A noble metal-modified heterogeneous hybrid oxide catalyst, preparation method and application

Abstract

The present invention discloses a noble metal modified heterogeneous hybrid oxide catalyst and a preparation method thereof, comprising the following steps: (1) adding cobalt nitrate hexahydrate, cerium nitrate hexahydrate and an acid solution into an anhydrous ethanol solution, and stirring to obtain a uniform precursor solution; (2) transferring the precursor solution to a kettle, placing nickel foam in the solution, and then carrying out a solvothermal reaction; (3) after the reaction is completed and cooled to room temperature, taking out the nickel foam and washing it several times with deionized water and alcohol, and drying the obtained material in a vacuum oven overnight to obtain an electrocatalyst. The present invention can prepare an electrocatalyst with a porous nanosheet array morphology and a unique amorphous / crystalline phase heterostructure, and has a large specific surface area, which is beneficial to exposing more active sites and accelerating the reaction mass transfer / charge transfer process, thereby showing a significantly reduced overpotential and Tafel slope in the hydrogen evolution reaction and oxygen evolution reaction, providing a new idea for the development of highly active catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and particularly relates to a noble metal modified amorphous / crystalline heterogeneous hybrid oxide catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Due to advantages such as sustainability and environmental friendliness, metal-air batteries and water electrolyzers are regarded as candidates for next-generation clean energy devices. However, the oxygen evolution reaction (OER) involving multi-step proton-coupled electron transfer requires a high potential to drive the reaction due to slow kinetics, which limits the energy conversion efficiency of energy storage devices. Currently, noble metal-based catalysts (Ru / RuO2, Ir / IrO2, etc.) exhibit excellent catalytic performance, but their scarcity and high cost limit their widespread application. Therefore, it is particularly important and urgent to explore low-cost and high-efficiency OER electrocatalysts.

[0003] In recent years, transition metal oxides (TMOs, such as Ni, Co, and Fe, etc.) have received extensive research attention due to their abundant reserves and low prices. It is worth noting that most reported TMOs are crystalline phase catalysts with long-range order and stable structures. However, their inherent catalytic activity is difficult to meet the requirements of commercialization. On the one hand, the inherent semiconductor properties of some TMOs lead to poor charge transfer ability. On the other hand, due to the rigid crystal structure, the exposure and subsequent activation of active sites in crystalline phase TMOs are restricted to a certain extent. Among various strategies for improving crystalline phase catalysts, amorphization, defect engineering, and introduction of heteroatoms are regarded as very effective modification methods. In recent years, amorphous catalysts, due to their characteristics of long-range order and short-range disorder, the high flexibility of surface atoms induces a larger specific surface area, more active sites, and faster charge transfer rates. More importantly, the local flexibility and dynamic arrangement of the distorted M-O polyhedral network in amorphous structure TMOs usually generate a large number of defects / vacancies and coordinatively unsaturated sites on the material surface, further increasing the electron density of adjacent metal atoms and increasing the intrinsic conductivity of the material, thereby enhancing the catalytic performance of the material. In addition, through crystal regulation and the introduction of heteroatoms in a coordinated manner, by means of amorphous / crystalline heterostructure and electronic structure regulation, it is possible to effectively increase the number of active sites and the intrinsic catalytic activity of the catalyst. Summary of the Invention

[0004] In view of this, the present invention provides a noble metal modified amorphous / crystalline heterogeneous hybrid oxide catalyst, a preparation method thereof, and an application thereof. The prepared catalyst exhibits characteristics such as high activity and cycle stability. The first object of the present invention is to provide a preparation method for a noble metal modified amorphous / crystalline heterostructure multi-metal oxide electrocatalyst, comprising the following steps:

[0005] (1) Add a certain amount of cobalt nitrate hexahydrate, cerium nitrate hexahydrate, and an acid solution to an anhydrous ethanol solution, and stir to obtain a homogeneous precursor solution;

[0006] (2) Transfer the precursor solution to a stainless-steel hydrothermal autoclave lined with polytetrafluoroethylene. Place a piece of cut foam nickel into the solution and carry out a solvothermal reaction under certain temperature and time conditions;

[0007] (3) After the reaction is completed and cooled to room temperature, take out the foam nickel and wash it several times with deionized water and alcohol. Place the obtained material in a vacuum oven and dry it overnight to obtain a noble metal-modified heterostructure multi-metal oxide electrocatalyst.

[0008] Further, in step (1), the molar ratio of the fed cobalt nitrate hexahydrate to cerium nitrate hexahydrate is 3:2.

[0009] Further, in step (1), the acid solution is chloroplatinic acid solution or chloroiridic acid solution.

[0010] Further, in step (1), the concentration of the acid solution is 5mg mL -1 .

[0011] Further, in step (1), the total amount of the added acid solution (x) and anhydrous ethanol (y) is 30 mL, that is, x + y = 30, where x = 2 - 6 mL.

[0012] Further, in step (2), the size of the foam nickel is 2*4 cm.

[0013] Further, in step (2), place a piece of cut foam nickel into the solution and carry out a solvothermal reaction at 150 - 170 °C for 14 - 16 h.

[0014] Further, in step (3), the drying temperature in the vacuum oven is 50 - 70 °C.

[0015] The second object of the present invention is to provide an electrocatalyst prepared by using the above-mentioned preparation method of a noble metal-modified amorphous / crystalline heterogeneous hybrid oxide catalyst (M-Co3O4 / CeO2, M = Pt or Ir) electrocatalyst.

[0016] The third object of the present invention is to provide an application of the above electrocatalyst in hydrogen evolution reaction and oxygen evolution reaction.

[0017] The present invention has the following technical advantages:

[0018] The present invention provides a preparation method of a noble metal-modified amorphous / crystalline heterogeneous hybrid oxide catalyst grown on the surface of nickel foam, and prepares a multi-metal oxide electrocatalyst with a unique amorphous / crystalline heterostructure and a nanosheet array morphology, which is beneficial to exposing more active sites and accelerating the penetration of the electrolyte and the gas transport process during the reaction, and thus shows a low HER / OER overpotential and enhanced electrical conductivity. The present invention provides a new way for the rational design and development of electrocatalytic efficient water splitting applications. Description of the Drawings

[0019] Figure 1 a, Figure 1 b and Figure 1 c are the scanning electron micrographs of Co3O4 / CeO2, Ir-Co3O4 / CeO2, and Pt-Co3O4 / CeO2 catalysts, respectively; Figure 1 d, Figure 1 e and Figure 1 f are the X-ray diffraction patterns of Co3O4 / CeO2, Ir-Co3O4 / CeO2, and Pt-Co3O4 / CeO2 catalysts, respectively;

[0020] Figure 2 is the high-resolution transmission electron micrograph of the Pt-Co3O4 / CeO2 catalyst of the present invention;

[0021] Figure 3 a, Figure 3 b, Figure 3 c and Figure 3 d are the water contact angle images of Ni foam, Co3O4 / CeO2, Ir-Co3O4 / CeO2, and Pt-Co3O4 / CeO2 catalysts, respectively;

[0022] Figure 4 are the hydrogen evolution reaction and oxygen evolution reaction performance diagrams of the Co3O4 / CeO2, Ir-Co3O4 / CeO2, and Pt-Co3O4 / CeO2 catalysts of the present invention: Figure 4 a is the LSV curve diagram of the hydrogen evolution reaction; Figure 4 b is the Tafel diagram obtained from Figure 4 a; Figure 4 c is the LSV curve diagram of the oxygen evolution reaction; Figure 4 d is the Tafel diagram obtained from Figure 4 c. Detailed Embodiments

[0023] The present invention provides a preparation method of a noble metal-modified amorphous / crystalline heterogeneous hybrid oxide catalyst, an electrocatalyst, and its application.

[0024] The noble metal-modified amorphous / crystalline heterogeneous hybrid oxides are Ir-Co3O4 / CeO2 and Pt-Co3O4 / CeO2 catalysts (M-Co3O4 / CeO2, M = Pt or Ir).

[0025] I. The preparation process of the M-Co3O4 / CeO2 catalyst includes the following steps:

[0026] (1) Cobalt nitrate hexahydrate and cerium nitrate hexahydrate are added to 26 mL of anhydrous ethanol solution according to a molar feed ratio of 3:2 and 4 mL of chloroplatinic acid solution (or chloroiridic acid solution, with a concentration of 5 mg mL -1 ) and stirred to obtain a homogeneous precursor solution;

[0027] (2) The precursor solution and a piece of cut foam nickel (2*4 cm) are transferred to a stainless steel autoclave with a polytetrafluoroethylene liner, maintained at 150 - 170 °C for 15 h, cooled to room temperature, and then rinsed with deionized water and anhydrous ethanol;

[0028] (4) The above materials are placed in a vacuum oven (50 - 70 °C) for overnight drying to obtain a noble metal-modified amorphous / crystalline heterogeneous hybrid oxide catalyst grown on the surface of foam nickel.

[0029] The application of the above-prepared electrocatalyst in the hydrogen evolution reaction and oxygen evolution reaction is as follows. The specific application steps are as follows:

[0030] (1) The prepared electrocatalyst is cut into a 1*1 working electrode, a carbon rod is used as the counter electrode, and an Ag / AgCl electrode is used as the reference electrode for three-electrode testing.

[0031] (2) Before the electrochemical performance test, aiming to remove impurities on the material surface, cyclic voltammetry activation treatment is carried out in a 1 M KOH solution saturated with N2 at a scanning rate of 50 mV s -1 .

[0032] (3) Linear sweep voltammetry is used to test the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of the catalyst. The test conditions are as follows: The test is carried out in a 1 M KOH electrolyte saturated with N2, the scanning rate is 5 mV s -1 , and the test voltage range for the hydrogen evolution reaction (HER) is: -0.35 - 0.05 V (relative to the reversible hydrogen electrode, the potential is corrected for IR). The test voltage range for the oxygen evolution reaction (OER) is: -1.2 - 1.7 V (relative to the reversible hydrogen electrode, the potential is corrected for IR).

[0033] Figure 1 a and Figure 1b shows that the prepared Co3O4 / CeO2 and Ir-Co3O4 / CeO2 materials exhibit a nanoparticle morphology; in contrast, the Pt-Co3O4 / CeO2 catalyst exhibits a porous array structure composed of vertically aligned nanosheets( Figure 1 c), and this unique porous array structure is beneficial to the penetration of the electrolyte and the gas diffusion process, thus enhancing the mass / charge transfer process. Figure 1 d is the X-ray diffraction pattern of the Co3O4 / CeO2 material. The prepared sample has obvious diffraction peaks at 28.9°, 31.3°, 33.4°, 36.8°, 47.8°, 56.7°, 59.4° and 65.3°. Among them, 28.9°, 33.4°, 47.8°, 56.7° correspond to the (111), (200), (220) and (311) crystal planes of CeO2 respectively; 31.3°, 36.8°, 59.4° and 65.3° correspond to the (220), (311), (511) and (440) crystal planes of Co3O4 respectively, further indicating the formation of the Co3O4 and CeO2 composite material. After doping with Ir and Pt, no other additional diffraction peaks appear, indicating that no other substances are introduced and the material maintains a good crystal structure( Figure 1 e and Figure 1 f). Figure 2 is the high-resolution transmission electron microscopy (HRTEM) image of the Pt-Co3O4 / CeO2 catalyst. The prepared Pt-Co3O4 / CeO2 catalyst exhibits obvious amorphous and crystalline regions, and there is a rich heterogeneous interface structure, further confirming that the prepared Pt-Co3O4 / CeO2 material has the structural characteristics of amorphous / crystalline heterophase hybridization. Based on the above analysis, the successful preparation of the noble metal-modified amorphous / crystalline heterophase hybrid oxide catalyst is proved.

[0034] As Figure 3 shown, compared with Ni foam (116.2°), Co3O4 / CeO2 (103.9°) and Ir-Co3O4 / CeO2 (94.2°), the Pt-Co3O4 / CeO2 catalyst shows the smallest water contact angle of 83.5°, indicating that Pt-Co3O4 / CeO2 has better hydrophilic performance, which is beneficial to accelerating the penetration of the electrolyte. Electrochemical performance tests on the prepared materials show that( Figure 4 a and Figure 4 b): Pt-Co3O4 / CeO2 exhibits a smaller hydrogen evolution overpotential (31 mV@10 mA cm -2 ) and Tafel slope (42.9 mV dec -1 ), which is significantly better than Co3O4 / CeO2 (215 mV@10 mA cm -2 , 151.7 mV dec-1 ), and Ir-Co3O4 / CeO2 (56 mV @ 10 mA cm -2 , 98.3 mV dec -1 ) catalyst. As Figure 4 c and Figure 4 d show, Pt-Co3O4 / CeO2 exhibits the best OER performance (348 mV @ 50 mA cm -2 , 60.1 mV dec -1 ), superior to Co3O4 / CeO2 (411 mV @ 50 mA cm -2 , 84.3 mV dec -1 ) and Ir-Co3O4 / CeO2 (362 mV @ 50 mA cm -2 , 71.2 mV dec -1 ) materials, indicating that Pt-Co3O4 / CeO2 has better bifunctional catalytic activities for HER and OER; in addition, the introduction of Ir and Pt can also show a positive effect compared with Co3O4 / CeO2.

[0035] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A preparation method of a noble metal-modified heterogeneous structure multi-metal oxide electrocatalyst, characterized in that It includes the following steps: (1) Add a certain amount of cobalt nitrate hexahydrate, cerium nitrate hexahydrate and an acid solution into an anhydrous ethanol solution, and stir to obtain a uniform precursor solution; (2) Transfer the precursor solution to a stainless-steel hydrothermal autoclave lined with polytetrafluoroethylene, place a piece of cut foam nickel into the solution, and carry out a solvothermal reaction under certain temperature and time conditions; (3) After the reaction is completed and cooled to room temperature, take out the foam nickel and wash it several times with deionized water and alcohol, and place the obtained material in a vacuum oven to dry overnight to obtain a noble metal-modified heterostructure multi-metal oxide electrocatalyst; In step (1), the molar ratio of the cobalt nitrate hexahydrate and cerium nitrate hexahydrate fed is 3:2; In step (1), the total volume x of the acid solution added and the volume y of the anhydrous ethanol is 30 mL, that is, x + y = 30 mL, where x = 2 - 6 mL; In step (2), place a piece of cut foam nickel into the solution, and carry out a solvothermal reaction at 150 - 170 °C for 14 - 16 h.

2. The preparation method of the noble metal-modified heterostructure multi-metal oxide electrocatalyst according to claim 1, wherein, The acid solution described in step (1) is a chloroplatinic acid solution or a chloroiridic acid solution.

3. The preparation method of the noble metal-modified heterostructure multi-metal oxide electrocatalyst according to claim 2, wherein, The concentration of the acid solution described in step (1) is 5 mg / mL -1 .

4. The preparation method of the noble metal-modified heterostructure multi-metal oxide electrocatalyst according to claim 1, wherein, The size of the foam nickel described in step (2) is 2 * 4 cm.

5. The preparation method of the noble metal-modified heterogeneous structure multi-metal oxide electrocatalyst according to claim 1, characterized in that, The drying temperature in the vacuum oven in step (3) is 50 - 70 °C.

6. A noble metal-modified heterostructure multi-metal oxide electrocatalyst prepared by the method according to any one of claims 1 - 5.

7. An application of the noble metal-modified heterostructure multi-metal oxide electrocatalyst according to claim 6 in hydrogen evolution reaction and oxygen evolution reaction.

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