Method and device for realizing heat energy recovery by using bipyridine salt flow battery

Abstract

The invention discloses a method and a device for realizing heat energy recovery by using a bipyridine salt flow battery. According to the device, end plates, gaskets, current collectors and graphite felt structures are sequentially and symmetrically arranged at the two ends of a diaphragm arranged in the middle from outside to inside; the graphite felt structure is a plate with a through hole, and a graphite felt is arranged in the through hole; storage tanks are respectively arranged on the outer sides of the two end plates; the two storage tanks are respectively provided with a positive electrode electrolyte and a negative electrode electrolyte, and an active material of the negative electrode electrolyte is N, N '-dicarboxypropyl-4, 4'-bipyridinium salt; each storage tank is in circulation loop connection with the graphite felt through an electrolyte circulation pipeline; each storage tank is also connected with the heat exchanger through a heat exchange pipe to form a circulation loop; the heat exchanger is connected with heat sources. The organic thermoelectric material is used as a negative electrode active material, heat energy is converted into electric energy in the low-temperature charging and high-temperature discharging processes, and low-cost and efficient heat energy recovery is achieved.

Description

Technical Field

[0001] The present invention relates to heat energy recovery, and more specifically to a method and device for realizing heat energy recovery by using a bipyridyl salt flow battery. Background Art

[0002] Low-grade thermal energy is widely present in nature and industrial production and life, and its distribution is characterized by extensiveness, dispersion, volatility, low grade and regionality. Compared with traditional temperature difference power generation technology (such as thermoelectric materials), certain chemical energy conversion systems (such as thermochemical batteries, redox flow batteries, etc.) have significant advantages and can theoretically achieve higher energy conversion efficiency, especially under low temperature difference conditions. This is because the driving force of chemical reactions depends not only on the temperature difference, but also on the change in Gibbs free energy of the chemical substances.

[0003] Currently, there are a variety of devices that can directly convert low-grade thermal energy into electrical energy, including thermoelectrochemical cells (TGCs) and thermal regenerative electrochemical cycles (TRECs). TGC generates a voltage difference at different temperatures through a single liquid aqueous redox couple, and has attracted attention due to its high Seebeck coefficient and low cost. TREC uses the voltage difference generated by the positive and negative redox couples at different temperatures to convert low-grade thermal energy into electrical energy, which can achieve energy storage and thermoelectric conversion at the same time. However, the above two direct thermoelectric conversion technologies are not sufficient to drive portable devices, and the system efficiency is low.

[0004] In the prior art, Battistel et al. (Reynard D, Dennison CR, Battistel A, et al. Efficiency improvement of an all-vanadium redox flow battery by harvesting low-grade heat [J]. Journal of Power Sources, 2018, 390: 30-37.) discovered the temperature effect in the redox pair of all-vanadium redox flow battery (VFB), which promoted the development of TREC-VFB. 2+ / VO2 electrode pair, the negative electrode is composed of V 2+ / 3+ Electrode composition. By measuring the formal potential of the electrode at different temperatures, the negative electrode temperature coefficient was obtained to be -1.013mV / K, and the coulomb efficiency of charge and discharge was only 94%, indicating the existence of self-discharge of the positive and negative electrodes. After the thermal regeneration cycle, the discharge energy density increased by 11% (compared to charge and discharge at 20°C). However, this technology is an inorganic system with a single structure and is difficult to control, and it relies on metal resources. Summary of the invention

[0005] The present invention provides a method and device for heat recovery using a bipyridyl salt flow battery, which uses thermoelectric materials as negative electrode active materials, converts heat energy into electrical energy through low-temperature charging and high-temperature discharging processes, and realizes low-cost and high-efficiency heat energy recovery.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A device for realizing heat energy recovery by using a bipyridyl salt flow battery; comprising a battery stack, a storage tank, a diaphragm pump, a heat exchanger and a heat source; the battery stack comprises a diaphragm, an end plate, a gasket, a current collector and a graphite felt structure; the two ends of the diaphragm arranged in the middle are symmetrically provided with end plates, gaskets, current collectors and graphite felt structures in sequence from the outside to the inside; the graphite felt structure is a plate with through holes, and the through holes are filled with graphite felt; storage tanks are respectively provided on the outsides of the two end plates; the two storage tanks are respectively provided with a positive electrode electrolyte and a negative electrode electrolyte, and the active material of the negative electrode electrolyte is N,N'-dicarboxypropyl-4,4'-bipyridyl salt; each storage tank is connected to the graphite felt through an electrolyte circulation pipeline to form a circulation loop; each storage tank is also connected to the heat exchanger through a heat exchange tube to form a circulation loop; the heat exchanger is connected to the heat source.

[0008] To further achieve the purpose of the present invention, preferably, the plastic end plate, gasket and current collector are all plate structures.

[0009] Preferably, the through holes are arranged in the middle of the gaskets on both sides of the diaphragm; the through holes and the graphite felt are square or circular.

[0010] Preferably, the through holes and graphite felt are in the shape of a square of 2 to 100 cm×2 to 100 cm or a circle of 2 to 100 cm in diameter; the thickness of the through holes and graphite felt is 2-6 mm.

[0011] Preferably, the electrolyte circulation pipeline passes through the metal end plate, the plastic end plate, the gasket, the current collector and is connected to the graphite felt in the graphite felt structure;

[0012] The electrolyte circulation pipeline is equipped with a diaphragm pump;

[0013] The two storage tanks are connected to the same heat exchanger through heat exchange pipes, or the two storage tanks are connected to different heat exchangers through heat exchange pipes.

[0014] Preferably, the end plate is composed of a metal end plate and a plastic end plate; the metal end plate is arranged on the outside of the plastic end plate; the metal of the metal end plate is titanium, iron, copper, or aluminum alloy; the plastic of the plastic end plate is polytetrafluoroethylene; the material of the gasket is silicone or fluororubber; the diaphragm is a Daramic diaphragm, a CSO membrane, a Nafion membrane, or a Nafion modified membrane; the current collector is graphite carbon felt, a conductive carbon layer, or a metal current collector; the heat source is water with a temperature less than 100°C heated by solar heat, industrial waste heat, or geothermal heat.

[0015] The method for realizing heat energy recovery by using a bipyridyl salt flow battery using the above device is as follows: the positive electrode electrolyte and the negative electrode electrolyte are added to two different storage tanks respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the battery stack on both sides of the diaphragm by using an electrolyte circulation pipeline and a diaphragm pump respectively, and charged at room temperature through a current collector; a heat source exchanges heat with a heat exchanger to heat the negative electrode electrolyte and the positive electrode electrolyte from the storage tank, and the negative electrode electrolyte and the positive electrode electrolyte are circulated between the storage tank and the graphite felt while being heated, and are discharged at high temperature through the current collector after being heated to 30-70°C to output current;

[0016] The positive electrode electrolyte is composed of a positive electrode active substance and a supporting electrolyte; the negative electrode electrolyte is composed of a negative electrode active substance and a supporting electrolyte; the negative electrode active substance is N,N'-dicarboxypropyl-4,4'-bipyridyl salt.

[0017] Preferably, the concentration of the positive electrode active material is 0.01M-1.5M, and the concentration of the supporting electrolyte in the positive electrode electrolyte is 0.5-6M; the concentration of the negative electrode active material is 0.01M-1.5M, and the concentration of the supporting electrolyte in the negative electrode active material is 0.5-6M.

[0018] Preferably, the positive electrode active material is a halogenated salt, an iron salt, a TEMPO derivative or a ferrocyanide.

[0019] The supporting electrolytes in the positive electrode electrolyte and the negative electrode electrolyte are electrolytes composed of cations and anions; the cations are selected from potassium ions, sodium ions, ammonium ions, and lithium ions; the anions are selected from halogen ions, nitrate ions, sulfate ions, and oxalate ions.

[0020] Preferably, the halogenated salt is potassium iodide, cesium iodide, sodium iodide or ammonium iodide;

[0021] The supporting electrolyte in the positive electrode electrolyte and the negative electrode electrolyte is potassium chloride, potassium oxalate, potassium sulfate, potassium nitrate, sodium chloride, sodium oxalate, sodium sulfate, sodium nitrate, ammonium chloride, ammonium oxalate, ammonium sulfate, ammonium nitrate, lithium chloride, lithium oxalate, lithium sulfate, lithium nitrate, potassium bromide or sodium bromide.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1) The bipyridyl salt in the present invention not only has good solubility, but also has excellent electrochemical stability, a high temperature coefficient, and a significant potential change under the influence of temperature.

[0024] 2) The bipyridyl salt negative electrode electrolyte in the present invention has the function of utilizing the recovered low-grade thermal energy to improve the energy efficiency of the system, thereby improving the energy utilization efficiency.

[0025] 3) The present invention uses it as the negative electrode electrolyte of the liquid flow battery, which can be stably circulated, has few side reactions, and has good charge and discharge capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The structure of a device for realizing heat energy recovery by using a bipyridyl salt flow battery according to the present invention is schematically shown.

[0027] Figure 2 This is a cyclic charge and discharge diagram of 1 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt applied to a liquid flow battery in Example 1.

[0028] Figure 3 This is a charge and discharge diagram of 1 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt applied to a hydrothermal flow battery at different temperatures in Example 1.

[0029] Figure 4 The charge-discharge curves and efficiency diagram of the liquid flow battery in Example 1 using 1 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt for low-temperature charging and high-temperature discharge.

[0030] Figure 5 This is a charge and discharge diagram of 0.1 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt applied to a hydrothermal flow battery at different temperatures in Example 2.

[0031] Figure 6 The charge and discharge curves and efficiency diagram of the liquid flow battery in Example 2 using 0.1 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt for low-temperature charging and high-temperature discharge.

[0032] Figure 7 This is the charge and discharge diagram of 0.5 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt applied to the hydrothermal flow battery at different temperatures in Example 3.

[0033] Figure 8 The charge-discharge curves and efficiency diagram of the liquid flow battery in Example 3 in which 0.5 mol / L N,N'-dicarboxypropyl-4,4'-bipyridinium salt is applied to low-temperature charging and high-temperature discharging.

[0034] Fig. 9 The cyclic voltammetry curve of N,N'-dicarboxypropyl-4,4'-bipyridyl salt in Example 5 with 0.5M potassium chloride as the supporting electrolyte

[0035] Fig.10 This is the temperature coefficient fitting diagram of different pyridinium salt molecules in Example 5.

[0036] Fig.11 This is a bar graph of the temperature coefficients obtained when using different counter ions for N,N'-dicarboxypropyl-4,4'-bipyridyl salt in Example 5. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the technical solution of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0038] In the field of thermal energy recovery, the existing all-vanadium liquid flow battery inorganic system has problems such as a single structure and difficulty in regulation, and is dependent on metal resources. Organic oxidative active materials are composed of highly abundant inorganic elements and have the advantages of adjustable structure and high solubility. The development of liquid flow batteries made of organic materials is the development direction.

[0039] Among organic materials, the core structure of bipyridine compounds (also known as viologen compounds) is composed of two pyridine rings connected by a carbon atom. The properties and functions of this type of compound can be regulated by introducing different substituents (such as alkyl, aryl, etc.) on the nitrogen atom of bipyridine. This type of compound is mainly used in the fields of catalysts and ligands, luminescent materials, analytical chemistry, flow batteries and organic synthesis. The pyridine ring provides electron deficiency, which enables it to exhibit good redox ability in electrochemical reactions. This feature makes bipyridine compounds have high solubility and strong redox ability, and can be used as negative electrode materials for organic flow batteries. However, current research on flow batteries mainly focuses on improving the stability, solubility and other electrochemical properties of redox couples, and no existing technology has been found to focus on the application of viologen compounds in the field of thermal energy recovery.

[0040] Viologen molecules have significant thermal response characteristics, and their application potential as a new type of thermal energy recovery electrode material has been verified through testing.

[0041] The structural formula of N,N'-dicarboxypropyl-4,4'-bipyridinium salt is However, the existing technology of this compound is mainly used to prepare photochromic semiconductors. There is a nitrogen cation on the pyridine ring of N,N'-dicarboxypropyl-4,4'-bipyridyl salt. This structural feature gives the compound unique redox properties. The chemical reaction equation for gaining and losing electrons is as follows:

[0042]

[0043] When N,N'-dicarboxypropyl-4,4'-bipyridinium salt gains an electron, a cationic radical is formed. The original carbon-carbon double bond is composed of a σ bond and a π bond. When the extra electron enters the conjugated system, the electron cloud density of the π bond increases. The electrons are distributed between the conjugated structures, so that the electron cloud density of the entire molecule is balanced.

[0044] The present invention found that N,N'-dicarboxypropyl-4,4'-bipyridinium salt has a high temperature coefficient, and the temperature coefficient of the compound is mainly due to the dimerization phenomenon that occurs in its reduced state. By measuring its dimerization equilibrium constant, compared with other bipyridyl molecules, N,N'-dicarboxypropyl-4,4'-bipyridinium salt has a stronger dimerization equilibrium constant, and it is precisely because of this advantage that it exhibits the characteristics of a high temperature coefficient.

[0045] It is worth emphasizing that by using N,N'-dicarboxypropyl-4,4'-bipyridinium salt as the active material of the negative electrode electrolyte, the present invention has achieved a breakthrough in the field of electrolyte systems and achieved ion regulation for the first time. Tests have shown that the electrode pair of the present invention using bipyridyl salt liquid flow battery to realize the thermal energy recovery method exhibits a temperature coefficient of up to -0.89mV / K.

[0046] Redox flow batteries have the ability to store thermal energy in the form of chemical bond energy, achieving energy storage and on-demand release. The present invention integrates heat recovery and power output into redox flow batteries, and uses the discharge process to convert heat into electrical energy, which can effectively alleviate the volatility, intermittency and low direct utilization efficiency of low-grade thermal energy, thereby improving the stability and reliability of energy supply. Compared with other devices in the prior art that directly convert thermal energy into electrical energy, the present invention provides the properties of continuous power output, pipeline heat recovery and energy decoupling.

[0047] On the basis of the above mechanism, the present invention proposes a device for realizing heat energy recovery by using bipyridyl salt liquid flow battery; the device comprises a battery stack, a storage tank, a diaphragm pump, a heat exchanger and a heat source; the battery stack comprises a diaphragm, an end plate, a gasket, a current collector and a graphite felt structure; the two ends of the diaphragm arranged in the middle are symmetrically provided with end plates, gaskets, current collectors and graphite felt structures from the outside to the inside; the graphite felt structure is a plate with through holes, and graphite felt is installed in the through holes; storage tanks are respectively provided on the outsides of the two end plates; the two storage tanks are respectively provided with positive electrode electrolyte and negative electrode electrolyte, and the active material of the negative electrode electrolyte is N,N'-dicarboxypropyl-4,4'-bipyridyl salt; each storage tank is connected to the graphite felt through an electrolyte circulation pipeline to form a circulation loop; each storage tank is also connected to the heat exchanger through a heat exchange tube to form a circulation loop; the heat exchanger is connected to the heat source.

[0048] Based on the use of N,N'-dicarboxypropyl-4,4'-bipyridyl salt as the active material of the negative electrode electrolyte, this technology combines the battery stack structure to develop a battery stack that cooperates with a heat exchanger and a heat source to achieve heat recovery. The shape and size of the through holes and graphite felt in the device can be adjusted according to application needs. Preferably, the through holes and graphite felt are 2-100cm×2-100cm square or 2-100cm circular in diameter; the thickness of the through holes and graphite felt is 2-6mm. For ease of installation, the plastic end plates, gaskets, and current collectors are preferably plate structures.

[0049] In the present invention, the electrolyte circulation pipeline can be directly connected to the graphite felt from the outside. Preferably, the electrolyte circulation pipeline passes through the metal end plate, the plastic end plate, the gasket, the current collector and is connected to the graphite felt in the graphite felt structure; for better circulation needs, a diaphragm pump is installed on the electrolyte circulation pipeline.

[0050] The present invention can use one heat exchanger or two heat exchangers. Preferably, the two storage tanks are connected to the same heat exchanger through heat exchange pipes, or the two storage tanks are connected to different heat exchangers through heat exchange pipes. The connection method of the storage tanks has a certain flexibility. The pipelines can be connected to two different storage tanks respectively so as to perform independent heat exchange operations on them; or the heat exchange pipe 11 can be connected to the two storage tanks at the same time through a heat exchanger to heat the two storage tanks, thereby meeting different operation requirements and improving the operability and applicability of the system.

[0051] In the present invention, the end plate can be one, two, or even more, preferably two, and the end plate is composed of a metal end plate and a plastic end plate; the metal end plate is arranged on the outside of the plastic end plate. The metal of the metal end plate is titanium, iron, copper or aluminum alloy; the plastic of the plastic end plate is polytetrafluoroethylene; the main function of the gasket is to prevent leakage of the electrolyte to ensure the sealing and safety of the system; the material of the gasket is selected from silicone or fluororubber; the diaphragm is selected from Daramic diaphragm, CSO membrane, Nafion membrane or Nafion modified membrane; the current collector is selected from graphite carbon felt, conductive carbon layer or metal current collector; the heat source is the low-grade position heat energy involved in the present invention, and the heat source is preferably water with a temperature less than 100°C heated by solar heat, industrial waste heat, or geothermal heat.

[0052] The method for realizing heat energy recovery by using a bipyridyl salt flow battery using the above device is as follows: the positive electrode electrolyte and the negative electrode electrolyte are added to two different storage tanks respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the battery stack on both sides of the diaphragm by using an electrolyte circulation pipeline and a diaphragm pump respectively, and charged at room temperature through a current collector; a heat source exchanges heat with a heat exchanger to heat the negative electrode electrolyte and the positive electrode electrolyte from the storage tank, and the negative electrode electrolyte and the positive electrode electrolyte are circulated between the storage tank and the graphite felt while being heated, and are discharged at high temperature through the current collector after being heated to 30-70°C to output current;

[0053] The positive electrode electrolyte is composed of a positive electrode active substance and a supporting electrolyte; the negative electrode electrolyte is composed of a negative electrode active substance and a supporting electrolyte; the negative electrode active substance is N,N'-dicarboxypropyl-4,4'-bipyridyl salt.

[0054] The present invention preferably has a positive electrode active material concentration of 0.01M to 1.5M, and a supporting electrolyte concentration of 0.5 to 6M in the positive electrode electrolyte; a negative electrode active material concentration of 0.01M to 1.5M, and a supporting electrolyte concentration of 0.5 to 6M in the negative electrode active material. The positive electrode active material is preferably a halogenated salt, an iron salt, a TEMPO derivative, or a ferrocyanide.

[0055] The supporting electrolyte in the positive electrode electrolyte and the negative electrode electrolyte is preferably an electrolyte composed of cations and anions; the cations are selected from potassium ions, sodium ions, ammonium ions, and lithium ions; the anions are selected from halogen ions, nitrate ions, sulfate ions, and oxalate ions.

[0056] Preferably, the halogenated salt is potassium iodide, cesium iodide, sodium iodide or ammonium iodide; the supporting electrolyte in the positive electrode electrolyte and the negative electrode electrolyte is potassium chloride, potassium oxalate, potassium sulfate, potassium nitrate, sodium chloride, sodium oxalate, sodium sulfate, sodium nitrate, ammonium chloride, ammonium oxalate, ammonium sulfate, ammonium nitrate, lithium chloride, lithium oxalate, lithium sulfate, lithium nitrate, potassium bromide or sodium bromide.

[0057] like Figure 1As shown, a device for realizing heat energy recovery by using bipyridyl salt flow battery; comprising a battery stack 10, positive and negative electrolytes, a storage tank 6, an electrolyte circulation pipeline 9, a diaphragm pump 8, a heat exchange tube 11, a heat exchanger 7 and a heat source 12; the battery stack 10 is mainly composed of a diaphragm, a metal end plate 1, a plastic end plate 2, a gasket 3, a current collector 4 and a graphite felt structure 5; the two ends of the diaphragm arranged in the middle are symmetrically provided with a metal end plate 1, a plastic end plate 2, a gasket 3, a current collector 4 and a graphite felt structure 5 from the outside to the inside; the metal end plate 1, the plastic end plate 2, the gasket 3, the current collector 4 and the graphite felt structure 5 are preferably a plate structure, and the graphite felt structure 5 is preferably composed of a through hole provided in the plate, and graphite felt is installed in the through hole; it is further preferred that the through hole is arranged in the middle of the plate; the through hole and the graphite felt are a square of 2.5 cm×2.5 cm, and the plate is preferably made of plastic material. Storage tanks 6 are provided on the outside of the two metal end plates 1 respectively; the two storage tanks 6 are provided with positive electrolyte and negative electrolyte respectively; each storage tank 6 is connected to the graphite felt in the graphite felt structure 5 through two electrolyte circulation pipelines 9 arranged at intervals; each storage tank 6 is also connected to the heat exchanger 7 through two heat exchange tubes 11; the heat exchanger 7 is connected to the heat source 12, and one of the two electrolyte circulation pipelines 9 connected to one storage tank 6 is equipped with a diaphragm pump 8; preferably, the electrolyte circulation pipeline 9 passes through the metal end plate 1, the plastic end plate 2, the gasket 3, and the current collector 4 to connect with the graphite felt in the graphite felt structure 5. After the symmetrical components of the battery stack 1 are arranged, the metal end plates 1 at both ends are fixed by bolts. The storage tank 6 preferably adopts a jacket structure, such as a jacketed beaker, to facilitate the exchange of heat with the outside.

[0058] Example 1

[0059] use Figure 1 A method for heat recovery using a bipyridyl salt flow battery comprises the following steps:

[0060] 1) Bipyridyl salt flow battery configuration:

[0061] Preparation of positive electrode electrolyte: Mix the solutions of positive electrode active material potassium iodide and positive electrode supporting electrolyte potassium chloride to form 12 ml positive electrode electrolyte, and control the concentration of positive electrode active material to 3M and the concentration of positive electrode supporting electrolyte to 2M.

[0062] Preparation of negative electrode electrolyte: Mix the solutions prepared by respectively coordinating the negative electrode electrolyte active material N,N'-dicarboxypropyl-4,4'-bipyridyl salt and the negative electrode supporting electrolyte potassium oxalate to obtain 6 ml of negative electrode electrolyte, wherein the concentration of the negative electrode electrolyte active material is 1M and the concentration of the negative electrode supporting electrolyte is 4M.

[0063] 2) Operation of bipyridyl salt flow battery: the positive electrode electrolyte and the negative electrode electrolyte are added into two different storage tanks 6 respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the graphite felt structure 5 of the two battery stacks 10 on both sides of the diaphragm by means of the electrolyte circulation pipeline 9 and the diaphragm pump 8 respectively, and the current collecting plate 3 is made of graphite plate, and the flow rate of the positive electrode electrolyte and the negative electrode electrolyte pumped in is equal.

[0064] The entire bipyridyl salt flow battery was subjected to the following flow battery cycle test and heat energy recovery in a nitrogen atmosphere.

[0065] The test clips of the battery test system are clamped on the current collectors 4 of the positive and negative electrodes respectively. The cycle curve test is divided into the following steps: 5s of suspension, constant current and constant voltage charging, 5s of suspension, constant current and constant voltage discharge. Set the constant current and constant voltage charging according to the following parameters: the charging current density is 20mA / cm 2 , the charging cut-off voltage is 1.05V, and the cut-off current is 10mA, that is, when the constant current charging voltage is charged to 1.05V, the constant voltage 1.05V is charged until the current is lower than 10mA, the step is completed, and jump to the next step; after the charging is completed, it is left for 5s, and the constant current and constant voltage discharge is performed according to the following parameters: the discharge current density is 20mA / cm 2 , the discharge cut-off voltage is 0.45V, and the cut-off current is 10mA, that is, when the constant current charging voltage is discharged to 0.45V, the constant voltage 0.45V is discharged until the current is lower than 10mA, and the process step is completed; completing four steps is a cycle, and the next cycle continues to repeat to the first step, and the number of cycles is 50.

[0066] Record the charge capacity and voltage and discharge capacity and voltage of each cycle. Coulomb efficiency refers to the ratio of discharge capacity to charge capacity, reflecting the charge utilization rate; voltage efficiency is the ratio of average discharge voltage to average charge voltage, reflecting the energy conversion efficiency after considering polarization; the energy efficiency of the battery is the product of coulomb efficiency and voltage efficiency, which is a comprehensive measure of battery performance. Figure 2 The curve Figure 2 The capacity-voltage curve of the battery is shown. According to the test data, the first cycle discharge capacity is 125.4mAh. After 80 cycles of charge and discharge, the coulomb efficiency remains above 99.6% and the energy efficiency remains at 76%. The discharge capacity of the 80th cycle is 117.7mAh, the capacity retention rate is 93.9%, and the capacity decay rate per cycle is 0.076%.

[0067] 3) Heat recovery: In this embodiment, the heat source 12 is derived from 66°C water, and the heat source 12 exchanges heat with the heat exchanger 7 to heat the negative electrode electrolyte or positive electrode electrolyte from the storage tank 6 (jacketed beaker). At the same time, the heated negative electrode electrolyte or positive electrode electrolyte is circulated between the storage tank 6 and the graphite felt. When the negative electrode electrolyte or positive electrode electrolyte is 25°C, the charging current density is set to 20mA / cm2 , the charging cut-off voltage is 1.05V, and the cut-off current is 10mA; after charging is completed, the battery is set aside, and heat is exchanged with the heat exchanger 7 through the heat source 12. When the temperature of the negative electrode electrolyte or the positive electrode electrolyte stabilizes at 60°C, a constant current and constant voltage discharge is performed, and the discharge current density is controlled to be 20mA / cm 2 , the discharge cut-off voltage is 0.45V, and the cut-off current is 10mA. Record the charge capacity and voltage and the discharge capacity and voltage, and plot them as Figure 3 The curve in Figure 3 shows the capacity-voltage curve of the bipyridyl salt flow battery.

[0068] According to the measurement results, the energy loss of the N,N'-dicarboxypropyl-4,4'-bipyridinium salt / potassium iodide flow battery in this embodiment when charged at 25°C and discharged at 25°C is 21.9mWh, and the energy loss when charged at 25°C and discharged at 60°C is 11.9mWh. The reduced heat loss energy is the result of the combined effect of heat conversion to work and the reduction of internal resistance loss. It is calculated that the energy converted from heat to electricity accounts for 4.6% of the discharge energy.

[0069] like Figure 4 As shown, the battery has an excellent performance under the charge and discharge test mode of 25°C charging and 60°C discharging. The coulombic efficiency of the battery is 98.32%, the voltage efficiency is 92.36%, and the energy efficiency is 90.81%.

[0070] The prior art document "A Sulfonate-Functionalized Viologen Enabling Neutral Cation Exchange, Aqueous Organic Redox Flow Batteries toward Renewable Energy Storage" discloses a sulfonate-functionalized viologen molecule 1,1'-bis(3-sulfopropyl)-4,4'-bipyridinium salt and potassium iodide to form a flow battery (hereinafter referred to as "reference document viologen"), and uses it in a neutral cation exchange aqueous organic redox flow battery. The positive electrode active material used in the prior art document is consistent with the system of the present invention.

[0071] Using the same test method as in this embodiment, the temperature coefficient of the viologen in the prior art document is less than 0.4mV / K, and the voltage of the flow battery is 1.0V. Using 0.5M viologen as the active material, 300 cycles were tested at a current density of 60mA / cm2, and the battery capacity retention rate was 94.1% (average capacity retention rate per cycle 99.99%), and the average energy efficiency was 58%. When the concentration of the viologen molecule was 1M, the energy efficiency was 76%.

[0072] It can be seen that the viologen of this embodiment has a significantly higher temperature coefficient (higher than 0.9 mV / K). The present invention significantly improves the temperature coefficient by introducing a carboxyl group to increase the dimerization constant. More importantly, this characteristic enables the flow battery containing the viologen of the present invention to not only have higher energy efficiency during conventional charge and discharge, but also to further improve the overall energy output of the electrical system by recovering heat energy.

[0073] Example 2

[0074] use Figure 1 A method for heat recovery using a bipyridyl salt flow battery comprises the following steps:

[0075] 1) Bipyridyl salt flow battery configuration:

[0076] Preparation of positive electrode electrolyte: Mix the solutions of positive electrode active material potassium iodide and positive electrode supporting electrolyte potassium chloride to form 12 ml positive electrode electrolyte. The concentration of positive electrode active material is controlled to be 0.5M and the concentration of positive electrode supporting electrolyte is controlled to be 0.5M.

[0077] Preparation of negative electrode electrolyte: Mix the solutions prepared by respectively coordinating the negative electrode electrolyte active material N,N'-dicarboxypropyl-4,4'-bipyridyl salt and the negative electrode supporting electrolyte potassium oxalate to obtain 6 ml of negative electrode electrolyte, wherein the concentration of the negative electrode electrolyte active material is 0.1M and the concentration of the negative electrode supporting electrolyte is 0.5M.

[0078] 2) Operation of bipyridyl salt flow battery: The positive electrode electrolyte and the negative electrode electrolyte are added into two different storage tanks 6 respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the graphite felt structure 5 of the two battery stacks 10 on both sides of the diaphragm by means of the electrolyte circulation pipeline 9 and the diaphragm pump 8 respectively. The current collecting plate 3 is made of high-purity titanium sheet, and the flow rate of the positive electrode electrolyte and the negative electrode electrolyte pumped in is equal.

[0079] The entire bipyridyl salt flow battery was subjected to the following flow battery cycle test and thermal energy recovery in a nitrogen atmosphere.

[0080] 3) Heat recovery: In this embodiment, the heat source 12 is derived from solar energy. The heat source 12 exchanges heat with the heat exchanger 7 to heat the negative electrode electrolyte or positive electrode electrolyte from the storage tank 6 (jacketed beaker). At the same time, the heated negative electrode electrolyte or positive electrode electrolyte is circulated between the storage tank 6 and the graphite felt. When the negative electrode electrolyte or positive electrode electrolyte is 25°C, the charging current density is set to 20 mA / cm 2 , the charging cut-off voltage is 1.05V, and the cut-off current is 10mA; after charging is completed, the battery is set aside, and heat is exchanged with the heat exchanger 7 through the heat source 12. When the temperature of the negative electrode electrolyte or the positive electrode electrolyte stabilizes at 60°C, a constant current and constant voltage discharge is performed, and the discharge current density is controlled to be 20mA / cm2 , the discharge cut-off voltage is 0.45V, and the cut-off current is 10mA. Record the charge capacity and voltage and the discharge capacity and voltage, and plot them as Figure 5 curve.

[0081] Figure 5 The battery performance test results of the battery at different temperatures are shown. According to the measurement results, the energy loss of N,N'-dicarboxypropyl-4,4'-bipyridinium salt|potassium iodide flow battery during charging and discharging at 25°C is 1.8mWh, while the energy loss under charging at 25°C and discharging at 60°C is 1.1mWh. The reduced heat loss energy is the result of the combined effect of heat conversion into work and reduced internal resistance loss. It is calculated that the energy converted from heat to electricity accounts for 3.9% of the discharge energy.

[0082] Figure 6 It was demonstrated that under the charge and discharge mode of 25°C charging and 60°C discharging, the battery's coulombic efficiency was 99.98%, the voltage efficiency reached 92.27%, and the energy efficiency reached 92.25%. At this low concentration, the battery performance is excellent.

[0083] Example 3

[0084] use Figure 1 A method for heat recovery using a bipyridyl salt flow battery comprises the following steps:

[0085] 1) Bipyridyl salt flow battery configuration:

[0086] Preparation of positive electrode electrolyte: Mix the solutions of positive electrode active material potassium iodide and positive electrode supporting electrolyte potassium chloride to form 12 ml positive electrode electrolyte. The concentration of positive electrode active material is controlled to 2M and the concentration of positive electrode supporting electrolyte is controlled to 0.5M.

[0087] Preparation of negative electrode electrolyte: Mix the solutions prepared by respectively coordinating the negative electrode electrolyte active material N,N'-dicarboxypropyl-4,4'-bipyridyl salt and the negative electrode supporting electrolyte potassium oxalate to obtain 6 ml of negative electrode electrolyte, wherein the concentration of the negative electrode electrolyte active material is 0.5M, and the concentration of the negative electrode supporting electrolyte is 0.5M.

[0088] 2) Operation of bipyridyl salt flow battery: the positive electrode electrolyte and the negative electrode electrolyte are added into two different storage tanks 6 respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the graphite felt structure 5 of the two battery stacks 10 on both sides of the diaphragm by means of the electrolyte circulation pipeline 9 and the diaphragm pump 8 respectively, and the current collecting plate 3 is made of graphite plate, and the flow rate of the positive electrode electrolyte and the negative electrode electrolyte pumped in is equal.

[0089] The entire bipyridyl salt flow battery was subjected to the following flow battery cycle test and heat energy recovery in a nitrogen atmosphere.

[0090] 3) Heat recovery: In this embodiment, the heat source 12 is derived from the waste heat of flue gas. The heat source 12 exchanges heat with the heat exchanger 7 to heat the negative electrode electrolyte or positive electrode electrolyte from the storage tank 6 (jacketed beaker). At the same time, the heated negative electrode electrolyte or positive electrode electrolyte is circulated between the storage tank 6 and the graphite felt. When the negative electrode electrolyte or positive electrode electrolyte is 25°C, the charging current density is set to 20 mA / cm 2 , the charging cut-off voltage is 1.05V, and the cut-off current is 10mA; after charging is completed, the battery is set aside, and heat is exchanged with the heat exchanger 7 through the heat source 12. When the temperature of the negative electrode electrolyte or the positive electrode electrolyte stabilizes at 60°C, a constant current and constant voltage discharge is performed, and the discharge current density is controlled to be 20mA / cm 2 , the discharge cut-off voltage is 0.45V, and the cut-off current is 10mA. Record the charge capacity and voltage and the discharge capacity and voltage, and plot them as Figure 7 curve.

[0091] Figure 7 The battery performance test results of the battery at different temperatures are shown. According to the measurement results, the energy loss of N,N'-dicarboxypropyl-4,4'-bipyridinium salt|potassium iodide flow battery during charging and discharging at 25°C is 7.7mWh, while the energy loss under charging at 25°C and discharging at 60°C is 3.5mWh. The reduced heat loss energy is the result of the combined effect of heat conversion into work and reduced internal resistance loss. It is calculated that the energy converted from heat to electricity accounts for 5.5% of the discharge energy.

[0092] Figure 8 It was demonstrated that under the charge and discharge mode of 25°C charging and 60°C discharging, the battery's coulombic efficiency was 98.27%, the voltage efficiency reached 91.39%, and the energy efficiency reached 89.81%. At this concentration, the battery's heat recovery efficiency was excellent.

[0093] The diaphragms described in Example 1, Example 2, and Example 3 all use modified membranes formed by coating PVDF@carbon black on Nafion115.

[0094] Example 4

[0095] use Figure 1 A method for heat recovery using a bipyridyl salt flow battery comprises the following steps:

[0096] 1) Bipyridyl salt flow battery configuration:

[0097] Preparation of positive electrode electrolyte: Mix the solutions of positive electrode active material 4-hydroxyTEMPO and positive electrode supporting electrolyte potassium chloride to form 12 ml positive electrode electrolyte. The concentration of positive electrode active material is controlled to 0.1M and the concentration of positive electrode supporting electrolyte is controlled to 0.5M.

[0098] Preparation of negative electrode electrolyte: Mix the solutions prepared by respectively coordinating the negative electrode electrolyte active material N,N'-dicarboxypropyl-4,4'-bipyridyl salt and the negative electrode supporting electrolyte potassium oxalate to obtain 6 ml of negative electrode electrolyte, wherein the concentration of the negative electrode electrolyte active material is 0.1M and the concentration of the negative electrode supporting electrolyte is 0.5M.

[0099] 2) Operation of bipyridyl salt flow battery: The positive electrode electrolyte and the negative electrode electrolyte are added into two different storage tanks 6 respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the graphite felt structure 5 of the two battery stacks 10 on both sides of the diaphragm by means of the electrolyte circulation pipeline 9 and the diaphragm pump 8 respectively. The current collecting plate 3 is made of graphite plate, and the diaphragm is made of an anion exchange membrane. The flow rate of the positive electrode electrolyte and the negative electrode electrolyte pumped in is equal.

[0100] Example 5

[0101] Temperature coefficient test of N,N'-dicarboxypropyl-4,4'-bipyridinium salt under different counterions:

[0102] In an electrochemical system, the mutual conversion of chemical energy and electrical energy is achieved through electrode reactions. The essence of electrode reactions is redox reactions, and their characteristics are determined by the redox couples involved in the reaction. The temperature coefficient is an indicator of the change in the equilibrium electrode potential of the redox couple under a unit temperature change (for example, per Kelvin). Its positive and negative signs indicate the direction in which the electrode potential changes with temperature. The larger the absolute value, the more sensitive the electrode potential is to temperature changes, that is, the greater the change in open circuit voltage under a unit temperature change. Its expression is as follows:

[0103]

[0104] The temperature coefficient is measured by cyclic voltammetry (CV) test. First, 4mM N,N'-dicarboxypropyl-4,4'-bipyridyl salt is dissolved in 0.5mM different supporting electrolyte ion solutions, and the prepared solution is added to the jacketed beaker. This method uses a three-electrode system, including a glassy carbon electrode as the working electrode, a silver-silver chloride electrode as the reference electrode, and a platinum electrode as the auxiliary electrode to achieve accurate measurement of current and potential. The cyclic voltammetry curve is measured under different temperature conditions using a three-electrode system. After reading the formal potential of the cyclic voltammetry curve, a linear fit is performed to obtain the temperature coefficient.

[0105] Fig. 9The cyclic voltammetry curves of N,N'-dicarboxypropyl-4,4'-bipyridinium salt at different temperatures are shown. The voltammetry curves obtained by cyclic voltammetry can be used to determine the formal potential of N,N'-dicarboxypropyl-4,4'-bipyridinium salt at different temperatures. As the temperature changes, the cyclic voltammetry curve shows a negative shift trend, and the formal potential also moves toward the negative potential direction, indicating that as the temperature increases, the redox couple potential of N,N'-dicarboxypropyl-4,4'-bipyridinium salt moves negatively.

[0106] Similarly, the temperature coefficients of various viologen derivatives were measured under 0.5M KCl supporting electrolyte conditions. First, for the basic bipyridyl salt, the substituents on the nitrogen atoms at both ends are methyl and ethyl, and the temperature coefficient of methyl viologen is measured to be -0.5mV / K; according to the literature report that the temperature coefficient of ethyl viologen is -0.3mv / K [Direct Conversion of Phase-Transition Entropy into Electrochemical Thermopower and the Peltier Effect], based on the mechanism of temperature coefficient generation, the molecule with carboxylate introduced on the side chain of viologen has a higher temperature coefficient. In the temperature coefficient of this type of substance, such as Fig.10 As shown, the temperature coefficient of N,N'-dicarboxyethyl-4,4'-bipyridinium salt ((CEt)2V) is -0.68mV / K, that of N,N'-dicarboxybutyl-4,4'-bipyridinium salt ((CBu)2V) is -0.45mV / K, and that of N,N'-dicarboxypropyl-4,4'-bipyridinium salt ((CPr)2V) is -0.85mV / K. Although N,N'-dicarboxyethyl-4,4'-bipyridinium salt and N,N'-dicarboxybutyl-4,4'-bipyridinium salt also have temperature coefficients, their one-electron reduced state has low solubility and is easily precipitated during the charge and discharge process of the thermoelectrochemical cell, which may lead to blockage of the flow channel, thereby reducing the cell stability and thermal energy conversion efficiency. In contrast, N,N'-dicarboxypropyl-4,4'-bipyridinium salt not only has a higher absolute value of the temperature coefficient, but also has a higher solubility. Therefore, this molecule is more suitable as a negative electrode active material for thermal conversion flow batteries.

[0107] Fig.11 The effect of different counterions on the temperature coefficient of N,N'-dicarboxypropyl-4,4'-bipyridinium salt is shown. Under a variety of supporting electrolytes, the compound exhibits a high absolute value of the temperature coefficient. Therefore, N,N'-di(carboxypropyl)-4,4'-bipyridinium salt has potential application value in liquid flow battery systems with convertible counterions.

Claims

1. A device for heat recovery using bipyridyl salt flow battery; characterized in that: It includes a battery stack, a storage tank, a diaphragm pump, a heat exchanger and a heat source; the battery stack includes a diaphragm, an end plate, a gasket, a current collector and a graphite felt structure; the two ends of the diaphragm arranged in the middle are symmetrically provided with end plates, gaskets, current collectors and graphite felt structures from the outside to the inside; the graphite felt structure is a plate with through holes, and the through holes are filled with graphite felt; storage tanks are respectively provided on the outsides of the two end plates; the two storage tanks are respectively provided with positive electrode electrolyte and negative electrode electrolyte, and the active material of the negative electrode electrolyte is N, N'-dicarboxypropyl-4,4'-bipyridyl salt; each storage tank is connected to the graphite felt through an electrolyte circulation pipeline to form a circulation loop; each storage tank is also connected to the heat exchanger through a heat exchange tube to form a circulation loop; the heat exchanger is connected to the heat source.

2. The device for realizing heat energy recovery using bipyridyl salt flow battery according to claim 1; characterized in that: The plastic end plate, gasket and current collector are all plate structures.

3. The device for realizing heat energy recovery using bipyridyl salt flow battery according to claim 1; characterized in that: The through holes are arranged in the middle of the washers on both sides of the diaphragm; the through holes and the graphite felt are square or circular.

4. The device for realizing heat energy recovery using bipyridyl salt flow battery according to claim 3; characterized in that: The through hole and the graphite felt are in the shape of a square of 2-100cm×2-100cm or a circle of 2-100cm in diameter; the thickness of the through hole and the graphite felt is 2-6mm.

5. The device for realizing heat energy recovery using bipyridyl salt flow battery according to claim 1; characterized in that: The electrolyte circulation pipeline passes through the metal end plate, the plastic end plate, the gasket, the current collector and is connected to the graphite felt in the graphite felt structure; The electrolyte circulation pipeline is equipped with a diaphragm pump; The two storage tanks are connected to the same heat exchanger through heat exchange pipes, or the two storage tanks are connected to different heat exchangers through heat exchange pipes.

6. The device for realizing heat energy recovery using bipyridyl salt flow battery according to claim 1; characterized in that: The end plate is composed of a metal end plate and a plastic end plate; the metal end plate is arranged on the outside of the plastic end plate; the metal of the metal end plate is titanium, iron, copper, or aluminum alloy; the plastic of the plastic end plate is polytetrafluoroethylene; the material of the gasket is silicone or fluororubber; the diaphragm is Daramic diaphragm, CSO membrane, Nafion membrane, or Nafion modified membrane; The current collector is selected from graphite carbon felt, conductive carbon layer or metal current collector; the heat source is water with a temperature less than 100° C. heated by solar heat, industrial waste heat or geothermal heat.

7. A method for realizing heat energy recovery by using a bipyridyl salt flow battery using the device of claim 1; characterized in that: The positive electrode electrolyte and the negative electrode electrolyte are added to two different storage tanks respectively, and the positive electrode electrolyte and the negative electrode electrolyte are pumped into the graphite felt of the battery stack on both sides of the diaphragm by the electrolyte circulation pipeline and the diaphragm pump respectively, and charged at room temperature through the current collector; the heat source exchanges heat with the heat exchanger to heat the negative electrode electrolyte and the positive electrode electrolyte from the storage tank, and the negative electrode electrolyte and the positive electrode electrolyte are circulated between the storage tank and the graphite felt while being heated, and are discharged at high temperature through the current collector after being heated to 30-70°C, and output current; The positive electrode electrolyte is composed of a positive electrode active substance and a supporting electrolyte; the negative electrode electrolyte is composed of a negative electrode active substance and a supporting electrolyte; the negative electrode active substance is N,N'-dicarboxypropyl-4,4'-bipyridyl salt.

8. The method for realizing heat energy recovery by using bipyridyl salt flow battery according to claim 7; characterized in that: The concentration of the positive electrode active material is 0.01M-1.5M, and the concentration of the supporting electrolyte in the positive electrode electrolyte is 0.5-6M; the concentration of the negative electrode active material is 0.01M-1.5M, and the concentration of the supporting electrolyte in the negative electrode active material is 0.5-6M.

9. The method for realizing heat energy recovery by using bipyridyl salt flow battery according to claim 7; characterized in that: The positive electrode active material is a halogenated salt, an iron salt, a TEMPO derivative or a ferrocyanide. The supporting electrolytes in the positive electrode electrolyte and the negative electrode electrolyte are electrolytes composed of cations and anions; the cations are selected from potassium ions, sodium ions, ammonium ions, and lithium ions; the anions are selected from halogen ions, nitrate ions, sulfate ions, and oxalate ions.

10. The method for realizing heat energy recovery by using bipyridyl salt flow battery according to claim 9; characterized in that: The halogenated salt is potassium iodide, cesium iodide, sodium iodide or ammonium iodide; The supporting electrolyte in the positive electrode electrolyte and the negative electrode electrolyte is potassium chloride, potassium oxalate, potassium sulfate, potassium nitrate, sodium chloride, sodium oxalate, sodium sulfate, sodium nitrate, ammonium chloride, ammonium oxalate, ammonium sulfate, ammonium nitrate, lithium chloride, lithium oxalate, lithium sulfate, lithium nitrate, potassium bromide or sodium bromide.

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