CN113957471A

CN113957471A - Preparation method of nickel-iron double-layer hydroxide for efficiently electrolyzing water

Info

Publication number: CN113957471A
Application number: CN202111087945.8A
Authority: CN
Inventors: 周学成; 颜晓红
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2021-09-16
Filing date: 2021-09-16
Publication date: 2022-01-21

Abstract

The invention belongs to the field of electrocatalysis, and particularly relates to a preparation method of nickel-iron double-layer hydroxide with a nanosheet stacking structure. The invention takes nickel nitrate hexahydrate, urea, ammonium fluoride and ferric nitrate nonahydrate aqueous solutions with different molar masses as raw materials, and prepares the nickel-iron double-layer hydroxide catalyst through one-time hydrothermal reaction. The carbon cloth is used as a substrate and the morphology of the nano-sheets is beneficial to improving the electron transmission capability of the double-layer hydroxide (LDH) and is beneficial to exposing active sites. The nickel-iron-based catalyst is used as an OER catalyst for water electrolysis, has smaller overpotential and low Tafel slope, has excellent electrocatalytic OER performance under the synergistic action of nickel and iron, has great significance for solving the energy crisis and improving the global environment problem, is simpler and more convenient in preparation process, has very rich earth reserves of nickel and iron, and has quite good application prospect in some battery fields.

Description

Preparation method of nickel-iron double-layer hydroxide for efficiently electrolyzing water

Technical Field

The invention belongs to the field of electrocatalysis, and particularly relates to a preparation method of a nickel-iron double-layer hydroxide with a nanosheet stacking structure.

Background

One of the key challenges throughout the world today is to establish a global-scale sustainable hydrogen energy system to address global energy crisis, climate change and environmental issues. Electrocatalytic water splitting reactions are the most attractive green technology for providing hydrogen and oxygen through cathodic Hydrogen Evolution Reactions (HER) and anodic Oxygen Evolution Reactions (OER), where efficient electrocatalysts are the key to ensuring such energy conversion. Noble metals (ruthenium, platinum, etc.) are currently the most excellent catalysts for electrocatalytic decomposition of water, but their widespread use in large-scale hydrogen production is still limited by high cost and low earth reserves. Under the condition, development of non-noble metal and high-activity electrocatalyst materials to improve the performance of the electrocatalytic OER and reduce the overpotential thereof becomes a research hotspot. Catalysts rich in earth reserves, particularly transition metal hydroxides, transition metal chalcogenides, oxides, carbides, nitrides, phosphides, and the like, have been extensively studied in recent decades, some of which do exhibit satisfactory catalytic performance. Layered Double Hydroxides (LDHs) are particularly specified as a large class of inorganic layered compounds, which are essentially characterized by a large number of anionic intercalation layers, usually considered as anionic layered compounds, due to the positive charges of the layers. Although studies of LDHs have been initiated very early, until 2002 researchers have not studied LDHs for the first time for their application as electrode materials for electrochemical energy storage. Studies on the electrochemical application of LDHs have since begun to be carried out on a large scale.

Layered Double Hydroxides (LDHs) have good electrical conductivity and excellent chemical stability, and are ideal electrode materials with high performance and low cost. The preparation method comprises a coprecipitation method, a hydrothermal synthesis method, an electrochemical deposition method and the like. Due to the advantages of large specific surface area, large interlayer spacing, convenience for electrolyte permeation and ion diffusion and the like, the LDH becomes an electrode material of an electrocatalytic OER catalyst which is popular in recent years. Currently, the bimetal composite strategy is widely used for modifying the electronic performance of the layered hydroxide, and the catalytic performance is improved by adjusting the valence state of elements through the synergistic effect of bimetal and generating defects at the same time. NiFe-LDH is the most promising catalyst material among the numerous layered double hydroxides because of the good synergy of nickel and iron ions. In view of this, the present invention provides a simple synthesis method for synthesizing a double metal hydroxide having a 2D nanosheet stacking structure, so as to reduce the overpotential of the electrocatalytic OER and improve the catalytic performance thereof.

Disclosure of Invention

The invention aims to provide a preparation method of a double-metal hydroxide with a 2D nanosheet stacked structure and excellent OER performance.

The invention adopts the following specific technical scheme:

a preparation method of nickel-iron double-layer hydroxide for electrocatalytic OER comprises the following steps:

(1) pretreatment of the carbon cloth: taking a piece of carbon cloth, cutting the piece of carbon cloth into blocks, wherein the size of each block is 3cm multiplied by 4 cm; and respectively carrying out ultrasonic cleaning in acetone, distilled water and absolute ethyl alcohol for 30 min. The purpose is to remove impurities on the surface of the carbon cloth. And (3) placing the carbon cloth subjected to the cleaning treatment in a nitric acid solution, wherein the mass percentage concentration of the nitric acid solution is 40%, and carrying out oxidation treatment under an ultrasonic condition for 30 min. Aims to improve the wettability of the carbon cloth, reduce the contact angle and improve the surface energy of a matrix.

(2) Preparing nickel-iron double-layer hydroxide: respectively weighing nickel nitrate hexahydrate, urea, ammonium fluoride and ferric nitrate nonahydrate into a glass beaker, weighing deionized water by using a measuring cylinder, and adding the deionized water into the beaker, wherein the proportion of the nickel nitrate hexahydrate, the urea, the ammonium fluoride, the ferric nitrate nonahydrate and the deionized water is 4 mmol: 20 mmol: 8 mmol: 0.55-2 mmol: 80 mL. Dissolving into brown yellow uniform solution by magnetic stirring at room temperature for 30 min. Transferring the mixed solution into a stainless steel high-pressure hydrothermal reaction kettle, soaking the carbon cloth treated in the step (1) in the reaction kettle, screwing a cover, and putting the hydrothermal reaction kettle into an oven to react for 8 hours at 120 ℃;

(3) and after the hydrothermal reaction is finished, cooling the hydrothermal reaction kettle to room temperature, taking out the carbon cloth loaded with the product, respectively washing the carbon cloth with deionized water and absolute ethyl alcohol for 3-5 times, and performing vacuum drying for 3 hours in a vacuum drying oven at the temperature of 60 ℃ for later use.

The iron nitrate nonahydrate in different molar weights in the step (2) is 0.55-2 mmol, the molar ratio of nickel to iron is different, and the catalytic OER performance is also different. When the proportion of nickel nitrate hexahydrate, urea, ammonium fluoride, ferric nitrate nonahydrate and deionized water is 4 mmol: 20 mmol: 8 mmol: 1 mmol: 80mL, the best electrocatalytic OER performance is obtained.

The NiFe-LDH/CC obtained by the method has a 2D nanosheet stacking structure, is beneficial to electron transfer and precipitation of oxygen products, and the large specific surface area of the nanosheet is also beneficial to improvement of catalytic performance and electrochemical stability, and complex means such as heat treatment and the like are not needed in the preparation process.

The NiFe-LDH/CC electrocatalyst obtained in the invention shows excellent electrochemical performance, and the current density of the catalyst reaches 50mA/cm in the electrocatalytic OER reaction through tests²The overpotential at this time was only 327mV, far exceeding the OER performance of commercial ruthenium oxide and oxiranes. Its charge transfer resistance (Rct) is also minimal, indicating its faster charge transfer capability, thereby enhancing the electrocatalytic kinetics of OER.

The raw materials used in the preparation process are mainly iron sources and nickel sources which are abundant in earth, and the raw materials are wide in source, environment-friendly and green and high in safety. The preparation method is simple, and the obtained product is nontoxic, has excellent OER catalytic performance and can replace commercial RuO in the future₂And IrO₂Has better prospect in large-scale application of hydrogen production by electrolyzing water.

Drawings

FIG. 1 is an XRD pattern of NiFe-LDH/CC with a 2D nanosheet stacking structure obtained in specific example 2.

FIG. 2 is an SEM image of NiFe-LDH/CC with a 2D nanosheet stacking structure obtained in specific example 2.

FIG. 3 is an (OER) Linear Scanning (LSV) graph of the oxygen evolution reaction of NiFe-LDH/CC with 2D nanosheet stacking structure in alkaline electrolyte, obtained in specific examples 1-4.

FIG. 4 is an electrochemical impedance diagram of NiFe-LDH/CC with a 2D nanosheet stacking structure obtained in specific examples 1-4 in an alkaline electrolyte.

Detailed Description

Instruments and reagents: the reagents used in the invention are all analytically pure, and the reagents are directly applied without special instructions and without any special treatment.

Nickel nitrate hexahydrate (Ni (NO)₃)₂·6H₂O), urea (CH)₄N₂O), iron nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), ammonium fluoride (NH)₄F) Nitric acid (HNO)₃) Acetone, absolute ethyl alcohol and potassium hydroxide (KOH) are analytically pure and purchased from chemical reagents of national drug group, Inc.; carbon cloth [ HCP330N (hydrophilic), 0.32. + -. 0.02mm]Purchased from shanghai and sen electric limited.

Analytical balance (Precisa, XJ220A), stainless steel high-pressure hydrothermal reaction kettle, air-blast drying oven (Shanghai Jinghong, DFG-9076A), vacuum drying oven (Shanghai Jinghong, DZF-6090), electrochemical workstation (Shanghai Chenghua, CHI760E)

Electrochemical testing: the electrocatalysis OER performance test adopts a Shanghai Chenghua electrochemical workstation and a three-electrode test system, a NiFe-LDH catalyst loaded by carbon cloth is cut into 1cm multiplied by 1cm to be used as a working electrode, and a reversible hydrogen reference electrode and a graphite rod electrode are respectively used as a reference electrode and a counter electrode. At O₂The electrochemical OER performance was tested in saturated 1.0M KOH solution to give an LSV curve at a sweep rate of 1 mV/s.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be fully described below with reference to the accompanying drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.

The present invention will be described in detail with reference to specific examples.

Example 1

(1) Pretreatment of the carbon cloth: a piece of carbon cloth which is not processed is taken, the carbon cloth is cut into a proper size (3cm multiplied by 4cm) by an art designer knife and a ruler, the cut carbon cloth is put into a 100mL glass beaker and is sequentially cleaned in acetone, deionized water and absolute ethyl alcohol for 30min by ultrasonic waves respectively, and the purpose of the step is to remove impurities on the surface of the carbon cloth. The carbon cloth after the ultrasonic cleaning treatment is placed in a nitric acid solution with the mass percentage concentration of 40%, the nitric acid solution is prepared by 68% concentrated nitric acid, the carbon cloth is subjected to oxidation treatment for 30min under the ultrasonic condition, and the nitric acid solution is replaced every 15min, so that the purposes of improving the wettability of the carbon cloth, reducing the contact angle, improving the surface energy of a substrate and better growing a catalyst are achieved.

(2) Preparing nickel-iron double-layer hydroxide: 1.1631g of nickel nitrate hexahydrate (4mmol) was weighed into a 100mL glass beaker, 1.2012g of urea (20mmol) and 0.2963g of ammonium fluoride (8mmol) were weighed into the beaker, and 0.2222g of iron nitrate nonahydrate (0.55mmol) was weighed into the above 100mL beaker. Measuring 80mL of deionized water by using a measuring cylinder, adding the deionized water into a 100mL beaker, adding magnetons, putting the beaker on a magnetic stirrer, and magnetically stirring the beaker at room temperature for 30min to dissolve the deionized water into a brown yellow uniform solution; and (3) finally, transferring the stirred mixed solution into a 100mL stainless steel high-pressure reaction kettle, obliquely placing the carbon cloth processed in advance in the step (1) into the reaction kettle, soaking the carbon cloth into the reaction kettle, screwing a kettle cover, and placing the stainless steel high-pressure hydrothermal reaction kettle into an oven to perform hydrothermal reaction for 8 hours at the temperature of 120 ℃.

(3) After the hydrothermal reaction is finished, after the hydrothermal reaction kettle is cooled to room temperature, taking out the carbon cloth, respectively washing the carbon cloth for 3 times by using deionized water and ethanol, and carrying out vacuum drying for 3 hours in a vacuum drying oven at the temperature of 60 ℃. Obtaining the double-layer hydroxide of nickel iron.

(4) Electrochemical OER performance testing: the test adopts a standard three-electrode test system, a reversible hydrogen reference electrode (RHE) is used as a reference electrode, a graphite rod is used as a counter electrode, and the prepared NiFe LDH is used as a working electrode. Cutting the catalyst-loaded carbon cloth prepared in the step (3) into sizes of 1cm multiplied by 1cm, taking two 25mL glass beakers, respectively adding 1.0M KOH solution and deionized water, putting the cut carbon cloth into the deionized water, soaking for 5min, then clamping the carbon cloth by a carbon rod electrode clamp, and soaking for 5min in the 1.0M KOH solution. At O₂Electrochemical OER performance was tested in a 1.0M KOH solution as saturated electrolyte, and all data were obtained without iR compensation testing.

The results of the OER performance test of the catalyst are shown in FIG. 3 at a current density of 50mA/cm²The overpotential at (E) is 367 mV. The electrochemical impedance spectrum of the catalyst is shown in fig. 4, and the charge transfer resistance (Rct) of the catalyst is small, which indicates that the electrocatalytic OER performance is general.

Example 2

(2) Preparing nickel-iron double-layer hydroxide: 1.1631g of nickel nitrate hexahydrate (4mmol) was weighed into a 100mL glass beaker, 1.2012g of urea (20mmol) and 0.2963g of ammonium fluoride (8mmol) were weighed into the beaker, and 0.4040g of iron nitrate nonahydrate (1mmol) was weighed into the above 100mL beaker. Measuring 80mL of deionized water by using a measuring cylinder, adding the deionized water into a 100mL beaker, adding magnetons, putting the beaker on a magnetic stirrer, and magnetically stirring the beaker at room temperature for 30min to dissolve the deionized water into a brown yellow uniform solution; and (3) finally, transferring the stirred mixed solution into a 100mL stainless steel high-pressure reaction kettle, obliquely placing the carbon cloth processed in advance in the step (1) into the reaction kettle, soaking the carbon cloth into the reaction kettle, screwing a kettle cover, and placing the stainless steel high-pressure hydrothermal reaction kettle into an oven to perform hydrothermal reaction for 8 hours at the temperature of 120 ℃.

(4) Electrochemical OER performance testing: testing with standard three-phase currentIn the pole test system, a reversible hydrogen reference electrode (RHE) is used as a reference electrode, a graphite rod is used as a counter electrode, and the prepared NiFe LDH is used as a working electrode. Cutting the catalyst-loaded carbon cloth prepared in the step (3) into sizes of 1cm multiplied by 1cm, taking two 25mL glass beakers, respectively adding 1.0M KOH solution and deionized water, putting the cut carbon cloth into the deionized water, soaking for 5min, then clamping the carbon cloth by a carbon rod electrode clamp, and soaking for 5min in the 1.0M KOH solution. At O₂Electrochemical OER performance was tested in a 1.0M KOH solution as saturated electrolyte, and all data were obtained without iR compensation testing.

The XRD pattern of the nickel iron double layer hydroxide prepared in example 2 is shown in fig. 1, and it can be seen that the diffraction peak corresponds well to NiFe LDH. As shown in the SEM image of FIG. 2, the morphology of the NiFe-LDH/CC is 2D nano sheets, the NiFe-LDH/CC nano sheets are stacked and obliquely inserted on the carbon cloth, and the sheets are uniform, so that the specific surface area of the catalyst is increased. The results of the OER performance test of the catalyst are shown in FIG. 3 at a current density of 50mA/cm²The overpotential of (A) is 327mV, which far exceeds the OER catalytic performance of commercial ruthenium oxide and ruthenium oxide, and the overpotential is far lower than that of the catalysts prepared in other examples. The electrochemical impedance spectrum of the catalyst is shown in FIG. 4, and the charge transfer resistance (Rct) of the catalyst is the minimum, and the test results show that the NiFe-LDH/CC catalyst prepared in example 2 has excellent OER electro-catalytic performance.

Example 3

(2) Preparing nickel-iron layered double hydroxide: 1.1631g of nickel nitrate hexahydrate (4mmol) was weighed into a 100mL glass beaker, 1.2012g of urea (20mmol) and 0.2963g of ammonium fluoride (8mmol) were weighed into the beaker, and 0.6060g of iron nitrate nonahydrate (1.5mmol) was weighed into the above 100mL beaker. Measuring 80mL of deionized water by using a measuring cylinder, adding the deionized water into a 100mL beaker, adding magnetons, putting the beaker on a magnetic stirrer, and magnetically stirring the beaker at room temperature for 30min to dissolve the deionized water into a brown yellow uniform solution; and (3) finally, transferring the stirred mixed solution into a 100mL stainless steel high-pressure reaction kettle, obliquely placing the carbon cloth processed in advance in the step (1) into the reaction kettle, soaking the carbon cloth into the reaction kettle, screwing a kettle cover, and placing the stainless steel high-pressure hydrothermal reaction kettle into an oven to perform hydrothermal reaction for 8 hours at the temperature of 120 ℃.

The results of the OER performance test of the catalyst are shown in FIG. 3 at a current density of 50mA/cm²The overpotential at (c) is 393 mV. The electrochemical impedance spectrum of the catalyst is shown in fig. 4, and the charge transfer resistance (Rct) of the catalyst is smaller, which indicates that the electrocatalytic OER performance is general.

Example 4

(2) Preparing nickel-iron double-layer hydroxide: 1.1631g of nickel nitrate hexahydrate (4mmol) was weighed into a 100mL glass beaker, 1.2012g of urea (20mmol) and 0.2963g of ammonium fluoride (8mmol) were weighed into the beaker, and 0.8080g of iron nitrate nonahydrate (2mmol) was weighed into the above 100mL beaker. Measuring 80mL of deionized water by using a measuring cylinder, adding the deionized water into a 100mL beaker, adding magnetons, putting the beaker on a magnetic stirrer, and magnetically stirring the beaker at room temperature for 30min to dissolve the deionized water into a brown yellow uniform solution; and (3) finally, transferring the stirred mixed solution into a 100mL stainless steel high-pressure reaction kettle, obliquely placing the carbon cloth processed in advance in the step (1) into the reaction kettle, soaking the carbon cloth into the reaction kettle, screwing a kettle cover, and placing the stainless steel high-pressure hydrothermal reaction kettle into an oven to perform hydrothermal reaction for 8 hours at the temperature of 120 ℃.

(4) Electrochemical OER performance testing: the test adopts a standard three-electrode test system, a reversible hydrogen reference electrode (RHE) is used as a reference electrode, a graphite rod is used as a counter electrode, and the prepared NiFe LDH is used as a working electrode. Cutting the catalyst-loaded carbon cloth prepared in the step (3) into sizes of 1cm multiplied by 1cm, taking two 25mL glass beakers, respectively adding 1.0M KOH solution and deionized water, putting the cut carbon cloth into the deionized water, soaking for 5min, then clamping the carbon cloth by a carbon rod electrode clamp, and soaking for 5min in the 1.0M KOH solution. At O₂Saturated electrolysisElectrochemical OER performance was tested in a quality 1.0M KOH solution, and all data were obtained without iR compensation testing.

The results of the OER performance test of the catalyst are shown in FIG. 3 at a current density of 50mA/cm²The overpotential at (b) is 530 mV. The electrochemical impedance spectrum of the catalyst is shown in FIG. 4, and the maximum charge transfer resistance (Rct) of the catalyst is known from the graph, which indicates that the electrocatalytic OER performance of the catalyst is poor.

It should be understood that while the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein, and any combination of the various embodiments may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

1. A preparation method of a nickel-iron double-layer hydroxide for efficiently electrolyzing water is characterized by comprising the following specific steps:

(1) carrying out ultrasonic cleaning and oxidation treatment on the carbon cloth to obtain a pretreated carbon cloth;

(2) preparing nickel-iron double-layer hydroxide: respectively weighing nickel nitrate hexahydrate, urea, ammonium fluoride and ferric nitrate nonahydrate into a glass beaker, measuring deionized water by using a measuring cylinder, adding the deionized water into the beaker, and magnetically stirring and dissolving the deionized water into a brown yellow uniform solution at room temperature; transferring the mixed solution into a stainless steel high-pressure hydrothermal reaction kettle, soaking the carbon cloth treated in the step (1) in the reaction kettle, screwing a cover, and putting the hydrothermal reaction kettle into an oven to react for 8 hours at 120 ℃;

(3) and after the hydrothermal reaction is finished, cooling the hydrothermal reaction kettle to room temperature, taking out the carbon cloth loaded with the product, cleaning and drying to obtain the nickel-iron double-layer hydroxide.

2. The method for preparing double-layer hydroxide of nickel iron for high-efficiency electrolysis of water according to claim 1, wherein in the step (1), the method for carrying out ultrasonic cleaning and oxidation treatment on the carbon cloth comprises the following steps: cutting a carbon cloth into blocks, respectively carrying out ultrasonic cleaning in acetone, distilled water and absolute ethyl alcohol, placing the carbon cloth subjected to the ultrasonic cleaning treatment in a nitric acid solution, and carrying out oxidation treatment under the ultrasonic condition.

3. The method for preparing a nickel-iron double hydroxide for high-efficiency electrolysis of water according to claim 2, wherein the block size is 3cm x 4cm, and the ultrasonic cleaning time is 30 min; the mass percentage concentration of the nitric acid solution is 40%, and the oxidation treatment time is 30 min.

4. The method for preparing a nickel iron double hydroxide for high efficiency electrolysis of water according to claim 1, wherein in the step (2), the ratio of nickel nitrate hexahydrate, urea, ammonium fluoride, iron nitrate nonahydrate and deionized water is 4 mmol: 20 mmol: 8 mmol: 0.55-2 mmol: 80 mL; the magnetic stirring time is 30 min.

5. The method for preparing a nickel iron double hydroxide for high efficiency electrolysis of water according to claim 4, wherein the ratio of nickel nitrate hexahydrate, urea, ammonium fluoride, iron nitrate nonahydrate and deionized water is 4 mmol: 20 mmol: 8 mmol: 1 mmol: 80 mL.

6. The method for preparing a double-layered nickel-iron hydroxide for electrolyzing water with high efficiency as claimed in claim 1, wherein in the step (3), the washing means washing with deionized water and absolute ethanol for 3-5 times, respectively, and the drying means vacuum drying in a vacuum drying oven at 60 ℃ for 3 hours.