Anion-cation co-doped NiMoO4 catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrocatalytic materials, and particularly relates to an anion-cation co-doped NiMoO4 catalyst as well as a preparation method and application thereof. According to the method, the modified NiMoO4 nanorod catalyst is obtained through co-doping of anions (S) and cations (Fe), the electronic structure of NiMoO4 is effectively adjusted through an anion-cation co-doping strategy, the catalytic performance of NiMoO4 is optimized, and a new thought and method are provided for design of a non-noble metal OER catalyst. The Fe-NiMoO4-S / NF catalyst and the preparation method thereof provided by the invention have a wide application prospect, are suitable for the fields of electrochemical water decomposition, alkaline seawater oxygen evolution reaction and the like, and have a relatively high practical application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and particularly relates to an anion-cation co-doped NiMoO4 catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Electrolysis of water is a clean and efficient way to produce hydrogen. The oxygen evolution reaction (OER), as a key half-reaction in the process of water electrolysis, seriously affects the overall efficiency. At present, noble metal-based catalysts (such as IrO2, RuO2) are widely used due to their excellent OER activity, but their high cost and low stability limit large-scale applications. Therefore, developing efficient, low-cost, and stable non-noble metal OER catalysts is the current research focus.

[0003] NiMoO4 has attracted attention due to its unique electronic structure and good catalytic performance, but its OER activity still needs to be improved. Summary of the Invention

[0004] In view of this, the present invention provides an anion-cation co-doped NiMoO4 catalyst, a preparation method thereof, and an application thereof. Through the anion-cation co-doping strategy, the electronic structure of the material can be effectively optimized, the charge transfer ability can be enhanced, and the catalytic activity can be improved.

[0005] The technical solution provided by the present invention is specifically a preparation method of an anion-cation co-doped NiMoO4 catalyst, including:

[0006] Using nickel foam NF as the substrate and aqueous solutions containing Ni and Mo as the precursor solutions to prepare a NiMoO4 / NF catalyst;

[0007] Doping and modifying the NiMoO4 / NF catalyst with Fe to obtain a Fe-NiMoO4 / N catalyst;

[0008] Modifying the Fe-NiMoO4 / N catalyst with S to obtain a sulfur-modified iron-doped NiMoO4 / NF catalyst.

[0009] Preferably, the preparation of the NiMoO4 / NF catalyst using nickel foam NF as the substrate and aqueous solutions containing Ni and Mo as the precursor solutions includes:

[0010] Step 1: Pretreat the nickel foam NF substrate;

[0011] Step 2: Prepare the precursor solutions: Dissolve Ni(NO3)2·6H2O in distilled water and stir to form solution A; dissolve Na2MoO4·2H2O in distilled water and stir to form solution B;

[0012] Step 3: Slowly add Solution A to Solution B and mix them thoroughly by stirring to obtain a mixed solution;

[0013] Step 4: Transfer the pretreated NF substrate and the mixed solution together to a reaction kettle and heat them;

[0014] Step 5: Cool the reactants to room temperature, wash and dry them;

[0015] Step 6: Calcinate the dried sample in a muffle furnace to obtain the NiMoO4 / NF catalyst.

[0016] Preferably, the pretreatment of the nickel foam NF substrate includes: successively cleaning the nickel foam NF substrate with acetone, 1M HCl solution, deionized water and ethanol under ultrasonic conditions.

[0017] Preferably, when transferring the pretreated NF substrate and the mixed solution together to a reaction kettle for heating, the heating temperature is 120 - 180 °C and the heating time is 6 hours.

[0018] Preferably, the dried sample is calcined in a muffle furnace at a heating rate of 2 °C / min at 300 - 500 °C.

[0019] Preferably, take a piece of NiMoO4 / NF catalyst, iron(III) nitrate nonahydrate Fe(NO3)3·9H2O, and one of ethylene glycol, glycerol or glycerin, add them together to a polytetrafluoroethylene high-pressure reaction kettle, seal it and react at 120 - 180 °C; after the reaction is completed, naturally cool it to room temperature, wash it repeatedly and dry it under vacuum to finally obtain the Fe-NiMoO4 / NF catalyst; where the concentration of the iron(III) nitrate nonahydrate Fe(NO3)3·9H2O solution is 0.1 - 0.5 mmol.

[0020] Preferably, for the S-modified Fe-NiMoO4 / N catalyst to obtain a sulfur-modified iron-doped NiMoO4 / NF catalyst, it includes: dissolving the S source in ethanol and forming a homogeneous solution by stirring; where the S source is one of thiourea, sodium sulfide or thioacetamide; the concentration of the S source homogeneous solution is 0.1 - 0.5 mmol;

[0021] Immerse the Fe-NiMoO4 / NF sample in the homogeneous solution, transfer it to a high-pressure reaction kettle and react at 120 - 180 °;

[0022] After the reaction is completed, naturally cool it to room temperature, wash and dry it to finally obtain the sulfur-modified iron-doped NiMoO4 / NF catalyst.

[0023] Second aspect, the present invention provides an anion-cation co-doped NiMoO4 catalyst prepared by the above preparation method. The catalyst has a nanorod array structure and is an anion-cation co-doped NiMoO4 catalyst, which is a nickel foam NF substrate and a one-dimensional nanorod Fe-NiMoO4-S / NF of Fe and S co-doped NiMoO4.

[0024] Third aspect, the present invention also provides the application of the anion-cation co-doped NiMoO4 catalyst. The catalyst is used in electrochemical water splitting and alkaline seawater oxygen evolution reaction.

[0025] The present invention provides an anion-cation co-doped NiMoO4 catalyst, its preparation method and application. The Fe-NiMoO4-S / NF catalyst with Fe and S co-doping in the present invention shows a significant performance improvement in the oxygen evolution reaction. In alkaline solution and simulated alkaline seawater, the catalyst realizes low overpotentials of 272 mV and 317 mV at a current density of 50 mA cm -2 respectively, showing excellent electrocatalytic activity. In addition, the catalyst also exhibits long-term stability and good cycling performance. Through the anion-cation co-doping strategy, the electronic structure of NiMoO4 can be effectively adjusted to optimize its catalytic performance, providing new ideas and methods for the design of non-precious metal OER catalysts.

[0026] The method of the present invention is simple, green and environmentally friendly, low-cost, easy to operate and control, and suitable for industrial continuous large-scale production. The raw materials involved in the present invention are environmentally friendly and inexpensive; with excellent performance, it is expected to achieve large-scale application.

[0027] The Fe-NiMoO4-S / NF catalyst provided by the present invention and its preparation method have broad application prospects, are applicable to fields such as electrochemical water splitting and alkaline seawater oxygen evolution reaction, and have high practical application value.

[0028] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the disclosure of the present invention. Brief Description of the Drawings

[0029] The drawings here are incorporated into the specification and constitute a part of this specification, showing the embodiments in line with the present invention, and are used together with the specification to explain the principles of the present invention.

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 Schematic diagram for the synthesis of Fe-NiMoO4-S / NF;

[0032] Figure 2 SEM and TEM images of NiMoO4 / NF;

[0033] Figure 3 SEM image of Fe-NiMoO4-S / NF;

[0034] Figure 4 TEM image of Fe-NiMoO4-S / NF;

[0035] Figure 5 XRD patterns of NiMoO4 / NF and Fe-NiMoO4-S / NF;

[0036] Figure 6 Linear sweep voltammetry (LSV) curves comparing the OER of Fe-NiMoO4-S / NF with other materials in alkaline solution;

[0037] Figure 7 Chronoamperometry curves of Fe-NiMoO4-S / NF in alkaline solution;

[0038] Figure 8 Linear sweep voltammetry (LSV) curves comparing the OER of Fe-NiMoO4-S / NF with other materials in simulated seawater solution;

[0039] Figure 9 Chronoamperometry curves of Fe-NiMoO4-S / NF in simulated seawater solution. Specific embodiments

[0040] The present invention will be further explained below in conjunction with specific embodiments, but it is not intended to limit the protection scope of the present invention.

[0041] 1. In order to further improve the OER activity of NiMoO4, first of all, this embodiment provides an anion-cation co-doped NiMoO4 catalyst and its preparation method. One-dimensional nanorods of Fe and S co-doped NiMoO4 (Fe-NiMoO4-S / NF) are prepared on a nickel foam (NF) substrate by a solvothermal method. This catalyst exhibits excellent catalytic performance in the oxygen evolution reaction. The co-doping of Fe and S can not only effectively regulate the morphology and electronic structure of the catalyst, but also optimize the adsorption behavior of OER intermediates, enhance charge transfer, increase the exposure of active sites, and thus improve the electrocatalytic activity.

[0042] Figure 1The synthesis process of Fe-NiMoO4-S / NF is shown, and commercial NF on the surface is selected as the conductive substrate. First, a high-density one-dimensional NiMoO4 nanorod (NiMoO4 / NF) is grown on the NF surface through hydrothermal reaction and calcination. Then, the synthesized NiMoO4 / NF is immersed in a Fe(NO3)3·9H2O solution at 120 °C for 2 hours to obtain Fe-doped NiMoO4 / NF (Fe-NiMoO4 / NF). Finally, S is doped into Fe-NiMoO4 / NF through thermal sulfidation reaction (Fe-NiMoO4-S / NF), thereby forming nanoparticles uniformly attached to the surface of the nanorods.

[0043] Preferably, an anion-cation co-doped NiMoO4 catalyst and its preparation method include the following steps:

[0044] Step 1: Substrate pretreatment: Cut nickel foam (NF) into a 1 cm × 2 cm sheet substrate, and immerse it in acetone, 1 M HCl solution, deionized water, and ethanol in sequence, and ultrasonically clean for 20 minutes respectively to remove surface impurities and oxides, and then dry it at 60 °C for later use.

[0045] Step 2: Preparation of precursor solution: Dissolve 0.7 g of Ni(NO3)2·6H2O in 20 mL of distilled water and stir for 30 minutes to form solution A. Separately, dissolve 0.6 g of Na2MoO4·2H2O in 20 mL of distilled water and stir for 30 minutes to form solution B.

[0046] Step 3: Preparation of NiMoO4 / NF catalyst: Slowly drop solution A into solution B, continue to stir for 10 minutes, then transfer it to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and react at 150 °C for 6 hours. After the reaction is completed, naturally cool to room temperature, wash it alternately with deionized water and ethanol 3 times, and dry it at 60 °C for 6 hours. Place the dried sample in a muffle furnace, heat it to 400 °C at a heating rate of 2 °C / min, and calcine for 1 hour to obtain a NiMoO4 nanomaterial supported on nickel foam (denoted as NiMoO4 / NF).

[0047] Step 4: Iron doping modification: Take one piece of the NiMoO4 / NF sample prepared in Step 3, add 0.2 mmol of ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and 30 mL of ethylene glycol to a 50 mL polytetrafluoroethylene autoclave, seal it, and react at 120 °C for 2 hours. After the reaction is completed, cool it to room temperature, wash it 3 times with ethanol and deionized water respectively to remove unreacted impurities, and then place it in a 60 °C vacuum oven and dry it for 12 hours to obtain an iron-doped NiMoO4 / NF catalyst (denoted as Fe-NiMoO4 / NF).

[0048] Step 6: S modification

[0049] Dissolve 2.5 mmol of thiourea (CH4N2S) in 40 mL of ethanol and stir for 30 minutes to form a homogeneous solution. Immerse the Fe-NiMoO4 / NF sample prepared in step 4 into this solution, transfer it to a 50 mL autoclave, and react at 150 °C for 5 hours. After the reaction, cool it naturally to room temperature, wash it alternately with deionized water and ethanol 3 times, and dry it at 60 °C for 6 hours to finally obtain a sulfur-modified iron-doped NiMoO4 / NF catalyst (denoted as Fe-NiMoO4-S / NF).

[0050] Note: In the above preparation method, the reagent dosage, reaction vessel size, and substrate size can be scaled up or down proportionally to meet the requirements of industrial production; the hydrothermal reaction temperature (120 - 180 °C), calcination temperature (300 - 500 °C), and dopant concentration (0.1 - 0.5 mmol) can be adjusted within the scope of the claims; ethylene glycol can be replaced with an equal volume of glycerol or glycerin, and thiourea can be replaced with sodium sulfide or thioacetamide to achieve a similar sulfur-modifying effect.

[0051] In the catalyst Fe-NiMoO4-S / NF of the present invention, the co-doping of Fe and S changes the electron distribution of NiMoO4, increases the exposure of active sites, and optimizes the adsorption of OER reaction intermediates. The doping of sulfur anions regulates the microstructure of the catalyst, and the unique core-shell array structure constructed by the encapsulation of nanoparticles on 1D nanorods helps to enhance the penetration of the electrolyte and establish an efficient channel for the release of H2 and O2 bubbles.

[0052] 2. The Fe-NiMoO4-S / NF prepared in this embodiment exhibits excellent OER activity, achieving low overpotentials of 272 and 317 mV at a current density of 50 mA cm -2 in alkaline solution and simulated alkaline seawater, respectively, and simultaneously having good cycling stability (after 24 h of cyclic reaction, its current density still maintains 95% of the initial value), showing excellent OER catalytic stability performance.

[0053] The Fe-NiMoO4-S / NF catalyst has a 1D nanoarray structure characteristic. Perform SEM and TEM tests on the nanorod array structure NiMoO4 / NF material: Figure 2 SEM and TEM photos of the nanorod array structure NiMoO4 / NF are shown. NiMoO4 shows a uniform and regular 1D nanorod structure deposited on the surface of NF. TEM analysis of a single nanorod shows that the diameter of NiMoO4 is about 150 nm..

[0054] Perform SEM test on the nanorod array structure Fe-NiMoO4-S / NF material: Figure 3SEM image of the Fe-NiMoO4-S / NF with a nanorod array structure. When both Fe and S are introduced, the morphology of the prepared Fe-NiMoO4-S / NF retains a stable one-dimensional nanorod structure, and some nanoparticles are decorated on the surface.

[0055] Perform TEM tests on the Fe-NiMoO4-S / NF material with a nanorod array structure: Figure 4 TEM image of the Fe-NiMoO4-S / NF with a nanorod array structure, showing that nanoparticles with a size of about 15 nm are tightly wrapped on the surface of the nanorod shell. This feature enhances the surface area and provides a wide reaction area.

[0056] Perform XRD tests on the NiMoO4 / NF and Fe-NiMoO4-S / NF materials: Figure 5 X-ray diffraction patterns of NiMoO4 / NF and Fe-NiMoO4-S / NF. The diffraction peaks of NiMoO4 / NF are in good agreement with the standard spectra of NiMoO4 (JCPDS No. 33-0948) and the NF substrate (JCPDS No. 04-085). Notably, no additional XRD peaks are observed for Fe-NiMoO4-S / NF, indicating that the crystal structure of NiMoO4 / NF remains unchanged after co-doping with Fe and S.

[0057] 3. Characterization and performance testing of the Fe-NiMoO4-S / NF catalyst in this embodiment:

[0058] 1) Structural characterization:

[0059] (a) Analyze the crystal structure of the sample using an X-ray diffractometer (XRD, Cu Kα radiation, 40 kV, 40 mA, scanning range 10°–90°);

[0060] (b) Determine the chemical states of surface elements by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha);

[0061] (c) Observe the micro-morphology using a scanning electron microscope (SEM, Zeiss Gemini 300) and a transmission electron microscope (TEM, JEOL JEM 2100), and perform elemental distribution mapping in combination with energy dispersive spectroscopy (EDS).

[0062] 2) Test the electrochemical performance of Fe-NiMoO4-S / NF:

[0063] The tests were carried out using a three - electrode system on a CHI760E electrochemical workstation: the prepared Fe - NiMoO4 - S / NF array electrode (0.5*0.5 cm) was directly used as the working electrode, a platinum mesh was used as the counter electrode, an Ag / AgCl electrode was used as the reference electrode, and the electrolytes were oxygen - saturated 1 mol / L KOH solution and simulated seawater electrolyte (1.0 M KOH + 0.5 M NaCl);

[0064] Prepare the electrolytes: Potassium hydroxide was used as the electrolyte, with a concentration of 1 mol / L. Simulated seawater was used as the electrolyte, with a potassium hydroxide concentration of 1 mol / L and a sodium chloride concentration of 0.5 mol / L.

[0065] Detect the electrocatalytic performance of the electrode: The Fe - NiMoO4 - S / NF electrocatalytic electrode with a nanorod array structure was placed in 1 mol / L KOH and simulated seawater solutions for measurement.

[0066] Using an electrochemical workstation, the prepared electrode to be tested was placed in an electrolyte solution that had been aerated with oxygen for about half an hour. First, cyclic voltammetry scanning was performed, and then linear sweep voltammetry scanning was carried out at a potential between - 0.2 V and 0.9 V with a scan rate controlled at 5 mV / s to test the electrochemical performance of the sample. Chronoamperometry was used to test the long - term stability (≥24 hours) of the catalyst at a constant potential;

[0067] Figure 6 The linear sweep voltammetry (LSV) shown was carried out in a 1 M KOH solution. To further study the enhancing effect of Fe and S co - doping on the OER activity of NiMoO4, the present invention also carried out comparative electrocatalytic tests using Fe - NiMoO4 / NF, NiMoO4 - S / NF, NiMoO4 / NF, RuO2 / NF, and NF as reference materials. At 50 mA cm -2 -2, the Fe - NiMoO4 - S / NF exhibited an extremely low overpotential of 272 mV, which was superior to NiMoO4 - S / NF (302 mV), Fe - NiMoO4 / NF (336 mV), NiMoO4 / NF (413 mV), RuO2 (327 mV), and bare NF (487 mV).

[0068] Figure 7 The chronoamperometry curve of the sample Fe - NiMoO4 - S / NF is shown. After 24 h of cyclic reaction, the Fe - NiMoO4 - S / NF material still maintained 95% of its initial current, confirming the excellent catalytic stability of the Fe - NiMoO4 - S / NF material in alkaline solution.

[0069] Figure 8The linear sweep voltammetry (LSV) shown was performed in a simulated seawater electrolyte (1.0 M KOH + 0.5 M NaCl) to evaluate its potential for hydrogen production through seawater electrolysis. Fe-NiMoO4-S / NF maintained the best OER activity in the simulated seawater electrolyte, reaching 50 mA cm -2 , with an overpotential of only 317 mV, significantly better than NiMoO4-S / NF (340 mV), Fe-NiMoO4 / NF (378 mV), and NiMoO4 / NF (456 mV) under the same conditions.

[0070] Figure 9 The chronoamperometry curve of the sample Fe-NiMoO4-S / NF is shown. The chronoamperometry test indicates that the initial current density of Fe-NiMoO4-S / NF remains stable within 24 h. Therefore, Fe-NiMoO4-S / NF also exhibits excellent OER stability in the simulated seawater electrolyte.

[0071] Other embodiments of the present invention will be readily apparent to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention, which follow the general principles of the invention and include common general knowledge or conventional technical means in the technical field not disclosed herein. The specification and examples are only to be considered exemplary, and the true scope and spirit of the invention are pointed out by the following claims.

[0072] It should be understood that the present invention is not limited to what has been described above and can be modified and changed without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A preparation method of an anion-cation co-doped NiMoO4 catalyst, characterized in that, Including: Using nickel foam NF as the substrate and aqueous solutions containing Ni and Mo as the precursor solutions to prepare the NiMoO4 / NF catalyst; Fe-doping modified NiMoO4 / NF catalyst to obtain the Fe-NiMoO4 / N catalyst; S-modifying the Fe-NiMoO4 / N catalyst to obtain the sulfur-modified iron-doped NiMoO4 / NF catalyst.

2. The preparation method of an anion-cation co-doped NiMoO4 catalyst according to claim 1, characterized in that, The preparation of the NiMoO4 / NF catalyst using nickel foam NF as the substrate and aqueous solutions containing Ni and Mo as the precursor solutions includes: Step 1: Pretreat the nickel foam NF substrate; Step 2: Prepare the precursor solutions: Dissolve Ni(NO3)2·6H2O in distilled water and stir to form solution A; dissolve Na2MoO4·2H2O in distilled water and stir to form solution B; Step 3: Slowly add solution A to solution B and mix well by stirring to obtain a mixed solution; Step 4: Transfer the pretreated NF substrate and the mixed solution to a reaction kettle and heat; Step 5: Cool the reactants to room temperature, wash and dry; Step 6: Calcinate the dried sample in a muffle furnace to obtain the NiMoO4 / NF catalyst.

3. The preparation method of an anion-cation co-doped NiMoO4 catalyst according to claim 2, characterized in that, The pretreatment of the nickel foam NF substrate includes: successively cleaning the nickel foam NF substrate with acetone, 1M HCl solution, deionized water and ethanol under ultrasonic conditions.

4. The preparation method of an anion-cation co-doped NiMoO4 catalyst according to claim 2, characterized in that, The temperature for heating when transferring the pretreated NF substrate and the mixed solution to the reaction kettle is 120 - 180 °C, and the heating time is 6 hours.

5. The preparation method of an anion-cation co-doped NiMoO4 catalyst according to claim 2, characterized in that, The dried sample is calcined in a muffle furnace at a heating rate of 2 °C / min at 300 - 500 °C.

6. The preparation method of an anion-cation co-doped NiMoO4 catalyst according to claim 1, characterized in that, Take a piece of NiMoO4 / NF catalyst, ferric nitrate nonahydrate Fe(NO3)3·9H2O, and one of ethylene glycol, glycerol or glycerin, add them to a polytetrafluoroethylene high-pressure reaction kettle, seal it and react at 120 - 180 °C; after the reaction, naturally cool to room temperature, wash repeatedly and dry under vacuum to finally obtain the Fe-NiMoO4 / NF catalyst; the concentration of the ferric nitrate nonahydrate Fe(NO3)3·9H2O solution is 0.1 - 0.5 mmol.

7. The preparation method of an anion-cation co-doped NiMoO4 catalyst according to claim 1, characterized in that, The S-modifying the Fe-NiMoO4 / N catalyst to obtain the sulfur-modified iron-doped NiMoO4 / NF catalyst includes: dissolving the S source in ethanol and stirring to form a homogeneous solution; the S source is one of thiourea, sodium sulfide or thioacetamide; the concentration of the S-source homogeneous solution is 0.1 - 0.5 mmol; Immerse the Fe-NiMoO4 / NF sample in the homogeneous solution, transfer it to a high-pressure reaction kettle and react at 120 - 180 °; After the reaction, naturally cool to room temperature, wash and dry to finally obtain the sulfur-modified iron-doped NiMoO4 / NF catalyst.

8. The anion-cation co-doped NiMoO4 catalyst prepared by the preparation method according to any one of claims 1-7, characterized in that, The catalyst has a nanorod array structure and is an anion-cation co-doped NiMoO4 catalyst, which is a one-dimensional nanorod Fe-NiMoO4-S / NF of NiMoO4 co-doped with Fe and S on the nickel foam NF substrate.

9. Use of the anion-cation co-doped NiMoO4 catalyst according to claim 8, characterized in that, The catalyst is used in electrochemical water splitting and alkaline seawater oxygen evolution reaction.

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