Transition metal phosphide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a transition metal phosphide catalyst and a preparation method and application thereof.The preparation method comprises the steps that metal nickel salt, vanadium salt, urea and ammonium fluoride are dissolved in deionized water, and a nickel-vanadium hydroxide nanosheet precursor is synthesized through a hydrothermal method; preparing a vanadium-doped nickel phosphide nanosheet catalyst by using a low-temperature phosphating method; the electronic structure of nickel phosphide is regulated and controlled by using a vanadium doping strategy, the catalytic reaction energy barrier is reduced, and the intrinsic catalytic activity is improved; the prepared catalyst has excellent hydrogen evolution reaction and sulfur ion oxidation reaction performance, low voltage 0.389 V is needed for outputting the current density of 10 mAcm <-2 > in a constructed two-electrode sulfur ion oxidation coupling hydrogen production electrolytic cell, and the purposes of efficient and energy-saving hydrogen production and sulfur ion oxidation upgrading into a high-added-value elemental sulfur product are achieved. The synthesis method is simple and controllable, raw materials are low in price and cost, batch preparation is easy, and the catalyst can be used as an efficient water electrolysis hydrogen production and sulfur ion oxidation upgrading catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of nano material preparation and application, and specifically relates to a transition metal phosphide catalyst and a preparation method and application thereof. Background Art

[0002] As a high energy density and environmentally friendly energy source, hydrogen is considered to be an ideal energy source to replace traditional conventional energy. Electrocatalytic water splitting technology powered by renewable energy has become an attractive technology for producing high-purity hydrogen due to its mild operating conditions and simple operation. However, due to the complex and slow oxygen evolution reaction process, this method requires a high electrolysis voltage, which limits its practical application. In order to reduce energy consumption, researchers have long been committed to developing electrocatalysts with high catalytic performance. Despite this, including RuO 2 and IrO 2 Precious metal-based materials including are still considered as advanced oxygen evolution reaction catalysts, but limited reserves and high prices are not conducive to their industrialization. Therefore, it is very necessary to develop cheap, highly active and stable catalysts.

[0003] In order to break through the thermodynamic energy barrier of the anode in the traditional water electrolysis system, the electrocatalytic oxidation reaction of small molecules with low thermodynamic potential (such as urea, hydrazine, and aldehydes) replaces the oxygen evolution reaction, and is coupled with the hydrogen evolution reaction to construct an effective strategy for the difficult problem of a hybrid water electrolysis system. Among them, the electrocatalytic oxidation reaction of sulfur ions has a lower theoretical thermodynamic oxidation potential than the above-mentioned oxidation reaction, and can significantly reduce the power consumption of the electrolysis system by replacing the oxygen evolution reaction; on the other hand, sulfur ions are common toxic substances in the printing and dyeing, papermaking, printing and other industries, and have certain hazards to the ecological environment and human health. Compared with the widely used Claus sulfur recovery process in industry, the electrocatalytic sulfur ion oxidation reaction can not only convert sulfur ions into valuable sulfur species without adding an oxidant, but also realize a low-energy hydrogen production process by coupling the hydrogen evolution reaction with the sulfur ion oxidation reaction in the hybrid water electrolysis system, and the current research on catalysts with dual-function hydrogen evolution reaction and sulfur ion oxidation reaction is still very limited. In view of this, the present invention provides a transition metal phosphide catalyst having good activity and stability in hydrogen evolution reaction and sulfur ion oxidation reaction. Summary of the invention

[0004] Technical issues solved:

[0005] The present invention aims at the shortcomings of the prior art and solves the problems of low overall water electrolysis efficiency caused by the slow kinetics of oxygen evolution reaction and the nickel phosphide (Ni 2 In order to solve the problems of low activity of hydrogen evolution reaction and sulfur oxidation reaction of transition metal vanadium-doped nickel phosphide (V-Ni P) catalyst, a transition metal vanadium-doped nickel phosphide (V-Ni P) catalyst was provided. 2P) catalyst, which has excellent catalytic performance and can achieve efficient and energy-saving hydrogen production and sulfur ion upgrading and recovery in a two-electrode sulfur ion oxidation coupled hydrogen production system.

[0006] Technical solution:

[0007] To achieve the above objectives, this application is implemented through the following technical solutions:

[0008] A method for preparing a transition metal phosphide catalyst comprises the following steps:

[0009] Step 1: dissolving 10 parts of metal nickel salt, 0.5-5 parts of metal vanadium salt, 30-100 parts of urea and 20-50 parts of ammonium fluoride in deionized water according to molar ratio to prepare a uniform solution;

[0010] Step 2: transferring the homogeneous solution to a reactor, adding the pretreated metal foam carrier, sealing the reactor and placing it in a forced air drying oven, and preparing a nickel vanadium hydroxide nanosheet precursor by a hydrothermal reaction;

[0011] Step 3: Place 1 part of nickel vanadium hydroxide precursor and 5-20 parts of phosphorus source in the downstream and upstream of the quartz boat respectively according to the mass ratio, and put it into the reaction furnace;

[0012] Step 4: Under the protection of inert gas, the reactor is heated to 280-350° C. at a heating rate of 2-5° C. / min and kept warm for 1-4 hours to obtain a vanadium-doped nickel phosphide catalyst, i.e., a transition metal phosphide catalyst.

[0013] Furthermore, in step 1, the metal nickel salt is nickel nitrate or nickel chloride, and the metal vanadium salt is vanadium chloride.

[0014] Furthermore, in step 2, the hydrothermal reaction temperature and reaction time are 100-150° C. and 4-12 hours, respectively.

[0015] Furthermore, in step 2, the metal foam is one or more of nickel foam, copper foam, cobalt foam, titanium foam, and titanium mesh.

[0016] Furthermore, the pretreatment method of the metal foam in step 2 is to treat it with 0.5 mmol / L hydrochloric acid.

[0017] Furthermore, the phosphorus source used in step 3 is sodium hypophosphite.

[0018] Furthermore, in step 4, the inert gas is nitrogen or argon.

[0019] A transition metal phosphide catalyst prepared by any of the above preparation methods, wherein the catalyst uses metal foam as a carrier, and phosphide nanosheets with uniform morphology grow on the surface of the carrier.

[0020] The present application also discloses the use of the transition metal phosphide catalyst prepared by any of the above preparation methods in electrocatalytic hydrogen evolution reaction, oxygen evolution reaction, sulfide ion oxidation reaction, two-electrode full water electrolysis reaction and sulfide ion oxidation coupled hydrogen production, wherein the transition metal phosphide catalyst is used as a catalyst for the electrocatalytic reaction and as an anode and cathode for the sulfide ion oxidation coupled hydrogen production system.

[0021] Furthermore, 2 mmol / L sulfuric acid is added to the electrolyte after the sulfide ion oxidation coupling hydrogen production, and the generated precipitate is separated, washed and dried to obtain an elemental sulfur product.

[0022] Beneficial effects:

[0023] The present application provides a transition metal phosphide catalyst and a preparation method and application thereof, which have the following beneficial effects compared with the prior art:

[0024] 1. V-Ni prepared in this application 2 P catalyst utilizes metal V doping and catalyst nanosheet morphology to regulate the electronic structure of the catalyst and expose abundant catalytic active sites, thereby improving the intrinsic catalytic activity, catalytic performance and material transfer rate during the catalytic process.

[0025] 2. V-Ni prepared in this application 2 The P catalyst showed good electrocatalytic hydrogen evolution reaction, sulfur ion oxidation reaction, complete water splitting reaction and sulfur ion oxidation coupled hydrogen production performance in alkaline electrolyte, solving the problem of high voltage required for hydrogen production by water electrolysis.

[0026] 3. V-Ni prepared in this application 2 When the P catalyst is used in a two-electrode sulfur ion oxidation coupled hydrogen production system, it can output 10 and 300 mA cm at low electrolysis voltages of 0.389 and 0.834 V, respectively. -2 The current density is 10000, and the required voltage is lower than that of the traditional water electrolysis hydrogen production system, achieving the goal of efficient and energy-saving hydrogen production and oxidation and upgrading of sulfur ions to high-value-added elemental sulfur products;

[0027] 4. The preparation method of this application has the advantages of simple operation, low raw material cost, and easy batch synthesis. It can replace expensive precious metal-based catalysts and accelerate the industrial application of hydrogen production by water electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Ni synthesized in Example 1 of the present application 2 P and V-Ni 2 X-ray diffraction spectrum of catalyst P;

[0029] Figure 2The NiV-LDH precursor and V-Ni synthesized in Example 1 of the present application 2 SEM and TEM images of the P catalyst; a and b are SEM images of the NiV-LDH precursor, and c is the SEM image of the V-Ni 2 SEM images of P catalyst, d is V-Ni 2 Transmission electron microscope photo of P catalyst;

[0030] Figure 3 Ni synthesized in Example 1 of the present application 2 P and V-Ni 2 The performance diagram of hydrogen evolution reaction of catalyst P in alkaline sodium hydroxide solution; wherein a is the polarization curve diagram of hydrogen evolution reaction, and b is the Tafel slope diagram of hydrogen evolution reaction;

[0031] Figure 4 Ni synthesized in Example 1 of the present application 2 P and V-Ni 2 Performance diagram of oxygen evolution reaction and sulfide ion oxidation reaction of P catalyst; a is the polarization curve diagram of oxygen evolution reaction, and b is the polarization curve diagram of sulfide ion oxidation reaction;

[0032] Figure 5 Ni synthesized in Example 1 of the present application 2 P and V-Ni 2 Polarization curve and stability test diagram of traditional water electrolysis and sulfur ion oxidation coupled water electrolysis hydrogen production of P catalyst; where a is the polarization curve diagram of the catalyst in the traditional water electrolysis and sulfur ion oxidation coupled hydrogen production system, and b is the stability curve diagram of the catalyst in the traditional water electrolysis and sulfur ion oxidation coupled hydrogen production system. DETAILED DESCRIPTION

[0033] The present invention will be described clearly and completely below in conjunction with specific embodiments, which will help those skilled in the art to better understand the present invention, thereby making a clearer definition of the protection scope of the present invention. It should be pointed out that the embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

[0034] Example 1

[0035] A method for preparing a vanadium-doped nickel phosphide catalyst comprises the following steps:

[0036] Step 1: Dissolve 1.6 mmol nickel nitrate, 0.4 mmol vanadium chloride, 6 mmol ammonium fluoride and 10 mmol urea in 35 mL deionized water according to a molar volume ratio to prepare a uniform solution;

[0037] Step 2: Transfer the homogeneous solution to a 50 mL reactor, add a piece of nickel foam carrier treated with 0.5 mmol / L hydrochloric acid, seal the reactor and place it in a forced air drying oven, and prepare NiV-LDH nanosheet precursor by hydrothermal reaction at 120 ° C for 6 hours;

[0038] Step 3: Place 1 part of NiV-LDH nanosheet precursor and 15 parts of sodium hypophosphite in the downstream and upstream of the quartz boat respectively according to the mass ratio, and put it into the reaction furnace;

[0039] Step 4: In the protection of inert gas nitrogen, the reactor was heated to 300°C at a heating rate of 2°C / min and kept at this temperature for 2 hours to obtain V-Ni 2 P catalyst.

[0040] The V-Ni prepared above 2 The P catalyst was tested in alkaline electrolyte for electrocatalytic hydrogen evolution reaction, oxygen evolution reaction, sulfide ion oxidation reaction, full water electrolysis reaction and sulfide ion oxidation coupled water electrolysis hydrogen production performance test; the working electrode in the electrolytic cell was the product of the present invention, and the electrolyte was 1mol / LNaOH and 1mol / LNaOH+1mol / LNa 2 The electrocatalytic performance of the aqueous solution of S was tested using an electrochemical workstation; all electrode potentials in the electrocatalytic test results have been converted to reversible hydrogen electrode potential (RHE).

[0041] The V-Ni prepared above 2 The phase, morphology, structure and electrocatalytic performance of P catalyst were studied. Figure 1 As shown, Ni 2 P and V-Ni 2 X-ray diffraction spectrum of P, Figure 1 This indicates that V-Ni was successfully prepared. 2 P product.

[0042] like Figure 2 As shown, NiV-LDH precursor and V-Ni 2 SEM and TEM images of P catalyst. Figure 2 The results showed that the prepared NiV-LDH precursor and V-Ni 2 P all have uniform nanosheet morphology.

[0043] like Figure 3 As shown, a is V-Ni 2 Polarization curve of hydrogen evolution reaction of P catalyst, b is V-Ni 2 The Tafel slope plot of hydrogen evolution reaction of P catalyst is shown in Figure 2. 2 The P catalyst has good hydrogen evolution reaction activity in alkaline electrolyte, and 10 mA cm-2 The overpotential required for the current density is 0.093 V and the Tafel slope is 81 mV dec. -1 .

[0044] like Figure 4 As shown, a is V-Ni 2 Polarization curve of oxygen evolution reaction of P catalyst, b is V-Ni 2 Polarization curve of sulfur ion oxidation reaction of P catalyst, the V-Ni 2 The P catalyst has excellent oxygen evolution reaction and sulfur ion oxidation reaction activity in alkaline electrolyte, with an output of 10mAcm -2 The potentials required for the current density are 1.505 and 0.313 V respectively.

[0045] like Figure 5 As shown, a is V-Ni 2 Polarization curves of P catalyst in the conventional water electrolysis and sulfur ion oxidation coupled hydrogen production process, b is V-Ni 2 Stability curve of the V-Ni P catalyst in the conventional water electrolysis and sulfur ion oxidation coupled hydrogen production process. 2 The P catalyst has excellent activity and stability in the full electrolysis of water and coupled hydrogen production by sulfur ion oxidation in alkaline electrolyte, with an output of 10 mA cm -2 The voltage required for the current density is 0.389V, which is 1.5V lower than the voltage required for seawater electrolysis.

[0046] Example 2

[0047] The same as Example 1, except that vanadium chloride was not added, Ni 2 P catalyst. Figure 3 and Figure 4 As shown in Figure 2, the catalyst has good activity in hydrogen evolution reaction and sulfur ion oxidation reaction in alkaline electrolyte, with an output of 10 mA cm -2 The potentials required for the current density are -0.139 and 0.394 V respectively.

[0048] Example 3

[0049] The same as Example 1, except that the amount of vanadium chloride added was changed to 0.1 mmol, and the current density of the output hydrogen evolution reaction and sulfide ion oxidation reaction was 10 mA cm -2 , the required potentials are -0.119 and 0.362 V respectively.

[0050] Example 4

[0051] The same as Example 1, except that the amount of vanadium chloride added was changed to 0.2 mmol, and the current density of the output hydrogen evolution reaction and sulfide ion oxidation reaction was 10 mA cm -2, the required potentials are -0.102 and 0.331 V respectively.

[0052] Example 5

[0053] The same as Example 1, except that the amount of vanadium chloride added was changed to 0.6 mmol, and the current density of the output hydrogen evolution reaction and sulfide ion oxidation reaction was 10 mA cm -2 , the required potentials are -0.108 and 0.328 V respectively.

[0054] The above is a description of the specific embodiments of the present invention. The description and practice disclosed in the present invention are easy to think and understand for those skilled in the art, and various improvements and modifications can be made within the scope of the claims, which does not affect the essential content of the present invention.

Claims

1. A method for preparing a transition metal phosphide catalyst, characterized in that: The specific steps include: Step 1: dissolving 10 parts of metal nickel salt, 0.5-5 parts of metal vanadium salt, 30-100 parts of urea and 20-50 parts of ammonium fluoride in deionized water according to molar ratio to prepare a uniform solution; Step 2: transferring the homogeneous solution to a reactor, adding the pretreated metal foam carrier, sealing the reactor and placing it in a forced air drying oven, and preparing a nickel vanadium hydroxide nanosheet precursor by a hydrothermal reaction; Step 3: Place 1 part of nickel vanadium hydroxide precursor and 5-20 parts of phosphorus source in the downstream and upstream of the quartz boat respectively according to the mass ratio, and put it into the reaction furnace; Step 4: Under the protection of inert gas, the reactor is heated to 280-350° C. at a heating rate of 2-5° C. / min and kept warm for 1-4 hours to obtain a vanadium-doped nickel phosphide catalyst, i.e., a transition metal phosphide catalyst.

2. The method for preparing a transition metal phosphide catalyst according to claim 1, characterized in that: In step 1, the metal nickel salt is nickel nitrate or nickel chloride, and the metal vanadium salt is vanadium chloride.

3. The method for preparing a transition metal phosphide catalyst according to claim 1, characterized in that: The hydrothermal reaction temperature and reaction time in step 2 are 100-150° C. and 4-12 hours, respectively.

4. The method for preparing a transition metal phosphide catalyst according to claim 1, characterized in that: In step 2, the metal foam is one or more of nickel foam, copper foam, cobalt foam, titanium foam, and titanium mesh.

5. The method for preparing a transition metal phosphide catalyst according to claim 1, characterized in that: The pretreatment method of the metal foam in step 2 is to treat it with 0.5 mmol / L hydrochloric acid.

6. The method for preparing a transition metal phosphide catalyst according to claim 1, characterized in that: The phosphorus source used in step 3 is sodium hypophosphite.

7. The method for preparing a transition metal phosphide catalyst according to claim 1, characterized in that: In step 4, the inert gas is nitrogen or argon.

8. A transition metal phosphide catalyst prepared by any preparation method according to any one of claims 1 to 7, characterized in that: The catalyst uses metal foam as a carrier, and phosphide nanosheets with uniform morphology grow on the surface of the carrier.

9. Use of a transition metal phosphide catalyst prepared by any preparation method of claims 1 to 7 in electrocatalytic hydrogen evolution reaction, oxygen evolution reaction, sulfide ion oxidation reaction, two-electrode full electrolysis of water reaction or sulfide ion oxidation coupled hydrogen production, characterized in that: The transition metal phosphide catalyst serves as a catalyst for the electrocatalytic reaction and as an anode and cathode for the sulfur ion oxidation coupled hydrogen production system.

10. The use according to claim 9, characterized in that: After adding 2 mmol / L sulfuric acid to the electrolyte after the sulfide ion oxidation coupling hydrogen production, the generated precipitate is separated, washed and dried to obtain an elemental sulfur product.

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