CN114959791A - Preparation method of Mg-doped NiFe-based (oxy) hydroxide and oxygen evolution electrocatalysis application thereof - Google Patents

Abstract

The invention relates to a preparation method of Mg-doped NiFe-based (oxy) hydroxide and oxygen evolution electrocatalysis application thereof. The method comprises the following steps: mixing MgCl ₂ 、NiCl ₂ ·6H ₂ Dissolving O in deionized water, and stirring to obtain mixed solution. Immersing the processed foam iron in the mixed solution, stirring, cleaning and drying to obtain Mg-doped NiFe-based (oxy) hydroxide; the method comprises the steps of designing Mg-doped NiFe-based (oxy) hydroxide with a nanosheet structure by using foamed iron as a substrate and a one-step corrosion method; the nano-sheet structure can be increasedThe specific surface area of the catalyst provides more active sites, and enhances electron transfer in the electrocatalytic process. The preparation method is simple and convenient, is easy to operate, and the Mg doping ensures that the catalyst obtains better stability and better inherent electrocatalytic activity.

Description

A kind of preparation method of Mg-doped NiFe-based (oxy) hydroxide and its oxygen evolution electrocatalysis application

technical field

The invention belongs to the field of electrocatalysis, and relates to a preparation method of Mg-doped NiFe-based (oxy) hydroxide and application of oxygen evolution electrocatalysis.

Background technique

At present, the development of clean and efficient renewable energy to replace traditional fossil energy is of great significance to the sustainable development of my country's economy. Hydrogen energy has become the most ideal clean energy due to its advantages of high combustion calorific value, non-toxic and harmless, and wide sources. Among them, electrocatalytic water splitting is one of the ideal methods for developing hydrogen energy. The overall water splitting consists of two half-reactions, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Both the hydrogen evolution reaction (2H ₂ O+2e ^- →H ₂ +2OH ^- ) and the oxygen evolution reaction (4OH ^- →O ₂ +2H ₂ O+4e ^- ) have problems such as slow kinetics, especially the oxygen evolution reaction, due to the The transfer to 4 electrons requires greater energy consumption. Efficient catalysts can reduce overpotentials, thereby improving energy conversion efficiency. Currently, noble metals and their oxides (Pt, RuO2, and _IrO2 , etc. ₎ are the most effective catalysts, but their high price and scarcity limit their large-scale industrial applications. In alkaline environments, transition metals such as Ni, Co, and Fe-based heterostructures have theoretically high electrocatalytic activity and low cost, and have been shown to be effective non-noble metal electrocatalysts. However, non-precious metal catalysts also have the problem of low reaction efficiency instead of noble metal catalysts, and it is very important to improve their catalytic performance.

NiFe-based (oxy)hydroxide is a potential OER catalyst with tunable metal cation types and ratios, and the anions in the structure are mobile and exchangeable. The synergistic effect between oxides and hydroxides endows NiFe-based (oxy)hydroxides with better OER performance. However, their intrinsic conductivity is poor, and the powder materials are prone to structural curling and stacking during testing, which is not conducive to electron transfer and exposure of active sites during electrocatalysis. Effective metal atom doping can expose more active sites to the catalyst, optimize the electronic structure, and optimize the adsorption of reaction intermediates, thereby reducing the energy barrier of the reaction and improving the intrinsic activity of OER electrocatalysts. Therefore, it is of great significance to design electrocatalysts with high performance for oxygen evolution.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problem that the catalytic activity of NiFe-based (oxy)hydroxide needs to be further improved, and propose a preparation method of Mg-doped NiFe-based (oxy)hydroxide and its oxygen evolution electrocatalytic application. A Mg-doped NiFe-based (oxy)hydroxide with nanosheet structure was designed by one-step etching method using iron foam as the substrate. The nanosheet structure can increase the specific surface area of the catalyst, provide more active sites, and at the same time enhance the electron transfer during electrocatalysis. The preparation method of the invention is simple and easy to operate, and the doping of Mg enables the catalyst to obtain better stability and better intrinsic electrocatalytic activity.

The technical scheme of the present invention is:

A preparation method of Mg-doped NiFe-based (oxy)hydroxide, the method comprising the steps of:

(1) Cleaning of the foamed iron material: Cut the foamed iron into small pieces of 1 × 1.5 cm ² , place it in hydrochloric acid for ultrasonic treatment, and then rinse it with deionized water and ethanol. The acid is 1-3 mol/L hydrochloric acid, and ultrasonically Ultrasonic in the machine for 8-10min, and then dry in a vacuum drying oven.

(2) Dissolve MgCl ₂ and NiCl ₂ ·6H ₂ O in deionized water, stir evenly to prepare a mixed solution; immerse the foamed iron in the mixed solution, stir for 2h to 4h, wash and dry to obtain Mg doped of NiFe-based (oxy)hydroxides.

Wherein, the molar ratio of Mg:Ni is 1～3:0.5～1; the total metal concentration of the mixed solution is 0.5～1mol/L;

The application of the Mg-doped NiFe-based (oxy) hydroxide prepared by the method is used for electrocatalytic oxygen evolution reaction. The raw materials involved are obtained through commercial purchase.

The beneficial effects of the present invention are:

1) The nanosheet structure of the catalyst provides abundant mass transfer channels and increases the active sites, which facilitates the gas diffusion and electrolyte transport.

2) NiFe-based (oxy)hydroxides combined with conductive substrates to construct 3D self-supporting electrocatalysts can enhance the conductivity of catalysts.

3) Appropriate Mg doping enables the catalyst to obtain better stability and higher intrinsic activity.

4) The overpotential of the Mg-doped NiFe-based (oxy)hydroxide catalyst at 100 mA cm ^-2 can be seen to be 330 mV from the measured linear scan of the oxygen evolution reaction. When Mg is not doped, the overpotential of this catalyst is 450 mV. This shows that the doping of Mg can show higher catalytic activity and can be well applied to the high-activity oxygen evolution reaction catalyst. And under the current density of 100mA cm ^-2 , after 50 hours of long-term durability test, the potential change of the electrode can be ignored, and the application prospect in the future energy industry is broad.

Description of drawings

FIG. 1 is the SEM image of the Mg-Ni/FF prepared in Example 1. FIG.

FIG. 2 is a TEM image of the Mg-Ni/FF prepared in Example 1. FIG.

FIG. 3 is the X-ray diffraction pattern of the Mg-Ni/FF prepared in Example 1. FIG.

FIG. 4 is an X-ray diffraction pattern of Ni/FF obtained in Example 2. FIG.

Fig. 5 is the oxygen evolution reaction (OER) of Mg-Ni/FF, Ni/FF, Mg/FF, pure foamed iron (FF) and commercialized Ir/C obtained in Examples 1-3 under alkaline electrolyte Linear sweep (LSV) plot.

6 is a bar graph of overpotentials of Mg-Ni/FF, Ni/FF, Mg/FF, pure foamed iron (FF) and commercial Ir/C obtained in Examples 1 to 3 at different current densities.

FIG. 7 shows the long-term durability test of Mg-Ni/FF prepared in Example 1 under the current density of 100 mA cm ^-2 for 50 hours.

8 is the linear scan (LSV) of the oxygen evolution reaction (OER) of catalysts doped with different Mg contents (Mg contents are 11 mmol, 15 mmol, 22 mmol) in an alkaline electrolyte in Example 1, Example 4, and Example 5. )picture.

Detailed ways

The present invention is described in detail below through specific embodiments, but the protection scope of the present invention is not limited.

Example 1:

(1) Treatment of foam iron

1×1.5cm ² , 1mm thick iron foam (porosity: 60-98%; porosity: ≥98; purity: 99.99%) was placed in 3mol/L hydrochloric acid for 10min ultrasonic treatment to remove the oxide layer, and then Rinse with deionized water and ethanol and dry.

(2) 1.428g MgCl ₂ (15mmol) and 2.05g NiCl ₂ ·6H ₂ O (7.5mmol) were dissolved in 30mL of deionized water, and magnetically stirred at room temperature for 5min to dissolve into a uniform solution; after the treatment in step (1) The foamed iron was immersed in the mixed solution, stirred for 2.5 h, and then the adhering matter on the catalyst was rinsed off with water, and then dried in a vacuum oven.

The Mg-Ni/FF prepared in Example 1 was characterized by means of TEM, SEM and XRD. The microstructure of the electrocatalysts was investigated by scanning electron microscopy (SEM, Quanta450FEG) and TEM (JEOL2010F). Their crystal structures were investigated by X-ray diffraction (XRD, D8 Discovery). In a standard three-electrode system, the electrolysis reaction was measured using a CORRTEST CS2350 electrochemical workstation, in which Mg-Ni/FF was used as the working electrode, a carbon rod was used as the counter electrode, a saturated calomel electrode (SCE) was used as the reference electrode, and the electrolyte was 1 mol koh. Linear scanning voltammetry (LSV) curve detection range is 0 ~ 1V (relative to saturated calomel), the scanning speed is 10mV s ^-1 . According to E _RHE = E _Hg/HgCl + 0.242 + 0.059pH, the potential vs. Conversion of HgCl to Potential vs. Standard Hydrogen Electrode (RHE).

It can be seen from the SEM and TEM images of Figure 1 and Figure 2 that the prepared Mg-Ni/FF has a nanosheet structure, which increases the active surface area of the catalyst, accelerates the charge transfer, and is more conducive to the oxygen evolution reaction. From the XRD pattern in Fig. 3, it can be seen that Mg-Ni/FF is consistent with the standard cards of NiFe-LDH (PDF#34-0205), FeOOH (PDF#18-0639) and Fe ₂ O ₃ (PDF#25-1402), respectively, This shows that NiFe-based (oxy)hydroxide was successfully synthesized.

Example 2:

(1) Treatment of foam iron

Place 1×1.5cm ² foam iron with a thickness of 1mm in 3mol/L hydrochloric acid for 10min ultrasonic treatment to remove the oxide layer, then rinse with deionized water and ethanol, and dry.

(2) Dissolve 2.05g NiCl ₂ ·6H ₂ O (7.5 mmol) in 30 mL of deionized water, stir magnetically for 5 min at room temperature and dissolve into a uniform solution; immerse the iron foam treated in step (1) in the mixed solution , stirred for 2.5 h, and then rinsed off the adhering matter on the catalyst with water, and then dried in a vacuum oven.

It can be seen from the XRD pattern in Fig. 4 that Ni/FF is consistent with the standard cards of _FeOOH (PDF#18-0639) and _Fe2O3 (PDF#25-1402), respectively. Through the LSV curve diagram in Figure 5, it can be obtained that its 100mA overpotential is 450mV.

The overpotential of Mg-Ni/FF is higher than that of Ni/FF, so the doping of Mg can improve the OER performance of the catalyst.

Example 3:

(1) Treatment of foam iron

Place 1×1.5cm ² foam iron with a thickness of 1mm in 3mol/L hydrochloric acid for 10min ultrasonic treatment to remove the oxide layer, then rinse with deionized water and ethanol, and dry.

(2) Dissolve 1.428g MgCl ₂ (15mmol) in 30mL deionized water, and dissolve into a uniform solution with magnetic stirring for 5min at room temperature; immerse the iron foam treated in step (1) in the mixed solution, stir for 2.5h, and then The deposits on the catalyst were rinsed with water and dried in a vacuum oven.

Figure 5 is the LSV curve diagram of Examples 1 to 3. It can be seen from the figure that under the premise of using foamed iron as the base, the Mg-doped NiFe-based (oxy)hydroxide (Example 1) has high performance For catalysts not doped with Mg or only doped with Mg (Examples 2-3). Comparing the Mg-Ni/FF catalyst obtained in Example 1 with the Ni/FF catalyst obtained in Example 2 without Mg element doping, it can be seen that the doping of Mg element improves the performance of the catalyst. Combined with Example 3, it is demonstrated that the synergistic effect between MgNiFe-based (oxy)hydroxides jointly promotes the electrocatalytic performance of the oxygen evolution reaction.

Fig. 6 is the histogram of the overpotential of Mg-Ni/FF, Ni/FF, Mg/FF, and FF and commercialized Ir/C obtained in Examples 1-3 at different current densities, it can be seen that Mg-Ni/ FF has a lower overpotential and exhibits the highest electrocatalytic activity, which is favorable for the reaction. Ni/FF, Mg/FF, FF and commercial Ir/C have higher overpotentials than Mg-Ni at different current densities. /FF. When the current density is 10 mA cm ^-2 , the OER overpotential on Mg-Ni/FF is 189 mV. The Ni/FF without Mg has a higher overpotential, indicating that the doping of Mg plays a certain role in improving the OER catalytic performance. In a standard three-electrode system, the electrolysis reaction was measured using a CORRTEST CS2350 electrochemical workstation, in which Mg-Ni/FF was used as the working electrode, a carbon rod was used as the counter electrode, a saturated calomel electrode (SCE) was used as the reference electrode, and the electrolyte was 1 mol KOH (pH=13.7). The detection range of linear sweep voltammetry (LSV) curve was 0～1V (relative to saturated calomel), and the scanning speed was 10mV s ^-1 . Convert Potential vs. Hg/HgCl to Potential vs. Standard Hydrogen Electrode (RHE) according to E _RHE = E _Hg/HgCl + 0.242 + 0.059 pH

FIG. 7 shows the long-term durability test of Mg-Ni/FF prepared in Example 1 under the current density of 100 mA cm ^-2 for 50 hours. It can be seen from the figure that the potential change of the electrode is negligible, indicating that Mg-Ni/FF has better stability.

Example 4:

(1) Treatment of foam iron

Place 1×1.5cm ² foam iron with a thickness of 1mm in 3mol/L hydrochloric acid for 10min ultrasonic treatment to remove the oxide layer, then rinse with deionized water and ethanol, and dry.

(2) 1.07g MgCl ₂ (11mmol) and 2.05g NiCl ₂ 6H ₂ O (7.5mmol) were dissolved in 30mL deionized water, and magnetically stirred at room temperature for 5min to dissolve into a uniform solution; The foamed iron was immersed in the mixed solution, stirred for 2.5 h, and then the adhering matter on the catalyst was rinsed off with water, and then dried in a vacuum oven.

Example 5:

(1) Treatment of foam iron

Place 1×1.5cm ² foam iron with a thickness of 1mm in 3mol/L hydrochloric acid for 10min ultrasonic treatment to remove the oxide layer, then rinse with deionized water and ethanol, and dry.

(2) 2.14g MgCl ₂ (22mmol) and 2.05g NiCl ₂ 6H ₂ O (7.5mmol) were dissolved in 30mL deionized water, and magnetically stirred at room temperature for 5min to dissolve into a uniform solution; The foamed iron was immersed in the mixed solution, stirred for 2.5 h, and then the adhering matter on the catalyst was rinsed off with water, and then dried in a vacuum oven.

8 is a linear scan of the oxygen evolution reaction (OER) of catalysts doped with different Mg contents (Mg contents are 11 mmol, 15 mmol, 22 mmol) obtained in Example 1, Example 4, and Example 5 under alkaline electrolyte ( LSV) diagram. It can be seen from the figure that when the content of doped Mg is adjusted in an appropriate range, it has better oxygen evolution reaction performance, and its performance is higher than that of Example 2 and Example 3.

The above related descriptions and descriptions of the embodiments are for the convenience of those of ordinary skill in the technical field to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these contents, and the general principles described herein can be applied to other embodiments without inventive step. Therefore, the present invention is not limited to the above-mentioned related descriptions and descriptions of the embodiments, and those skilled in the art can make improvements and modifications without departing from the scope of the present invention based on the disclosure of the present invention, which should fall within the protection scope of the present invention.

Matters not addressed in the present invention are known in the art.

Claims (3)

1. A method for preparing Mg-doped NiFe-based (oxy) hydroxide, characterized in that the method comprises the steps of:

mixing MgCl ₂ 、NiCl ₂ ·6H ₂ Dissolving O in deionized water, and stirring to obtain a mixed solution; immersing the processed foam iron in the mixed solution, stirring for 2-4 h, cleaning and drying to obtain Mg-doped NiFe-based (oxy) hydroxide;

wherein, Mg: the molar ratio of Ni is 1-3: 0.5 to 1; the total metal concentration of the mixed solution is 0.5-1 mol/L.

2. The method for preparing Mg-doped NiFe-based (oxy) hydroxide as set forth in claim 1, wherein the foamed iron in the step (1) is a cleaned material: sequentially placing the materials in hydrochloric acid, absolute ethyl alcohol and deionized water for ultrasonic cleaning, then performing ultrasonic cleaning for 8-10 min, respectively washing with ethyl alcohol and water, and then drying in a vacuum drying oven;

the concentration of the hydrochloric acid is 1-3 mol/L.

3. Use of Mg doped NiFe based (oxy) hydroxides prepared by the process of claim 1, characterized by electrocatalytic oxygen evolution reaction.

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