Preparation method of hollow carbon sphere embedded with titanium dioxide, electrode catalytic material and application thereof

Abstract

The present invention discloses a preparation method, electrode catalytic material and application of hollow carbon spheres embedded with titanium dioxide, belonging to the technical field of all-vanadium liquid flow batteries. The preparation method uses silicon dioxide as a template, phenolic resin as a carbon source to uniformly coat silicon dioxide, and after high-temperature carbonization under an inert gas atmosphere, hollow carbon spheres are obtained by chemical etching; a hydrolyzable titanium source is introduced into the hollow carbon spheres, the titanium on the surface of the hollow carbon spheres is washed and removed, and the titanium inside the hollow carbon spheres is washed and hydrolyzed, and after repeated washing and drying, hollow carbon spheres embedded with amorphous titanium dioxide are obtained; in an inert gas atmosphere, the hollow carbon spheres embedded with amorphous titanium dioxide are subjected to high-temperature treatment, and the temperature is controlled to obtain hollow carbon spheres embedded with titanium dioxide of different crystal forms. It is used as an electrode catalytic material in mixed acid system all-vanadium liquid flow batteries to achieve Cl in the positive electrode electrolyte. ‑ / Cl2 can be reversibly oxidized and reduced, and chlorine can be adsorbed to prevent it from volatilizing into the air, thereby improving the safety and stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-vanadium redox flow batteries, and in particular relates to a preparation method of hollow carbon spheres embedded with titanium dioxide, an electrode catalytic material and applications thereof. Background Art

[0002] As environmental awareness grows, the full development and utilization of green energy sources such as wind and solar energy has become a focus of public attention. However, these energy sources are susceptible to the influence of the natural environment and geographical conditions, are unevenly distributed in time and space, and are difficult to accurately predict. Direct integration into the power grid poses significant risks to the safe and stable operation of the grid. The evolving energy storage system is the key to unlocking the vast energy treasure trove of renewable energy. All-vanadium liquid flow batteries, with their unique advantages such as safety, low explosion resistance, extremely long cycle life, environmental friendliness, flexible assembly, and fast response, have emerged as a prominent energy storage battery and are steadily increasing their share of the large-scale energy storage market.

[0003] In recent years, all-vanadium liquid flow battery energy storage media using hydrochloric acid and sulfuric acid as supporting electrolytes have gradually replaced the pure sulfuric acid system. This system has the advantages of high power density and good energy efficiency. However, the concentration of hydrochloric acid in the mixed acid system is usually higher than 5 mol / L. The introduction of high-concentration hydrochloric acid makes the system face a huge risk of chlorine gas precipitation. Chlorine gas is highly toxic and has strong corrosive properties to battery devices. More importantly, when chlorine gas reaches a certain concentration, it may cause an explosion, which is a fatal flaw for large-scale energy storage. There have been several reports of explosions in commercial mixed-acid system all-vanadium liquid flow batteries.

[0004] However, there is still no reliable and effective solution to the problem of chlorine evolution at the positive electrode of mixed acid system all-vanadium redox flow batteries. Summary of the Invention

[0005] In view of the lack of effective solutions to the problem of chlorine gas precipitation in the positive electrode of mixed acid system all-vanadium redox flow batteries in the current existing technology, the present invention aims to provide a method for preparing hollow carbon spheres embedded with titanium dioxide. Hollow carbon spheres embedded with titanium dioxide of different crystal forms are prepared and can be used as electrode catalyst materials for mixed acid system all-vanadium redox flow batteries. Titanium dioxide is used to adsorb the precipitated chlorine gas and store it in the hollow carbon spheres, preventing it from diffusing into the air; at the same time, the Cl - The reversibility of the Cl2 redox reaction avoids the accumulation of chlorine, thereby greatly reducing the harm of chlorine.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a preparation method of hollow carbon spheres embedded with titanium dioxide. The method comprises the following steps: using silicon dioxide as a template and phenolic resin as a carbon source to uniformly coat the silicon dioxide; performing high-temperature carbonization under an inert gas atmosphere; and obtaining hollow carbon spheres by chemical etching; introducing a hydrolyzable titanium source into the hollow carbon spheres, washing and removing titanium on the surface of the hollow carbon spheres, and then washing and hydrolyzing the titanium inside the hollow carbon spheres. After repeated washing and drying, hollow carbon spheres embedded with amorphous titanium dioxide are obtained; and performing high-temperature treatment on the hollow carbon spheres embedded with amorphous titanium dioxide under an inert gas atmosphere, and regulating the temperature to obtain hollow carbon spheres embedded with titanium dioxide of different crystal forms.

[0008] Furthermore, the method of using silica as a template and phenolic resin as a carbon source to uniformly coat silica is to synthesize silica through the hydrolysis and condensation reaction of tetraethyl orthosilicate, gradually add formaldehyde and resorcinol under stirring, continue stirring, transfer the reaction mixture to a hydrothermal reactor for hydrothermal treatment, and collect the mixture after filtration and drying.

[0009] Furthermore, the temperature of high-temperature carbonization is 700° C.-900° C., and the time is 1 h-4 h.

[0010] Furthermore, the chemical etching method uses analytically pure hydrofluoric acid with a mass concentration of ≥40%.

[0011] Furthermore, a hydrolyzable titanium source, titanium sulfate, is introduced into the hollow carbon spheres and continuously stirred until uniform.

[0012] Furthermore, the mass ratio of the hollow carbon spheres to titanium sulfate is 1:(1.5-1.7).

[0013] Furthermore, the washing to remove titanium from the surface of the hollow carbon spheres uses anhydrous ethanol, and the mass volume ratio of the hollow carbon spheres to the anhydrous ethanol used for washing to remove titanium is 1:(500-700) g / mL;

[0014] Distilled water or deionized water is used to wash and hydrolyze the titanium inside the hollow carbon spheres, and the mass volume ratio of the hollow carbon spheres to the water used for washing and hydrolysis is 1:(400-800) g / mL.

[0015] Furthermore, the temperature of the high-temperature treatment of the hollow carbon spheres embedded with amorphous titanium dioxide is 500° C.-900° C., and the time is 1 h-4 h.

[0016] The present invention also provides an electrode catalytic material, wherein the hollow carbon spheres embedded with titanium dioxide of different crystal forms prepared by the method for preparing hollow carbon spheres embedded with titanium dioxide are used as the electrode catalytic material.

[0017] The present invention also provides an application of the electrode catalytic material, wherein the hollow carbon spheres embedded with titanium dioxide of different crystal forms are sprayed on carbon felt as electrode catalytic materials and used as positive and negative electrodes of mixed acid system all-vanadium redox flow batteries.

[0018] Advantages and effects of the present invention:

[0019] The hollow carbon spheres with different crystal forms of embedded titanium dioxide prepared by the present invention are used as electrode catalyst materials in mixed acid system all-vanadium redox flow batteries, which can achieve the conversion of Cl in the positive electrode electrolyte of the battery. - / Cl2 can be reversibly oxidized and reduced, while adsorbing chlorine to prevent it from volatilizing into the air, greatly reducing the risk of highly toxic and explosive chlorine gas precipitation and improving battery safety and stability;

[0020] The electrode catalytic material of the present invention can increase the reaction activity of vanadium ions, an active substance, in the positive and negative electrode electrolytes of an all-vanadium redox flow battery, thereby improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a scanning electron microscope (SEM) image of the hollow carbon spheres prepared in Example 1;

[0022] Figure 2 This is a transmission electron microscope (TEM) image of the hollow carbon spheres prepared in Example 1;

[0023] Figure 3 This is a scanning electron microscope (SEM) image of the hollow carbon sphere embedded with amorphous titanium dioxide prepared in Example 1;

[0024] Figure 4 This is a transmission electron microscope (TEM) image of the hollow carbon sphere embedded with amorphous titanium dioxide prepared in Example 1;

[0025] Figure 5 This is the X-ray diffraction (XRD) pattern of the hollow carbon spheres embedded with amorphous titanium dioxide prepared in Example 1;

[0026] Figure 6 This is a scanning electron microscope (SEM) image of the hollow carbon spheres with embedded anatase / rutile crystal-type titanium dioxide prepared in Example 1;

[0027] Figure 7 This is a transmission electron microscope (TEM) image of the hollow carbon spheres with embedded anatase / rutile crystal-type titanium dioxide prepared in Example 1;

[0028] Figure 8 This is the X-ray diffraction (XRD) pattern of the hollow carbon spheres with embedded anatase / rutile crystal type titanium dioxide prepared in Example 1;

[0029] Figure 9Cyclic voltammetry (CV) curves of the hollow carbon spheres and hollow carbon spheres embedded with anatase / rutile titanium dioxide prepared in Example 1 in a blank mixed acid system containing only sulfuric acid and hydrochloric acid, wherein: (a) is hollow carbon, and (b) is hollow carbon spheres embedded with anatase / rutile titanium dioxide;

[0030] Figure 10 The positive electrode cyclic voltammetry (CV) curves of the hollow carbon spheres and the hollow carbon spheres embedded with anatase / rutile crystal-type titanium dioxide prepared in Example 1 are shown;

[0031] Figure 11 The negative electrode cyclic voltammetry (CV) curves of the hollow carbon spheres and the hollow carbon spheres embedded with anatase / rutile crystal-type titanium dioxide prepared in Example 1 are shown;

[0032] Figure 12 Figure 1 shows the battery performance test of hollow carbon spheres, hollow carbon spheres embedded with amorphous titanium dioxide, and hollow carbon spheres embedded with anatase / rutile crystalline titanium dioxide prepared in Example 1 as electrode catalyst materials in a mixed acid all-vanadium redox flow battery system, wherein: (a) is a blank control group, (b) is a hollow carbon sphere, (c) is a hollow carbon sphere embedded with amorphous titanium dioxide, and (d) is a hollow carbon sphere embedded with anatase / rutile crystalline titanium dioxide;

[0033] Figure 13 This is a scanning electron microscope (SEM) image of the hollow carbon spheres embedded with anatase crystal-type titanium dioxide prepared in Example 2;

[0034] Figure 14 This is a transmission electron microscope (TEM) image of the hollow carbon spheres embedded with anatase crystal-type titanium dioxide prepared in Example 2;

[0035] Figure 15 This is the X-ray diffraction (XRD) pattern of the hollow carbon spheres with embedded anatase crystal form titanium dioxide prepared in Example 2;

[0036] Figure 16 Cyclic voltammetry (CV) curves of the hollow carbon spheres and hollow carbon spheres embedded with anatase crystalline titanium dioxide prepared in Example 2 in a blank mixed acid system containing only sulfuric acid and hydrochloric acid;

[0037] Figure 17 The positive electrode cyclic voltammetry (CV) curves of the hollow carbon spheres and the hollow carbon spheres embedded with anatase crystalline titanium dioxide prepared in Example 2;

[0038] Figure 18 The negative electrode cyclic voltammetry (CV) curves of the hollow carbon spheres and hollow carbon spheres embedded with anatase crystalline titanium dioxide prepared in Example 2;

[0039] Figure 19This is a battery performance test chart of the hollow carbon spheres embedded with anatase crystal titanium dioxide prepared in Example 2 as electrode catalyst materials in a mixed acid all-vanadium redox flow battery system;

[0040] Figure 20 This is a scanning electron microscope (SEM) image of the hollow carbon spheres embedded with rutile crystal-type titanium dioxide prepared in Example 3;

[0041] Figure 21 This is a transmission electron microscope (TEM) image of the hollow carbon spheres embedded with rutile crystal-type titanium dioxide prepared in Example 3;

[0042] Figure 22 This is the X-ray diffraction (XRD) pattern of the hollow carbon spheres with embedded rutile crystal-type titanium dioxide prepared in Example 3;

[0043] Figure 23 Cyclic voltammetry (CV) curves of the hollow carbon spheres and hollow carbon spheres embedded with rutile crystalline titanium dioxide prepared in Example 3 in a blank mixed acid system containing only sulfuric acid and hydrochloric acid;

[0044] Figure 24 The positive electrode cyclic voltammetry (CV) curves of the hollow carbon spheres and hollow carbon spheres embedded with rutile crystalline titanium dioxide prepared in Example 3;

[0045] Figure 25 The negative electrode cyclic voltammetry (CV) curves of the hollow carbon spheres and hollow carbon spheres embedded with rutile crystalline titanium dioxide prepared in Example 3;

[0046] Figure 26 This is a battery performance test chart of the hollow carbon spheres embedded with rutile crystal titanium dioxide prepared in Example 3 as electrode catalyst materials in a mixed acid all-vanadium redox flow battery system. DETAILED DESCRIPTION

[0047] The present invention is described in detail below with reference to the embodiments.

[0048] Example 1

[0049] The present invention provides a method for preparing hollow carbon spheres embedded with titanium dioxide, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours to uniformly coat the silicon dioxide with the phenolic resin; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900°C for 2 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silicon dioxide template; then washing the product with ethanol and distilled water several times, and drying the product. Figure 1 and 2 As shown, hollow carbon spheres are obtained;

[0050] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 h. Then, 30 mg of the prepared hollow carbon spheres were added to the solution and stirred continuously at room temperature for 12 h. The hollow carbon spheres were then washed with 15 mL of anhydrous ethanol to remove the titanium sulfate on the surface of the hollow carbon spheres. The hollow carbon spheres were then washed with 12 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was washed repeatedly and dried in a vacuum oven at 60 ° C for 6 h to obtain hollow carbon spheres embedded with amorphous titanium dioxide, such as Figure 3 and 4 As shown, the morphology of hollow carbon spheres can be seen, such as Figure 5 As shown in FIG, the XRD diffraction pattern does not show the characteristic peaks of the fixed crystal form of titanium dioxide; the prepared hollow carbon spheres with embedded amorphous titanium dioxide are placed in an alumina crucible, and then heated in a tube furnace at a heating rate of 5°C / min to 700°C under an argon atmosphere for 3 h until the hollow carbon spheres with embedded anatase / rutile titanium dioxide are formed. Figure 6 and 7 As shown, the morphology of the hollow carbon spheres can be seen, such as Figure 8 As shown, the XRD diffraction pattern shows characteristic peaks of two titanium dioxide crystal forms, one is anatase PDF #21-1272, and the other is rutile PDF #21-1276.

[0051] An electrode catalytic material of the present invention is prepared using hollow carbon spheres of titanium dioxide embedded with anatase / rutile crystals prepared in Example 1.

[0052] An electrode catalytic material of Example 1, containing hollow carbon spheres of anatase / rutile titanium dioxide, was applied to a mixed acid system all-vanadium redox flow battery.

[0053] Performance testing:

[0054] (1) Cl - Reversibility analysis of Cl2 redox reaction:

[0055] Cyclic voltammetry test conditions:

[0056] A three-electrode system was used: the working electrode was a glassy carbon electrode (GCE, 3 mm in diameter), the counter electrode was a graphite rod, and the reference electrode was a saturated calomel electrode (SCE, 0.24 V vs. SHE). The electrode catalytic material was coated on the working electrode, and the working electrode, counter electrode, and reference electrode were respectively installed in a three-port electrolytic cell. Relevant electrochemical tests were carried out in a blank mixed acid system containing only sulfuric acid and hydrochloric acid.

[0057] like Figure 9 As shown in (a), hollow carbon spheres as electrode catalytic materials only have oxidation peaks, while Figure 9 As shown in (b), the hollow carbon spheres embedded with anatase / rutile crystal titanium dioxide as electrode catalysts produce obvious reduction peaks, which means that the precipitation of Cl2 is effectively suppressed and the conversion of Cl2 to Cl2 is promoted. - reversible reaction.

[0058] (2) Catalytic performance analysis:

[0059] Cyclic voltammetry test conditions:

[0060] A three-electrode system was used: the working electrode was a glassy carbon electrode (GCE, 3 mm in diameter), the counter electrode was a graphite rod, and the reference electrode was a saturated calomel electrode (SCE, 0.24 V vs. SHE). The electrode catalytic material was coated on the working electrode, and then the working electrode, counter electrode, and reference electrode were respectively installed in a three-port electrolytic cell and heated at 2 M VO 2+ 、2M SO4 2- and 5M Cl - of cathode electrolyte and 2M V 3+ 、2M SO4 2- and 5M Cl - Related electrochemical tests were carried out in the negative electrode electrolyte.

[0061] like Figure 10 In the positive electrode cyclic voltammetry curve shown, the solid line is the hollow carbon sphere, and the dotted line is the hollow carbon sphere with anatase / rutile crystalline titanium dioxide embedded. It can be seen that the hollow carbon sphere with anatase / rutile crystalline titanium dioxide embedded has a larger redox peak current, indicating that the electrochemical activity of the hollow carbon sphere increases after the anatase / rutile crystalline titanium dioxide is embedded, and the anatase / rutile crystalline titanium dioxide plays a role in it.

[0062] like Figure 11In the negative electrode cyclic voltammetry curve shown, the solid line is the hollow carbon sphere, and the dotted line is the hollow carbon sphere with anatase / rutile crystalline titanium dioxide embedded. It can be seen that the hollow carbon sphere with anatase / rutile crystalline titanium dioxide embedded has a larger redox peak current, indicating that the electrochemical activity of the hollow carbon sphere increases after the anatase / rutile crystalline titanium dioxide is embedded, and the anatase / rutile crystalline titanium dioxide plays a role in it.

[0063] (3) Battery performance analysis:

[0064] Mixed acid system all-vanadium redox flow battery test conditions: positive and negative electrodes are 800cm 2 The carbon felt electrode, the positive and negative electrodes are all made of mixed acid all-vanadium flow battery electrolyte, the electrolyte mainly contains 1M V 3+ 、1M VO 2+ 、2M SO4 2- and 5M Cl - Hollow carbon balls, hollow carbon balls embedded with unfixed titanium dioxide, and hollow carbon balls embedded with anatase / rutile titanium dioxide were sprayed on the carbon felt electrode as electrode catalytic materials; 80 mA / cm 2 The charge and discharge cycles are carried out at a current density of 1.6V and the discharge cut-off condition is that the voltage is not higher than 1.6V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0065] like Figure 12 As shown in (a), the blank control group without electrode catalytic materials has a coulombic efficiency of 94.67%, a voltage efficiency of 87.49%, and an energy efficiency of 82.83%. Figure 12 As shown in (b), hollow carbon spheres are used as electrode catalyst materials for mixed acid system all-vanadium redox flow batteries, with a coulombic efficiency of 95.88%, a voltage efficiency of 87.23%, and an energy efficiency of 83.64%. Figure 12 As shown in (c), hollow carbon spheres embedded with free-standing titanium dioxide are used as electrode catalysts for mixed acid system all-vanadium flow batteries. The coulombic efficiency of the battery is 96.47%, the voltage efficiency is 87.41%, and the energy efficiency is 84.33%. Figure 12 As shown in (d), hollow carbon spheres with embedded anatase / rutile crystal titanium dioxide were used as electrode catalytic materials for mixed acid system all-vanadium redox flow batteries. The coulombic efficiency of the battery was 97.44%, the voltage efficiency was 89.52%, and the energy efficiency was 87.23%, which were 2.93%, 2.32%, and 5.31% higher than those of the blank control group, respectively, 1.63%, 2.63%, and 4.29% higher than those of hollow carbon spheres, respectively, and 1.01%, 2.41%, and 3.44% higher than those of hollow carbon spheres with embedded non-fixed titanium dioxide, respectively.

[0066] Example 2

[0067] The present invention provides a method for preparing hollow carbon spheres embedded with titanium dioxide, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and performing a hydrothermal treatment at 120° C. for 12 hours to uniformly coat the silicon dioxide with the phenolic resin; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900° C. for 2 hours in an argon atmosphere at a heating rate of 5° C. / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silicon dioxide template; then washing the product with ethanol and deionized water several times, and drying the product to obtain hollow carbon spheres;

[0068] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 h. Then, 30 mg of the prepared hollow carbon spheres were added to the solution and stirred continuously at room temperature for 12 h. Then, the hollow carbon spheres were washed with 18 mL of anhydrous ethanol to remove the titanium sulfate on the surface of the hollow carbon spheres, and then washed with 18 mL of deionized water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 ° C for 6 h to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 ° C / min to 500 ° C under an argon atmosphere for 4 h to obtain embedded anatase titanium dioxide hollow carbon spheres, such as Figure 13 and 14 As shown, the morphology of the hollow carbon spheres can be seen, such as Figure 15 As shown, the XRD diffraction pattern shows the characteristic peaks of anatase titanium dioxide crystal form (PDF #21-1272).

[0069] An electrode catalytic material of the present invention is prepared using hollow carbon spheres with embedded anatase crystal-type titanium dioxide prepared in Example 2.

[0070] An electrode catalytic material of Example 2, containing hollow carbon spheres of anatase-type titanium dioxide, was applied to a mixed acid system all-vanadium redox flow battery.

[0071] Performance testing:

[0072] (1) Cl - Reversibility analysis of Cl2 redox reaction:

[0073] Cyclic voltammetry test conditions:

[0074] A three-electrode system was used: the working electrode was a glassy carbon electrode (GCE, 3 mm in diameter), the counter electrode was a graphite rod, and the reference electrode was a saturated calomel electrode (SCE, 0.24 V vs. SHE). The electrode catalytic material was coated on the working electrode, and the working electrode, counter electrode, and reference electrode were respectively installed in a three-port electrolytic cell. Relevant electrochemical tests were carried out in a blank mixed acid system containing only sulfuric acid and hydrochloric acid.

[0075] like Figure 16 As shown in Figure 2, the hollow carbon spheres embedded with anatase-type titanium dioxide as electrode materials produce obvious reduction peaks, which effectively inhibit the precipitation of Cl2 and promote the conversion of Cl2 to Cl - reversible reaction.

[0076] (2) Catalytic performance analysis:

[0077] Cyclic voltammetry test conditions:

[0078] A three-electrode system was used: the working electrode was a glassy carbon electrode (GCE, 3 mm in diameter), the counter electrode was a graphite rod, and the reference electrode was a saturated calomel electrode (SCE, 0.24 V vs. SHE). The electrode catalytic material was coated on the working electrode, and then the working electrode, counter electrode, and reference electrode were respectively installed in a three-port electrolytic cell and heated at 2 M VO 2+ 、2M SO4 2- and 5M Cl - of cathode electrolyte and 2M V 3+ 、2M SO4 2- and 5M Cl - Related electrochemical tests were carried out in the negative electrode electrolyte.

[0079] like Figure 17 In the positive electrode cyclic voltammetry curve shown, the solid line is the hollow carbon sphere, and the dotted line is the hollow carbon sphere embedded with anatase crystalline titanium dioxide. It can be seen that the hollow carbon sphere embedded with anatase crystalline titanium dioxide has a larger redox peak current, indicating that the electrochemical activity of the hollow carbon sphere increases after the anatase crystalline titanium dioxide is embedded, and the anatase crystalline titanium dioxide plays a role in it.

[0080] like Figure 18 In the negative electrode cyclic voltammetry curve shown, the solid line is the hollow carbon sphere, and the dotted line is the hollow carbon sphere embedded with anatase crystalline titanium dioxide. It can be seen that the hollow carbon sphere embedded with anatase crystalline titanium dioxide has a larger redox peak current, indicating that the electrochemical activity of the hollow carbon sphere increases after the anatase crystalline titanium dioxide is embedded, and the anatase crystalline titanium dioxide plays a role in it.

[0081] (3) Battery performance analysis:

[0082] Mixed acid system all-vanadium redox flow battery test conditions: positive and negative electrodes are 800cm 2 The carbon felt electrode, the positive and negative electrodes are all made of mixed acid all-vanadium flow battery electrolyte, the electrolyte mainly contains 1M V 3+ 、1M VO 2+ 、2M SO4 2- and 5M Cl - Hollow carbon balls and hollow carbon balls embedded with anatase-type titanium dioxide were sprayed on the carbon felt electrodes as electrode catalytic materials; 80 mA / cm 2 The charge and discharge cycles are carried out at a current density of 1.6V and the discharge cut-off condition is that the voltage is not higher than 1.6V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0083] like Figure 19 As shown, hollow carbon spheres with embedded anatase crystal titanium dioxide were used as electrode catalytic materials for mixed acid system all-vanadium redox flow batteries. The coulombic efficiency of the battery was 96.84%, the voltage efficiency was 89.37%, and the energy efficiency was 86.55%, which were 2.29%, 2.15%, and 4.49% higher than those of the blank control group, 1.00%, 2.45%, and 3.48% higher than those of hollow carbon spheres, and 0.38%, 2.24%, and 2.63% higher than those of hollow carbon spheres with embedded non-fixed titanium dioxide.

[0084] Example 3

[0085] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and performing a hydrothermal treatment at 120° C. for 12 hours to uniformly coat the silica with the phenolic resin; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900° C. for 2 hours in an argon atmosphere at a heating rate of 5° C. / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times and drying the product to obtain hollow carbon spheres;

[0086] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. Then, the hollow carbon spheres were washed with 21 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 24 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 ° C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 ° C / min to 900 ° C under an argon atmosphere for 1 hour to obtain embedded rutile crystal titanium dioxide hollow carbon spheres, such as Figure 20 and 21 As shown, the morphology of the hollow carbon spheres can be seen, such as Figure 22 As shown, the XRD diffraction pattern shows the characteristic peaks of rutile titanium dioxide crystal form (PDF #21-1276).

[0087] An electrode catalytic material of the present invention is prepared using hollow carbon spheres with embedded rutile crystal-type titanium dioxide prepared in Example 3.

[0088] An electrode catalytic material of Example 3, containing hollow carbon spheres embedded with rutile-crystalline titanium dioxide, was applied to a mixed-acid all-vanadium redox flow battery.

[0089] Performance testing:

[0090] (1) Cl - Reversibility analysis of Cl2 redox reaction:

[0091] Cyclic voltammetry test conditions:

[0092] A three-electrode system was used: the working electrode was a glassy carbon electrode (GCE, 3 mm in diameter), the counter electrode was a graphite rod, and the reference electrode was a saturated calomel electrode (SCE, 0.24 V vs. SHE). The electrode catalytic material was coated on the working electrode, and the working electrode, counter electrode, and reference electrode were respectively installed in a three-port electrolytic cell. Relevant electrochemical tests were carried out in a blank mixed acid system containing only sulfuric acid and hydrochloric acid.

[0093] like Figure 23 As shown in Figure 2, the hollow carbon spheres embedded with rutile crystal titanium dioxide as electrode materials produce obvious reduction peaks, which means that the precipitation of Cl2 is effectively suppressed and the conversion of Cl2 to Cl2 is promoted. - reversible reaction.

[0094] (2) Catalytic performance analysis:

[0095] Cyclic voltammetry test conditions:

[0096] A three-electrode system was used: the working electrode was a glassy carbon electrode (GCE, 3 mm in diameter), the counter electrode was a graphite rod, and the reference electrode was a saturated calomel electrode (SCE, 0.24 V vs. SHE). The electrode catalytic material was coated on the working electrode, and then the working electrode, counter electrode, and reference electrode were respectively installed in a three-port electrolytic cell and heated at 2 M VO 2+ 、2M SO4 2- and 5M Cl - of cathode electrolyte and 2M V 3+ 、2M SO4 2- and 5M Cl - Related electrochemical tests were carried out in the negative electrode electrolyte.

[0097] like Figure 24 In the positive electrode cyclic voltammetry curve shown, the solid line is the hollow carbon sphere, and the dotted line is the hollow carbon sphere embedded with rutile crystalline titanium dioxide. It can be seen that the hollow carbon sphere embedded with rutile crystalline titanium dioxide has a larger redox peak current, indicating that the electrochemical activity of the hollow carbon sphere increases after the rutile crystalline titanium dioxide is embedded, and the rutile crystalline titanium dioxide plays a role in it.

[0098] like Figure 25 In the negative electrode cyclic voltammetry curve shown, the solid line is the hollow carbon sphere, and the dotted line is the hollow carbon sphere embedded with rutile crystalline titanium dioxide. It can be seen that the hollow carbon sphere embedded with rutile crystalline titanium dioxide has a larger redox peak current, indicating that the electrochemical activity of the hollow carbon sphere increases after the rutile crystalline titanium dioxide is embedded, and the rutile crystalline titanium dioxide plays a role in it.

[0099] (3) Battery performance analysis:

[0100] Mixed acid system all-vanadium redox flow battery test conditions: positive and negative electrodes are 800cm 2 The carbon felt electrode, the positive and negative electrodes are all made of mixed acid all-vanadium flow battery electrolyte, the electrolyte mainly contains 1M V 3+ 、1M VO 2+ 、2M SO4 2- and 5M Cl - Hollow carbon balls and hollow carbon balls embedded with rutile-type titanium dioxide were sprayed on the carbon felt electrodes as electrode catalytic materials; 80 mA / cm 2 The charge and discharge cycles are carried out at a current density of 1.6V and the discharge cut-off condition is that the voltage is not higher than 1.6V, and the discharge cut-off condition is that the voltage is not lower than 0.1V.

[0101] like Figure 26As shown in the figure, hollow carbon spheres with embedded rutile crystal titanium dioxide are used as electrode catalytic materials for mixed acid system all-vanadium redox flow batteries. The coulombic efficiency of the battery is 96.78%, the voltage efficiency is 89.34%, and the energy efficiency is 86.47%; these are 2.23%, 2.11%, and 4.39% higher than those of the blank control group, 0.94%, 2.42%, and 3.38% higher than those of hollow carbon spheres, and 0.32%, 2.21%, and 2.54% higher than those of hollow carbon spheres with embedded non-fixed titanium dioxide.

[0102] Example 4

[0103] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering, drying, collecting the mixture, and carbonizing it at 900°C for 1 hour in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing it with ethanol and distilled water several times, and drying it.

[0104] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 15 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 21 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 ° C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 ° C / min to 700 ° C under an argon atmosphere for 1 hour to obtain embedded anatase / rutile crystalline titanium dioxide hollow carbon spheres.

[0105] Example 5

[0106] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering, drying, collecting the mixture, and carbonizing it at 800°C for 3 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing it with ethanol and distilled water several times, and drying it.

[0107] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 15 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 24 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 ° C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 ° C / min to 700 ° C under an argon atmosphere for 2 hours to obtain embedded anatase / rutile crystalline titanium dioxide hollow carbon spheres.

[0108] Example 6

[0109] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120 ° C for 12 hours; filtering and drying the mixture, collecting the mixture, carbonizing it at 700 ° C for 4 hours in an argon atmosphere at a heating rate of 5 ° C / min, treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template, and then washing it with ethanol and distilled water several times and drying it to obtain hollow carbon spheres;

[0110] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 15 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 12 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 500 °C under an argon atmosphere for 1 hour to obtain embedded anatase crystal titanium dioxide hollow carbon spheres.

[0111] Example 7

[0112] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900°C for 3 hours in a nitrogen atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0113] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 18 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 15 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 500 °C in a nitrogen atmosphere for 2 hours to obtain embedded rutile crystal titanium dioxide hollow carbon spheres.

[0114] Example 8

[0115] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 800°C for 2 hours in a helium atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0116] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 21 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 18 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 900 °C in a helium atmosphere for 1 hour to obtain embedded rutile crystal titanium dioxide hollow carbon spheres.

[0117] Example 9

[0118] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 800°C for 3 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0119] 48 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 15 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 21 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 900 °C under an argon atmosphere for 2 hours to obtain embedded rutile crystal titanium dioxide hollow carbon spheres.

[0120] Example 10

[0121] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120° C. for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 800° C. for 4 hours in an argon atmosphere at a heating rate of 5° C. / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0122] 45 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. Then, the hollow carbon spheres were washed with 15 mL of anhydrous ethanol to remove the titanium sulfate on the surface of the hollow carbon spheres, and then washed with 12 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 ° C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 ° C / min to 700 ° C under an argon atmosphere for 4 hours to embed anatase / rutile crystalline titanium dioxide hollow carbon spheres.

[0123] Example 11

[0124] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 700°C for 3 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0125] 51 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres were added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 18 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 12 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 ° C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 ° C / min to 700 ° C under an argon atmosphere for 4 hours to obtain embedded anatase / rutile crystalline titanium dioxide hollow carbon spheres.

[0126] Example 12

[0127] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 700°C for 2 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times and drying the product to obtain hollow carbon spheres;

[0128] 45 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 18 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 18 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 500 °C under an argon atmosphere for 4 hours to obtain embedded anatase crystal titanium dioxide hollow carbon spheres.

[0129] Example 13

[0130] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900°C for 2 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0131] 51 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 21 mL of anhydrous ethanol to remove the titanium sulfate on the surface, and then washed with 18 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 500 °C under an argon atmosphere for 4 hours to obtain embedded anatase crystal titanium dioxide hollow carbon spheres.

[0132] Example 14

[0133] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900°C for 2 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0134] 45 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 21 mL of ethanol to remove the titanium sulfate on the surface, and then washed with 24 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 900 °C under an argon atmosphere for 4 hours to obtain embedded rutile crystal titanium dioxide hollow carbon spheres.

[0135] Example 15

[0136] The present invention provides a method for preparing hollow carbon spheres of titanium dioxide with different embedded crystal forms, comprising the following steps: adding 2.5 mL of tetraethyl orthosilicate to 45 mL of ethanol and stirring for 3 minutes, then adding 40 mL of water and 5 mL of ammonia solution, stirring for 1 hour, gradually adding 0.6 g of resorcinol and 0.8 mL of formaldehyde under stirring, and stirring for 12 hours; then transferring the resulting mixture to a hydrothermal reactor and subjecting it to a hydrothermal treatment at 120°C for 12 hours; filtering and drying the mixture, collecting the mixture, and carbonizing it at 900°C for 2 hours in an argon atmosphere at a heating rate of 5°C / min; treating the product with a hydrofluoric acid solution for 20 hours to remove the silica template; then washing the product with ethanol and distilled water several times, and drying the product to obtain hollow carbon spheres;

[0137] 51 mg of titanium sulfate was added to 20 mL of sulfuric acid (3 mol / L) solution and stirred for 1 hour. Then, 30 mg of the prepared hollow carbon spheres was added to the solution and stirred continuously at room temperature for 12 hours. The hollow carbon spheres were then washed with 15 mL of ethanol to remove the titanium sulfate on the surface, and then washed with 24 mL of distilled water to hydrolyze the titanium sulfate inside the hollow carbon spheres. The resulting product was repeatedly washed and dried in a vacuum oven at 60 °C for 6 hours to obtain embedded amorphous titanium dioxide hollow carbon spheres. The prepared embedded amorphous titanium dioxide hollow carbon spheres were placed in an alumina crucible and then heated in a tubular furnace at a heating rate of 5 °C / min to 900 °C under an argon atmosphere for 4 hours to obtain embedded rutile crystal titanium dioxide hollow carbon spheres.

Claims

1. A method for preparing hollow carbon spheres embedded with titanium dioxide, characterized in that: Using silica as a template and phenolic resin as a carbon source to uniformly coat silica, silica is synthesized through the hydrolysis and condensation reaction of tetraethyl orthosilicate, and formaldehyde and resorcinol are gradually added under stirring, and stirring is continued. The mixture formed by the reaction is transferred to a hydrothermal reactor for hydrothermal treatment, filtered, dried, and collected. After high-temperature carbonization at 700°C-900°C in an inert gas atmosphere, hollow carbon spheres are obtained by chemical etching; a hydrolyzable titanium source is introduced into the hollow carbon spheres, and the titanium on the surface of the hollow carbon spheres is washed and removed, and the titanium inside the hollow carbon spheres is washed and hydrolyzed. After repeated washing and drying, hollow carbon spheres with embedded amorphous titanium dioxide are obtained; the hollow carbon spheres with embedded amorphous titanium dioxide are subjected to high-temperature treatment at 500°C-900°C in an inert gas atmosphere, and the temperature is controlled to obtain hollow carbon spheres with embedded titanium dioxide of different crystal forms.

2. The method for preparing hollow carbon spheres embedded with titanium dioxide according to claim 1, wherein: The high temperature carbonization time is 1h-4h.

3. The method for preparing hollow carbon spheres embedded with titanium dioxide according to claim 1, wherein: The chemical etching method uses analytically pure hydrofluoric acid with a mass concentration of ≥40%.

4. The method for preparing hollow carbon spheres embedded with titanium dioxide according to claim 1, wherein: A hydrolyzable titanium source, titanium sulfate, is introduced into the hollow carbon spheres and continuously stirred until uniform.

5. The method for preparing hollow carbon spheres embedded with titanium dioxide according to claim 4, wherein: The mass ratio of the hollow carbon spheres to titanium sulfate is 1:(1.5-1.7).

6. The method for preparing hollow carbon spheres embedded with titanium dioxide according to claim 1, wherein: The washing to remove titanium from the surface of the hollow carbon spheres uses anhydrous ethanol, and the mass volume ratio of the hollow carbon spheres to the anhydrous ethanol used for washing and removing titanium is 1:(500-700) g / mL; Distilled water or deionized water is used to wash and hydrolyze the titanium inside the hollow carbon spheres, and the mass volume ratio of the hollow carbon spheres to the water used for washing and hydrolysis is 1:(400-800) g / mL.

7. The method for preparing hollow carbon spheres embedded with titanium dioxide according to claim 1, wherein: The high-temperature treatment time of the hollow carbon spheres embedded with amorphous titanium dioxide is 1h-4h.

8. An electrode catalytic material, characterized in that: Hollow carbon spheres embedded with titanium dioxide of different crystal forms prepared by the preparation method of hollow carbon spheres embedded with titanium dioxide according to any one of claims 1 to 7 are used as electrode catalytic materials.

9. Use of the electrode catalytic material according to claim 8, characterized in that: The hollow carbon spheres embedded with titanium dioxide of different crystal forms are sprayed on carbon felt as electrode catalytic materials and used as positive and negative electrodes of a mixed acid system all-vanadium redox flow battery.

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