Application of nanoflower-shaped CoP catalyst in electrochemical plastic recovery and hydrogen evolution

Abstract

The invention provides application of a nanoflower-shaped CoP catalyst in electrochemical plastic recovery and hydrogen evolution, and relates to the technical field of electrochemistry. And the nanoflower-shaped CoP catalyst is used as an anode electrode and / or a cathode electrode of the electrolysis system. According to the nano flower-shaped CoP catalyst, the three-dimensional porous material is used as the carrier, the catalyst with the bifunctional characteristic is prepared by adopting a hydrothermal method and a roasting method, the technological process is simplified, the cost is reduced, and the nano flower-shaped CoP catalyst has economical efficiency and sustainability. The CoP catalyst with the nanoflower-shaped structure is used as an anode electrode and / or a cathode electrode of an electrochemical recovery plastic electrolysis system, the specific surface area of the CoP catalyst is remarkably increased due to an open frame and a petal shape of the nanoflower-shaped structure, more active sites are provided, rapid transmission of electrons is effectively promoted through the staggered nanosheet structure, and the electrochemical recovery efficiency is improved. Therefore, the excellent catalytic activity is shown, the rate and the overall performance of the electro-catalytic reaction are improved, high formic acid product selectivity and Faraday efficiency are obtained, and the energy efficiency is improved.

Description

Technical Field

[0001] This application belongs to the technical field of electrochemistry, and particularly relates to the application of a nanoflower-shaped CoP catalyst in the electrochemical recycling of plastics and hydrogen evolution. Background Art

[0002] Electrochemical plastic recycling converts waste plastics into high-value chemicals or monomers through electrocatalytic technology, achieving the dual goals of resource recycling and environmental protection. This technology provides a low-energy-consumption and low-pollution solution for the plastic circular economy.

[0003] Recycling waste polyester plastics such as polyethylene terephthalate (PET) is of great significance for reducing environmental pollution and saving petrochemical resources. Existing studies have shown that the anodic electrooxidation of PET hydrolyzate can effectively convert waste PET into terephthalic acid (PTA) and highly selective potassium formate, accompanied by the hydrogen evolution reaction (HER) at the cathode.

[0004] Electrocatalysts play a key role in the electrochemical recycling of PET coupled with the hydrogen evolution reaction, improving efficiency by accelerating reaction kinetics, reducing activation energy, and enhancing product selectivity. Although significant progress has been made in the development of electrocatalysts for anodic PET oxidation and cathodic hydrogen evolution, such as noble metal catalysts, alloy and composite catalysts, there is still a lack of efficient bifunctional catalysts in the coupled reaction system. The lack of such efficient bifunctional catalysts hinders the improvement of the reaction rate, product selectivity, and stability of the coupled system, and complicates the process flow due to the use of different catalysts for the cathode and anode reactions, thus increasing the cost. Summary of the Invention

[0005] The present disclosure provides an application of a nanoflower-shaped CoP catalyst in the electrochemical recycling of plastics and hydrogen evolution, so as to solve at least the above technical problems existing in the prior art.

[0006] The present disclosure provides an application of a nanoflower-shaped CoP catalyst in the electrochemical recycling of plastics and hydrogen evolution, and the nanoflower-shaped CoP catalyst serves as the anode electrode and / or cathode electrode of the electrolysis system.

[0007] In an implementable embodiment, the electrolysis system includes:

[0008] An electrolytic cell, which is separated into an anode chamber and a cathode chamber by a cation exchange membrane. The anode chamber is used to place the plastic hydrolysis solution, and the cathode chamber is used to place the potassium hydroxide solution;

[0009] An anode, which is inserted into the anode chamber;

[0010] A cathode, which is inserted into the cathode chamber;

[0011] A reference electrode, which is inserted into the cathode chamber for monitoring the cathode potential;

[0012] A platinum sheet counter electrode, which is inserted into the cathode chamber for assisting the cathode reaction;

[0013] An electrochemical workstation, which is respectively connected to the anode electrode, the reference electrode and the platinum sheet counter electrode.

[0014] In an implementable embodiment, if one of the anode electrode and the cathode electrode is the nanoflower-shaped CoP catalyst, the other is a platinum sheet electrode.

[0015] In an implementable embodiment, the plastic hydrolysis solution is prepared by subjecting plastic to hydrothermal reaction in a potassium hydroxide solution.

[0016] In an implementable embodiment, the mass-volume ratio of the plastic to the potassium hydroxide solution is 1:(40 - 70) g / mL.

[0017] In an implementable embodiment, the preparation method of the nanoflower-shaped CoP catalyst includes:

[0018] Dissolving a soluble cobalt salt, a fluoride and a pH regulator in deionized water to obtain a mixed solution;

[0019] Placing a three-dimensional porous support in the mixed solution for hydrothermal reaction, the hydrothermal reaction temperature being 100 - 160 °C and the reaction time being 4 - 10 h; after washing and drying the product after the hydrothermal reaction, a catalyst precursor is obtained;

[0020] Roasting the catalyst precursor and a phosphorus source compound in an inert gas to obtain a nanoflower-shaped CoP catalyst.

[0021] In an implementable embodiment, in the mixed solution, the molar ratio of the soluble cobalt salt to the fluoride is 1:(1 - 3).

[0022] In an implementable embodiment, the mass ratio of the catalyst precursor to the phosphorus source compound is 1:(1.5 - 5).

[0023] In an implementable embodiment, the roasting temperature is 300 - 350 °C and the roasting time is 1 - 4 h.

[0024] In an implementable embodiment, the mass of cobalt element in the soluble cobalt salt accounts for 10 - 50 wt.% of the mass of the three-dimensional porous support.

[0025] The present disclosure provides an application of a nanoflower-shaped CoP catalyst in the electrochemical recycling of plastics and hydrogen evolution. The nanoflower-shaped CoP catalyst is applied to the electrochemical recycling of plastics coupled with hydrogen evolution reaction, serving as an anode electrode or a cathode electrode. The open framework and petal shape of the nanoflower structure significantly increase its specific surface area, providing more active sites, and the interlaced nanosheet structure effectively promotes the rapid transfer of electrons, thereby demonstrating excellent catalytic activity, improving the rate and overall performance of the electrocatalytic reaction, and obtaining high product selectivity and Faraday efficiency, thus improving the energy efficiency.

[0026] In addition, as a bifunctional catalyst, the nanoflower-shaped CoP catalyst can switch functions at different electrode positions without the need to additionally add other catalysts, simplifying the process flow, reducing costs, and being economical and sustainable.

[0027] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present disclosure, nor is it used to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] By referring to the accompanying drawings and reading the following detailed description, the above and other objects, features, and advantages of the exemplary embodiments of the present disclosure will become easily understood. In the drawings, several embodiments of the present disclosure are shown in an exemplary rather than restrictive manner, wherein:

[0029] In the drawings, the same or corresponding reference numerals represent the same or corresponding parts.

[0030] Figure 1 It is a schematic diagram of the preparation process of the nanoflower-shaped CoP catalyst CoP-F / NF in Example 1 of the present application;

[0031] Figure 2 It is a physical diagram of the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 of the present application;

[0032] Figure 3 It is an SEM image of the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 of the present application;

[0033] Figure 4 It is an SEM image of the non-nanoflower-shaped cobalt-based phosphide catalyst CoP / NF prepared in Comparative Example 2;

[0034] Figure 5 It is an XRD pattern of the nanoflower-shaped CoP catalyst CoP-F / NF prepared in the examples and the catalysts CoO-F / NF and CoP / NF prepared in Comparative Examples 1 and 2;

[0035] Figure 6 It is a schematic diagram of a plastic electrochemical recycling coupled hydrogen evolution system;

[0036] Figure 7 It is the LSV graph of the hydrolysis liquid oxidation of waste plastics by the nano-flower-like CoP catalyst CoP-F / NF prepared in the example, the catalysts CoO-F / NF and CoP / NF prepared in Comparative Examples 1 and 2, and the catalyst carrier NF at the anode of the electrolytic cell;

[0037] Figure 8 It is the LSV graph of the nano-flower-like CoP catalyst CoP-F / NF prepared in the example, the catalysts CoO-F / NF and CoP / NF prepared in Comparative Examples 1 and 2, and the catalyst carrier NF for hydrogen evolution in potassium hydroxide solution at the cathode of the electrolytic cell;

[0038] Figure 9 It is the Faraday efficiency FE and selectivity of formic acid, the electrochemical conversion product of the anode plastic hydrolysis liquid, at different potentials when the nano-flower-like CoP catalyst CoP-F / NF prepared in the example is used as both the anode electrode and the cathode electrode in the anode plastic electrochemical recycling coupled cathode hydrogen evolution system. Detailed implementation manners

[0039] To make the objectives, features, and advantages of the present disclosure more obvious and understandable, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present disclosure.

[0040] In the electrochemical recycling of waste plastics coupled with hydrogen evolution reaction, the anode needs to efficiently oxidize plastic hydrolysis products (such as ethylene glycol) to generate high-value chemicals, and the cathode needs to simultaneously catalyze the hydrogen evolution reaction (HER) to obtain clean energy. Bifunctional catalysts can optimize the reactions at both the anode and cathode simultaneously, avoiding the complexity of separately designing and loading single-functional catalysts. Therefore, it is crucial to develop efficient bifunctional catalysts for the electrochemical recycling of waste plastics. Based on this, the present disclosure provides an application of a nano-flower-like CoP catalyst in the electrochemical recycling of plastics and hydrogen evolution.

[0041] An application of a nano-flower-like CoP catalyst in the electrochemical recycling of plastics and hydrogen evolution, wherein the nano-flower-like CoP catalyst is used as the anode electrode and / or the cathode electrode of the electrolysis system.

[0042] The nano-flower-shaped CoP catalyst is a nanomaterial with a three-dimensional petal-like morphology, usually composed of multiple intertwined and extended nanosheets / nanowires, presenting a flower-like shape. Compared with traditional spherical or columnar nanomaterials, the open framework and petal shape of the nano-flower structure significantly increase its specific surface area, providing more active sites, which helps to improve the efficiency of catalytic reactions. In addition, the staggered nanosheet structure can effectively promote the rapid transfer of electrons and increase the rate of electrochemical reactions.

[0043] In one example, the electrolysis system includes:

[0044] An electrolytic cell, which is separated into an anodic chamber and a cathodic chamber by a cation exchange membrane. The anodic chamber is used to place the plastic hydrolysis solution, and the cathodic chamber is used to place the potassium hydroxide solution;

[0045] An anode, which is inserted into the anodic chamber;

[0046] A cathode, which is inserted into the cathodic chamber;

[0047] A reference electrode, which is inserted into the cathodic chamber and used to monitor the cathode potential;

[0048] A platinum sheet counter electrode, which is inserted into the cathodic chamber and used to assist the cathode reaction;

[0049] An electrochemical workstation, which is connected to the anode electrode, the reference electrode, and the platinum sheet counter electrode respectively.

[0050] Specifically, the electrochemical plastic recycling coupled hydrogen evolution system includes: a computer, a chi660E Chenhua electrochemical workstation, an H-type electrolytic cell, a cation exchange membrane, a mercury / mercuric oxide reference electrode, a platinum sheet counter electrode, a cathode electrode, and an anode electrode.

[0051] Among them, the specific connection method of the electrochemical plastic recycling coupled hydrogen evolution system is as follows: Place the cation exchange membrane in the H-type electrolytic cell to divide the electrolytic cell into two compartments. Put the hydrolysis solution of waste plastics in one compartment on one side of the cation exchange membrane, and put the potassium hydroxide solution in the other compartment. Place the anode electrode and the cathode electrode in the compartments with the hydrolysis solution of waste plastics and the potassium hydroxide solution respectively; Clip the working electrode clamp of the electrochemical workstation onto the anode electrode inserted into the hydrolysis solution of waste plastics, and clip the reference electrode clamp and the counter electrode clamp onto the cathode electrode inserted into the potassium hydroxide solution at the same time. Finally, connect the electrochemical workstation to the computer. The electrochemical workstation is connected to the anode and the cathode through electrode clamps to form a closed circuit, enabling electrons to flow from the anode to the cathode.

[0052] In one example, one or both of the anode electrode and the cathode electrode are nano-flower-shaped CoP catalysts. When the anode electrode is a nano-flower-shaped CoP catalyst, the corresponding cathode electrode is a platinum sheet electrode; when the cathode electrode is a nano-flower-shaped CoP catalyst, the corresponding anode electrode is a platinum sheet electrode.

[0053] The nano-flower-shaped CoP acts as the anode electrode and participates in the ethylene glycol oxidation reaction. The P sites on the surface of CoP preferentially adsorb the α-OH group of ethylene glycol. Through the cooperative dual-site mechanism, Co activates the C-H bond, and P stabilizes the intermediate, guiding the cleavage of the C-C bond to generate formate.

[0054] The nano-flower-shaped CoP acts as the cathode electrode and participates in the cathodic hydrogen evolution reaction, catalyzing the decomposition of water to generate H2 at the cathode.

[0055] In one example, the plastic hydrolysis solution is prepared by subjecting plastic to a hydrothermal reaction in a potassium hydroxide solution, where the plastic includes one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT). The mass-volume ratio of the plastic to the potassium hydroxide solution is 1:(40 - 70) g / mL, and the concentration of the potassium hydroxide solution is 1 mol / L.

[0056] The preparation of the waste plastic hydrolysis solution is a key pretreatment step for the plastic electrochemical recycling coupled hydrogen evolution system. The core lies in depolymerizing the high molecular polymer into electrolyzable small molecule products through an alkaline hydrothermal reaction. Taking polyethylene terephthalate (PET) as an example, PET is dispersed in a potassium hydroxide solution and then subjected to a hydrothermal reaction. The reaction temperature of the hydrothermal reaction is 160 - 200 °C, and the reaction time is 6 - 10 h. Under the action of potassium hydroxide, the ester bond in the PET molecule undergoes a saponification reaction to generate potassium terephthalate (K2C8H4O4) and ethylene glycol (HOCH2CH2OH). That is, the hydrolysis solution of PET simultaneously includes potassium terephthalate (K2C8H4O4) and ethylene glycol (HOCH2CH2OH). During electrocatalysis, potassium terephthalate (K2C8H4O4) does not participate in the reaction, and ethylene glycol (HOCH2CH2OH) becomes formate in the alkaline system. Subsequently, by adding acid, potassium terephthalate (K2C8H4O4) can be made to precipitate as terephthalic acid from the solution, leaving formate and formic acid for subsequent separation.

[0057] In one example, the above-mentioned nano-flower-shaped CoP catalyst can be prepared by the following method:

[0058] S1. Dissolve a soluble cobalt salt, a fluoride, and a pH regulator in deionized water to obtain a mixed solution;

[0059] S2. Place the three-dimensional porous carrier in the mixed solution for hydrothermal reaction. The hydrothermal reaction temperature is 100 - 160 °C, and the reaction time is 4 - 10 h. After washing and drying the product of the hydrothermal reaction, a catalyst precursor is obtained.

[0060] S3. Calcinate the catalyst precursor and a phosphorus source compound in an inert gas to obtain a nanoflower-like CoP catalyst.

[0061] Among them, in step S1, the soluble cobalt salt serves as the cobalt source to provide the active metal (Co 2+ ), and finally forms cobalt-based hydroxide (such as CoOOH), which is the precursor of the active component of the catalyst. Soluble cobalt salts include cobalt nitrate hexahydrate (Co(NO3)2·6H2O), cobalt chloride (CoCl2), cobalt sulfate (CoSO4), cobalt acetate (Co(CH3COO)2), and other cobalt salts.

[0062] In the fluoride, F- is used to coordinate with metal ions, regulate the crystal growth direction, and promote the formation of a specific morphology (such as nanoflowers). In addition, it promotes the dissolution and recrystallization of reactants and enhances the crystallinity of the product. Fluorides include ammonium fluoride (NH4F), sodium fluoride (NaF), potassium fluoride (KF), and other fluorides.

[0063] The pH regulator is a weakly basic reagent, such as urea (CO(NH2)2), hexamethylenetetramine (HMT), thiourea, and other weakly basic reagents. Taking urea as an example, under hydrothermal conditions, urea slowly decomposes into NH3 and CO2, gradually increasing the pH value of the solution and inducing the precipitation of metal hydroxide / oxide.

[0064] In one example, in the mixed solution, the molar ratio of the soluble cobalt salt to the fluoride is 1:(1 - 3). For example, if the soluble cobalt salt is cobalt nitrate hexahydrate and the fluoride is ammonium fluoride, the molar ratio of cobalt nitrate hexahydrate to ammonium fluoride is 1:(1 - 3). If the pH regulator is urea, the molar ratio of cobalt nitrate hexahydrate to urea is 1:(2 - 6); the mass ratio of cobalt nitrate hexahydrate to deionized water is 1:(600 - 800).

[0065] The three-dimensional porous carrier has a high porosity and specific surface area, which can provide rich active sites and good mass transfer channels for the reaction. For example, in this embodiment, the three-dimensional porous carrier is foam nickel. Foam nickel serves as the carrier, providing a support and attachment site for the reaction, enabling the generated catalyst to be loaded on its surface. Moreover, foam nickel has good conductivity and a large specific surface area, which is beneficial to improving the performance of the catalyst. In one example, the mass of cobalt element in the soluble cobalt salt accounts for 10 - 50 wt.% of the mass of foam nickel.

[0066] In one example, nickel foam needs to be pretreated to remove impurities on the surface of nickel foam. For example, in the pretreatment process, the grease and oxide layer caused by processing of nickel foam are cleaned. For example, nickel foam is immersed in a hydrochloric acid solution, then taken out and immersed in absolute ethanol to form the first ultrasonic treatment. Then, nickel foam is taken out from absolute ethanol and placed in deionized water to form the second ultrasonic treatment. The second ultrasonic treatment can be cycled multiple times to obtain pretreated nickel foam.

[0067] In step S2, the hydrothermal process is illustrated by taking cobalt nitrate hexahydrate (Co(NO3)2·6H2O), ammonium fluoride (NH4F), and urea as examples. When adding ammonium fluoride (NH4F), F- forms a complex (such as [CoF6] 2+ ) with metal ions (Co 4- ), which is preferentially adsorbed on a specific crystal plane of the crystal (such as the {001} plane), inhibiting the growth in this direction and forcing the crystal to expand along other directions (such as the {100} plane) to form two-dimensional nanosheets. The surface of the nanosheets is charged (such as positively charged), and under weak alkaline conditions (urea decomposes to generate NH3) or electrostatic action, the sheet-like structures self-assemble into a three-dimensional flower-like structure through edge-edge or face-face interactions. Therefore, through the synergistic effects of coordination chemistry regulation, pH slow release, and self-assembly kinetics, the hydrothermal reaction stacks the nanosheets step by step into a nanoflower morphology.

[0068] Furthermore, the catalyst precursor obtained after the hydrothermal reaction is dried, and it and the phosphorus source are respectively placed in the second layer and the first layer of a double-layer sand-core quartz hanging basket, and the double-layer sand-core quartz hanging basket is placed in a vertical tube furnace and calcined in an inert gas atmosphere (such as argon). The calcination temperature in the vertical tube furnace is 300 - 350 °C, and the calcination time is 1 - 4 h to obtain a nanoflower-like CoP catalyst.

[0069] Among them, the phosphorus source is sodium hypophosphite, sodium dihydrogen phosphate, red phosphorus, PH3, etc., which are used to react the cobalt oxide formed on the nickel foam into CoP. Taking sodium hypophosphite as an example, as the phosphorus source, it decomposes at high temperature to produce PH3. PH3 reacts with the nickel foam after hydrothermal treatment. When the generated PH3 gas contacts the surface of the nickel foam, due to the van der Waals force between molecules and the interaction between the lone pair electrons on the phosphorus atom in the PH3 molecule and the metal ions on the surface of the cobalt oxide, PH3 will be preferentially adsorbed on the surface of the cobalt oxide. During calcination, under high temperature and argon atmosphere, the PH3 molecules adsorbed on the surface of the cobalt oxide obtain sufficient energy, and the P-H bonds inside it break, generating hydrogen atoms and phosphorus radicals. At the same time, the cobalt-oxygen bonds in the cobalt oxide (such as CoO, Co2O3, or CoOOH, etc.) will also partially break, forming cobalt atoms with a certain activity and oxygen vacancies. The phosphorus radicals have high reactivity, and they will combine with cobalt atoms to form Co-P bonds, and then gradually generate CoP.

[0070] The preparation process of the above CoP controllably constructs a cobalt-based hydroxide precursor through hydrothermal synthesis, and then converts it into a nanostructured CoP catalyst through phosphating calcination. Through the synergistic effects of various raw materials, such as coordination regulation, pH control, and phosphorus source supply, the morphology, structure, and catalytic performance of the final CoP product are ensured. This catalyst has bifunctional properties and can simultaneously serve as an oxidation catalyst at the anode and a hydrogen evolution catalyst at the cathode: at the anode, CoP can efficiently catalyze the oxidation reaction of plastic hydrolysis solution to produce high-value-added products such as terephthalic acid (TPA) and formic acid; at the cathode, CoP generates hydrogen through the hydrogen evolution reaction (HER), with a low overpotential and high catalytic activity.

[0071] The following further elaborates on this application in conjunction with the attached drawings and specific embodiments:

[0072] Example 1

[0073] As Figure 1 shown is a schematic flow chart of a preparation method of a nanoflower-shaped CoP catalyst, including the following specific steps:

[0074] Step 1: Immerse nickel foam in a hydrochloric acid solution, then take out the nickel foam and immerse it in absolute ethanol for the first ultrasonic treatment. Then take out the nickel foam from the absolute ethanol and place it in deionized water for the second ultrasonic treatment. The second ultrasonic treatment is repeated three times to obtain pretreated nickel foam.

[0075] Step 2: Put the pretreated nickel foam into a mixed solution of deionized water containing cobalt nitrate hexahydrate, ammonium fluoride, and urea for hydrothermal reaction, and wash and dry the nickel foam after the reaction.

[0076] Step 3: Place the dried nickel foam and sodium hypophosphite in the second and first layers of a double-layer sand core quartz basket respectively, and put the double-layer sand core quartz basket into a vertical tube furnace, and calcine it in an argon atmosphere to obtain the nanoflower-shaped CoP catalyst.

[0077] In a specific embodiment, in Step 1, 42 mg of nickel foam (NF) is immersed in 50 ml of 3 mol / L hydrochloric acid solution for half an hour, then taken out and placed in 50 ml of absolute ethanol for ultrasonic treatment for half an hour. Then taken out again and placed in 50 ml of deionized water for ultrasonic treatment for half an hour and repeated three times to obtain pretreated nickel foam (NF).

[0078] In an embodiment, cobalt nitrate hexahydrate is 41.48 mg, ammonium fluoride is 10.37 mg, urea is 33.63 mg, and deionized water is 30 ml.

[0079] In one embodiment, in step 2, the pretreated NF and the mixed solution are placed in a hydrothermal autoclave and subjected to hydrothermal reaction at 120 °C in a muffle furnace for 6 h.

[0080] In one embodiment, in step 2, the NF after hydrothermal reaction is taken out, washed three times with ethanol and rinsed three times with deionized water, and then dried in an oven at 60 °C for 12 h.

[0081] In one embodiment, in step 3, the NF dried in step 2 is taken out and placed in the second layer of a double-layer sintered quartz basket, 0.5 g of sodium hypophosphite is added to the first layer, and then the basket is placed in a vertical tube furnace and calcined at 300 °C for 2 h in an argon atmosphere. During the reaction, the argon flow rate is 30 cm 3 / min, and a nano-flower-like CoP catalyst is prepared, denoted as CoP-F / NF.

[0082] The physical map and SEM map of the nano-flower-like CoP catalyst CoP-F / NF prepared in Example 1 are respectively as Figure 2 and 3 shown. From Figure 3 it can be clearly seen that the surface morphology of the CoP-F / NF catalyst is nano-flower-like.

[0083] Comparative Example 1

[0084] According to the preparation process of Example 1, the difference is that in step 3, no sodium hypophosphite is added to the first layer of the double-layer sintered quartz basket, and a catalyst is prepared, denoted as CoO-F / NF.

[0085] Comparative Example 2

[0086] According to the preparation process of Example 1, the difference is that in step 2, 41.48 mg of cobalt nitrate hexahydrate and 33.63 mg of urea are respectively weighed and dissolved in 30 ml of deionized water, and no ammonium fluoride is added additionally to prepare a mixed solution, which is used in step 3; a non-nano-flower-like CoP catalyst is prepared, denoted as CoP / NF.

[0087] The SEM map of the catalyst CoP / NF prepared in Comparative Example 2 is as Figure 4 shown. From Figure 4 it can be seen that the surface morphology of the catalyst prepared in Comparative Example 2 is not nano-flower-like.

[0088] As Figure 5 shown are the XRD patterns of the nano-flower-like CoP catalyst CoP-F / NF prepared in Example 1 and the catalysts (CoO-F / NF, CoP / NF) prepared in Comparative Examples 1 and 2. From Figure 5It can be seen that the CoP-F / NF catalyst prepared in Example 1 and the CoP / NF catalyst prepared in Comparative Example 2 both show the characteristic peaks of CoP, indicating the synthesis of cobalt-based phosphide CoP. However, the catalyst CoO-F / NF prepared in Comparative Example 1 only shows the characteristic peaks of CoO and no characteristic peaks of CoP, indicating that the CoO-F / NF prepared in Comparative Example 1 is not a cobalt-based phosphide but a cobalt-based oxide.

[0089] Example 2

[0090] The embodiment of the present application provides an application of a nanoflower-shaped CoP catalyst in electrochemical plastic recycling and hydrogen evolution, specifically the application of the nanoflower-shaped CoP catalyst as an anode electrode and / or a cathode electrode in the electrochemical plastic recycling coupled with hydrogen evolution reaction.

[0091] As Figure 6 shown is a schematic diagram of an electrochemical plastic recycling coupled with hydrogen evolution system, and the system includes the following devices and materials: a computer, a chi660E Chenhua electrochemical workstation, a set of H-type electrolytic cells with a single cell volume of 10 mL, a circular cation exchange membrane with a diameter of 3 cm, a mercury / mercuric oxide reference electrode, a platinum sheet counter electrode, a cathode electrode, and an anode electrode.

[0092] The connection method of the above devices and materials is as follows: Place the circular cation exchange membrane with a diameter of 3 cm in the H-type electrolytic cell, put 10 mL of the hydrolysis solution of waste plastics in one side of the cell and 10 mL of 1 mol / L potassium hydroxide solution in the other side; Place the anode electrode and the cathode electrode in the cells of the hydrolysis solution of waste plastics and potassium hydroxide solution respectively, then clamp the working electrode clamp of the electrochemical workstation on the anode electrode inserted into the hydrolysis solution of waste plastics, clamp the reference electrode clamp and the counter electrode clamp together on the cathode electrode inserted into the potassium hydroxide solution, and finally connect the electrochemical workstation to the computer.

[0093] Among them, the preparation method of the hydrolysis solution of waste plastics is: Put 0.77 g of polyethylene terephthalate (PET) and 40 mL of 1 mol / L potassium hydroxide solution into a 50 mL hydrothermal reactor, and then place the hydrothermal reactor in a muffle furnace and react at 180 °C for 6 h to obtain the hydrolysis solution of waste plastics.

[0094] Using Figure 6 the electrochemical plastic recycling coupled with hydrogen evolution system shown in, use the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 and the catalysts (CoO-F / NF, CoP / NF) prepared in Comparative Examples 1 and 2 and the catalyst carrier NF as the anode electrode respectively, and use the platinum sheet electrode as the cathode electrode to test the LSV spectra of the oxidation of the hydrolysis solution of waste plastics by different anode electrodes, and the results are as Figure 7 shown.

[0095] It can be seen from Figure 7 that the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 has a lower initial potential and a larger current density, indicating that CoP-F / NF has a higher catalytic activity for the hydrolysis solution of waste plastics. Compared with the control group (CoO-F / NF, CoP / NF, support NF), it is confirmed that the higher catalytic activity of CoP-F / NF comes from the presence of the nanoflower structure and the cobalt-based phosphide CoP.

[0096] Using Figure 6 the plastic electrochemical recycling coupled hydrogen evolution system shown in Figure 8 , the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 and the catalysts (CoO-F / NF, CoP / NF) prepared in Comparative Examples 1 and 2 and the catalyst support NF were used as the cathode electrodes, and a platinum plate electrode was used as the anode electrode to test the LSV diagrams of hydrogen evolution in potassium hydroxide solution for different cathode electrodes, as shown in

[0097] It can be seen from Figure 8 that the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 has a lower initial potential and a larger current density, indicating that CoP-F / NF has a higher catalytic activity for hydrogen evolution in potassium hydroxide solution. Compared with the control group (CoO-F / NF, CoP / NF, support NF), it is again confirmed that the higher catalytic activity of CoP-F / NF comes from the presence of the nanoflower structure and the cobalt-based phosphide CoP. Combining Figure 7 the results, it shows that the nanoflower-shaped cobalt-based phosphide catalyst CoP-F / NF prepared in Example 1 is a bifunctional catalyst, which has a high catalytic activity for both the oxidation of the hydrolysis solution of anode waste plastics and the hydrogen evolution in cathode potassium hydroxide solution.

[0098] Using Figure 6 the plastic electrochemical recycling coupled hydrogen evolution system shown in Figure 9 , the nanoflower-shaped CoP catalyst CoP-F / NF prepared in Example 1 was used as the cathode electrode and the anode electrode respectively to test the Faraday efficiency FE and selectivity of the electrochemical conversion product formic acid of the hydrolysis solution of anode waste plastics at different potentials, and the results are as shown in

[0099] It can be seen from Figure 9It can be seen that when the potential increases from 1.3 V to 1.55 V, the FE of the product formic acid slightly decreases, but still maintains a high FE (greater than 86%), while the selectivity first increases and then decreases, reaching a maximum value of 95.82% at 1.45 V. This result once again indicates that CoP-F / NF can be used as a bifunctional catalyst in the electrochemical recycling of anode plastics coupled with cathodic hydrogen evolution system, and has excellent electrocatalytic performance for both plastic anodic oxidation and cathodic hydrogen evolution. Furthermore, it makes the products of plastic electrochemical recycling have high selectivity and Faraday efficiency, which helps to improve the overall current efficiency of this system.

Claims

1. Application of a nanoflower-like CoP catalyst in electrochemical recycling of plastics and hydrogen evolution, characterized in that: The nanoflower-shaped CoP catalyst is used as an anode electrode and / or a cathode electrode of an electrolysis system.

2. The use according to claim 1, characterized in that: The electrolysis system comprises: An electrolytic cell, wherein the electrolytic cell is divided into an anode chamber and a cathode chamber by a cation exchange membrane, the anode chamber is used to store plastic hydrolyzate, and the cathode chamber is used to store potassium hydroxide solution; an anode, the anode being inserted into the anode chamber; a cathode, the cathode being inserted into the cathode chamber; A reference electrode, which is inserted into the cathode chamber and is used to monitor the cathode potential; A platinum counter electrode, the platinum counter electrode is inserted into the cathode chamber to assist cathode reaction; The electrochemical workstation is respectively connected to the anode electrode, the reference electrode and the platinum counter electrode.

3. The use according to claim 1 or 2, characterized in that: If one of the anode electrode and the cathode electrode is the nanoflower-shaped CoP catalyst, the other is a platinum sheet electrode.

4. The use according to claim 2, characterized in that: The plastic hydrolyzate is prepared by placing the plastic into a potassium hydroxide solution for hydrothermal reaction.

5. The use according to claim 4, characterized in that: The mass volume ratio of the plastic to the potassium hydroxide solution is 1: (40-70) g / mL.

6. The use according to claim 1, characterized in that: The preparation method of the nanoflower-shaped CoP catalyst comprises: dissolving a soluble cobalt salt, a fluoride, and a pH adjuster in deionized water to obtain a mixed solution; Placing the three-dimensional porous carrier in the mixed solution for hydrothermal reaction, wherein the hydrothermal reaction temperature is 100 to 160° C. and the reaction time is 4 to 10 hours; washing and drying the product after the hydrothermal reaction to obtain a catalyst precursor; The catalyst precursor and the phosphorus source compound are placed in an inert gas and calcined to obtain a nano-flower-shaped CoP catalyst.

7. The use according to claim 6, characterized in that: In the mixed solution, the molar ratio of the soluble cobalt salt to the fluoride is 1:(1-3).

8. The use according to claim 6, characterized in that: The mass ratio of the catalyst precursor to the phosphorus source compound is 1:(1.5-5).

9. The use according to claim 6, characterized in that: The calcination temperature is 300-350° C., and the calcination time is 1-4 hours.

10. The use according to claim 6, characterized in that: The mass of the cobalt element in the soluble cobalt salt accounts for 10 to 50 wt.% of the mass of the three-dimensional porous carrier.

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