In-situ grown nickel-cobalt nanosheet electrocatalyst and preparation method and application thereof

Abstract

The present application relates to a kind of in situ grown nickel cobalt nanosheet electrocatalyst and its preparation method and application, foam metal is soaked in the mixed solution of nickel salt and cobalt salt, reaction obtains nickel cobalt nanosheet array electrocatalyst in situ grown on foam metal, wherein, the foam metal selects the metal that the cobalt, nickel is active than. Compared with prior art, the in situ growth strategy of the present application avoids using adhesive, and the regular arrangement of nickel cobalt nanosheet array structure prepared in situ grown on foam iron is beneficial to accelerate the diffusion mass transfer of catalytic reaction, accelerate the rapid desorption of cumulative bubble and have large specific surface area, so that active site is fully exposed, improve reaction kinetics, can effectively improve catalytic activity and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to an in-situ grown nickel-cobalt nanosheet electrocatalyst and a preparation method and application thereof. BACKGROUND

[0002] Plastics are widely used in human society due to their low cost and versatility, but they are difficult to decompose and cause great pollution to the environment. Polyethylene terephthalate (PET) is the most widely used polyester plastic due to its excellent performance and diversified applications, with an annual output of more than 700 million tons. However, only 20% of PET is recycled, and most of it is discarded, causing environmental pollution. In the past few decades, some chemical methods for PET recycling such as hydrolysis, alcoholysis, etc. have been reported. According to relevant research, PET can be completely hydrolyzed into terephthalic acid and ethylene glycol in an alkaline environment. Terephthalic acid can be recovered from the hydrolysis solution through acidification and recrystallization processes, which is beneficial to reduce pollution and increase economic value. However, ethylene glycol is difficult to separate due to its high boiling point (197.3℃) and good water solubility. Therefore, it is very meaningful to explore methods for separating or converting ethylene glycol from the hydrolysis solution.

[0003] Electrochemical oxidation of ethylene glycol is a new idea for separation and conversion, which drives the oxidation of ethylene glycol in PET hydrolysate into high-value chemicals by renewable electricity, improving economic value. Ethylene glycol is more easily oxidized than water, and can be selectively oxidized into glycolic acid or formic acid. Formic acid or formate is widely used in the pharmaceutical, feed, and leather industries, and ethylene glycol oxidation (EGOR) is considered a clean and economically beneficial value-added chemical process. However, current electrochemical oxidation of ethylene glycol often uses noble metal catalysts such as palladium, platinum, and gold, so it is very meaningful to develop high-activity non-noble metal electrocatalysts. SUMMARY

[0004] The purpose of the present application is to overcome the defect that the catalyst used in the current electrochemical oxidation of ethylene glycol is a noble metal catalyst, thereby providing an in-situ grown nickel-cobalt nanosheet electrocatalyst and a preparation method and application thereof.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] The technical scheme of the present application provides a preparation method of an in-situ grown nickel-cobalt nanosheet electrocatalyst: soaking a foam metal in a mixed solution of nickel salt and cobalt salt to obtain a nickel-cobalt nanosheet array electrocatalyst in-situ grown on the foam metal, wherein the foam metal is selected from a metal more active than cobalt and nickel.

[0007] In some specific embodiments, the nickel salt is selected from any one of nickel sulfate, nickel sulfate hexahydrate, nickel chloride, and nickel nitrate.

[0008] In some embodiments, the cobalt salt is selected from any one of cobalt sulfate, cobalt sulfate heptahydrate, cobalt chloride, and cobalt nitrate.

[0009] In some embodiments, the total concentration of the nickel salt and the cobalt salt in the mixed solution is 50 mM, and the molar ratio of the nickel salt to the cobalt salt is 3 / 7-7 / 3.

[0010] In some embodiments, the molar ratio of the nickel salt to the cobalt salt is 7:3, 1:1, or 3:7.

[0011] In some embodiments, the foam metal is iron foam (IF).

[0012] In some embodiments, the reaction temperature is room temperature, and the reaction time is (1.5-2.5) h.

[0013] In some embodiments, the preparation method further comprises: performing CV oxidation on the nickel-cobalt nanosheet array electrocatalyst grown in situ on the foam metal, specifically:

[0014] The mercury / mercury oxide electrode is used as a reference electrode, the platinum sheet is used as a counter electrode, and the nickel-cobalt nanosheet array electrocatalyst grown in situ on the foam metal is used as a working electrode, which is placed in 1M KOH and subjected to CV treatment at a scan rate of 10 mV / s in the range of 0.146V-0.946V to obtain the nickel-cobalt oxide covering the foam metal.

[0015] The CV oxidation oxidizes the nickel and cobalt into nickel oxide and cobalt oxide, which covers the surface of the foam metal and prevents rusting.

[0016] The second technical solution of the present application provides a nickel-cobalt nanosheet array electrocatalyst grown in situ, which is obtained based on the method of the first technical solution.

[0017] The third technical solution of the present application provides an application of the nickel-cobalt nanosheet array electrocatalyst grown in situ as described in the first technical solution, and the nickel-cobalt nanosheet array electrocatalyst grown in situ is used to treat ethylene glycol and plastic into value-added chemicals.

[0018] In some embodiments, under alkaline conditions, the nickel-cobalt nanosheet array electrocatalyst grown in situ catalytically oxidizes ethylene glycol and PET hydrolysis products to generate formate.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] (1) The in-situ growth strategy of the present application avoids the use of adhesives, ensures the close contact of the cobalt-nickel nanosheet array electrocatalyst with the foam metal conductive substrate interface, and promotes the rapid transfer of electric charges. The doping of cobalt can promote the transfer of electric charges, adjust the position of the Ni 2+ / Ni 3+ redox couple, thereby effectively improving the catalytic activity.

[0021] (2) Iron in the foam iron is more active than cobalt and nickel, and can be used for electrochemical displacement reaction. The regularly arranged nickel-cobalt nanosheet array structure grown in-situ on the foam iron is beneficial to accelerate the diffusion mass transfer of the catalytic reaction, accelerate the rapid detachment of the accumulated bubbles, and has a large specific surface area, so as to fully expose the active sites, improve the reaction kinetics, and effectively improve the catalytic activity and stability.

[0022] (3) The preparation method of the present application has low cost, easy operation, zero energy consumption, expandability, and the product prepared has good ethylene glycol oxidation (EGOR) electrocatalytic activity in alkaline electrolyte, and can realize the production of value-added chemicals formate under lower voltage input. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Ni 0.3 Co 0.7 / IF scanning electron microscope (SEM) (A, B) and transmission electron microscope (TEM) (C) images.

[0024] Figure 2 A to D are scanning electron microscope images of NiCo / IF with different nickel-cobalt ratios.

[0025] Figure 3 Ni 0.3 Co 0.7 / IF catalyst element distribution map.

[0026] Figure 4 Linear sweep voltammetry curve (A) of the catalyst with different nickel-cobalt ratios in ethylene glycol oxidation and EGOR stability diagram (B) of the Ni 0.3 Co 0.7 / IF electrode.

[0027] Figure 5 Ni 0.3 Co 0.7 / IF electrocatalytic ethylene glycol electrolysis product nuclear magnetic hydrogen spectrum (A) and nuclear magnetic carbon spectrum (B).

[0028] Figure 6 The reaction path of ethylene glycol oxidation to formate in alkaline medium.

[0029] Figure 7Tafel slope values of catalysts with different nickel cobalt ratios.

[0030] Figure 8 Electrochemical impedance spectrograms of catalysts with different nickel cobalt ratios.

[0031] Figure 9 Double-layer capacitances of catalysts with different nickel cobalt ratios.

[0032] Figure 10 Standard curve for liquid phase calibration of formic acid.

[0033] Figure 11 Linear sweep voltammograms (A) of PET plastic hydrolysis solution by catalysts with different nickel cobalt ratios, nuclear magnetic hydrogen spectrum (B) of electrolysis products, and cyclic voltammograms (C) of blank alkaline solution by catalysts with different nickel cobalt ratios. DETAILED DESCRIPTION

[0034] The present application will be described in detail below with reference to the accompanying drawings and specific examples. The present embodiment is implemented on the premise of the technical solution of the present application, and gives a detailed implementation and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0035] In the following examples and comparative examples, cobalt sulfate heptahydrate, nickel sulfate hexahydrate, and ethylene glycol were purchased from Shanghai Maikelin Biotechnology Co., Ltd., and electrochemical data was collected by CHI760E (Shanghai Chenhua). The remaining raw materials or processing technologies not specifically described are all conventional commercially available products or conventional processing technologies in the art.

[0036] Example 1:

[0037] 0.263 g of nickel sulfate hexahydrate and 0.281 g of cobalt sulfate heptahydrate were weighed and dissolved in 20 mL of deionized water to form a uniform mixed solution. The solution was added to a beaker containing clean foamed iron. After 2 h of reaction at room temperature, a nickel cobalt nanosheet array loaded on foamed iron was obtained, denoted as Ni 0.5 Co 0.5 / IF, and placed in a 80°C vacuum drying oven for drying.

[0038] Example 2:

[0039] Compared with Example 1, most of them are the same, and the only difference is that the total concentration of nickel sulfate hexahydrate and cobalt sulfate heptahydrate is controlled to be 50 mM, and the molar ratio of nickel sulfate hexahydrate to cobalt sulfate heptahydrate is adjusted to 3:7. A nickel cobalt nanosheet array loaded on foamed iron was prepared, denoted as Ni 0.3 Co 0.7 / IF.

[0040] Example 3:

[0041] Compared with Example 1, most of them are the same, the difference is only that the total concentration of nickel sulfate hexahydrate and cobalt sulfate heptahydrate is controlled to be 50 mM, and the molar ratio of nickel sulfate hexahydrate and cobalt sulfate heptahydrate is adjusted to 7:3, and a nickel-cobalt nanosheet array loaded on a foamed iron is prepared, denoted as Ni 0.7 Co 0.3 / IF.

[0042] Example 4:

[0043] Based on the Ni 0.5 Co 0.5 / IF obtained in Example 1, CV oxidation is performed, specifically:

[0044] Since the displaced metal elements Ni and Co will form micro-batteries with the foamed iron substrate to accelerate the rusting of the foamed iron surface. Therefore, the obtained Ni 0.5 Co 0.5 / IF is subjected to CV oxidation, specifically:

[0045] A mercury / mercury oxide electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, and the Ni 0.5 Co 0.5 / IF is used as a working electrode, which is placed in 1M KOH and subjected to CV treatment at a scan rate of 10 mV / s from 0.146V to 0.946V, to obtain an oxidized nickel-cobalt covered on the foamed iron, denoted as NiCoOx / IF.

[0046] Comparative Example 1:

[0047] Compared with Example 1, most of them are the same, the difference is only that the cobalt sulfate heptahydrate is replaced by the same molar amount of nickel sulfate hexahydrate, and a nickel nanosheet array loaded on a foamed iron is prepared, denoted as NiFe.

[0048] Comparative Example 2:

[0049] Compared with Example 1, most of them are the same, the difference is only that the nickel sulfate hexahydrate is replaced by the same molar amount of cobalt sulfate heptahydrate, and a cobalt nanosheet array loaded on a foamed iron is prepared, denoted as CoFe.

[0050] Figure 1 The scanning electron microscope and transmission electron microscope images of the Ni 0.3 Co 0.7 / IF are shown, from which it can be seen that the nickel and cobalt are uniformly loaded on the surface of the foamed iron, and the Ni 0.3 Co 0.7 / IF exhibits a two-dimensional sheet-like morphology and a smooth surface.

[0051] Figure 2The scanning electron microscope images of different NiCo / IF with different Ni / Co ratios are shown. It can be seen that they all present a nanosheet array structure.

[0052] Figure 3 The elemental mapping of Ni 0.3 Co 0.7 / IF shows that the product is mainly composed of Ni, Co and Fe.

[0053] The prepared Ni 0.3 Co 0.7 / IF catalyst was used as a catalyst for oxidation of ethylene glycol or products of PET hydrolysis:

[0054] At room temperature, the reaction system was a three-electrode system, and the Ni 0.3 Co 0.7 / IF catalyst was used as the working electrode, a graphite rod was used as the counter electrode, and mercury / mercury oxide was used as the reference electrode.

[0055] (1) OER test was carried out in 1.0M KOH solution.

[0056] (2) EGOR test was carried out in 1.0M KOH solution containing 0.5M EG (ethylene glycol) or PET hydrolysate.

[0057] The preparation method of the PET hydrolysate is as follows:

[0058] 5.6g of dry PET powder was added to 50mL of 2M KOH solution and transferred to a 100mL Teflon-lined autoclave, which was sealed and kept at 160℃ for 4 hours. After cooling to room temperature, the filtered solution containing ethylene glycol and terephthalic acid was used as the electrolyte for electrochemical tests and analysis.

[0059] (3) The scan rate of cyclic voltammetry curves and linear sweep voltammetry curves was 5mV s -1 .

[0060] (4) Electrochemical impedance spectroscopy (EIS) measurement was carried out in the frequency range of 1MHz to 0.01Hz with an amplitude of 5mV.

[0061] (5) Tafel slope was obtained from LSV plots using linear fitting applied to points in the Tafel region.

[0062] (6) Double-layer capacitance (Cdl) was calculated by CV at different scan rates in the potential range of 0.824V to 0.924V (vs. RHE).

[0063] (7) Catalyst stability evaluation was tested by chronoamperometry.

[0064] (8) Detection methods for electrolysis products:

[0065] After electrolysis, the electrolyte solution was collected and quantitatively analyzed by high-performance liquid chromatography (HPLC). For each HPLC measurement, 50 μL of the electrolyte solution containing the product was diluted to 1 mL with dilute H₂SO₄ solution, and then 20 μL of the prepared sample was injected into a BioRad Aminex 87H column. 5 mM H₂SO₄ solution was used as the mobile phase at a constant flow rate of 0.6 mL / min. The product category was determined by comparing the retention time of the elution peak with that of a single standard sample solution.

[0066] The results are as follows:

[0067] (1) Evaluation of the EGOR performance of electrocatalysts with different nickel-cobalt ratios in ethylene glycol:

[0068] Figure 4 Figure A shows the linear sweep voltammetry curves of EGOR for different catalysts, where Ni can be seen. 0.3 Co 0.7 / IF catalysts exhibit lower onset oxidation potentials and higher catalytic activity. Figure 4 B indicates that Ni 0.3 Co 0.7 / IF catalysts exhibit good ethylene glycol oxidation stability.

[0069] Figure 5 Figure A shows Ni. 0.3 Co 0.7 The 1H NMR spectrum of the product was collected after prolonged electrolysis of ethylene glycol using the / IF catalyst. The blue and green shading represents the characteristic peak positions of the 1H NMR spectrum of ethylene glycol and formate, respectively. It can be seen that after prolonged electrolysis, the ethylene glycol peak disappears, and a strong formate peak appears at 8.4 ppm, indicating that ethylene glycol is effectively converted to formate. Figure 5 B is the carbon NMR spectrum. As can be seen, after prolonged electrolysis, the peak of ethylene glycol disappears, and a strong peak of formate appears.

[0070] Figure 6 This paper describes a possible reaction pathway for the oxidation of ethylene glycol to formate in an alkaline medium. First, formic acid formation begins with the oxidation of ethylene glycol to glycolaldehyde as the C-C bonds break. Subsequently, glycolaldehyde undergoes oxidative cleavage to produce formic acid and formaldehyde. Formaldehyde then undergoes an intermolecular redox reaction (Cannizzaro reaction) in alkaline solution to produce methanol and formic acid, ultimately oxidizing methanol to formic acid.

[0071] Figure 7 , 8 9 represents the Tafel slope, electrochemical impedance spectroscopy, and double-layer capacitance of catalysts with different nickel-cobalt ratios, respectively.

[0072] (2) Performance evaluation of electrocatalysts with different Ni / Co ratios for PET catalysis:

[0073] Polyethylene terephthalate (PET) can be hydrolyzed in alkaline solution to obtain monomers such as terephthalic acid (PTA) and ethylene glycol (EG). Converting the ethylene glycol component in PET plastic into high-value-added formate through electrocatalytic method is a green, environmentally friendly, and economically sustainable method, which greatly improves the profit benefit of waste PET recycling.

[0074] The amount of formic acid is obtained by a standard curve in Figure 10 A series of formic acid standard solutions are prepared, 50 μL of the formic acid standard solution is diluted to 1 mL with dilute H2SO4 solution, and then 20 μL of the prepared sample is injected into the BioRad Aminex 87H column. A 5 mM H2SO4 solution is used as the mobile phase, with a constant flow rate of 0.6 mL / min. A standard curve is prepared by plotting the peak area of the elution peak.

[0075] Figure 11 A shows the polarization curves of electrocatalysts with different Ni / Co ratios for PET hydrolysate catalysis. The PET hydrolysate is used as the electrolyte, which shows very similar EGOR performance, with a lower initial oxidation potential and catalytic activity compared to OER (reference Figure 11 C). Figure 11 B shows the 1 H NMR results of the electrochemical oxidation products of PET plastic hydrolysate. The blue, yellow, and green shadows represent the characteristic peak positions of the nuclear magnetic hydrogen spectrum of ethylene glycol, terephthalate, and formate, respectively. It can be seen that after complete electrolysis, the peak of ethylene glycol disappears and the characteristic peak of formate appears, indicating that the PET hydrolysate is effectively converted into value-added formate and terephthalate in the electrolyte. Therefore, the electrocatalytic reforming strategy of upgrading waste PET plastic to high-value-added formate chemicals by the catalyst prepared by the present application is feasible.

[0076] The above description of the embodiments is to facilitate the understanding and use of the invention by those of ordinary skill in the art. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and improvements and modifications made by those skilled in the art within the scope of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method for preparing an in-situ grown nickel-cobalt nanosheet electrocatalyst, characterized in that, The foam metal is immersed in a mixture of nickel and cobalt salts to react and obtain an in-situ grown nickel-cobalt nanosheet array electrocatalyst on the foam metal, wherein the foam metal is selected as a metal more reactive than cobalt and nickel; The total concentration of nickel and cobalt salts in the mixture is 50 mM, and the molar ratio of nickel to cobalt salts is 3 / 7 to 7 / 3.

2. The preparation method according to claim 1, characterized in that, The nickel salt is selected from any one of nickel sulfate, nickel sulfate hexahydrate, nickel chloride, and nickel nitrate.

3. The preparation method according to claim 1, characterized in that, The cobalt salt is selected from any one of cobalt sulfate, cobalt sulfate heptahydrate, cobalt chloride, and cobalt nitrate.

4. The preparation method according to claim 1, characterized in that, The foamed metal is foamed iron.

5. The preparation method according to claim 1, characterized in that, The reaction was carried out at room temperature for 1.5 to 2.5 hours.

6. The preparation method according to claim 1, characterized in that, The preparation method further includes: performing CV oxidation on the nickel-cobalt nanosheet array electrocatalyst grown in situ on foam metal, specifically: A mercury / mercury oxide electrode was used as the reference electrode, a platinum sheet as the counter electrode, and a nickel-cobalt nanosheet array electrocatalyst grown in situ on foam metal was used as the working electrode. The electrode was placed in 1 M KOH and subjected to CV treatment at a scan rate of 10 mV / s in the range of 0.146V-0.946V to obtain nickel-cobalt oxide covering the foam metal.

7. An in-situ grown nickel-cobalt nanosheet array electrocatalyst, characterized in that, It is obtained based on the preparation method described in any one of claims 1 to 6.

8. An application of the in-situ grown nickel-cobalt nanosheet array electrocatalyst as described in claim 7, characterized in that, The in-situ grown nickel-cobalt nanosheet array electrocatalyst is used to process ethylene glycol and plastics into value-added chemicals.

9. The application according to claim 8, characterized in that, The in-situ grown nickel-cobalt nanosheet array electrocatalyst catalytically oxidizes ethylene glycol and PET plastic hydrolysis products to form formate.

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