A porous composite electrode for inducing high electrochemical catalytic reaction of polybrominates and its preparation method and application

Abstract

The present invention discloses a porous composite electrode for inducing high electrochemical catalytic reaction of polybromides, and a preparation method and application thereof, comprising a substrate of a porous carbon-based material, and a precious metal oxide coating applied on the surface of the substrate; the precious metal oxide coating is composed of any one or more metal oxides of ruthenium, iridium, tantalum, and platinum. The porous composite electrode of the present invention not only has good electrical conductivity and corrosion resistance, but also can work stably for a long time in acidic and alkaline solutions and has a long service life; most importantly, the porous composite electrode has a large specific surface area, high electrochemical active sites, and has excellent electrochemical catalytic effect on polybromides, which can significantly improve the charge and discharge efficiency of bromine-based batteries, while reducing battery polarization.

Description

Technical Field

[0001] The present invention belongs to the field of secondary power sources in energy conversion and energy storage, and specifically relates to a porous composite electrode for inducing high electrochemical catalytic reaction of polybromides, and a preparation method and application thereof. Background Art

[0002] The use of renewable energy (such as solar and wind energy) is considered to be a key factor in solving global climate change, while large-scale energy storage technology is considered to be a key technology for achieving the popularization of renewable energy. Liquid flow batteries have good application prospects in the field of large-scale energy storage due to their high safety, high efficiency, large energy storage scale and long life.

[0003] In recent years, Br is commonly used as the cathode active species of bromine-based aqueous batteries. 2 / Br - Bromine redox couple, because the bromine redox couple has a high potential (1.08V vs. SHE) and theoretical specific capacity (206Ah / L). At the same time, bromine is a "marine element" that can be directly extracted from seawater, and bromine salts have a high solubility in water, which makes bromine-based aqueous batteries have a high energy density and have attracted widespread attention. Bromine-based aqueous batteries include zinc-bromine flow batteries, hydrogen-bromine flow batteries, vanadium-bromine flow batteries, and tin-bromine flow batteries. Among them, zinc-bromine flow batteries are the most mature system currently and are in the application demonstration stage.

[0004] During the charging process of bromine-based aqueous batteries, bromide ions in the electrolyte undergo oxidation reaction on the cathode side to generate Br 2 ,Br 2 The polybrominates formed by the complexing agent are stable in the electrolyte; during the discharge process, the Br 2 A reduction reaction occurs to generate bromide ions which return to the electrolyte. The reaction equation is as follows:

[0005]

[0006] However, the entire reaction process requires the electrode to have high electrochemical activity. Therefore, the cathode material of aqueous bromine-based batteries needs to have high conductivity to accelerate electron transfer and high electrocatalytic activity to promote Br 2 / Br - reaction, good hydrophilicity to reduce electrode-electrolyte interface resistance, and high chemical and electrochemical stability to resist bromine corrosion. Summary of the invention

[0007] Purpose of the invention: The technical problem to be solved by the present invention is to provide a porous composite electrode with high catalytic activity in view of the poor electrochemical activity of bromine redox batteries on existing electrode systems.

[0008] The second object of the present invention is to provide a method for preparing the above-mentioned porous composite electrode with high catalytic activity.

[0009] The third object of the present invention is to provide the application of the above-mentioned porous composite electrode in bromine-based batteries.

[0010] The fourth object of the present invention is to provide a bromine-based battery prepared from the above-mentioned porous composite electrode, and a preparation method thereof.

[0011] In order to achieve the first purpose, the technical solution adopted by the present invention is as follows:

[0012] A porous composite electrode for inducing high electrochemical catalytic reaction of polybromines, comprising a substrate of a porous carbon-based material and a noble metal oxide coating applied on the surface of the substrate; the noble metal oxide coating is composed of any one or more metal oxides of ruthenium, iridium, tantalum and platinum.

[0013] Preferably, the substrate of the porous carbon-based material is selected from any one of carbon felt, graphite felt and carbon cloth. Such carbon substrates have a unique pore structure and a high specific surface area, which can not only reduce the amount of catalyst used and reduce the cost of the electrode; more importantly, the use of the porous carbon substrate can also make the catalyst firmly bonded to the substrate and realize uniform loading of the catalyst on the substrate, thereby increasing the service life of the electrode.

[0014] Preferably, the noble metal oxide coating is a ruthenium-iridium-platinum oxide coating, a ruthenium-iridium oxide coating, a ruthenium-platinum oxide coating or a ruthenium oxide coating. The preferred coating loading is 2 to 4 g / m 2 .

[0015] This composite electrode retains the inherent advantages of porous carbon-based materials such as high specific surface area, high electrical conductivity, high mechanical and chemical stability, and more importantly, has high catalytic activity for polybromide redox.

[0016] In order to achieve the second purpose, the technical solution adopted by the present invention is as follows:

[0017] A method for preparing a porous composite electrode for inducing a high electrochemical catalytic reaction of polybrominates comprises the following steps:

[0018] (1) Substrate pretreatment

[0019] The porous carbon-based material substrate is immersed in acetone to remove surface grease, and then subjected to hydrothermal reaction in concentrated acid to improve the hydrophilicity and affinity of the surface of the porous carbon substrate, and finally washed with water and dried for standby use;

[0020] (2) Preparation of precious metal oxide coating precursor solution

[0021] Dissolve the metal salt or alcohol salt containing precious metal in deionized water, and stir and mix thoroughly;

[0022] (3) Immersion Adhesion

[0023] Completely immersing the substrate pretreated in step (1) in the precursor solution prepared in step (2);

[0024] (4) taking out the substrate immersed in the precursor solution in step (3), drying it, and then heat treating it at a temperature of 350 to 600° C.

[0025] Preferably, in step (1), the temperature of the hydrothermal reaction is 70 to 90° C., and the reaction time is 8 to 10 hours.

[0026] Preferably, in step (2), the total mass concentration of the noble metal elements in the precursor solution is 1 g / L to 2 g / L.

[0027] Furthermore, in step (3), in order to improve the impregnation efficiency and the adhesion firmness of the precursor on the substrate, a vacuum decompression impregnation method can be used, with an initial pressure of one atmosphere, evacuated to -50 kPa, and impregnated under pressure for 30 seconds. After pretreatment, the porous carbon substrate is placed in a vacuum container, and the precursor solution is added to the container, and the precursor is attached to the porous carbon substrate by vacuum decompression. The vacuum method can effectively remove the gas adsorbed inside the pores of the porous material, which is conducive to the precursor solution entering the pores and being evenly distributed, while improving the impregnation efficiency.

[0028] In addition, there are many methods and ways to achieve the coating, such as brush, roller, electroplating, dipping, in-situ growth, spraying method, chemical vapor deposition or physical vapor deposition, etc. can all be used to apply the coating.

[0029] Preferably, in step (4), the heating rate of the heat treatment is 5 to 10° C. / min, and the treatment time is 3 to 5 hours.

[0030] In order to achieve the third object, the present invention also provides the use of the above-mentioned porous composite electrode as a positive electrode in a bromine-based battery.

[0031] In order to achieve the fourth object, the present invention also provides a bromine-based aqueous battery, wherein the positive electrode adopts the above-mentioned porous composite electrode, the negative electrode selects zinc sheet, and the electrolyte contains 1-3M zinc bromide (active substance), 1-3M potassium chloride (supporting electrolyte) and 0.1-0.5M 1-methyl-1-ethylpyrrolidine bromide (bromine complexing agent MEP), wherein M represents mol / L. 2 As the active material of the battery, KCI acts as a supporting electrolyte to improve the ionic conductivity of the electrolyte, and MEP acts as a bromine complexing agent to complex polybromines.

[0032] In the bromine-based aqueous battery of the present invention, the types of polybrominates include Br 2 Through electrochemical-chemical mechanism - The polybrominated Br 3 - Br 5 - Br 7 - etc. polybrominated anions, the reaction formula is as follows:

[0033]

[0034] The polybrominated anion combines with the cation Q, and the reaction formula is as follows:

[0035]

[0036] Among them, the cation Q includes tetramethylammonium cation, tetraethylammonium cation, tetrabutylammonium cation, tetrapropylammonium cation, N-methyl-N-ethylimidazolium cation, N-methyl-N-butylpyrrole cation, 1-methyl-3-propylimidazolium cation, 1-ethyl-3-methylimidazolium cation and N-butyl-N-methylpiperidinium cation, etc.

[0037] The composite electrode of the present invention is used in the cathode-induced polybromide reaction in a bromine-based aqueous battery, and the reaction equation is as follows:

[0038]

[0039] Beneficial effects:

[0040] (1) The porous composite electrode of the present invention has a high specific surface area (2 to 5 m 2 / g), high conductivity (2.5-10S / cm) and excellent electrocatalytic activity, which are beneficial to the reversible transformation of polybromines, can greatly improve the charge and discharge efficiency of bromine-based aqueous batteries (charge and discharge efficiency increased by about 15%), and reduce battery polarization; secondly, it has high mechanical and chemical stability. After the porous composite electrode is immersed in an acidic or alkaline solution for 200 hours, the precious metal oxide coating attached to the electrode does not fall off. The battery is assembled with the porous composite electrode after immersion, and the battery can still be stably cycled without performance degradation. . Therefore, the present invention is the first to use a porous composite electrode modified with a precious metal oxide coating as the cathode of a bromine-based battery, which has a superior effect on the catalysis of polybromines, so that the overall performance of bromine-based aqueous batteries is greatly improved.

[0041] (2) The porous composite electrode obtained by the present invention achieves a voltage efficiency of 90% and an energy efficiency greater than 80%. The short-term stability of the composite electrode is evaluated by performing 100 charge / discharge cycles, and the voltage efficiency and energy efficiency retention rate can reach 99.9% after each operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0043] Figure 1 The ruthenium-coated graphite felt composite electrode (RuO 2 Optical images of the original graphite felt electrode (GF) and the original graphite felt electrode (GF).

[0044] Figure 2 XRD patterns of the ruthenium-coated graphite felt composite electrode and the original graphite felt electrode prepared in Example 1;

[0045] Figure 3 The battery charge and discharge curves of the positive electrodes of the ruthenium-coated graphite felt composite electrode of Example 1, the original graphite felt electrode, and the ruthenium-coated titanium electrode of Comparative Example 2 are respectively shown. DETAILED DESCRIPTION

[0046] The present invention can be better understood with reference to the following examples.

[0047] Example 1

[0048] Commercial graphite felt with a thickness of 5 mm was used as the substrate for the precious metal oxide coating. Before deposition, a piece of 6 cm × 6 cm graphite felt was cut as the substrate (GF). The graphite felt was first soaked in acetone for 24 hours to remove surface grease, washed with deionized water, and then hydrothermally heated at 80 ° C for 8 hours using concentrated nitric acid to improve the hydrophilicity and affinity of the graphite felt surface. After washing with deionized water, it was dried for use. 20 mg of ruthenium chloride was dissolved in 20 ml of deionized water under magnetic stirring, 2 ml of hydrochloric acid was added and stirred evenly, and the graphite felt was immersed in vacuum decompression for 30 seconds and then taken out, and annealed at 350 ° C for 3 hours in a muffle furnace (heating rate: 10 ° C / min) to obtain a ruthenium-coated graphite felt composite electrode (RuO 2 @GF), such as Figure 1 The ruthenium-coated graphite felt composite electrode sample was tested using X-ray diffraction technology. Figure 2 As shown, the test results show that the surface of the graphite felt contains a ruthenium oxide coating.

[0049] The obtained ruthenium-coated graphite felt composite electrode was used as the positive electrode of the zinc-bromine battery. The negative electrode was a zinc sheet that had been soaked in acetone in advance and the surface oxide layer was polished with sandpaper. The composition of the electrolyte was 2M ZnBr2 +2M KCI+0.4MMEP, ZnBr 2 As the active material of the battery, KCI acts as a supporting electrolyte to improve the ionic conductivity of the electrolyte, and MEP acts as a bromine complexing agent to complex polybromines. Using a customized battery mold, the battery is assembled, and the charge and discharge tests are performed and the battery voltage is monitored. Figure 3 As shown, it was found that the voltage efficiency of the battery was 90% and the energy efficiency could reach 82%. The short-term stability of the porous composite electrode was evaluated by performing 100 charge / discharge cycles, and the voltage efficiency retention rate could reach 99.9% after each run.

[0050] Example 2

[0051] Commercial graphite felt with a thickness of 5 mm was used as the substrate for the precious metal oxide coating. Before deposition, a piece of 6 cm × 6 cm graphite felt was cut as the substrate. The graphite felt was first soaked in acetone for 24 hours to remove surface grease, washed with deionized water, and then hydrothermaled at 80 ° C for 8 hours using concentrated nitric acid to improve the hydrophilicity and affinity of the graphite felt surface. After washing with deionized water, it was dried for use. 10 mg of ruthenium chloride and 10 mg of chloroiridic acid were dissolved in 20 ml of deionized water under magnetic stirring, 2 ml of hydrochloric acid was added and stirred evenly, and the graphite felt was immersed in vacuum decompression for 30 seconds and then taken out, and annealed at 350 ° C for 3 hours in a muffle furnace (heating rate: 10 ° C / min) to obtain a ruthenium-iridium coated graphite felt composite electrode.

[0052] The obtained ruthenium-iridium coated graphite felt composite electrode was used as the positive electrode of the zinc-bromine battery, and the negative electrode was a zinc sheet that had been soaked in acetone in advance and the surface oxide layer was polished with sandpaper. The composition of the electrolyte was 2M ZnBr 2 +2M KCI+0.4MMEP. Using a customized battery mold, the battery was assembled, and the charge and discharge tests were performed and the battery voltage was monitored. It was found that the battery voltage efficiency was 90%, and the energy efficiency could reach 82.5%. The short-term stability of the porous composite electrode was evaluated by performing 100 charge / discharge cycles, and the voltage efficiency retention rate could reach 99.9% after each operation.

[0053] Example 3

[0054] A carbon cloth with a thickness of 0.5 mm was used as the substrate for the precious metal oxide coating. Before deposition, a piece of 6 cm × 6 cm carbon cloth was cut as the substrate. The carbon cloth was first soaked in acetone for 24 hours to remove surface grease, washed with deionized water, and then hydrothermally heated at 80 ° C for 8 hours using concentrated nitric acid to improve the hydrophilicity and affinity of the carbon cloth surface. After washing with deionized water, it was dried for use. 10 mg of ruthenium chloride and 10 mg of platinum chloride were dissolved in 20 ml of deionized water under magnetic stirring, 2 ml of hydrochloric acid was added and stirred evenly, the carbon cloth was vacuum-decompressed and immersed for 30 seconds, then taken out, and annealed at 350 ° C for 3 hours in a muffle furnace (heating rate: 10 ° C / min) to obtain a ruthenium-platinum coated carbon cloth composite electrode.

[0055] The obtained ruthenium-platinum-coated carbon cloth composite electrode was used as the positive electrode of the zinc-bromine battery. The negative electrode was a zinc sheet that had been soaked in acetone in advance and the surface oxide layer was polished with sandpaper. The composition of the electrolyte was 2M ZnBr 2 +2M KCI+0.4MMEP. Using a customized battery mold, the battery was assembled, and the charge and discharge tests were performed and the battery voltage was monitored. It was found that the battery voltage efficiency was 90%, the energy efficiency could reach 81%, and the short-term stability of the porous composite electrode was evaluated by performing 100 charge / discharge cycles. After each operation, the voltage efficiency retention rate could reach 99.9%.

[0056] Example 4

[0057] A commercial carbon felt with a thickness of 5 mm was used as the substrate for the precious metal oxide coating. Before deposition, a piece of 6 cm × 6 cm carbon felt was cut as the substrate. The carbon felt was first soaked in acetone for 24 hours to remove surface grease, washed with deionized water, and then hydrothermaled at 80 ° C for 8 hours using concentrated nitric acid to improve the hydrophilicity and affinity of the carbon felt surface. After washing with deionized water, it was dried for use. 7 mg of ruthenium chloride, 7 mg of chloroiridic acid, and 7 mg of platinum chloride were dissolved in 20 ml of deionized water under magnetic stirring, 2 ml of hydrochloric acid was added and stirred evenly, and the graphite felt was immersed in vacuum decompression for 30 seconds and then taken out, and annealed at 350 ° C for 3 hours in a muffle furnace (heating rate: 10 ° C / min) to obtain a ruthenium iridium platinum coated carbon felt composite electrode.

[0058] The obtained ruthenium-iridium-platinum coated carbon felt composite electrode was used as the positive electrode of the zinc-bromine battery. The negative electrode was a zinc sheet that had been soaked in acetone in advance and the surface oxide layer was polished with sandpaper. The composition of the electrolyte was 2M ZnBr 2 +2M KCI+0.4MMEP. Using a customized battery mold, the battery was assembled, and the charge and discharge tests were performed and the battery voltage was monitored. It was found that the battery voltage efficiency was 90%, and the energy efficiency could reach 82.5%. The short-term stability of the porous composite electrode was evaluated by performing 100 charge / discharge cycles, and the voltage efficiency retention rate could reach 99.9% after each operation.

[0059] Comparative Example 1

[0060] In the comparative example, the cathode uses an unmodified commercial graphite felt with a thickness of 5 mm. Before use, a piece of graphite felt of 6 cm×6 cm is cut, immersed in acetone overnight to remove surface grease, washed with deionized water, and then hydrothermally heated at 80°C for 8 hours using concentrated nitric acid to improve the hydrophilicity and affinity of the graphite felt surface, washed with deionized water, and dried for use.

[0061] The pretreated graphite felt electrode was used as the positive electrode of the zinc-bromine battery. The negative electrode was a zinc sheet that had been soaked in acetone in advance and had its surface oxide layer removed by sandpaper. The electrolyte composition was 2M ZnBr 2 +2M KCI+0.4M MEP. Using a customized battery mold, the battery was assembled, and the charge and discharge tests were performed and the battery voltage was monitored. It was found that the battery voltage efficiency was 85% and the energy efficiency was only 65%. The stability of the electrode was evaluated by performing 100 charge / discharge cycles. As the cycle ran, the voltage efficiency and energy efficiency decreased after each run.

[0062] Comparative Example 2

[0063] In comparative example 2, an industrial pure titanium (TA2) plate is used as the substrate of the oxide coating. Before deposition, a 6cm×6cm piece of pure titanium is cut as a substrate, and the substrate is sandblasted to remove impurities, variegated colors and oxide layers on the surface. At the same time, the sandblaster roughens the surface of the titanium substrate, increases the effective contact area of ​​the titanium surface, and enhances the adhesion between the coating and the titanium surface. Then, it is etched in a boiling solution of 20% oxalic acid for 2 to 3 hours, washed with distilled water, dried in air, and finally stored in ethanol. A ruthenium salt solution is used as a metal precursor, and the molar ratio of ruthenium salt, citric acid and ethylene glycol is 1:4.6:0.3. Citric acid is dissolved in ethanol, mixed with the ruthenium salt ethanol solution and the ethylene glycol solution, and stirred continuously at 60°C. The obtained solution is heated at 100-140°C for 24h, and the solution is continuously stirred for about 7 days to obtain a high-viscosity polyester resin. The obtained coating sol was coated on a pretreated titanium plate and dried under an infrared lamp. The sample was sintered in a muffle furnace at 450° C. for 10 minutes and then cooled to room temperature to obtain a ruthenium-coated titanium electrode.

[0064] The obtained ruthenium-coated titanium electrode was used as the positive electrode of the zinc-bromine battery. The negative electrode was a zinc sheet that had been soaked in acetone in advance and the surface oxide layer was polished off with sandpaper. The composition of the electrolyte was 2M ZnBr 2 +2M KCI+0.4M MEP. Using a customized battery mold, the battery was assembled, and the charge and discharge tests were performed and the battery voltage was monitored. It was found that the battery voltage efficiency was 86% and the energy efficiency was only 69%.

[0065] Figure 3 The following are the charge and discharge curves of the batteries using the ruthenium-coated graphite felt composite electrode of Example 1, the original graphite felt electrode, and the ruthenium-coated titanium electrode of Comparative Example 2 as positive electrodes, respectively. As shown in the figure, the three different batteries mentioned above were charged to 200mAh under the same conditions. The results showed that the battery discharge capacity of the ruthenium-coated graphite felt composite electrode as the positive electrode could reach 190mAh (Coulomb efficiency 95%), and the median voltage was as high as 1.7V, while the battery discharge capacity of the original graphite felt electrode as the positive electrode was only 154mAh (Coulomb efficiency 77%), and the median voltage was only 1.65V. It can be concluded that the metal oxide coating attached to the surface of the ruthenium-coated graphite felt composite electrode has an excellent electrochemical catalytic effect on polybromides. In order to highlight the advantages of the porous composite electrode, the ruthenium-coated titanium electrode was compared with the ruthenium-coated graphite felt composite electrode. Figure 3 It can be seen from the above that the discharge capacity of the battery with ruthenium-coated titanium electrode as the positive electrode is only 160mAh (Coulomb efficiency 80%), and the median voltage is only 1.65V, both lower than that of the ruthenium-coated graphite felt composite electrode. Although both have metal oxide coatings with high catalytic activity for polybromides, the ruthenium-coated graphite felt composite electrode is a 3D porous electrode with a very high specific surface area, which allows it to fully contact with the electrolyte and provide more active sites for the catalytic conversion of polybromides. The ruthenium-coated titanium electrode is a planar electrode with much lower active sites than the ruthenium-coated graphite felt composite electrode. At the same time, polybromides easily cover the electrode surface and increase battery polarization. Therefore, using the ruthenium-coated graphite felt composite electrode as the positive electrode of the bromine-based battery will bring better performance.

[0066] The present invention provides a porous composite electrode for inducing high electrochemical catalytic reaction of polybrominates and its preparation method and application ideas and methods. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A bromine-based aqueous battery, characterized in that: The positive electrode adopts a porous composite electrode that induces a high electrochemical catalytic reaction of polybromides, the negative electrode adopts a zinc sheet, and the electrolyte contains 1~3 M zinc bromide, 1~3 M potassium chloride and 0.1~0.5 M 1-methyl-1-ethylpyrrolidine bromide; The porous composite electrode for inducing high electrochemical catalytic reaction of polybrominates comprises a substrate of porous carbon-based material and a noble metal oxide coating applied on the surface of the substrate; The substrate of the porous carbon-based material is selected from any one of carbon felt, graphite felt and carbon cloth; The noble metal oxide coating is a ruthenium-iridium-platinum oxide coating, a ruthenium-iridium oxide coating or a ruthenium-platinum oxide coating, and the loading amount of the coating is 2-4 g / m 2 ; The porous composite electrode for inducing high electrochemical catalytic reaction of polybrominates is prepared by the following steps: (1) Substrate pretreatment The porous carbon-based material substrate is immersed in acetone to remove surface grease, and then subjected to hydrothermal reaction in concentrated acid to improve the hydrophilicity and affinity of the surface of the porous carbon substrate, and finally washed with water and dried for standby use; (2) Preparation of precious metal oxide coating precursor solution Dissolve the metal salt or alcohol salt containing precious metal in deionized water, and stir and mix thoroughly; (3) Immersion Adhesion Completely immersing the substrate pretreated in step (1) in the precursor solution prepared in step (2); (4) taking out the substrate immersed in the precursor solution in step (3), drying it, and heat treating it at a temperature of 350 to 600° C. to obtain a porous composite electrode that induces a high electrochemical catalytic reaction of polybrominates; In step (1), the temperature of the hydrothermal reaction is 70-90° C., and the reaction time is 8-10 hours; In step (2), the total mass concentration of the noble metal elements in the precursor solution is 1 g / L to 2 g / L; In step (3), the pretreated substrate is immersed in the precursor solution under vacuum pressure, the initial pressure is one atmosphere, the pressure is evacuated to -50 kPa, and the pressure is maintained for 30 seconds; In step (4), the heating rate of the heat treatment is 5-10°C / min, and the treatment time is 3-5 hours.

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