Iron-doped molybdate nano composite material, preparation method thereof and method for oxygen evolution of alkaline salt through electro-catalysis of iron-doped molybdate nano composite material

Abstract

The invention belongs to the technical field of inorganic advanced nano materials, and particularly relates to an iron-doped molybdate nano composite material and a preparation method thereof, and a method for oxygen evolution by electrocatalysis of alkaline salt. The iron-doped molybdate nano material comprises a conductive substrate and an iron-doped molybdate nano material grown or coated on the surface of the conductive substrate. According to the invention, the iron-doped molybdate nano material which is doped with non-noble metal and has high activity is applied for the first time. The iron-doped molybdate nanometer material is used as the seawater electrolysis anode catalyst for the first time. According to the catalyst, an iron molybdate protective substance coated on an anode and molybdate released when molybdate is converted into an active substance, namely oxyhydroxide, have a synergistic effect to achieve a rejection effect of resisting halogen ions; and due to doping of iron, the electronic structure of single molybdate is improved, so that the molybdate has excellent activity.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic advanced nanomaterials, and specifically relates to a highly active non-noble metal iron-doped molybdate nanomaterial and a method for preparing the same and electrocatalyzing oxygen precipitation from alkaline salt. Background Art

[0002] Seawater electrolysis is a sustainable hydrogen production technology and has gradually become a research hotspot due to its low cost and abundant resources. However, there are many challenges in the seawater electrolysis process, among which the core challenges are the oxygen evolution reaction activity of the anode and its operational stability in an environment with high concentrations of chloride ions in seawater.

[0003] The commonly used regulation method for the activity of oxygen evolution reaction is to use some precious metal-based catalysts, but their high cost and scarcity limit their large-scale application. The activity and stability of common non-precious metal-based anode catalysts are difficult to achieve the industrial standards of low energy consumption and high stability, so it is very necessary to develop a highly active and highly stable non-precious metal-based seawater electrolysis anode catalyst. In order to solve the above problems, the present invention is proposed. Summary of the invention

[0004] The present invention provides a highly active non-precious metal iron-doped molybdate nanomaterial as a catalyst for an electrocatalytic alkaline salt / seawater anode and a preparation method thereof. In the present invention, the highly active non-precious metal iron-doped molybdate nanomaterial is in an alkaline solution, and because the molybdate needs to be reconstructed into a hydroxy oxide, the material will precipitate molybdate radicals, and due to the influence of the anode electric field force, adsorb on the anode surface. At the same time, iron is doped into the molybdate nanocomposite material to form iron molybdate. Due to its stable chemical properties and poor solubility, the iron molybdate in the catalyst will be coated on the surface of the material. Both iron molybdate and molybdate radicals act simultaneously, and simultaneously achieve the effect of repelling halogen ions, thereby effectively improving the stability of the material. In addition, due to the incorporation of iron ions, the electronic structure of the single molybdate is improved, thereby greatly improving the oxygen evolution reaction activity of the material.

[0005] The first aspect of the present invention provides a highly active non-precious metal iron-doped molybdate nanocomposite material, wherein the iron-doped molybdate nanocomposite material comprises: a conductive substrate, and an iron-doped molybdate nanomaterial grown or sprayed on the surface of the conductive substrate.

[0006] Preferably, the molar fraction of the iron ions is 1%-50%, based on the total molar number of metals other than molybdenum in the iron-doped molybdate nanomaterial.

[0007] The iron-doped molybdate nanomaterial is a rod-shaped structure, and the elements are evenly distributed.

[0008] The second aspect of the present invention provides a method for preparing the non-noble metal iron-doped molybdate nanomaterial according to the first aspect, wherein the preparation method comprises one of a hydrothermal method and a co-precipitation method, specifically:

[0009] The hydrothermal method comprises the following steps: mixing a metal salt aqueous solution and a molybdenum source aqueous solution and then ultrasonically dispersing the mixture until the solution is clarified to obtain a first clarified solution;

[0010] Then, the iron source aqueous solution is mixed with the first clear solution and then ultrasonically dispersed until the solution is clear, thereby obtaining a second clear solution;

[0011] The second clarified solution and the conductive substrate are subjected to a hydrothermal reaction in a hydrothermal reactor, and the solid-liquid separation is performed to obtain a solid which is the iron-doped molybdate nanocomposite material;

[0012] The co-precipitation method comprises the following steps:

[0013] Dissolving the iron source and the metal salt with an aqueous solution of a first organic solution to obtain a first mixed solution;

[0014] dissolving the molybdate in an aqueous solution of a second organic solution to obtain a second mixed solution;

[0015] The second mixed solution is added to the first mixed solution to obtain a coprecipitation mixed solution, which is stirred, solid-liquid separated, and the solid is dried, heat treated and sprayed onto a conductive substrate to obtain the iron-doped molybdate nanocomposite material.

[0016] Preferably, in the hydrothermal reaction, in the second clear solution, the concentration of the metal salt is 0.01 to 0.5 mol / L, the concentration of the molybdate is 0.05 to 1 mol / L, and the concentration of the iron salt is 0.005 to 0.2 mol / L.

[0017] The hydrothermal reaction time is 6 hours to 12 hours, and the temperature is 120° C. to 170° C.

[0018] In the co-precipitation method, the second mixed solution can be added to the first mixed solution by dropwise addition.

[0019] In the coprecipitation mixed solution, the concentration of metal salt is 0.1-0.8 mol / L, the concentration of molybdate is 0.2-1 mol / L, and the concentration of iron salt is 0.02-0.3 mol / L.

[0020] The heat treatment temperature is 150° C. to 200° C., and the time is 1 to 3 hours.

[0021] Preferably, the metal salt does not contain iron salt, and includes: one or more of nickel salt, cobalt salt, manganese salt, chromium salt, copper salt, and vanadium salt. When there are multiple types of metal salts, the concentration of the metal salt is the total concentration of the metal in the metal salt.

[0022] Preferably, the conductive substrate is one of: nickel foam, nickel mesh, copper foam, copper mesh, nickel molybdenum foam and carbon paper.

[0023] A fourth aspect of the present application provides a method for electrolyzing alkaline salt water to precipitate oxygen, including at least one of the following two schemes:

[0024] Solution 1: using an electrode containing the iron-doped molybdate nanocomposite material as an anode of an electrolytic reactor;

[0025] Option 2: Use an electrolyte containing molybdate.

[0026] Preferably, the electrolyte comprises an alkaline substance and seawater; and / or the electrolyte comprises an alkaline substance and a halide.

[0027] When the electrolyte includes alkaline substances and seawater, it can be considered as electrolysis of alkaline seawater for oxygen evolution. The seawater can be real seawater or simulated seawater.

[0028] Preferably, the alkaline substance is selected from one or both of sodium hydroxide and potassium hydroxide, the total concentration of the alkaline substance is 0.01 to 10 mol / L, and the total concentration of the halide is 0.01 to 5.5 mol / L or the maximum solubility of the halide under these conditions.

[0029] Preferably, the molybdate is a water-soluble molybdate, such as one or more of sodium molybdate and ammonium molybdate.

[0030] The electrolyte contains alkaline substances, halides and molybdate. Neither the cathode nor the anode materials of the electrolysis are doped with molybdate ions. The halide is selected from one or more of chloride, bromide and iodide.

[0031] Preferably, the concentration of molybdate ions in the molybdate-containing electrolyte is 0.001-2 mol / L.

[0032] Compared with the prior art, the present invention has the following excellent effects:

[0033] 1. The present invention is the first to use non-precious metal iron to dope molybdate nanomaterials as an anode catalyst for electrocatalytic sea / brine water reactions. Since the molybdate catalyst needs to be reconstructed into hydroxy oxides in addition to iron, molybdate ions will precipitate from the material, and due to the influence of the anode electric field force, they are adsorbed on the anode surface. At the same time, the iron molybdate in the catalyst will be coated on the surface of the material due to its stable chemical properties and poor solubility. In addition, molybdate ions are at the interface between the electrolyte and the electrode, and iron molybdate is on the electrode. Both molybdate ions and iron molybdate act simultaneously, and at the same time, they achieve the effect of repelling halogen ions, thereby effectively improving the stability of the material.

[0034] 2. The present invention improves the electronic structure of the single molybdate for the first time by incorporating iron ions, and helps to generate the active substance oxyhydroxide, thereby greatly improving the oxygen evolution reaction activity of the material.

[0035] 3. Compared with other slightly soluble molybdates, iron salts and molybdates are very likely to produce heterogeneous suspensions during the mixing process, which leads most people to believe that iron is not easy to be used as a doping ion in molybdate products, and it is not easy to imagine that iron doping can have such a great improvement in the activity and stability of molybdate nanomaterials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the XRD spectrum of the iron-doped nickel molybdate nanocomposite electrode prepared by the hydrothermal method in Example 1.

[0037] Figure 2 This is the SEM image and EDS-Mapping of the iron-doped nickel molybdate nanocomposite electrode prepared by the hydrothermal method in Example 1.

[0038] Figure 3 This is the EDS-Mapping of the iron-doped nickel molybdate nanocomposite electrode prepared by the hydrothermal method in Example 1.

[0039] Figure 4 This is a constant current curve diagram of the iron-doped nickel molybdate nanocomposite electrode prepared by the hydrothermal method in Example 1.

[0040] Figure 5 This is a constant current curve diagram of the iron-doped nickel molybdate nanocomposite electrode prepared by the co-deposition method in Example 2.

[0041] Figure 6 This is the ICP result of the electrolyte after the stability of the iron-doped nickel molybdate nanocomposite electrode in Example 1.

[0042] Figure 7 This is the XPS spectrum of the electrolyte after the stability test of the iron-doped nickel molybdate nanomaterial electrode in Example 1.

[0043] Figure 8 This is the CV curve diagram of the iron-doped nickel molybdate nanomaterial composite electrode in Example 1.

[0044] Fig. 9 This is a constant current curve of the nickel foam electrode using molybdate as an additive in Example 3.

[0045] Fig.10 The SEM image and EDS-Mapping of the nickel molybdate electrode of Comparative Example 1.

[0046] Fig.11 This is a constant current curve diagram of the nickel molybdate nanocomposite electrode of comparative example 1.

[0047] Fig.12 This is the CV curve of the nickel molybdate nanocomposite electrode of comparative example 1.

[0048] Fig.13 This is a constant current curve of the nickel foam electrode in comparative example 2 without other ions as additives. DETAILED DESCRIPTION

[0049] The present invention is described below in conjunction with specific examples, but the embodiments of the present invention are not limited thereto. Experimental methods without specific conditions in the examples are usually carried out according to conventional conditions and conditions described in the manual, or according to the conditions recommended by the manufacturer. The general equipment, materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified. The raw materials required in the following examples and comparative examples are all commercially available.

[0050] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. If not otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution. If not otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0052] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0053] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B".

[0054] Example 1 - Preparation of iron-doped molybdate nanocomposite materials by hydrothermal method

[0055] This experimental example adopts the following method to prepare iron-doped molybdate nanomaterials, and those skilled in the art may make adjustments by referring to the prior art:

[0056] First, 0.3 mmol of ammonium heptamolybdate, 1.2 mmol of nickel nitrate, and 0.15 mmol of ferric nitrate were dissolved in 8 ml of water. After that, the ammonium molybdate solution was mixed with the nickel nitrate solution and ultrasonicated to clarify. Then, the ferric nitrate solution was slowly added to the mixed solution and fixed to 30 ml, and ultrasonicated for 15 minutes until the solution was clarified again. The solution was poured into a reactor (in the reactor, the nickel salt concentration was 0.04 mol per liter, the molybdate concentration was 0.07 mol per liter, and the iron salt concentration was 0.005 mol per liter). The nickel foam washed with water, ethanol, and acid was soaked in the solution and put into an oven. The reaction temperature was 150 degrees Celsius for 6 hours. The obtained material was washed with water and ethanol 3 times respectively, and vacuum dried at 60°C for 10 hours. The nickel foam loaded with iron-doped nickel molybdate nanomaterial was obtained. The molar fraction of iron in the material was calculated to be 10%, based on the total molar number of metal elements other than molybdenum in the iron-doped molybdate nanomaterial.

[0057] Other conditions remain unchanged, and the molar ratio of the metal salt (nickel salt) to the iron salt in the above step is adjusted to obtain iron-doped nickel molybdate nanomaterials with different molar ratios.

[0058] Under the same conditions, the nickel nitrate in the above step is replaced with one or more of manganese salt, chromium salt, copper salt, vanadium salt and cobalt salt with the same total molar number, and iron ion-doped manganese molybdate (chromium, copper, vanadium, cobalt) nanomaterials can be prepared respectively.

[0059] Other conditions remain unchanged, and the nickel foam in the above steps is replaced with copper foam. The following can be prepared respectively:

[0060] Iron ion-doped nickel molybdate nanomaterials supported on copper foam.

[0061] Example 2 - Preparation of iron-doped molybdate nanocomposite materials by coprecipitation

[0062] Prepare 30 ml of metal salt and iron salt solution: add 8 mmol of nickel nitrate, 2 mmol of iron nitrate and 30 ml of 50% acetone aqueous solution into a beaker and stir well.

[0063] Prepare 30 ml of molybdate solution: 2 mmol of ammonium heptamolybdate, 30 ml of 50% acetone aqueous solution, and stir well.

[0064] The ammonium heptamolybdate solution is slowly added to the metal salt solution while stirring until the dropwise addition is completed. In the obtained coprecipitation mixed solution, the nickel salt concentration is 0.13 mol / L, the molybdate concentration is 0.21 mol / L, and the iron salt concentration is 0.03 mol / L. The coprecipitation mixed solution is stirred at room temperature for 30-60 minutes, the precipitate is separated by centrifugation or suction filtration, the precipitate is washed with deionized water and ethanol for multiple times to remove surface impurities, the washed precipitate is placed in a drying oven, dried at 80° C. for 12 hours, and a precursor powder is obtained. The precursor powder is heat-treated at 180° C. for 2 hours to obtain an iron-doped molybdate nanomaterial. The molar fraction of iron in the material is calculated to be 16.7%, based on the total molar number of metal elements other than molybdenum in the iron-doped molybdate nanomaterial. The iron-doped molybdate nanomaterial is then sprayed onto a conductive substrate to obtain the iron-doped molybdate nanocomposite material.

[0065] Materials Characterization and Testing:

[0066] (1) The iron-doped nickel molybdate nanocomposite material prepared in Example 1 was subjected to X-ray diffraction (XRD) to determine its phase structure. The results are as follows: Figure 1As shown, it can be found that the obtained XRD is not a uniform phase, but a mixed phase of iron molybdate and nickel molybdate. During the electrolysis process, nickel molybdate precipitates molybdate at the anode, and the molybdate is adsorbed on the electrode surface due to electrostatic repulsion. Iron molybdate is coated on the electrode. Molybdate and iron molybdate play different roles in resisting halogen ions, improving the corrosion resistance and stability of the electrode.

[0067] (2) The iron-doped nickel molybdate nanocomposite material prepared in Example 1 was subjected to scanning electron microscopy (SEM) and X-ray energy dispersive spectrometer-element distribution test (EDS-Mapping), as shown in FIG. Figure 2 and Figure 3 As shown, the results show that the synthesized iron-doped nickel molybdate nanomaterials have obvious molybdate rod-like structure and uniform element distribution.

[0068] (3) The anode corrosion resistance stability of the iron ion-doped molybdate nanocomposite electrode of Example 1 in alkaline salt water electrolysis was tested using a two-electrode system: the cathode was a nickel foam electrode, the anode was an iron ion-doped molybdate nanocomposite electrode of Example 1 with an effective area of ​​1*1 square centimeter, and the electrolyte was a mixed solution of sodium hydroxide and sodium chloride, wherein the concentration of sodium hydroxide was 6.0 mol / L and the concentration of sodium chloride was 2.8 mol / L. A constant current test of 1 ampere per square centimeter was performed, and the constant current curve obtained was as follows: Figure 4 As shown. Figure 4 It can be seen that the iron ion-doped molybdate nanocomposites can effectively prevent chloride corrosion and thus maintain anode stability for a longer period of time, at least for 1000 hours of operation.

[0069] (4) The corrosion resistance of the anode of the molybdate nanomaterial electrode doped with iron ions in Example 2 was tested by a two-electrode system: the cathode was a nickel foam electrode, and the anode was a nickel-molybdenum foam electrode of the molybdate nanomaterial doped with iron ions in Example 2 with an effective area of ​​1*1 square centimeters. The electrolyte was sodium hydroxide added to real seawater to make the sodium hydroxide concentration 6.0 mol / L. Then a constant current test of 1 ampere per square centimeter was performed, and the constant current curve obtained was as follows: Figure 5 As shown. Figure 5 It can be seen that the iron ion-doped molybdate nanocomposites can effectively prevent halide corrosion in seawater, and thus can maintain anode stability for a longer time, and can operate for at least 1000 hours.

[0070] (5) The electrolyte after the reaction in (3) is subjected to an inductively coupled plasma (ICP) test, such as Figure 6 As shown in the results, it can be seen that the doped iron ions are almost not dissolved (less than 20 μg), and the XPS after the reaction still has a strong iron signal ( Figure 7), which also shows the protective effect of iron molybdate on the surface of the material. Similarly, the strong molybdate signal in the ICP result proves the precipitation of molybdate and the adsorption protective effect around the electrode. Similarly, the strong Fe signal in XPS before and after the reaction can also indicate the trace dissolution of Fe.

[0071] (6) The electrocatalytic oxygen evolution performance of the iron-doped molybdate nanomaterial obtained in Example 1 in electrolyzing real seawater was tested using a three-electrode system: the reference electrode was a calomel electrode, the counter electrode was a platinum sheet electrode, and the working electrode was an iron-doped nickel molybdate nanocomposite material in Example 1 with an effective area of ​​1*1 square centimeter. The electrolyte was made by adding sodium hydroxide to real seawater to make the sodium hydroxide concentration of 1.0 mol / L of sodium hydroxide. Cyclic voltammetry was first performed in the range of 1-2 V vs RHE until the electrode reached a stable state. After that, a new electrolyte was replaced and a linear scan was performed at 2 mV / s in the range of 1-2 V vs RHE. The resulting linear scan voltammogram is shown as follows: Figure 8 As shown. Figure 8 It can be seen that the overpotential of the iron-doped molybdate nanomaterial in Example 1 at a current density of 10 mA cm-2 is 205 mV.

[0072] Example 3 Adding molybdate to the electrolyte and testing the oxygen evolution stability of nickel foam

[0073] When molybdate is used as an additive, the corrosion resistance stability of the anode of the foam nickel electrode in alkaline salt water electrolysis is tested using a two-electrode system: the cathode is a foam nickel electrode, the anode is a foam nickel electrode with an effective area of ​​1*1 square centimeter, and the electrolyte is a mixed aqueous solution containing sodium hydroxide, sodium chloride and sodium molybdate, wherein the sodium hydroxide concentration is 6.0 mol / L of sodium hydroxide, the sodium chloride is a saturated concentration (sodium chloride concentration is 2.8 mol / L), and the sodium molybdate concentration is 0.3 mol / L. After that, a constant current test of 200 mA / cm2 is performed, and the constant current curve obtained is as follows Fig. 9 It can be seen that under this condition, the stability can be maintained up to 500 hours.

[0074] The same steps as above are used to adjust the concentration of sodium molybdate to 0.05, 0.1, 0.2, 0.4, and 0.5 mol / L, so as to obtain electrolytes of sodium molybdate with different concentrations. Through attempts, the stability is improved.

[0075] The above description shows that adding molybdate to the electrolyte also has the effect of improving stability. The principle is that molybdate ions will be adsorbed on the surface of the anode to prevent the anode from being corroded by halide ions.

[0076] Comparative Example 1-Preparation of molybdate nanomaterials by hydrothermal method

[0077] The method for preparing molybdate nanomaterials is the same as that in Example 1, except that the iron source is not doped to obtain iron-free molybdate nanomaterials. The prepared nickel molybdate nanomaterials are subjected to scanning electron microscopy (SEM) and X-ray energy dispersive spectrometer-element distribution test (EDS-Mapping). Fig.10 As shown. The results show that the synthesized nickel molybdate nanomaterials also have obvious molybdate rod-like structures, but the EDS-Mapping results show that no iron signals appear. A two-electrode system was used to test the anode corrosion stability of molybdate nanomaterial electrodes in alkaline salt water electrolysis: the cathode was a nickel foam electrode, and the anode was a molybdate nanomaterial electrode with an effective area of ​​1*1 square centimeter. The electrolyte used was a mixed solution of sodium hydroxide and sodium chloride, in which the concentration of sodium hydroxide was 6.0 mol per liter and the concentration of sodium chloride was 2.8 mol per liter. A constant current test of 1 ampere per square centimeter was performed, and the constant current curve obtained was as shown below. Fig.11 As shown. It can be seen that the nickel molybdate nanomaterials show corrosion phenomenon after 200 hours under this condition, which causes a voltage rise. The nickel molybdate nanomaterials that are not doped with iron still have a certain anti-corrosion effect because the nickel molybdate material will release molybdate ions adsorbed on the electrode surface, but its anti-corrosion effect is poorer than that of the iron-doped nickel molybdate nanomaterials. The electrocatalytic oxygen evolution performance of the nickel molybdate nanomaterials in the electrolysis of real seawater obtained by the three-electrode system test: the reference electrode is a calomel electrode, the counter electrode is a platinum sheet electrode, and the working electrode is a nickel molybdate array material with an effective area of ​​1*1 square centimeter. The electrolyte uses a mixed solution of 1 mol per liter of sodium hydroxide and real seawater. First, a cyclic voltammetric scan is performed in the range of 1 to 2V vs RHE until the electrode reaches a stable state. After that, a new electrolyte is replaced, and a linear scan is performed at 2mV / s in the range of 1 to 2V vs RHE. The resulting linear scan voltammogram is shown as follows Fig.12 As shown. Fig.12 It can be seen that nickel molybdate nanomaterials have a -2 The overpotential under current density is 252 mV, which is much higher than that of iron-doped nickel molybdate nanomaterials, proving that iron doping greatly improves activity.

[0078] Comparative Example 2-Oxygen evolution stability test of nickel foam without adding other anions to the electrolyte

[0079] A two-electrode system was used to test the corrosion resistance of the nickel foam electrode in alkaline salt water electrolysis: the cathode was a nickel foam electrode, the anode was a nickel foam electrode with an effective area of ​​1*1 square centimeter, and the electrolyte was a mixed aqueous solution containing sodium hydroxide and sodium chloride, wherein the concentration of sodium hydroxide was 6.0 mol / L and the sodium chloride was a saturated concentration (the concentration of sodium chloride was 2.8 mol / L). A constant current test was performed at 200 mA / cm2, and the constant current curve obtained was as follows Fig.13As shown. It can be seen that under this condition, the stability can only run for less than 10 hours. Comparison between Comparative Example 2 and Example 3 shows that adding molybdate to the electrolyte also has the effect of improving stability.

Claims

1. An iron-doped molybdate nanocomposite material, characterized in that: The iron-doped molybdate nanocomposite material comprises: a conductive substrate and an iron-doped molybdate nanomaterial grown or coated on the surface of the conductive substrate.

2. The iron-doped molybdate nanocomposite material according to claim 1, characterized in that: The iron-doped molybdate nanomaterial is a rod-shaped structure, and the elements are evenly distributed.

3. The iron-doped molybdate nanocomposite material according to claim 1, characterized in that: The molar fraction of the iron ions is 1%-50%, based on the total molar number of metals except molybdenum in the iron-doped molybdate nanomaterial.

4. A method for preparing the iron-doped molybdate nanocomposite material according to claim 1, characterized in that: The synthesis method of the iron-doped molybdate nanocomposite material is selected from: a hydrothermal method and co-deposition, specifically: The hydrothermal method comprises the following steps: Mixing the metal salt aqueous solution and the molybdenum source aqueous solution and then ultrasonically dispersing the mixture until the solution becomes clear to obtain a first clear solution; Then, the iron source aqueous solution is mixed with the first clear solution and then ultrasonically dispersed until the solution is clear, thereby obtaining a second clear solution; The second clarified solution and the conductive substrate are subjected to a hydrothermal reaction in a hydrothermal reactor, and the solid-liquid separation is performed to obtain a solid which is the iron-doped molybdate nanocomposite material; The co-precipitation method comprises the following steps: Dissolving the iron source and the metal salt with an aqueous solution of a first organic solution to obtain a first mixed solution; dissolving the molybdate in an aqueous solution of a second organic solution to obtain a second mixed solution; The second mixed solution is added to the first mixed solution to obtain a coprecipitation mixed solution, which is stirred, solid-liquid separated, and the solid is dried, heat treated and sprayed onto a conductive substrate to obtain the iron-doped molybdate nanocomposite material.

5. The preparation method according to claim 4, characterized in that: The iron source is one or more of iron salt, iron powder or iron oxide; the metal salt is one or more of nickel salt, cobalt salt, manganese salt and vanadium salt; the molybdate is one or two of sodium molybdate and ammonium molybdate.

6. The preparation method according to claim 4, characterized in that: The conductive substrate is one or more of foamed nickel, nickel mesh, foamed copper, copper mesh, foamed nickel-molybdenum and carbon paper.

7. A method for electrocatalytic oxygen precipitation of alkaline salt, characterized in that: Include at least one of the following two options: Solution 1: Using an electrode containing the iron-doped molybdate nanocomposite material according to any one of claims 1 to 3 as an anode of an electrolytic reactor; Option 2: Use an electrolyte containing molybdate.

8. The method for electrocatalytic oxygen precipitation of alkaline salt according to claim 7, characterized in that: The electrolyte includes an alkaline substance and seawater; and / or the electrolyte includes an alkaline substance and a halide.

9. The method for electrocatalytic oxygen precipitation of alkaline salt according to claim 8, wherein the alkaline substance is selected from one or both of sodium hydroxide and potassium hydroxide, the total concentration of the alkaline substance is 0.01 to 10 mol per liter, and the total concentration of the halide is 0.01 to 5.5 mol per liter or the maximum solubility of the halide under these conditions.

10. The method for electrocatalytic oxygen precipitation using alkaline salt according to claim 7, characterized in that: The molybdate is water-soluble molybdate.

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