Defect-rich cobaltosic oxide electrocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrocatalysis, in particular to a defect-rich cobaltosic oxide electrocatalyst and a preparation method and application thereof.The preparation method includes the steps that cobalt nitrate and di-methylimidazole are dissolved and centrifuged through solvation to obtain a precursor, then the precursor and potassium bromide are annealed together, finally, washing is conducted, and the defect-rich cobaltosic oxide electrocatalyst is obtained; the defect-rich cobaltosic oxide electrocatalyst can be obtained through vacuum drying, and the defect-rich cobaltosic oxide electrocatalyst has excellent water desorption oxygen desorption reaction electrocatalytic activity and stability and has the potential of large-scale industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and in particular to a defect-rich cobalt tetroxide electrocatalyst, a preparation method and applications thereof. Background Art

[0002] Hydrogen is the most common element in nature. It has high calorific value, good combustion performance, and only produces heat energy and water during the combustion process. It is an efficient and clean energy that can perfectly replace fossil energy.

[0003] Electrocatalytic water splitting to produce hydrogen is an effective technology for obtaining hydrogen energy. However, the oxygen evolution half-reaction (OER) involves a four-electron transfer process, and the reaction process is slow, which restricts the efficiency of water electrolysis to produce hydrogen. Therefore, improving the catalytic efficiency of the oxygen evolution reaction electrocatalyst is the key to achieving efficient water electrolysis to produce hydrogen.

[0004] Currently, electrocatalysts used in water electrolysis mostly use precious metals such as iridium and ruthenium, and their oxides. These metals not only exhibit poor stability under strongly acidic conditions, but are also expensive and have low reserves in the Earth's crust, significantly hindering their commercial application. Therefore, the development and design of non-precious metal-based oxygen evolution electrocatalysts is needed to meet the needs of large-scale industrial applications of water electrolysis to produce hydrogen. Among them, non-precious transition metal-based spinel Co3O4 is considered an economical, resource-rich, and highly active oxygen evolution electrode electrocatalyst, but its stability under acidic conditions is poor.

[0005] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice using a brand-new method. Summary of the Invention

[0006] The purpose of the present invention is to solve the problem of poor oxygen evolution performance and stability of existing electrocatalysts, and to provide a defect-rich cobalt tetroxide electrocatalyst, a preparation method and application thereof.

[0007] In order to achieve the above object, the present invention discloses a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0008] S1: Weigh cobalt nitrate and dimethylimidazole respectively and dissolve them in methanol solution;

[0009] S2: pouring the solution containing dimethylimidazole in step S1 into the solution containing cobalt nitrate, stirring, allowing to stand, centrifuging, and vacuum drying;

[0010] S3: Take the dried product in S2, add potassium bromide and grind it, and anneal it in a muffle furnace;

[0011] S4: The product annealed in S3 is washed and vacuum dried to obtain a defect-rich cobalt oxide electrocatalyst.

[0012] In step S1, the mass of cobalt nitrate is 4.0 g, and the mass of dimethylimidazole is 9.0 g.

[0013] In step S1, the volume of methanol used to dissolve cobalt nitrate is 200 mL, and the volume of methanol used to dissolve dimethylimidazole is 320 mL.

[0014] In step S2, the stirring time is 30 minutes, the standing time is 12 hours, and the vacuum drying temperature is 60° C. and the time is 6 hours.

[0015] In step S3, the amount of potassium bromide is 1 g, the amount of the dried product is 0.2 g, the annealing temperature is 250° C. to 500° C., and the annealing time is 4 h (the heating rate is 2° C. / min).

[0016] In step S4, the product is washed three times with deionized water and ethanol respectively, and the vacuum drying temperature is 60° C. and the time is 6 hours.

[0017] The invention also discloses a defect-rich cobalt tetroxide electrocatalyst prepared by the preparation method and application of the defect-rich cobalt tetroxide electrocatalyst in electrocatalytic water decomposition of oxygen.

[0018] Compared with existing technologies, the present invention has the following advantages: Using cobalt nitrate and dimethylimidazole as raw materials, the cobalt nitrate and dimethylimidazole are first dissolved by solvation and centrifuged to obtain a precursor. This precursor is then annealed with potassium bromide, washed, and vacuum-dried to obtain a defect-rich cobalt oxide electrocatalyst. The electrocatalyst of the present invention has a simple preparation process and exhibits excellent electrocatalytic activity and stability in the water-to-oxygen reaction.

[0019] The defect-rich cobalt oxide electrocatalyst prepared by the present invention has excellent catalytic performance when applied to the electrocatalytic oxygen evolution reaction. 2 When the defect-rich cobalt tetroxide electrocatalyst prepared by the method of the present invention is applied with 10mA / cm 2 The electrocatalytic oxygen evolution performance remains stable after the current is applied for 45 h. Therefore, the electrocatalyst of the present invention has excellent electrocatalytic activity and stability in the water-oxygen evolution reaction, meeting the requirements of large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an SEM image of defect-rich cobalt tetroxide prepared in Example 3;

[0021] Figure 2 TEM image of defect-rich cobalt tetroxide prepared in Example 3;

[0022] Figure 3XRD patterns of defect-rich cobalt oxide prepared in Example 3 and Example 7;

[0023] Figure 4 The XRD patterns of defect-rich cobalt oxide prepared in Examples 2 to 6 are as follows;

[0024] Figure 5 XPS graphs of defect-rich cobalt tetroxide electrocatalysts prepared in Examples 3 and 7 and cobalt tetroxide without potassium bromide treatment;

[0025] Figure 6 The linear sweep voltammetry curve of the oxygen evolution reaction of the defect-rich cobalt trioxide prepared in Examples 1 to 6;

[0026] Figure 7 Linear sweep voltammetry curves of oxygen evolution reaction of defect-rich cobalt tetroxide electrocatalysts prepared in Example 3 and Example 7 and cobalt tetroxide without potassium bromide treatment;

[0027] Figure 8 The Tafel curves are those of the defect-rich cobalt oxide electrocatalyst prepared in Example 3 and the cobalt oxide electrocatalyst prepared in Example 7 without potassium bromide treatment;

[0028] Figure 9 The linear sweep voltammetry curves of the oxygen evolution reaction of the electrocatalysts prepared in Example 3, Example 8 and Example 9;

[0029] Figure 10 These are the stability test results of the defect-rich cobalt oxide electrocatalyst prepared in Example 3 and the cobalt oxide electrocatalyst prepared in Example 7 without potassium bromide treatment. DETAILED DESCRIPTION

[0030] The above and other technical features and advantages of the present invention are described in more detail below with reference to the accompanying drawings.

[0031] Example 1

[0032] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0033] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0034] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0035] (3) Weigh 0.2 g of the dried product and add 1.0 g of potassium bromide to grind.

[0036] (4) Annealing at 250 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0037] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt oxide electrocatalyst.

[0038] Example 2

[0039] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0040] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0041] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0042] (3) Weigh 0.2 g of the dried product and add 1.0 g of potassium bromide to grind.

[0043] (4) Annealing at 300 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0044] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt oxide electrocatalyst.

[0045] Example 3

[0046] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0047] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0048] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0049] (3) Weigh 0.2 g of the dried product and add 1.0 g of potassium bromide to grind.

[0050] (4) Annealing at 350 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0051] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt oxide electrocatalyst.

[0052] Example 4

[0053] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0054] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0055] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0056] (3) Weigh 0.2 g of the dried product and add 1.0 g of potassium bromide to grind.

[0057] (4) Annealing at 400 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0058] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt oxide electrocatalyst.

[0059] Example 5

[0060] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0061] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0062] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0063] (3) Weigh 0.2 g of the dried product and add 1.0 g of potassium bromide to grind.

[0064] (4) Annealing at 450 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0065] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt oxide electrocatalyst.

[0066] Example 6

[0067] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0068] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0069] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0070] (3) Weigh 0.2 g of the dried product and add 1.0 g of potassium bromide to grind.

[0071] (4) Annealing at 500 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0072] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt oxide electrocatalyst.

[0073] Example 7

[0074] This embodiment provides a method for preparing a defect-rich cobalt tetroxide electrocatalyst, comprising the following steps:

[0075] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0076] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0077] (3) Weigh 0.2 g of the dried product and grind it.

[0078] (4) Annealing at 350 °C for 4 h in a muffle furnace (heating rate of 2 °C / min) to obtain a cobalt tetroxide electrocatalyst.

[0079] Example 8

[0080] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0081] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0082] (3) Weigh 0.2 g of the dried product and add 1.0 g of lithium bromide to grind.

[0083] (4) Annealing at 350 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0084] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt tetroxide electrocatalyst.

[0085] Example 9

[0086] (1) Weigh appropriate amounts of 4.0 g of cobalt nitrate and 9.0 g of dimethylimidazole and dissolve them in 200 mL and 320 mL of methanol, respectively.

[0087] (2) Pour the methanol solution containing dimethylimidazole into the methanol solution containing cobalt nitrate, stir for 30 minutes, let it stand for 12 hours, centrifuge and vacuum dry at 60°C for 6 hours.

[0088] (3) Weigh 0.2 g of the dried product and add 1.0 g of lithium bromide and 1.0 g of potassium bromide to grind.

[0089] (4) Annealing at 350 °C for 4 h in a muffle furnace (heating rate of 2 °C / min).

[0090] (5) The above product was washed and vacuum dried at 60°C for 6 h to obtain a defect-rich cobalt tetroxide electrocatalyst.

[0091] from Figure 1 The SEM image of the defect-rich cobalt oxide electrocatalyst prepared in Example 3 shows that it is a mixture of octahedral and tetrahedral structures, its TEM image shows its nanocrystalline structure, and its XRD image shows that its phase composition is cobalt oxide.

[0092] from Figure 4 The XRD patterns of defect-rich cobalt tetroxide electrocatalysts prepared at different annealing temperatures and the qualitative analysis of the standard cards show that the prepared catalysts only contain the (111), (220), (311), (222), (400), (422), (511) and (440) crystal planes of the Co3O4 phase. At the same time, it can be observed from the figure that the half-peak width of the (311) crystal plane (36.84°) of the Co3O4 phase gradually narrows as the calcination temperature increases from 300℃ to 500℃, indicating that the crystallinity of the sample improves with increasing temperature. In order to further explore the change in the grain size of cobalt tetroxide at different calcination temperatures, the average grain size of the above samples was calculated using the Scherrer formula. The Scherrer formula is as follows:

[0093] D=kλ / (βcosθ) (1)

[0094] Where: D is the grain size; k is a constant; λ is the wavelength of the Kα1 spectrum of the Cu target of the diffractometer; β is the half-height width of the diffraction peak; θ is the diffraction half-angle.

[0095] In formula (1), the value of the constant k is related to the definition of β. When β is the half-height width, k is 0.89. Substituting the half-height width into formula (1), the FWHM calculated based on the X-ray diffraction data obtained from the test, and the FWHM value of each sample into the Scherrer formula, the grain sizes of the (220), (311), (400), (511) and (440) crystal planes are obtained. The average value is then taken to obtain V o - Average particle size of Co3O4 nanoparticles. When the temperature is 300℃, 350℃, 400℃, 450℃, and 500℃, the corresponding average particle size is 7.82nm, 16.74nm, 18.76nm, 19.78nm, and 20.88nm. In general, as the calcination temperature increases from 300℃ to 500℃, the grain size of the sample increases with the increase of temperature, which also shows that V o The crystallinity of -Co3O4 becomes better with increasing temperature. However, the peak intensity of the electrocatalyst prepared in Example 3 is weaker and the grain size is smaller, which indicates that there are more defects in it.

[0096] XPS characterization of defect-rich cobalt oxide electrocatalyst (Vo-Co3O4) and cobalt oxide electrocatalyst not treated with potassium bromide (Co3O4) was performed. Figure 5 ) found that the high-resolution Co 2p XPS spectra of the two catalysts can be decomposed into two groups of peaks, corresponding to Co 2+ (796.7 and 781.4 eV) and Co 3+ (795.1 and 779.8 eV), indicating that the peak position distribution of the two groups of samples is similar. The Co of the defect-rich cobalt oxide electrocatalyst (Vo-Co3O4) obtained after potassium bromide treatment 2+ / Co 3+ The ratio is larger than that of the cobalt oxide electrocatalyst (Co3O4) that has not been treated with potassium bromide, indicating that oxygen vacancies have been successfully introduced. The introduced oxygen vacancies shift the center of the metal d-band toward a higher Fermi level, resulting in a decrease in antibonding state filling, providing more active sites for the adsorption of oxygen-containing intermediates (OH*, OOH*, and O*), thereby promoting the OER kinetics.

[0097] The defect-rich cobalt tetroxide electrocatalysts (V o -Co3O4) to compare its electrocatalytic oxygen evolution ability with that of the cobalt oxide electrocatalyst (Co3O4) that has not been treated with potassium bromide. The specific process is as follows:

[0098] 10 mg of the electrocatalyst prepared in different examples was added to 375 μL of deionized water and 125 μL of ethanol, and then 30 μL of Nafion was added. After ultrasonication for 60 minutes, 200 μL of the solution was applied (in two batches, 100 μL each time) to a 2 cm 2 The carbon paper was used as the working electrode, the platinum electrode was used as the counter electrode, the Hg / HgSO4 electrode was used as the reference electrode, and the freshly prepared 0.5MH2SO4 aqueous solution (pH = 0) was used as the electrolyte to test the polarization curve of the electrocatalytic oxygen evolution reaction ( Figure 6 All polarization curves have been corrected by iR compensation. Figure 6 It can be seen that when the annealing temperature is 350℃, the electrocatalytic performance of the obtained catalyst is optimal.

[0099] V o -Co3O4, Co3O4 as electrocatalyst, take 10mg, add 375μL deionized water and 125μL ethanol and add 30μL Nafion. After ultrasonication for 60min, take 200μL solution and apply it on 2cm (apply twice, 100μL each time) 2 The carbon paper was used as the working electrode, the platinum electrode was used as the counter electrode, the Hg / HgSO4 electrode was used as the reference electrode, and the freshly prepared 0.5M H2SO4 aqueous solution (pH = 0) was used as the electrolyte to test the polarization curve of the electrocatalytic oxygen evolution reaction ( Figure 7 ). Compare V o -Co3O4, Co3O4 at 10mA / cm 2 The overpotential under Figure 7 ), we can see that V o -Co3O4 at 10mA / cm 2 Only an overpotential of 377 mV is required at this current density, and its performance is far superior to the electrocatalytic performance of the catalyst that has not been treated with potassium bromide.

[0100] contrast Figure 8 V o - Co3O4, Co3O4 Tafel curve, we know that V o -The Tafel slope of Co3O4 is 86.02 mV·dec -1 , compared with the Tafel slope of Co3O4 of 98.18mV·dec -1 The Tafel slope indicates the difficulty of the electrochemical reaction. The smaller the slope, the easier the electrochemical reaction occurs.

[0101] pass Figure 9 It can be seen that the OER activity of the defect-rich cobalt oxide electrocatalyst obtained by potassium bromide treatment is much better than that obtained by lithium bromide and a mixture of potassium bromide and lithium bromide.

[0102] V o -Co3O4, Co3O4 applied 10mA / cm 2 The electrocatalytic stability was tested by current. Figure 10 The results show that the electrocatalytic oxygen evolution performance of Vo-Co3O4 remains stable after 45 hours of testing, and is suitable for industrial application.

[0103] The above description is merely a preferred embodiment of the present invention and is intended to be illustrative rather than restrictive of the present invention. Those skilled in the art will appreciate that many changes, modifications, and even equivalents may be made to the present invention within the spirit and scope of the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a defect-rich cobalt trioxide electrocatalyst, characterized in that: The following steps are involved: S1: Weigh cobalt nitrate and dimethylimidazole respectively and dissolve them in methanol solution; S2: pouring the solution containing dimethylimidazole in step S1 into the solution containing cobalt nitrate, stirring, allowing to stand, centrifuging, and vacuum drying; S3: Take the dried product in S2, add potassium bromide and grind it, and anneal it in a muffle furnace; S4: The product annealed in S3 is washed and vacuum dried to obtain a defect-rich cobalt oxide electrocatalyst.

2. The method for preparing a defect-rich cobalt trioxide electrocatalyst according to claim 1, wherein: In step S1, the mass of cobalt nitrate is 4.0 g, and the mass of dimethylimidazole is 9.0 g.

3. The method for preparing a defect-rich cobalt oxide electrocatalyst according to claim 1, wherein: In step S1, the volume of methanol used to dissolve cobalt nitrate is 200 ml, and the volume of methanol used to dissolve dimethylimidazole is 320 ml.

4. The method for preparing a defect-rich cobalt tetroxide electrocatalyst according to claim 1, wherein: In step S2, the stirring time is 30 minutes, the standing time is 12 hours, and the vacuum drying temperature is 60° C. and the time is 6 hours.

5. The method for preparing a defect-rich cobalt trioxide electrocatalyst according to claim 1, wherein: In step S3, the amount of potassium bromide is 1 g, the amount of the dried product is 0.2 g, the annealing temperature is 250° C. to 500° C., the annealing time is 4 h, and the heating rate during annealing is 2° C. / min.

6. The method for preparing a defect-rich cobalt trioxide electrocatalyst according to claim 1, wherein: In step S4, the product is washed three times with deionized water and ethanol respectively, and the vacuum drying temperature is 60° C. and the time is 6 hours.

7. A defect-rich cobalt trioxide electrocatalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the defect-rich cobalt trioxide electrocatalyst according to claim 7 in electrocatalytic water decomposition of oxygen.

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