CN114196983B - Preparation method of metal hydroxide composite electrocatalyst and product thereof - Google Patents

Abstract

The invention discloses a method for preparing a metal hydroxide composite electrocatalyst and its product, comprising the following steps: 1) mixing at least one of metal salt A, metal salt B and metal salt C according to a set ratio It is placed in a solvent, and after stirring and dissolving, a solution D is obtained; 2) The conductive substrate Y is pretreated, and the pretreated conductive substrate Y is placed in the solution D, and adsorption is carried out at a set temperature. After the adsorption is completed, , carry out vacuum drying, after the drying is completed, the precursor is obtained; 3) the precursor is placed in an alkaline solution for soaking, and after soaking, a metal hydroxide composite electrocatalyst is obtained. The composite electrocatalyst of the invention has a nanoporous structure, rich defects, large specific surface area, good electrical conductivity, and excellent charge transport characteristics and stability. Among them, the catalyst with the best activity only needs an overpotential of 180mV when the current density is 10mAcm ^-2 under normal conditions, and the system remains stable after 900h of reaction.

Description

A kind of preparation method of metal hydroxide composite electrocatalyst and its product

technical field

The invention belongs to the technical field of electrocatalysis, and in particular relates to a preparation method of a metal hydroxide composite electrocatalyst and a product thereof.

Background technique

Due to the depletion of fossil energy, the development of renewable clean energy has attracted more and more attention. However, after the vigorous development of clean energy such as solar energy, water energy, and wind energy, the instability of energy output and storage and transportation have become new problems. Electrochemical water splitting is an effective way to transfer unstable energy and produce sustainable and efficient hydrogen energy. The water electrolysis reaction includes anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). The theoretical driving voltage for water electrolysis is 1.23 V, but the complex electron transfer mechanism and sluggish kinetics during the reaction increase the start-up energy threshold, thus requiring a higher overpotential. Currently, noble metal-based materials have the best performance, such as _IrO2 and _RuO2 for OER and Pt for HER, but their scarcity and high price limit their wide application. Efficient and stable non-precious metal-based catalysts are feasible catalysts to reduce cost and process complexity, and bifunctional monolithic water-splitting electrocatalysts are a good choice among them. Alkaline solutions are often used as ideal electrolytes due to their good stability to metal-based catalysts. Therefore, there is a need to explore electrocatalysts with high electrocatalytic activity for OER and HER in alkaline electrolytes.

Metal hydroxides have attracted extensive attention of researchers because of their high hydrogen/oxygen evolution performance and low price. However, compared with noble metal catalysts, metal hydroxides still have the disadvantages of lower activity and poorer stability. Therefore, researchers have prepared single/multi-metal hydroxides with high catalytic activity for hydrogen/oxygen electrolysis through the combination of various transition metal elements, such as Co, Mo, Fe, etc. At the same time, nanometer metal-based metal hydroxide catalyst materials are prepared by different methods, such as atomic deposition method, electrochemical deposition method, sol-gel method and so on. As reported in the literature, Li et al. synthesized MoO ₃ /Ni-NiO/CC catalyst, (Adv. Mater. 2020, 2003414). Pang et al. synthesized NiFe LDH-rGO in two steps and used it as an electrocatalyst for OER under alkaline conditions (J. Power Sources 2016, 33, 53–60). Although the above-mentioned preparation method has made great progress in hydrogen evolution/oxygen electrocatalysis activity, it still has defects such as complex process, high toxicity and easy residue of the used drugs, which makes it difficult for large-scale industrial production, or requires the use of additives in the preparation process And the conductive agent, which reduces the binding force between the catalyst and the collective, resulting in a decrease in its stability.

Contents of the invention

The purpose of the present invention is to provide a kind of preparation method and the product thereof of the metal hydroxide composite electrocatalyst used in the hydrogen/oxygen reaction in the water splitting process that can be prepared simply and on a large scale; In the way of site growth, the metal hydroxide is assembled on the conductive substrate material in a strong alkali solution, and a composite electrocatalyst with excellent activity and stability is obtained; the composite electrocatalyst prepared by this method has a porous structure, and the catalyst active material and The combination between the conductive matrix is tight and the mechanical stability is high.

The preparation method of this metal hydroxide composite electrocatalyst of the present invention comprises the following steps:

1) At least one of metal salt A, metal salt B and metal salt C is placed in a solvent according to a set ratio, and after stirring and dissolving, a solution D is obtained;

2) Pretreat the conductive substrate Y, place the pretreated conductive substrate Y in the solution D in step 1), and perform adsorption at a set temperature. After the adsorption is completed, perform vacuum drying. After drying, get the precursor;

3) The precursor in step 2) is placed in an alkaline solution for soaking, and after soaking, a metal hydroxide composite electrocatalyst is obtained.

In said step 1), the metal salt A is in the acetylacetonate, citrate, acetate, chloride, nitrate, sulfate or phosphate corresponding to each element in iron, nickel, cobalt and manganese At least one; metal salt B is at least one of acetylacetonate, citrate, acetate, chloride, nitrate, sulfate or phosphate corresponding to each element in vanadium, chromium, copper, and zinc Metal salt C is at least one of acetylacetonate, citrate, acetate, chloride, nitrate, sulfate or phosphate corresponding to each element in ruthenium, gold, platinum and iridium; metal salt A. The mass setting ratio of the mixture of metal salt B and metal salt C is (5-10):(0-4):(0-3).

Preferably, the metal salt A, metal salt B and metal salt C are one of chloride or nitrate.

In the step 1), the solvent is at least one of methanol, ethanol, ethylene glycol, isopropanol, N,N-dimethylformamide, carbon tetrachloride, dimethyl sulfoxide and deionized water, Choosing a suitable solvent for different metal salts is beneficial to improve the dispersion on the conductive substrate Y; when stirring, the temperature is 20-80°C, and the rotation speed is 10-1000 rpm; in solution D, the total concentration of the metal salt is 0.5- 20mol/L.

In the step 2), the conductive substrate Y is one of metal foam, carbon paper, and carbon cloth, and the metal foam is one of nickel foam, copper, titanium, and iron; the thickness of the metal foam is 1.0-4.0 mm, and the pores The rate is 20-99%; the thickness of carbon cloth is 0.1-0.3mm, and the tensile strength is greater than 4000Mpa; the thickness of carbon paper is 0.1-0.3mm, and the porosity is 20-99%; a certain thickness of high-porosity material can effectively absorb the reaction substances, increasing the active substance loading. If the thickness is too thin, the support performance of the material will decrease, and it cannot be used as an electrode; if the thickness is too thick, the adsorption effect will be affected, and the active material will be dispersed unevenly. The specific steps of the pretreatment of the conductive substrate Y are: ultrasonically clean the conductive substrate Y to pH=7 with a 1mol/L hydrochloric acid solution (the hydrochloric acid used will not react with the substrate, and the purpose is to remove the oxide on the surface), and then Put it at a temperature of 60-80°C and a vacuum condition of ^10-2-10-6 Pa, and dry for ^6-24 hours; the pre-treated and cleaned conductive substrate is beneficial to remove the oil and oxides on the surface.

In the step 2), 100-50000 uL of solution D needs to be added per square centimeter of the conductive substrate Y; the set temperature is 25-120°C, and the adsorption method is one of static adsorption, ultrasonic adsorption and suction filtration adsorption, A reasonable adsorption method can increase the metal hydroxide load on the conductive substrate Y, and the adsorption time is 30-600 min; the vacuum drying conditions are: the vacuum degree is 10 ^-2 -10 ^-6 Pa, and the drying time is 6-24 hours.

In the step 3), the concentration of the alkaline solution is 1 to 10mol/L, and the strong base is at least _one of KOH, NaOH, LiOH and Ca(OH) in the solution. Preferably, the alkaline solution is KOH and NaOH At least one of the solutions has a concentration of 1-4 mol/L. If the concentration of lye is too low, the reaction will go smoothly, and if the concentration is too high, the material will be seriously agglomerated; the soaking time is 1-3600 min, preferably 20-40 min.

The metal hydroxide composite electrocatalyst was prepared according to the above preparation method.

The metal hydroxide composite electrocatalyst includes a conductive substrate and a metal hydroxide grown on the conductive substrate Y, and its general structural formula is M(OH) _x @Y, 1≤x≤5, and Y represents the conductive substrate Y , M represents a metal, and the M(OH) _x is at least one of nano-sheet, nano-wire, nano-rod or nano-cluster, with a thickness of 10-100 nm and a specific surface area of 150-250 cm ³ g ^-1 .

Beneficial effects of the present invention:

(1) The composite electrocatalyst of the present invention has a nanoporous structure, abundant defects, large specific surface area, good electrical conductivity, and excellent charge transport characteristics and stability. It exhibits excellent activity and stability in electrocatalytic water splitting. Among them, the catalyst with the best activity only needs an overpotential of 180mV when the current density is 10mAcm ^-2 under 1molL ^-1 KOH solution and room temperature, and the system remains stable after 900 hours of reaction.

(2) The preparation method of the present invention is simple to operate, the required raw materials are all cheap and easy to obtain, has the advantage of rapid mass production, good industrial adaptability, and can ensure the high catalytic activity of metal hydroxides. The conductive substrate provides A good conductive network is formed, which makes the catalyst exhibit excellent conductivity, electron transport characteristics and stability

(3) The preparation method of the present invention obtains an electrode system with high activity and high stability by adjusting parameters such as metal salt components, concentration, reaction temperature, and reaction time, thereby meeting different requirements for catalytic performance. At the same time, the in-situ preparation method is conducive to the close combination between the catalyst and the conductive carrier, thereby improving its charge transport characteristics and mechanical stability, and has a high industrial application prospect.

Description of drawings

Fig. 1 is the SEM figure of the ferronickel hydroxide/carbon cloth of the embodiment of the present invention 1;

Fig. 2 is the oxygen evolution reaction LSV curve of embodiment 1～3 of the present invention;

Fig. 3 is the Tafel curve of embodiment 1～3 of the present invention;

Fig. 4 is the stability test curve of embodiment 1～3 of the present invention;

Fig. 5 is the oxygen evolution reaction LSV curve of comparative examples 1 and 2 of the present invention

Detailed ways

In order to illustrate the present invention more clearly, further descriptions are given through implementation cases. The following examples do not limit the scope of the invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

The test conditions for the oxygen evolution activity used in the present invention are: 1.0mol L ^-1 KOH is used as the electrolyte for oxygen evolution, the test is a three-electrode system, a platinum sheet is used as a counter electrode, the purity is higher than 99.99%, and saturated Ag/AgCl is used as a reference Electrodes and testing equipment are electrochemical workstations of Gamry Company of the United States. All test voltage values are converted to standard hydrogen electrode voltage values

Example 1

Step (1): Weigh 500 mg of ferric nitrate and dissolve it in 10 ml of ethanol solution, and fully dissolve with mechanical stirring at 200 r/min to obtain solution D.

Step (2): Cut the carbon cloth with a thickness of 0.167mm and a tensile strength greater than 4000MPa into 4×3cm ² , then ultrasonically clean it with 1mol/L hydrochloric acid solution until pH=7, and then place it at 60°C and 10 ^{- 2} ~ 10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated carbon cloth. Arrange the treated carbon in a glass vessel, then drop 3000 microliters of solution D into it for static adsorption at 25°C for 180min, then vacuum at 10 ^-2 ~ 10 ^-6 Pa and drying temperature at 80°C, vacuum Dry for 12 hours to obtain the precursor.

Step (3): Soak the precursor in 1mol/L KOH solution for 0.5h to obtain FeOOH@CC.

Example 2

Step (1): Weigh 400 mg of nickel nitrate and 100 g of ferric nitrate and dissolve them in 10 ml of ethanol solution, and fully dissolve with mechanical stirring at 200 r/min to obtain solution D.

Step (2): Cut the carbon cloth with a thickness of 0.167mm and a tensile strength greater than 4000MPa into 4×3cm ² , then ultrasonically clean it with 1mol/L hydrochloric acid solution until pH=7, and then place it at 60°C and 10 ^-2 ~10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated carbon cloth. Arrange the treated carbon in a glass vessel, then drop 3000 microliters of solution D into it for static adsorption at 25°C for 180min, then vacuum at 10 ^-2 ~ 10 ^-6 Pa and drying temperature at 80°C, vacuum Dry for 12 hours to obtain the precursor.

Step (3): Soak the precursor in 1mol/L KOH solution for 0.5 hours to obtain NiFe _X (OH) _Y @CC.

Comparative example 1

Step (1): Weigh 400g of nickel nitrate and 100g of ferric nitrate and dissolve them in 10ml of ethanol solution, and fully dissolve with mechanical stirring at 200r/min to obtain solution D.

Step (2): Cut the carbon cloth with a thickness of 0.167mm and a tensile strength greater than 4000MPa into 4×3cm ² , then ultrasonically clean it with 1mol/L hydrochloric acid solution until pH=7, and then place it at 60°C and 10 ^-2 ~10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated carbon cloth. Arrange the treated carbon in a glass vessel, then drop 3000 microliters of solution D into it for static adsorption at 25°C for 180min, then vacuum at 10 ^-2 ~ 10 ^-6 Pa and drying temperature at 80°C, vacuum Dry for 12 hours to obtain the precursor.

Step (3): Soak the precursor in 0.2mol/L KOH solution for 0.5 hours to obtain NiFe _X (OH) _Y @CC.

Comparative example 2

Step (1): Prepare 5 mL of 100 mg ferric nitrate aqueous solution a and 5 mL of 400 mg nickel nitrate aqueous solution b.

Step (2): Prepare 28ml of 0.2M urea aqueous solution c and 4mL of 0.01M sodium citrate aqueous solution d.

Step (3): Arrange solutions a, b, c, d and carbon with an area of 4×3cm ² , a thickness of 0.167mm, and a tensile strength greater than 4000MPa in a 100mL polytetrafluoroethylene bottle, and heat them under the condition of 150 degrees Reaction 3h.

Step (4): The carbon cloth after the hydrothermal reaction is washed with ethanol and aqueous solution, and then the NiFe-LDH is obtained under the conditions of a vacuum degree of 10 ^-2 ~ 10 ^{- 6} Pa and a drying temperature of 80°C.

Example 3

Step (1): Weigh 30g of nickel nitrate, 10g of ferric nitrate and 10g of ruthenium chloride and dissolve them in 10ml of ethanol solution, and fully dissolve with mechanical stirring at 200r/min to obtain solution D.

Step (2): Cut the carbon cloth with a thickness of 0.167mm and a tensile strength greater than 4000MPa into 4×3cm ² , then ultrasonically clean it with 1mol/L hydrochloric acid solution until pH=7, and then place it at 60°C and 10 ^{- 2} ~ 10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated carbon cloth. Arrange the treated carbon in a glass vessel, then drop 3000 microliters of solution D into it for static adsorption at 25°C for 180min, then vacuum at 10 ^-2 ~ 10 ^-6 Pa and drying temperature at 80°C, vacuum Dry for 12 hours to obtain the precursor.

Step (3): Soak the precursor in 1mol/L KOH solution for 0.5 hours to obtain NiFeRu _X (OH) _Y @CC.

Figure 1 is the SEM image of the electrocatalyst prepared in Example 2. It can be clearly found from Figure 1 that NiFe _X (OH) _Y @CC is composed of many very thin nanosheets, which can significantly improve the catalytic performance of the catalyst. The specific surface area increases the active sites, thereby improving the reaction efficiency.

Figure 2 shows the results of oxygen evolution activity measured in Examples 1-3. The overpotentials of FeOOH@CC, NiFe _X (OH) _Y @CC and NiFeRu _X (OH) _Y @CC are 260mV, 190mV and 180mV respectively when the current density is 10mA cm ^-2 . The slopes are 102.1, 60.4 and 39.5dec ^-1 , and the stability is 20h, 600h and 900h, respectively. The corresponding catalyst thicknesses are 35, 48 and 64 nm, and the specific surface areas are 200, 205 and 218 cm ³ g ^-1 . When the current density is 10mA cm ^-2 , the overpotential in Comparative Example 1 is 452mV, the Tafel slope is 185dec ^-1 , and the electrocatalytic activity is poor. For the sample prepared by the traditional hydrothermal method in Comparative Example 2, the overpotential was 280mV, and the Tafel slope was 90dec ^-1 .

Example 4

Step (1): Weigh 40 g of nickel nitrate and 10 g of ferric nitrate and dissolve them in 10 ml of ethanol solution, and fully dissolve them under mechanical stirring at 200 r/min to obtain solution D.

Step (2): Nickel foam (50% porosity) with a thickness of 0.167mm is cut into 4×3cm ² , then ultrasonically cleaned with 1mol/L hydrochloric acid solution to pH=7, and then placed at 60°C and 10 ^-2 ~ 10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated nickel foam. Put the treated nickel foam in a glass container, then drop 5000 microliters of solution D into ^it and let it stand for adsorption at 25°C for ^180min . Vacuum dried for 12 hours to obtain the precursor.

Step (3): Soak the precursor in 4mol/L NaOH solution for 0.5 hours to obtain NiFe _X (OH) _Y @NiFoam.

Example 5

Step (1): Weigh 40 g of nickel nitrate and 10 g of ferric nitrate and dissolve them in 10 ml of ethanol solution, and fully dissolve them under mechanical stirring at 200 r/min to obtain solution D.

Step (2): Cut foamed copper (46% porosity) with a thickness of 3.5 mm into 4×3 cm ² , then ultrasonically clean it with 1 mol/L hydrochloric acid solution until pH = 7, and then place it at 60°C and 10 ^-2 ~10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated copper foam. Put the treated foamed copper in a glass container, then drop 5000 microliters of solution D into it and let it stand for adsorption at 25°C for 180min, then under the conditions of vacuum degree of 10 ^-2 ~ 10 ^-6 Pa and drying temperature of 80°C, Vacuum dried for 12 hours to obtain the precursor.

Step (3): Soak the precursor in 4mol/L KOH solution for 0.5 hours to obtain NiFe _X (OH) _Y @CuFoam.

Example 6

Step (1): Weigh 40 g of nickel nitrate and 10 g of ferric nitrate and dissolve them in 10 ml of ethanol solution, and fully dissolve them under mechanical stirring at 200 r/min to obtain solution D.

Step (2): Cut foam iron (54% porosity) with a thickness of 4 mm into 4×3 cm ² , then ultrasonically clean it with 1 mol/L hydrochloric acid solution until pH = 7, and then place it at 60°C and 10 ^-2 ~ 10 ^-6 Pa vacuum condition, vacuum drying for 18 hours, to obtain the treated foam iron. Put the treated foam iron in a glass container, then drop 5000 microliters of solution D into it and let it sit for 180 minutes at 25°C, then vacuum at 10 ^-2 ~ 10 ^-6 Pa and dry at 80°C. Vacuum drying for 12h to obtain the precursor

Step (3): Soak the precursor in 4mol/L KOH solution for 0.5 hours to obtain NiFe _X (OH) _Y @FeFoam.

The morphology of the catalysts prepared in Examples 4-6 are all nanoporous materials, the corresponding catalyst thicknesses are 45, 48 and 44 nm, and the specific surface areas are 204, 205 and 208 cm ³ g ^-1 . When the current density is 10mA cm ^-2 , the overpotential is 185mV, and the stability test of NiFe _X (OH) _Y @Ni Foam is tested for 300 hours at the current density of 10, 50, 80 and 100mA cm ^-2 , Still very stable.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (6)

1. A preparation method of metal hydroxide composite electrocatalyst, comprising the following steps: 1) Put iron nitrate and nickel nitrate, or iron nitrate, nickel nitrate and ruthenium chloride in the solvent according to the set ratio, stir and dissolve to obtain solution D; The solvent is at least one of methanol, ethanol, ethylene glycol, and isopropanol; when stirring, the temperature is 20~80°C, and the rotation speed is 10~1000 rpm; in solution D, the total concentration of the metal salt is 0.5~20mol /L; 2) Pretreat the conductive substrate Y, place the pretreated conductive substrate Y in the solution D in step 1), and perform adsorption at a set temperature. After the adsorption is completed, perform vacuum drying. After drying, you can get Precursor; The conductive substrate Y is one of foam metal, carbon paper, and carbon cloth; The adsorption time is 30~600min; The vacuum drying conditions are: the vacuum degree is 10 ^-2 ~ 10 ^-6 Pa, and the drying time is 6 ~ 24h; 3) Soak the precursor in step 2) in an alkaline solution, and after soaking, a metal hydroxide composite electrocatalyst is obtained; The concentration of the alkaline solution is 1-10 mol/L, the alkaline solution is at least one of KOH, NaOH and LiOH solutions, and the soaking time is 1-3600min. 2. The preparation method of the metal hydroxide composite electrocatalyst according to claim 1, characterized in that, in the step 2), the metal foam is one of nickel foam, copper, titanium, and iron; the thickness of the metal foam is 1.0-4.0mm, porosity 20-99%; carbon cloth thickness 0.1-0.3mm, tensile strength greater than 4000Mpa; carbon paper thickness 0.1-0.3mm, porosity 20-99%. 3. The preparation method of metal hydroxide composite electrocatalyst according to claim 1, characterized in that, in the step 2), the specific steps of pretreatment of the conductive substrate Y are: using 1 mol/L hydrochloric acid solution on Conductive substrate Y is ultrasonically cleaned to pH = 7, and then placed at a temperature of 60-80° C. and a vacuum condition of 10 ^-2 -10 ^-6 Pa, and dried for 6-24 hours. 4. The method for preparing a metal hydroxide composite electrocatalyst according to claim 1, characterized in that in step 2), 100-50000uL of solution D needs to be added to each square centimeter of conductive substrate Y; the adsorption method is Static adsorption, one of ultrasonic adsorption and suction filtration adsorption, a reasonable adsorption method can increase the loading capacity of metal hydroxide on the conductive substrate Y. 5. the preparation method of metal hydroxide composite electrocatalyst according to claim 1 is characterized in that, described alkaline solution is at least one in KOH and NaOH, and concentration is 1～4mol/L, soaking time 20~40min. 6. According to the preparation method described in any one of claims 1 to 5, a metal hydroxide composite electrocatalyst is prepared, wherein the metal hydroxide composite electrocatalyst includes a conductive substrate and a Y substrate grown on a conductive substrate. The metal hydroxide on the surface has a general structural formula of M(OH) _x @Y, 1≤x≤5, Y represents the conductive substrate Y, M represents the metal, and the M(OH) _x is nanosheet, nanometer At least one of wire-like, nano-rod-like or nano-cluster-like, with a thickness of 10-100 nm.

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