Composite catalyst modified graphite felt electrode and preparation method and application thereof

Abstract

The application relates to the technical field of electrodes of all-vanadium redox flow batteries, and discloses a composite catalyst modified graphite felt electrode and a preparation method and application thereof, which comprises the following steps: preparing carbon-nitrogen doped cerium oxide; preparing graphite phase carbon nitride; loading the composite catalyst on the graphite felt through an adhesive and carrying out high-temperature calcination to prepare a loaded composite catalyst graphite felt electrode. The graphite phase carbon nitride and the carbon-nitrogen doped cerium oxide are used to modify the graphite felt electrode, the synergistic effect of carbon-nitrogen doping not only improves the electronic conductivity and structural stability of the metal oxide, but also enhances the hydrophilicity, and the voltage efficiency, the discharge capacity and the cycle stability of the vanadium battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of all-vanadium redox flow battery, and particularly relates to a composite catalyst modified graphite felt electrode and a preparation method and application thereof. BACKGROUND

[0002] All-vanadium redox flow battery (VRFB) is a new large-scale energy storage technology, the power of which is determined by the size and number of electrochemical reaction stacks, and the capacity is determined by the volume of electrolyte stored in the external electrolyte tank. VRFB operates by using the reversible oxidation-reduction reaction of vanadium ions in different oxidation states dissolved in an acidic electrolyte. The electrolyte is circulated in the electrochemical reaction stack, and the oxidation-reduction reaction occurs on the electrode, promoting the conversion between chemical energy and electrical energy. The electrode, as a key component of VRFB, its physical and chemical properties play a crucial role in the performance of vanadium battery. Graphite felt has high electrical conductivity, excellent chemical stability and excellent processability, and is one of the most commonly used electrode materials in VRFB. However, untreated graphite felt has poor hydrophilicity and electrocatalytic activity, resulting in poor overall battery performance. Therefore, graphite felt modification is crucial to improve the performance of vanadium battery. SUMMARY

[0003] The present application aims to provide a composite catalyst modified graphite felt electrode and a preparation method and application thereof to overcome the deficiencies in the prior art.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0005] In a first aspect, a preparation method of a composite catalyst modified graphite felt electrode is disclosed, comprising the following steps:

[0006] Step S1: carbon and nitrogen source, cerium source and deionized water are stirred and dissolved, heated and evaporated, ground, pretreated, carbonized to obtain carbon and nitrogen doped cerium oxide;

[0007] Step S2: carbon and nitrogen doped cerium oxide, carbon nitride precursor, adhesive and deionized water are uniformly dispersed to obtain an aqueous slurry;

[0008] Step S3: the graphite felt electrode is immersed in the aqueous slurry, taken out and dried, calcined to obtain a composite catalyst modified graphite felt electrode loaded with graphite phase carbon nitride and carbon and nitrogen doped cerium oxide.

[0009] In one embodiment, in step S1:

[0010] The mass ratio of the carbon and nitrogen source, the cerium source and the deionized water is 1:(1-3):50.

[0011] The carbon and nitrogen source and the cerium source are pretreated and carbonized to form carbon and nitrogen doped cerium oxide. The synergistic effect of carbon and nitrogen doping not only improves the electronic conductivity and structural stability of cerium oxide, but also enhances the hydrophilicity. At the same time, the introduced nitrogen defects can effectively increase the reaction active sites of vanadium ions.

[0012] In one embodiment, in the step S1:

[0013] The carbon and nitrogen source is one of urea, dicyandiamide and melamine;

[0014] The cerium source is one of cerium nitrate, cerium carbonate and cerium oxalate.

[0015] In one embodiment, in the step S1:

[0016] The stirring and dissolving time is 3h;

[0017] The heating and evaporation temperature is 80℃.

[0018] In one embodiment, in the step S1:

[0019] The pretreatment temperature is 100-200℃, the time is 100-150min, the heating rate is 10℃ / min, and the atmosphere is nitrogen;

[0020] The carbonization temperature is 1000-1200℃, the time is 2-4h, the heating rate is 2-5℃ / min, and the atmosphere is nitrogen.

[0021] In one embodiment, in the step S2:

[0022] The mass ratio of carbon and nitrogen doped cerium oxide, carbon nitride precursor, adhesive and deionized water is (1-2):(20-40):1:50.

[0023] In one embodiment, in the step S2:

[0024] The adhesive is one of polyvinyl alcohol water-based adhesive, polyurethane water-based adhesive and epoxy resin water-based adhesive;

[0025] The adhesive forms carbon material in the calcination process, forms a conductive network on the graphite felt, and enhances the adhesion of the catalyst on the graphite felt, improves the voltage efficiency and cycle stability of the graphite felt.

[0026] The carbon nitride precursor is one of urea, dicyandiamide, melamine and thiourea.

[0027] The carbon nitride precursor can be calcined to form graphite phase carbon nitride, which has highly uniformly distributed nitrogen atoms, the nitrogen atoms have lone pair electrons, have strong adsorption and anchoring effect on vanadium ions, not only increase the reaction area of vanadium ions, but also form N-V bond, so as to improve the voltage efficiency, cycle stability and capacity retention rate of the vanadium battery.

[0028] In one embodiment, the step S3 is:

[0029] The calcination temperature is 450-500 DEG C, and the time is 2-4h.

[0030] The second aspect discloses a composite catalyst modified graphite felt electrode, which is prepared by the preparation method of the composite catalyst modified graphite felt electrode.

[0031] The third aspect discloses an application of the composite catalyst modified graphite felt electrode, the composite catalyst modified graphite felt electrode prepared by the preparation method or the composite catalyst modified graphite felt electrode is applied to a vanadium redox flow battery.

[0032] The beneficial effects of the present application are:

[0033] The synergistic effect of carbon and nitrogen doping not only improves the electronic conductivity and structural stability of the metal oxide, but also enhances the hydrophilicity. The introduced nitrogen defects increase the reaction active sites of vanadium ions, and improve the voltage efficiency, discharge capacity and cycle stability of the vanadium battery.

[0034] The graphite phase carbon nitride has highly uniformly distributed nitrogen atoms, the nitrogen atoms have lone pair electrons, have strong adsorption and anchoring effect on vanadium ions, not only increase the reaction area of vanadium ions, but also form N-V bond, so as to improve the voltage efficiency, cycle stability and capacity retention rate of the vanadium battery.

[0035] The adhesive forms a carbon material during calcination, forms a conductive network on the graphite felt electrode, and enhances the adhesion of the catalyst on the graphite felt electrode, improves the voltage efficiency and cycle stability of the graphite felt electrode. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The scanning electron microscope image of the carbon and nitrogen doped cerium oxide prepared in Example 1 of the present application.

[0037] Figure 2 The scanning electron microscope image of the composite catalyst modified graphite felt electrode prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with the aid of drawings and examples. However, it should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the scope of the present application. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application.

[0039] A preparation method of a composite catalyst modified graphite felt electrode, comprising the following steps:

[0040] Step S1: 1 part by mass of a carbon and nitrogen source and 1-3 parts by mass of a cerium source are dissolved in 50 parts by mass of deionized water, stirred for 3 h, and then heated to 80°C to evaporate the solvent. The obtained sample is collected and ground into a powder and transferred to a crucible with a cover. The crucible is placed in a tube furnace under nitrogen for pretreatment, the temperature is 100-200°C, the time is 100-150 min, and the heating rate is 10°C / min. Then the temperature is increased for carbonization, the carbonization temperature is 1000-1200°C, the time is 2-4 h, and the heating rate is 2-5°C / min, to obtain carbon and nitrogen doped cerium oxide.

[0041] Step S2: 1-2 parts by mass of carbon and nitrogen doped cerium oxide, 20-40 parts by mass of carbon nitride precursor, and 1 part by mass of adhesive are dispersed in 50 parts by mass of deionized water, and uniformly stirred to obtain an aqueous slurry;

[0042] Step S3: The graphite felt electrode is immersed in the aqueous slurry, taken out and dried, and then calcined at a temperature of 450-500°C for 2-4 h to obtain a composite catalyst modified graphite felt electrode loaded with graphite phase carbon nitride and carbon and nitrogen doped cerium oxide.

[0043] Example 1: This example is specifically obtained by the following operations

[0044] Step S1: 1 part by mass of urea and 1 part by mass of cerium nitrate are dissolved in 50 parts by mass of deionized water, stirred for 3 h, and then heated to 80°C to evaporate the solvent. The obtained sample is collected and ground into a powder and transferred to a crucible with a cover. The crucible is placed in a tube furnace under nitrogen for pretreatment, the temperature is 100°C, the time is 100 min, and the heating rate is 10°C / min. Then the temperature is increased for carbonization, the carbonization temperature is 1000°C, the time is 2 h, and the heating rate is 2°C / min, to obtain carbon and nitrogen doped cerium oxide.

[0045] Step S2: 1 part by mass of carbon and nitrogen doped cerium oxide, 20 parts by mass of urea, and 1 part by mass of polyvinyl alcohol aqueous adhesive are dispersed in 50 parts by mass of deionized water, and uniformly stirred to obtain an aqueous slurry;

[0046] Step S3: The graphite felt electrode was immersed in the aqueous slurry, dried after taking out, and calcined, the calcination temperature was 450℃, the time was 2h, to obtain the graphite felt electrode modified by the composite catalyst of graphite phase carbon nitride and carbon-nitrogen-doped cerium oxide.

[0047] Example 2: This example was specifically obtained by the following operation

[0048] Step S1: 1 part by mass of dicyandiamide and 2 parts by mass of cerium carbonate were dissolved in 50 parts by mass of deionized water, stirred for 3h, and then heated to 80℃ to evaporate the solvent. The obtained sample was collected and ground into powder and transferred to a covered crucible. The crucible was pre-treated in a tube furnace under nitrogen, the temperature was 150℃, the time was 120min, and the heating rate was 10℃ / min; then the temperature was increased for carbonization, the carbonization temperature was 1100℃, the time was 3h, and the heating rate was 4℃ / min, to obtain carbon-nitrogen-doped cerium oxide.

[0049] Step S2: 1.5 parts by mass of carbon-nitrogen-doped cerium oxide, 30 parts by mass of dicyandiamide and 1 part by mass of polyurethane aqueous adhesive were dispersed in 50 parts by mass of deionized water, and an aqueous slurry was obtained after uniform stirring.

[0050] Step S3: The graphite felt electrode was immersed in the aqueous slurry, dried after taking out, and calcined, the calcination temperature was 475℃, the time was 3h, to obtain the graphite felt electrode modified by the composite catalyst of graphite phase carbon nitride and carbon-nitrogen-doped cerium oxide.

[0051] Example 3: This example was specifically obtained by the following operation

[0052] Step S1: 1 part by mass of melamine and 3 parts by mass of cerium oxalate were dissolved in 50 parts by mass of deionized water, stirred for 3h, and then heated to 80℃ to evaporate the solvent. The obtained sample was collected and ground into powder and transferred to a covered crucible. The crucible was pre-treated in a tube furnace under nitrogen, the temperature was 200℃, the time was 150min, and the heating rate was 10℃ / min; then the temperature was increased for carbonization, the carbonization temperature was 1200℃, the time was 4h, and the heating rate was 5℃ / min, to obtain carbon-nitrogen-doped cerium oxide.

[0053] Step S2: 2 parts by mass of carbon-nitrogen-doped cerium oxide, 40 parts by mass of melamine and 1 part by mass of epoxy resin aqueous adhesive were dispersed in 50 parts by mass of deionized water, and an aqueous slurry was obtained after uniform stirring.

[0054] Step S3: The graphite felt electrode was immersed in the aqueous slurry, dried after taking out, and calcined, the calcination temperature was 500℃, the time was 4h, to obtain the graphite felt electrode modified by the composite catalyst of graphite phase carbon nitride and carbon-nitrogen-doped cerium oxide.

[0055] Comparative Example 1: Specifically obtained by the following operation

[0056] This comparative example is a blank control group, using an untreated blank graphite felt electrode.

[0057] Comparative Example 2: Specifically obtained by the following operation

[0058] The preparation process of this comparative example is only different from Example 1 in that no carbon nitride precursor is added in step S2.

[0059] Comparative Example 3: Specifically obtained by the following operation

[0060] The preparation process of this comparative example is only different from Example 1 in that no carbon and nitrogen source urea is added in step S1.

[0061] Comparative Example 4: Specifically obtained by the following operation

[0062] The preparation process of this comparative example is only different from Example 1 in that 0.5 parts by mass of urea is added in step S1.

[0063] Comparative Example 5: Specifically obtained by the following operation

[0064] The preparation process of this comparative example is only different from Example 1 in that 5 parts by mass of urea is added in step S1.

[0065] Comparative Example 6: Specifically obtained by the following operation

[0066] The preparation process of this comparative example is only different from Example 1 in that no polyvinyl alcohol aqueous adhesive is added in step S2.

[0067] Comparative Example 7: Specifically obtained by the following operation

[0068] The preparation process of this comparative example is only different from Example 1 in that 0.1 parts by mass of polyvinyl alcohol aqueous adhesive is added in step S2.

[0069] Comparative Example 8: Specifically obtained by the following operation

[0070] The preparation process of this comparative example is only different from Example 1 in that 10 parts by mass of polyvinyl alcohol aqueous adhesive is added in step S2.

[0071] 1. Mechanical strength test of modified graphite felt electrode: The graphite felt electrodes prepared in the examples and comparative examples were cut into 3*3 cm, placed in deionized water, oscillated at 30°C for 3h, then washed with deionized water, dried, and the mass change before and after weighing the graphite felt electrode was measured.

[0072] 2. Battery test: the graphite felt electrodes prepared in examples 1-3 and comparative examples 1-3 were assembled into a battery stack and subjected to charge-discharge test under the same test conditions, and the battery coulombic efficiency, voltage efficiency, energy efficiency, capacity retention after 100 cycles were recorded.

[0073] The test results are shown in Table 1:

[0074] Table 1: Performance test results of graphite felt electrodes of examples and comparative examples

[0075]

[0076] As can be seen from Table 1, compared with comparative example 1, examples 1-3 and comparative examples 2 and 3 have higher voltage efficiency, energy efficiency and capacity retention, mainly because the graphite felt electrode is modified by the composite catalyst of graphite phase carbon nitride and carbon-nitrogen doped cerium oxide, and the graphite phase carbon nitride and carbon-nitrogen doped cerium oxide as catalysts provide more active sites for vanadium ions to enhance the redox reaction of vanadium ions. As can be seen from the results data of example 1 and comparative examples 6-8, the adhesive forms carbon material during calcination, forms a conductive network on the graphite felt, and enhances the adhesion of the catalyst on the graphite felt electrode, thereby improving the voltage efficiency and cycle stability of the graphite felt electrode. However, too much adhesive added will cause insufficient exposure of graphite fibers, thereby affecting the battery efficiency, and too little adhesive added will not achieve the best bonding effect, thereby affecting the battery performance. Compared with comparative example 2, examples 1-3 have higher voltage efficiency, energy efficiency and capacity retention, mainly because the graphite phase carbon nitride has highly uniform distribution of nitrogen atoms, and these nitrogen atoms have lone pair electrons, which have strong adsorption and anchoring effect on vanadium ions, not only increasing the reaction area of vanadium ions but also forming N-V bond, thereby improving the voltage efficiency, cycle stability and capacity retention of vanadium battery. Compared with comparative examples 3-5, example 1 has higher voltage efficiency and energy efficiency, mainly because the synergistic effect of carbon-nitrogen doping not only improves the electronic conductivity and structural stability of cerium oxide, but also enhances the hydrophilicity, and the introduced nitrogen defects increase the reaction active sites of vanadium ions, thereby improving the voltage efficiency, capacity efficiency, discharge capacity and cycle stability of vanadium battery. However, too much carbon-nitrogen source will cause insufficient exposure of active sites of cerium oxide, affecting the battery performance, and too little carbon-nitrogen source will result in that the synergistic effect of carbon-nitrogen and cerium oxide cannot reach the best state, thereby affecting the battery performance.

[0077] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement or improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a composite catalyst modified graphite felt electrode, characterized by, The preparation method comprises the following steps: Step S1: dissolving and stirring a carbon-nitrogen source, a cerium source and deionized water, evaporating under heating, grinding, pretreating, and carbonizing to obtain carbon-nitrogen-doped cerium oxide; Step S2: uniformly dispersing the carbon-nitrogen-doped cerium oxide, a carbon nitride precursor, an adhesive and deionized water to obtain an aqueous slurry; Step S3: immersing a graphite felt electrode in the aqueous slurry, taking out and drying, and calcining to obtain a composite catalyst modified graphite felt electrode loaded with graphite-phase carbon nitride and carbon-nitrogen-doped cerium oxide.

2. The production method according to claim 1, wherein In the step S1: The mass ratio of the carbon-nitrogen source, the cerium source and the deionized water is 1:(1-3):

50.

3. The preparation method of claim 1, characterized in that: The carbon-nitrogen source is one of urea, dicyandiamide and melamine; The cerium source is one of cerium nitrate, cerium carbonate and cerium oxalate.

4. The production method according to claim 1, wherein In the step S1: The stirring and dissolving time is 3 h; The heating and evaporating temperature is 80℃.

5. The production method according to claim 1, wherein In the step S1: The pretreating temperature is 100-200℃, the time is 100-150 min, the temperature rising speed is 10℃ / min, and the atmosphere is nitrogen; The carbonizing temperature is 1000-1200℃, the time is 2-4 h, the temperature rising speed is 2-5℃ / min, and the atmosphere is nitrogen.

6. The production method according to claim 1, wherein In the step S2: The mass ratio of the carbon-nitrogen-doped cerium oxide, the carbon nitride precursor, the adhesive and the deionized water is (1-2):(20-40):1:

50.

7. The preparation method of claim 1, characterized in that: The adhesive is one of polyvinyl alcohol water-based adhesive, polyurethane water-based adhesive and epoxy resin water-based adhesive; The carbon nitride precursor is one of urea, dicyandiamide, melamine and thiourea.

8. The production method according to claim 1, wherein In the step S3: The calcining temperature is 450-500℃, and the time is 2-4 h.

9. A composite catalyst modified graphite felt electrode, characterized by, The composite catalyst modified graphite felt electrode is prepared by the preparation method of the composite catalyst modified graphite felt electrode according to any one of claims 1-8.

10. Use of a composite catalyst modified graphite felt electrode, characterized in that, The composite catalyst modified graphite felt electrode prepared by the preparation method of any one of claims 1-8 or the composite catalyst modified graphite felt electrode of claim 9 is applied to a full vanadium redox flow battery.

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