Composite catalyst and preparation method thereof, modified electrolyte and flow battery

Abstract

The invention provides a composite catalyst and a preparation method thereof, a modified electrolyte and a flow battery. The composite catalyst comprises a carbon core body and a titanium carbonitride coating layer coating the surface of the carbon core body, wherein the surface of the carbon core body is bonded with a hydrophilic functional group, and the carbon core body is in a nano-particle shape. The composite catalyst prepared by adopting the method has high uniformity, stability and dispersity, catalytic activity sites are remarkably increased, high catalytic activity and good catalytic performance are shown, and the preparation method is simple, low in preparation cost and suitable for large-scale production and has industrial application prospects.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a composite catalyst and a preparation method thereof, a modified electrolyte and a flow battery. Background Art

[0002] In recent years, with the extensive use of traditional fossil energy leading to many problems such as climate warming and environmental pollution, based on the proposal of the "carbon peak and carbon neutrality" goals, renewable energy represented by wind and solar energy has been vigorously developed. However, renewable energy is volatile and intermittent, which often causes a greater impact on the power grid, thus limiting its large-scale application. The high-power, high-capacity, and low-cost energy storage technology that goes with it has become a key technology for promoting energy structure adjustment and popularizing the development of renewable energy. As a new generation of energy storage technology, flow batteries have broad development prospects because of their advantages of good scalability, good safety, and long life. Among them, all-vanadium flow batteries only use vanadium (the negative electrode is V 2+ With V 3+ , the positive side is VO 2+ and VO2 + ) As an energy storage medium, there is no problem of cross-contamination between multiple metal ions. It is the most widely studied flow battery and is also the one closest to commercialization.

[0003] Currently, the biggest challenge facing the large-scale commercialization of flow batteries is their high cost. Their unit construction cost is approximately two to three times that of lithium-ion batteries, with the battery stack accounting for over 60% of the cost. Therefore, effectively reducing the cost of the battery stack is a key approach to accelerating the commercialization of flow batteries. Improving the power density of the battery stack—that is, maintaining the same power requirement—can effectively reduce the stack size and the number of membranes, electrodes, and ion exchange membranes required, thereby lowering the manufacturing cost. However, the key to improving power density lies in developing high-performance electrodes. All polarization losses in flow batteries, including activation polarization, ohmic polarization, and concentration polarization, are closely related to the electrode structure and surface properties. Traditional flow battery electrodes are primarily based on commercially available materials such as graphite felt, carbon felt, and carbon paper. However, these materials have low specific surface areas and poor catalytic activity. To address this, numerous methods have been proposed to enhance the catalytic activity of electrodes, including heat treatment, surface etching, electroplating, and catalyst growth. However, most of these methods are cumbersome and complex. For example, heat treatment requires a high-temperature muffle furnace, surface etching requires an etchant and a high-temperature atmosphere furnace, catalyst growth requires a high-temperature atmosphere and high-temperature cracking gas, and when treating large areas of electrodes in a high-temperature furnace, the size of the furnace limits the need for repeated bending and curling of the porous electrodes, making it difficult to ensure uniform heating of the electrodes and the uniformity of the catalyst and etched pores. Therefore, most traditional modified flow battery preparation methods are difficult to commercialize on a large scale.

[0004] In summary, facing the technical problems of high preparation cost, complicated preparation steps, or poor catalytic activity in the existing flow battery technology, there is an urgent need to provide a composite catalyst and its preparation method to improve the above problems in the flow battery. Summary of the Invention

[0005] The main purpose of the present invention is to provide a composite catalyst and its preparation method, a modified electrolyte and a liquid flow battery, so as to solve the technical problems of liquid flow batteries in the prior art, such as high preparation cost, complicated preparation steps or poor catalytic activity.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a composite catalyst is provided, comprising: a carbon core and a titanium carbonitride coating layer coated on the surface of the carbon core; wherein the surface of the carbon core is bonded with hydrophilic functional groups, and the carbon core is in the form of nanoparticles.

[0007] Furthermore, in the composite catalyst, the hydrophilic functional groups bonded to the surface of the carbon core are carboxyl and / or sulfonic acid functional groups; and in terms of weight percentage, the weight ratio of the carbon core to the titanium carbonitride coating is preferably (0.1-0.2):1.

[0008] Furthermore, the average particle size of the carbon core is 30 to 70 nm.

[0009] Furthermore, the thickness of the titanium carbonitride coating layer is 2 to 10 nm.

[0010] To achieve the above object, according to one aspect of the present invention, a method for preparing a composite catalyst is provided, which comprises: providing a carbon core; and coating a titanium carbonitride coating layer on the outer surface of a carbon carrier to obtain a composite catalyst.

[0011] Furthermore, the preparation method includes: step S1, taking nano-carbon powder containing carboxyl groups and sulfonic acid groups, dispersing it in a titanium tetrachloride dilution solution, and then drying it to coat the outer surface of the nano-carbon powder containing carboxyl groups and sulfonic acid groups with a titanium oxide coating layer to obtain a carbon core body; step S2, taking the carbon core body and performing a carbon thermal reaction in a tubular furnace, and then performing a nitriding reaction in an ammonia atmosphere to coat the outer surface of the carbon core body with a titanium carbonitride coating layer to obtain a composite catalyst.

[0012] Furthermore, in step S1, the dispersion treatment time is 30 to 60 minutes, and the stirring speed is 100 to 500 rpm.

[0013] Furthermore, in step S1, the titanium tetrachloride dilution solution comprises: taking a 0.2 mol / L titanium tetrachloride solution and mixing concentrated hydrochloric acid in a volume ratio of 1.1:48.9 to obtain a titanium tetrachloride dilution solution.

[0014] Furthermore, in step S1, the drying process after the dispersion process needs to be repeated 3 to 10 times until the weight of the titanium oxide coating layer on the outer surface of the nano-carbon powder accounts for 10 to 20 wt% of the weight of the nano-carbon powder containing carboxyl groups and sulfonic acid groups.

[0015] Furthermore, in step S1, the drying process is performed in an air atmosphere, and the process time is 0.5 to 1 hour.

[0016] Furthermore, in step S2, the reaction temperature of the carbothermal reaction is gradually increased from room temperature to a carbothermal reaction temperature of 1200-1300°C, the reaction time is 0.5-1h, and the heating rate is 5°C / min.

[0017] Furthermore, in step S2, the carbothermal reaction is carried out under an inert atmosphere, and the inert atmosphere is selected from one or more of nitrogen, argon or helium.

[0018] Furthermore, the reaction temperature of the nitridation reaction is cooled from the carbon thermal reaction temperature to the reaction temperature of 750-850°C, the reaction time is 1-2h, and the cooling rate is 2°C / min; preferably, after the nitridation reaction, the reaction material needs to be gradually cooled to room temperature under a nitrogen atmosphere.

[0019] According to another aspect of the present invention, a modified electrolyte is provided, comprising a composite catalyst and a vanadium ion-containing electrolyte. The composite catalyst is the composite catalyst described above, or is obtained by the preparation method of the composite catalyst described above.

[0020] Furthermore, the modified electrolyte also includes a surfactant.

[0021] Furthermore, the surfactant is acetylene glycol and ethanol; preferably, the volume ratio of acetylene glycol to ethanol is 1:1, and the total volume of acetylene glycol and ethanol accounts for 0.1 to 0.5% of the volume of the modified electrolyte.

[0022] Furthermore, in the modified electrolyte, the ratio of the weight of the composite catalyst to the area of ​​the electrode is 2 to 3 mg / cm 2 .

[0023] Furthermore, the preparation method of the modified electrolyte includes: taking the composite catalyst, acetylene glycol, ethanol and vanadium ion-containing electrolyte and performing ultrasonic treatment to obtain the modified electrolyte.

[0024] Furthermore, the ultrasonic frequency of the ultrasonic treatment is 20 to 100 kHz, and the ultrasonic time is 0.5 to 4 hours.

[0025] According to another aspect of the present invention, a flow battery is provided, comprising a modified electrolyte, wherein the modified electrolyte is the modified electrolyte described above.

[0026] The composite catalyst prepared by applying the technical solution of the present invention has high uniformity, stability and dispersibility, and the catalytic active sites are significantly increased, showing high catalytic activity and good catalytic performance. The preparation method is simple, saves preparation costs, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the description, serve to explain the principles of the present application. In the drawings:

[0028] Figure 1 The cyclic voltammetry test curves of the products prepared according to Example 1 and Comparative Example 1 of the present invention are shown;

[0029] Figure 2 The color diagram of the catalyst and intermediates prepared according to Example 1 of the present invention is shown;

[0030] Figure 3 shows the XRD pattern of the catalyst prepared according to Example 1 of the present invention;

[0031] Figure 4The figure shows a SEM image of the catalyst prepared according to Example 1 of the present invention on the electrode surface (magnification 10000 times);

[0032] Figure 5 Shown are cyclic voltammetry test curves of the catalysts prepared according to Examples 1 and 2 of the present invention;

[0033] Figure 6 The voltage efficiency diagram of the electrolyte prepared according to Example 1 of the present invention and Comparative Example 1 is shown;

[0034] Figure 7 The voltage / energy efficiency diagram of the electrolyte prepared according to Example 1 and Comparative Example 1 of the present invention is shown;

[0035] Figure 8 Shown are charge and discharge curves of the electrolytes prepared according to Example 1 and Comparative Example 1 of the present invention;

[0036] Figure 9 A graph showing the cyclic stability test of the catalyst prepared according to Example 1 of the present invention is shown;

[0037] Figure 10 shows the XRD pattern of the catalyst prepared according to Example 3 of the present invention;

[0038] Figure 11 shows the XRD pattern of the catalyst prepared according to Example 4 of the present invention;

[0039] Figure 12 The SEM image (magnification 5000 times) showing that the catalyst prepared according to Example 5 of the present invention is not adsorbed on the electrode surface;

[0040] Figure 13 shows a SEM image of the catalyst prepared according to Example 5 of the present invention on the electrode surface (magnification 10000 times); and

[0041] Figure 14 The figure shows a SEM image (magnification 5000 times) of the catalyst prepared according to Example 6 of the present invention on the electrode surface. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0043] As described in the background of the present invention, existing flow batteries suffer from technical issues such as high production costs, complex preparation steps, or poor catalytic activity. Based on these issues, the present invention provides a composite catalyst comprising: a carbon core and a titanium carbonitride coating coated on the surface of the carbon core; the carbon core has hydrophilic functional groups bonded to its surface and is in the form of nanoparticles.

[0044] Based on the fact that traditional liquid flow battery catalyst materials use graphite felt, carbon felt, and carbon paper, the specific surface area of ​​such materials is low, resulting in low catalytic activity, and the adhesive used in traditional catalyst materials, which mainly uses perfluorosulfonic acid type polymer solution (Nafion solution) or polytetrafluoroethylene (PTFE), such materials themselves are not conductive, and are very easy to cover the catalyst during the bonding process, resulting in the active sites of some catalysts being unable to be exposed, making their catalytic performance poor. Based on this, the present invention provides a composite catalyst, which includes a carbon core and a titanium carbonitride coating coated on the surface of the carbon core. The titanium carbonitride coating can greatly improve the catalytic performance of the catalyst. Mainly based on the fact that although titanium carbide has higher antioxidant properties than titanium nitride, it is suitable as a catalyst on the negative electrode side of the liquid flow battery. However, the dispersibility of titanium carbide in solution is weaker than that of titanium nitride, and it is easy to deposit in the solution. Therefore, the present invention combines the advantages of the above two and adopts a titanium carbonitride coating, which can make the dispersion of the catalyst in the battery electrolyte more uniform and stable, and can also avoid the risk of oxidation of the solution caused by contact with air and water. Secondly, since the carbon core itself has very good dispersibility, after the titanium carbonitride coating layer is coated on its surface, on the one hand, the specific surface area of ​​the catalyst can be significantly increased, so that the titanium carbonitride in the coating layer is better exposed as an active site, thereby improving the catalytic activity; on the other hand, it can further increase the electronic conductivity between the titanium carbonitride and the porous electrode, thereby improving the electron transfer rate and enhancing the catalytic performance. In particular, the carbon core surface of the present invention is bonded with hydrophilic functional groups, for example, the structural formula of the hydrophilic functional groups can be: -CHO (aldehyde group), -COOH (carboxyl group), -C=O (carbonyl group), -HSO3 (sulfonic acid group), and its morphology is nanoparticles. The carbon core material containing hydrophilic functional groups has excellent adsorption properties. During the catalytic process, when it reaches the interior of the porous electrode, the carbon material can be effectively adsorbed to the surface of the porous electrode. The interaction between the two can produce a strong adhesion effect, thereby not being easily washed away by the electrolyte. Furthermore, it is recyclable and environmentally friendly. After the used electrode is treated in an organic solvent, the catalyst and porous electrode can be separated and completely recycled. Conventional catalysts, on the other hand, use adhesives to bond the electrode and catalyst, making it impossible to separate and recycle the electrode after the catalyst is discarded.

[0045] In a preferred embodiment, in the composite catalyst, the hydrophilic functional groups bonded to the surface of the carbon core are carboxyl and / or sulfonic acid functional groups, so as to further improve the adsorption performance of the carbon core, increase the contact area between the catalyst and the electrode, and further evenly cover the surface of the electrode, thereby greatly improving the performance of the battery; in terms of weight percentage, the weight ratio of the carbon core to the titanium carbonitride coating is further preferably (0.1 to 0.2):1.

[0046] In order to further improve the dispersion and uniformity of the catalyst, enhance its stability, further increase the specific surface area of ​​the catalyst, and better expose titanium carbonitride as active sites; at the same time, further increase the electronic conductivity between titanium carbonitride and the porous electrode, the average particle size of the carbon core is preferably 30 to 70 nm.

[0047] In a preferred embodiment, the thickness of the titanium carbonitride coating is 2 to 10 nm, so as to further improve the dispersion of the catalyst in the battery electrolyte to be more uniform and stable, and also to avoid the risk of the solution being oxidized due to contact with air and water.

[0048] Another aspect of the present invention provides a method for preparing a composite catalyst, comprising: providing a carbon core; and then coating the outer surface of a carbon support with a titanium carbonitride coating layer to obtain the composite catalyst. Those skilled in the art first obtain a carbon core; and then coating the outer surface of the carbon support with a titanium carbonitride coating layer to obtain the composite catalyst. This method is easy to operate, has a simple process, and operates under mild conditions, showing promise for large-scale production.

[0049] In a preferred embodiment, the preparation method includes: step S1, taking nano-carbon powder containing carboxyl groups and sulfonic acid groups, dispersing it in a titanium tetrachloride dilution solution and then drying it to coat the outer surface of the nano-carbon powder containing carboxyl groups and sulfonic acid groups with a titanium oxide coating layer to obtain a carbon core body; step S2, taking the carbon core body and performing a carbon thermal reaction in a tube furnace, and then performing a nitriding reaction in an ammonia atmosphere to coat the outer surface of the carbon core body with a titanium carbonitride coating layer to obtain a composite catalyst.

[0050] The skilled person in the art first disperses the nano-carbon powder containing carboxyl and sulfonic acid groups in a titanium tetrachloride dilution solution and then air-dries it to coat the outer surface of the nano-carbon powder containing carboxyl and sulfonic acid groups with a titanium oxide coating layer, thereby obtaining a carbon core body; then, the above-mentioned carbon core body is subjected to a carbon thermal reaction in a tubular furnace, and then subjected to a nitridation reaction under an ammonia atmosphere to coat the outer surface of the carbon core body with a titanium carbonitride coating layer to obtain a composite catalyst. The entire preparation process of the composite catalyst of the present invention is carried out at room temperature, and no additional high-temperature operation is required, thereby greatly simplifying the preparation process; and no binder is added in the preparation process, and compared with the traditional preparation method, the preparation process is simple, saving preparation costs. Moreover, the composite catalyst of the present invention has high uniformity, stability and dispersibility, and the catalytic active sites are significantly improved, showing high catalytic activity and good catalytic performance.

[0051] To coat the outer surface of nano-carbon powder containing carboxyl and sulfonic acid groups with a titanium oxide coating, the nano-carbon powder containing carboxyl and sulfonic acid groups is first dispersed in a titanium tetrachloride dilution to coat the nano-carbon powder surface with a titanium oxide intermediate. Furthermore, preferably, in step S1, the titanium tetrachloride dilution comprises mixing a 0.2 mol / L titanium tetrachloride solution with concentrated hydrochloric acid in a volume ratio of 1.1:48.9 to obtain a titanium tetrachloride dilution. The hydrolysis reaction equation involved is: TiCl4 + H2O → TiO2 + HCl.

[0052] In a preferred embodiment, in step S1, the drying process after the dispersion process needs to be repeated 3 to 10 times until the weight of the titanium oxide coating layer on the outer surface of the nano-carbon powder accounts for 10 to 20 wt% of the weight of the nano-carbon powder containing carboxyl and sulfonic acid groups, so that a thin TiO2 coating layer is generated on the surface of the nano-carbon powder by hydrolysis of titanium tetrachloride; it is further preferred that the drying process is carried out in an air atmosphere for a treatment time of 0.5 to 1 h.

[0053] In order to further prepare the titanium carbonitride coating, the TiO2 in step S1 is converted into a mixture of TiC and TiO2, collectively referred to as TiC x O y , where TiO2 comes from the surface hydrolyzed TiO2 coating, and C comes from the part of the carbon powder in contact with the TiO2 coating. The carbon core is then placed in a tubular furnace for a carbon thermal reaction. The temperature of the carbon thermal reaction is gradually increased from room temperature to a carbon thermal reaction temperature of 1200-1300°C, the reaction time is 0.5-1h, and the heating rate is 5°C / min. The equation for the carbon thermal reaction is: TiO2+C→TiC x O y + CO2; preferably, the carbon thermal reaction is carried out under an inert atmosphere, the inert atmosphere being selected from one or more of nitrogen, argon or helium.

[0054] In order to further the nitriding process, the TiO2 that does not participate in the reaction is converted into TiC x N y After the carbon thermal reaction, a nitridation reaction is carried out in an ammonia atmosphere to coat the outer surface of the carbon core with a titanium carbonitride coating. The nitridation reaction equation is: TiC x O y +NH3→TiC x N y +H2O; the reaction temperature of the nitridation reaction is cooled from the carbothermal reaction temperature to the nitridation reaction temperature of 750-850°C, the reaction time is 1-2h, and the cooling rate is 2°C / min; preferably, after the nitridation reaction, the nitridation reaction material is gradually cooled to room temperature under a nitrogen atmosphere.

[0055] Another aspect of the present invention provides a modified electrolyte comprising a composite catalyst and a vanadium ion-containing electrolyte. The composite catalyst is the composite catalyst described above, or is obtained by the method for preparing the composite catalyst described above. The modified electrolyte, containing the composite catalyst, exhibits good catalytic activity toward the vanadium ion-containing electrolyte therein. In particular, the carbon with hydrophilic functional groups exhibits excellent adsorption properties. The synergistic effect of the aforementioned components allows the catalyst to be very evenly adsorbed onto the electrode surface, thereby providing a good catalytic effect on the battery.

[0056] In order to enable the composite catalyst to be better dispersed in the modified electrolyte and at the same time have a good antioxidant effect, it is preferred that the modified electrolyte also includes a surfactant, and it is further preferred that the surfactant is acetylene glycol and ethanol, the volume ratio of acetylene glycol to ethanol is 1:1, and the total volume of acetylene glycol and ethanol accounts for 0.1 to 0.5% of the volume of the modified electrolyte, thereby further enhancing the dispersion uniformity and stability of the composite catalyst in the electrolyte, so that the catalyst maintains a good suspension effect in the electrolyte, thereby providing a possibility for preparing a new electrolyte.

[0057] In order to further optimize the dosage of the composite catalyst so that the catalyst evenly covers the electrode surface without affecting the electrolyte transmission inside the electrode, it is preferred that the ratio of the weight of the composite catalyst to the area of ​​the electrode in the modified electrolyte is 2-3 mg / cm 2 .

[0058] In a preferred embodiment, the preparation method of the modified electrolyte comprises: taking a composite catalyst, acetylene glycol, ethanol and a vanadium ion-containing electrolyte and performing ultrasonic treatment to obtain a modified electrolyte; further preferably, the ultrasonic frequency of the ultrasonic treatment is 20 to 100 kHz, and the ultrasonic time is 0.5 to 4 hours; thereby increasing the proton transfer rate of the electrolyte and improving the catalytic performance.

[0059] Another aspect of the present invention provides a liquid flow battery comprising a modified electrolyte, wherein the modified electrolyte is the modified electrolyte described above. As described above, the liquid flow battery exhibits good electrochemical performance and stability.

[0060] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0061] Example 1

[0062] Nano-carbon powder containing carboxyl and sulfonic acid groups was placed in a 0.2 mol / L dilute titanium tetrachloride solution (the volume ratio of concentrated titanium tetrachloride solution to concentrated hydrochloric acid was 1.1:48.9). The mixture was dispersed and stirred for 30 minutes at 300 rpm, then air-dried for 1 hour. The dispersion-drying-dispersion process was repeated five times until the surface TiO2 weight increased to 20% of the carbon powder weight, resulting in a layer of TiO2 oxide adsorbed on the carbon powder surface. The product was then placed in a tube furnace, continuously purged with nitrogen, and the temperature was raised to 1200°C at a rate of 5°C / min and maintained at this temperature for 1 hour to allow a carbothermal reaction to occur. The temperature was then lowered to 800°C at a rate of 2°C / min. The nitrogen atmosphere was removed, and an ammonia atmosphere was introduced to allow nitridation to occur. The temperature was then maintained for 2 hours. The nitrogen atmosphere was then released, the ammonia atmosphere was removed, and the tube furnace was gradually cooled to room temperature to obtain the composite catalyst.

[0063] The obtained catalyst was directly added to the electrolyte on the negative electrode side of the flow battery, where the amount of catalyst added divided by the area of ​​the electrode was 3 mg / cm 2 , acetylene glycol and ethanol were added to the electrolyte in a volume ratio of 1:1, and their combined volume accounted for 0.1% of the electrolyte volume. Finally, the entire mixed liquid containing the catalyst was ultrasonicated for 2 hours at a frequency of 50 kHz to obtain a modified electrolyte.

[0064] The weight ratio of the carbon core to the titanium carbonitride coating layer in the composite catalyst is 0.2:1, the average particle size of the carbon core is 50 nm, and the thickness of the titanium carbonitride coating layer is 5 nm.

[0065] Example 2

[0066] The only difference from Example 1 is that the weight of the titanium oxide coating layer coated on the outer surface of the nano-carbon powder accounts for 10 wt % of the weight of the nano-carbon powder containing carboxyl groups and sulfonic acid groups.

[0067] Example 3

[0068] The only difference from Example 1 is that the reaction temperature of the carbothermal reaction is 1100°C.

[0069] Example 4

[0070] The only difference from Example 1 is that the reaction temperature of the nitriding reaction is 700°C.

[0071] Example 5

[0072] The only difference from Example 1 is that in the modified electrolyte, the ratio of the weight of the composite catalyst to the area of ​​the electrode is 4 mg / cm.

[0073] Example 6

[0074] The only difference from Example 1 is that in the modified electrolyte, the ratio of the weight of the composite catalyst to the area of ​​the electrode is 1 mg / cm.

[0075] Example 7

[0076] The only difference from Example 1 is that the total volume of the acetylene glycol and the ethanol accounts for 0.5% of the volume of the modified electrolyte.

[0077] Comparative Example 1

[0078] The difference from Example 1 is that the catalyst used is a catalyst of titanium carbonitride coated conventional carbon core, and the conventional carbon core has no bonded hydrophilic functional groups on its surface.

[0079] Performance testing:

[0080] The composite catalyst and modified electrolyte prepared in the above examples and comparative examples were placed in a flow cell at a flow rate of 1 mL / min / cm 2 Start the pump at a speed of 1000 nm and rotate it for 1 hour to allow the composite catalyst to fully adsorb onto the porous electrode surface. After 1 hour, gradually increase the flow rate of the battery to the set flow rate of 4 mL / min / cm 2 , then power on and test.

[0081] 1) Catalytic activity

[0082] The activity of the electrode was verified by a three-electrode method, in which the three electrodes were: a working electrode was a glassy carbon electrode loaded with titanium carbonitride, a reference electrode was a saturated calomel electrode, and a counter electrode was a platinum mesh electrode. The test conditions were -0.7 to 0 V, and the voltage sweep rate was 10 mV / s.

[0083] 2) Voltage efficiency

[0084] The voltage efficiency test is based on the Arbin BT2000 battery performance tester from the United States. The battery tester's discharge energy / charge energy is energy efficiency, discharge capacity / charge capacity is coulombic efficiency, and energy efficiency / coulombic efficiency is voltage efficiency. Voltage efficiency is the average discharge voltage / average charge voltage during the battery discharge process.

[0085] 3) Suspension sedimentation test

[0086] 1 g of the catalyst was ultrasonically treated in 10 mL of aqueous solution, and a dispersion test was performed.

[0087] 4) Antioxidant test

[0088] The catalyst was placed in an aqueous solution into which air was introduced for oxidation resistance testing.

[0089] 5) Electrolyte test

[0090] Take the above electrolyte at 4mL / min / cm 2 The test was started at a flow rate of , and a constant current was loaded. The test equipment was the American Arbin BT2000 battery performance tester.

[0091] 6) Cyclic stability

[0092] The battery prepared by taking the electrolyte was tested at 100mA / cm 2 The efficiency change was tested under the current density of 100 nm.

[0093] The products prepared in the above examples and comparative examples were subjected to the above performance tests, and the test results are shown in the accompanying drawings.

[0094] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0095] Depend on Figure 1 It can be found from the cyclic voltammetry test curves of the products prepared in Example 1 and Comparative Example 1 that, compared with Comparative Example 1, the composite catalyst prepared by the present invention has better catalytic activity for liquid flow batteries than carbon materials and graphite felt materials. In Comparative Example 1, almost no redox peaks were observed on the carbon surface of the product, which shows that its catalytic activity for the redox reaction of vanadium ions is extremely poor. This is mainly based on the fact that the reduction peak is completely covered by the hydrogen evolution current. On the surface of the activated carbon powder coated with titanium carbonitride, a very obvious redox peak can be observed. This proves that the titanium carbonitride-coated carbon material greatly improves the reversibility of the redox reaction. On the other hand, it can also be found that the peak current also increases significantly, proving that the reaction current also increases significantly, which is mainly due to the substantial increase in the reaction area, that is, the reaction active sites.

[0096] Depend on Figure 2It can be found from the color diagram of the catalyst and intermediates prepared in Example 1 that the color of the carbon core is white wrapped in black. The color of TiO2 is white, and the color of carbon powder is black. The color of TiO2 wrapped in carbon powder is white wrapped in black. The temperature of the tubular furnace was raised to 1200°C and kept warm for 1 hour, and a carbon thermal reaction occurred. Most of the TiO2 was converted into TiC. Since the color of TiC is black, the color of the observed catalyst is black. When the temperature was lowered to 800°C and ammonia was introduced, it was found that the remaining TiO2 was successfully converted into the brown-red color of TiN through the nitridation reaction. The color change also proves that the proposed process successfully converts the TiO2-loaded carbon powder nanoparticles into the required titanium carbonitride-coated carbon powder composite catalyst.

[0097] Depend on Figure 3 The XRD pattern of the catalyst prepared in Example 1 and Figure 10 From the XRD pattern of the catalyst prepared in Example 3, it can be found that when the temperature is 1100°C, the product generated by the preparation of the nanocatalyst precursor is still TiO2, and no carbon thermal reaction occurs, because the temperature in the tubular furnace has not yet reached the temperature required for TiO2 and carbon thermal reaction. TiO2 is not successfully converted into TiC. When the temperature is higher than 1300°C, it is found that although TiO2 is successfully converted into TiC. However, the carbon powder base particles are severely corroded. The increase in temperature is conducive to the conversion of TiO2 to titanium carbide. However, too high a temperature will make the reaction too violent, which is not conducive to the stable existence of the carbon base. Taking all factors into consideration, the temperature of the carbon thermal reaction in the tubular furnace of the present invention is preferably 1200-1300°C.

[0098] Depend on Figure 5 The cyclic voltammetry curves of the catalysts prepared in Examples 1 and 2 show that when the ratio of TiO2 to carbon (the weight of the titanium oxide coating on the outer surface of the nano-carbon powder relative to the weight of the nano-carbon powder containing carboxyl and sulfonic acid groups) is 10%, the amount of titanium carbonitride in the catalyst prepared by the subsequent method of nanocatalyst precursor preparation is too low, and the catalytic activity is weak, significantly lower than that of Example 1. However, when the ratio of TiO2 to carbon is 30%, it is found that the tested sample contains almost no carbon. Although the material also has excellent electrocatalytic activity for vanadium ions due to the presence of titanium carbonitride, the resulting material cannot be well dispersed in the solution. Therefore, the ratio of TiO2 to carbon is limited to between 10 and 20% in the present invention.

[0099] Depend on Figure 6The voltage efficiency graphs of the electrolytes prepared in Example 1 and Comparative Example 1 show that the modified electrolyte consistently has a higher voltage efficiency than Comparative Example 1. In a test at 100 mAh / cm², the voltage efficiency of the electrolyte in Comparative Example 1 was only 78%, while the modified electrolyte achieved a high efficiency of 89%, an 11% increase over that of Comparative Example 1. This demonstrates that the modified electrolyte can significantly improve the performance of flow batteries.

[0100] Depend on Figure 7 From the voltage / energy efficiency diagram of the electrolytes prepared in Example 1 and Comparative Example 1, it can be found that the modified electrolyte of the present invention has a lower charging platform and a higher discharging platform, and the charge and discharge capacity is significantly higher than that of Comparative Example 1; the voltage efficiency is significantly higher than the electrolyte in the original Comparative Example 1. Therefore, the modified electrolyte of the present invention can significantly improve the performance of the liquid flow battery.

[0101] Depend on Figure 8 The charge-discharge curves of the electrolytes prepared in Example 1 and Comparative Example 1 show that the addition of the modified electrolyte results in a lower charging plateau and a higher discharging plateau, with charge and discharge capacities significantly higher than those in Comparative Example 1. The voltage efficiency is also significantly higher than that in Comparative Example 1, indicating that the modified electrolyte can significantly improve the performance of flow batteries.

[0102] Depend on Figure 9 From the cycle stability test chart of the catalyst prepared in Example 1, it can be found that the battery prepared by the modified electrolyte was further subjected to a long cycle test of 100 mAh / cm2, and it was found that during the long cycle process, it was still able to maintain very good cycle performance.

[0103] From the test results of Example 1 and Example 4, it can be found that when the nitriding temperature is 700°C, the XRD test shows that Figure 11 It was found that the composite catalyst precursor powder still primarily contained TiO2, indicating that this temperature did not yet reach the required nitridation reaction temperature. At temperatures between 750°C and 950°C, TiO2 was found to gradually transform into TiN under the action of ammonia. At temperatures above 950°C, ammonia also exhibited strong corrosive and igniting properties, resulting in an overly intense nitridation reaction and corrosion of the substrate. Therefore, the preferred temperature for the nitridation reaction in the tube furnace of the present invention is 750°C to 950°C.

[0104] From the test results of Example 1 and Example 5, it can be found that when the catalyst loading is increased to 4 mg / cm2, the flow rate of the battery is significantly reduced. After disassembling the battery, it was found that when the catalyst loading is too high, the pores in the graphite felt electrode are seriously blocked. Scanning electron microscopy shows that the smooth graphite felt surface is Figure 12As shown, it was further found that the graphite felt surface that blocked the composite catalyst had obvious agglomeration on the electrode surface as shown in Figure 13. Figure 14 From the SEM image of the catalyst prepared in Example 6 on the electrode surface, it can be found that when the catalyst loading is reduced to 1 mg / cm2, the battery performance improvement is not as good as 3 mg / cm2. This is due to the insufficient amount of catalyst. From the SEM image, it can be seen that although the surface of the graphite felt is very evenly covered with a layer, it is only a very thin layer. Therefore, the catalyst loading of this type of electrode is still low and there is room for improvement. However, when the loading of the modified electrolyte is 3 mg / cm2, it can be seen that the battery performance is the best. At the same time, from Figure 4 From the SEM image, it can be seen that the surface of the graphite felt is very evenly covered with a layer. Therefore, in the battery flow state, the data analysis of the battery's energy efficiency and voltage efficiency shows that the amount of the composite catalyst added to the modified electrolyte in the present invention is preferably 1 to 3 mg / cm2 compared to the electrode weight, and the performance is better.

[0105] The test results of Examples 1 and 7 show that when the volume of the surfactant accounts for 0.5% of the electrolyte volume, and when the volume fraction of the dispersant is too high, the coulombic efficiency decreases significantly. This is because polymers such as ethanol and acetylenic diols cause the ion exchange membrane to shrink significantly, causing structural damage and increasing the pore size. Therefore, this example shows that the volume of the dispersant should not exceed 0.5% of the electrolyte volume.

[0106] Although this specification includes many specific implementation details, these should not be interpreted as limiting the scope of any invention or the scope of protection claimed, but are mainly used to describe the features of specific embodiments of specific inventions. Certain features described in multiple embodiments within this specification may also be implemented in combination in a single embodiment. On the other hand, the various features described in a single embodiment may also be implemented separately in multiple embodiments or in any suitable sub-combination. In addition, although features may work in certain combinations as described above and even initially claimed as such, one or more features from the claimed combination may be removed from the combination in some cases, and the claimed combination may point to a sub-combination or a variation of the sub-combination.

[0107] Similarly, although operations are depicted in a particular order in the accompanying drawings, this should not be understood as requiring that these operations be performed in the particular order shown or performed sequentially, or that all illustrated operations be performed to achieve the desired results. In some cases, multitasking and parallel processing may be advantageous. In addition, the separation of various system modules and components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product, or packaged into multiple software products.

[0108] Thus, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the particular order shown or sequential sequence to achieve the desired results. In some implementations, multitasking and parallel processing may be advantageous.

[0109] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0110] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A composite catalyst, characterized in that The composite catalyst comprises: a carbon core and a titanium carbonitride coating layer coated on the surface of the carbon core; wherein the surface of the carbon core is bonded with a hydrophilic functional group, and the carbon core is in the form of nanoparticles.

2. The composite catalyst according to claim 1, characterized in that In the composite catalyst, the hydrophilic functional groups bonded to the surface of the carbon core are carboxyl and / or sulfonic acid functional groups; and / or In terms of weight percentage, the weight ratio of the carbon core to the titanium carbonitride coating layer is (0.1-0.2):

1.

3. The composite catalyst according to claim 1 or 2, characterized in that The average particle size of the carbon core is 30 to 70 nm.

4. The composite catalyst according to any one of claims 1 to 3, characterized in that The thickness of the titanium carbonitride coating layer is 2 to 10 nm.

5. A method for preparing a composite catalyst according to any one of claims 1 to 4, characterized in that: The preparation method comprises: Providing carbon nuclei; A titanium carbonitride coating layer is coated on the outer surface of the carbon support to obtain the composite catalyst.

6. The method for preparing the composite catalyst according to claim 5, wherein The preparation method comprises: Step S1, dispersing nano-carbon powder containing carboxyl and sulfonic acid groups in a titanium tetrachloride dilution solution and then drying the dispersed nano-carbon powder to coat the outer surface of the nano-carbon powder containing carboxyl and sulfonic acid groups with a titanium oxide coating layer to obtain the carbon core; Step S2: taking the carbon core body and performing a carbon thermal reaction in a tube furnace, and then performing a nitridation reaction in an ammonia atmosphere to coat a titanium carbonitride coating layer on the outer surface of the carbon core body to obtain the composite catalyst.

7. The method for preparing the composite catalyst according to claim 6, wherein In the step S1, the dispersion treatment time is 30 to 60 minutes, and the stirring speed is 100 to 500 rpm.

8. The method for preparing the composite catalyst according to claim 6, wherein In the step S1, the titanium tetrachloride dilution solution is prepared by mixing 0.2 mol / L of the titanium tetrachloride solution with concentrated hydrochloric acid in a volume ratio of 1.1:48.9 to obtain the titanium tetrachloride dilution solution.

9. The method for preparing the composite catalyst according to claim 6, wherein: In step S1, the drying process after the dispersion process needs to be repeated 3 to 10 times until the weight of the titanium oxide coating layer on the outer surface of the nano-carbon powder accounts for 10 to 20 wt% of the weight of the nano-carbon powder containing carboxyl groups and sulfonic acid groups.

10. The method for preparing the composite catalyst according to claim 6, wherein: In the step S1, the drying process is performed in an air atmosphere for a process time of 0.5 to 1 hour.

11. The method for preparing the composite catalyst according to claim 6, wherein: In step S2, the reaction temperature of the carbothermal reaction is gradually increased from room temperature to the carbothermal reaction temperature of 1200-1300°C, the reaction time is 0.5-1h, and the heating rate is 5°C / min.

12. The method for preparing the composite catalyst according to claim 6, wherein: In step S2, the carbothermal reaction is carried out under an inert atmosphere, and the inert atmosphere is selected from one or more of nitrogen, argon or helium.

13. The method for preparing the composite catalyst according to claim 6, characterized in that: The reaction temperature of the nitridation reaction is cooled from the carbothermal reaction temperature to the nitridation reaction temperature of 750-850° C., the reaction time is 1-2 hours, and the cooling rate is 2° C. / min; and / or After the nitridation reaction, the material after the nitridation reaction needs to be gradually cooled to room temperature under a nitrogen atmosphere.

14. A modified electrolyte comprising a composite catalyst and a vanadium ion-containing electrolyte, characterized in that: The composite catalyst is the composite catalyst according to any one of claims 1 to 4, or is obtained by the preparation method of the composite catalyst according to any one of claims 5 to 13.

15. The modified electrolyte according to claim 14, characterized in that The modified electrolyte also includes a surfactant.

16. The modified electrolyte according to claim 14, characterized in that The surfactant is acetylenediol and ethanol; and / or The volume ratio of the acetylene glycol to the ethanol is 1:1, and the total volume of the acetylene glycol and the ethanol accounts for 0.1 to 0.5% of the volume of the modified electrolyte.

17. The modified electrolyte according to claim 14, characterized in that In the modified electrolyte, the ratio of the weight of the composite catalyst to the area of ​​the electrode is 2 to 3 mg / cm 2 .

18. The modified electrolyte according to claim 14, characterized in that The preparation method of the modified electrolyte comprises: taking a composite catalyst, acetylene glycol, ethanol and a vanadium ion-containing electrolyte and performing ultrasonic treatment to obtain the modified electrolyte.

19. The modified electrolyte according to claim 18, characterized in that The ultrasonic treatment has an ultrasonic frequency of 20 to 100 kHz and an ultrasonic time of 0.5 to 4 hours.

20. A flow battery comprising a modified electrolyte, characterized in that: The modified electrolyte is the modified electrolyte according to any one of claims 14 to 19.

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