An etched graphene oxide hybrid membrane for aqueous organic flow batteries, methods of making and uses

Abstract

The application discloses a simple and rapid etching method of graphene oxide and application thereof. The etching method is sulfuric acid etching, and more oxygen-containing groups are exposed by twice oxidation of sulfuric acid, and more ion transmission channels are provided by penetrating pore-forming on the surface of two-dimensional sheet layer. In the application, sulfonated polyether ether ketone with low cost and simple synthesis process is selected as a polymer substrate, and etching graphene oxide is used as a filler to prepare a flow battery diaphragm by doping with the polymer substrate. On one hand, the etching graphene oxide contains more exposed oxygen-containing groups, and is more conducive to forming hydrogen bonds with sulfonic acid groups in the polymer substrate, so as to promote ion transmission. On the other hand, the two-dimensional sheet layer of the etching graphene oxide hinders ion transmission, and the etching can make the size of the two-dimensional sheet layer be fragmented and penetrate pore-forming on the surface, so that more transmission channels are provided by the surface channels. The ion transmission capacity of the etching graphene oxide is improved while the high ion selectivity of the etching graphene oxide is retained, so that the double performance of the hybrid membrane is improved.

Description

Technical Field

[0001] This invention relates to a hybrid membrane for aqueous organic flow batteries, its preparation method, and its application, belonging to the technical field of aqueous organic flow batteries. Background Technology

[0002] The rapid development of human society and economy has led to a dramatic increase in energy demand. The massive consumption of fossil fuels has resulted in serious environmental and social problems. The demand for and utilization of renewable energy has received particular attention. Wind and solar energy, due to their cleanliness and renewability, have seen significant development as alternative energy sources. However, due to the inherent randomness and intermittency of renewable alternative energy sources, large-scale, cost-effective energy storage systems have attracted considerable attention. Large-scale energy storage technologies include physical energy storage, electromagnetic energy storage, electrochemical energy storage, and thermal energy storage (TES). Among the energy storage devices successfully applied in practice, redox flow batteries (RFBs) are considered to have the greatest potential for large-scale energy storage applications due to their high safety, long cycle life, and flexible site selection.

[0003] Most widely studied aqueous redox flow batteries (ARFBs), such as all-vanadium, iron / chromium, and zinc / bromine RFB systems, are based on inorganic redox pairs, particularly metal-based electroactive materials. Due to the inherent limitations of inorganic redox species, the widespread adoption of traditional ARFBs is restricted by relatively low coulombic efficiency and high system cost. The utilization of redox-active organic species in aqueous redox flow batteries offers great promise for large-scale and sustainable energy storage. Sulfonated polyether ether ketone (PEEK) materials are used in the RFB field due to their ease of synthesis and low cost; however, their performance is significantly affected by the degree of sulfonation. High sulfonation results in low ion selectivity, while low sulfonation leads to low ion conductivity. Therefore, developing a stable, efficient, and low-cost battery separator is of long-term significance for the development of flow batteries. Summary of the Invention

[0004] This invention addresses the problems mentioned in the background section by providing a hybrid membrane for aqueous organic flow batteries, its preparation method, and its applications.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A hybrid membrane for an aqueous organic flow battery includes an inorganic filler and a polymer substrate casting solution. The inorganic filler is graphene oxide oxidized by secondary sulfuric acid, and the polymer substrate is sulfonated polyether ether ketone (SPEEK), which is easy to synthesize and has a low cost, with a sulfonation degree ranging from 50% to 75%. The sulfonated SPEEK casting solution is doped with etched graphene oxide (PGO) filler to form the membrane.

[0007] Etching graphene oxide materials is used to improve the mechanical strength, hydrophilicity, and voltage efficiency of hybrid films.

[0008] The weight ratio of etched graphene oxide in the polymer substrate is 0.1%-10%, preferably 0.5%-4%; the thickness of the hybrid film is 10-70 μm, preferably 20-40 μm.

[0009] A method for preparing a hybrid membrane for an aqueous organic flow battery includes the following steps:

[0010] S1: Add sulfuric acid and graphene oxide in a mass-to-volume ratio of 0.008-0.02:3-5 to the reaction solvent, stir vigorously until completely mixed, then transfer to a high-pressure reactor and react at 60-120℃ for 6-20 hours. Wash with water to remove acid and freeze dry to obtain etched graphene oxide.

[0011] S2: Mix the etched graphene oxide filler with the sulfonated polyether ether ketone casting solution in a certain proportion;

[0012] S3: Add grinding beads to the mixture, stir evenly and remove air bubbles, then pour the solution onto the substrate;

[0013] S4: After drying the film obtained on the substrate, a hybrid film is obtained.

[0014] In step S1, the solvent used is DMF, and the deacidification process uses deionized water.

[0015] Application of a hybrid membrane for aqueous organic flow batteries in flow batteries.

[0016] The aforementioned flow battery is an aqueous organic flow battery with ferrocyanide as the positive electrode and phenazine derivative as the negative electrode.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] This invention involves doping graphene oxide material with surface pores with sulfonated polyether ether ketone (PEE ketone) to create a hybrid membrane. The resulting membrane exhibits optimized ion selectivity and ion conductivity, thus developing a new generation of high-performance PEMs for RFB (Reduction-Based Fluid) systems. By adding surface-pore graphene oxide material to a polymer substrate, this invention improves the application of the hybrid membrane in redox flow batteries, including vanadium redox flow batteries, zinc-iron flow batteries, and aqueous organic flow batteries. Introducing etched graphene oxide material allows its oxygen-containing groups to form hydrogen bonds with sulfonic acid groups in the polymer substrate, and the pores remaining on the etched surface effectively enhance the ion selectivity and ion conductivity of the hybrid membrane. Attached Figure Description

[0019] Figure 1The images are: a) Infrared images of GO and PGO; b) Raman images of GO and PGO; c) TEM image of GO; d) TEM image of PGO.

[0020] Figure 2 TEM characterization of graphene oxide obtained under different etching conditions

[0021] Figure 3 These are SPEEK / PGO-X cross-sectional electron micrographs (X = 0, 0.5, 1, 2, 3, 4%).

[0022] Figure 4 The following are the properties of SPEEK / PGO-X: a) proton conductivity, b) water absorption and swelling rate, c) tensile strength, and d) organic matter permeation and selectivity (X = 0, 1, 2, 3, 4, 5%).

[0023] Figure 5 Here are schematic diagrams of flow batteries: a) Performance diagram of an aqueous organic flow battery; b) CE; c) VE; d) EE at 20-100 mA / cm². -2 Under current density

[0024] Figure 6 The diagrams for the cycle test of an aqueous organic flow battery are a) CE, b) EE (current density of 80 mA / cm²). -2 )

[0025] Figure 7 This is a comparative experiment of battery performance using SPEEK / GO-X films. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention discloses a simple and rapid method for etching graphene oxide (GO) and its applications. The method described in this invention involves sulfuric acid etching, which exposes more oxygen-containing groups through secondary oxidation with sulfuric acid, creating pores on the surface of the two-dimensional sheet and providing more ion transport channels. Sulfonated polyether ether ketone (SPEEK), which has low cost and a simple synthesis process, is selected as the polymer substrate.

[0028] Etched graphene oxide (PGO) is used as a filler and doped with it to prepare flow battery separators. On the one hand, etched graphene oxide contains more exposed oxygen-containing groups, which are more conducive to forming hydrogen bonds with sulfonic acid groups in the polymer substrate, promoting ion transport. On the other hand, the two-dimensional sheets of graphene oxide hinder ion transport. Etching can fragment its size and create pores through the surface. The surface pores provide more transport channels, thus improving its ion conductivity while retaining the high ion selectivity of graphene oxide, thereby achieving a dual performance improvement of the hybrid film.

[0029] The PGO used in the following examples is a hydrophilic material with surface pores, and graphene oxide is a stable material resistant to strong acids and alkalis, suitable for use in aqueous organic flow batteries. The oxygen-containing groups on the edges of GO itself can transport ions. The oxygen-containing groups exposed by etching form a hydrogen bond network with the sulfonic acid groups in the polymer substrate, which can promote ion transport. The surface pores remaining after etching can further enhance the ion transport capability.

[0030] For the materials in this invention, the degree of sulfonation of sulfonated polyether ether ketone is controlled at 60%-70%. Excessive or insufficient sulfonation has an impact. When the degree of sulfonation is high, its ion selectivity is low; when the degree of sulfonation is low, its ion conductivity is low.

[0031] Example 1

[0032] Synthesis and Etching of Graphene Oxide

[0033] Synthesis of GO: 2g of graphite powder and 2g of sodium nitrate were mixed in a 500ml beaker. 96ml of concentrated sulfuric acid was added and stirred until homogeneous. 12g of potassium permanganate was added in four portions, each addition lasting approximately 10 minutes, at a rotation speed of 230 rpm. Using a syringe pump, 80ml of water was added in two portions, with the program set to draw 40ml from a 60ml volume, at an injection rate of 2ml / min. The temperature was controlled at 60-70℃, and water addition was stopped promptly based on temperature changes. 200ml of water was added in five portions using the same syringe pump. 10ml of hydrogen peroxide was added, generating numerous bubbles during this process; stirring was continued for approximately 30 minutes. The product was centrifuged and washed 4-5 times. Then, 100ml of concentrated hydrochloric acid was added, and the mixture was allowed to stand in the beaker for 24 hours. The supernatant was collected, centrifuged again until neutral, and then freeze-dried to obtain GO.

[0034] Synthesis of PGO: GO and sulfuric acid (3M) were added to a reaction flask at a mass-to-volume ratio of 0.01:4. The mixture was stirred vigorously until completely mixed, and then transferred to a high-pressure reactor and reacted at 100°C for 15 hours. After sedimentation, a large amount of acid in the supernatant was removed. The product was etched and washed repeatedly by centrifugation to remove residual acid. After freeze-drying, the product PGO was obtained.

[0035] Infrared images, Raman images, and TEM images of the product, such as Figure 1 As shown.

[0036] Characterization results of graphene oxide obtained under different etching conditions are shown in [reference needed]. Figure 2 It can be seen that if the etching time is too short, an open-pore structure cannot be formed, while if the etching time is too long, the structure of the nanosheet will be destroyed.

[0037] Example 2

[0038] Preparation of SPEEK / PGO hybrid film

[0039] SPEEK was prepared by adding peek powder to a 1000 ml three-necked flask, reacting it in a water bath, and then sulfonating it with 98 wt.% sulfuric acid for 5 hours.

[0040] SPEEK and PGO were dissolved in N,N-dimethylformamide at a concentration ratio of 1.5 g / 10 ml, and a certain volume of each solution was weighed out according to the mass fraction ratio and mixed thoroughly. The mixed casting solution was ultrasonically and ball-milled to form a homogeneous SPEEK / PGO casting solution. A 400 mm doctor blade was used to coat the solution onto a glass plate, which was then transferred to an oven. The temperature was set at 60℃ and then increased to 100℃ until completely dried. The resulting hybrid film is denoted as SPEEK / PGO-X, where X represents the mass percentage of PGO in the total material.

[0041] In contrast, GO-hybrid polymer films without etching were also prepared for battery performance testing, SPEEK / GO-X. In comparison, the amount of GO added to the polymer film was 0.5%-4%.

[0042] Test methods

[0043] Swelling rate and water absorption rate

[0044] The membrane's SR (swelling ratio) and WU (water absorption ratio) are obtained from the following two equations:

[0045]

[0046] In the formula, d and W are the diameter and mass of the membrane in the wet and dry states, respectively.

[0047] Test results are as follows Figure 4 As shown in b).

[0048] Mechanical properties

[0049] At a tensile speed of 5mm / min -1The mechanical properties of the membrane were obtained using a universal testing machine. Samples were cut into strips of 35mm × 10mm. Before testing, the wet membrane surface was wiped dry. To minimize testing error, three samples were tested for each membrane, and the data were averaged. The formula for calculating the tensile strength of the thin film sample is as follows:

[0050]

[0051] In the formula, F Max The maximum tension is given by W and D, which represent the width and thickness of the sample film, respectively. The test results are as follows: Figure 3 As shown in d).

[0052] Proton transfer rate

[0053] The proton transfer rate of the membrane was measured using electrochemical impedance spectroscopy on an electrochemical workstation (Solartron analytical 1470E+1260A). The sample was clamped between two circular titanium plates, which were secured with button battery clips. The measurement frequency was 10 Hz. 3 Up to 10 6 Between Hertz, the AC amplitude is 5 mV. The proton transfer rate of the membrane was measured using the latest method from Professor Li's team, and the calculation formula is as follows:

[0054]

[0055] In the formula, σ is the proton transfer rate of the membrane. L is the thickness of the sample. R is the impedance of the membrane. A is the effective area of ​​the membrane, i.e., the area of ​​the titanium sheet. The test results are as follows: Figure 4 As shown in a).

[0056] The film surface resistance can be calculated using the following formula:

[0057] RA = R × A

[0058] R A It is the film surface resistance.

[0059] Ion permeation rate and ion selectivity

[0060] With an effective area of ​​0.78 cm 2 The test was conducted in an H-type diffusion cell. One diffusion cell contained 50 mL of 1M KOH + 0.1M BHPC solution or 1M KOH + 0.2M potassium ferrocyanide solution, while the other diffusion cell contained the same volume of 1M KOH solution. Magnetic stirring was used during the test to reduce concentration polarization. Samples were taken from the aqueous solution every 12 hours, and the absorbance was measured at 315 nm / 323 nm using a UV-Vis spectrophotometer. The BHPC organic compounds or F... were identified using a standard absorbance / concentration curve. e 2+The concentration of organic matter and ferrocyanide in BHPC can be calculated using the following formula:

[0061]

[0062] Where V B The volume of 1M KOH + 0.1M BHPC solution is 50 ml in this experiment; C B (t) represents the concentration of BHPC organic matter in a 1M KOH + 0.1MBHPC solution at time t; C A The concentration of BHPC organic matter in a 1M KOH + 0.1M BHPC solution can be considered a constant to simplify calculations, provided the experimental time is not too long. A and L represent the effective membrane area and membrane thickness, respectively; P is the permeation rate of BHPC organic matter. The results are as follows: Figure 4 As shown in d).

[0063] Ion selectivity is defined as the relationship between proton transfer rate and BHPC organic matter. - The ratio of permeation rates is calculated using the following formula:

[0064]

[0065] Basic characterization of membranes

[0066] Figure 3 It is a photograph of a cross-section of the diaphragm. Figure 4 The following are the properties of SPEEK / PGO-X: a) proton conductivity, b) water absorption and swelling rate, c) tensile strength, and d) organic matter permeation and selectivity (X = 0, 1, 2, 3, 4, 5%).

[0067] Single battery performance

[0068] The performance of the self-made aqueous organic flow battery (AORFBs) was tested using a membrane (effective distance 10.5 cm). 2 The system consists of a carbon felt electrode, two graphite plate current collectors, and a pair of housings. A membrane separates the negative electrode electrolyte (10 ml 1M KOH + 0.1M BHPC) and the positive electrode electrolyte (40 ml 1M KOH + 0.2M potassium ferrocyanide), and is sandwiched between the two electrodes. For charge / discharge testing, the cutoff voltages for charging and discharging are 1.7V and 0.8V, respectively, and the test current densities are 20, 40, 60, 80, and 100 mA / cm². -2 For cyclic testing, the constant current density is 80 mA cm⁻¹. -2 Tested at the same cutoff voltage. Nitrogen protection was used during the test. The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of the battery were calculated using the following formulas:

[0069]

[0070] Where C d and C c These are discharge capacity and charge capacity, respectively; E d and E c These are discharge energy and charging energy, respectively.

[0071] The AORFBs performance of the SPEEK / PGO-X hybrid membrane was evaluated (at 20-100 mA cm⁻¹). -2 (Under a series of current densities). For example... Figure 5 , 6 As shown, doping with PGO can significantly improve the battery performance (CE, VE) of the SPEEK film. This result indicates that incorporating etched graphene oxide materials into polymers can effectively improve battery performance. Figure 5 As can be seen, the battery performance parameters reach their optimal level when the PGO doping concentration is 2%. This is because a smaller PGO doping concentration cannot effectively improve the proton transport rate, while a larger doping concentration will affect the surface structure of the film and degrade battery performance. Furthermore, during the PGO etching process, if the etching time is too short, the surface structure of GO cannot be significantly altered, while a longer etching time will lead to structural damage, also affecting battery performance.

[0072] In addition, the comparative experimental results of SPEEK / GO-X membranes are as follows: Figure 7 Compared to SPEEK / PGO-X, both its coulombic efficiency and voltage efficiency decreased.

[0073] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. The application of a hybrid membrane in an aqueous organic flow battery, wherein the flow battery is an aqueous organic flow battery with a positive electrode of ferrocyanide and a negative electrode of a phenazine derivative, characterized in that... The hybrid film comprises an inorganic filler and a polymer substrate, wherein the inorganic filler is etched graphene oxide (GO) and is dispersed in the polymer substrate; The etching process mentioned refers to sulfuric acid etching of graphene oxide; The preparation method of the hybrid membrane includes the following steps: S1: Add sulfuric acid and graphene oxide to the reaction solvent, stir vigorously until completely mixed, then transfer to a high-pressure reactor and react at 60-120℃ for 6-20 h. Wash with water to remove acid and freeze dry to obtain etched graphene oxide. S2: Mix the etched graphene oxide filler with the sulfonated polyether ether ketone casting solution in a certain proportion; S3: Add grinding beads to the mixture, stir evenly and remove air bubbles, then pour the solution and coat it onto the substrate; S4: After drying the film obtained on the substrate, a hybrid film is obtained; The weight percentage of etched graphene oxide (GO) in the polymer substrate is 0.5%-4%. The method for preparing a hybrid membrane is characterized in that, in step S1, the mass-to-volume ratio of sulfuric acid to graphene oxide is 0.008-0.02:3-5, and the reaction conditions in the high-pressure reactor are 60-120℃ for 6-20 h. In step S2, the solvent used in the sulfonated polyether ether ketone casting solution is DMF, and deionized water is used in the deacidification process.

2. The application according to claim 1, characterized in that, The polymer substrate is sulfonated polyether ether ketone with a sulfonation degree ranging from 50% to 75%.

3. The application according to claim 1, characterized in that, The thickness of the hybrid film is 10-70 μm.

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