Precious metal aerogel surface electron regulation and control method and electro-catalytic oxygen reduction application thereof

Abstract

The invention relates to the field of aerogel, in particular to a precious metal aerogel surface electron regulation and control method and application thereof to electro-catalytic oxygen reduction. The regulation and control method comprises the following steps: reducing a metal salt solution through sodium borohydride to obtain precious metal hydrogel; and compounding the ionic liquid and the noble metal hydrogel in a solution, and purifying and drying to obtain the ionic liquid / noble metal aerogel composite material. The ionic liquid / noble metal aerogel composite material is formed by adopting a simple ionic liquid surface modification method based on the excellent electro-catalytic performance of the noble metal aerogel, so that the electro-catalytic oxygen reduction activity and stability of the noble metal aerogel can be effectively improved, and the use cost of a catalyst can be greatly reduced; the practical application of the fuel cell electrocatalyst can be further promoted.

Description

Technical Field

[0001] The invention relates to the field of aerogels, and in particular to a method for regulating the surface electrons of a noble metal aerogel and an application of the method for electrocatalytic oxygen reduction, and belongs to the field of aerogels. Background Art

[0002] The oxygen reduction reaction is the core reaction of electrochemical energy conversion devices such as metal-air batteries and fuel cells. Its slow reaction kinetics severely limits the further practical application of such devices. Therefore, it is urgent to develop efficient and stable oxygen reduction electrocatalysts to accelerate this reaction process.

[0003] Metal aerogels are a type of hierarchical porous nanomaterials constructed from metals. They have ultra-low density, large specific surface area, and rich pore structures. They not only have excellent catalytic properties of the metal itself and good electronic conductivity, but also can provide abundant reactive active sites, accelerate the material / electron transfer process, and show great application prospects in the field of electrocatalysis. In particular, platinum (Pt)-based metal aerogels are expected to be excellent oxygen reduction electrocatalysts.

[0004] At present, the performance of Pt-based metal aerogel electrocatalysts needs to be further improved. The surface design and regulation of Pt-based metal aerogels can effectively improve their catalytic performance and expand their application prospects. However, there are few studies on the surface regulation of Pt-based metal aerogels, and the mechanism of the influence of their surface / interface properties on catalytic performance is insufficient, which greatly limits the further functional design and practical application of Pt-based metal aerogels. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned background technology, the present invention provides a surface electronic regulation method of a metal aerogel and its electrocatalytic oxygen reduction application, aiming to broaden the surface regulation means of a metal aerogel, obtain high-performance oxygen reduction electrocatalysts, and facilitate its further application in sustainable energy conversion devices such as fuel cells.

[0006] The technical solution provided by the present invention is as follows:

[0007] The present invention comprises the following steps:

[0008] (1) Preparation of noble metal hydrogels

[0009] The metal salt solution is reduced by sodium borohydride to obtain a noble metal hydrogel;

[0010] (2) Preparation of ionic liquid / noble metal aerogel composites

[0011] The ionic liquid and the noble metal hydrogel are compounded in a solution, and the ionic liquid / noble metal aerogel composite material is obtained after purification and drying.

[0012] As an improvement, the noble metal salt solution in step (1) is a mixed solution of chloroplatinic acid and other metal salts;

[0013] The other metal salt is one of nickel chloride, copper chloride, cobalt chloride and potassium chloropalladate;

[0014] The ratio of platinum to metal atoms in other metal salts is 3:1, and the total concentration of metal ions in the noble metal salt aqueous solution is 0.4 mM. In step (1), sodium borohydride is used as a reducing agent, wherein the ratio of metal ions to sodium borohydride is 1:1.5, the reduction temperature is 25°C, and then the noble metal hydrogel is obtained by standing at room temperature overnight.

[0015] As an improvement, the ionic liquid is compounded with the noble metal hydrogel, and the ionic liquid can be coated on the surface of the hydrogel to form a stable ionic liquid coating layer. The thickness of the coating layer can be controlled by the ratio of the ionic liquid to the noble metal hydrogel.

[0016] As an improvement, in step (2), the purification method is to wash the hydrogel in pure water for 5 to 6 times. The purified ionic liquid / noble metal hydrogel is freeze-dried at -50°C for 24 hours to obtain the ionic liquid / noble metal aerogel.

[0017] The present invention also provides the use of the above-mentioned ionic liquid / noble metal aerogel in an electrocatalytic oxygen reduction reaction. The specific method is as follows:

[0018] An appropriate amount of ionic liquid / precious metal aerogel powder catalyst was added to a mixed solution of deionized water and Nafion to make the concentration of the ionic liquid / precious metal aerogel be 1 mg / mL, and then the corresponding catalyst ink was obtained by ultrasonication in an ice-water bath; an appropriate amount of ink was dropped onto the surface of a rotating disk platinum carbon electrode and dried at room temperature, and the electrode was used as a working electrode; a Pt wire electrode and an Ag / AgCl electrode were used as a counter electrode and a reference electrode, respectively, to form a three-electrode system with the working electrode; an electrochemical polarization curve test was carried out in a saturated 0.1M KOH electrolyte, and the applied rotation speed was 1600rpm.

[0019] The present invention has the advantages that:

[0020] (1) The present invention prepares the noble metal hydrogel first and then composites it with the ionic liquid for drying, thereby achieving the regulation of the surface electronic structure of the noble metal aerogel. The method is simple and effective, which overcomes the problem that the noble metal aerogel is difficult to functionalize and provides guidance for the functional modification of the noble metal aerogel.

[0021] (2) Based on the rich reaction active sites, faster electron / matter transmission channels and extremely high intrinsic catalytic activity of precious metal aerogels, the present invention can accelerate the desorption and conversion of oxygen species in the oxygen reduction reaction process by effectively regulating its surface electronic structure, thereby improving the intrinsic activity and stability of the catalyst. It can be used as an efficient oxygen reduction reaction catalyst, thereby promoting the application of metal aerogels in sustainable energy conversion and storage devices such as fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a SEM picture of the PtNi-based ionic liquid / noble metal aerogel provided in the examples of the present invention.

[0023] Figure 2 It is a TEM picture of the PtNi-based ionic liquid / noble metal aerogel provided in the examples of the present invention.

[0024] Figure 3 It is an XPS comparison chart of the PtNi-based ionic liquid / noble metal aerogel provided by the example of the present invention and the original PtNi-based noble metal aerogel.

[0025] Figure 4 This is a test graph of the oxygen reduction activity of the PtNi-based ionic liquid / noble metal aerogel catalyst in 0.1M KOH solution provided by an example of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0027] Example 1

[0028] This embodiment discloses a method for controlling the surface electrons of a noble metal aerogel, wherein the noble metal aerogel is a platinum nickel (PtNi)-based noble metal aerogel, and mainly comprises the following steps:

[0029] (1) Preparation of PtNi-based noble metal hydrogel

[0030] At room temperature, add 318.84 mL of deionized water to a 500 mL round-bottom flask and add 197 μL of 10% H 2 PtCl 6 solution and 160 μL of 0.1 M NiCl 2The solution was added to deionized water and stirred at room temperature for 10 minutes. 0.8 mL of freshly prepared 0.1 M NaBH 4 The solution quickly changes from light yellow to light gray, and the solution is stirred for 30 minutes at room temperature, and the color gradually changes from light gray to dark brown. Then, the solution is allowed to stand at room temperature overnight to obtain a PtNi-based noble metal hydrogel.

[0031] (2) Preparation of PtNi-based ionic liquid / noble metal aerogel

[0032] The PtNi-based noble metal hydrogel was fully dispersed by ultrasound, and the ionic liquid (1-(3-aminopropyl)-3-methylimidazolium bromide) was dissolved in an isopropanol solution in advance to obtain an ionic liquid solution, and then an excess of the ionic liquid solution was slowly added while ultrasonically treating, and the resulting mixed solution was ultrasonically treated for 30 minutes to fully mix the two. Finally, the mixed solution was left to stand overnight to allow the sample to completely settle. The prepared sample was washed 3 times with deionized water to remove excess unmodified ionic liquid, and then the sample was placed in a refrigerator and frozen for 5 hours. After freeze drying for 36 hours, a powdered PtNi-based ionic liquid / noble metal aerogel was obtained.

[0033] Electrochemical tests show that the PtNi-based ionic liquid / noble metal aerogel has excellent oxygen reduction performance in 0.1 M KOH solution, with a half-wave potential of 0.944 V and a mass activity of 0.87 A·mg at 0.9 V (RHE). Pt -1 .

[0034] Example 2

[0035] This embodiment discloses a method for regulating the surface electrons of a noble metal aerogel, wherein the noble metal aerogel is a platinum-copper (PtCu)-based noble metal aerogel, and mainly comprises the following steps:

[0036] (1) Preparation of PtCu-based noble metal hydrogel

[0037] At room temperature, add 318.84 mL of deionized water to a 500 mL round-bottom flask and add 197 μL of 10% H 2 PtCl 6 solution and 160 μL of 0.1 M CuCl 2 The solution was added to deionized water and stirred at room temperature for 10 minutes. 0.8 mL of freshly prepared 0.1 M NaBH 4The solution quickly changed from light yellow to light gray, and the solution was stirred for 30 minutes at room temperature, and the color gradually changed from light gray to dark brown. Then, the solution was allowed to stand at room temperature overnight to obtain a PtCu-based noble metal hydrogel.

[0038] (2) Preparation of PtCu-based ionic liquid / noble metal aerogel

[0039] The PtCu-based noble metal hydrogel was fully dispersed by ultrasound, and the ionic liquid (1-(3-aminopropyl)-3-methylimidazolium bromide) was dissolved in an isopropanol solution in advance to obtain an ionic liquid solution, and then an excess of the ionic liquid solution was slowly added while ultrasonically treating, and the resulting mixed solution was ultrasonically treated for 30 minutes to fully mix the two. Finally, the mixed solution was left to stand overnight to allow the sample to completely settle. The prepared sample was washed 3 times with deionized water to remove excess unmodified ionic liquid, and then the sample was placed in a refrigerator and frozen for 5 hours. After freeze drying for 36 hours, a powdered PtCu-based ionic liquid / noble metal aerogel was obtained.

[0040] Electrochemical tests show that the PtCu-based ionic liquid / noble metal aerogel has excellent oxygen reduction performance in 0.1 M KOH solution, with a half-wave potential of 0.931 V and a mass activity of 0.82 A·mg at 0.9 V (RHE). Pt -1 .

[0041] Example 3

[0042] This embodiment discloses a method for controlling the surface electrons of a noble metal aerogel, wherein the noble metal aerogel is a platinum-cobalt (PtCo)-based noble metal aerogel, and mainly comprises the following steps:

[0043] (1) Preparation of PtCo-based noble metal hydrogels

[0044] At room temperature, add 318.84 mL of deionized water to a 500 mL round-bottom flask and add 197 μL of 10% H 2 PtCl 6 solution and 160 μL of 0.1 M CoCl 2 The solution was added to deionized water and stirred at room temperature for 10 minutes. 0.8 mL of freshly prepared 0.1 M NaBH 4 The solution quickly changed from light yellow to light gray, and the solution was stirred for 30 minutes at room temperature, and the color gradually changed from light gray to dark brown. Then, the solution was allowed to stand at room temperature overnight to obtain a PtCo-based noble metal hydrogel.

[0045] (2) Preparation of PtCo-based ionic liquid / noble metal aerogels

[0046] The PtCo-based noble metal hydrogel was fully dispersed by ultrasound, and the ionic liquid (1-(3-aminopropyl)-3-methylimidazolium bromide) was dissolved in an isopropanol solution in advance to obtain an ionic liquid solution, and then an excess of the ionic liquid solution was slowly added while ultrasonically treating, and the resulting mixed solution was ultrasonically treated for 30 minutes to fully mix the two. Finally, the mixed solution was left to stand overnight to allow the sample to completely settle. The prepared sample was washed 3 times with deionized water to remove excess unmodified ionic liquid, and then the sample was placed in a refrigerator and frozen for 5 hours. After freeze drying for 36 hours, a powdered PtCo-based ionic liquid / noble metal aerogel was obtained.

[0047] Electrochemical tests show that the PtCo-based ionic liquid / noble metal aerogel has excellent oxygen reduction performance in 0.1 M KOH solution, with a half-wave potential of 0.919 V and a mass activity of 0.53 A·mg at 0.9 V (RHE). Pt -1 .

[0048] Example 4

[0049] This embodiment discloses a method for regulating the surface electrons of a noble metal aerogel, wherein the noble metal aerogel is a platinum-palladium (PtPd)-based noble metal aerogel, and mainly comprises the following steps:

[0050] (1) Preparation of PtPd-based noble metal hydrogels

[0051] At room temperature, add 318.84 mL of deionized water to a 500 mL round-bottom flask and add 197 μL of 10% H 2 PtCl 6 solution and 160 μL of 0.1 M K 2 PdCl 4 The solution was added to deionized water and stirred at room temperature for 10 minutes. 0.8 mL of freshly prepared 0.1 M NaBH 4 The solution quickly changed from light yellow to light gray, and the solution was stirred for 30 minutes at room temperature, and the color gradually changed from light gray to dark brown. Then, the solution was allowed to stand at room temperature overnight to obtain a PtPd-based noble metal hydrogel.

[0052] (2) Preparation of PtPd-based ionic liquid / noble metal aerogels

[0053] The PtPd-based noble metal hydrogel was fully dispersed by ultrasound, and the ionic liquid (1-(3-aminopropyl)-3-methylimidazolium bromide) was dissolved in an isopropanol solution in advance to obtain an ionic liquid solution, and then an excess of the ionic liquid solution was slowly added while ultrasonically treating, and the resulting mixed solution was ultrasonically treated for 30 minutes to fully mix the two. Finally, the mixed solution was left to stand overnight to allow the sample to completely settle. The prepared sample was washed 3 times with deionized water to remove excess unmodified ionic liquid, and then the sample was placed in a refrigerator and frozen for 5 hours. After freeze drying for 36 hours, a powdered PtPd-based ionic liquid / noble metal aerogel was obtained.

[0054] Electrochemical tests show that the PtPd-based ionic liquid / noble metal aerogel has excellent oxygen reduction performance in 0.1 M KOH solution, with a half-wave potential of 0.933 V and a mass activity of 0.83 A·mg Pt -1 .

[0055] In order to further illustrate the relevant behaviors of the ionic liquid / noble metal aerogel composite material provided by the present invention, the ionic liquid / noble metal aerogel composite material provided by Example 1 is taken as an example for description.

[0056] Figure 1 is a SEM photo of a PtNi-based ionic liquid / noble metal aerogel provided by an example of the present invention;

[0057] like Figure 1 As shown, the hierarchical porous structure of the aerogel can be seen in the SEM image, indicating that the modification of the ionic liquid will not destroy the structure of the aerogel itself, and the aerogel can still have a self-supporting structure, a large specific surface area and a rich pore structure, which can provide more reaction active sites and accelerate the material / electron transfer rate, and can be used as an excellent electrocatalyst.

[0058] Figure 2 is a TEM photo of a PtNi-based ionic liquid / noble metal aerogel provided by an example of the present invention;

[0059] like Figure 2 As shown, in the TEM photo, the presence of an ionic liquid coating layer can be clearly seen on the surface of the metal aerogel, with a thickness of about 3.4 nm, indicating that the ionic liquid has been successfully modified onto the surface of the metal aerogel. The surface-modified ionic liquid can adjust the electronic structure of the metal and play a role in protecting the internal metal from dissolution during the electrocatalytic process.

[0060] Figure 3 This is an XPS comparison diagram of the PtNi-based ionic liquid / noble metal aerogel provided by the example of the present invention and the original PtNi-based noble metal aerogel;

[0061] like Figure 3 As shown, the Pt 4f 7 / 2 The binding energy of the orbital peak is located at 71.3 eV, and the Pt 4f 7 / 2 The binding energy of the orbital peak is located at 71.5eV, which is 0.2eV shifted toward the high binding energy direction, indicating that the electrons are transferred from the PtNi-based noble metal aerogel to the surface-modified ionic liquid; the binding energy of the Ni 2p orbital peak in the original PtNi-based noble metal aerogel is located at 852.4eV, while the binding energy of the Ni 2p orbital peak in the PtNi-based ionic liquid / noble metal aerogel composite is located at 852.6eV, which is consistent with the direction of the binding energy change of the Pt 4f orbital. The above results show that after the ionic liquid is modified on the PtNi-based noble metal aerogel, the electrons are transferred from the metal surface to the ionic liquid, which increases the binding energy and realizes the regulation of the surface electronic structure of the PtNi-based noble metal aerogel.

[0062] Figure 4 This is a test graph of the oxygen reduction activity of the PtNi-based ionic liquid / noble metal aerogel catalyst provided by an example of the present invention in an oxygen-saturated 0.1M KOH solution;

[0063] like Figure 4 As shown in the figure, by comparing the LSV curves of commercial Pt / C catalyst, original PtNi-based noble metal aerogel and PtNi-based ionic liquid / noble metal aerogel catalyst in oxygen-saturated 0.1M KOH solution, the PtNi-based ionic liquid / noble metal aerogel catalyst exhibits the highest starting potential and half-wave potential (1.024V and 0.944V), which are much higher than the original PtNi-based noble metal aerogel (1.006V and 0.912V) and commercial Pt / C catalyst (0.982V and 0.875V), indicating that the PtNi-based ionic liquid / noble metal aerogel catalyst has a lower reaction overpotential and the oxygen reduction reaction is easier to proceed. In addition, a trend similar to the half-wave potential is also observed in the Tafel slope value, that is, the PtNi-based ionic liquid / noble metal aerogel catalyst exhibits the smallest Tafel slope (49.1mV dec -1 ), which is smaller than the original PtNi-based noble metal aerogel (60.9 mV dec -1 ) and commercial Pt / C catalyst (67.3mV dec-1), indicating that the PtNi-based ionic liquid / precious metal aerogel catalyst has the fastest oxygen reduction reaction kinetics. The oxygen reduction performance of different catalysts was further compared by mass activity and specific activity. The PtNi-based ionic liquid / precious metal aerogel catalyst showed the highest mass activity and specific activity, with a mass activity and specific activity of 0.87A mgPt -1 and 1.21 mA cm -2 , which is higher than the original PtNi-based noble metal aerogel (0.44A mg Pt -1 and 0.58 mA cm -2 ) and commercial Pt / C catalyst (0.13A mg Pt -1 and 0.16 mA cm -2 ). Compared with the original PtNi-based noble metal aerogel, the mass activity and specific activity of the PtNi-based ionic liquid / noble metal aerogel catalyst increased by 2.0 times and 2.1 times, respectively, indicating that the oxygen reduction activity can be effectively improved after the ionic liquid is modified with the noble metal aerogel.

[0064] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for regulating the surface electrons of a noble metal aerogel, characterized in that: The following steps are involved: (1) Preparation of noble metal hydrogels reducing an aqueous solution of a noble metal salt to obtain a noble metal hydrogel; (2) Preparation of ionic liquid / noble metal aerogel composites The noble metal hydrogel is mixed with the ionic liquid, and the ionic liquid can be coated on the surface of the hydrogel. Then, the ionic liquid / noble metal aerogel composite material is obtained through purification, drying and other processes.

2. The surface electron regulation method of a noble metal aerogel according to claim 1, characterized in that: In step (1), the noble metal salt solution is a mixed solution of chloroplatinic acid and other metal salts; The other metal salt is one of nickel chloride, copper chloride, cobalt chloride and potassium chloropalladate; The ratio of platinum to metal atoms in other metal salts is 3:1, and the total concentration of metal ions in the noble metal salt aqueous solution is 0.4 mM.

3. The surface electron regulation method of a noble metal aerogel according to claim 1, characterized in that: In step (1), sodium borohydride is used as a reducing agent to synthesize the noble metal hydrogel by a one-step method, wherein the ratio of metal ions to sodium borohydride is 1:1.

5.

4. The surface electron regulation method of a noble metal aerogel according to claim 3, characterized in that: In step (1), the synthesis temperature of the noble metal hydrogel is 25° C. After adding the sodium borohydride solution, stirring is continued for 30 minutes, and then the mixture is allowed to stand at room temperature to obtain the noble metal hydrogel.

5. The surface electron regulation method of a noble metal aerogel according to claim 1, characterized in that: In step (2), the ionic liquid is compounded with the noble metal hydrogel, and the ionic liquid is coated on the surface of the hydrogel to form a stable ionic liquid coating layer; The ionic liquid layer coated on the surface plays a role in regulating the electronic structure of the metal on the surface of the metal aerogel.

6. The surface electron regulation method of a noble metal aerogel according to claim 1, characterized in that: In step (2), the purification method is to wash the hydrogel in pure water for 5 to 6 times, and the purified ionic liquid / noble metal hydrogel is freeze-dried at -50°C for 24 hours.

7. The surface electron regulation method of a noble metal aerogel according to claim 6, characterized in that: In step (2), the ionic liquid is: 1-aminopropyl-3-methylimidazolium bromide.

8. An ionic liquid / noble metal aerogel composite material, characterized in that: Prepared by the method according to any one of claims 1 to 6.

9. Use of the ionic liquid / noble metal aerogel composite material as claimed in claim 7 in an electrocatalytic oxygen reduction reaction.

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