Graphite phase carbon nitride modified electrode, and preparation method and application thereof

Abstract

The application relates to the technical field of electrodes of all-vanadium redox flow batteries, and discloses a graphite-phase carbon nitride modified electrode as well as a preparation method and application thereof, which comprises the following steps: preparing a composite catalyst of carbon material, graphite-phase carbon nitride and bismuth oxide; loading the composite catalyst on graphite felt through an adhesive and carrying out high-temperature calcination to prepare a graphite felt electrode loaded with the composite catalyst; and assembling the modified electrode as a negative electrode into an electric pile for in-situ electrochemical deposition. The graphite-phase carbon nitride modified electrode is used, the graphite-phase carbon nitride has a graphite-like layered structure, can not only help mass transfer, but also provide more active sites to enhance the oxidation-reduction reaction of vanadium ions, and can improve the voltage efficiency and energy efficiency of the battery; the graphite-phase carbon nitride is combined with the carbon material, the conductivity of the graphite-phase carbon nitride is improved, the charge transfer resistance is reduced, the ohmic polarization of the battery is reduced, and the voltage efficiency and energy efficiency of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery electrode technology, and particularly to a graphite-phase carbon nitride modified electrode, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow battery (VRFB) uses VO 2+ / VO2 + and V 2+ / V 3+ As a redox couple acting as both the positive and negative electrodes, it reduces cross-contamination of the electrolyte and extends its service life. Since the power density of VRFB primarily depends on VO... 2+ / VO2 + and V 2 + / V 3+ Redox reactions at the electrode / electrolyte interface are crucial for electrochemical reactions. Electrode structure plays a vital role in promoting the transport of vanadium ions, protons, and electrons, which is essential for reducing electrochemical polarization. Therefore, electrode design is of great significance for improving the performance of VRFBs (Vanadium Reduction Fusion Batteries). Carbon-based electrodes, such as carbon cloth, carbon felt, and graphite felt, are widely used in VRFBs due to their electrochemical stability and low cost. However, the limited kinetic reversibility, poor catalytic activity of redox reactions, and large overpotentials of carbon-based electrodes restrict their application in VRFBs. Currently, loading catalysts to improve the electrochemical activity of electrodes is the most effective and widely adopted method for modifying vanadium battery electrodes. Summary of the Invention

[0003] The purpose of this invention is to provide a graphite-phase carbon nitride modified electrode, its preparation method and application, so as to overcome the shortcomings of the prior art.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] In the first aspect, a method for preparing a graphite-phase carbon nitride modified electrode is disclosed, comprising the following steps:

[0006] Step S1: Disperse carbon materials, graphitic carbon nitride precursor and bismuth oxide in deionized water, perform hydrothermal treatment, wash the product with deionized water, dry, and perform heat treatment to obtain composite catalyst.

[0007] Step S2: Disperse the composite catalyst and adhesive in deionized water to obtain an aqueous slurry; immerse the graphite felt electrode in the aqueous slurry, remove it, dry it, and then calcine it to obtain a graphite felt electrode loaded with the composite catalyst.

[0008] Step S3: Using the graphite felt electrode with the supported composite catalyst as the negative electrode, electrochemical deposition is performed to obtain a graphite phase carbon nitride modified electrode.

[0009] In one embodiment, in step S1, the mass ratio of the carbon material, the graphitic carbon nitride precursor, bismuth sulfate, and deionized water is (1~3):(10~20):(5~10):(500~600).

[0010] In one implementation method

[0011] The carbon material is one of multi-walled carbon nanotubes, graphene, and carbon nanofibers;

[0012] The graphitic carbon nitride precursor is either urea or melamine.

[0013] Urea or melamine, after heat treatment, forms graphitic carbon nitride, which has a graphitic layered structure. This structure not only helps with mass transfer in the redox reaction of the battery, but also provides more active sites to enhance the redox reaction of vanadium ions, thereby effectively improving the voltage efficiency and energy efficiency of the battery.

[0014] In one implementation, in step S1:

[0015] The hydrothermal treatment is performed at a temperature of 160~200℃ for 8~10 hours.

[0016] The heat treatment method is to heat the material in an oxygen atmosphere at a temperature of 500~550℃ for 4~6 hours, with a heating rate of 5℃ / min.

[0017] In one embodiment, in step S2, the mass ratio of the composite catalyst, adhesive, and deionized water is (1~2):1:20.

[0018] In one implementation method

[0019] The adhesive is one of polyvinyl alcohol water-based adhesive, polyurethane water-based adhesive, and epoxy resin water-based adhesive.

[0020] Adhesives can increase the viscosity of the slurry, improve the dispersibility of the composite catalyst in the aqueous slurry, and also improve the bonding strength between the composite catalyst and the graphite felt fiber, thereby enhancing the stability of the modified electrode.

[0021] In one implementation, in step S2:

[0022] The calcination temperature is 380~420℃, the time is 2~4h, and the atmosphere is air.

[0023] Higher calcination temperatures and longer calcination times result in excessive loss of carbon content in the electrode, which in turn affects the integrity of the graphite felt fibers, leading to reduced conductivity and fiber strength, ultimately negatively impacting battery performance. Lower calcination temperatures and shorter calcination times fail to decompose the organic components in the aqueous slurry, resulting in less exposure of active sites and reduced electrode catalytic activity, which also negatively affects battery performance.

[0024] In one implementation, in step S3:

[0025] The current density of the electrochemical deposition is 10~20 mA / cm². 2 The deposition time is 30-60 minutes.

[0026] During deposition, bismuth oxide reacts with sulfuric acid in the electrolyte to form easily soluble bismuth sulfate, which is then etched onto the graphitic carbon nitride to form a porous structure, increasing the active sites for redox reactions. Subsequently, free bismuth ions are reduced to metallic bismuth during electrochemical deposition and loaded onto the graphite felt electrode. Metallic bismuth not only improves the electrode's conductivity, but also, due to its high hydrogen evolution overpotential and its inherent resistance to hydrogen evolution reactions, it increases the overall hydrogen evolution overpotential of the electrode, thermodynamically increasing the difficulty of the hydrogen evolution reaction. This effectively suppresses the hydrogen evolution side reaction at the negative electrode, improving the voltage efficiency, energy efficiency, and capacity retention of the vanadium battery.

[0027] Secondly, a graphite-phase carbon nitride modified electrode is disclosed, which is prepared using the above-mentioned method for preparing graphite-phase carbon nitride modified electrodes.

[0028] Thirdly, an application of a graphite-phase carbon nitride modified electrode is disclosed, wherein the graphite-phase carbon nitride modified electrode prepared by the above preparation method or the above-mentioned graphite-phase carbon nitride modified electrode is applied to an all-vanadium redox flow battery.

[0029] The beneficial effects of this invention are:

[0030] This invention uses graphitic carbon nitride modified electrodes. Graphitic carbon nitride has a graphitic layered structure, which not only helps mass transfer, but also provides more active sites to enhance the redox reaction of vanadium ions, thereby improving the voltage efficiency and energy efficiency of the battery.

[0031] This invention combines graphitic carbon nitride with carbon materials, which improves the conductivity of graphitic carbon nitride, reduces charge transfer resistance, lowers ohmic polarization of the battery, and improves the voltage efficiency and energy efficiency of the battery.

[0032] This invention combines bismuth oxide with graphitic carbon nitride, using bismuth oxide as both a porous soft template and a bismuth source for metallic bismuth, enabling in-situ growth of metallic bismuth. During deposition, bismuth oxide gradually dissolves in the electrolyte and reacts with sulfuric acid to form bismuth sulfate, creating a porous structure on the graphitic carbon nitride and increasing the number of active sites for redox reactions. Subsequently, bismuth sulfate is reduced to metallic bismuth during electrochemical deposition. The metallic bismuth not only improves the electrode conductivity but also suppresses the hydrogen evolution side reaction at the negative electrode, thereby improving the voltage efficiency, energy efficiency, and capacity retention of the vanadium battery. Attached Figure Description

[0033] Figure 1 This is a scanning electron microscope image of the composite catalyst prepared in Example 1 of the present invention.

[0034] Figure 2 This is a scanning electron microscope image of the composite catalyst prepared in Example 1 of the present invention after electrochemical deposition. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0036] A method for preparing a graphite-phase carbon nitride modified electrode includes the following steps:

[0037] S1. Dissolve and disperse 1-3 parts of carbon material, 10-20 parts of graphitic carbon nitride precursor, and 5-10 parts of bismuth oxide in 500-600 parts of deionized water. After hydrothermal treatment at 160-200℃ for 8-10 h, wash the product with deionized water and dry at 60℃. Finally, heat-treat the sample at 500-550℃ for 4-6 h in an oxygen atmosphere at a heating rate of 5℃ / min to obtain a composite catalyst of carbon material, graphitic carbon nitride, and bismuth oxide.

[0038] S2. Disperse and dissolve 5-10 parts by weight of composite catalyst and 5 parts by weight of adhesive in 100 parts by weight of deionized water, stir evenly to obtain an aqueous slurry; immerse the graphite felt electrode in the aqueous slurry, take it out and dry it, and then calcine it at 380-420℃ for 2-4 hours to obtain a graphite felt electrode loaded with composite catalyst.

[0039] S3. Using a graphite felt electrode supported on a composite catalyst as the negative electrode, electrochemical deposition is performed in a vanadium battery at a current density of 10~20 mA / cm². 2The deposition time is 30-60 min. During deposition, bismuth oxide in the composite catalyst on the electrode is dissolved by sulfuric acid to form bismuth sulfate, and graphite-phase carbon nitride forms a porous structure. Subsequently, bismuth sulfate is reduced to metallic bismuth and loaded on the electrode to obtain a graphite-phase carbon nitride modified electrode.

[0040] Example 1: This example is obtained through the following operations.

[0041] S1. One part of multi-walled carbon nanotubes, 10 parts of urea, and 5 parts of bismuth oxide were dissolved and dispersed in 500 parts of water. After hydrothermal treatment at 160℃ for 8 hours, the product was washed with deionized water and dried at 60℃. Finally, the sample was heat-treated at 500℃ for 4 hours in an oxygen atmosphere at a heating rate of 5℃ / min to obtain a composite catalyst of multi-walled carbon nanotubes, graphitic carbon nitride, and bismuth oxide. Figure 1 The image shown is a scanning electron microscope image of the composite catalyst prepared in this embodiment. The graphitic carbon nitride surface has not yet formed an obvious porous structure.

[0042] S2. Disperse and dissolve 5 parts by mass of composite catalyst and 5 parts by mass of adhesive in 100 parts by mass of deionized water, stir evenly to obtain an aqueous slurry; immerse the graphite felt electrode in the aqueous slurry, take it out, dry it, and calcine it at 380℃ for 2 hours to obtain a graphite felt electrode loaded with composite catalyst.

[0043] S3. Using a graphite felt electrode supported on a composite catalyst as the negative electrode, electrochemical deposition is performed in a vanadium battery at a current density of 10 mA / cm². 2 The deposition time was 30 min. During deposition, bismuth oxide in the composite catalyst on the electrode was dissolved by sulfuric acid to form bismuth sulfate, and graphitic carbon nitride formed a porous structure. Subsequently, bismuth sulfate was reduced to metallic bismuth and loaded on the electrode to obtain a graphitic carbon nitride modified electrode. Figure 2 The image shows a scanning electron microscope image of the composite catalyst prepared in this embodiment after electrochemical deposition. Bismuth oxide, as a soft template, was dissolved by sulfuric acid and formed a distinct porous structure on the graphitic carbon nitride.

[0044] Example 2: This example is obtained through the following operations.

[0045] S1. Two parts of graphene, 15 parts of urea, and 8 parts of bismuth oxide were dissolved and dispersed in 550 parts of water. After hydrothermal treatment at 180℃ for 9 hours, the product was washed with deionized water and dried at 60℃. Finally, the sample was heat-treated at 525℃ for 5 hours in an oxygen atmosphere at a heating rate of 5℃ / min to obtain a composite catalyst of graphene, graphitic carbon nitride, and bismuth oxide.

[0046] S2. Disperse and dissolve 8 parts by mass of composite catalyst and 5 parts by mass of polyurethane waterborne adhesive in 100 parts by mass of deionized water, stir evenly to obtain waterborne slurry; immerse graphite felt electrode in waterborne slurry, take it out, dry it, and calcine it at 400℃ for 3h to obtain graphite felt electrode loaded with composite catalyst.

[0047] S3. Using a graphite felt electrode supported on a composite catalyst as the negative electrode, electrochemical deposition is performed in a vanadium battery at a current density of 15 mA / cm². 2 The deposition time was 45 min. During deposition, bismuth oxide in the composite catalyst on the electrode was dissolved by sulfuric acid to form bismuth sulfate, and graphitic carbon nitride formed a porous structure. Subsequently, bismuth sulfate was reduced to metallic bismuth and loaded on the electrode to obtain a graphitic carbon nitride modified electrode.

[0048] Example 3: This example is obtained through the following operations.

[0049] S1. Three parts of carbon nanofibers, 20 parts of melamine, and one part of bismuth oxide were dissolved and dispersed in 600 parts of water. After hydrothermal treatment at 200℃ for 10 h, the product was washed with deionized water and dried at 60℃. Finally, the sample was heat-treated at 550℃ for 6 h in an oxygen atmosphere at a heating rate of 5℃ / min to obtain a composite catalyst of carbon nanofibers, graphitic carbon nitride, and bismuth oxide.

[0050] S2. Disperse and dissolve 10 parts by mass of composite catalyst and 5 parts by mass of epoxy resin water-based adhesive in 100 parts by mass of deionized water, stir evenly to obtain water-based slurry; immerse graphite felt electrode in water-based slurry, take it out, dry it, and calcine it at 420℃ for 4h to obtain graphite felt electrode loaded with composite catalyst.

[0051] S3. Using a graphite felt electrode supported on a composite catalyst as the negative electrode, electrochemical deposition is performed in a vanadium battery at a current density of 20 mA / cm². 2 The deposition time was 60 min. During deposition, bismuth oxide in the composite catalyst on the electrode was dissolved by sulfuric acid to form bismuth sulfate, and graphitic carbon nitride formed a porous structure. Subsequently, bismuth sulfate was reduced to metallic bismuth and loaded on the electrode to obtain a graphitic carbon nitride modified electrode.

[0052] Comparative Example 1: The following scheme was adopted

[0053] This comparative example is a blank control group, that is, using untreated blank graphite felt electrodes.

[0054] Comparative Example 2: The following scheme was adopted.

[0055] The difference between the preparation process of this comparative example and that of Example 1 is that bismuth oxide is not added in step S1.

[0056] Comparative Example 3: The following scheme was adopted.

[0057] The only difference between the preparation process of this comparative example and that of Example 1 is that electrochemical deposition is not performed in step S2.

[0058] Comparative Example 4: The following scheme was adopted.

[0059] The only difference between the preparation process of this comparative example and that of Example 1 is that the calcination temperature in step S2 is 350°C.

[0060] Comparative Example 5: The following scheme was adopted.

[0061] The only difference between the preparation process of this comparative example and that of Example 1 is that the calcination temperature in step S2 is 450°C.

[0062] The graphite felt electrodes prepared in Examples 1-3 and Comparative Examples 1-3 were assembled into battery stacks and subjected to charge-discharge tests under the same test conditions. The coulombic efficiency, voltage efficiency, energy efficiency, and capacity retention after 100 cycles were recorded. The test results are shown in Table 1.

[0063] Table 1. Performance test results of graphite felt electrodes in the examples and comparative examples.

[0064]

[0065] As can be seen from Table 1, compared with Comparative Example 1, Examples 1-3 and Comparative Examples 2 and 3 have higher voltage efficiency, energy efficiency and capacity retention. This is mainly because the present invention uses graphite-phase carbon nitride modified electrodes. Graphite-phase carbon nitride has a graphite-like layered structure, which not only helps mass transfer, but also provides more active sites to enhance the redox reaction of vanadium ions. Furthermore, this invention combines graphitic carbon nitride with carbon materials, improving the conductivity of graphitic carbon nitride, reducing charge transfer resistance, lowering ohmic polarization of the battery, and improving the voltage efficiency and energy efficiency of the battery. Compared with Comparative Example 2, Examples 1-3 and Comparative Example 3 have higher voltage efficiency and energy efficiency, mainly because this invention combines bismuth oxide with graphitic carbon nitride. Bismuth oxide gradually dissolves in the electrolyte and reacts with sulfuric acid to form bismuth sulfate, forming a porous structure on the graphitic carbon nitride, increasing the active sites for redox reactions, and improving the voltage efficiency and energy efficiency of the battery. Compared with Comparative Example 3, Examples 1-3 have higher voltage efficiency and energy efficiency, mainly because bismuth sulfate is reduced to metallic bismuth during electrochemical deposition. Metallic bismuth not only improves the conductivity of the electrode but also suppresses the hydrogen evolution side reaction of the negative electrode, improving the voltage efficiency, energy efficiency, and capacity retention of the vanadium battery. A comparison of Example 1 with Comparative Examples 4-5 shows that higher calcination temperatures and longer calcination times result in excessive loss of electrode carbon content, which in turn affects the integrity of the graphite felt fibers, leading to reduced conductivity and fiber strength, ultimately negatively impacting battery performance. Lower calcination temperatures and shorter calcination times fail to decompose the organic components in the aqueous slurry, resulting in less exposure of active sites and reduced electrode catalytic activity, which also negatively affects battery performance.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a graphite-phase carbon nitride modified electrode, characterized in that, Includes the following steps: Step S1: Disperse carbon materials, graphitic carbon nitride precursor and bismuth oxide in deionized water, perform hydrothermal treatment, wash the product with deionized water, dry, and perform heat treatment to obtain composite catalyst. Step S2: Disperse the composite catalyst and adhesive in deionized water to obtain an aqueous slurry; immerse the graphite felt electrode in the aqueous slurry, remove it, dry it, and then calcine it to obtain a graphite felt electrode loaded with the composite catalyst. Step S3: Using the graphite felt electrode with the supported composite catalyst as the negative electrode, electrochemical deposition is performed to obtain a graphite-phase carbon nitride modified electrode; the current density of the electrochemical deposition is 10~20 mA / cm². 2 The deposition time is 30-60 min. During the deposition process, bismuth oxide reacts with sulfuric acid in the electrolyte to generate easily soluble bismuth sulfate, which then etches a porous structure on the graphite phase carbon nitride, increasing the active sites for redox reactions. Subsequently, free bismuth ions are reduced to metallic bismuth and loaded onto the graphite felt electrode during the electrochemical deposition process.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the carbon material, graphitic carbon nitride precursor, bismuth oxide and deionized water is (1~3):(10~20):(5~10):(500~600).

3. The preparation method according to claim 1, characterized in that, The carbon material is one of multi-walled carbon nanotubes, graphene, and carbon nanofibers; The graphitic carbon nitride precursor is either urea or melamine.

4. The preparation method according to claim 1, characterized in that, In step S1: The hydrothermal treatment is performed at a temperature of 160~200℃ for 8~10 hours. The heat treatment method is to heat the material in an oxygen atmosphere at a temperature of 500~550℃ for 4~6 hours, with a heating rate of 5℃ / min.

5. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of the composite catalyst, adhesive and deionized water is (1~2):1:

20.

6. The preparation method according to claim 1, characterized in that, The adhesive is one of polyvinyl alcohol water-based adhesive, polyurethane water-based adhesive, and epoxy resin water-based adhesive.

7. The preparation method according to claim 1, characterized in that, In step S2: The calcination temperature is 380~420℃, the time is 2~4h, and the atmosphere is air.

8. A graphite-phase carbon nitride modified electrode, characterized in that, The graphite-phase carbon nitride modified electrode is prepared using the preparation method of the graphite-phase carbon nitride modified electrode as described in any one of claims 1-7.

9. An application of a graphite-phase carbon nitride modified electrode, characterized in that, The graphite-phase carbon nitride modified electrode prepared by the preparation method according to any one of claims 1-7 or the graphite-phase carbon nitride modified electrode according to claim 8 is applied to an all-vanadium redox flow battery.

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