A self-supported electrode for highly efficient electrocatalytic overall water splitting over the entire pH range and its preparation method

Abstract

The present invention discloses a self-supporting electrode for highly efficient electrocatalytic overall water splitting over the entire pH range and a preparation method thereof, including: the self-supporting electrode is a vanadium-based metal-organic framework (V-MOF) electrode supported on nickel foam (V-MOF / NF), the V-MOF is a nanosheet array structure, and the diameter of the nanosheets is 450-550 nm. The V-MOF / NF electrode can also be a non-metal or metal or metal-non-metal co-doped V-MOF / NF electrode. The preparation method is to first prepare the V-MOF / NF self-supporting electrode from nickel foam, a vanadium source, and an organic ligand, and then obtain it through pyrolysis treatment. According to the present invention, it has highly efficient electrocatalytic hydrogen production activity for water splitting over the entire pH range, and realizes highly efficient electrocatalytic overall water splitting. The preparation method has the advantages of mild conditions, simple process, low cost, etc., and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic materials, and particularly relates to a self-supporting electrode for highly efficient electrocatalytic overall water splitting over the entire pH range and a preparation method thereof. Background Art

[0002] As a clean, efficient, and sustainable green energy, hydrogen energy has the advantages of high energy density, clean recyclability, and wide applicability, and has received great attention from countries around the world. Electrocatalytic water splitting is an important way to effectively produce hydrogen energy and thus realize renewable clean energy. Designing and synthesizing highly efficient overall water splitting catalysts is the focus of current research. Noble metal platinum (Pt)-based materials have the best metal-hydrogen binding energy and extremely low Gibbs free energy of H adsorption, and are considered to be high-performance hydrogen evolution catalysts. Noble metal IrO2 and RuO2 are currently oxygen evolution catalysts with better performance and stability. However, their high prices and scarce resources seriously limit their large-scale use.

[0003] Currently, a large number of studies are devoted to developing derivative materials of metal-organic frameworks (MOFs). Using MOFs materials as templates, highly efficient and stable phosphides, sulfides / selenides, nitrides, carbides, carbon nanostructures, oxides, metal composites, single-atom, etc. electrocatalysts are synthesized through phosphorus / sulfur / selenium / nitrogen / carbonization and other routes. However, nanoparticles are stacked in the pores of MOFs-derived materials, resulting in a reduction in the active surface area of the materials. As porous functional materials, MOFs have the advantages of adjustable pore network structure, high specific surface area, and abundant active sites. Excellent electrocatalytic performance can be achieved through reasonable designs such as morphology regulation, crystal structure optimization, defect introduction, size reduction, and element doping.

[0004] Although some research progress has been made in electrocatalysis using MOFs materials, there are still some key problems at present, such as: only a few MOFs materials exhibit electrocatalytic activity; MOFs materials are mainly imidazole-containing ZIF and MIL materials; the conductivity of MOFs materials themselves is low; their stability is poor in a wide pH range of strong acids and strong bases; they only act as single-functional electrocatalysts; and the structure is prone to collapse during the pyrolysis process. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a self-supporting electrode for highly efficient electrocatalytic overall water splitting over the entire pH range and a preparation method thereof, which has highly efficient electrocatalytic water splitting hydrogen production activity over the entire pH range, and realizes highly efficient electrocatalytic overall water splitting. The preparation method has the advantages of mild conditions, simple process, low cost, etc., and is suitable for industrial production. To achieve the above object and other advantages of the present invention, there is provided a self-supporting electrode for highly efficient electrocatalytic overall water splitting over the entire pH range, including:

[0006] Nickel foam-supported vanadium-based metal-organic framework (V-MOF) electrode (V-MOF / NF), wherein the V-MOF is a nanosheet array structure with a nanosheet diameter of 450 - 550 nm;

[0007] The self-supporting electrode is doped V-MOF / NF, and the doping is non-metal doping, metal doping or metal-non-metal co-doping.

[0008] Preferably, the non-metal includes P, S or N, and the metal includes Fe, Co or Ni.

[0009] Preferably, the doping mass ratio is 5 - 10 wt%.

[0010] A preparation method of a self-supporting electrode for efficient electrocatalytic overall water splitting over the entire pH range, comprising the following steps:

[0011] S1. Disperse nickel foam, vanadium source, and organic ligand in absolute ethanol and deionized water, ultrasonicate and stir at room temperature to obtain a homogeneous mixed solution;

[0012] S2. Transfer the mixed solution to a hydrothermal reaction kettle, react at a constant temperature of 120 - 180 °C for 12 - 24 h, centrifuge, wash, and dry to obtain the V-MOF / NF electrode.

[0013] Preferably, in step S1, the vanadium source is at least one of vanadium trichloride, ammonium vanadate, and vanadium acetylacetonate, and the organic ligand is at least one of dipotassium naphthalenedicarboxylate, terephthalic acid, dimethyl terephthalate, and 2-methylimidazole.

[0014] Preferably, in the mixed solution in step S1, the concentration of the vanadium source is 5 - 10 mmol / L, the concentration of the organic ligand is 5 - 10 mmol / L, the molar ratio of the vanadium source to the organic ligand is 1 - 2, and the volume ratio of the absolute ethanol to the deionized water is 1 - 4.

[0015] Preferably, in the mixed solution in step S1, a metal precursor is added, and after the hydrothermal reaction in step S2, a metal-doped V-MOF / NF electrode is obtained. The metal precursor is ferric chloride, cobalt chloride, or nickel chloride, and the mass ratio of the metal in the precursor is 5% - 10%.

[0016] Preferably, the obtained V-MOF / NF is mixed with sulfur or sodium hypophosphite, placed in a tubular furnace, annealed at 300 - 500 °C for 1 - 2 h under a nitrogen atmosphere, and the heating rate is 2 - 5 °C / min to obtain an S or P and C co-doped V-MOF / NF electrode.

[0017] Preferably, the obtained V-MOF / NF is treated under an ammonia atmosphere, with other conditions unchanged, and after treatment, an N-C co-doped V-MOF / NF electrode is obtained.

[0018] Preferably, the self-supporting electrode is an M-C@V-MOF / NF electrode, which has high electrocatalytic hydrogen evolution activity for water splitting in the whole pH range and realizes efficient electrocatalytic overall water splitting.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: By adjusting the morphology and structure of the organic ligand-expanded MOF material and through multi-heteroatom doping, different structures and multi-synergistic effects of the MOF electrocatalyst are realized, and a V-MOF overall water splitting catalyst with excellent performance in the whole pH range is obtained to meet the requirements of efficient electrocatalytic water splitting. The preparation method is simple, the conditions are mild, the operation is convenient, and the cost is low. The prepared electrode has excellent electrocatalytic hydrogen production, oxygen production, and overall water splitting performance in the whole pH range, and is suitable for industrial production and promotion. Description of the Drawings

[0020] Figure 1 Figure 1 is a scanning electron microscope image and an element distribution map of the P-C@V-MOF / NF electrode of the self-supporting electrode for efficient electrocatalytic overall water splitting in the whole pH range according to the present invention and its preparation method;

[0021] Figure 2 Figure 2 is an X-ray diffraction pattern of the P-C@V-MOF / NF electrode of the self-supporting electrode for efficient electrocatalytic overall water splitting in the whole pH range according to the present invention and its preparation method;

[0022] Figure 3 Figure 3 is a hydrogen evolution LSV diagram of the P-C@V-MOF / NF electrode of the self-supporting electrode for efficient electrocatalytic overall water splitting in the whole pH range according to the present invention and its preparation method in alkaline, acidic, and neutral electrolytes;

[0023] Figure 4 Figure 4 is an LSV diagram of overall water electrolysis of the P-C@V-MOF / NF electrode of the self-supporting electrode for efficient electrocatalytic overall water splitting in the whole pH range according to the present invention and its preparation method in 1 M potassium hydroxide solution;

[0024] Figure 5 Figure 5 is a stability result diagram of overall water electrolysis of the P-C@V-MOF / NF electrode of the self-supporting electrode for efficient electrocatalytic overall water splitting in the whole pH range according to the present invention and its preparation method. Detailed Embodiments

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0026] Refer toFigures 1-5 , a self-supported electrode for efficient electrocatalytic overall water splitting over the entire pH range, comprising: a vanadium-based metal-organic framework (V-MOF) electrode supported on nickel foam (V-MOF / NF), wherein the V-MOF has a nanosheet array structure and the diameter of the nanosheets is 450 - 550 nm;

[0027] The self-supported electrode is a doped V-MOF / NF, and the doping is non-metal doping, metal doping or metal-non-metal co-doping.

[0028] Furthermore, the non-metal includes P, S or N, and the metal includes Fe, Co or Ni.

[0029] Furthermore, the doping concentration is 5 - 10%.

[0030] A preparation method of a self-supported electrode for efficient electrocatalytic overall water splitting over the entire pH range, comprising the following steps:

[0031] S1. Disperse nickel foam, a vanadium source, and an organic ligand in absolute ethanol and deionized water, ultrasonically treat and stir at room temperature to obtain a homogeneous mixed solution;

[0032] S2. Transfer the mixed solution to a hydrothermal reaction kettle, react at a constant temperature of 120 - 180 °C for 12 - 24 h, centrifuge, wash, and dry to obtain a V-MOF / NF electrode.

[0033] Furthermore, in step S1, the vanadium source is at least one of vanadium trichloride, ammonium vanadate, and vanadium acetylacetonate, and the organic ligand is at least one of dipotassium naphthalenedicarboxylate, terephthalic acid, dimethyl terephthalate, and 2-methylimidazole.

[0034] Furthermore, in the mixed solution in step S1, the concentration of the vanadium source is 5 - 10 mmol / L, the concentration of the organic ligand is 5 - 10 mmol / L, the molar ratio of the vanadium source to the organic ligand is 1 - 2, and the volume ratio of the absolute ethanol to the deionized water is 1 - 4.

[0035] Furthermore, in the mixed solution in step S1, a metal precursor is added, and after the hydrothermal reaction in step S2, a metal-doped V-MOF / NF electrode is obtained. The metal precursor is ferric chloride, cobalt chloride or nickel chloride, and the mass ratio of the metal in the precursor is 5% - 10%.

[0036] Furthermore, mix the obtained V-MOF / NF with sulfur or sodium hypophosphite, place it in a tube furnace, anneal at 300 - 500 °C for 1 - 2 hours under a nitrogen atmosphere, and the heating rate is 2 - 5 °C / min to obtain an S or P and C co-doped V-MOF / NF electrode.

[0037] Further, the obtained V-MOF / NF was treated in an ammonia atmosphere with other conditions unchanged, and the N-C co-doped V-MOF / NF electrode was obtained after treatment.

[0038] Further, the self-supporting electrode is the M-C@V-MOF / NF electrode, which has efficient electrocatalytic hydrogen evolution activity for water splitting in the full pH range and realizes efficient electrocatalytic overall water splitting.

[0039] Example 1

[0040] The self-supporting electrode for efficient electrocatalytic overall water splitting in the full pH range of the present invention can be prepared by the following steps:

[0041] 0.08 mmol of vanadium trichloride and 0.08 mmol of dipotassium naphthalenedicarboxylate were dispersed in a mixed solution of 10 ml of absolute ethanol and deionized water (volume ratio 4:1), ultrasonically dispersed, and magnetically stirred at room temperature to obtain a uniform solution A. Subsequently, the cleaned nickel foam was placed in solution A and ultrasonically treated for 30 min to obtain a uniform mixed solution B. Then, solution B was transferred to a hydrothermal reaction kettle and reacted at a constant temperature of 180 °C for 20 h, centrifuged, washed, and dried to obtain the V-MOF / NF electrode.

[0042] The test method for electrocatalytic hydrogen evolution from water splitting is as follows:

[0043] Using an electrochemical workstation and adopting a three-electrode system, the electrocatalytic hydrogen evolution performance of the electrode was tested in alkaline, neutral, and acidic electrolytes. The test electrolytes were 1 M potassium hydroxide, 1 M phosphate buffer, and 0.5 M sulfuric acid solution (50 mL); the prepared electrode was the working electrode; the carbon rod was the counter electrode; the mercury oxide electrode was the reference electrode for testing in alkaline electrolyte; the saturated calomel electrode was the reference electrode for testing in neutral and acidic electrolytes. The test condition was to perform linear voltammetric scanning at 5 mV s -1 Before the electrochemical test, 10 or more CV or LSV scans were performed at 50 mV s -1 until the curve was stable to ensure full contact between the electrode and the electrolyte. The obtained test data were not compensated for IR.

[0044] Example 2

[0045] 0.08 mmol of vanadium trichloride and 0.08 mmol of dipotassium naphthalenedicarboxylate were dispersed in a mixed solution of 10 ml of absolute ethanol and deionized water (volume ratio 4:1), ultrasonically dispersed, and magnetically stirred at room temperature to obtain a uniform solution A. Subsequently, the cleaned nickel foam was placed in solution A and ultrasonically treated for 30 min to obtain a uniform mixed solution B. Then, solution B was transferred to a hydrothermal reaction kettle and reacted at a constant temperature of 180 °C for 20 h, centrifuged, washed, and dried to obtain the V-MOF / NF electrode.

[0046] The V-MOF / NF electrode was placed in an alumina crucible and put into a tube furnace. It was heat-treated at 350 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C / min to obtain a carbon-doped V-MOF / NF electrode (C@V-MOF / NF).

[0047] The test method described in Example 1 was used to test the performance of the electrode prepared in this example for electrocatalytic water splitting to produce hydrogen under alkaline, neutral, and acidic conditions

[0048] Example 3

[0049] 0.08 mmol of vanadium trichloride and 0.08 mmol of dipotassium naphthalenedicarboxylate were dispersed in a mixed solution of 10 ml of absolute ethanol and deionized water (volume ratio 4:1), ultrasonically dispersed, and magnetically stirred at room temperature to obtain a uniform solution A. Subsequently, the cleaned nickel foam was put into solution A and ultrasonically treated for 30 min to obtain a uniform mixed solution B. Then, solution B was transferred to a hydrothermal reaction kettle and reacted at a constant temperature of 180 °C for 20 h, centrifuged, washed, and dried to obtain the V-MOF / NF electrode.

[0050] The V-MOF / NF electrode and 350 mg of sodium hypophosphite were placed in a tube furnace and heat-treated at 350 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C / min to obtain a carbon-doped V-MOF / NF electrode (P-C@V-MOF / NF).

[0051] The test method described in Example 1 was used to test the performance of the electrode prepared in this example for electrocatalytic water splitting to produce hydrogen under alkaline, neutral, and acidic conditions

[0052] The test method described in Example 1 was used to test the performance of the electrode prepared in this example for electrocatalytic overall water splitting. The working electrodes for the anode and cathode were both the electrodes prepared in this example; the electrolyte was a 1 M potassium hydroxide (50 mL) solution; and the mercury oxide electrode was the reference electrode. At the same time, during the electrochemical test, the i-t curve at 10 mA current was recorded to test the stability of the prepared electrode.

[0053] Figure 1 SEM images and elemental distribution maps of the P-C@V-MOF / NF electrode, which is a self-supporting electrode for efficient electrocatalytic overall water splitting at all pH values and its preparation method according to the present invention. It can be seen from the figure that the prepared P-C@V-MOF / NF has a nanosheet array structure, and the diameter of the nanosheets is 450 - 550 nm. The results of the elemental distribution maps show that the V, P, N, and C elements are uniformly distributed in the prepared sample, proving that the synthesized sample is a P-C@V-MOF material.

[0054] Figure 2X-ray diffraction pattern of the P-C@V-MOF / NF electrode for the all-pH efficient electrocatalytic overall water splitting self-supporting electrode and its preparation method according to the present invention. It can be found from the figure that the X-ray diffraction spectra of P-C@V-MOF / NF and V-MOF are similar, both having diffraction peaks of V-MOF. In addition, no diffraction peak of vanadium phosphide is observed in the X-ray diffraction spectrum of P-C@V-MOF / NF, proving that V-MOF is not converted into vanadium phosphide during the heat treatment process, which is attributed to the relatively stable 3d layer electronic structure of vanadium metal. However, new diffraction peaks appear in the X-ray diffraction spectrum of P-C@V-MOF / NF, corresponding to Ni2P (PDF 74-1385), which corresponds to the phosphorization of the nickel foam substrate into phosphide during the heat treatment process.

[0055] Figure 3 LSV diagram of hydrogen evolution of the P-C@V-MOF / NF electrode for the all-pH efficient electrocatalytic overall water splitting self-supporting electrode and its preparation method according to the present invention in alkaline, acidic and neutral electrolytes. It can be seen from the figure that when the current density of this electrode is 10 mA cm -2 the overpotentials in alkaline, acidic and neutral environments are 77, 94 and 178 mV respectively.

[0056] Figure 4 LSV diagram of overall water electrolysis of the P-C@V-MOF / NF electrode for the all-pH efficient electrocatalytic overall water splitting self-supporting electrode and its preparation method according to the present invention in 1 M potassium hydroxide solution. It can be seen from the figure that the P-C@V-MOF / NF electrode simultaneously acts as the cathode and anode for the overall water splitting reaction. When the current density is 10 mA cm -2 the voltage is 1.53 V.

[0057] Figure 5 Stability result diagram of overall water electrolysis of the P-C / V-MOF / NF electrode for the all-pH efficient electrocatalytic overall water splitting self-supporting electrode and its preparation method according to the present invention. It can be seen from the figure that the P-C@V-MOF / NF electrode can operate stably for 100 h under the condition of mA cm -2

[0058] It can be seen that the P-C@V-MOF / NF electrode of the present invention can be used as an all-pH efficient electrocatalytic overall water splitting self-supporting electrode, showing excellent catalytic activity in acidic, alkaline and neutral environments, and at the same time showing excellent overall water splitting performance. This patent provides a new idea for the preparation of electrocatalytic overall water splitting self-supporting nanosheet array electrodes, and promotes the application of MOFs in the field of energy conversion. The preparation process of the present invention is simple, the reaction temperature is low, the reaction conditions are mild, the operation is convenient, the cost is low, and it is suitable for industrial production.

[0059] ​The number of devices and the processing scale described herein are used to simplify the description of the present invention, and the application, modification, and variation of the present invention will be obvious to those skilled in the art. Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated examples described herein.

Claims

1. A preparation method of a self-supported electrode for highly efficient electrocatalytic overall water splitting over the entire pH range, characterized in that, It includes the following steps: S1. Dispersing 0.08 mmol of vanadium trichloride and 0.08 mmol of dipotassium naphthalenedicarboxylate in a mixed solution of absolute ethanol and deionized water to obtain a uniform solution A; S2. Putting the cleaned nickel foam into solution A and subjecting it to ultrasonic treatment to obtain a uniformly mixed solution B; S3. Transferring solution B to a hydrothermal reaction kettle, reacting at a constant temperature, centrifuging, washing, and drying to obtain a V-MOF / NF electrode; putting the V-MOF / NF electrode and 350 mg of sodium hypophosphite into a tubular furnace and heat-treating them at 350 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C / min to obtain a carbon-doped V-MOF / NF electrode, namely P-C@V-MOF / NF.

2. The preparation method of a self-supporting electrode for efficient electrocatalytic overall water splitting at all pH values according to claim 1, characterized in that In step S3, reacting at a constant temperature of 180 °C for 20 h, centrifuging, washing, and drying to obtain a V-MOF / NF electrode.

3. A self-supporting electrode prepared by the method for preparing a self-supporting electrode for efficient electrocatalytic overall water splitting at all pH values according to any one of claims 1-2, wherein the self-supporting electrode is a doped nickel foam supporting a vanadium-based metal-organic framework, and the doping is non-metal doping.

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