Catalytic electrode and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrochemical energy storage, and particularly relates to a catalytic electrode and a preparation method and application thereof. The catalytic electrode is a graphite felt subjected to high-temperature calcination treatment, and the surface of the catalytic electrode has the activity of catalyzing an electrochemical hydrogenation and / or dehydrogenation reaction of a nitrogen-containing heterocyclic ring organic compound in an aqueous electrolyte.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage, and particularly relates to a catalytic electrode and a preparation method and application thereof. BACKGROUND

[0002] With the increasing emphasis on sustainable development worldwide, the proportion of renewable energy such as wind energy and solar energy in the energy structure continues to rise. However, these energies are intermittent and unstable, and their large-scale grid connection and efficient utilization require advanced energy storage technologies. Liquid flow batteries are considered one of the ideal technologies in the field of large-scale grid-level energy storage due to their high safety, long cycle life, and the ability to independently design energy storage capacity and output power. At present, the most mature commercialized technology is the all-vanadium redox flow battery. However, the scarcity of vanadium resources and the dramatic price fluctuations, combined with potential environmental problems, to some extent, limit its more widespread application.

[0003] To overcome the bottlenecks of traditional inorganic flow batteries, the development of low-cost, environmentally friendly aqueous organic flow batteries has become a research hotspot in the field of energy storage in recent years. This technology system uses organic compounds with high abundance on earth and strong designability of molecular structure as electrochemically active substances. Among them, nitrogen-containing heterocyclic organic compounds such as quinoxaline have attracted much attention due to their suitable and flat redox potential, high theoretical capacity, and other advantages. However, the electrochemical oxidation-reduction reaction kinetics of such organic molecules on conventional electrode materials (such as untreated graphite felt, carbon paper, etc.) is usually very slow, with high overpotential and poor reversibility, which directly leads to the energy efficiency and power density of the battery being far below the actual application requirements, seriously hindering the practicalization process of aqueous organic flow batteries.

[0004] Therefore, there is an urgent need in the art to provide a new type of electrode material that can exhibit excellent catalytic activity for the electrochemical reaction of nitrogen-containing heterocyclic organic compounds in aqueous electrolyte. Through the application of this electrode material, the reaction overpotential of the above-mentioned organic active substances can be significantly reduced, and their reaction kinetics rate and reversibility can be improved, thereby solving the technical problems of low efficiency and poor performance of organic flow batteries in the prior art, and ultimately improving the overall electrochemical performance of the battery. SUMMARY

[0005] The purpose of the present application is to solve the above problems and provide a catalytic electrode and a preparation method and application thereof.

[0006] In a first aspect, a catalytic electrode is provided by the following technical solution: A catalytic electrode, wherein the catalytic electrode is graphite felt treated by high-temperature calcination, and the surface of the catalytic electrode has activity for catalyzing the electrochemical hydrogenation and / or dehydrogenation reaction of nitrogen-containing heterocyclic organic compounds in aqueous electrolyte.

[0007] Further, the catalytic electrode is prepared by heating the graphite felt to 500 ℃ at a heating rate of 5 ℃ / min, keeping the temperature constant for 2.5 h, and then naturally cooling to room temperature.

[0008] Further, the nitrogen-containing heterocyclic organic compound is selected from one or more of pyrazine, phenazine, pyridazine, pyridine, pyrimidine, quinoline, isoquinoline, quinoxaline, purine and derivatives thereof.

[0009] In a second aspect, a method for preparing a catalytic electrode is provided, which comprises the following steps: A method for preparing a catalytic electrode, which comprises the following steps: placing a graphite felt in an oxygen-containing atmosphere, heating to a calcination temperature of 200-600 ℃ and keeping the temperature constant for 1-4 h, and then naturally cooling to room temperature to obtain the catalytic electrode.

[0010] Further, the method further comprises a pretreatment step of washing and drying the graphite felt before the high-temperature calcination step.

[0011] Further, the graphite felt is ultrasonically washed in deionized water and an alcohol solvent for 20-60 min, and then vacuum dried for 12-36 h.

[0012] In a third aspect, a catalytic electrode is provided, which comprises the following technical solutions: A catalytic electrode for use in an organic flow battery, which is used as the negative electrode of the organic flow battery to catalyze the electrochemical reaction of a nitrogen-containing heterocyclic organic compound dissolved in an aqueous strong base electrolyte.

[0013] Further, the positive electrode of the organic flow battery is a graphite felt or carbon paper that has not been catalytically treated, and the electrolyte of the positive electrode comprises a ferrocyanide / ferricyanide redox couple dissolved in an aqueous strong base solution.

[0014] Further, the nitrogen-containing heterocyclic organic compound is quinoxaline or a derivative thereof.

[0015] Further, the nitrogen-containing heterocyclic organic compound is a quinoxaline / tetrahydroquinoxaline redox couple.

[0016] The beneficial effects of the present application are as follows: Compared with the prior art, the catalytic electrode provided by the application has extremely low catalytic activity on the electrochemical reaction of quinoline and other nitrogen-containing heterocyclic organic compounds when using untreated graphite felt and other carbon materials as the electrode of an organic flow battery, which leads to slow reaction kinetics and high overpotential. The catalytic electrode provided by the application successfully solves this technical problem. Experimental results show that when the catalytic electrode is used for cyclic voltammetry test on quinoline, the redox peak current density is greatly improved compared with the untreated graphite felt electrode, and the peak potential difference is significantly reduced. The catalytic electrode of the application can greatly promote the electrochemical hydrogenation and dehydrogenation reaction rate of nitrogen-containing heterocyclic organic compounds, effectively reduce the reaction overpotential, and significantly improve the reversibility of the reaction, thereby laying a key foundation for improving the comprehensive performance of the energy efficiency, power density and cycle stability of the organic flow battery. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 GF–500℃ 2.5 h provided for Example 1, CV test of GF in 0.01 M QXL + 1 M KOH solution.

[0018] Figure 2 GF–500℃ 2.5 h catalytic electrode provided for Example 1 as the negative electrode of the organic flow battery, in the QXL||K4[Fe(CN)6] flow battery system, at 20 mA·cm –2 (a) GCD test at the charge current density, (b) time-voltage, current curve corresponding to the GCD test, (c) GC test after charging to 120 mAh, (d) GC test after standing for 30 min after charging to 120 mAh, (e) GC test after discharging to –0.2 V after charging to 120 mAh, and (f) the state of the H-type battery after charging to 120 mAh.

[0019] Figure 3 GF–500℃ 2.5 h catalytic electrode provided for Example 1 as the negative electrode of the organic flow battery, in the THQXL||K3[Fe(CN)6] flow battery system, at 2 mA·cm –2 (a) constant current discharge test at the discharge current density, (b) time-voltage, current curve corresponding to the constant current discharge test, and (c) GC test after discharging to –0.2 V. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the application clearer, the application will be described in further detail below with reference to the drawings, and the described embodiments should not be regarded as limiting the application. All other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the application.

[0021] In the following description, reference is made to "some embodiments" which describe only a subset of all possible embodiments, and which can be understood to be the same subset or a different subset from one another, and which can be combined with each other, without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the application have the same meaning as commonly understood by one of ordinary skill in the art in the field of the embodiments of the application. The terminology used in the embodiments of the application is for describing the embodiments of the application only and is not intended to be limiting of the application.

[0022] It should be understood by those skilled in the art that, in the following description of the embodiments of the application, the order of the serial numbers does not mean the order of execution, and some or all steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the application.

[0023] The terminology used in the embodiments of the application is only for the purpose of describing specific embodiments, and is not intended to be limiting of the application. The singular forms "a", "an" and "the" used in the embodiments of the application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0024] It should be understood by those skilled in the art that in the embodiments of the application, the numerical range should be understood to also specifically disclose each intermediate value between the upper limit and the lower limit of the range. Each smaller range between any stated value and stated range, and between any stated value or intermediate value within the stated range, is also included within the application. The upper and lower limits of these smaller ranges can be included or excluded independently from the range.

[0025] Unless otherwise defined, technical / scientific terms used herein have the same meaning to those commonly understood by one of ordinary skill in the art to which the embodiments of the application belong. Although preferred methods and materials are described in the embodiments of the application, any methods and materials similar or equivalent to those described herein can also be used in the embodiments of the application or test examples. All documents mentioned in the specification are generally incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of conflict between any incorporated document and the content of the present application, the content of the present application shall prevail.

[0026] It should be noted that all raw materials and / or reagents in the embodiments of the application are purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0027] The embodiments provide a catalytic electrode, which is a graphite felt treated by high-temperature calcination, and the surface of the catalytic electrode has catalytic activity for electrochemical hydrogenation and / or dehydrogenation reaction of nitrogen-containing heterocyclic organic compounds in an aqueous electrolyte.

[0028] In some embodiments, the catalytic electrode is prepared by heating the graphite felt to 500 ℃ at a temperature ramping rate of 5 ℃ / min and keeping the temperature constant for 2.5 h, and then naturally cooling the graphite felt to room temperature.

[0029] In some embodiments, the nitrogen-containing heterocyclic organic compound is selected from one or more of pyrazine, phenazine, pyridazine, pyridine, pyrimidine, quinoline, isoquinoline, quinoxaline, purine, and derivatives thereof.

[0030] The catalytic electrode provided in this embodiment has a graphite felt (GF) as the base material, and other porous conductive carbon materials such as carbon paper (CP) can also be used. The special feature of this electrode is that it has been subjected to a specific high-temperature calcination process, which enables its surface to have high-efficiency catalytic activity for the reversible electrochemical hydrogenation and dehydrogenation reactions of nitrogen-containing heterocyclic organic compounds in aqueous electrolyte.

[0031] To obtain such a catalytic electrode, a specific preparation method is as follows: commercially available graphite felt (GF) is used as the raw material and cut into a suitable size, for example, 5 cm × 5 cm. First, the surface is cleaned by pretreatment, and then it is placed in a muffle furnace. It is heated to 500 ℃ at a programmed temperature ramping rate of 5 ℃ / min under an oxygen-containing atmosphere containing air. When the furnace temperature reaches 500 ℃, constant temperature is maintained for 2.5 hours. After the constant temperature is maintained, the heating program is turned off, and the graphite felt is naturally cooled to room temperature with the furnace, thereby obtaining the final catalytic electrode.

[0032] The types of nitrogen-containing heterocyclic organic compounds catalyzed by the catalytic electrode are very extensive, and can be selected from one or more of pyrazine, phenazine, pyridazine, pyridine, pyrimidine, quinoline, isoquinoline, quinoxaline, purine, and derivatives thereof. It also includes derivatives of these parent compounds, such as derivatives containing alkyl, halogen, carboxyl, amino, and other substituents. In a preferred example, the catalytic electrode exhibits excellent catalytic activity for quinoxaline.

[0033] The preparation method of the catalytic electrode provided in this embodiment is as follows: the graphite felt is placed in an oxygen-containing atmosphere, heated to a calcination temperature of 200 ℃-600 ℃ and kept for 1 h-4 h, and then naturally cooled to room temperature, thereby obtaining the catalytic electrode.

[0034] In some embodiments, before the high-temperature calcination step, a pretreatment step of washing and drying the graphite felt is also included.

[0035] In some embodiments, the graphite felt is ultrasonically washed in deionized water and an alcohol solvent for 20 min-60 min, and vacuum dried for 12 h-36 h.

[0036] The present application provides a method for preparing a catalytic electrode. The core step of the method is to place a graphite felt as a precursor into a heating device (e.g. a muffle furnace) containing an oxygen-containing atmosphere, and to heat it to a specific calcination temperature interval, which can range from 200°C to 600°C. The temperature is maintained for 1 to 4 hours. After the heat treatment is completed, the heating is stopped, and the material is allowed to cool naturally to room temperature, thereby obtaining an electrode with catalytic activity.

[0037] In a preferred embodiment, in order to obtain better catalytic performance, the graphite felt raw material can be pretreated before the above-mentioned high-temperature calcination step. The specific pretreatment steps are as follows: the cut graphite felt (e.g. 5 cm x 5 cm) is first placed in deionized water and ultrasonically cleaned for 20 to 60 minutes (e.g. 30 minutes) to remove inorganic impurities on the surface. Subsequently, it is taken out of the deionized water and placed in an alcohol solvent, such as isopropyl alcohol or ethanol solution, and again ultrasonically cleaned for 20 to 60 minutes (e.g. 30 minutes) to remove organic impurities on the surface. After cleaning, the graphite felt is placed in a vacuum drying oven and dried at a temperature of, for example, 60°C for 12 to 36 hours (e.g. 24 hours) to completely remove residual solvents and moisture. The clean and dry graphite felt obtained after such pretreatment is then subjected to the aforementioned high-temperature calcination treatment, thereby preparing a catalytic electrode with excellent performance.

[0038] The present embodiment provides an application of a catalytic electrode in an organic flow battery, which is used as the negative electrode of the organic flow battery to catalyze the electrochemical reaction of a nitrogen-containing heterocyclic organic compound dissolved in an aqueous strong base electrolyte.

[0039] In some embodiments, the positive electrode of the organic flow battery is a graphite felt or carbon paper that has not been catalytically treated, and the electrolyte of the positive electrode comprises a ferrocyanide / ferricyanide redox couple dissolved in an aqueous strong base solution.

[0040] In some embodiments, the nitrogen-containing heterocyclic organic compound is quinoxaline or a derivative thereof.

[0041] In some embodiments, the nitrogen-containing heterocyclic organic compound is a quinoxaline / tetrahydroquinoxaline redox couple.

[0042] The catalytic electrode described in the present embodiment is mainly used in the field of organic flow batteries, specifically as the negative electrode of the battery. In this application, the catalytic electrode is placed on the negative side of the battery, with its catalytically active surface in contact with the negative electrolyte, for efficient catalysis of the electrochemical reaction of the negative active material (i.e. the nitrogen-containing heterocyclic organic compound). The negative electrolyte is an aqueous strong base electrolyte, for example, the active material is dissolved in a 1 M KOH aqueous solution to form.

[0043] In a complete organic flow battery system, its structure can be built as follows: the catalytic electrode described in the present application as the negative electrode; the conventional graphite felt or carbon paper without any catalytic treatment as the positive electrode. The negative electrode electrolyte is composed of nitrogen-containing heterocyclic organic compounds (for example, 0.01 M quinoxaline) as the active substance and aqueous strong alkali solvent (for example, 1 M KOH). The positive electrode electrolyte can be composed of inorganic redox couples (for example, 0.1 M ferrocyanide / ferricyanide redox couple, i.e. K4[Fe(CN)6] / K3[Fe(CN)6]) and aqueous strong alkali solvent (for example, 1 M KOH). The negative electrode and the positive electrode are separated by an ion exchange membrane. During the operation of the battery, the preferred negative electrode active substance is quinoxaline (QXL) and its derivatives. During the charging process, QXL is reduced and hydrogenated on the surface of the catalytic electrode to form tetrahydroquinoxaline (THQXL); during the discharging process, THQXL is oxidized and dehydrogenated on the surface of the catalytic electrode to return to QXL, thereby forming a complete and reversible quinoxaline / tetrahydroquinoxaline (QXL / THQXL) redox couple, realizing the storage and release of electrical energy.

[0044] Examples Example 1 I. Preparation of catalytic electrode (OGF-500℃-2.5 h) (1) Pretreatment of graphite felt (GF) A piece of commercially purchased graphite felt (GF) was cut into a size of 5 cm × 5 cm. The cut graphite felt was placed in a beaker containing deionized water and subjected to ultrasonic cleaning at room temperature for 30 minutes to remove inorganic large particle impurities on its surface. Subsequently, the graphite felt was taken out of the deionized water and placed in a beaker containing isopropanol solution, and again subjected to ultrasonic cleaning at room temperature for 30 minutes to remove organic impurities on its surface. After the cleaning was completed, the graphite felt was taken out and placed in a vacuum drying oven for drying at 60℃ for 24 hours to completely remove the residual isopropanol and moisture, obtaining clean and dry graphite felt, denoted as P-GF.

[0045] (2) High-temperature calcination treatment The P-GF obtained after the above pretreatment step was cut into a size of 10 × 10 × 10 mm 3A block-shaped sample was prepared. The sample was placed in a clean crucible and covered with a lid. The crucible containing the sample was then placed in the center of a muffle furnace. Under an air atmosphere (i.e., an oxygen-containing atmosphere), the muffle furnace was programmed to heat from room temperature to 500 °C at a rate of 5 °C / min. Once the furnace temperature reached 500 °C, a isothermal calcination treatment was performed at this temperature for 2.5 hours. After the isothermal program was completed, the power to the muffle furnace was turned off, allowing the crucible and the sample inside to cool naturally to room temperature. After cooling, the sample was removed from the crucible, yielding the catalytic electrode of this embodiment, denoted as OGF-500 °C-2.5 h.

[0046] II. Electrochemical Performance Testing (1) Cyclic Voltammetry (CV) Test To verify the catalytic activity of the prepared catalytic electrode, a three-electrode system was constructed for cyclic voltammetry testing. In this system, the prepared OGF-500℃-2.5 h electrode was used as the working electrode, the saturated calomel electrode (SCE) as the reference electrode, and the platinum wire electrode as the counter electrode. The electrolyte was a 1 M KOH aqueous solution containing 0.01 M quinoxaline (QXL). Using an electrochemical workstation, scans were performed at a scan rate of 0.02 V / s within the potential range of -1.5 V to 0.8 V (vs. SCE).

[0047] Meanwhile, a piece of P-GF that had only undergone pretreatment but had not been calcined at high temperature was taken as a control sample (denoted as GF-500℃0 h) and tested under exactly the same conditions.

[0048] Test results are as follows Figure 1 As shown, compared with the control sample, the OGF-500℃-2.5 h electrode prepared in this embodiment exhibits a significantly higher peak current density and a smaller peak spacing at the corresponding redox potential. This indicates that the high-temperature calcination treatment greatly enhances the electrocatalytic activity of the electrode for the hydrogenation / dehydrogenation reaction of quinoxaline.

[0049] (2) Full battery charge and discharge test To test the performance of the catalytic electrode in a practical battery, an organic-inorganic hybrid flow battery was constructed. The battery used OGF-500℃-2.5 h prepared in this embodiment as the negative electrode and a piece of untreated ordinary graphite felt as the positive electrode.

[0050] The negative electrode electrolyte (negative electrode solution) is composed of 0.01 M quinoxaline (QXL) dissolved in 40 mL of 1 M KOH aqueous solution.

[0051] The positive electrode electrolyte (positive electrode liquid) is composed of 0.1 M K4[Fe(CN)6] dissolved in 40 mL of 1 M KOH aqueous solution.

[0052] A constant current charge-discharge test was performed on the battery. The charging process used a 20 mA·cm² charge-discharge current. -2 The current density is controlled by time; the discharge process uses 2 mA·cm⁻¹. -2 The current density is controlled by voltage, and the discharge cutoff voltage is set to -0.2V.

[0053] Test results are as follows Figure 2 As shown, after charging to 120 mAh, a pale yellow precipitate was observed in the negative electrode electrolyte. Analysis revealed that this substance was dihydroquinoxaline, which has extremely low solubility. This indicates that under these conditions, the catalyst activity was insufficient to completely hydrogenate quinoxaline to the target product tetrahydroquinoxaline (THQXL), and instead, an intermediate product was formed.

[0054] (3) Verification of the THQXL dehydrogenation performance of the catalytic electrode To separately verify the catalytic performance of the catalytic electrode for the discharge reaction (i.e., the dehydrogenation reaction), a separate flow battery representing the fully charged state of the battery was constructed. The negative electrode of this battery remained OGF-500℃-2.5 h, but the negative electrode solution was replaced with a 1 M KOH solution containing tetrahydroquinoxaline (THQXL), and the positive electrode solution was replaced with a 1 M KOH solution containing K3[Fe(CN)6].

[0055] The battery was tested at 2 mA·cm -2 A constant current discharge test was performed using the specified current density. The test results are as follows: Figure 3 As shown, the battery can discharge stably and release a capacity of approximately 20 mAh. This result strongly demonstrates that the OGF-500℃-2.5 h catalytic electrode prepared in this embodiment has excellent catalytic activity for the dehydrogenation reaction of THQXL.

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A catalytic electrode, characterized in that, The catalytic electrode is a graphite felt that has been calcined at high temperature, and the surface of the catalytic electrode has the activity of catalyzing the electrochemical hydrogenation and / or dehydrogenation reactions of nitrogen-containing heterocyclic organic compounds in an aqueous electrolyte.

2. The catalytic electrode according to claim 1, characterized in that, The catalytic electrode was prepared by heating graphite felt to 500 ℃ at a heating rate of 5 ℃ / min, holding it at that temperature for 2.5 h, and then naturally cooling it to room temperature.

3. The catalytic electrode according to claim 1, characterized in that, The nitrogen-containing heterocyclic organic compound is selected from one or more of pyrazine, phenazine, pyridazine, pyridine, pyrimidine, quinoline, isoquinoline, quinoxaline, purine and their derivatives.

4. A method for preparing a catalytic electrode, characterized in that, The graphite felt is placed in an oxygen-containing atmosphere, heated to a calcination temperature of 200℃-600℃ and held for 1-4 hours, and then naturally cooled to room temperature to obtain the catalytic electrode.

5. The method for preparing a catalytic electrode according to claim 4, characterized in that, Before the high-temperature calcination step, a pretreatment step of cleaning and drying the graphite felt is also included.

6. The method for preparing a catalytic electrode according to claim 5, characterized in that, The graphite felt was ultrasonically cleaned in deionized water and alcohol solvent for 20-60 minutes, and then vacuum dried for 12-36 hours.

7. An application of a catalytic electrode in an organic flow battery, characterized in that, The catalytic electrode is used as the negative electrode of an organic flow battery to catalyze the electrochemical reaction of nitrogen-containing heterocyclic organic compounds dissolved in an aqueous strong alkaline electrolyte.

8. The application according to claim 7, characterized in that, The positive electrode of the organic flow battery is uncatalyzed graphite felt or carbon paper, and the electrolyte of the positive electrode includes a ferrocyanate / ferrocyanate couple dissolved in an aqueous strong alkaline solution.

9. The application according to claim 7, characterized in that, The nitrogen-containing heterocyclic organic compound is quinoxaline or its derivative.

10. The application according to claim 9, characterized in that, The nitrogen-containing heterocyclic organic compound is a quinoxaline / tetrahydroquinoxaline redox couple.

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