Iron-chromium liquid flow battery negative chromium reaction side catalytic carbon felt electrode and preparation method thereof

Abstract

The application discloses a kind of for iron-chromium liquid flow battery negative pole chromium reaction side catalytic carbon felt electrode and preparation method, the electrode includes porous carbon felt matrix and the bismuth-cobalt double coordination polymer catalytic layer supported on its surface, the catalytic layer is generated by bismuth source, cobalt source and organic ligand under hydrothermal condition in situ reaction and is supported on carbon felt surface.The preparation method includes: carbon felt is pretreated by pickling;Bismuth source, cobalt source and organic ligand are added in deionized water to form mixed precursor solution;Carbon felt is immersed in mixed precursor solution and is placed in polytetrafluoroethylene lining autoclave, and is reacted at 100-160 ℃ for 48-96 h, after cooling, take out, wash and dry to obtain catalytic electrode.The electrode is used for the negative pole of iron-chromium liquid flow battery, can improve Cr 3+ / Cr 2+ Reaction kinetics and inhibit hydrogen evolution side reaction, so as to reduce polarization, improve coulombic efficiency and energy efficiency and improve cycle stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery and its preparation method. Background Technology

[0002] Redox flow batteries store energy through reversible redox reactions of soluble active materials in an external tank, offering advantages such as power-energy decoupling, modularity, scalability, and long lifespan. Iron-chromium flow batteries are one of the earliest developed and widely studied aqueous flow battery systems, typically using Fe3C in an acidic aqueous solution. 2+ / Fe 3+ With Cr 2+ / Cr 3+ As an electric pair.

[0003] However, the actual efficiency and lifespan of iron-chromium flow batteries are largely limited by the kinetic constraints of the chromium couple on the negative electrode side and the hydrogen evolution side reaction. 3+ / Cr 2+ Slow redox kinetics in chromium redox couples lead to significant polarization and reduced power density. Simultaneously, because the potential of the chromium redox couple is close to the hydrogen evolution potential, hydrogen evolution easily occurs in acidic media, reducing coulombic efficiency and causing gas management, safety, and electrolyte imbalance problems. Porous carbon felt / graphite felt is a commonly used electrode due to its good conductivity, chemical stability, and suitable pore structure, but its resistance to chromium redox couples is significant. 3+ / Cr 2+ The intrinsic reactivity and surface wettability of the reaction may be insufficient, making it difficult to simultaneously achieve both the chromium reaction rate and hydrogen evolution inhibition.

[0004] To improve anode performance, existing technologies often employ Bi-based catalysis strategies, such as adding Bi to the electrolyte. 3+ In-situ electrodeposition is performed during operation. However, published studies indicate that this type of in-situ electrodeposition may lead to uneven deposition distribution, increased flow resistance, or even pore blockage. Furthermore, Bi requires "bismuth management" due to deposition / dissolution, and may cause increased hydrogen evolution under certain operating conditions. Existing patents also disclose schemes for coating multi-metal catalysts to promote chromium reactions, but a catalytic electrode that can achieve stable immobilization through synthesis and balance kinetics and hydrogen evolution inhibition without blocking the pore structure is still lacking.

[0005] Therefore, a new negative electrode and its preparation method are urgently needed to improve Cr 3+ / Cr 2+ Improve reaction kinetics and reduce hydrogen evolution, while avoiding the risks of non-uniformity and blockage caused by electrodeposition during operation. Summary of the Invention

[0006] The purpose of this invention is to provide a highly active and stable catalytic electrode suitable for the chromium reaction side of the negative electrode in iron-chromium flow batteries, and its preparation method, in order to solve the problem of Cr commonly present in existing negative electrodes in acidic electrolytes. 3+ / Cr 2+ It avoids problems such as slow redox kinetics, high polarization, poor reversibility, and severe hydrogen evolution side reactions, thereby avoiding defects such as reduced coulombic efficiency and energy efficiency, aggravated gas evolution and electrolyte imbalance, and limited long-term operational stability and safety.

[0007] To achieve the above objectives, this invention constructs a bismuth-cobalt dual-coordination polymer catalytic layer on the surface of acid-washed carbon felt. This achieves synergistic catalysis of the chromium reaction and inhibition of hydrogen evolution without significantly increasing mass transfer resistance and reducing the risk of uneven deposition and blockage. This improves the rate performance, coulombic efficiency, energy efficiency, and cycle life of the iron-chromium flow battery.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A catalytic carbon felt electrode includes a porous carbon felt matrix and a bismuth-cobalt dual-coordination polymer catalytic layer supported on the surface of the carbon felt matrix; wherein the dual-coordination polymer is generated by reacting a bismuth source, a cobalt source and an organic ligand.

[0009] A catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery is characterized by comprising a porous carbon felt matrix and a bismuth-cobalt dual-coordination polymer catalytic layer supported on the surface of the porous carbon felt matrix; the bismuth-cobalt dual-coordination polymer catalytic layer is generated by an in-situ reaction of a bismuth source, a cobalt source and an organic ligand under hydrothermal conditions and is immobilized on the surface of the porous carbon felt matrix.

[0010] The organic ligand is 2,4-pyridinedicarboxylic acid.

[0011] The bismuth source is selected from one or more of bismuth nitrate, bismuth sulfate, organic carboxylic acid bismuth, ethyl camphorate bismuth, and isooctanoate bismuth.

[0012] The cobalt source is selected from one or more of cobalt acetate, cobalt sulfate, cobalt nitrate, cobalt naphthenate, and cobalt isooctanoate.

[0013] The porous carbon felt matrix is ​​acid-washed before hydrothermal reaction, and the acid washing is performed using hydrochloric acid, sulfuric acid, nitric acid or a mixture thereof.

[0014] The acid concentration for the pickling treatment is 0.5–3 mol / L, the pickling temperature is room temperature to 80 °C, and the pickling time is 0.5–24 h.

[0015] The hydrothermal conditions are 100–160℃ and the reaction time is 48–96 h.

[0016] The molar ratio of the bismuth source to the cobalt source in the precursor solution is 1:(0.2–5).

[0017] A preparation method includes the following steps: Step 1) Carbon felt pretreatment: Immerse the carbon-based electrode material in an acidic solution and perform ultrasonic cleaning. Remove the electrode material and wash it with deionized water until neutral, then dry it for later use.

[0018] Step 2) Prepare the precursor solution: Add appropriate amounts of bismuth source and cobalt source to deionized water, and add appropriate amounts of organic ligands, and stir thoroughly to form a mixed solution; Step 3) Hydrothermal reaction: Transfer the mixed solution to a polytetrafluoroethylene-lined autoclave, add pretreated carbon felt and immerse it, react fully in a water bath, and then cool naturally to room temperature.

[0019] Step 4) Post-processing: Remove the carbon felt, wash it at least three times with distilled water or deionized water, and dry it in a vacuum drying oven to obtain a carbon felt electrode loaded with bismuth-cobalt dual coordination polymer.

[0020] In this application, the electrode is used as the negative electrode chromium reaction side of an iron-chromium flow battery to promote the reaction of Cr. 3+ / Cr 2+ It can react with redox reactions and inhibit hydrogen evolution reactions.

[0021] Preferably, in step 1), the carbon-based electrode material is carbon felt, graphite felt, or carbon cloth; the pickling can be done with hydrochloric acid, sulfuric acid, nitric acid, or a mixture thereof, with a concentration of 1-3 mol / L, a pickling temperature of room temperature to 80°C, and a pickling time of 0.5–24 h.

[0022] Preferably, in step 2), the bismuth source is one or more of bismuth nitrate, bismuth sulfate, organic carboxylic acid bismuth, ethyl camphorate bismuth, and isooctanoate bismuth.

[0023] Preferably, in step 2), the cobalt source is one or more of cobalt acetate, cobalt sulfate, cobalt nitrate, cobalt naphthenate, and cobalt isooctanoate.

[0024] Preferably, in step 2), the organic ligand is 2,4-pyridinedicarboxylic acid, or it can be compounded with a small amount of surfactant (such as PVP) to disperse the metal source.

[0025] Preferably, in step 2), the stirring temperature is 25-50 ℃ and the stirring time is 30-60 min.

[0026] Preferably, in step 3), the water bath reaction conditions are 100–160 °C for 48–96 h.

[0027] Preferably, in step 4), the vacuum drying temperature is 60-80 ℃ and the drying time is 30-60 min.

[0028] Advantages of this invention: Chromium reaction kinetics were significantly enhanced: by constructing a coordination polymer catalytic layer containing Bi / Co dual centers in situ on the surface of carbon felt fibers, the effective active site density and interfacial electronic coupling efficiency were increased, promoting chromium reaction. 3+ / Cr 2+ The charge transfer process reduces overpotential and polarization and improves rate performance.

[0029] Hydrogen evolution competition is effectively suppressed: Co-related sites and their coordination environment regulate the selectivity of interfacial reactions, increase the kinetic threshold of hydrogen evolution reaction, weaken the competition of HER for electrons in acidic media, reduce the risk of gas evolution and electrolyte imbalance, and thus improve coulombic efficiency and energy efficiency.

[0030] In-situ fixation is more stable and more pore-structure friendly: Hydrothermal in-situ growth enables the catalyst layer to be tightly bonded to the carbon fiber skeleton, reducing the possibility of catalyst migration, agglomeration and shedding during operation; Compared with electrodeposition modification, it is less likely to cause local accumulation and pore blockage, which is conducive to maintaining electrode permeability and mass transfer channel stability, thereby enhancing long-cycle consistency and reliability.

[0031] The preparation is simple and scalable: the process is mainly based on an aqueous system, the conditions are mild and it is compatible with a variety of bismuth / cobalt sources. It does not require a complex coating and binder system, which facilitates repeated preparation and large-scale scale-up, and it is compatible with existing flow battery electrode manufacturing processes. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of a single cell structure of an iron-chromium redox flow battery. Figure 2 This is a graph showing the rate efficiency of an iron-chromium redox flow battery. Detailed Implementation

[0033] The present invention will be further explained below with reference to specific implementation schemes, but it is not limited to the present invention. The structures, proportions, sizes, etc. shown in the accompanying drawings are only used to complement the content disclosed in the specification, so as to enable those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effect and purpose that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0034] Example 1: Bismuth nitrate / cobalt acetate system (1) Carbon felt pretreatment: Cut the carbon felt into 3 cm × 3 cm pieces (or according to battery assembly requirements), place them in a 1.0 mol / L hydrochloric acid solution, and acid wash at 60 ℃ for 2 h to remove impurities and introduce oxygen-containing functional groups. After removal, rinse repeatedly with deionized water until the pH of the washing solution is ≈6–7. Then dry in a 60 ℃ oven for 2 h for later use.

[0035] (2) Preparation of precursor solution: Take 50 mL of deionized water as solvent and add in sequence: 1.0 mol of nitric acid (Bi(NO3)3•5H2O), 1.0 mmol of cobalt acetate (Co(CH3COO)2•4H2O), and 2.0 mmol of 2,4-pyridinedicarboxylic acid. Stir magnetically for 20 min at room temperature until the solution is clear or basically homogeneous.

[0036] (3) Hydrothermal in-situ growth: The precursor solution was transferred to a 100 mL PTFE-lined reactor, and the pretreated carbon felt was completely immersed. After sealing, the reactor was placed at 140 °C for 72 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the carbon felt was removed.

[0037] (4) Washing and drying: Wash three times with deionized water until the washing solution is nearly neutral. Finally, dry in a vacuum drying oven at 60°C for 12 h to obtain a carbon felt electrode loaded with bismuth-cobalt dual-coordination polymer.

[0038] Example 2: Bismuth organic carboxylic acid / cobalt isooctanoate system (enhanced hydrophobic salt solubility adaptation) (1) The acid washing steps for carbon felt are the same as in Example 1.

[0039] (2) Preparation of precursor solution: Take 50 mL of deionized water as solvent, and add 1.0 mmol of bismuth sulfate (BiSO4) and 1.0 mmol of cobalt isooctanoate (C16H) in sequence. 30 C o O4) and 2.0 mmol of 2,4-pyridinedicarboxylic acid were mixed thoroughly and dispersed. Then, 1.0 g / L of PVP or a small amount of nonionic surfactant was added as a dispersion stabilizer. (3) Hydrothermal in-situ growth: The precursor solution was transferred to a 100 mL PTFE-lined reactor, and the pretreated carbon felt was completely immersed. After sealing, the reactor was placed at 120 °C for 96 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the carbon felt was removed.

[0040] (4) Post-treatment: Wash with deionized water at least three times and vacuum dry at 60°C for 6–12 h to obtain carbon felt electrode loaded with bismuth-cobalt dual coordination polymer.

[0041] Example 2 highlights the organometallic source system and dispersion stability, which is used to further suppress organometallic salt aggregation and is more suitable for isooctanoate / carboxylate precursors. A uniform and dense bismuth-cobalt dual-coordination polymer has been obtained.

[0042] Example 3: Bismuth nitrate / cobalt nitrate system Similar to the steps in Example 1, the difference is that the same amount of cobalt nitrate (Co(NO3)2) is used as the cobalt source to synthesize the bismuth-cobalt dual-coordination polymer.

[0043] Application Example 1: Assembly and use of the negative electrode of an iron-chromium redox flow battery An iron-chromium redox flow battery was assembled using the electrodes from Example 1 as the negative electrode. The battery was constructed according to... Figure 1 The flow battery structure shown is assembled in the following sequence: end plate - bipolar plate - electrode - perfluorosulfonic acid membrane - electrode - bipolar plate - end plate. This battery is tested at 40-100 mA / cm². 2 A constant current charge-discharge rate test was performed, and the results are as follows: Figure 2 As shown. The results indicate that, compared with unmodified carbon felt, the electrode of the present invention can reduce negative electrode polarization and suppress hydrogen evolution, thereby improving coulombic efficiency, energy efficiency, and cycle stability. Matters not covered in this invention are prior art.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery, characterized in that: It includes a porous carbon felt matrix and a bismuth-cobalt dual-coordination polymer catalyst layer supported on the surface of the porous carbon felt matrix; the bismuth-cobalt dual-coordination polymer catalyst layer is generated by the in-situ reaction of a bismuth source, a cobalt source and an organic ligand under hydrothermal conditions and is immobilized on the surface of the porous carbon felt matrix.

2. The catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery according to claim 1, characterized in that: The organic ligand is 2,4-pyridinedicarboxylic acid.

3. The catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery according to claim 1 or 2, characterized in that: The bismuth source is selected from one or more of bismuth nitrate, bismuth sulfate, organic carboxylic acid bismuth, ethyl camphorate bismuth, and isooctanoate bismuth.

4. The catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery according to claim 1 or 2, characterized in that: The cobalt source is selected from one or more of cobalt acetate, cobalt sulfate, cobalt nitrate, cobalt naphthenate, and cobalt isooctanoate.

5. The catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery according to claims 1 to 4, characterized in that: The porous carbon felt matrix is ​​acid-washed before hydrothermal reaction, and the acid washing is performed using hydrochloric acid, sulfuric acid, nitric acid or a mixture thereof.

6. The catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium redox flow battery according to claim 5, characterized in that: The acid concentration for the pickling treatment is 0.5–3 mol / L, the pickling temperature is room temperature to 80°C, and the pickling time is 0.5–24 h.

7. The catalytic carbon felt electrode for the negative electrode chromium reaction side of an iron-chromium redox flow battery according to any one of claims 1 to 6, characterized in that, The molar ratio of the bismuth source to the cobalt source in the precursor solution is 1:(0.2–5).

8. A method for preparing the catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery as described in any one of claims 1 to 7, characterized in that, The process includes the following steps: (1) Carbon felt pretreatment: The carbon felt is acid-washed and then washed with deionized water until neutral and dried; (2) Precursor solution preparation: Bismuth source, cobalt source and organic ligand are added to deionized water and stirred to form a mixed precursor solution; (3) Hydrothermal in-situ growth: The mixed precursor solution is transferred to a polytetrafluoroethylene-lined high-pressure reactor, the pretreated carbon felt is immersed in the mixed precursor solution, and the reaction is carried out at 100–160℃ for 48–96 h, and then naturally cooled to room temperature; (4) Posttreatment: The carbon felt is taken out, washed with deionized water or distilled water at least three times, and dried to obtain a catalytic carbon felt electrode loaded with a bismuth-cobalt dual-coordination polymer catalytic layer.

9. An application of a catalytic carbon felt electrode for the chromium reaction side of the negative electrode in an iron-chromium flow battery, wherein the negative electrode of the iron-chromium flow battery adopts the catalytic carbon felt electrode as described in any one of claims 1 to 8.

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