Preparation method of catalytically active electrode for vanadium battery, catalytically active electrode and application of catalytically active electrode

Abstract

The invention relates to the technical field of electrodes for vanadium batteries, in particular to a preparation method of a catalytically active electrode for a vanadium battery, the catalytically active electrode and application of the catalytically active electrode. The preparation method comprises the following steps: loading a bismuth oxide water-phase dispersion liquid as a precursor on the surface of a graphite felt electrode substrate, placing the graphite felt electrode in an inert atmosphere to carry out a carbon thermal reduction reaction, and carrying out a solid-phase reaction on bismuth oxide and the graphite felt carbon substrate in the inert atmosphere to generate a strongly combined catalytic active site in situ. By pertinently controlling the concentration of the bismuth oxide water-phase dispersion liquid and the temperature of the carbon thermal reduction reaction, active components in the prepared catalytic active electrode for the vanadium battery are uniformly and firmly combined on the surface of a matrix, and high uniformity and high stability are shown. And meanwhile, a loading-first and one-step carbon thermal reduction method is adopted, so that large-scale production can be realized, the electrochemical activity of the product is effectively improved, the uniformity and consistency of the performance can be realized, and the multi-dimensional strict requirements of commercial production on the electrode performance and the manufacturing efficiency are effectively met.

Description

Technical Field

[0001] This invention relates to the field of electrode preparation technology for vanadium batteries, and particularly to a method for preparing a catalytically active electrode for vanadium batteries, the catalytically active electrode itself, and its applications. Background Technology

[0002] The commercialization of vanadium redox flow batteries requires that their core component, the catalytic electrode, not only possess excellent electrochemical performance but also meet the stringent requirements of high efficiency, high consistency, and high stability for industrial production. As a general-purpose electrode substrate, the surface catalytic modification of graphite felt is considered crucial for improving battery performance.

[0003] Currently, introducing bismuth-based catalytic materials onto graphite felt is a mainstream research direction, with common methods including electrodeposition, hydrothermal synthesis, and physical coating. However, electrodeposition inherently relies on a uniform electric field and conductivity. When processing large-size or multi-layered stacked electrodes, it inevitably produces edge effects and uneven deposition thickness, resulting in large performance dispersion and poor uniformity in batch products. While hydrothermal methods can obtain fine microstructures, their high-pressure closed reaction process is opaque, has a long production cycle, high energy consumption, and is difficult to control for batch repeatability, severely restricting production efficiency and cost control. Simple physical coating of commercial bismuth powder, due to the weak binding force between the catalyst and the carbon matrix mainly being physical adsorption, is prone to detachment and deactivation during long-term electrolyte scouring and electrochemical cycling, affecting the electrode's service life and long-term stability. Existing methods struggle to simultaneously meet the comprehensive requirements of high production efficiency, coating uniformity, loading stability, and uniform performance in batch production necessary for industrial-scale production while ensuring high catalytic activity.

[0004] Therefore, developing a method for preparing a vanadium battery catalytic active electrode that is adaptable to large-scale production and can ensure uniform distribution and stable loading of catalytic materials on graphite felt, as well as uniform and consistent performance in batch production, is of great significance for promoting the development of the vanadium battery industry. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem in existing methods for preparing catalytic active electrodes for vanadium batteries that are difficult to simultaneously ensure high catalytic activity while meeting the comprehensive requirements of high production efficiency, coating uniformity, loading stability, and uniform performance in batch production necessary for industrial applications. This invention provides a method for preparing a catalytic active electrode for vanadium batteries, along with the electrode itself and its applications. This preparation method is suitable for large-scale production and ensures uniform distribution and stable loading of the catalytic material on graphite felt, while also exhibiting good performance uniformity in batch production.

[0006] The first aspect of the present invention provides a method for preparing a catalytically active electrode for vanadium batteries, comprising the following steps: Step 1: Load the bismuth oxide aqueous dispersion onto the surface of the graphite felt electrode substrate and dry it. Step 2: Place the dried graphite felt electrode under an inert atmosphere to carry out a carbothermic reduction reaction to obtain a catalytically active electrode.

[0007] This invention provides a method for preparing a catalytically active electrode for vanadium batteries. Using an aqueous bismuth oxide dispersion as a precursor, it is loaded onto the surface of a graphite felt electrode substrate. The graphite felt electrode is then subjected to a carbothermal reduction reaction under an inert atmosphere. In this inert atmosphere, bismuth oxide undergoes a solid-phase reaction with the graphite felt carbon substrate, generating strongly bonded catalytically active sites in situ. By selectively controlling the concentration of the bismuth oxide aqueous dispersion and the temperature of the carbothermal reduction reaction, the active components in the prepared vanadium battery catalytically active electrode are uniformly and firmly bonded to the substrate surface, exhibiting high uniformity and high stability. Furthermore, this application employs a pre-loading followed by carbothermal reduction method, enabling large-scale production, effectively improving the electrochemical activity of the product, achieving uniform performance, and effectively meeting the stringent requirements of commercial production for electrode performance and manufacturing efficiency.

[0008] Furthermore, in step 1, the concentration of the bismuth oxide aqueous dispersion is 10-30 g / L. Preferably, in step 1, the concentration of the bismuth oxide aqueous dispersion is 20-25 g / L.

[0009] Furthermore, in step 1, the loading method is one of spraying, dipping, or roller brushing.

[0010] Furthermore, in step 1, the drying process is carried out in a forced-air drying oven at a temperature of 80-200℃ for 2-12 hours.

[0011] Furthermore, in step 2, the temperature of the carbothermic reduction reaction is 600-900℃, and / or the time of the carbothermic reduction reaction is 2-4 hours. Preferably, in step 2, the temperature of the carbothermic reduction reaction is 700-800℃.

[0012] Furthermore, in step 2, the carbothermic reduction reaction is carried out under a slightly positive pressure inert atmosphere, specifically including: first, evacuating the heat treatment device to below -0.08 MPa, then introducing an inert gas and maintaining the pressure inside the furnace at 0.01-0.05 MPa; wherein, the inert gas is one of nitrogen, argon, helium and carbon dioxide, and is continuously introduced during the heat preservation stage to maintain the slightly positive pressure.

[0013] Furthermore, in step 2, multiple graphite felt electrodes are stacked to perform the carbothermic reduction reaction; and / or, the thickness of the graphite felt electrodes is 1mm-5mm, and the number of stacked electrodes is 10-50. Further, they are placed on a multi-layer high-temperature resistant metal frame, with high-temperature resistant ceramic blocks placed between adjacent graphite felt electrodes, and several graphite felt electrodes are directly stacked.

[0014] A second aspect of the present invention provides a catalytically active electrode obtained by the above-described method for preparing a catalytically active electrode for a vanadium battery.

[0015] A third aspect of the present invention provides a catalytically active electrode obtained by the above-described method for preparing a catalytically active electrode for a vanadium battery, and / or, the application of the catalytically active electrode as described above in a vanadium redox flow battery.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a method for preparing a catalytically active electrode for vanadium batteries. A bismuth oxide aqueous dispersion is used as a precursor, loaded onto the surface of a graphite felt electrode substrate. The graphite felt electrode is then subjected to a carbothermal reduction reaction under an inert atmosphere. In this inert atmosphere, bismuth oxide undergoes a solid-phase reaction with the graphite felt carbon substrate, generating strongly bonded catalytically active sites in situ. By selectively controlling the concentration of the bismuth oxide aqueous dispersion and the temperature of the carbothermal reduction reaction, the active components in the prepared vanadium battery catalytically active electrode are uniformly and firmly bonded to the substrate surface, exhibiting high uniformity and high stability. Furthermore, this application employs a pre-loading followed by carbothermal reduction method, enabling large-scale production, effectively improving the electrochemical activity of the product, achieving uniform performance, and effectively meeting the stringent requirements of commercial production for electrode performance and manufacturing efficiency.

[0017] 2. The catalytic active electrode for vanadium batteries prepared by this invention can reduce its energy efficiency by less than 1.25% after 500 cycles at 240 mA / cm2. The relative standard deviation of energy efficiency of the same batch of products produced in mass production can be controlled within 1.5%, achieving excellent results. Attached Figure Description

[0018] Figure 1 This is a SEM image of the active electrode prepared in Example 1.

[0019] Figure 2 This is a SEM image of the active electrode after 500 cycles.

[0020] Figure 3 The active electrode prepared for this invention operates at a current density of 240 mA / cm². 2 The graph shows the changes in coulombic efficiency and energy efficiency over the next 500 cycles. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0022] The first aspect of this embodiment provides a method for preparing a catalytically active electrode for vanadium batteries, comprising the following steps: Step 1: Load the bismuth oxide aqueous dispersion onto the surface of the graphite felt electrode substrate and dry it. Step 2: Place the dried graphite felt electrode under an inert atmosphere to carry out a carbothermic reduction reaction to obtain a catalytically active electrode.

[0023] By selectively controlling the concentration of the bismuth oxide aqueous dispersion and the temperature of the carbothermic reduction reaction, the active components in the prepared vanadium battery catalytic active electrode are uniformly and firmly bonded to the substrate surface, exhibiting high uniformity and high stability. Furthermore, this application employs a pre-loading followed by carbothermic reduction method, enabling large-scale production, effectively improving the electrochemical activity of the product, achieving uniform performance, and effectively meeting the stringent requirements of commercial production for electrode performance and manufacturing efficiency.

[0024] In some embodiments, the concentration of the bismuth oxide aqueous dispersion in step 1 is 10-30 g / L. Studies have found that the concentration of the bismuth oxide aqueous dispersion is a key factor affecting the overall performance of the catalytically active electrode. Reasonably controlling the concentration range allows for the formation of a uniformly thick pre-coating layer on the graphite felt surface, completely covering the fiber surface without blocking the pores. This enables bismuth oxide to undergo a sufficient and uniform solid-phase reaction with carbon throughout the entire electrode substrate, thereby generating uniformly distributed and firmly bonded bismuth catalytic active sites in situ. For example, in one or more embodiments, the concentration of the bismuth oxide aqueous dispersion is 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, 26 g / L, 27 g / L, 28 g / L, 29 g / L, or 30 g / L. Preferably, in step 1, the concentration of the bismuth oxide aqueous dispersion is 20-25 g / L.

[0025] In some embodiments, in step 1, the loading method is one of spraying, dipping, or roller brushing.

[0026] In some embodiments, in step 1, the drying process is carried out in a forced-air drying oven at a temperature of 80-200°C for 2-12 hours. For example, in step 1, the drying process is carried out in a forced-air drying oven at a temperature of 80°C for 12 hours. Alternatively, in step 1, the drying process is carried out in a forced-air drying oven at a temperature of 100°C for 8 hours. Or, in step 1, the drying process is carried out in a forced-air drying oven at a temperature of 200°C for 2 hours. All of these are feasible.

[0027] In some embodiments, the temperature of the carbothermic reduction reaction in step 2 is 600-900℃. For example, the temperature of the carbothermic reduction reaction in step 2 is 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃. Preferably, the temperature of the carbothermic reduction reaction in step 2 is 700-800℃. Studies have found that the temperature of the carbothermic reduction reaction is closely related to the overall performance of the catalytically active electrode. Reasonable control of the carbothermic reduction reaction temperature helps to induce a stronger solid-phase interfacial reaction between metallic bismuth and the carbon fiber surface, forming a strong chemical bond, which greatly enhances the adhesion stability of the catalyst. At the same time, in the process of mass production, it can effectively improve the uniformity of performance of the same batch of products.

[0028] In some embodiments, the carbothermic reduction reaction takes 2-4 hours. For example, the carbothermic reduction reaction takes 2 hours, 3 hours, or 4 hours.

[0029] In some embodiments, step 2, the carbothermic reduction reaction is carried out under a slightly positive pressure inert atmosphere, specifically including: first, evacuating the heat treatment device to below -0.08 MPa, then introducing an inert gas and maintaining the furnace pressure at 0.01-0.05 MPa; wherein the inert gas is one of nitrogen, argon, helium, and carbon dioxide, and is continuously introduced during the heat preservation stage to maintain the slightly positive pressure. For example, the furnace pressure is 0.01 MPa, 0.02 MPa, 0.03 MPa, 0.04 MPa, or 0.05 MPa. Experimental studies have found that during mass production, under slightly positive pressure, the continuously introduced inert gas can form a uniform, stable, and slightly penetrating protective atmosphere, ensuring that heat transfer and the reaction atmosphere are highly uniform in each layer and each region of the multilayer graphite felt, allowing the bismuth oxide precursor to undergo a solid-phase reaction with the carbon matrix in a relatively uniform environment. Therefore, this micro-positive pressure control technology is an indispensable precision process condition for achieving the core goal of ultra-high consistency (RSD<1.5%) of electrode products in large-scale and batch production. Its synergistic effect with specific temperature and concentration windows constitutes a key bridge from laboratory samples to industrial products.

[0030] In some embodiments, in step 2, a carbothermic reduction reaction is carried out by stacking multiple graphite felt electrodes; and / or, the thickness of the graphite felt electrodes is 1mm-5mm, and the number of stacked electrodes is 10-50.

[0031] The second aspect of this embodiment provides a catalytically active electrode obtained by the above-described method for preparing a catalytically active electrode for vanadium batteries.

[0032] The third aspect of this embodiment provides a catalytically active electrode obtained by the above-described method for preparing a catalytically active electrode for a vanadium battery, and / or, the application of the catalytically active electrode as described above in a vanadium redox flow battery.

[0033] To better understand the above solution, the following more detailed implementation examples are provided for further explanation.

[0034] Example 1 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed from a spraying distance of 25cm to uniformly load a 10g / L bismuth oxide aqueous dispersion onto the surface of a graphite felt electrode substrate measuring 800mm × 350mm × 2.5mm. Spray 1L of solution onto two 80cm*35cm graphite felts, spraying both sides. Dry in a vertical electric thermostatic drying oven at 80℃ for 12 hours until no obvious liquid film remains on the electrode surface. Step 2: Place the dried graphite felt electrode in a vacuum atmosphere furnace, start the vacuum pump, evacuate to -0.08 MPa, and introduce nitrogen gas to form a slight positive pressure of 0.01 MPa in the furnace. Maintain this pressure throughout the heating and holding stages. The inert gas flow rate is 7 L / h. Under the protection of nitrogen atmosphere, hold at 600℃ for 4 hours. During this process, bismuth oxide undergoes a carbothermic reduction reaction with the carbon element on the fiber to generate elemental bismuth, thus obtaining a catalytically active electrode.

[0035] Example 2 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed at a spraying distance of 25cm to uniformly load a bismuth oxide aqueous dispersion with a concentration of 20g / L onto the surface of a graphite felt electrode substrate with a size of 800mm×350mm×2.5mm. Control the single-sided load to be the same as in Example 1. Dry at 100℃ for 4 hours using a vertical electric heating constant temperature drying oven. Step 2: Place the dried graphite felt electrode in a vacuum atmosphere furnace, start the vacuum pump, evacuate to -0.08 MPa, and introduce nitrogen gas to form a slight positive pressure of 0.02 MPa in the furnace. Maintain this pressure throughout the heating and holding stages. The inert gas flow rate is 7 L / h. Under the protection of nitrogen atmosphere, hold at 700℃ for 3 hours. During this process, bismuth oxide undergoes a carbothermic reduction reaction with the carbon element on the fiber to generate elemental bismuth, thus obtaining a catalytically active electrode.

[0036] Example 3 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed at a spraying distance of 25cm to uniformly load a bismuth oxide aqueous dispersion with a concentration of 22g / L onto the surface of a graphite felt electrode substrate with a size of 800mm×350mm×2.5mm. Control the single-sided load to be the same as in Example 1. Dry at 100℃ for 4 hours using a vertical electric heating constant temperature forced air drying oven. Step 2: Place the dried graphite felt electrode in a vacuum atmosphere furnace, start the vacuum pump, evacuate to -0.08 MPa, and introduce nitrogen gas to form a slight positive pressure of 0.03 MPa in the furnace. Maintain this pressure throughout the heating and holding stages. The inert gas flow rate is 7 L / h. Under the protection of nitrogen atmosphere, hold at 800℃ for 3 hours. During this process, bismuth oxide undergoes a carbothermic reduction reaction with the carbon element on the fiber to generate elemental bismuth, thus obtaining a catalytically active electrode.

[0037] Example 4 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed at a spraying distance of 25cm to uniformly load a bismuth oxide aqueous dispersion with a concentration of 25g / L onto the surface of a graphite felt electrode substrate with a size of 800mm×350mm×2.5mm. Control the single-sided load to be the same as in Example 1. Dry at 100℃ for 4 hours using a vertical electric heating constant temperature drying oven. Step 2: Place the dried graphite felt electrode in a vacuum atmosphere furnace, start the vacuum pump, evacuate to -0.08 MPa, and introduce nitrogen gas to form a slight positive pressure of 0.04 MPa in the furnace. Maintain this pressure throughout the heating and holding stages. The inert gas flow rate is 7 L / h. Under the protection of nitrogen atmosphere, hold at 750℃ for 3 hours. During this process, bismuth oxide undergoes a carbothermic reduction reaction with the carbon element on the fiber to generate elemental bismuth, thus obtaining a catalytically active electrode.

[0038] Example 5 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed at a spraying distance of 25cm to uniformly load a 30g / L bismuth oxide aqueous dispersion onto the surface of a graphite felt electrode substrate measuring 800mm×350mm×2.5mm. Control the single-sided load to be the same as in Example 1. Dry at 200℃ for 2 hours using a vertical electric thermostatic drying oven. Step 2: Place the dried graphite felt electrode in a vacuum atmosphere furnace, start the vacuum pump, evacuate to -0.08 MPa, and introduce nitrogen gas to form a slight positive pressure of 0.05 MPa in the furnace. Maintain this pressure throughout the heating and holding stages. The inert gas flow rate is 7 L / h. Under the protection of nitrogen atmosphere, hold at 900℃ for 2 hours. During this process, bismuth oxide undergoes a carbothermic reduction reaction with the carbon element on the fiber to generate elemental bismuth, thus obtaining a catalytically active electrode.

[0039] Example 6 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed at a spraying distance of 25cm to uniformly load a bismuth oxide aqueous dispersion with a concentration of 20g / L onto the surface of a graphite felt electrode substrate with a size of 800mm×350mm×2.5mm. Control the single-sided load to be the same as in Example 1. Dry at 100℃ for 4 hours using a vertical electric heating constant temperature drying oven. Step 2: Place the dried graphite felt electrode in a vacuum atmosphere furnace, start the vacuum pump, evacuate to -0.08 MPa, close the valve, and perform heat treatment at 700℃ for 3 hours under static negative pressure to obtain the catalytically active electrode.

[0040] Example 7 Preparation of catalytically active electrodes Step 1: Using an electric paint spray gun, move at a constant speed at a spraying distance of 25cm to uniformly load a bismuth oxide aqueous dispersion with a concentration of 20g / L onto the surface of a graphite felt electrode substrate with a size of 800mm×350mm×2.5mm. Control the single-sided load to be the same as in Example 1. Dry at 100℃ for 4 hours using a vertical electric heating constant temperature drying oven. Step 2: Directly introduce nitrogen gas into the dried graphite felt electrode and keep it at 700℃ for 3 hours under normal pressure and flow conditions. During this process, bismuth oxide undergoes a carbothermic reduction reaction with the carbon element on the fiber to generate elemental bismuth, thus obtaining a catalytically active electrode.

[0041] It should also be noted that if oxidizing gases are present during the research process, the graphite felt fired in the vacuum atmosphere furnace may soften, crack, or even burn directly into ash.

[0042] Comparative Example 1 The same specifications, batch and size were used, but the original graphite felt electrode was not modified in any way.

[0043] Comparative Example 2 Comparative Example 2 used an electrode deposition method to prepare the electrode sample.

[0044] Weigh out bismuth nitrate pentahydrate and dissolve it in an aqueous solution containing 1.0 mol / L nitric acid. Stir continuously until completely dissolved to prepare bismuth ions (Bi). 3+ A clear acidic electrolyte with a concentration of 0.1 mol / L.

[0045] The original graphite felt was used as the working electrode (cathode); a platinum sheet was used as the counter electrode (anode).

[0046] A standard three-electrode system was used on an electrochemical workstation. The parameters were set as follows: constant current deposition, current density of -3 mA / cm², deposition time of 600 seconds (i.e., total charge of approximately 1.8 C / cm²), and the entire deposition process was carried out at room temperature.

[0047] By controlling the amount of deposited charge, the bismuth loading on the electrode was made comparable to that in Example 2. After deposition, the electrode was removed and immediately rinsed with plenty of deionized water to thoroughly remove residual nitric acid and bismuth nitrate.

[0048] The electrode was placed in a forced-air drying oven and dried at 80°C for 6 hours to obtain the electrode sample of Comparative Example 2.

[0049] Comparative Example 3 Comparative Example 3 used a physical coating method to prepare the electrode sample.

[0050] Weigh commercial micron-sized bismuth powder (particle size approximately 1-5 μm) and polyvinylidene fluoride binder, and mix them at a mass ratio of 90:10. Add an appropriate amount of N-methylpyrrolidone as a solvent, and grind in an agate mortar or high-speed mixer for 2 hours to form a uniform, viscous conductive slurry.

[0051] Using a doctor blade or coating machine, the above slurry was manually coated onto the surface of a graphite felt of the same specifications as in Example 2. The coating amount was controlled so that the bismuth loading after drying was approximately equivalent to that in Example 2. The coated electrode was first placed in a 60°C oven for preliminary drying for 2 hours to evaporate most of the solvent. It was then transferred to a vacuum drying oven and vacuum dried at 120°C for 12 hours to obtain the electrode sample of Comparative Example 3.

[0052] Comparative Example 4 Compared with Example 2, Comparative Example 4 changed the temperature of the carbothermic reduction reaction, but the rest of the preparation process was completely the same as that of Example 2.

[0053] In Comparative Example 4-I, the temperature of the carbothermic reduction reaction was set to 500℃; in Comparative Example 4-II, the temperature of the carbothermic reduction reaction was adjusted to 1000℃.

[0054] The electrochemical performance of the electrodes formed in Examples 1-7 and Comparative Examples 1-4 was tested, and the testing process is as follows: Test 1: Examples 1-7 and Comparative Examples 1-4 were used as negative electrodes, and ordinary graphite felt was used as positive electrodes.

[0055] A perfluorosulfonic acid proton exchange membrane was used as the diaphragm.

[0056] Both the positive and negative electrode electrolytes contain 1.6 M vanadium ions (in V). 3+ / V 4+ The solution is mainly composed of sulfuric acid, with the initial state of charge (SOC) adjusted to 50%, and the volume is 40 mL.

[0057] Assemble the electrodes, separator, current collector, and flow field plate into the standard single-cell test fixture in sequence, ensuring a good seal. Circulate the electrolyte at a constant flow rate (60 mL / min) using a peristaltic pump.

[0058] High-performance battery testing systems (such as Arbin BT2000 or LAND CT3001A) are used for charge and discharge control and data acquisition.

[0059] The entire battery system was placed in a constant temperature environment (25±1℃). The test used a constant current charge-discharge mode.

[0060] Test program: Activation phase: First, perform 3 charge-discharge cycles at a current density of 80 mA / cm² to fully wet and activate the electrode.

[0061] Efficiency testing phase: Current density set to 240 mA / cm² 2 Conduct formal testing.

[0062] Charging: Charge until the battery voltage reaches the cutoff voltage of 1.65 V.

[0063] Discharge: Discharge immediately until the cutoff voltage of 1.00 V is reached.

[0064] This charge-discharge process is repeated for at least 5 cycles, and the data from the last 3 stable cycles are used for calculation.

[0065] The testing system automatically records the charging time, discharging time, charging capacity, discharging capacity, average charging voltage, and average discharging voltage for each cycle. The average coulombic efficiency and average energy efficiency are then calculated. The test results are shown in Table 1.

[0066] Test 2: A constant current charge / discharge mode was adopted, with the current density set to 240 mA / cm². 2 The charging cutoff voltage was 1.65 V, and the discharging cutoff voltage was 1.00 V. 500 complete charge-discharge cycles were performed continuously. The test system automatically recorded the charging capacity, discharging capacity, average charging voltage, and average discharging voltage for each cycle, and calculated the coulombic efficiency, voltage efficiency, and energy efficiency in real time. The reduction in energy efficiency after 500 cycles was calculated, and the results are shown in Table 1.

[0067] Table 1

[0068] Example 8 The solution concentration and spraying process of Example 2 were used.

[0069] Fifty graphite felt sheets (each 1 mm thick, with the same size specifications as in Example 2) were neatly stacked and placed on a multi-layer high-temperature resistant metal frame, with a high-temperature resistant ceramic block placed between adjacent graphite felt electrodes.

[0070] After drying, the whole thing is placed in an atmosphere furnace and carbothermic reduction is carried out under a slight positive pressure of 0.02 MPa and a temperature of 700℃ for 3 hours.

[0071] Example 9 The solution concentration and spraying process of Example 2 were used.

[0072] Ten graphite felt sheets (each 5 mm thick, with the same size specifications as in Example 2) were neatly stacked and placed on a multi-layer high-temperature resistant metal frame, with a high-temperature resistant ceramic block placed between adjacent graphite felt electrodes.

[0073] After drying, the whole thing is placed in an atmosphere furnace and carbothermic reduction is carried out under a slight positive pressure of 0.02 MPa and a temperature of 700℃ for 3 hours.

[0074] Example 10 The solution concentration and spraying process of Example 2 were used.

[0075] Thirty graphite felt sheets (each 2.5 mm thick, with the same size specifications as in Example 2) were neatly stacked and placed on a multi-layer high-temperature resistant metal frame, with a high-temperature resistant ceramic block placed between adjacent graphite felt electrodes.

[0076] After drying, the whole thing is placed in an atmosphere furnace and carbothermic reduction is carried out under a slight positive pressure of 0.02 MPa and a temperature of 700℃ for 3 hours.

[0077] Test 3: Scientific sampling was performed on the batch of catalytically active electrodes prepared in Examples 8-10. Specifically, representative samples were extracted from the stacked electrodes at three spatial positions: top, middle, and bottom.

[0078] Sample preparation: Cut at least three 5cm × 5cm test samples from the center and edge areas (5cm from the edge) of each sampling electrode and mark their positions.

[0079] Electrochemical performance tests were performed on all the cut samples.

[0080] Test cells: Each sample is used as the negative electrode and paired with a positive electrode to assemble them into identical single-cell test units.

[0081] Testing standards: The exact same test conditions as those used to verify other embodiments are employed to ensure data comparability. Electrolyte: 1.6 MV 3+ / V 4+ 50% SOC; Current density: 240 mA / cm² 2 Temperature: 25°C; Charge / discharge cutoff voltage: 1.65 V / 1.00 V. Each sample was tested for at least 3 stable cycles, and its average energy efficiency (EE), average voltage efficiency (VE), and average coulombic efficiency (CE) were recorded.

[0082] Data aggregation: The performance data (with energy efficiency as the key indicator) of all samples from different spatial locations (upper, middle and lower layers) and different regions of the same electrode (center and edge) are aggregated.

[0083] Calculate the overall mean and standard deviation: Calculate the arithmetic mean (μ) of the energy efficiency of all samples; calculate the standard deviation (σ) of the energy efficiency of all samples.

[0084] Calculate the relative standard deviation: RSD = (σ / μ) × 100%. The RSD value is a core indicator for evaluating batch uniformity; the smaller the value, the smaller the data dispersion and the better the uniformity. Calculate the average and standard deviation of the energy efficiency of the upper, middle, and lower layers of samples respectively, and compare them to verify whether the temperature and atmosphere at different heights within the furnace are uniform.

[0085] Test data shows that the average energy efficiency of all sampled samples in Examples 8-10 is basically consistent with the average energy efficiency of a production sample, with a relative standard deviation (RSD) of energy efficiency (EE) of less than 1.5% (for example, the RSD of the batch electrodes in Example 10 is only 1.2%). Meanwhile, analysis shows that the average energy efficiency difference between the upper, middle, and lower electrode layers is less than 0.3%, and the efficiency difference between the center and edge regions of the same electrode sheet is less than 0.5%.

[0086] Comparative Example 5 Comparative Example 5 was tested using the same batch production process as Example 10, except that the temperature of the carbothermic reaction in Comparative Example 5 was controlled at 1000°C, while the rest was the same as in Example 10.

[0087] The same method as in Test 3 was used to test the performance uniformity. The test results showed that the average energy efficiency of the batch electrodes in Comparative Example 5 decreased, and the performance uniformity was significantly reduced, with a relative standard deviation (RSD) as high as 5.2% and an interlayer performance difference of 2.0%. This may be because the temperature is too high, which may cause uneven thermal field and volatilization and aggregation of active components.

[0088] Comparative Example 6 Comparative Example 6 was tested using the same batch production process as Example 10. The difference was that when Comparative Example 6 underwent a carbothermic reaction, the vacuum was evacuated to -0.08 MPa, the valve was closed, and it was heat-treated at 700°C for 3 hours under static negative pressure.

[0089] The same method as in Test 3 was used to test the performance uniformity. The test results showed that the performance uniformity of the batch electrodes of Comparative Example 6 was significantly lower than that of the present invention, with a relative standard deviation (RSD) of 3.5%. Moreover, the average efficiency of the upper, middle and lower electrodes showed obvious gradient differences (the middle layer was about 1.5% lower).

[0090] Therefore, the method of this invention for multi-layer stacking and mass production ensures extremely high performance consistency of electrode products, with a key indicator RSD of less than 1.5%, meeting the stringent requirements of industrial production for product uniformity. Common electrodeposition and physical coating methods are difficult to implement for mass industrial production, and also require ensuring high uniformity of electrode performance in mass production. The technical solution of this invention achieves unexpected results. The preparation method adopted in this invention is simple to operate, has a short production process, and low equipment cost. It provides a highly efficient and feasible new technical paradigm for realizing the leap from "laboratory" to "industrial production" of catalytic active electrodes.

[0091] Example 11 The following stack-level tests were conducted to test the actual performance of the catalytically active electrode prepared in this invention in a commercial fuel cell stack: 1. Electrode fabrication and fuel cell stack assembly Using the exact same solution concentration, spraying process, and carbothermic reduction conditions (0.02 MPa, 700 °C) as in Example 2, 64 catalytically active electrodes measuring 800 mm × 350 mm × 2.5 mm were prepared. These electrodes were then assembled with bipolar plates, separators, and other components to form a vanadium redox flow battery stack with a rated power of 48 kW.

[0092] 2. Test Platform and Operating Conditions Electrolyte system: Electrolyte in the positive and negative electrode tanks (1.6 MV) 3+ / V 4+ The sulfuric acid system has a volume of 150L.

[0093] Circulation control: The electrolyte circulation flow rate is controlled by the inlet pressure, which was set to 0.08 MPa in this test (controllable range 0.06-0.12 MPa).

[0094] Charge / discharge program: Constant current charge / discharge mode is adopted. Based on the voltage of a single battery cell, the charging cut-off voltage is set to 1.65 V and the discharging cut-off voltage is set to 1.00 V.

[0095] Test conditions: Ambient temperature controlled at 25±2°C.

[0096] 3. Test Results and Conclusions The stack was tested at a current density of 240 mA / cm², and its initial energy efficiency reached 80.5%. After 500 charge-discharge cycles, the energy efficiency decay rate of the stack was less than 1.0%, and the voltage deviation between individual cells remained within ±30 mV, demonstrating excellent operational consistency and long-cycle stability.

[0097] 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, and 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 catalytically active electrode for a vanadium cell, characterized in that The method comprises the following steps: Step 1, loading a bismuth oxide aqueous dispersion on the surface of a graphite felt electrode substrate and drying treatment; Step 2, placing the dried graphite felt electrode in an inert atmosphere to perform a carbothermal reduction reaction to obtain a catalytically active electrode.

2. The method for preparing a catalytically active electrode for a vanadium cell according to claim 1, characterized in that In step 1, the concentration of the bismuth oxide aqueous dispersion is 10-30 g / L.

3. The method for preparing a catalytically active electrode for a vanadium cell according to claim 2, characterized in that In step 1, the concentration of the bismuth oxide aqueous dispersion is 20-25 g / L.

4. The method for preparing a catalytically active electrode for a vanadium cell according to claim 1, characterized in that, In step 1, the loading method is one of spraying, dipping or rolling.

5. The method for preparing a catalytically active electrode for a vanadium cell according to claim 1, characterized in that, In step 1, during the drying treatment, the drying temperature is 80-200 ℃ and the drying time is 2-12 h.

6. The method for preparing a catalytically active electrode for a vanadium cell according to claim 1, characterized in that, In step 2, the temperature of the carbothermal reduction reaction is 600-900 ℃ and / or the time of the carbothermal reduction reaction is 2-4 h.

7. The method for preparing a catalytically active electrode for a vanadium cell according to claim 1, characterized in that, In step 2, the carbothermal reduction reaction is performed in a micro-positive pressure inert atmosphere, specifically comprising: first vacuumizing the heat treatment device to below -0.08 MPa, then introducing an inert gas and maintaining the pressure in the furnace at 0.01-0.05 MPa; wherein the inert gas is one of nitrogen, argon, helium and carbon dioxide, and the inert gas is continuously introduced to maintain the micro-positive pressure during the heat preservation stage.

8. The process for the preparation of catalytically active electrodes for vanadium cells according to any one of claims 1 to 7, characterized in that, In step 2, a plurality of graphite felt electrodes are stacked to perform the carbothermal reduction reaction; and / or the thickness of the graphite felt electrode is 1-5 mm and the number of stacked electrodes is 10-50.

9. The catalytically active electrode obtained by the preparation method of the catalytically active electrode for a vanadium battery according to any one of claims 1-8.

10. The catalytically active electrode obtained by the preparation method of the catalytically active electrode for a vanadium battery according to any one of claims 1-8, and / or the use of the catalytically active electrode according to claim 9 in a full vanadium liquid flow battery.

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