Palladium carbon catalytic electrode, preparation method thereof and organic-inorganic hybrid redox flow battery
By using a palladium-carbon catalytic electrode in an organic-inorganic hybrid flow battery, the problem of sluggish kinetics was solved, achieving a highly efficient electrochemical reaction and improving the battery's charge-discharge efficiency and energy density.
Patent Information
- Application Number
- CN202511161881.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-19
- Publication Date
- 2025-12-23
AI Technical Summary
The electrochemical reaction kinetics of existing organic-inorganic hybrid flow batteries are slow, resulting in low charge-discharge efficiency and insufficient power density. Furthermore, the inorganic reaction at the positive electrode exhibits polarization at high current densities.
By employing a palladium-on-carbon catalytic electrode, the reaction current density is increased and polarization is reduced by catalyzing the hydrogenation/dehydrogenation reaction of nitrogen-containing heterocyclic organic compounds at the negative electrode and the redox reaction of iron-based inorganic compounds at the positive electrode.
It improves the reversibility of the reaction and the electrochemical performance of the flow battery, and promotes electrochemical reactions with high power density and high energy efficiency.
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Figure CN121192185A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochemical energy storage technology, and particularly relates to a palladium-carbon catalytic electrode and its preparation method, and an organic-inorganic hybrid redox flow battery. Background Technology
[0002] With the transformation of the global energy structure, the proportion of renewable energy sources such as wind and solar power is rapidly increasing. However, these energy sources are characterized by intermittency and volatility, and their large-scale grid connection poses a significant challenge to the stable operation of the power grid. Developing large-scale, high-efficiency, and low-cost energy storage technologies is key to solving this problem. Among numerous energy storage technologies, redox flow batteries are considered one of the most promising large-scale energy storage solutions due to their unique advantages, such as independently designable power and capacity, high safety, and long cycle life.
[0003] Currently, the most commercially mature technology is the vanadium redox flow battery. However, its active material, vanadium, is scarce and expensive, and it is highly dependent on strongly acidic electrolytes, posing certain safety and corrosion problems. These factors limit its widespread application. To reduce costs and improve environmental friendliness, researchers have developed organic redox flow batteries, utilizing abundant elements such as carbon, hydrogen, oxygen, and nitrogen to form organic active molecules. Among these, the organic-inorganic hybrid system, which combines stable and inexpensive inorganic materials (such as iron-based compounds) as positive electrode active materials with high-energy-density organic materials (such as nitrogen-containing heterocyclic compounds) as negative electrode active materials, is considered a highly promising technological direction.
[0004] However, the practical application of such hybrid flow batteries still faces bottlenecks. Their performance is primarily limited by the complex hydrogenation / dehydrogenation reactions of the organic molecules at the negative electrode, which are typically kineticly sluggish, resulting in low charge / discharge efficiency and insufficient power density. Simultaneously, although the reaction kinetics of the inorganic redox couple at the positive electrode are relatively fast, significant polarization occurs at high current densities, affecting energy efficiency. Therefore, there is an urgent need in the field for a technique that can effectively improve electrochemical reactivity. This technique needs to simultaneously reduce the overpotential of the organic reaction at the negative electrode and the polarization of the inorganic reaction at the positive electrode, thereby comprehensively improving the overall electrochemical performance of organic-inorganic hybrid flow batteries. Summary of the Invention
[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a palladium-carbon catalytic electrode, its preparation method, and an organic-inorganic hybrid redox flow battery.
[0006] Firstly, a palladium-on-carbon catalytic electrode employs the following technical solution: A palladium-carbon catalytic electrode includes a conductive substrate and a palladium-carbon active catalytic layer supported on its surface. The palladium-carbon active catalytic layer is used to catalyze the hydrogenation / dehydrogenation reaction of nitrogen-containing heterocyclic organic compounds at the negative electrode and / or to catalyze the redox reaction of iron-based inorganic compounds at the positive electrode. The palladium-carbon catalytic electrode is used as the positive electrode and / or negative electrode of a flow battery.
[0007] Furthermore, the conductive substrate is selected from one of carbon paper, nickel foam, and graphite felt.
[0008] Secondly, a palladium-on-carbon catalytic electrode employs the following technical solution: A method for preparing a palladium-on-carbon catalytic electrode involves uniformly mixing a palladium-on-carbon catalyst, a binder, and a solvent to form a homogeneous catalyst ink; then dropwise coating the catalyst ink onto a conductive substrate and drying it at room temperature to obtain the palladium-on-carbon catalytic electrode.
[0009] Furthermore, the adhesive is a perfluorosulfonic acid polymer; the solvent is an aqueous solution of an alcohol.
[0010] Thirdly, an organic-inorganic hybrid redox flow battery adopts the following technical solution: An organic-inorganic hybrid redox flow battery, the flow battery comprising a positive electrode and a negative electrode, wherein at least one of the positive and / or negative electrodes is a palladium-carbon catalytic electrode.
[0011] Furthermore, the positive electrode electrolyte of the flow battery includes an iron-based inorganic compound dissolved in an aqueous strong alkaline solution.
[0012] Furthermore, the iron-based inorganic compound is a ferrocyanate / ferrous cyanate redox couple.
[0013] Furthermore, the negative electrode electrolyte of the flow battery includes a nitrogen-containing heterocyclic organic compound dissolved in an aqueous strong alkaline solution.
[0014] Furthermore, the nitrogen-containing heterocyclic organic compound is selected from one or more of quinoxaline, pyrazine, phenazine, quinoline and its derivatives.
[0015] Furthermore, the nitrogen-containing heterocyclic organic compound is a quinoxaline / tetrahydroquinoxaline redox couple; or a pyrazine / piperazine redox couple.
[0016] The beneficial effects of this invention are: This invention provides a palladium-carbon catalytic electrode that addresses the problem of sluggish electrochemical reaction kinetics in existing hybrid flow batteries. When applied to the positive electrode, this palladium-carbon catalytic electrode can efficiently catalyze the redox reactions of iron-based inorganic compounds. Compared to a purely conductive substrate, it significantly increases the electrode's reaction current density and effectively reduces electrochemical polarization, thereby improving the reversibility of the positive electrode reaction. When applied to the negative electrode, this palladium-carbon catalytic electrode solves the core problem of slow kinetics in the complex hydrogenation / dehydrogenation reactions of nitrogen-containing heterocyclic organic compounds. Through catalysis, it enables multi-electron transfer reactions that are difficult to occur on traditional inert electrodes to proceed efficiently. By simultaneously promoting the reactions at both the positive and negative electrodes, this palladium-carbon catalytic electrode provides a key solution for constructing high-power-density, high-energy-efficiency organic-inorganic hybrid redox flow batteries. Attached Figure Description
[0017] Figure 1 The Pd / C@CP catalytic electrode provided in Example 1 was used as the positive electrode of a flow battery. CV tests were conducted at different scan rates, with a voltage range of 0.65-1.25 V. The electrolyte was 1 M KCl + 0.1 M K₄Fe(CN)₆. (a) CV tests at different scan rates, (b) 5 mV s -1 (c) 10 mV s -1 (d) 15 mV s -1 (e) 20 mV s -1 (f) 25 mV s -1 .
[0018] Figure 2 For Comparative Example 1, the working electrode was CP, and CV tests were conducted at different scan rates, with a voltage range of 0.65-1.25 V. The electrolyte was 1 M KCl + 0.1 M K4Fe(CN)6. (a) CV tests at different scan rates, (b) 5 mV s -1 (c) 10 mV s -1 (d) 15 mV s -1 (e) 20 mV s -1 (f) 25 mV s -1 .
[0019] Figure 3 The Pd / C@NF catalytic electrode provided in Example 2 was used as the negative electrode of a flow battery. GCD was tested in the QXL|| K4[Fe(CN)6] flow battery system at a quinoxaline concentration of 0.025 M.
[0020] Figure 4Using the Pd / C@NF catalytic electrode provided in Example 2 as the negative electrode of a flow battery, GCD was tested in a QXL|| K4[Fe(CN)6] flow battery system at a quinoxaline concentration of 0.050 M.
[0021] Figure 5 The Pd / C@NF catalytic electrode provided in Example 2 was used as the negative electrode of the flow battery, and the Pd / C@CP catalytic electrode provided in Example 1 was used as the positive electrode of the flow battery. Constant current charge-discharge tests were conducted in the pyrazine||K4[Fe(CN)6] flow battery system. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the present application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0023] In the following description, references to "some embodiments" refer to a subset of all possible embodiments; however, it is understood that "some embodiments" may be the same or different subsets of all possible embodiments and may be combined with each other without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the invention have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the invention pertain. The terminology used in the embodiments of the invention is for the purpose of describing the embodiments of the invention only and is not intended to limit the invention.
[0024] Those skilled in the art should understand that, in the following description of the embodiments of the present invention, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.
[0025] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.
[0026] Those skilled in the art will understand that the numerical ranges in the embodiments of the present invention should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value and an intermediate value within the stated range, as well as any other stated value or an intermediate value within the stated range, is also included within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0027] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in embodiments or test cases of the invention. All references to this specification are generally incorporated herein by reference to disclose and describe methods and / or materials associated with said references. In the event of any conflict with any incorporated reference, the contents of this application shall prevail.
[0028] It should be noted that all raw materials and / or reagents in the embodiments of the present invention were purchased from the market or prepared according to conventional methods known to those skilled in the art.
[0029] This embodiment provides a palladium-carbon catalytic electrode, which includes a conductive substrate and a palladium-carbon active catalytic layer supported on its surface. The palladium-carbon active catalytic layer is used to catalyze the hydrogenation / dehydrogenation reaction of nitrogen-containing heterocyclic organic compounds at the negative electrode and / or to catalyze the redox reaction of iron-based inorganic compounds at the positive electrode. The palladium-carbon catalytic electrode is used as the positive electrode and / or negative electrode of a flow battery.
[0030] In some embodiments, the conductive substrate is selected from carbon paper, nickel foam, and graphite felt.
[0031] This embodiment provides a palladium-on-carbon catalytic electrode, the core structure of which includes a porous conductive substrate and a palladium-on-carbon (Pd / C) active catalytic layer uniformly loaded on the surface of the conductive substrate. The conductive substrate provides an attachment carrier for the catalyst and serves as a current current collector. In one specific embodiment, the conductive substrate can be a porous conductive material commonly used in the art. To ensure good conductivity and electrolyte permeability, carbon paper, nickel foam, or graphite felt are preferably selected. The unique feature of this catalytic electrode is that its catalytic active layer can be used in organic-inorganic hybrid flow batteries. When used as a negative electrode, it can effectively catalyze the electrochemical reactions of hydrogenation / dehydrogenation of nitrogen-containing heterocyclic organic compounds; when used as a positive electrode, it can effectively catalyze the redox reactions of iron-based inorganic compounds. Therefore, this electrode can be flexibly applied as the positive electrode, negative electrode, or both electrodes of a flow battery.
[0032] This embodiment provides a method for preparing a palladium-on-carbon catalytic electrode, wherein a palladium-on-carbon catalyst, a binder, and a solvent are mixed uniformly to form a homogeneous catalyst ink; the catalyst ink is dropwise coated onto a conductive substrate and dried at room temperature to obtain the palladium-on-carbon catalytic electrode.
[0033] In some embodiments, the adhesive is a perfluorosulfonic acid polymer; the solvent is an aqueous solution of an alcohol.
[0034] This embodiment also provides a method for preparing the above-mentioned palladium-on-carbon catalytic electrode. The method is simple and easy to operate. Specifically, a uniform catalyst ink can be prepared first. For example, 2-5 mg of palladium-on-carbon (Pd / C) catalyst powder, 80-200 μL of a perfluorosulfonic acid polymer solution (such as Nafion solution) as a binder, and a mixed solvent consisting of water and an alcohol (such as isopropanol) are placed in a container and ultrasonically treated for 10-60 minutes to ensure uniform mixing, forming a black catalyst ink. Subsequently, the prepared catalyst ink is uniformly coated onto a pre-cut (e.g., 10 × 10 mm²) and cleaned conductive substrate by drop addition or other methods. Finally, the coated electrode is allowed to air dry at room temperature until the solvent has completely evaporated, resulting in the final product where the palladium-on-carbon active catalyst layer is stably loaded onto the surface of the conductive substrate.
[0035] This embodiment provides an organic-inorganic hybrid redox flow battery, the flow battery including a positive electrode and a negative electrode, and at least one of the positive and / or negative electrodes being a palladium-carbon catalytic electrode.
[0036] In some embodiments, the positive electrolyte of the flow battery comprises an iron-based inorganic compound dissolved in an aqueous strong alkaline solution.
[0037] In some embodiments, the iron-based inorganic compound is a ferrocyanate / ferrous cyanate redox couple.
[0038] In some embodiments, the negative electrode electrolyte of the flow battery comprises a nitrogen-containing heterocyclic organic compound dissolved in an aqueous strong alkaline solution.
[0039] In some embodiments, the nitrogen-containing heterocyclic organic compound is selected from one or more of quinoxaline, pyrazine, phenazine, quinoline and its derivatives.
[0040] In some embodiments, the nitrogen-containing heterocyclic organic compound is a quinoxaline / tetrahydroquinoxaline redox couple; or a pyrazine / piperazine redox couple.
[0041] This embodiment also provides an organic-inorganic hybrid redox flow battery employing the aforementioned palladium-on-carbon catalytic electrode. The battery includes a positive electrode, a negative electrode, a positive electrode electrolyte, and a negative electrode electrolyte, wherein at least one of the positive and / or negative electrodes is the aforementioned palladium-on-carbon catalytic electrode.
[0042] In one specific embodiment, the positive electrode can be a palladium-on-carbon catalytic electrode (Pd / C@CP) based on carbon paper. The corresponding positive electrode electrolyte is an aqueous solution containing an iron-based inorganic compound. Preferably, the electrolyte can be composed of a ferrocyanate / ferrocyanate couple dissolved in a 0.5-3.0 mol / L aqueous strong alkaline solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH), with the concentration of the active material not exceeding 1.5 mol / L.
[0043] In another specific embodiment, the negative electrode can be a palladium-on-carbon catalytic electrode (Pd / C@NF) based on nickel foam. The corresponding negative electrode electrolyte is an aqueous solution of a nitrogen-containing heterocyclic organic compound, which can also be dissolved in a 0.5-3.0 mol / L aqueous strong alkaline solution of KOH or NaOH. The nitrogen-containing heterocyclic organic compound can be selected from quinoxaline or pyrazine, which form quinoxaline / tetrahydroquinoxaline redox couples or pyrazine / piperazine redox couples respectively during charge and discharge. Those skilled in the art will understand that, to obtain the best overall battery performance, the palladium-on-carbon catalytic electrode of this application can be used simultaneously for both the positive and negative electrodes.
[0044] Example Example 1: Preparation of Pd / C@CP catalytic electrode and its cathode performance test This embodiment provides a method for preparing a palladium-carbon catalytic electrode (Pd / C@CP) supported on a carbon paper substrate, and verifies its performance as a positive electrode catalyst.
[0045] Preparation of Pd / C@CP catalytic electrode Cut a 10×10 mm piece 2 The carbon paper (CP) is washed with purified water and anhydrous ethanol in sequence to remove surface impurities, and then dried at room temperature for later use.
[0046] In a 2 mL centrifuge tube, accurately weigh 3.2 mg of commercial palladium on carbon (Pd / C) catalyst powder, and sequentially add 120 μL of Nafion solution (as a binder), 810 μL of deionized water, and 270 μL of isopropanol (as a solvent). Place the mixture in an ultrasonic cleaner and sonicate for 20 minutes to ensure uniform dispersion of the components, forming a homogeneous and stable black catalyst ink.
[0047] Using a pipette, a suitable amount of catalyst ink is carefully added and coated onto the pretreated carbon paper substrate. The coated electrode is then allowed to air dry at room temperature until the solvent has completely evaporated, resulting in a Pd / C@CP catalytic electrode with a palladium-on-carbon active catalyst layer firmly attached to the carbon paper.
[0048] Electrochemical performance testing The prepared Pd / C@CP catalytic electrode was used as the working electrode, a saturated calomel electrode (SCE) was used as the reference electrode, and a platinum electrode was used as the counter electrode to construct a three-electrode testing system. The electrolyte was 50 mL of a 1 M KCl + 0.01 M K4Fe(CN)6 aqueous solution.
[0049] Cyclic voltammetry (CV) scans were performed using an electrochemical workstation with a voltage range of 0.65–1.25 V (vs. RHE) and scan rates of 5, 10, 15, 20, and 25 mV / s.
[0050] Test results are as follows Figure 1 As shown. The results are compared with those of Comparative Example 1 ( Figure 2 Compared to other electrodes, the Pd / C@CP electrode exhibits better redox peak symmetry and a significantly higher peak current density. As shown in Table 1, at a scan rate of 20 mV / s, the oxidation peak current density reaches 24.67 mA / cm². 2 The reduction peak current density reached -21.60 mA / cm². 2 The efficiency is significantly higher than that of a pure carbon paper electrode. This indicates that the Pd / C catalytic layer greatly promotes the redox reaction of the ferrocyanate / ferrous cyanate couple, exhibiting excellent electrocatalytic activity and reversibility.
[0051] Table 1 Redox performance of Pd / C@CP electrode
[0052] Comparative Example 1 Comparative Example 1 is intended to illustrate the electrochemical performance of a conventional electrode without the use of the catalyst of this application.
[0053] Pure carbon paper (CP) without any catalyst loading was used as the working electrode. The electrode preparation and testing conditions were the same as in Example 1, except for the working electrode itself.
[0054] Cyclic voltammetry (CV) tests were performed on the pure carbon paper electrode using an electrochemical workstation in a three-electrode system. The electrolyte was a 1 M KCl + 0.1 M K4Fe(CN)6 aqueous solution. The voltage scan range was 0.65–1.25 V (vs. RHE), and the scan rates were 5, 10, 15, 20, and 25 mV / s.
[0055] Test results are as follows Figure 2 As shown. From Figure 2 As can be seen, without the palladium-on-carbon catalyst, the redox peak shape of the electrode is poor, the peak current density is low, and the peak potential difference is large, indicating that its catalytic activity for the ferrocyanate / ferrous cyanate couple is limited and its electrochemical reversibility is poor.
[0056] Example 2: Preparation of Pd / C@NF catalytic electrode and its performance test in quinoxaline anode full cell This embodiment provides a palladium-carbon catalytic electrode (Pd / C@NF) supported on a nickel foam substrate, and uses it as the negative electrode to assemble a full cell to verify its catalytic performance on the organic compound quinoxaline.
[0057] Preparation of Pd / C@NF catalytic electrode The electrode preparation method is basically the same as in Example 1, except that the conductive substrate is replaced with nickel foam (NF) of the same size (10×10 mm²). The specific steps are as follows: the cleaned and dried nickel foam substrate is placed in a petri dish, and palladium-on-carbon catalyst ink that has been uniformly mixed by ultrasonication is drop-coated onto its surface. After natural drying at room temperature, a Pd / C@NF catalytic electrode is obtained.
[0058] Assembly and testing of full batteries Assemble a flow battery and conduct tests. The battery system is as follows: (-) Pd / C@NF (negative electrode) | 1 M KOH + n M quinoxaline (negative electrode electrolyte) || 1 M KCl + 0.01 M K4Fe(CN)6 (positive electrode electrolyte) | Pd / C@CP (positive electrode) (+) The positive electrode is the Pd / C@CP electrode prepared in Example 1, and the negative electrode is the Pd / C@NF electrode prepared in this example. The electrolyte volume for both the positive and negative electrodes is 50 mL.
[0059] Constant current charge-discharge (GCD) tests were performed for quinoxaline concentrations of n=0.025 M and n=0.050 M, respectively.
[0060] Test results are as follows Figure 3 (n=0.025 M) and Figure 4 As shown in (n=0.050 M). At a quinoxaline concentration of 0.025 M, after charging the battery to 0.5 mAh, its discharge capacity is 0.114 mAh, corresponding to a coulombic efficiency of 22.8%. At a quinoxaline concentration of 0.050 M, after charging to 0.5 mAh, the discharge capacity is 0.064 mAh, with a coulombic efficiency of 12.8%.
[0061] The above results indicate that the Pd / C@NF electrode of this application can effectively catalyze the hydrogenation and dehydrogenation reactions of the organic compound quinoxaline / tetrahydroquinoxaline redox couple, enabling the battery to perform normal charge-discharge cycles.
[0062] Example 3: Performance testing of Pd / C@NF catalytic electrode in a pyrazine anode full cell In this embodiment, the negative electrode active material in Example 2 is replaced with pyrazine to further verify the catalytic universality of the Pd / C@NF electrode.
[0063] Assembly and testing of full batteries The negative electrode of the battery uses the Pd / C@NF electrode prepared in Example 2, and the positive electrode uses the Pd / C@CP electrode prepared in Example 1. The battery system is as follows: (-) Pd / C@NF (negative electrode) | 1 M KOH + 0.04 M pyrazine (negative electrode electrolyte) || 1 M KCl + 0.01 M K4Fe(CN)6 (positive electrode electrolyte) | Pd / C@CP (positive electrode) (+) The negative electrode electrolyte has a volume of 50 mL and contains 1 M KOH and 0.04 M pyrazine; the positive electrode electrolyte has a volume of 50 mL and contains 1 M KCl and 0.01 M K4Fe(CN)6.
[0064] The flow battery was subjected to constant current charge-discharge (GCD) testing, and the results are as follows: Figure 5 As shown.
[0065] Test Results The battery was charged to 2.0 mAh and then discharged. In the first cycle, the battery's discharge capacity was 1.23 mAh and the coulombic efficiency was 61.5%. After activation in the first cycle, in the second cycle, the battery's discharge capacity increased to 1.48 mAh and the coulombic efficiency also increased accordingly to 74.0%.
[0066] This result strongly demonstrates that the Pd / C@NF catalytic electrode of this application can also efficiently catalyze the hydrogenation / dehydrogenation reaction of pyrazine / piperazine pairs, and exhibits higher coulombic efficiency and better cycle performance than the quinoxaline system, indicating that the catalytic electrode has excellent catalytic activity in different nitrogen-containing heterocyclic organic systems.
[0067] 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 palladium-on-carbon catalytic electrode, characterized in that, The palladium-carbon catalytic electrode includes a conductive substrate and a palladium-carbon active catalytic layer supported on its surface. The palladium-carbon active catalytic layer is used to catalyze the hydrogenation / dehydrogenation reaction of nitrogen-containing heterocyclic organic compounds at the negative electrode and / or to catalyze the redox reaction of iron-based inorganic compounds at the positive electrode. The palladium-carbon catalytic electrode is used as the positive electrode and / or negative electrode of a flow battery.
2. The palladium-on-carbon catalytic electrode according to claim 1, characterized in that, The conductive substrate is selected from one of carbon paper, nickel foam, and graphite felt.
3. A method for preparing a palladium-on-carbon catalytic electrode, characterized in that, The palladium-on-carbon catalyst, binder, and solvent are mixed uniformly to form a homogeneous catalyst ink; the catalyst ink is dropwise coated onto a conductive substrate and dried at room temperature to obtain the palladium-on-carbon catalytic electrode.
4. The method for preparing a palladium-on-carbon catalytic electrode according to claim 3, characterized in that, The adhesive is a perfluorosulfonic acid polymer; the solvent is an aqueous solution of alcohol.
5. An organic-inorganic hybrid redox flow battery, characterized in that, The flow battery includes a positive electrode and a negative electrode, and at least one of the positive and / or negative electrodes is the palladium-carbon catalytic electrode according to any one of claims 1-2.
6. The flow battery according to claim 5, characterized in that, The positive electrode electrolyte of the flow battery includes an iron-based inorganic compound dissolved in an aqueous strong alkaline solution.
7. The flow battery according to claim 6, characterized in that, Iron-based inorganic compounds are ferrocyanate / ferrous cyanate redox couples.
8. The flow battery according to claim 5, characterized in that, The negative electrode electrolyte of the flow battery includes a nitrogen-containing heterocyclic organic compound dissolved in an aqueous strong alkaline solution.
9. The flow battery according to claim 8, characterized in that, The nitrogen-containing heterocyclic organic compound is selected from one or more of quinoxaline, pyrazine, phenazine, quinoline and their derivatives.
10. The flow battery according to claim 9, characterized in that, The nitrogen-containing heterocyclic organic compound is a quinoxaline / tetrahydroquinoxaline redox couple; or a pyrazine / piperazine redox couple.