CN111686812A

CN111686812A - Ligand-activated transition metal layered dihydroxy compound, preparation method and application

Info

Publication number: CN111686812A
Application number: CN201910189114.8A
Authority: CN
Inventors: 杨世和; 龙霞; 王亚琼; 王政
Original assignee: Peking University Shenzhen Graduate School
Current assignee: Peking University Shenzhen Graduate School
Priority date: 2019-03-13
Filing date: 2019-03-13
Publication date: 2020-09-22
Anticipated expiration: 2039-03-13
Also published as: CN111686812B

Abstract

The invention relates to the technical field of new energy and electrocatalysis materials, and discloses a preparation method of a ligand-activated transition metal layered double hydroxide compound (TM LDH). The preparation method uses sodium borohydride to activate the hydroxyl ligand of TM LDH to become TM LDH activated by hydride, and can also use Cl^‑Negative ion, Br^‑Negative ion, I^‑And further activating one or more of negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions. The invention also discloses the prepared ligand-activated TM LDH and application thereof, and a water-splitting anode and a water-splitting three-electrode system which take the ligand-activated TM LDH as a catalyst. The water isThe decomposition anode is applied to the electric decomposition water, and compared with the traditional foam nickel electrode, the decomposition anode shows lower overpotential and Tafel slope, greatly improves the water decomposition capacity, and reduces the cost of hydrogen production by water decomposition.

Description

Ligand-activated transition metal layered dihydroxy compound, preparation method and application

Technical Field

The invention relates to the technical field of new energy and electrocatalysis materials, in particular to a preparation method of a ligand-activated transition metal layered dihydroxy compound, the prepared ligand-activated transition metal layered dihydroxy compound and application thereof, and a water-splitting anode and a water-splitting three-electrode system containing the ligand-activated transition metal layered dihydroxy compound.

Background

The global energy shortage and the aggravation of the environmental pollution problem make the demand for clean and renewable energy more and more urgent. Hydrogen has the advantages of high energy density, no pollution of combustion products and the like, and is considered to be one of the most ideal green energy sources capable of replacing fossil fuels. The existing methods for preparing hydrogen mainly comprise natural gas steam conversion hydrogen production, methanol cracking hydrogen production and water decomposition hydrogen production. The hydrogen production by natural gas steam reforming and methanol cracking requires the use of natural gas or methanol fuel as raw material, and more importantly, the product contains more impurities such as carbon dioxide, carbon monoxide, methane and the like besides hydrogen. The hydrogen production by water decomposition has the advantages of high efficiency, simple process and high purity of reaction products. The first hydrogen energy field group standard of China (T/CECA-G0015-2017) has strict requirements on the purity of hydrogen, the volume fraction of the hydrogen is more than or equal to 99.99 percent, and the hydrogen with the purity can only be prepared by water decomposition.

The hydrogen production by water decomposition is to prepare hydrogen by decomposing water by electricity or light, and the chemical reaction formula is 2H ₂0→2H₂+O₂. The reaction process includes a cathodic Hydrogen Evolution Reaction (HER) and an anodic Oxygen Evolution Reaction (OER). The reaction kinetics of the anode oxygen production reaction is very slow, and the process of hydrogen production by water decomposition is greatly limited. The price of hydrogen production by water electrolysis is higher than that of hydrogen production by natural gas steam conversion and hydrogen production by methanol cracking at present.Therefore, the development of the efficient and cheap water decomposition catalyst, the reduction of the energy barrier of the OER reaction and the reduction of the energy consumption required by hydrogen production through water decomposition are of great importance for the large-scale preparation of high-purity hydrogen, the development of new energy, the promotion of the development of fields such as hydrogen energy automobiles and the like and the alleviation of environmental pollution.

Layered Double Hydroxide (LDH) is composed of a positively charged main plate layer formed by metal ions and hydroxyl ligands and interlayer anions for charge compensation, wherein the species and molar ratio of the metal ions in the main plate layer are adjustable within a certain range, and the interlayer anions can be changed by ion exchange. Transition metal-based layered double hydroxide (TM LDH) is an LDH in which metal ions in the main plate layer are transition metal ions. In recent years, the application of TM LDH in the field of hydrogen production by water decomposition has been greatly developed. The catalytic oxygen production activity and stability of the TM LDH are close to those of a noble metal oxygen production catalyst iridium oxide (IrO)₂) And ruthenium oxide (RuO)₂). And the reserves of non-noble metals such as transition metals on the earth are abundant, so that the non-noble metal water decomposition catalyst such as TM LDH has larger application potential compared with a noble metal catalyst.

The TM LDH may be optimized to further improve its catalytic performance. Optimization is usually achieved by adjusting the type and molar ratio of transition metal ions (see, for example, SCI paper published in 2015 by the inventor's topic group: A Structure synthesized graphite and Ni Double Hydroxide anion and Decumber 2014) or by changing the interlayer anion of TM LDH (see, for example, SCI paper published in 2014 by the inventor's topic group: A Structure synthesized graphite and Ni Double Hydroxide anion and excel electrochemical Reaction for the OxyEsolution Reaction and Angewand International chemical chemistry experiment (53) 201429).

The optimization can effectively regulate and control the electronic structure of transition metal ions playing a catalytic role, the conductivity of the catalyst and the micro morphology such as the interlayer spacing, the specific surface area and the like of TM LDH, thereby effectively optimizing the catalytic performance of the transition metal-based water splitting catalyst. However, due to the limitation of the atomic structure of the layered dihydroxy compound, the optimization of the transition metal ion species can only be selected from limited elements, the optimization of the molar ratio of the transition metal ions can only be performed in a limited range, and the interlayer anions are far away from the transition metal ions which play a catalytic role, so that the interlayer spacing and further the specific surface area of the water-splitting catalyst can only be changed to a certain extent.

However, modification of hydroxyl ligands attached to transition metal ions has not been reported.

Disclosure of Invention

The invention aims to modify and activate a hydroxyl ligand of a transition metal layered double hydroxyl compound (TM LDH) to obtain a ligand-activated TM LDH which can be used as a catalyst for an oxygen production reaction in a water splitting reaction to improve the hydrogen production performance by water splitting.

Accordingly, a first aspect of the invention provides a process for the preparation of a ligand-activated TM LDH, the process comprising the steps of:

(1) uniformly dispersing TM LDH in a polar solvent to obtain a TM LDH suspension, wherein the transition metal is any combination of divalent and trivalent transition metal ions;

(2) and (2) adding sodium borohydride with appropriate amount for activation reaction into the suspension obtained in the step (1) to carry out activation reaction, so as to obtain the ligand activated TM LDH.

In a preferred embodiment of the first aspect of the present invention, the atomic ratio of the divalent/trivalent transition metal ion is between (3-10):1, more preferably between (4-8):1, still more preferably between (5-6): 1.

In a preferred embodiment of the first aspect of the invention, the transition metal ion is a combination of ni (ii)/fe (iii), ni (ii)/mn (iii), ni (ii)/co (iii) or co (ii)/fe (iii), more preferably ni (ii)/fe (iii).

In a preferred embodiment of the first aspect of the invention, in step (1), the weight to volume ratio of the TM LDH to the polar solvent is (0.5-2) mg:1ml, more preferably (0.8-1.8) mg:1ml, still more preferably (1.0-1.5) mg:1 ml.

In a preferred embodiment of the first aspect of the present invention, in step (2), the activation reaction is suitably used in an amount such that the final concentration of the sodium borohydride in the suspension of step (1) is 0.001-0.01M, more preferably, 0.003-0.008M.

In a preferred embodiment of the first aspect of the present invention, the activation reaction is carried out at a reaction temperature of 20 to 80 ℃ for a reaction time of 0.5 to 10 hours, more preferably at a reaction temperature of 40 to 60 ℃ for a reaction time of 1 to 5 hours.

In a preferred embodiment of the first aspect of the present invention, the polar solvent is deionized water or ethanol or a mixed solvent thereof.

In a particularly preferred embodiment of the first aspect of the invention, the preparation process comprises the following specific steps:

(1) uniformly dispersing Ni (II)/Fe (III), Ni (II)/Mn (III), Ni (II)/Co (III) or Co (II)/Fe (III) TM LDH with the atomic ratio of (3-10):1 in deionized water or ethanol or a mixed solvent thereof, wherein the weight volume ratio of the TMLDH to the polar solvent is (0.5-2) mg:1ml, and uniformly dispersing by ultrasonic vibration and stirring to obtain a TMLDH suspension;

(2) adding sodium borohydride with the final concentration of 0.001-0.01M into the suspension obtained in the step (1), stirring and dispersing uniformly at the stirring speed of 400-80 rpm, then reacting for 0.5-10 hours at the reaction temperature of 20-80 ℃ and the stirring speed of 700-1000rpm, naturally cooling to room temperature, adding a proper amount of deionized water or absolute ethyl alcohol as a washing solvent, centrifugally washing for three times at 6000-8000rpm for 5-10 minutes each time, and then drying in vacuum for 3-6 hours to obtain the TM LDH activated by the hydride ligand.

In the above-mentioned particularly preferred embodiment of the first aspect of the invention, the weight to volume ratio of the TM LDH to the polar solvent is more preferably (0.8-1.8) mg:1ml, still more preferably (1.0-1.5) mg:1 ml.

In the above-mentioned specifically preferred embodiment of the first aspect of the present invention, in step (2), the final concentration of sodium borohydride is more preferably 0.003 to 0.008M; the reaction temperature of the reaction is more preferably 40 to 60 ℃ and the reaction time is more preferably 3 to 8 hours.

A second aspect of the invention provides a method of preparing a ligand-activated TM LDH, the method comprising the steps of:

(1) uniformly dispersing TM LDH in a polar solvent to obtain TM LDH suspension; the transition metal is any combination of divalent and trivalent transition metal ions;

(2) adding sodium borohydride with proper amount for activation reaction into the suspension obtained in the step (1), and adding Cl with proper amount for activation reaction^-Negative ion, Br^-Negative ion, I^-And (3) performing an activation reaction on one or more of negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions to obtain the ligand activated TM LDH.

In a preferred embodiment of the second aspect of the present invention, the atomic ratio of the divalent/trivalent transition metal ion is between (3-10):1, more preferably between (4-8):1, still more preferably between (5-6): 1.

In a preferred embodiment of the second aspect of the invention, the transition metal ion is a combination of ni (ii)/fe (iii), ni (ii)/mn (iii), ni (ii)/co (iii) or co (ii)/fe (iii), more preferably ni (ii)/fe (iii).

In a preferred embodiment of the second aspect of the invention, in step (1), the weight to volume ratio of the TM LDH to the polar solvent is (0.5-2) mg:1ml, more preferably (0.8-1.8) mg:1ml, still more preferably (1.0-1.5) mg:1 ml.

In a preferred embodiment of the second aspect of the present invention, in step (2), the activation reaction is suitably used in an amount such that the final concentration of the sodium borohydride in the suspension of step (1) is 0.001-0.01M, more preferably 0.003-0.008M.

In a preferred embodiment of the second aspect of the present invention, in step (2), the activating reaction is suitably carried out in an amount such that the Cl is present^-Negative ion, Br^-Negative ion, I^-The total final concentration of one or more of negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions in the suspension of step (1) is 0.1-10M, more preferably 1-8M, and still more preferably 3-6M.

In a preferred embodiment of the second aspect of the present invention, the activation reaction is carried out at a reaction temperature of 20 to 80 ℃ for a reaction time of 0.5 to 10 hours, more preferably at a reaction temperature of 40 to 60 ℃ for a reaction time of 1 to 5 hours.

In a preferred embodiment of the second aspect of the present invention, the polar solvent is deionized water or ethanol or a mixed solvent thereof.

In a particularly preferred embodiment of the second aspect of the invention, the preparation process comprises the following specific steps:

(2) adding sodium borohydride to the suspension of step (1) to a final concentration of 0.001-0.01M and adding the Cl to a total final concentration of 0.1-10M^-Negative ion, Br^-Negative ion, I^-One or more of negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions are stirred and dispersed uniformly at the stirring speed of 400-80 rpm, then the reaction is carried out for 0.5 to 10 hours at the reaction temperature of 20 to 80 ℃ and the stirring speed of 700-1000rpm, after the reaction is naturally cooled to the room temperature, a proper amount of deionized water or absolute ethyl alcohol is added as a washing solvent, the centrifugal washing is carried out for three times at 6000-8000rpm, each time lasts for 5 to 10 minutes, and then the vacuum drying is carried out for 3 to 6 hours, so as to obtain the ligand activated TM LDH.

In the above-mentioned particularly preferred embodiment of the second aspect of the invention, the weight to volume ratio of the TM LDH to the polar solvent is more preferably (0.8-1.8) mg:1ml, still more preferably (1.0-1.5) mg:1 ml.

In the above-mentioned specifically preferred embodiment of the second aspect of the present invention, in step (2), the final concentration of sodium borohydride is more preferably 0.003 to 0.008M; the Cl^-Negative ion, Br^-Negative ion, I^-The total final concentration of one or more of the negative ions, N-containing negative ions, P-containing negative ions, or S-containing negative ions in combination is more preferably 1-8M, still more preferably3-6M; the reaction temperature of the reaction is more preferably 40 to 60 ℃ and the reaction time is more preferably 3 to 8 hours.

In the second aspect of the present invention, the N-containing anion, the P-containing anion or the S-containing anion is preferably NSC^-、SCN^-、CN^-、NH₃、PO₃ ^3-、PO₄ ^3-And the like.

A third aspect of the invention provides a ligand-activated TM LDH prepared by the preparation method according to the first or second aspect of the invention.

The ligand-activated TM LDH prepared according to the preparation method of the first aspect of the present invention is a hydride (H) ion^-) Activated TM LDH.

The ligand-activated TM LDH prepared according to the preparation method of the second aspect of the present invention is a chloride anion (Cl)^-) Bromine anion (Br)^-) Iodine anion (I)^-) A TM LDH activated by a combination of one or more of nitrogen (N) -containing anions, phosphorus (P) -containing anions, and sulfur (S) -containing anions.

A fourth aspect of the invention provides the use of the ligand-activated TM LDH of the third aspect of the invention as an oxygen-producing catalyst for water-splitting anodes.

A fifth aspect of the invention provides a water-splitting anode comprising a foamed nickel, carbon cloth or iron substrate and a ligand-activated TM LDH of the third aspect of the invention coated thereon. The ligand-activated TM LDH serves as an oxygen-producing catalyst for water-splitting anodes.

The water-splitting anode can be prepared as follows. 1-2mg of the ligand activated TM LDH catalyst is taken and placed in 1ml of absolute ethyl alcohol, and strong ultrasonic dispersion is carried out to obtain catalyst dispersion liquid. Uniformly mixing 200-500 mu L of catalyst dispersion liquid prepared with PTFE aqueous solution with the mass fraction of 4-8% according to the volume ratio of (1-3) to 1, and performing ultrasonic dispersion. And uniformly coating the obtained mixed dispersion liquid on a foamed nickel, carbon cloth or iron substrate, and drying in an oven at 40-70 ℃ for 20-40 minutes.

A sixth aspect of the invention provides a water-splitting three-electrode system comprising a water-splitting anode according to the fifth aspect of the invention, Pt wire as a counter electrode, Ag/AgCl as a reference electrode and 0.5-1.5M aqueous potassium hydroxide or sodium hydroxide solution as an electrolyte. Preferably, the electrolyte is a 1M aqueous solution of potassium hydroxide or sodium hydroxide.

The invention has the beneficial effects that:

according to the preparation method of the ligand-activated TM LDH, the problem of difficulty in electron transfer between transition metal ions can be solved by activating the hydroxyl ligand directly connected with the transition metal ions, the condition that the electron arrangement of the transition metal ions is not ideal is solved, the optimal arrangement of catalytic active atom electrons is realized, the coordination environment of the transition metal ions is effectively changed, and the synergistic interaction between the metal ions is enhanced.

The TM LDH activated by the ligand prepared by the preparation method can be used as a water decomposition anode catalyst, so that efficient and stable oxygen production is realized, and the hydrogen production performance of the catalyst in water decomposition is improved. The water decomposition anode prepared by the ligand activated TM LDH is applied to the electrolysis of water, and compared with the traditional foam Nickel (NF) electrode, the water decomposition anode shows lower overpotential and Tafel slope, greatly improves the water decomposition capability and reduces the cost of hydrogen production by water decomposition.

Drawings

FIG. 1 is a Scanning Electron Micrograph (SEM) and a Transmission Electron Micrograph (TEM) of a NiFe LDH (A, C, D) prior to sodium borohydride activation and a H-NiFeLDH (B, E, F) after activation according to example 1 of the present invention, wherein (A, B) is an SEM image, (C, E) is a TEM image, and (D, F) is a High Resolution TEM (HRTEM) image;

FIG. 2 is an XRD image of NiFe LDH before and H-NiFe LDH after sodium borohydride activation according to example 1 of the present invention;

FIG. 3 is the preparation of H-NiFe LDH after sodium borohydride activation according to example 1 of the present invention²H magic angle spin nuclear magnetic resonance (MAS NMR) plot;

FIG. 4 is a graph of the electrochemical impedance of H-NiFe LDH at 300mV overpotential after sodium borohydride activation, versus NiFe LDH and H-Ni (OH) in accordance with example 1 of the present invention₂Carrying out comparison;

FIG. 5 is a schematic structural diagram of a three-electrode system with NiFe LDH as the water electrolysis anode catalyst according to a test example of the present invention, wherein 1 denotes a working electrode, 2 denotes a reference electrode, and 3 denotes a counter electrode;

FIG. 6 is a comparative plot of the catalytic hydrogen production polarization curves for foamed nickel, NiFe LDH and H-NiFe LDH in accordance with test examples of the present invention;

FIG. 7 is a comparative graph of catalytic oxygen production tafel curves for foamed nickel, NiFe LDH and H-NiFe LDH in accordance with test examples of the present invention;

FIG. 8 is a graph of H-NiFe LDH at 10, 20 and 50mA cm in accordance with test examples of the present invention^-2The current density of (a) is measured in a chronopotentiometric test graph, wherein the inset is H-NiFe LDH at 50mA cm^-2A long-time chronopotentiometric test pattern exceeding 12 hours at a current density of (a);

FIG. 9 is a comparative graph of the catalytic hydrogen production polarization curves of NCS-NiFe LDH and NiFe LDH in accordance with the test examples of the present invention.

Detailed Description

The present invention will be described in further detail below with reference to specific embodiments and accompanying drawings.

Transition metal layered double hydroxides (TM LDHs) have been extensively studied as one of the most effective oxygen generating reaction (OER) catalysts. However, there is no report on the effect of hydroxyl (-OH) ligands of LDH on OER catalysis. According to the rule of superexchange interaction, electrons can be transferred from one transition metal ion to an adjacent transition metal ion through a non-magnetic anion, so the inventors believe that the electron transfer inside the TM LDH during OER may be affected by hydroxyl ligands octahedrally complexed directly with the transition metal ion, thereby affecting the catalytic performance of the TM LDH. Due to the negative ion of hydrogen (H)^-) Small size and strong complexing ability, so the inventors believe that it can readily react with protons to form one molecule of hydrogen, thus affecting the hydroxyl ligand of TM LDH. To confirm this hypothesis, the inventors used sodium borohydride (NaBH)₄) As a hydride source, DFT calculations were performed using the most efficient OER catalyst, NiFe LDH, as a typical TM LDH model. The results show that the hydride of sodium borohydride takes one proton from the hydroxyl ligand of NiFe LDH, producing one molecule of H₂At the same time will formStrong B-O sigma bond. Since B has an empty p orbital, O has a lone pair of electrons, and the B-O bond has a strong tendency to form a B-O double bond, the hydride can easily migrate to the metal center to form a transition metal-hydride bond (Fe-H or Ni-H), accompanied by the formation of NaBOH₂Which can further form NaBO₂。

Since hydride is a strong field ligand, the energy of the reverse bonded d-orbitals of the complexed transition metal ions can be easily increased. The d orbitals of both fe (iii) and ni (ii) are occupied, rendering NiFe LDH treated with hydride ions unstable. Therefore, in order to reduce the energy of the system, one electron is transferred from the opposite bonding orbital of ni (ii) to the bonding orbital of fe (iii) via a hydride bridge by superexchange interaction, thereby forming ni (iii) and fe (ii). The present inventors calculated the partial charge densities at the fermi level of NiFe LDH and H-NiFe LDH in order to understand the influence of the hydride ions, and as a result, found that a higher charge density appears in the region near the activated transition metal ion, indicating that the transition metal ion can be activated by substituting the hydroxyl (-OH) ligand of TM LDH. However, the generated transition metal-hydride ions are close to each other, and a reduction elimination reaction can easily occur, generating hydrogen gas and reducing the transition metal, resulting in the formation of metal nanoparticle decorated LDH. To avoid the reduction of the transition metal, the inventors greatly reduced the concentration of sodium borohydride to 1mM to obtain a low concentration of transition metal-hydride, while the hydroxyl ligand of the TM LDH can still be substituted for the hydride.

In conclusion, after intensive research, inspired by the super-exchange interaction, the invention discovers that activating the hydroxyl ligand of the TM LDH by using low-concentration sodium borohydride can influence electron transfer, adjust the coordination condition of transition metal ions, and influence the surface physical and chemical properties of the transition metal ions, thereby influencing the catalytic performance of the TM LDH. Taking NiFe LDH as an example, activation of the hydroxyl ligand causes electrons to be transferred from the low oxidation state ni (ii) to the high oxidation state fe (iii) via hydrogen ion bridges by superexchange interactions, thereby generating OER activity ni (iii) resulting in an increase in OER performance of NiFe LDH, with the concentration of ni (iii) being proportional to OER performance. Having hydroxyl ligands and hydrogen ion ligands in activated NiFe LDHNiFe₄The unit is a catalytically active center in which Ni sites serve as absorption/desorption sites, while adjacent Fe ions accumulate electrons through superexchange interactions. In addition to NiFe LDH, the present inventors found that TM LDHs such as NiMn LDH, NiCo LDH, and CoFe LDH also have the same effect. Furthermore, the hydroxyl ligands of TM LDH may be further activated with the Cl in addition to the hydrogen anions^-Negative ion, Br^-Negative ion, I^-The negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions activate the hydroxyl ligands of the TM LDH.

Thus, the present inventors have developed a method for the preparation of a ligand-activated TM LDH, the prepared ligand-activated TM LDH and its use, as well as a water-splitting anode and a water-splitting three-electrode system comprising the ligand-activated TM LDH, as described in the summary of the invention section above. Among them, the present inventors found that the concentration of sodium borohydride, the reaction temperature and the reaction time are important in the method for preparing the ligand-activated TM LDH of the present invention. When the concentration of sodium borohydride is higher, the transition metal ions are reduced into corresponding metal nano particles, so that the catalytic action is reduced. The water bath temperature is too low or the reaction time is too short, the ligand activation is difficult to carry out or is incomplete, and the catalytic action is not ideal; and the water bath temperature is too high or the reaction time is too long, the reduction is excessive, and the catalytic action is not ideal.

The invention is illustrated by the following non-limiting examples.

Example 1: synthesis and characterization of hydride activated NiFe LDH catalyst (H-NiFe LDH)

1.1 Synthesis of NiFe LDH

NiFe LDH nano powder is synthesized by a hydrothermal method, and the specific operation is as follows. 0.725ml of 1M nickel chloride (NiCl) was added in a beaker₂) Aqueous solution and 0.145ml of 1M iron chloride (FeCl)₃) The aqueous solution was mixed with 70.8ml of deionized water. Then 5.6ml of 0.5M aqueous urea solution and 2ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. Inverse directionAfter that, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare NiFe LDH nanopowder, which is a Ni (II)/Fe (III) transition metal layered double hydroxide compound.

1.2 Synthesis of H-NiFe LDH catalyst

Adding 1mg of the NiFe LDH powder prepared in the above step into 10ml of deionized water in a 15ml sealed bottle, and preparing a NiFe LDH suspension by ultrasonic vibration at the vibration frequency of 50KHz and uniformly stirring and dispersing at the stirring speed of 800 rmp. Adding 1.9mg NaBH into a sealed bottle₄Stirring and dispersing evenly at the stirring speed of 500rpm to obtain NaBH₄The final concentration was 0.005M. The sealed bottle was placed in a 50 ℃ water bath and reacted for 2 hours at a stirring speed of 800 rpm. After the reaction, the reaction mixture was naturally cooled to room temperature, 5ml of deionized water was added to the beaker to dilute the reaction mixture, and the diluted solution was transferred to a 10ml centrifuge tube and washed by centrifugation at 7000rpm for 10 minutes. The supernatant was discarded and centrifuged again twice in the same manner. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the H-NiFe LDH catalyst.

1.3 characterization of hydride activated NiFe LDH (H-NiFe LDH) catalyst

FIG. 1 shows the present example in NaBH₄Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images of NiFe LDH (a, C, D) before activation and H-NiFe LDH (B, E, F) after activation, where (a, B) is the SEM image, (C, E) is the TEM image, and (D, F) is the high resolution TEM (hrtem). It can be seen that the nanostructure of NiFe LDH was maintained after sodium borohydride treatment.

FIG. 2 shows the present example in NaBH₄XRD images of the NiFe LDH before activation and the H-NiFe LDH after activation show the same characteristic diffraction peak, and show that the crystalline phase is unchanged and the crystallinity is high.

FIG. 3 shows the present example in NaBH₄Of activated H-NiFe LDH²H magic angle spin nuclear magnetic resonance (MAS NMR) pattern, showing the formation of H-M bonds, indicating the activation and substitution of hydroxyl ligands in H-NiFe LDH.

FIG. 4 showsThis example is described in NaBH₄Electrochemical impedance plot of post-activation H-NiFe LDH at 300mV overpotential, with NiFe LDH and H-Ni (OH)₂And (6) carrying out comparison. As can be seen from FIG. 4, NaBH₄The H-NiFe LDH catalyst had the lowest resistance after activation, indicating that the catalyst had the best electron conductivity.

Among them, H-Ni (OH) for comparison₂Synthesized as follows. Firstly, synthesizing Ni (OH) by a hydrothermal method₂The specific operation is as follows. 0.87ml of 1M nickel chloride (NiCl)₂) The aqueous solution was mixed with 70.8ml of deionized water in a beaker. Then 5.6ml of 0.5M aqueous urea solution and 2ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to obtain Ni (OH)₂. Then, H-Ni (OH) was prepared in a similar manner to 1.2₂。

Example 2: synthesis of hydride activated NiMn LDH catalyst (H-NiMn LDH)

2.1 Synthesis of NiMn LDH

NiMn LDH nano powder is synthesized by a hydrothermal method, and the specific operation is as follows. 0.435ml of 1M nickel chloride (NiCl) was added in a beaker₂) Aqueous solution and 0.145ml of 1M manganese chloride (MnCl)₂) The aqueous solution was mixed with 70ml of deionized water. 4.48ml of a 0.5M aqueous urea solution and 1.6ml of a 0.01M aqueous trisodium citrate solution were then added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml stainless steel autoclave lined with polytetrafluoroethylene, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare NiMn LDH nanopowder, which is a layered double hydroxy compound of Ni (II)/Mn (III) transition metal.

2.2 Synthesis of H-NiMn LDH catalyst

0.5mg of the NiMn LDH powder prepared above was added to 1ml of deionized water in a 15ml sealed bottle, and a NiMn LDH suspension was prepared by ultrasonic vibration at an amplitude of 50KHz and uniformly dispersed with stirring at a stirring speed of 800 rmp. Add 3.8mg NaBH to sealed bottle₄Stirring and dispersing evenly at the stirring speed of 500rpm to obtain NaBH₄The final concentration was 0.001M. The sealed bottle was placed in a water bath at 80 ℃ and reacted at a stirring speed of 800rpm for 10 hours. After the reaction, the reaction mixture was naturally cooled to room temperature, 5ml of deionized water was added to the beaker to dilute the reaction mixture, and the diluted solution was transferred to a 20ml centrifuge tube and washed by centrifugation at 7000rpm for 10 minutes. The supernatant was discarded and centrifuged again twice in the same manner. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the H-NiMn LDH catalyst.

Example 3: synthesis of hydride activated NiCo LDH catalyst (H-NiCo LDH)

3.1 Synthesis of NiCo LDH

NiCo LDH nano powder is synthesized by a hydrothermal method, and the specific operation is as follows. 1.16ml of 1M nickel chloride (NiCl) was placed in a beaker₂) Aqueous solution and 0.145ml of 1M cobalt chloride (CoCl)₂) The aqueous solution was mixed with 70ml of deionized water. Then 10.1ml of 0.5M aqueous urea solution and 1.1ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml teflon-lined stainless steel autoclave, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare NiCo LDH nanopowder, which is a Ni (II)/Co (III) transition metal layered dihydroxy compound.

3.2 Synthesis of H-NiCo LDH catalyst

1.5mg of the NiCo LDH powder prepared above was put into 10ml of anhydrous ethanol in a 15ml sealed bottle, and dispersed uniformly by ultrasonic vibration at an amplitude of 50KHz and stirring at a stirring speed of 800rmp to prepare a NiCo LDH suspension. Adding 3mg NaBH into a sealed bottle₄Stirring speed at 500rpmStirring and dispersing evenly under the temperature to obtain NaBH₄The final concentration was 0.008M. The sealed bottle was placed in a 30 ℃ water bath and reacted at a stirring speed of 800rpm for 5 hours. After the reaction, the reaction mixture was naturally cooled to room temperature, and 5ml of absolute ethanol was added to the beaker to dilute the reaction mixture, and the diluted solution was transferred to a 20ml centrifuge tube and washed by centrifugation at 7000rpm for 10 minutes. The supernatant was discarded and centrifuged again twice in the same manner. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the H-NiCo LDH catalyst.

Example 4: synthesis of hydride activated CoFe LDH catalyst (H-CoFe LDH)

4.1 Synthesis of CoFe LDH

CoFe LDH nanopowder was synthesized by a hydrothermal method, specifically as follows. 0.145ml of 1M cobalt chloride (CoCl) was placed in a beaker₂) Aqueous solution and 1.45ml of 1M iron chloride (FeCl)₃) The aqueous solution was mixed with 70ml of deionized water. Then 11.2ml of 0.5M aqueous urea solution and 4ml of 0.01M aqueous trisodium citrate solution were added to the beaker with magnetic stirring. The resulting mixed solution was then transferred to a 100ml teflon-lined stainless steel autoclave, sealed and subjected to hydrothermal reaction in an oven at 150 ℃ for 24 hours. After the reaction, the powder was collected by centrifugation at 7500rpm for 10 minutes, then washed several times with deionized water and high-purity ethanol, and then dried overnight in an oven at 50 ℃ to prepare CoFe LDH nanopowder, which is a Co (II)/Fe (III) transition metal layered dihydroxy compound.

4.2 Synthesis of H-CoFe LDH catalyst

2mg of the CoFe LDH powder prepared above was added to 10ml of anhydrous ethanol in a 15ml sealed bottle, and a CoFe LDH suspension was prepared by ultrasonic vibration at an amplitude of 50KHz and uniformly dispersed with stirring at a stirring speed of 800 rmp. Add 3.8mg NaBH to sealed bottle₄Stirring and dispersing evenly at the stirring speed of 500rpm to obtain NaBH₄The final concentration was 0.01M. The sealed bottle was placed in a 60 ℃ water bath and reacted at a stirring speed of 800rpm for 0.5 hour. After the reaction, the mixture is naturally cooled to room temperature, 5ml of absolute ethyl alcohol is added into the beaker to dilute the reactant, and the diluent is changed intoThe cells were transferred to a 20ml centrifuge tube and washed by centrifugation at 7000rpm for 10 minutes. The supernatant was discarded and centrifuged again twice in the same manner. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the H-CoFe LDH catalyst.

Example 5: synthesis of NiFe LDH catalyst (Cl-NiFe LDH) activated by chlorine anion

5.1 Synthesis of NiFe LDH

NiFe LDH nanopowders were synthesized as in 1.1 of example 1.

5.2 Synthesis of NiFe LDH catalyst activated by chlorine anion

1mg of the NiFe LDH powder prepared above was added to 10ml of deionized water in a 15ml sealed bottle, and a NiFe LDH suspension was prepared by ultrasonic vibration at an amplitude of 50KHz and uniformly stirred at a stirring speed of 800 rmp. Adding 1.9mg NaBH into a sealed bottle₄And 584mg of sodium chloride is added to be stirred and dispersed evenly at the stirring speed of 500rpm to obtain NaBH₄Final concentration of 0.005M, Cl-1M. The sealed bottle was placed in a 50 ℃ water bath and reacted for 5 hours at a stirring speed of 800 rpm. After the reaction, the reaction mixture was naturally cooled to room temperature, 5ml of deionized water was added to the beaker to dilute the reaction mixture, and the diluted solution was transferred to a 20ml centrifuge tube and washed by centrifugation at 7000rpm for 10 minutes. The supernatant was discarded and centrifuged again twice in the same manner. And (3) drying the final precipitate for 5 hours in vacuum at the pressure of-100 KPa relative to the atmospheric pressure to obtain the Cl-NiFe LDH catalyst.

Example 6: synthesis of NiFe LDH catalyst (Br-NiFe LDH) activated by bromine negative ions

This example was carried out in the same manner as in example 5 except that sodium chloride was replaced with sodium bromide so that the final concentration of Br in the reaction solution was 1M, to finally obtain a Br-NiFe LDH catalyst.

Example 7: synthesis of NiFe LDH catalyst (I-NiFe LDH) activated by iodide anion

This example was carried out in the same manner as in example 5 except that sodium chloride was replaced with sodium iodide so that the final Br concentration in the reaction solution was 1M, to finally obtain an I-NiFe LDH catalyst.

Example 8: synthesis of NiFe LDH catalyst (N-NiFe LDH) activated by nitrogen anions

This example was carried out in the same manner as in example 5 except that potassium isothiocyanate (NCS) was used in place of sodium chloride so that the final Br concentration in the reaction solution was 1M, to finally obtain an N-NiFe LDH catalyst.

Example 9: synthesis of NiFe LDH catalyst (P-NiFe LDH) activated by phosphorus negative ion

This example was carried out in the same manner as in example 5 except that sodium chloride was replaced with sodium phosphate so that the final Br concentration in the reaction solution was 1M, to finally obtain a P-NiFe LDH catalyst.

Example 10: synthesis of NiFe LDH catalyst (S-NiFe LDH) activated by sulfur anion

This example was carried out in the same manner as in example 5 except that potassium thiocyanate was used in place of sodium chloride so that the final Br concentration in the reaction solution was 1M, to finally obtain an S-NiFe LDH catalyst.

Example 11: preparation of catalyst/foamed nickel electrode

The nickel foam was immersed in 1M HCl solution for 10 minutes to remove surface oxides, then washed several times with deionized water and ethanol, and dried in an oven at 60 ℃ until use. 1mg of the H-NiFe LDH catalyst synthesized in example 1 was ultrasonically and uniformly dispersed in 1ml of ethanol for 2 hours to obtain a catalyst dispersion. Uniformly mixing 500uL of prepared catalyst dispersion liquid with 5% of PTFE aqueous solution according to the volume ratio of 2:1, and performing ultrasonic dispersion. And uniformly coating the obtained mixed dispersion liquid on a piece of foamed nickel (1cm x 1cm), and drying in a 60 ℃ oven for 30 minutes to obtain the H-NiFe LDH catalyst/foamed nickel electrode.

Electrodes can be prepared in a similar manner on carbon cloth or iron substrates using the H-NiFe LDH catalyst prepared in example 1. Also, electrodes can be prepared in a similar manner on foamed nickel, carbon cloth or iron substrates using the catalysts prepared in examples 2-10.

Test example: water decomposition catalytic performance of H-NiFe LDH catalyst

Using the H-NiFe LDH catalyst/foamed nickel electrode prepared in example 11 as a water-splitting anode (working electrode), Pt wire as a counter electrode, Ag/AgCl as a reference electrode, and 1M aqueous potassium hydroxide solution as an electrolyte, a water-splitting three-electrode system was constructed as shown in FIG. 5, in which reference numeral 1 denotes a working electrode, 2 denotes a reference electrode, and 3 denotes a counter electrode. A NiFe LDH catalyst/foamed nickel electrode was prepared in the same manner as in example 11, and a water-splitting three-electrode system having the NiFe LDH catalyst/foamed nickel electrode as a working electrode was constructed in the same manner as in this test example. In addition, a water-splitting three-electrode system having a nickel foam electrode as a working electrode was constructed in the same manner as in the present test example.

The three water splitting three-electrode systems constructed above were tested on an EC-lab (Bio-Logic) and a Chi electrochemical workstation (Shanghai Chenghua) to verify the water splitting catalytic performance of the H-NiFe LDH catalyst of the present invention. FIG. 6 shows a comparative plot of the catalytic hydrogen production polarization curves for foamed nickel, NiFe LDH and H-NiFe LDH. As can be seen from fig. 6, the activated H-nifehd catalyst has the lowest overpotential, indicating that the same current density is achieved with the lowest energy consumption. FIG. 7 shows a comparative graph of catalytic oxygen production tafel curves for foamed nickel, NiFe LDH and H-NiFe LDH. As can be seen from fig. 7, the H-NiFe LDH catalyst after ligand activation has the lowest tafel slope, representing the fastest oxygen production reaction rate.

The stability of H-NiFe LDH was tested by chronopotentiometry. FIG. 8 is a graph showing H-NiFeLDH at 10, 20 and 50mA cm^-2The current density of (a), wherein the inset is H-NiFe LDH at 50mAcm^-2A long-time chronopotentiometric test pattern exceeding 12 hours at a current density of (1). As can be seen from FIG. 8, the catalyst after ligand activation has good stability and industrial application prospect.

In addition, an NCS-NiFe LDH catalyst/nickel foam electrode was also prepared in the same manner as in example 10 using the NCS-NiFe LDH catalyst prepared in example 8, and compared with the H-NiFe LDH catalyst/nickel foam electrode prepared in example 11 in the same operation as in this test example. FIG. 9 shows a comparative plot of the catalytic hydrogen production polarization curves of NCS-NiFe LDH and NiFe LDH. As can be seen in FIG. 9, the activated NCS-NiFe LDH catalyst has the lowest overpotential, similar to H-NiFe LDH, indicating that the same current density is achieved with the lowest energy consumption.

The present invention has been described above using specific examples, which are only for the purpose of facilitating understanding of the present invention, and are not intended to limit the present invention. Numerous simple deductions, modifications or substitutions may be made by those skilled in the art in light of the teachings of the present invention. Such deductions, modifications or alternatives also fall within the scope of the claims of the present invention.

Claims

1. A method for preparing a ligand-activated transition metal layered dihydroxy compound, comprising the steps of:

(1) uniformly dispersing a transition metal layered dihydroxy compound in a polar solvent to obtain a transition metal layered dihydroxy compound suspension, wherein the transition metal is any combination of divalent and trivalent transition metal ions; preferably, the atomic ratio of the divalent/trivalent transition metal ions is between (3-10): 1; preferably, the transition metal ion is a combination of Ni (II)/Fe (III), Ni (II)/Mn (III), Ni (II)/Co (III), or Co (II)/Fe (III);

(2) and (2) adding sodium borohydride with appropriate amount for activation reaction into the suspension obtained in the step (1) to carry out activation reaction, so as to obtain the ligand-activated transition metal layered dihydroxy compound.

2. The production method according to claim 1, wherein in the step (1), the weight-to-volume ratio of the transition metal layered double hydroxide compound to the polar solvent is (0.5-2) mg:1 ml; in the step (2), the appropriate amount of the activation reaction is such that the final concentration of the sodium borohydride in the suspension liquid in the step (1) is 0.001-0.01M, the reaction temperature of the activation reaction is 20-80 ℃, and the reaction time is 0.5-10 hours.

3. The preparation method according to claim 1, comprising the following specific steps:

(1) uniformly dispersing Ni (II)/Fe (III), Ni (II)/Mn (III), Ni (II)/Co (III) or Co (II)/Fe (III) transition metal layered dihydroxy compound with the atomic ratio of (3-10):1 in deionized water or ethanol or a mixed solvent thereof, wherein the weight-volume ratio of the transition metal layered dihydroxy compound to the polar solvent is (0.5-2) mg:1ml, and uniformly dispersing by ultrasonic vibration and stirring to obtain a transition metal layered dihydroxy compound suspension;

(2) adding sodium borohydride with the final concentration of 0.001-0.01M into the suspension obtained in the step (1), stirring and dispersing uniformly at the stirring speed of 400-80 rpm, then reacting for 0.5-10 hours at the reaction temperature of 20-80 ℃ and at the stirring speed of 700-1000rpm, naturally cooling to room temperature, adding a proper amount of deionized water or absolute ethyl alcohol as a washing solvent, centrifugally washing for three times at 6000-8000rpm, each time for 5-10 minutes, and then drying in vacuum for 3-6 hours to obtain the ligand-activated transition metal layered dihydroxy compound.

4. A method for preparing a ligand-activated transition metal layered dihydroxy compound, comprising the steps of:

(2) adding sodium borohydride with proper amount for activation reaction into the suspension obtained in the step (1), and adding Cl with proper amount for activation reaction^-Negative ion, Br^-Negative ion, I^-And (3) carrying out activation reaction on one or more of negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions to obtain the ligand-activated transition metal layered dihydroxy compound.

5. The production method according to claim 4, wherein in the step (1), the weight-to-volume ratio of the transition metal layered double hydroxide compound to the polar solvent is(0.5-2) mg:1 ml; in the step (2), the appropriate amount of the activation reaction is such that the final concentration of the sodium borohydride in the suspension liquid in the step (1) is 0.001-0.01M, and the Cl is^-Negative ion, Br^-Negative ion, I^-The total final concentration of one or more of negative ions, negative ions containing N, negative ions containing P or negative ions containing S in the suspension liquid in the step (1) is 0.1-10M, the reaction temperature of the activation reaction is 20-80 ℃, and the reaction time is 0.5-10 hours.

6. The preparation method according to claim 4, comprising the following specific steps:

(2) adding sodium borohydride with final concentration of 0.001-0.01M into the suspension obtained in the step (1), and adding the Cl with total final concentration of 0.1-10M^-Negative ion, Br^-Negative ion, I^-One or more of negative ions, N-containing negative ions, P-containing negative ions or S-containing negative ions are stirred and dispersed uniformly at the stirring speed of 400-80 rpm, then the mixture is reacted for 0.5 to 10 hours at the reaction temperature of 20 to 80 ℃ and the stirring speed of 700-1000rpm, after the mixture is naturally cooled to the room temperature, a proper amount of deionized water or absolute ethyl alcohol is added as a washing solvent, the mixture is centrifugally washed for three times at 6000-8000rpm, each time is for 5 to 10 minutes, and then the mixture is dried in vacuum for 3 to 6 hours, so that the ligand-activated transition metal layered double-hydroxy compound is obtained.

7. A ligand-activated transition metal layered dihydroxy compound, characterized in that it is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the ligand-activated transition metal layered dihydroxy compound of claim 7 as an oxygen production catalyst for water-splitting anodes.

9. A water-splitting anode comprising a foamed nickel, carbon cloth or iron substrate and the ligand-activated transition metal layered double hydroxide according to claim 7 coated on the foamed nickel, carbon cloth or iron substrate.

10. A water-splitting three-electrode system comprising the water-splitting anode of claim 9, Pt wire as a counter electrode, Ag/AgCl as a reference electrode and 0.5-1.5M potassium hydroxide or sodium hydroxide aqueous solution as an electrolyte; preferably, the electrolyte is a 1M aqueous solution of potassium hydroxide or sodium hydroxide.