Preparation and application of cobalt-based catalyst for electrooxidation of 5-hydroxymethylfurfural

Abstract

The invention belongs to the technical field of functional materials and energy, and particularly relates to preparation and application of a cobalt-based catalyst for electrooxidation of 5-hydroxymethylfurfural (HMF). Cobalt oxide (CoOx) rich in oxygen vacancies (VO) is prepared on a three-dimensional porous framework substrate through a cathode electrodeposition method, and the cobalt-based catalyst is obtained through cleaning and drying. According to the present invention, the VO rich in the catalyst can promote the oxidation reconstruction of CoOx into the gamma-CoOOH phase so as to rapidly convert the CoOx into the active phase CoO2, such that the oxidation of the hydroxyl group in the HMF molecule is important so as to substantially improve the HMF oxidation reaction performance, and the synthesized CoOx has the nanosheet array structure and the rich active site; an electro-catalysis result shows that the catalyst has very excellent catalytic activity, selectivity and stability under relatively high current density, so that the catalyst has relatively great application potential in the aspect of electro-oxidation of HMF.

Description

Technical Field

[0001] The present invention belongs to the technical fields of functional materials and energy, and particularly relates to the preparation and application of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural (HMF). Background Art

[0002] With the consumption of fossil energy and the intensification of environmental crises, it has become urgent to find an environmentally friendly and pollution-free sustainable clean energy. Hydrogen energy is considered to be one of the cleanest and most promising energies at present because of its high calorific value and the combustion product being zero-pollution water. At present, the electrochemical water splitting process for hydrogen production is mature, highly productive, and nearly pollution-free, and is considered to be the most promising hydrogen production method. However, the anodic oxygen evolution reaction (OER) in water electrolysis for hydrogen production has slow kinetics and a relatively high theoretical potential, which severely limits the application of water electrolysis for hydrogen production technology. The reaction of HMF oxidation to produce 2,5-furandicarboxylic acid (FDCA) not only has a very low theoretical potential (0.3V vs RHE), but also the product FDCA has higher applicability. It has been reported as a "green" platform chemical in the chemical industry and is expected to replace terephthalic acid as the basic raw material for synthesizing valuable polymers. Replacing OER with the HMF oxidation reaction (HMFOR) can significantly reduce the energy consumption for hydrogen production and improve the energy utilization efficiency, becoming a promising application method at present.

[0003] Currently, the catalysts for HMFOR mainly focus on transition metal-based materials. Among them, cobalt-based materials have received extensive attention from researchers due to their advantages such as low oxidation potential and excellent activity in catalyzing HMFOR. CoO x has become a research hotspot in the field of electrocatalytic HMFOR due to its rich active sites and variable valence states. CoO x will turn into high-valent cobalt species as the active sites for catalytic reactions under alkaline conditions. Co 4+ (CoO2) is generally considered to be the main active site for catalyzing HMFOR. In order to promote the oxidative reconstruction of CoO x and improve the catalytic activity and clarify the catalytic mechanism, many efforts have been made. However, the process of in-situ electrochemical oxidation of CoO x to generate CoO2 is still unclear and blocked, and its performance is not satisfactory. The design of cobalt-based materials for catalyzing HMFOR still has a long way to go. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the above-mentioned existing technologies and provide the preparation and application of a cobalt-based catalyst for electro-oxidizing HMF. The present invention uses a one-step electrodeposition method to prepare CoO x on a three-dimensional porous framework substrate for efficiently oxidizing HMF to FDCA. This method is simple, rapid, and easy to scale up, and the synthesized CoOx It is rich in oxygen vacancies (V O ), has a dense nanosheet array structure, and has abundant active sites, providing an effective reference for studying the mechanism of V O promoting CoO x reconstruction.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] The first aspect of the present invention provides a preparation method of a cobalt-based catalyst for electro-oxidizing HMF, including the following steps: preparing CoO O rich in V x on a three-dimensional porous framework substrate by cathodic electrodeposition method, and obtaining the cobalt-based catalyst after washing and drying.

[0007] Further, the cathodic electrodeposition method uses a three-electrode system, wherein a three-dimensional porous framework substrate is used as the working electrode, Ag / AgCl is used as the reference electrode, a Pt column is used as the counter electrode, and an aqueous cobalt sulfate solution is used as the electrolyte.

[0008] Further, the three-dimensional porous framework substrate is copper foam or nickel foam.

[0009] Further, the three-dimensional porous framework substrate is ultrasonically cleaned in HCl, ultrapure water, and absolute ethanol in sequence before use to remove the oxides and residual organic substances on its surface.

[0010] Further, the current density of the cathodic electrodeposition is 50 mA cm -2 , and the time is 300 s.

[0011] Further, the aqueous cobalt sulfate solution is formed by adding CoSO4·7H2O to ultrapure water.

[0012] Further, the medium used for washing is ultrapure water and ethanol.

[0013] Further, the drying temperature is room temperature and the time is 12 h.

[0014] The second aspect of the present invention provides the cobalt-based catalyst prepared by the preparation method described in the first aspect.

[0015] The third aspect of the present invention provides the application of the cobalt-based catalyst described in the second aspect in electro-oxidizing HMF. The V O rich in the catalyst can promote the reconstruction of CoO x into the γ-CoOOH phase, and then be faster transformed into the active phase CoO2, which is crucial for the oxidation of the hydroxyl group in the HMF molecule, greatly improving the HMFOR performance, and the synthesized CoO xIt has a nanosheet array structure and is rich in active sites. The electrocatalysis results show that the catalyst has very excellent catalytic activity and selectivity at a relatively high current density, which makes it have extremely high potential in the application of electrooxidation of HMF.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) Excellent selectivity and stability. The catalyst can obtain excellent catalytic performance and stability under conditions close to industrial catalysis. The conversion rate is close to 100% and the Faraday efficiency reaches 98% at a cell voltage of 1.8 V vs RHE in the membrane electrode assembly (MEA).

[0018] (2) Rich in V O . By controlling the type of deposited substrate, CoO O phases containing different contents of V x can be obtained. Among them, CoO O with a higher V x content can be more easily converted into the CoO2 active phase for catalyzing HMFOR.

[0019] (3) The design idea of the present invention is reasonable. A simple electrodeposition method is used to prepare a V O -rich CoO x catalyst on a three-dimensional porous framework substrate to explore the influence of rich V O on the CoO x oxidation and reconstruction process during the HMFOR process, which has great research value. Description of the Drawings

[0020] Figure 1 SEM images of the catalysts prepared in Examples 1 and 2 (a-c are the catalysts prepared in Example 1, and d-f are the catalysts prepared in Example 2);

[0021] Figure 2 TEM images of the catalysts prepared in Examples 1 and 2 (a-b are the catalysts prepared in Example 1, and c-d are the catalysts prepared in Example 2);

[0022] Figure 3 X-ray diffraction patterns of the catalysts prepared in Examples 1 and 2;

[0023] Figure 4 X-ray diffraction pattern of CF prepared in Comparative Example 1;

[0024] Figure 5 Raman spectra of the catalysts prepared in Examples 1 and 2;

[0025] Figure 6XPS spectra of the catalysts prepared in Examples 1 and 2 (a is the full spectrum, b is the Co 2p energy spectrum);

[0026] Figure 7 XPS spectra of the catalysts prepared in Examples 1 and 2 (O 1s energy spectrum);

[0027] Figure 8 In-situ Raman graphs of the catalysts prepared in Examples 1 and 2 during the HMFOR process (a is the catalyst prepared in Example 1, b is the catalyst prepared in Example 2);

[0028] Figure 9 Performance graphs of the catalysts prepared in Examples 1 and 2 (a is the LSV curve, b is the Tafel slope graph, c is the electrochemical impedance spectrum, d is the fitted double-layer capacitance graph);

[0029] Figure 10 Performance graph of the CF prepared in Comparative Example 1;

[0030] Figure 11 Liquid chromatography graphs of the catalysts prepared in Examples 1 and 2 (a and b are the intermediate product concentration change graph and the liquid chromatography graph of the catalyst prepared in Example 1 respectively, c and d are the intermediate product concentration change graph and the liquid chromatography graph of the catalyst prepared in Example 2 respectively);

[0031] Figure 12 Stability graph of the catalyst prepared in Example 1 at a potential of 1.5 V in an H-type electrolytic cell;

[0032] Figure 13 Stability graph of the catalyst prepared in Example 1 at a cell voltage of 1.8 V in an MEA. Detailed implementation manners

[0033] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0034] Example 1

[0035] CoO x / CF catalyst preparation, including the following steps:

[0036] Step 1, treatment of copper foam (CF)

[0037] The purchased commercial CF was cut into a shape of 1 cm × 2 cm, and then ultrasonically cleaned in 2M HCl, ultrapure water, and absolute ethanol for 10 min each to remove surface oxides and residual organic substances, and finally dried for later use.

[0038] Step 2, Prepare CoO on CF x , including the following steps:

[0039] Step 2.1, Add 0.8433 g of CoSO4·7H2O into ultrapure water (60 mL) and stir evenly;

[0040] Step 2.2, After the solution is stirred evenly (15 min), use a three-electrode system to perform electrodeposition operation in the above solution: The treated CF substrate is used as the working electrode, Ag / AgCl is used as the reference electrode, and the Pt column is used as the counter electrode. All are placed in the above solution for cathodic electrodeposition (current density is 50 mA cm -2 , for 300 s);

[0041] Step 2.3, After the reaction is completed, wash the CF with ultrapure water and ethanol (volume ratio 1:1) and dry it at room temperature for 12 h. The obtained sample is labeled as CoO x / CF.

[0042] Example 2

[0043] CoO x / NF catalyst preparation, including the following steps:

[0044] Step 1, Treatment of nickel foam (NF)

[0045] Cut the purchased commercial NF into a shape of 1 cm × 2 cm, and then ultrasonically clean it in 2 M HCl, ultrapure water and absolute ethanol for 10 min each to remove surface oxides and residual organic substances, and finally dry it for standby.

[0046] Step 2, Prepare CoO on NF x , including the following steps:

[0047] Step 2.1, Add 0.8433 g of CoSO4·7H2O into ultrapure water (60 mL) and stir evenly;

[0048] Step 2.2, After the solution is stirred evenly (15 min), use a three-electrode system to perform electrodeposition operation in the above solution: The treated NF substrate is used as the working electrode, Ag / AgCl is used as the reference electrode, and the Pt column is used as the counter electrode. All are placed in the above solution for cathodic electrodeposition (current density is 50 mA cm -2 , for 300 s);

[0049] Step 2.3, After the reaction is completed, wash the NF with ultrapure water and ethanol (volume ratio 1:1) and dry it at room temperature for 12 h. The obtained sample is labeled as CoO x / NF.

[0050] Comparative Example 1

[0051] The purchased commercial CF was cut into a shape of 1 cm × 2 cm, and then ultrasonically cleaned in 2M HCl, ultrapure water, and absolute ethanol for 10 min each to remove surface oxides and residual organic matter, and finally dried for standby.

[0052] Structure Characterization

[0053] Taking CoO x / CF obtained in Example 1 above as an example, first SEM characterization was carried out, and it was found that CoO x / CF exhibited a nanosheet array structure ( Figure 1 ); secondly, the TEM image presented the characteristics of long-range disorder and short-range order, and the few lattice fringes that appeared corresponded to the crystal planes of Co3O4 and CoO respectively ( Figure 2 ); the XRD results showed that the crystallinity of CoO x / CF was poor ( Figure 3 ); in the Raman spectrum, CoO x / CF showed characteristic peaks belonging to Co3O4 and a large peak belonging to the characteristics of CoO, indicating that CoO x catalyst was successfully synthesized on CF ( Figure 5 ); it can be seen from the XPS results that cobalt in the catalyst existed in the forms of Co 2+ and Co 3+ , which was in line with the valence state distribution of Co when Co3O4 and CoO coexisted ( Figure 6 ); while the O1s spectrum of the catalyst showed that CoOx / CF contained richer Vo ( Figure 7 ); in-situ Raman tests were also carried out on CoO x / CF to deeply explore the reconstruction process of CoO x / CF during the HMFOR process. The results showed that the CoO x phase was reconstructed into β-CoOOH and γ-CoOOH at 1 V (vs RHE), and further reconstructed into the CoO2 phase at 1.3 V (vs RHE) (the starting potential of HMFOR); in contrast, the reconstruction process of CoO x / NF did not show γ-CoOOH, resulting in a lower degree of reconstruction of the CoO2 phase and poor catalytic activity ( Figure 8 ). The above results showed that CoO x / CF had a unique structure in HMFOR and could be more easily reconstructed into the active phase.

[0054] Performance Test

[0055] CoO x / CF, CoO x The electrochemical HMFOR performance of / NF and the substrate CF was tested in a standard three - electrode system at room temperature and atmospheric pressure. The test conditions specifically included: 1 M KOH with or without 5 mM HMF as the electrolyte, the prepared catalyst as the working electrode, a Pt mesh as the counter electrode, and Hg / HgO as the reference electrode. The scanning rate of the LSV curve was 5 mV s -1 , and the liquid - phase data was tested at a potential of 1.5 V (vs RHE).

[0056] Taking CoO x / CF as an example, the HMFOR potential of CoO x / CF at 20 mA cm -2 was 1.39 V, lower than that of CoO x / NF (1.51 V) and CF (1.48 V) under the same conditions (as shown in Figure 9 a and Figure 10 ), and the kinetic process also had obvious advantages (as shown in Figure 9 b and c), indicating that CoO x grown on CF had better HMFOR catalytic activity. By collecting the products and analyzing the contents, it was found that: after complete electrolysis, HMF was almost completely converted into FDCA ( Figure 11 ), and the stability test showed that CoO x / CF could still maintain a HMF conversion rate of more than 90% and a Faraday efficiency of FDCA after five consecutive complete electrolyses, indicating its excellent stability (as shown in Figure 12 ), which was very important in practical applications.

[0057] In summary, the present invention uses a simple cathode electrodeposition method to grow CoO x nanosheets on CF. The prepared CoO x / CF can be directly used as an efficient and stable HMFOR catalyst. Studying the reconstruction process of CoO O containing rich V x during the HMFOR process is of great significance for deeply understanding the mechanism.

[0058] The above - mentioned are only examples for better explaining the present invention, not a limitation thereof. Any modification or equivalent replacement without departing from the spirit and scope of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural, characterized in that, It includes the following steps: Rich in oxygen vacancies CoO was prepared on a three-dimensional porous framework substrate by cathodic electrodeposition method x , and the cobalt-based catalyst was obtained after washing and drying.

2. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 1, characterized in that, The cathodic electrodeposition method uses a three-electrode system. Among them, a three-dimensional porous framework substrate is used as the working electrode, Ag / AgCl is used as the reference electrode, a Pt column is used as the counter electrode, and an aqueous cobalt sulfate solution is used as the electrolyte.

3. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 2, characterized in that, The three-dimensional porous framework substrate is copper foam or nickel foam.

4. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 1 or 2 or 3, characterized in that, Before use, the three-dimensional porous framework substrate is ultrasonically cleaned successively in HCl, ultrapure water, and absolute ethanol to remove the oxides and residual organic substances on its surface.

5. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 4, characterized in that, The current density of the cathodic electrodeposition is 50 mA cm -2 , and the time is 300 s.

6. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 2, characterized in that, The aqueous cobalt sulfate solution is formed by adding CoSO4·7H2O to ultrapure water.

7. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 1, characterized in that, The media used for the cleaning are ultrapure water and ethanol.

8. The preparation method of a cobalt-based catalyst for electro-oxidizing 5-hydroxymethylfurfural according to claim 1, characterized in that, The drying temperature is room temperature and the time is 12 h.

9. A cobalt-based catalyst prepared by the preparation method according to any one of claims 1-8.

10. Application of the cobalt-based catalyst according to claim 9 in the electrooxidation of 5-hydroxymethylfurfural.

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