Preparation method and application of monatomic doped ferronickel-based oxygen evolution electrocatalyst

Abstract

The invention relates to the technical field of oxygen evolution catalysts, in particular to a preparation method and application of a monatomic doped ferronickel-based oxygen evolution electrocatalyst, and the preparation method comprises the following steps: growing a NiFe-LDH nanosheet substrate on the surface of a carbon-based carrier in situ through a hydrothermal method, and then precisely regulating and controlling transition metal monatomic doping in combination with an electrochemical deposition technology. The monatomic doped ferronickel-based oxygen evolution electrocatalyst prepared by the preparation method has the advantages of excellent catalytic activity, low cost, greenness and no toxicity.

Description

Technical Field

[0001] The present invention relates to the technical field of oxygen evolution catalysts, and particularly relates to a preparation method and application of a single-atom doped nickel-iron-based oxygen evolution electrocatalyst. Background Art

[0002] With the global energy structure transforming towards cleaner and lower-carbon, the electrochemical water splitting technology for hydrogen production has become one of the core paths for renewable energy storage and utilization due to its zero-carbon emission characteristics. However, the large-scale application of this technology is limited by the high overpotential of the anodic oxygen evolution reaction (OER) and the slow kinetic process of four-electron transfer. There is an urgent need for efficient catalysts to reduce energy consumption.

[0003] The current research on oxygen evolution catalysts mainly focuses on the following two types of materials: The first type is noble metal oxides represented by iridium dioxide (IrO2) and ruthenium dioxide (RuO2). As the currently most excellent commercial OER catalysts, their industrial applications are severely restricted due to the extremely low reserves and high prices of noble metals. The second type is transition metal-based (such as Ni, Fe, Co, Mn) catalysts, mainly including oxides, hydroxides, sulfides, and layered double hydroxides (LDH), etc. These catalysts have lower costs but also have defects such as easy reconstruction leading to a sudden drop in stability and low utilization rate of active sites.

[0004] Among them, NiFe-LDHs catalysts have received extensive research attention due to their good catalytic activity. However, NiFe-LDHs have poor electrical conductivity and their active sites cannot be fully exposed, resulting in a large gap in catalytic activity compared with noble metal-based catalysts. To address the above problems, an effective improvement method is to perform noble metal single-atom doping, which can not only maximize the utilization rate of noble metal atoms but also reduce costs. For example, the invention patent with the publication number CN117089885A discloses an iridium-doped nickel-iron-based composite catalyst and its preparation method and application. The preparation method includes the following steps: After stirring and mixing a nickel source, an iron source, an iridium source, and a polyhexabenzocoronene network material, calcination treatment is carried out to obtain the iridium-doped nickel-iron-based composite catalyst.

[0005] The above method can achieve noble metal single-atom doping through high-temperature calcination, but there are still some defects: 1. During high-temperature calcination, the layered structure of NiFe LDH will collapse at high temperatures, losing its high specific surface area, and thus reducing the active sites for catalytic reactions; 2. High temperatures will cause noble metals to volatilize or sinter, and excessive use of noble metals is often required during preparation to maintain performance, greatly increasing the preparation cost. Summary of the Invention

[0006] To solve the above problems, the present invention provides a preparation method and application of a single-atom doped nickel-iron-based oxygen evolution electrocatalyst. The single-atom doped nickel-iron-based oxygen evolution electrocatalyst prepared by the preparation method has the advantages of excellent catalytic activity, low cost, and being green and non-toxic.

[0007] To achieve the above invention object, the present invention is realized through the following technical solutions: In the first aspect, the present invention provides a preparation method of a single-atom doped nickel-iron-based oxygen evolution electrocatalyst, which is characterized by including the following steps: S1. Disperse a nickel source and an iron source in a solvent in proportion until completely dissolved to obtain a uniform metal salt solution; S2. Add a precipitating agent to the metal salt solution, and after dispersion treatment, obtain a first suspension; S3. Immerse a carbon-based carrier in a mixed solution of concentrated nitric acid and water to obtain a carbon-based carrier with hydrophilic treatment; S4. Immerse the carbon-based carrier with hydrophilic treatment in the first suspension, and in-situ grow a nickel-iron-based active phase on the carbon-based carrier with hydrophilic treatment through a hydrothermal reaction. After washing, centrifuging, and drying at a constant temperature, obtain a carbon-based carrier with a first precursor attached; S5. Add a transition metal source and a strongly acidic solution to a solvent, and after dispersion treatment, obtain a second suspension; S6. Use the carbon-based carrier with the first precursor attached as a working electrode, and immerse it together with an inert counter electrode and a reference electrode in the second suspension. Through electrochemical deposition, achieve atomic-level dispersion of transition metal single atoms on the carbon-based carrier with the first precursor attached to obtain a carbon-based carrier with a second precursor attached; S7. Perform drying treatment on the carbon-based carrier with the second precursor attached to obtain a transition metal single-atom doped nickel-iron-based oxygen evolution electrocatalyst.

[0008] The present invention first in-situ grows a NiFe-LDH nanosheet substrate on the surface of a carbon-based carrier through a hydrothermal method, and then precisely regulates the doping of transition metal single atoms in combination with an electrochemical deposition technique. In the prior art, the hydrothermal method is often combined with calcination and solvothermal methods to prepare a single-atom doped nickel-iron-based oxygen evolution electrocatalyst. However, high-temperature calcination easily leads to the loss of active sites, and the dependence of the solvothermal method on organic solvents limits its application scenarios. To solve the above problems, the present invention uses an electrodeposition method to achieve atomic-level dispersion of noble metals under mild conditions. Moreover, since the electrodeposition method requires the precursor to have good conductivity and high uniformity of attachment to the substrate, it is not usually a conventional choice combined with the hydrothermal method. The present invention enhances the interfacial binding force of the material through acid etching treatment of the substrate, and cooperates with the processes of alternating washing and low-temperature drying to effectively maintain the porous morphology and structural stability of the catalyst, providing an ideal site for the subsequent anchoring of transition metals. The performance of the catalyst prepared by the two-step synergy of hydrothermal-electrochemistry is significantly superior to that of the traditional calcination doping system.

[0009] Preferably, in the step S1, the molar ratio of the nickel source to the iron source is (1~3):1.

[0010] Preferably, in the step S1, the total concentration of metal ions in the metal salt solution is 0.1~0.3M.

[0011] Preferably, in the step S1, the dispersion method is ultrasonic dispersion, and the dispersion duration is 30~60min.

[0012] Preferably, in the step S2, the precipitating agent includes urea.

[0013] Preferably, in the step S2, the concentration of urea is 0.3~0.9M.

[0014] Preferably, in the step S2, the dispersion method is ultrasonic dispersion, and the dispersion duration is 10~30min.

[0015] Preferably, in the step S3, the carbon-based carrier includes carbon cloth.

[0016] Preferably, in the step S3, the volume ratio of concentrated nitric acid to water is 1:(10~20).

[0017] Preferably, in the step S3, the soaking time is 6~12h.

[0018] Using concentrated nitric acid to oxidize the carbon cloth and introducing high-density carboxyl / hydroxyl functional groups can effectively enhance the conductivity of the substrate and the chemical bonding force with LDH, providing a basis for the subsequent electrodeposition process.

[0019] Preferably, in the step S4, the conditions for the hydrothermal reaction are as follows: the heating time is 6 to 10 h, and the heating temperature is 120 to 150 °C.

[0020] Preferably, in the step S4, the conditions for washing and centrifuging are as follows: wash and centrifuge three times each with deionized water and ethanol.

[0021] Preferably, in the step S4, the conditions for constant-temperature drying are as follows: the constant-temperature drying time is 10 to 12 h, and the constant-temperature drying temperature is 60 °C.

[0022] Through fractional washing and low-temperature vacuum drying, the porous structure of the LDH nanosheets can be effectively maintained, further providing a basis for the subsequent electrodeposition process.

[0023] Preferably, in the step S5, the transition metal source includes iridium salt. More preferably, the concentration of the iridium salt is not more than 0.001 M.

[0024] Benefiting from the rich active sites exposed by the layered structure of this application, a very low concentration of iridium salt can effectively improve the catalytic activity, greatly reduce the dependence on precious metals in the catalyst product, and significantly improve the utilization rate of precious metals.

[0025] Preferably, in the step S5, the strong acidic solution includes concentrated hydrochloric acid. More preferably, the volume ratio of concentrated hydrochloric acid to the solvent is 1:(10 - 20).

[0026] Preferably, in the step S5, the dispersion method is ultrasonic dispersion, and the dispersion duration is 30 to 60 min.

[0027] Preferably, in the step S6, the inert counter electrode includes a carbon rod, and the reference electrode includes a saturated calomel electrode.

[0028] Preferably, in the step S6, the electrochemical deposition includes the following steps: connect the working electrode, the inert counter electrode, and the reference electrode to an electrochemical workstation respectively, and apply a voltage. More preferably, the conditions for applying the voltage are as follows: the voltage range is -1.0 to -1.5 V, and the application time is 5 to 30 min.

[0029] Since the precursor prepared by the hydrothermal method has poor conductivity and phase change or structural relaxation may occur during the electrodeposition process, it is necessary to precisely control parameters such as the voltage range and the pressure application time during electrodeposition to prevent over-deposition from clogging pores or under-deposition from resulting in incomplete coverage, which affects the performance.

[0030] Preferably, in the step S7, the conditions for the drying treatment are as follows: the drying time is 10 to 12 h, and the drying temperature is 60 °C.

[0031] In a second aspect, the present invention also provides an application of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst prepared by the preparation method as described above in the field of electrochemical water splitting for hydrogen production.

[0032] The beneficial effects of the present invention are as follows: 1. This application adopts a two-step synergistic strategy of hydrothermal-electrochemical method to achieve atomic-level dispersion of noble metals under mild conditions. Compared with the traditional high-temperature calcination method, it can avoid the structural collapse and loss of active sites caused by high temperature, and at the same time, there is no need to use toxic organic reagents in the solvothermal method. Therefore, the single-atom doped nickel-iron-based oxygen evolution electrocatalyst prepared by the preparation method provided in this application exhibits more excellent oxygen evolution reaction kinetic characteristics and has the advantage of being green and non-toxic.

[0033] 2. This application uses non-noble metals Ni / Fe as the main body, only requires trace amounts of noble metal single-atom doping (low loading), and the hydrothermal-electrochemical two-step method has low requirements for process equipment and does not require complex post-treatment, making the preparation method of this application have the advantages of good batch repeatability and low cost. Description of the Drawings

[0034] Figure 1 XRD pattern of Example 1 of the present invention; Figure 2 SEM image of Example 1 of the present invention; Figure 3 OER performance graphs of Example 1 and Comparative Example 1 of the present invention; Figure 4 Current-voltage characteristic (I-V) curve of Example 1 of the present invention for AEMWEs. Detailed Embodiments

[0035] The present invention will be further described below in conjunction with the drawings of the specification and specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0036] Example 1 S1. Dissolve nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 4.36 g) and iron nitrate nonahydrate (Fe(NO3)3·9H2O, 2.02 g) in 80 mL of deionized water according to a molar ratio of Ni:Fe = 3:1. After magnetic stirring for 30 minutes, solution A is obtained, wherein the total concentration of metal ions is 0.25 M; S2. Add urea (4.80 g, 0.8 M) to Solution A and disperse it by ultrasonication for 20 minutes to obtain Solution B; S3. Immerse the carbon cloth in a concentrated nitric acid / water (5 mL / 75 mL, volume ratio 1:15) mixture, perform acidification treatment for 6 hours, and rinse it 3 times with deionized water to obtain Carbon Cloth A; S4. Transfer Solution B to a 100 mL Teflon hydrothermal reactor, insert Carbon Cloth A, seal it, heat it at 140 °C for 8 hours, take out Carbon Cloth A after natural cooling, wash it 3 times by alternating centrifugation with deionized water and ethanol to obtain Carbon Cloth B, and then dry Carbon Cloth B at 60 °C for 12 hours to obtain Carbon Cloth C; S5. Dissolve iridium(IV) chloride (IrCl4, 0.016 g) and concentrated hydrochloric acid (0.5 mL) in 50 mL of deionized water to prepare Solution C with a concentration of 0.001 M; S6. Clamp Carbon Cloth C as the working electrode, use a carbon rod as the counter electrode, and a saturated calomel electrode as the reference electrode, and immerse them together in Solution C; then connect the carbon rod, saturated calomel electrode, and working electrode to a Chenhua workstation respectively, and apply a voltage of 15 min at -1.2 V vs SCE (i.e., under the condition that the potential relative to the standard calomel electrode is -1.2 V) to obtain Carbon Cloth D; S7. After rinsing Carbon Cloth D with deionized water, dry it at 60 °C for 12 hours to finally obtain the Ir@NiFe LDH catalyst.

[0037] Example 2 S1. Dissolve nickel nitrate hexahydrate (3.49 g) and iron(III) nitrate nonahydrate (1.62 g) in 80 mL of deionized water according to a molar ratio of Ni:Fe = 3:1, and obtain Solution A after magnetic stirring for 30 minutes, where the total concentration of metal ions is 0.2 M; S2. Add urea (4.32 g, 0.9 M) to Solution A and disperse it by ultrasonication for 30 minutes to obtain Solution B; S3. Immerse the carbon cloth in a concentrated nitric acid / water (3 mL / 60 mL, volume ratio 1:20) mixture, perform acidification treatment for 6 hours, and rinse it 3 times with deionized water to obtain Carbon Cloth A; S4. Transfer Solution B to a 100 mL Teflon hydrothermal reactor, insert Carbon Cloth A, seal it, heat it at 120 °C for 10 hours, take out Carbon Cloth A after natural cooling, wash it 3 times by alternating centrifugation with deionized water and ethanol to obtain Carbon Cloth B, and then dry Carbon Cloth B at 60 °C for 12 hours to obtain Carbon Cloth C; S5. Dissolve iridium(IV) chloride (0.016 g) and concentrated hydrochloric acid (0.5 mL) in 50 mL of deionized water to prepare Solution C with a concentration of 0.001 M; S6. Clamp the carbon cloth C as the working electrode, use a carbon rod as the counter electrode, and a saturated calomel electrode as the reference electrode. Immerse them together in solution C; then connect the carbon rod, saturated calomel electrode, and working electrode to the Chenhua workstation respectively, and apply a voltage of -1.0 V vs SCE for 5 min to obtain carbon cloth D; S7. After rinsing the carbon cloth D with deionized water, dry it at 60 °C for 12 h to finally obtain the Ir@NiFe LDH catalyst.

[0038] Example 3 S1. Dissolve nickel nitrate hexahydrate (2.18 g) and iron nitrate nonahydrate (1.01 g) in 50 mL of deionized water according to a molar ratio of Ni:Fe = 3:1. After magnetic stirring for 30 min, obtain solution A, where the total concentration of metal ions is 0.2 M; S2. Add urea (1.80 g, 0.6 M) to solution A and ultrasonically disperse for 30 min to obtain solution B; S3. Immerse the carbon cloth in a concentrated nitric acid / water (3 mL / 60 mL, volume ratio 1:20) mixture, perform acidification treatment for 8 h, and rinse with deionized water 3 times to obtain carbon cloth A; S4. Transfer solution B to a 100 mL polytetrafluoroethylene hydrothermal autoclave, insert carbon cloth A and seal it. Heat it at 120 °C for 8 h. After natural cooling, take out carbon cloth A, wash it alternately with deionized water and ethanol by centrifugation 3 times to obtain carbon cloth B, and then dry carbon cloth B at 60 °C for 12 h to obtain carbon cloth C; S5. Dissolve iridium(IV) chloride (0.016 g) and concentrated hydrochloric acid (0.5 mL) in 50 mL of deionized water to prepare a solution C with a concentration of 0.001 M; S6. Clamp the carbon cloth C as the working electrode, use a carbon rod as the counter electrode, and a saturated calomel electrode as the reference electrode. Immerse them together in solution C; then connect the carbon rod, saturated calomel electrode, and working electrode to the Chenhua workstation respectively, and apply a voltage of -1.0 V vs SCE for 30 min to obtain carbon cloth D; S7. After rinsing the carbon cloth D with deionized water, dry it at 60 °C for 12 h to finally obtain the Ir@NiFe LDH catalyst.

[0039] Example 4 S1. Dissolve nickel nitrate hexahydrate (1.94 g) and iron nitrate nonahydrate (1.35 g) in 50 mL of deionized water according to a molar ratio of Ni:Fe = 2:1. After magnetic stirring for 30 min, obtain solution A, where the total concentration of metal ions is 0.2 M; S2. Add urea (1.80 g, 0.6 M) to solution A and ultrasonically disperse for 30 min to obtain solution B; S3. Immerse the carbon cloth in a mixture of concentrated nitric acid / water (3 mL / 60 mL, volume ratio 1:20), perform acidification treatment for 8 hours, and rinse with deionized water 3 times to obtain carbon cloth A; S4. Transfer solution B to a 100 mL polytetrafluoroethylene hydrothermal autoclave, insert carbon cloth A, seal it, heat at 120 °C for 10 hours, take out carbon cloth A after natural cooling, wash it alternately with deionized water and ethanol by centrifugation 3 times to obtain carbon cloth B, and then dry carbon cloth B at 60 °C for 12 hours to obtain carbon cloth C; S5. Dissolve iridium(IV) chloride (0.016 g) and concentrated hydrochloric acid (0.5 mL) in 50 mL of deionized water to prepare solution C with a concentration of 0.001 M; S6. Clamp carbon cloth C as the working electrode, use a carbon rod as the counter electrode, and a saturated calomel electrode as the reference electrode, and immerse them together in solution C; then connect the carbon rod, saturated calomel electrode, and working electrode to a Chenhua workstation respectively, apply a voltage of -1.5 V vs SCE for 25 min to obtain carbon cloth D; S7. After rinsing carbon cloth D with deionized water, dry it at 60 °C for 12 hours to finally obtain the Ir@NiFe LDH catalyst.

[0040] Comparative Example 1 S1. Dissolve nickel nitrate hexahydrate (4.36 g) and iron(III) nitrate nonahydrate (2.02 g) in 80 mL of deionized water according to a molar ratio of Ni:Fe = 3:1, and stir magnetically for 30 minutes to obtain solution A, where the total metal ion concentration is 0.25 M; S2. Add urea (4.80 g, 0.8 M) to solution A and disperse it by ultrasonic treatment for 20 minutes to obtain solution B; S3. Transfer solution B to a 100 mL polytetrafluoroethylene hydrothermal autoclave, insert carbon cloth, seal it, heat at 140 °C for 8 hours, take out the carbon cloth after natural cooling, wash it alternately with deionized water and ethanol by centrifugation 3 times, and then dry it at 60 °C for 12 hours to obtain precursor A; S4. Take precursor A (200 mg) and mix it with iridium(IV) chloride (0.016 g) in 50 mL of deionized water, stir ultrasonically for 15 min, centrifuge once, and then dry it at 60 °C for 12 hours to obtain precursor B. Add precursor B to a tubular furnace and pyrolyze it at 300 °C for 2 h in a N2 atmosphere. After cooling to room temperature, obtain the target catalyst NiFe LDH - high-temperature calcined Ir.

[0041] Application Example Using Example 1 as the anode catalyst and commercial Pt / C as the cathode catalyst, an anion exchange membrane water electrolyzer (AEMWE) was assembled to evaluate the performance of Example 1 under actual water electrolysis conditions, and the results are as Figure 4 shown.

[0042] Performance test Figure 1 This is the XRD pattern of Example 1 of the present invention. The XRD diffraction pattern was used to detect the structure of the product obtained in Example 1 of the present invention, and the characteristic peaks corresponding to the standard NiFe LDH card were obtained, and there were no characteristic peaks of Ir metal, which proved that the catalyst sample prepared by the method of the present invention was an Ir single-atom doped NiFe LDH electrocatalyst.

[0043] Figure 2 This is the SEM image of Example 1 of the present invention. The SEM image was used to observe the morphology of the product obtained in Example 1 of the present invention. It can be seen that the catalyst prepared by the method of the present invention presents a nanoflower morphology and has a high exposed specific surface area.

[0044] Figure 3 This is the OER performance diagram of Example 1 and Comparative Example 1 of the present invention. By comparing the OER performance of high-temperature doped Ir noble metal (NiFe LDH-high temperature calcined Ir), it can be seen that the catalyst obtained in Example 1 of the present invention has more excellent OER activity under alkaline conditions.

[0045] Figure 4 is the current-voltage characteristic (I-V) curve of Example 1 for AEMWEs, which reached a high current density of 2 A·cm at 2.0 V -2 showing broad prospects for industrial application.

Claims

1. A preparation method of a single-atom doped nickel-iron-based oxygen evolution electrocatalyst, characterized in that It includes the following steps: S1. Disperse the nickel source and iron source in a solvent in proportion until completely dissolved to obtain a uniform metal salt solution; S2. Add a precipitating agent to the metal salt solution, and after dispersion treatment, obtain a first suspension; S3. Immerse the carbon-based support in a mixed solution of concentrated nitric acid and water to obtain a hydrophilically treated carbon-based support; S4. Immerse the hydrophilically treated carbon-based support in the first suspension, and in-situ grow the nickel-iron-based active phase on the hydrophilically treated carbon-based support through a hydrothermal reaction. After constant-temperature heating, washing and centrifuging, and constant-temperature drying, obtain a carbon-based support with a first precursor attached; S5. Add a transition metal source and a strongly acidic solution to a solvent, and after dispersion treatment, obtain a second suspension; S6. Using the carbon-based support with the first precursor attached as the working electrode, immerse it together with an inert counter electrode and a reference electrode in the second suspension, and achieve atomic-level dispersion of the transition metal on the carbon-based support with the first precursor attached through electrochemical deposition to obtain a carbon-based support with a second precursor attached; S7. Perform a drying and curing treatment on the carbon-based support with the second precursor attached to obtain a transition metal single-atom doped nickel-iron-based oxygen evolution electrocatalyst.

2. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, wherein In the step S1, the molar ratio of the nickel source to the iron source is (1-3):

1.

3. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, characterized in that, In the step S2, the precipitating agent includes urea.

4. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, characterized in that, In the step S3, the carbon-based support includes carbon cloth.

5. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, wherein, In the step S4, the conditions of the hydrothermal reaction are: the heating time is 6-10 h, and the heating temperature is 120-150 °C.

6. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, wherein, In the step S5, the transition metal source includes iridium salt.

7. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, characterized in that In the step S6, the inert counter electrode includes a carbon rod, and the reference electrode includes a saturated calomel electrode.

8. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 1, wherein, In the step S6, the electrochemical deposition includes the following steps: Connect the working electrode, the inert counter electrode, and the reference electrode to an electrochemical workstation respectively and apply a voltage.

9. The preparation method of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst according to claim 8, characterized in that The conditions for applying the voltage are: the voltage range is -1.0 to -1.5 V, and the application time is 5-30 min.

10. Application of the single-atom doped nickel-iron-based oxygen evolution electrocatalyst prepared by the preparation method according to any one of claims 1-9 in the aspect of electrochemical water splitting for hydrogen production.

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