [based on Na9(A-α-PW9O 34 )].

[0058] Example 3

[0059] High-purity ammonia was prepared in the same manner as in Example 1, except that the molar ratio of polyacid to iron salt was 1:6. The yield of polyacid-based crystalline material was 23% [based on Na9(A-α-PW9O 34 )].

[0060] Example 4

[0061] High-purity ammonia was prepared by the same method as in Example 1, except that the molar ratio of polyacid to 4,4'-(1,3-propanediyl)bipyridine ligand was 1:2. The yield of polyacid-based crystalline material was 45% [based on Na9(A-α-PW9O 34 )].

[0062] Example 5

[0063] High-purity ammonia was prepared in the same manner as in Example 1, except that the pH of the mixture was 4.5. The yield of the polyacid-based crystalline material was 33% [based on Na9(A-α-PW9O 34 )].

[0064] Example 6

[0065] High-purity ammonia was prepared in the same manner as in Example 1, except that the mixture was reacted at 130°C for 7 days before being taken out. The yield of the polyacid-based crystalline material was 21% [based on Na9(A-α-PW9O 34 )].

[0066] Example 7

[0067] High-purity ammonia was prepared in the same manner as in Example 1, except that the ligand was 1,4-bis(imidazol-1-yl)butane. The yield of the polyacid-based crystalline material was 32% [based on Na9(A-α-PW9O 34 )].

[0068] Comparative Example 1

[0069] According to the report "Research Progress of N-Methyldiethanolamine Wastewater Treatment Technology" (Modern Chemical Industry, Vol. 42, No. 12), the main treatment technologies for N-methyldiethanolamine (MDEA) wastewater and their MDEA degradation rates are as follows:

[0070] Biological method: 98.42%; electrolysis method: 97%; oxidant direct oxidation technology: 85%; technology coupling: 96%.

[0071] Performance Testing

[0072] (1) Structural characterization of polyacid-based crystalline materials

[0073] The polyacid-based crystalline materials prepared in Examples 1 and 7 respectively have the chemical formulas of [Fe2(H6P2W 22 O 78 )]·4(C 13 H 15 N2)2 and [Fe2(H6P2W 22 O 78 )]·(C 10 H 16 N4)4·3H2O, the molecular formulas are C 52 H 66 Fe2N8O 78 P2W 22 and C 40 H 70 Fe2N 16 O 81 P2W 22 .

[0074] In the polyacid-based crystalline materials prepared in Examples 1 and 7, two single vacancies (PW 11 ) unit encapsulates a (Fe2O2) unit in the middle, thus forming a nanocluster based on a dimer structure (such as Figure 1The diverse metal atoms and abundant oxygen atoms provide abundant active centers for the oxidative degradation of MDEA.

[0075] The polyacid-based crystal materials of good quality were selected under a high-power microscope and fixed on an X-ray single crystal diffractometer for data collection, wherein the X-ray diffraction source was Mo target Kα radiation. The dimer structure and chemical formula were obtained by using the SHELXL-2018 / 3 software package. The crystal structure was initially solved by the direct method and the least squares method F was used. 2 The data were refined, and all non-hydrogen atoms in the crystal structure were anisotropically refined. The C and N atoms were hydrogenated using the theoretical hydrogenation method.

[0076] The X-ray crystallographic parameters of the polyacid-based crystalline materials prepared in Examples 1 and 7 are shown in Tables 1 and 2, respectively.

[0077] Table 1

[0078]

[0079] Table 2

[0080]

[0081]

[0082] X-ray single crystal diffraction analysis showed that the polyacid-based crystalline material [Fe2(H6P2W 22 O 78 )]·4(C 13 H 15 N2)2 can reach the nanometer size level, and the basic composition structure includes iron atom single substitution (FePW 11 ) units and free 4,4′-(1,3-propanediyl)bispyridine ligands. Figure 1 This is a schematic diagram of the structure of the polyacid-based crystal material prepared in Example 1, wherein the Fe atom is connected to the oxygen atom in the polyacid to form a six-coordinated pattern, and the bond length of the Fe-O bond is between 1.927 (15) and

[0083] Figure 2 The powder X-ray diffraction spectrum of the polyacid-based crystalline material prepared in Example 1 is as follows; Figure 2 It can be seen that the diffraction peaks of XRD are consistent with the theoretical XRD spectrum, indicating that the synthesized polyacid-based crystalline material is pure phase.

[0084] Figure 3 This is the infrared spectrum of the polyacid-based crystalline material prepared in Example 1. Figure 3 It can be seen that at 3475cm -1The peak in the range is attributed to the stretching vibration of OH, at 3079 cm -1 The range corresponds to the CH stretching vibration peak on the organic ligand, which is 1504-1639 cm -1 The peaks at 1057 cm-1 are attributed to the C=C and C=N stretching vibrations of the organic ligands. -1 The stretching vibration peak at 960 cm belongs to the PO in the polyacid anion. -1 It is attributed to the absorption peak of W=O at 802cm -1 The absorption peak at is attributed to the absorption of WOW. The above characteristic absorption peaks can also prove that Figure 2 The chemical structure of the polyacid-based crystalline material with a dimer structure is shown.

[0085] Figure 4 Schematic diagram of the structure of the polyacid-based crystalline material prepared in Example 7. Figure 4 It can be seen that X-ray single crystal diffraction analysis shows that the nano-sized polyacid-based crystalline material [Fe2(H6P2W 22 O 78 )]·(C 10 H 16 The basic structure of N4)4·3H2O includes single iron substitution (FePW 11 ) units and free 1,4-bis(imidazol-1-yl)butane ligands.

[0086] Figure 5 This is a thermogravimetric diagram of a polyacid-based crystalline material with a dimer structure prepared in Example 1. Figure 5 It can be seen that when the temperature rises from room temperature to 345°C, the mass of the polyacid-based crystal material remains stable. When the temperature continues to rise, the polyacid-based crystal material loses weight significantly, which is caused by the collapse of the 4,4′-(1,3-propanediyl)bipyridine ligand and part of the metal skeleton.

[0087] (2) Verification of the effect of polyacid-based crystal materials on MDEA degradation

[0088] Using an electrochemical workstation, 7 mg of polyacid-based crystalline material [Fe2(H6P2W 22 O 78 )]·4(C 13 H 15N2)2 was dispersed in an ethanol solution containing a Nafion solution, and after ultrasonic homogenization, it was dropped onto glassy carbon and used as a working electrode. At the same time, platinum wire was used as a counter electrode and Ag / AgCl was used as a reference electrode. In a Na2SO4 solution containing 0.05 mol / L MDEA, the electrocatalytic oxidation degradation efficiency of the glassy carbon electrode modified with polyacid-based nanocluster materials could reach 99.92%. When the [Fe2(H6P2W 22 O 78 )]·4(C 13 H 15 When the dosage of N2)2 reaches 9 mg, the electrocatalytic oxidation degradation efficiency of MDEA can reach 99.89%; 22 O 78 )]·4(C 13 H 15 N2)2 is replaced by [Fe2(H6P2W 22 O 78 )]·(C 10 H 16 The electrocatalytic oxidation reaction of the above-mentioned MDEA was carried out with N4)4·3H2O, and the degradation efficiency was 99.41%.

[0089] Figure 6 The cyclic voltammetry curve of the polyacid-based crystalline material prepared in Example 1; Figure 6 It can be seen that triethanolamine has an oxidation peak in the electrolyte but no reduction peak, and the oxidation peaks are all in the potential range of 0.87 V, indicating that MDEA undergoes irreversible direct electrocatalytic oxidation reaction.

[0090] Figure 7 and Figure 8 The liquid chromatograms of the polyacid-based crystalline material prepared in Example 1 before and after the MDEA reaction are shown respectively; Figure 8 It can be seen that compared with Figure 7 , Figure 8 The peak area corresponding to MDEA in the solution decreased significantly, indicating that an obvious oxidation reaction occurred in MDEA.

[0091] Figure 9 This is the IT curve of the polyacid-based crystalline material prepared in Example 1, which shows that the polyacid-based crystalline material remains stable after 10 hours of use, indicating that the polyacid-based crystalline material is firmly adhered to the glassy carbon electrode during this time and does not fall off.

[0092] In summary, the embodiments of the technical solution of the present invention can efficiently prepare polyacid-based crystalline materials, whose chemical formulas are [Fe2(H6P2W 22 O 78 )]·4(C 13 H 15N2)2 and [Fe2(H6P2W 22 O 78 )]·(C 10 H 16 N4)4·3H2O, the polyacid-based crystal material has the effect of electrocatalytic degradation of MDEA, which can make the degradation rate of MDEA reach more than 99%, which is significantly better than the existing technology.

[0093] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A polyacid-based crystalline material, characterized in that: The chemical formula of the polyacid-based material is [Fe2(H6P2W 22 O 78 )]·p(C x H y N z ) r qH2O; Among them, p is an integer between 1 and 4; x is an integer between 10 and 13; y is 15 or 16; z is an integer between 2 and 4; r is an integer between 2 and 4; and q is a natural number between 0 and 3.

2. The polyacid-based crystalline material according to claim 1, wherein The crystal system of the polyacid-based crystal material is a triclinic system; The space group of the polyacid-based crystal material is P-1: the single package parameters of the polyacid-based crystal material include: a=11.671(12)-12.148(3), b=13.394(2)-13.591(13), c=17.080(3)-18.132(18), α=86.366(3)-101.532(5), β=74.056(2)-95.030(5), γ=67.280(2)-108.957(5), V=2540.0(8)-2547.9(4), Z=1.

3. A method for preparing a polyacid-based crystalline material, the method comprising: (1) mixing a polyacid, an iron salt, a ligand, and water to obtain a mixture; (2) The mixture is subjected to a chemical reaction, and after post-treatment, the polyacid-based crystalline material is obtained. Wherein, in step (1), the iron salt is selected from ferrous acetate and / or ferrous chloride; The polyacid is selected from Keggin-type vacant phosphotungstic acid; The ligand is 4,4′-(1,3-propanediyl)bipyridine or 1,4-bis(imidazol-1-yl)butane.

4. The method according to claim 3, wherein: In step (1), the molar ratio of the polyacid to the iron salt is 1:3-6.

5. The method according to claim 4, wherein The molar ratio of the polyacid to the ligand is 1:2-3.

6. The method according to claim 3, wherein: The pH of the mixture is 2.5-4.

5.

7. The method according to claim 3, wherein in step (2), the temperature of the chemical reaction is 130-140°C.

8. The method according to claim 3, wherein in step (2), the reaction time of the chemical reaction is 5-7 days.

9. A polyacid-based crystalline material prepared by the method according to any one of claims 3 to 8.

10. Use of the polyacid-based crystalline material according to any one of claims 1, 2 and 9 in the field of degradation of N-methyldiethanolamine.

11. An electrode comprising the polyacid-based crystalline material according to any one of claims 1, 2 and 9.

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