A kind of iron-nickel co-doped ammonium phosphomolybdate and its preparation method and application

Abstract

The present invention belongs to the technical field of hydrogen production by electrolyzing water, and particularly relates to an ammonium iron-nickel co-doped phosphomolybdate, a preparation method thereof and an application thereof. The ammonium iron-nickel co-doped phosphomolybdate uses molybdate, phosphate, iron salt and nickel salt as starting materials, and under mild conditions of 40-80 °C, adjusts the ratio of raw materials and the pH of the solution to prepare the ammonium iron-nickel co-doped phosphomolybdate. The obtained ammonium iron-nickel co-doped phosphomolybdate is made into an oxygen evolution electrode and applied to hydrogen production by electrolyzing water. The present invention performs linear sweep in a 0.5 mol / L H2SO4 solution, and its oxygen evolution overpotential is only 210 mV at 10 mA / cm 2 2, which is lower than the oxygen evolution overpotential of the noble metal iridium oxide of 370 mV. Its oxygen evolution Tafel slope in acidic medium is also smaller than that of the noble metal IrO2, and the alternating current impedance reaction resistance is also lower than that of the noble metal oxygen evolution reaction resistance. Its electrochemical characteristics make the ammonium iron-nickel co-doped phosphomolybdate material have obvious technical advantages and cost advantages in PEM mode hydrogen production by electrolyzing water.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen production by electrolysis of water, and in particular to iron-nickel co-doped ammonium phosphomolybdate and a preparation method and application thereof. Background Art

[0002] At present, the main methods of producing hydrogen by water electrolysis are alkaline water electrolysis (ALK), proton exchange membrane water electrolysis (PEM), anion exchange membrane water electrolysis (AEM) and solid oxide water electrolysis (SOEC). In these four water electrolysis hydrogen production modes, electrocatalytic materials are the key materials to improve water electrolysis hydrogen production. In particular, the anode oxygen evolution process involves 4 electron transfer reactions. Compared with hydrogen evolution, its reaction is more complicated, involves more reaction steps, and has greater reaction resistance. Therefore, oxygen evolution electrocatalysts are the key core materials in the entire water electrolysis hydrogen production system. In the PEM mode of water electrolysis hydrogen production, oxygen is released after anode oxidation, and acidic hydrogen ions are left. In an acidic environment and under high potential conditions, it is easy to corrode the electrode material, thereby destroying the structure of the electrode material and reducing the electrocatalytic activity. For this reason, precious metal electrocatalysts need to be used, but precious metals are expensive and difficult to popularize.

[0003] Among the four modes of hydrogen production by water electrolysis, the PEM mode has particularly significant advantages: (1) High hydrogen purity and no pollution. The PEM mode uses a proton exchange membrane solid electrolyte, and the gas produced does not need to be de-alkali treated. The thickness of the cation membrane is very small, and it is not easy to produce hydrogen reverse osmosis. The PEM mode only requires pure water, does not require any additives, does not contain corrosive liquids, and does not pollute the environment. (2) High conversion efficiency and energy saving. The electrodes of the PEM mode are tightly attached to both sides of the cation membrane and its internal pores. It is a zero-distance catalytic electrode with a large electrode reaction area and high Coulomb efficiency. (3) The stack is light and small in size. The collector structure of the two-stage chamber in the PEM mode electrolyzer is compact and flexible, which makes the electrolyzer light and small in size. The weight is only about 1 / 3 of that of an ordinary electrolyzer with the same hydrogen production capacity. The advantage is zero inter-electrode distance and small internal resistance of the cell. (4) Strong adaptability to current and voltage fluctuations of renewable energy sources. The PEM water electrolysis hydrogen production system has a fast response speed and adapts to dynamic operation, which is very suitable for the uneven, intermittent and volatile transmission of renewable energy (wind and solar energy). Therefore, the research and development of electrode materials for PEM mode has important application value. However, the acidic environment of PEM mode and the oxidizing environment of high anode potential require the use of expensive precious metal iridium or ruthenium materials for anode materials, which makes it difficult to promote the application of PEM mode.

[0004] Patent application number 202211051214.2 discloses a method for preparing MoRuP-loaded carbon nanobelts, MoRuP-loaded carbon nanobelts and applications, and reports the electrocatalytic hydrogen evolution performance under acidic and alkaline conditions. Nevertheless, these public materials do not involve the preparation of iron-nickel co-doped ammonium phosphomolybdate and its application in electrolysis of water to produce hydrogen in an acidic medium. In order to overcome the shortcomings of the prior art, the present invention proposes an iron-nickel co-doped ammonium phosphomolybdate, a preparation method and its application in electrolysis of water to produce hydrogen and oxygen in an acidic medium. Summary of the invention

[0005] The purpose of the present invention is to provide an iron-nickel co-doped ammonium phosphomolybdate and a preparation method and application thereof, which can effectively solve the technical problems encountered in the production of hydrogen by electrolysis of water in an acidic medium and in a PEM mode.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] An iron-nickel co-doped ammonium phosphomolybdate, characterized in that the chemical formula is:

[0008] Fe x Ni y (NH 4 ) 3 Mo (12-x-y) PO 40 ·4H 2 Oh,

[0009] Wherein, x is the molar ratio of iron to molybdenum, and y is the molar ratio of nickel to molybdenum.

[0010] Preferably, the molar ratio x of iron to molybdenum is 3.0-7.0%, the molar ratio y of nickel to molybdenum is 2.0-6.0%, and the molar number of the phosphate is 1 / 12 of the total metal ions.

[0011] Furthermore, the iron-nickel co-doped ammonium phosphomolybdate is used in hydrogen production by water electrolysis.

[0012] Furthermore, the application is to grind the iron-nickel co-doped ammonium phosphomolybdate and then apply it on carbon paper to prepare an oxygen evolution electrode.

[0013] Preferably, the application is to mix and grind the iron-nickel co-doped ammonium phosphomolybdate with graphite and boron carbide, and then spray the mixture on a cation exchange membrane to prepare an oxygen evolution electrode.

[0014] Furthermore, the oxygen evolution electrode is used to electrolyze water to produce hydrogen in neutral and acidic media.

[0015] A method for preparing iron-nickel co-doped ammonium phosphomolybdate comprises the following steps:

[0016] S1: dissolving molybdate in deionized water, dissolving phosphate in another container, and slowly adding the phosphate solution dropwise to the molybdate solution to form a reaction mixture A;

[0017] S2: Weigh iron salt and nickel salt and dissolve them in deionized water until they are completely dissolved to form solution B;

[0018] S3: adding the solution B obtained in S2 dropwise to the solution A under stirring at 40°C, and after the addition is complete, adding concentrated nitric acid, maintaining the reaction system at 80°C and a pH between 1.0 and 2.0, heating and continuing stirring to obtain a precipitated product;

[0019] S4: After the precipitated product is washed, filtered and dried, iron-nickel co-doped ammonium phosphomolybdate is obtained.

[0020] Preferably, the molybdate in S1 is one, two or three selected from potassium molybdate, sodium molybdate and ammonium molybdate; the phosphate includes one, two or three selected from potassium hydrogen phosphate, sodium hydrogen phosphate, ammonium phosphate and / or potassium dihydrogen phosphate and sodium dihydrogen phosphate.

[0021] Preferably, the iron salt in S2 is any one of sulfate, nitrate and chloride.

[0022] Preferably, the nickel salt in S2 is any one of its sulfate, nitrate and chloride.

[0023] An iron-nickel co-doped ammonium phosphomolybdate is prepared from phosphate, molybdate, iron salt and nickel salt as starting materials by adjusting the proportion of raw materials and solution pH under mild conditions of 40-80 DEG C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a new electrocatalytic material, which realizes electrocatalytic oxygen evolution by using iron-nickel co-doped ammonium phosphomolybdate. The iron-nickel co-doped ammonium phosphomolybdate carbon paste electrode is used as the working electrode. 2 SO 4 Linear scan in solution at 10 mA / cm 2 The oxygen evolution overpotential is only 200mV, while under the same conditions, IrO 2 The overpotential of the electrode is 370mV; the Tafel slope of oxygen evolution of iron-nickel doped ammonium phosphomolybdate in acidic medium is 61.60mVdec -1 Also lower than IrO 2 Tafel 81.91mVdec -1 The AC impedance reaction resistance is also lower than the oxygen evolution reaction resistance of noble metals. These electrochemical characteristics make the iron-nickel co-doped ammonium phosphomolybdate material of the present invention have obvious technical and cost advantages in the PEM mode water electrolysis hydrogen production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD diagram of ammonium phosphomolybdate and iron-nickel co-doped ammonium phosphomolybdate designed by the present invention;

[0027] Figure 2 This is the XPS elemental analysis diagram of the iron-nickel co-doped ammonium phosphomolybdate, a material designed in the present invention;

[0028] Figure 3 The electron affinity spectrum of the molybdenum element in the XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate, a material designed in the present invention;

[0029] Figure 4 The electron affinity spectrum of phosphorus in the XPS elemental analysis diagram of iron-nickel co-doped ammonium phosphomolybdate, a material designed in the present invention;

[0030] Figure 5 The electron affinity spectrum of the iron element in the XPS elemental analysis diagram of the iron-nickel co-doped ammonium phosphomolybdate designed as the material of the present invention;

[0031] Figure 6 The electron affinity spectrum of the nickel element in the XPS elemental analysis diagram of the iron-nickel co-doped ammonium phosphomolybdate designed as the material of the present invention;

[0032] Figure 7 Ammonium phosphomolybdate co-doped with iron and nickel in 0.5 mol / L H 2 SO 4 Linear sweep voltammogram in;

[0033] Figure 8 Ammonium phosphomolybdate co-doped with iron and nickel in 0.5 mol / L H 2 SO 4 The Tafel curve in

[0034] Fig. 9 Ammonium phosphomolybdate co-doped with iron and nickel in 0.5 mol / L H 2 SO 4 The AC impedance diagram in . DETAILED DESCRIPTION

[0035] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0036] Embodiment 1

[0037] Preparation of iron-nickel co-doped ammonium phosphomolybdate:

[0038] Weigh 0.15g of sodium dihydrogen phosphate and dissolve it in 20mL of deionized water. After it is completely dissolved, add 40mL of 2.3g of ammonium molybdate aqueous solution and stir while adding to form solution A. Weigh 4% nickel salt and 1% iron salt of molybdate in a molar ratio and dissolve them in 20mL of deionized water to form solution B. Keep the temperature of the solution at 40℃, and slowly add solution B to solution A under stirring. After the addition is complete, add concentrated nitric acid, maintain the pH of the reaction system between 1.0-2.0, increase the temperature to 80℃, and continue stirring for 18h to obtain the precipitated product. Wash, filter, and dry to obtain the desired iron-nickel co-doped ammonium phosphomolybdate.

[0039] Similarly, by changing the ratio of nickel and iron salts, pure ammonium phosphomolybdate co-doped with iron-nickel can be prepared, in which the molar ratio of iron salt to molybdate is 0.1-2.0%, the ratio of nickel salt to molybdate is 2.0-8.0%, and the molar number of phosphate is 1 / 12 of the total metal ions.

[0040] Embodiment 2

[0041] The following experiments were conducted based on the iron-nickel co-doped ammonium phosphomolybdate and pure ammonium phosphomolybdate in Example 1. The test results are as follows: Figure 1 shown.

[0042] XRD test of ammonium phosphomolybdate and iron-nickel co-doped ammonium phosphomolybdate:

[0043] The prepared samples were subjected to XRD test. Diffraction peaks appeared at 2θ = 10.97°, 15.40°, 21.82°, 26.82°, 30.95° and 36.52°, corresponding to the (110), (200), (220), (222), (400) and (332) crystal plane structures, which are consistent with (NH 4 ) 3 PO 4 (MoO 3 ) 12 ·4H 2 The above test results show that the synthesized product is iron-nickel co-doped ammonium phosphomolybdate. The diffraction peak 2θ=21.77° of the undoped pure ammonium phosphomolybdate (220) crystal plane is positively shifted by 0.05° after doping, which also confirms that iron and nickel with smaller ionic radius are doped into the crystal structure of ammonium phosphomolybdate.

[0044] Embodiment 3

[0045] According to the XRD test of ammonium phosphomolybdate and iron-nickel co-doped ammonium phosphomolybdate in Example 2, the test results are as follows: Figures 2 to 6 shown.

[0046] XPS elemental analysis was performed on the prepared iron-nickel co-doped ammonium phosphomolybdate. Elements such as carbon, nitrogen, oxygen, phosphorus, molybdenum, nickel and iron were detected in the whole image. Figure 2 As shown, the high-resolution electron affinities of molybdenum, phosphorus, iron, and nickel are Figures 2 to 6 This proves that nickel and iron elements are doped into the crystals of ammonium phosphomolybdate.

[0047] Embodiment 4

[0048] Method for preparing oxygen evolution electrode by iron-nickel co-doped ammonium phosphomolybdate compound and application of iron-nickel co-doped ammonium phosphomolybdate in electrocatalytic oxygen evolution:

[0049] Take 56% graphite powder by mass, add 40% boron carbide, and then add 4.0% iron-nickel co-doped ammonium phosphomolybdate, mix and dissolve in 30mL of deionized water, stir evenly to obtain a mixed suspension, evaporate at a certain temperature, cool and take out to assemble into a carbon paste electrode. Use this electrode as the working electrode in 0.5mol / LH 2 SO 4 The potential was scanned in the solution at room temperature and pressure with a scanning rate of 5mV / s. The instrument used was Shanghai Chenhua CHI660D electrochemical workstation. The working electrode was prepared as follows: 0.5g of the sample to be tested was weighed, ground with an agate mortar, 0.1mL of silicone oil was added, and stirred thoroughly to obtain a fine-grained, uniform paste sample. The sample was filled into a polytetrafluoroethylene electrode tube and connected to the three-electrode system with copper wire as a conductor. The electrode potential corresponding to the LSV test curve was calculated according to the formula E REH =E SCE +0.242+0.059pH(V) is converted into reversible electrode potential (RHE).

[0050] The obtained linear sweep voltammetry curve is as follows Figure 7 As shown in Figure e, the measured Tafel curve is as follows Figure 8 As shown in Figure e, the measured AC impedance curve is as follows Fig. 9 As shown in a.

[0051] from Figure 8 It can be seen that the oxygen evolution overpotential of Fe-Ni doped ammonium phosphomolybdate in acidic medium is 210 mV, which is lower than that of precious metal IrO 2 The oxygen evolution overpotential is 370mV, and its Tafel slope is 66.34mVdec -1 Also lower than IrO 2 81.91mVdec -1 , showing good acidic oxygen evolution characteristics.

[0052] Ammonium phosphomolybdate produced by co-doping with iron and nickel has the smallest reaction resistance, as shown in Table 1:

[0053] Table 1 AC impedance test results

[0054]

[0055] In Table 1:

[0056] a: 4.0wt% ammonium phosphomolybdate doped with 4% nickel and 5% iron + 40% boron carbide + 56.0wt% carbon powder;

[0057] b: 40.0wt% ammonium phosphomolybdate doped with 5% iron + 60.0wt% carbon powder;

[0058] c: 40.0wt% ammonium phosphomolybdate doped with 4% nickel + 60.0wt% carbon powder;

[0059] d: 40.0wt% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 60.0wt% carbon powder.

[0060] In summary, iron-nickel doped ammonium phosphomolybdate has good electrocatalytic oxygen evolution properties in acidic solution and can play an important role in hydrogen production by acidic water electrolysis.

[0061] It should be noted that:

[0062] Figure 7 a is 40% pure ammonium phosphomolybdate + 60% graphite powder, b is 40% ammonium phosphomolybdate doped with 4% nickel + 60% graphite powder, c is 40% ammonium phosphomolybdate doped with 5% iron + 60% graphite powder, d is 40% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 60% graphite powder, e is IrO 2 , f is 4% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 40% boron carbide + 56% carbon powder;

[0063] Figure 8 a is 40% pure ammonium phosphomolybdate + 60% graphite powder, b is 40% ammonium phosphomolybdate doped with 5% iron + 60% graphite powder, c is 40% ammonium phosphomolybdate doped with 4% nickel + 60% graphite powder, d is 40% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 60% graphite powder, e is IrO 2 , f is 4% ammonium phosphomolybdate doped with 4% nickel and 6% iron + 40% boron carbide + 56% carbon powder;

[0064] Fig. 9 Where a is 4.0wt% ammonium phosphomolybdate doped with 4% nickel and 1% iron + 40% boron carbide + 56.0wt% carbon powder, b is 40.0wt% ammonium phosphomolybdate doped with 3% iron + 60.0wt% carbon powder, c is 40.0wt% ammonium phosphomolybdate doped with 4% nickel and 1% iron + 60.0wt% carbon powder, d is 40.0wt% ammonium phosphomolybdate doped with 4% nickel + 60.0wt% carbon powder. The measured solution resistance Rs, reaction resistance Rct and double-layer capacitance related parameters CPE are shown in Table 1.

[0065] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. For ordinary technicians in this technical field, after knowing the contents recorded in the present invention, they can make several equivalent changes and substitutions without departing from the principle of the present invention. These equivalent changes and substitutions should also be regarded as belonging to the protection scope of the present invention.

Claims

1. An iron-nickel co-doped ammonium phosphomolybdate, characterized in that: The chemical formula is: <h2 style=";text-align:left;direction:ltr">Fe<h2 style=";text-align:left;direction:ltr"> x <h2 style=";text-align:left;direction:ltr"> Ni<h2 style=";text-align:left;direction:ltr"> y <h2 style=";text-align:left;direction:ltr"> (NH4)3Mo(<h2 style=";text-align:left;direction:ltr"> 12-x-y <h2 style=";text-align:left;direction:ltr"> )PO<h2 style=";text-align:left;direction:ltr"> 40 <h2 style=";text-align:left;direction:ltr"> 4H2O, Among them, x is the molar ratio of iron to molybdenum, y is the molar ratio of nickel to molybdenum, the molar ratio x of iron to molybdenum is 3.0-7.0%, the molar ratio y of nickel to molybdenum is 2.0-6.0%, and the molar number of the phosphate is 1 / 12 of the total metal ions.

2. The iron-nickel co-doped ammonium phosphomolybdate according to claim 1, characterized in that: The application of the iron-nickel co-doped ammonium phosphomolybdate in hydrogen production by water electrolysis.

3. The iron-nickel co-doped ammonium phosphomolybdate according to claim 2, characterized in that: The application is to grind the iron-nickel co-doped ammonium phosphomolybdate and then apply it on carbon paper to prepare an oxygen evolution electrode.

4. The iron-nickel co-doped ammonium phosphomolybdate according to claim 2, characterized in that: The application is to mix and grind the iron-nickel co-doped ammonium phosphomolybdate with graphite and boron carbide, and then spray the mixture on a cation exchange membrane to prepare an oxygen evolution electrode.

5. The iron-nickel co-doped ammonium phosphomolybdate according to claim 3 or 4, characterized in that: The oxygen evolution electrode is used for electrolyzing water to produce hydrogen in neutral and acidic media.

6. A method for preparing the iron-nickel co-doped ammonium phosphomolybdate according to claim 1, characterized in that: The following steps are involved: S1: dissolving molybdate in deionized water, dissolving phosphate in another container, and slowly adding the phosphate solution dropwise to the molybdate solution to form a reaction mixture A; S2: Weigh iron salt and nickel salt and dissolve them in deionized water until they are completely dissolved to form solution B; S3: adding the solution B obtained in S2 dropwise to the solution A under stirring at 40°C, and after the addition is complete, adding concentrated nitric acid, maintaining the reaction system at 80°C and a pH between 1.0 and 2.0, heating and continuing stirring to obtain a precipitated product; S4: After the precipitated product is washed, filtered and dried, iron-nickel co-doped ammonium phosphomolybdate is obtained.

7. The preparation method according to claim 6, characterized in that: The molybdate in S1 is any one, two or three of potassium molybdate, sodium molybdate and ammonium molybdate; the phosphate includes any one, two or three of potassium hydrogen phosphate, sodium hydrogen phosphate, ammonium phosphate and / or potassium dihydrogen phosphate and sodium dihydrogen phosphate.

8. The preparation method according to claim 6, characterized in that: The iron salt in S2 is any one of sulfate, nitrate and chloride.

9. The preparation method according to claim 6, characterized in that: The nickel salt in S2 is any one of its sulfate, nitrate and chloride.

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