Carbon felt electrodes for polysulfide-iron cyanide flow batteries and methods of making

Abstract

This invention relates to the field of electrode fabrication technology, and particularly to a carbon felt electrode for polysulfide-ferricyanide flow batteries and its fabrication method, wherein the carbon felt electrode surface is coated with (NH₄)₂Mo₃S. 13 Catalytic layer. This invention significantly improves the conversion kinetics of polysulfides and accelerates the conversion of S... x 2‑ The redox reaction rate is reduced, lowering the polarization overpotential of the battery and thus improving the energy efficiency of the flow battery; the interfacial stability between the electrode and the electrolyte is enhanced through (NH4)2Mo3S 13 The chemisorption of the catalyst layer effectively suppressed the shuttle effect of polysulfides, improving the coulombic efficiency and cycle stability of the battery; (NH₄)₂Mo₃S was prepared by a one-step hydrothermal method. 13 The catalyst layer has a simple and low-cost process, and (NH₄)₂Mo₃S 13 The catalyst exhibits good stability and self-healing ability, and can dynamically reconstruct surface defects during long cycles to maintain catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of electrode preparation technology, and particularly relates to a carbon felt electrode for polysulfide-ferricyanide flow batteries and its preparation method. Background Technology

[0002] Currently, polysulfide-ferricyanide flow batteries (PFRFBs) have shown great potential for long-term energy storage due to their abundant raw materials and environmental friendliness. However, the slow redox kinetics of polysulfide ions significantly limit their energy efficiency and voltage efficiency, requiring further improvement. Traditional carbon-based electrodes (such as carbon felt) have limited specific surface area (typically <5 m²). 2 (g) and lacking catalytically active sites, it exhibits low efficiency in promoting multi-electron cascade reactions of polysulfides. Although existing studies have explored heterostructure engineering methods such as depositing metal nanoparticles, transition metal sulfides, or nitrogen-doped carbon composites on carbon substrates to enhance the catalytic activity of S... x 2- Chemoadsorption capacity and charge transfer kinetics of species.

[0003] Existing technologies still suffer from the following problems: precious metal catalysts are costly and lack stability; metal sulfides are prone to structural collapse or dissolution in strongly acidic and oxidizing electrolytes; and the regulatory mechanisms of polysulfide conversion reaction pathways are unclear, especially regarding S... x 2- Design of effective catalytic sites for the critical step of deep oxidation. Summary of the Invention

[0004] The purpose of this invention is to provide a carbon felt electrode for polysulfide-ferricyanide flow batteries, aiming to solve the problems of high cost and insufficient stability of precious metal catalysts, and the tendency of metal sulfides to undergo structural collapse or dissolution in strongly acidic and oxidizing electrolytes.

[0005] This invention is achieved by using a carbon felt electrode for a polysulfide-ferricyanide flow battery, wherein the surface of the carbon felt electrode is coated with (NH4)2Mo3S. 13 Catalytic layer.

[0006] Another object of the present invention is to provide a method for preparing a carbon felt electrode for a polysulfide-ferricyanide flow battery as described above, wherein the (NH4)2Mo3S 13 The catalyst layer is attached to the surface of the carbon felt electrode via a one-step hydrothermal method. The specific process is as follows: 4.0g-12.0g (NH4)3Mo7O 24• Add 4H2O, 3.0 g - 8.0 g NH4Cl and 80~150 ml of 14~20 wt% (NH4)2S solution to the reaction vessel and stir at 25°C until completely dissolved; The reaction was carried out in an oven at 200°C for 24 hours. The reactants were filtered, washed, and dried to obtain (NH4)2Mo3S. 13 Carbon felt electrode of catalyst layer.

[0007] Preferably, (NH4)3Mo7O 24 The mass of 4H2O is 4.0 g, the mass of NH4Cl is 3.0 g, and the volume of the 14wt% (NH4)2S solution is 130 ml.

[0008] Preferably, in the step of filtering and washing the reactants, carbon disulfide and acetone are used to wash the precipitate and carbon felt multiple times to remove sulfur generated during the reaction.

[0009] Preferably, the reactants are filtered, washed, and dried to obtain (NH4)2Mo3S. 13 In the process of assembling the carbon felt electrode of the catalyst layer, drying is carried out at 60°C while maintaining vacuum conditions.

[0010] This invention significantly improves the conversion kinetics of polysulfides and accelerates the conversion of S... x 2- The redox reaction rate is reduced, lowering the polarization overpotential of the battery and thus improving the energy efficiency of the flow battery; the interfacial stability between the electrode and the electrolyte is enhanced, through (NH4)2Mo3S 13 The chemisorption of the catalyst layer effectively suppressed the shuttle effect of polysulfides, improving the coulombic efficiency and cycle stability of the battery; (NH4)2Mo3S was prepared by a one-step hydrothermal method. 13 The catalyst layer has a simple process and low cost, and (NH4)2Mo3S 13 The catalyst exhibits good stability and self-healing ability, and can dynamically reconstruct surface defects during long-term cycling to maintain catalytic activity. The electrode material of this invention is not only suitable for the negative electrode of polysulfide-ferricyanide flow batteries, but can also be applied to other electrochemical energy storage systems involving polysulfide redox reactions, showing broad application prospects. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the carbon felt electrode and catalyst layer structure provided in an embodiment of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] like Figure 1 The diagram shown is a schematic of the carbon felt electrode and catalyst layer structure provided in an embodiment of the present invention. The carbon felt electrode surface is coated with (NH4)2Mo3S. 13 Catalytic layer.

[0014] The preparation process of the carbon felt electrode for the polysulfide-ferricyanide flow battery is as follows: Electrode preparation method: (NH4)2Mo3S was constructed on the surface of carbon felt using a one-step hydrothermal method. 13 Catalytic layer.

[0015] The specific steps are as follows: 4.0g (NH4)3Mo7O 24 • Add 4H2O and 3.0g NH4Cl to 130mL (NH4)2S solution and stir at 25℃ until completely dissolved.

[0016] The reactor was placed in an oven at 200°C and reacted for 24 hours.

[0017] The precipitate and carbon felt in the reaction products are separated by filtration technology.

[0018] The precipitate and carbon felt were washed repeatedly with carbon disulfide and acetone to remove any excess sulfur that may have been generated during the process.

[0019] Vacuum drying at 60°C was used to remove residual solvent and moisture, ultimately yielding (NH4)2Mo3S. 13 -CF.

[0020] Electrode structure: (NH4)2Mo3S 13 The catalyst layer forms a regular hexahedral nanorod-shaped microcrystalline structure on the surface of the carbon felt. This structure is closely related to the growth orientation and kinetics of the crystals.

[0021] The main working principle of this invention is as follows: Localized crystal fragmentation or surface cracks are caused by uneven precursor concentration gradients or prolonged heat treatment during synthesis. These fragmented hexahedral shapes offer various catalytic advantages to the electrode; their fracture surfaces expose numerous Mo-S coordination unsaturated sites, which can act as polysulfides (S... x 2- It is an active center for chemisorption and electron transfer, promoting the breaking / recombination kinetics of SS bonds.

[0022] In addition, surface cracks and pores increase the roughness of the electrode, forming a layered porous channel that facilitates electrolyte penetration and mass transfer of sulfur species, while reducing interfacial concentration polarization.

[0023] Application of flow batteries: The prepared (NH4)2Mo3S 13 -CF, as the negative electrode in polysulfide-ferricyanide flow batteries, significantly improves the energy efficiency and cycle stability of the battery compared to traditional carbon felt negative electrodes. In single-cell tests, (NH4)2Mo3S 13 -CF electrode at 100mA / cm 2 At a current density, the single-cell energy efficiency was improved by 10.56%. In long-cycle testing, (NH4)2Mo3S... 13 - CF-type flow batteries with CF as the negative electrode operate at 40 mA / cm². 2 At the current density, the energy efficiency can still be maintained at 55% after 1580 cycles, with an average coulombic efficiency of over 99%, while the energy efficiency of the unmodified carbon felt drops rapidly to 35% after 1300 cycles.

[0024] The following are the test data corresponding to this invention: Electrode preparation: (NH4)2Mo3S was prepared according to the steps described above. 13 -CF electrode, and its morphology and composition were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to confirm the successful construction and structural features of the catalyst layer.

[0025] Electrochemical testing: Cyclic voltammetry: In an electrolyte containing 50 mmol / L K₂S and 1.0 mol / L KCl, (NH₄)₂Mo₃S was used as the electrolyte. 13 -CF is used as the working electrode for cyclic voltammetry testing, with a scan rate range of 1-50 mV / s.

[0026] The results show that (NH4)2Mo3S 13 The redox peak currents of -CF are higher than those of the original carbon felt electrode, (NH4)2Mo3S 13 -CF peak current is significantly improved, (NH4)2Mo3S 13 It can enhance the conductivity of carbon felt electrodes.

[0027] Rate performance testing: at different current densities (20-100 mA / cm²) 2 The flow battery was charged and discharged under the following conditions, and its coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were recorded.

[0028] The results show that at 100 mA / cm 2At the current density, the voltage efficiency increased from 39.11% to 49.65%, and the energy efficiency increased from 39.09% to 49.65%, representing improvements of 10.54% and 10.56% respectively compared to unmodified carbon felt. (NH4)2Mo3S 13 -CF electrodes exhibit higher energy efficiency and voltage efficiency at high current densities.

[0029] Long-cycle stability test: at 40mA / cm 2 The flow battery was subjected to long-cycle testing at a certain current density, and the changes in its energy efficiency were recorded.

[0030] Test results show that (NH4)2Mo3S 13 The -CF electrode maintained an energy efficiency of 55% after 1580 cycles, while the unmodified carbon felt electrode rapidly decreased to 35% after 1300 cycles. This indicates that (NH4)2Mo3S 13 -CF electrodes exhibit excellent long-term cycling stability and self-healing capabilities.

[0031] Bipolar electrode test: To further verify (NH4)2Mo3S 13 - The versatility of the CF electrode allows it to be used as both the positive and negative electrodes in flow batteries.

[0032] Test results show that the bipolar electrode flow cell operates at 80 mA / cm². 2 The discharge capacity at the current density is 1014mAh, while the discharge capacity of the unmodified carbon felt is 160mAh, which is about 6.3 times higher. Moreover, the energy efficiency can still be maintained at 55% after 1580 cycles, showing better self-healing ability and cycle stability.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon felt electrode for a polysulfide-ferricyanide flow battery, characterized in that, The carbon felt electrode surface is coated with (NH4)2Mo3S. 13 Catalytic layer.

2. A method for preparing a carbon felt electrode for the polysulfide-ferricyanide flow battery of claim 1, characterized in that, The (NH4)2Mo3S 13 The catalyst layer is attached to the surface of the carbon felt electrode via a one-step hydrothermal method. The specific process is as follows: 4.0g-12.0g (NH4)3Mo7O 24 • Add 4H2O, 3.0 g - 8.0 g NH4Cl and 80~150 ml of 14~20 wt% (NH4)2S solution to the reaction vessel and stir at 25°C until completely dissolved; The reaction was carried out in an oven at 200°C for 24 hours. The reactants were filtered, washed, and dried to obtain (NH4)2Mo3S. 13 Carbon felt electrode of catalyst layer.

3. The method for preparing the carbon felt electrode of the polysulfide-ferricyanide flow battery according to claim 2, characterized in that, (NH4)3Mo7O 24 The mass of 4H2O is 4.0 g, the mass of NH4Cl is 3.0 g, and the volume of the 14wt% (NH4)2S solution is 130 ml.

4. The method for preparing the carbon felt electrode of the polysulfide-ferricyanide flow battery according to claim 2, characterized in that, In the steps of filtering and washing the reactants, carbon disulfide and acetone are used to wash the precipitate and carbon felt multiple times to remove the sulfur generated during the reaction.

5. The method for preparing the carbon felt electrode of the polysulfide-ferricyanide flow battery according to claim 2, characterized in that, The reactants were filtered, washed, and dried to obtain (NH4)2Mo3S. 13 In the process of assembling the carbon felt electrode of the catalyst layer, drying is carried out at 60°C while maintaining vacuum conditions.

Images