A method for producing combustible gas and simultaneously preparing a high-performance hydrogen evolution electrode by molten salt electrochemical oxidation of carbon fiber composite materials

Abstract

This invention belongs to the technical field of carbon fiber recovery and value-added utilization, and relates to a method for producing combustible gas and simultaneously preparing a high-performance hydrogen evolution electrode through molten salt electrochemical oxidation of carbon fiber composite materials. This method utilizes molten salt as an electrolyte to construct a two-electrode system consisting of a cathode and an anode. The anode is electrolytically converted to produce combustible gas and a hydrogen evolution electrode. The molten salt operates at a temperature of 400-600°C, and the anode is a carbon fiber composite material. By utilizing the molten salt medium's simultaneous characteristics of enhanced heat transfer, catalytic conversion, and electrochemical conversion, a molten salt thermo-electrochemically coupled conversion system is constructed, achieving efficient conversion of the carbon fiber composite material into combustible gas and recycling of the carbon fiber material on the anode side.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber recovery and value-added utilization, and in particular to a method for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode. Background Art

[0002] Carbon fiber composites, typically composed of carbon fibers and resins, are widely used in aerospace, automotive, and construction industries due to their excellent mechanical properties and lightweight properties. However, with the increasing use of carbon fiber composites, the disposal and resource utilization of these wastes have become urgent issues. The latest technologies for recycling and repurposing carbon fiber composites include high-temperature pyrolysis, supercritical fluid processing, chemical recovery, and physical recovery.

[0003] Traditional chemical or physical recycling methods often suffer from low recycling efficiency and high costs. Chemical reagents or physical crushing can damage the fibers, making it difficult to maintain their original strength and modulus. The use of organic chemical reagents is potentially toxic and poses safety risks. High-temperature pyrolysis of carbon fiber composites to recover carbon fibers is of great significance in the field of carbon fiber recycling, as it is currently the only commercially viable recycling method. However, this technology also faces several challenges: it requires high temperatures and high energy consumption; the high-temperature pyrolysis process requires precise control of temperature, atmosphere, and other conditions to ensure pyrolysis efficiency and product quality, but controlling thermochemical operating conditions is difficult, especially in large-scale production. During the pyrolysis process, in addition to obtaining carbon fibers, the resin pyrolysis conversion produces a number of gas-liquid-solid three-phase products, such as combustible gas and solid carbon. However, these products are of low quality and difficult to utilize, and the solid carbon often adheres to the carbon fiber surface, affecting its subsequent use. During the high-temperature pyrolysis process, carbon fibers may be affected by high temperatures (>800°C) and surface oxidation, resulting in a significant reduction in their mechanical properties. Therefore, how to maximize the value-added utilization of carbon fibers remains a challenge. Summary of the Invention

[0004] In response to the shortcomings of existing high-temperature pyrolysis and recovery technologies for carbon fiber composite materials, the present invention provides a method for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode. By utilizing the enhanced heat transfer and electrolyte properties of molten salt, the carbon fiber composite material undergoes a thermo-electrochemical coupled conversion reaction on the anode side of a molten salt electrolytic cell. The strong heat transfer properties and catalytic reaction ability of the molten salt can reduce the conversion temperature of the carbon fiber composite material to a medium temperature range, while catalytically improving the quality of the resin thermally converted into combustible gas. The electrochemical oxidation process can precisely control the degree of oxidation on the carbon fiber surface, and enhance the catalytic activity of the recycled carbon fiber as a hydrogen evolution electrode by constructing a porous structure and defective active sites.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is to provide a method for producing combustible gas and simultaneously preparing a high-performance hydrogen evolution electrode by electrochemically oxidizing carbon fiber composite materials with molten salt, the steps comprising:

[0007] A two-electrode system consisting of a cathode and an anode is constructed using molten salt as an electrolyte, and the anode is converted by electrolysis to produce a combustible gas and a hydrogen evolution electrode;

[0008] The operating temperature of the molten salt is 400-600°C;

[0009] The anode is made of carbon fiber composite material.

[0010] Furthermore, the molten salt is at least one of carbonate, chloride, sulfate, fluoride and hydroxide.

[0011] Preferably, the carbonate is at least one of Li2CO3, Na2CO3, K2CO3 and CaCO3.

[0012] Preferably, the chloride salt is at least one of LiCl, NaCl, KCl and CaCl2.

[0013] Preferably, the sulfate is at least one of Li2SO4, Na2SO4, K2SO4 and CaSO4.

[0014] Preferably, the fluoride is at least one of LiF, NaF, KF and CaF2.

[0015] Preferably, the hydroxide is at least one of LiOH, NaOH, KOH and Ca(OH)2.

[0016] The molten salts are selected from carbonates, chlorides, sulfates, fluorides and hydroxides having a melting point or eutectic point of about 400-600° C. and chemically stable and non-decomposable properties.

[0017] Furthermore, the cathode is one of Au, Ag, Pt, Ni, Cu, Mo, NiFe alloy, NiFeCu alloy and graphite.

[0018] Furthermore, the electrolysis step is: heating the molten salt electrolyte to 400-600° C., then immersing the anode and cathode in the molten salt electrolyte, and performing electrolysis in a constant current or constant voltage manner for 0.5-3 h.

[0019] Preferably, the constant voltage is 1.5 to 5V; the constant current is 50mA to 2A.

[0020] Furthermore, the combustible gas includes at least one of H2, CO and CH4.

[0021] Furthermore, the method further includes the step of washing the anode with water after electrolysis.

[0022] Furthermore, the carbon fiber composite material is a sheet structure with a thickness of less than 0.5 cm.

[0023] After the electrolysis is completed, the carbon fiber material is recovered from the liquid molten salt, and then the residual molten salt on the surface is removed by water washing to obtain a carbon fiber-based electrode for electrochemical hydrogen evolution.

[0024] Using molten salt electrochemical means, carbon fiber composite materials are converted into molten salt thermal / electrochemical coupling to produce high-value combustible gas and recycled carbon fiber. The recycled carbon fiber can be used as a hydrogen evolution electrode.

[0025] Molten salt is an excellent heat medium, with a thermal conductivity 10 times that of nitrogen. Molten salt also has the ability to catalyze the pyrolysis and conversion of organic matter into high-value combustible gas. Therefore, the conversion of carbon fiber composites in a molten salt environment can be carried out at medium temperatures (400-600°C), avoiding high energy consumption and damage to the quality of the carbon fibers at high temperatures, while catalytically converting the resin matrix into high-value combustible gas. The unique liquid-phase reaction environment of molten salt can promote the separation of the resin solid phase product and the carbon fibers through surface tension and interfacial interactions.

[0026] Molten salt is also an ionic liquid in its molten state and can serve as an electrolyte. Carbon fiber itself is conductive, so carbon fiber composites can be used as the anode of a molten salt electrolysis cell, simultaneously utilizing thermochemical and electrochemical conversion processes. The electrochemical process allows for precise control of the chemical reaction kinetics by adjusting the electrode potential. Compared to simple thermal reaction conditions, electrochemical parameter regulation is more precise.

[0027] Considering the inherently good electrical conductivity of carbon fiber, recycled carbon fiber can be used as hydrogen evolution electrodes in electrochemical hydrogen evolution, realizing value-added utilization of carbon fiber. The thermoelectrochemical coupling of molten salts can precisely control the degree of oxidation on the carbon fiber surface, thereby constructing a porous structure and defective active hydrogen evolution sites on the carbon fiber surface, enhancing the catalytic capacity of the carbon fiber-based hydrogen evolution electrode.

[0028] The second technical solution of the present invention is to provide a hydrogen evolution electrode prepared by the above method.

[0029] The third technical solution of the present invention is to provide a resource processing method for carbon fiber composite materials, comprising the following steps:

[0030] A two-electrode system consisting of a cathode and an anode is constructed using a carbon fiber composite material as an anode and a molten salt as an electrolyte. The carbon fiber composite material is converted into a combustible gas and a hydrogen evolution electrode through electrolysis;

[0031] The working temperature of the molten salt is 400-600°C.

[0032] Furthermore, the molten salt is at least one of carbonate, chloride, sulfate, fluoride and hydroxide.

[0033] Preferably, the carbonate is at least one of Li2CO3, Na2CO3, K2CO3 and CaCO3.

[0034] Preferably, the chloride salt is at least one of LiCl, NaCl, KCl and CaCl2.

[0035] Preferably, the sulfate is at least one of Li2SO4, Na2SO4, K2SO4 and CaSO4.

[0036] Preferably, the fluoride is at least one of LiF, NaF, KF and CaF2.

[0037] Preferably, the hydroxide is at least one of LiOH, NaOH, KOH and Ca(OH)2.

[0038] Furthermore, the cathode is one of Au, Ag, Pt, Ni, Cu, Mo, NiFe alloy, NiFeCu alloy and graphite.

[0039] Furthermore, the electrolysis step is: heating the molten salt electrolyte to 400-600° C., then immersing the anode and cathode in the molten salt electrolyte, and performing electrolysis in a constant current or constant voltage manner for 0.5-3 h.

[0040] Preferably, the constant voltage is 1.5 to 5V; the constant current is 50mA to 2A.

[0041] Furthermore, the combustible gas includes at least one of H2, CO and CH4.

[0042] Furthermore, the method further includes the step of washing the anode with water after electrolysis.

[0043] The present invention discloses the following technical effects:

[0044] The present invention utilizes the molten salt medium's simultaneous characteristics of enhanced heat transfer, catalytic conversion, and electrochemical conversion. By constructing a molten salt thermo-electrochemical coupled conversion system, the method achieves efficient conversion of carbon fiber composites into combustible gas and recycling of carbon fiber materials at the anode side. The enhanced heat transfer properties of the molten salt lower the thermal conversion temperature, thereby reducing energy consumption; the catalytic effect of the molten salt increases the concentration of combustible gas; and by precisely controlling the electrochemical operating conditions and finely controlling the degree of carbon fiber surface oxidation, a pore structure and defective active sites suitable for hydrogen evolution reaction are constructed on the carbon fiber surface, improving the carbon fiber's hydrogen evolution reaction capability and thus achieving value-added utilization of the recycled carbon fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 This is a scanning electron microscope image of the hydrogen evolution electrode prepared in Example 1;

[0047] Figure 2 This is a scanning electron microscope image of the carbon fiber-based electrode for electrochemical hydrogen evolution prepared in Comparative Example 1;

[0048] Figure 3 is the concentration change of combustible gas in Example 1 and Comparative Example 1;

[0049] Figure 4 Linear voltammetric scan graphs of the hydrogen evolution electrode prepared in Example 1 and the carbon fiber-based electrode for electrochemical hydrogen evolution prepared in Comparative Example 1 used as electrochemical hydrogen evolution electrodes in 1 M KOH solution;

[0050] Figure 5 1 is the XRD pattern of the carbon fiber-based electrodes in Example 1 and Comparative Example 2;

[0051] Figure 6 is the concentration change of the combustible gas in Example 2. DETAILED DESCRIPTION

[0052] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0053] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0054] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0055] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0056] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0057] Example 1

[0058] The method steps for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode are as follows:

[0059] S1. Preparation of electrolyte: 500 g of a mixture of three carbonates, Li2CO3, Na2CO3, and K2CO3, with a molar ratio of 43.5:31.5:25, is selected. The melting point of the three carbonate mixture is 393°C, and the mixture is placed in an alumina crucible. The electrolyte operating temperature range is about 500°C to form a molten electrolyte.

[0060] S2, cutting the carbon fiber composite material into a sheet structure with a thickness of 2 mm, connecting it to the electrode collector through a conductive metal clip to serve as the anode;

[0061] S3, using a metal Ni sheet as the cathode material and connecting it to the electrode current collector through a conductive metal clip as the cathode;

[0062] S4. Immerse the anode and cathode in a molten electrolyte at about 500°C, perform electrolysis at a constant cell voltage of 2.0V, and perform electrolysis for 2 hours. Use an online gas analyzer to analyze the concentration changes of the coupled conversion gas phase products (such as H2, CO, and CH4). Figure 3 After the electrolysis is completed, the anode is recovered from the molten electrolyte, and the residual electrolyte on the surface is removed by washing with water to obtain a carbon fiber-based electrode for electrochemical hydrogen evolution, which is referred to as a hydrogen evolution electrode.

[0063] Figure 1 This is a scanning electron microscope image of the hydrogen evolution electrode prepared in Example 1. Figure 1 It can be seen that there is no resin conversion product residue on the fiber surface, and many micropores are evenly distributed on the fiber surface.

[0064] Example 2

[0065] The method steps for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode are as follows:

[0066] S1. Preparation of electrolyte: 500 g of a mixed salt of three chlorides, LiCl, NaCl, and KCl, with a molar ratio of 47.5:15:37.5, having a melting point of 399° C., was selected and placed in an alumina crucible. The electrolyte operating temperature range was about 600° C. to form a molten electrolyte.

[0067] S2, cutting the carbon fiber composite material into a sheet structure with a thickness of 2 mm, connecting it to the electrode collector through a conductive metal clip to serve as the anode;

[0068] S3, using a metal Ni sheet as the cathode material and connecting it to the electrode current collector through a conductive metal clip as the cathode;

[0069] S4. Immerse the anode and cathode in a molten electrolyte at about 600°C, perform electrolysis at a constant current of 200 mA, and use an online gas analyzer to analyze the concentration changes of the coupled conversion gas phase products (such as H2, CO and CH4). Figure 6 After the electrolysis is completed, the anode is recovered from the molten electrolyte, and the residual electrolyte on the surface is removed by washing with water to obtain a carbon fiber-based electrode for electrochemical hydrogen evolution, which is referred to as a hydrogen evolution electrode.

[0070] Example 3

[0071] The method steps for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode are as follows:

[0072] S1. Preparation of electrolyte: 500 g of a mixture of two sulfates, Li2SO4 and K2SO4, with a molar ratio of 80.9:19.1, with a melting point of 546°C, was placed in an alumina crucible. The electrolyte operating temperature range was around 600°C to form a molten electrolyte.

[0073] S2, cutting the carbon fiber composite material into a sheet structure with a thickness of 2 mm, connecting it to the electrode collector through a conductive metal clip to serve as the anode;

[0074] S3, using a metal Ni sheet as the cathode material and connecting it to the electrode current collector through a conductive metal clip as the cathode;

[0075] S4. Immerse the anode and cathode in a molten electrolyte at about 600°C, perform electrolysis at a constant current of 200 mA, and use an online gas analyzer to analyze the concentration changes of the coupled conversion gas-phase products, combustible gases (H2, CO, and CH4). After the electrolysis is completed, recover the anode from the molten electrolyte and remove the residual electrolyte on the surface by washing with water to obtain a carbon fiber-based electrode for electrochemical hydrogen evolution, which is recorded as a hydrogen evolution electrode.

[0076] Comparative Example 1

[0077] 500 g of a mixed salt of three carbonates, Li2CO3, Na2CO3, and K2CO3, with a molar ratio of 43.5:31.5:25, was selected. The melting point of the three carbonate mixture was 393 ° C. The mixture was placed in an alumina crucible and heated to about 500 ° C to form a molten salt. The same carbon fiber composite material as in Example 1 was placed in the molten salt medium and pyrolyzed for 2 h. The concentration changes of the combustible gases (H2, CO, and CH4) of the pyrolysis conversion gas phase products were analyzed by an online gas analyzer (such as Figure 3 After the pyrolysis is completed, the carbon fiber material is recovered from the liquid molten salt, and then the residual molten salt on the surface is removed by water washing to obtain a carbon fiber-based electrode for electrochemical hydrogen evolution.

[0078] Comparative Example 2

[0079] The method steps for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode are as follows:

[0080] S1. Preparation of electrolyte: 500 g of a mixture of three carbonates, Li2CO3, Na2CO3, and K2CO3, with a molar ratio of 43.5:31.5:25, is selected. The melting point of the three carbonate mixture is 393°C, and the mixture is placed in an alumina crucible. The electrolyte operating temperature range is about 500°C to form a molten electrolyte.

[0081] S2, cutting the carbon fiber composite material into a sheet structure with a thickness of 2 mm, connecting it to the electrode collector through a conductive metal clip to serve as the anode;

[0082] S3, using a metal Ni sheet as the cathode material and connecting it to the electrode current collector through a conductive metal clip as the cathode;

[0083] S4. Immerse the anode and cathode in a molten electrolyte at about 500°C, perform electrolysis at a constant cell voltage of 4.0V, and perform electrolysis for 2 hours. Use an online gas analyzer to analyze the concentration changes of the coupled conversion gas-phase products, combustible gases (H2, CO, and CH4). After the electrolysis is completed, recover the anode from the molten electrolyte and remove the residual electrolyte on the surface by washing with water to obtain a carbon fiber-based electrode for electrochemical hydrogen evolution, which is referred to as a hydrogen evolution electrode.

[0084] Figure 5 Figure 2 is the XRD pattern of the carbon fiber-based electrodes in Example 1 and Comparative Example 2. As can be seen from the figure, around 25° corresponds to the diffraction peak of carbon. Compared with Example 1, the electrolytic cell pressure of Comparative Example 2 is higher, and the degree of oxidation of the carbon fiber surface is higher, which is manifested in the reduced peak intensity and increased half-peak width of the carbon fiber XRD diffraction peak of Comparative Example 2.

[0085] Figure 2 The scanning electron microscope image of the carbon fiber-based electrode for electrochemical hydrogen evolution prepared in Comparative Example 1 is shown in FIG. Figure 2 It can be seen that there are many solid products produced by resin pyrolysis attached to the fiber surface.

[0086] Figure 3 is the concentration change of combustible gas in Example 1 and Comparative Example 1, Figure 3 It can be seen that when electrochemistry participates in the reaction, the output of combustible gas is higher than that of pure thermochemical reaction.

[0087] Figure 4 The linear voltammetric scan diagram of the hydrogen evolution electrode prepared in Example 1 and the carbon fiber-based electrode for electrochemical hydrogen evolution prepared in Comparative Example 1 used as electrochemical hydrogen evolution electrodes in 1M KOH solution is shown in FIG. Figure 4 It can be seen that the carbon fiber obtained in Example 1 has a larger hydrogen production polarization current density and exhibits stronger electrochemical hydrogen evolution performance.

[0088] Figure 6 2 is the concentration change of the combustible gas in Example 2. It can be seen that when constant current electrolysis is adopted, the combustible gas generation rate is relatively stable.

[0089] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for producing combustible gas by electrochemically oxidizing carbon fiber composite materials with molten salt and simultaneously preparing a high-performance hydrogen evolution electrode, characterized in that the steps include: A two-electrode system consisting of a cathode and an anode is constructed using molten salt as an electrolyte, and the anode is converted by electrolysis to produce a combustible gas and a hydrogen evolution electrode; The operating temperature of the molten salt is 400-600°C; The anode is made of carbon fiber composite material.

2. The method according to claim 1, characterized in that The molten salt is at least one of carbonate, chloride, sulfate, fluoride and hydroxide.

3. The method according to claim 2, characterized in that The carbonate is at least one of Li2CO3, Na2CO3, K2CO3 and CaCO3; the chloride salt is at least one of LiCl, NaCl, KCl and CaCl2; the sulfate is at least one of Li2SO4, Na2SO4, K2SO4 and CaSO4; the fluoride is at least one of LiF, NaF, KF and CaF2; the hydroxide is at least one of LiOH, NaOH, KOH and Ca(OH)2.

4. The method according to claim 1, wherein The cathode is one of Au, Ag, Pt, Ni, Cu, Mo, NiFe alloy, NiFeCu alloy and graphite.

5. The method according to claim 1, wherein The electrolysis step is: heating the molten salt electrolyte to 400-600° C., then immersing the anode and cathode in the molten salt electrolyte, and performing electrolysis in a constant current or constant voltage manner for 0.5-3 hours.

6. The method according to claim 5, characterized in that The constant voltage is 1.5~5V; the constant current is 50mA~2A.

7. The method according to claim 1, characterized in that The combustible gas includes at least one of H2, CO and CH4.

8. The method according to claim 1, characterized in that The method further comprises the step of washing the anode with water after electrolysis.

9. A resource processing method for carbon fiber composite materials, characterized in that the steps include: A two-electrode system consisting of a cathode and an anode is constructed using a carbon fiber composite material as an anode and a molten salt as an electrolyte. The carbon fiber composite material is converted into a combustible gas and a hydrogen evolution electrode through electrolysis; The operating temperature of the molten salt is 400-600°C.

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