An in-situ online method for detecting total Cr concentration in the electrolyte of an iron-chromium flow battery

Abstract

This invention belongs to the field of energy storage and flow battery technology, and relates to an in-situ online detection method for the total Cr concentration in the electrolyte of an iron-chromium flow battery. The method first obtains the Cr concentration based on the absorbance at 800 nm. 2+ The initial concentration was determined; then the electrolyte was reduced to a high-charge state, and the spectral signal changes were monitored simultaneously to determine the charging termination conditions and hydrogen evolution amount, and the Cr content during the charging process was calculated. 2+ Concentration increment, combined with absorbance at 407 nm to obtain Cr 3+ The concentration is then used to obtain the total Cr concentration. This invention overcomes the limitations of traditional offline detection, avoids measurement errors, provides accurate data support, and is low-interference and compatible with the intelligent operation and maintenance of megawatt-level iron-chromium redox flow battery energy storage systems.

Description

Technical Field

[0001] This invention belongs to the field of energy storage and flow battery technology, and relates to an in-situ online detection method for the total Cr concentration in the electrolyte of an iron-chromium flow battery. Background Technology

[0002] The long-term operating capacity and state of health (SOH) of an iron-chromium redox flow battery fundamentally depend on the total amount of active material in its electrolyte. On the negative electrode side, the total chromium concentration directly determines the upper limit of the battery's theoretical energy storage capacity and is the core basis for assessing battery capacity decay, formulating electrolyte rebalancing strategies, and achieving life prediction.

[0003] During normal charge and discharge, Cr occurs at the negative electrode of the iron-chromium redox flow battery. 3+ With Cr 2+ The conversion between these processes does not lead to a change in the total chromium content. However, due to the ion-selective permeability of the battery separator, chromium and iron ions (Fe...) are present in the electrolyte. 2+ Fe 3+ Cr 2+ Cr 3+ During charging and discharging, transmembrane migration occurs, leading to continuous changes in the concentration of metal ions in the positive and negative electrode electrolytes. Furthermore, the transmembrane penetration of water molecules during long-term operation is often significant, causing changes in the concentrations of total chromium and iron ions. These changes not only directly affect battery efficiency and capacity but also pose higher requirements and challenges for accurate online detection of ion concentrations.

[0004] However, existing technologies have a significant blind spot: conventional SOC monitoring methods (such as the open-circuit voltage method) can only reflect the relative proportion of the state of charge and cannot detect the absolute loss of total capacity; while models used for SOH assessment often have limited accuracy or require frequent offline calibration due to the lack of real-time input data on the total active substance concentration. Currently, obtaining the total chromium concentration heavily relies on destructive, periodic offline sampling and laboratory analysis (such as atomic absorption spectroscopy and titration), which is not only cumbersome and time-consuming, but also fails to capture the continuous and slow drift of the total concentration during operation.

[0005] Patent CN120652334A provides a method for online monitoring of the evolution of chromium ion speciation, but its focus is on the complexed state of Cr. 3+ The relative distribution of chromium is used to indicate the aging mechanism, but it does not provide a means of measuring the absolute amount of total chromium. In a Fe-filled environment... 2+ / Fe 3+ Cr 2+ / Cr 3+The main challenge currently facing the technology is how to accurately determine the total chromium concentration online and in situ in complex mixed solutions that support electrolytes, while avoiding serious interference from other metal ions (especially iron ions).

[0006] Therefore, there is an urgent need in this field to develop a method that can adapt to the complex electrolyte environment of iron-chromium flow batteries and achieve online in-situ detection of total chromium concentration. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art by providing an in-situ online detection method for the total Cr concentration in the electrolyte of an iron-chromium flow battery.

[0008] The objective of this invention can be achieved through the following technical solutions: An in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium redox flow battery, the detection system of which includes a detection battery module, an online spectral detection module, and a data processing and control unit; The battery detection module includes a detection battery and a charge / discharge detector; the charge / discharge detector is electrically connected to the electrode group of the detection battery and is used to regulate the charge / discharge state of the detection battery. The online spectral detection module includes a light source, a flow-through detection cell, and a spectral detection unit; the light incident end of the flow-through detection cell is connected to the light source through an incident optical fiber, and its light emitting end is connected to the spectral detection unit through an emitting optical fiber. The flow-through detection cell is connected in series to the electrolyte circulation path of the detection battery to form a closed-loop detection circuit for the electrolyte, so that the electrolyte can circulate through the detection battery and the flow-through detection cell. The data processing and control unit is electrically connected to the detection battery module and the online spectral detection module, respectively, and is used to synchronously acquire the charging and discharging parameters of the detection battery and collect and process spectral data.

[0009] Furthermore, the electrode assembly of the detection battery includes an upstream porous electrode and a downstream porous electrode.

[0010] Furthermore, the thickness of the upstream porous electrode Porosity is 1.0~5.0 mm. >0.6; downstream porous electrode thickness Porosity >0.6.

[0011] Furthermore, the flow-through detection cell is connected to the upstream porous electrode via a flow-through detection cell inlet pipe; the volume of the flow-through detection cell inlet pipe... The volume should be 5-50% of the upstream porous electrode volume to ensure that the hydrogen production volume within the upstream porous electrode during charging is equal to the volume of the inlet pipe of the flow-through detection cell. Similarly, this promotes the smooth flow of electrolyte in the inlet pipe of the flow-through detection cell through the flow-through detection cell; Furthermore, the light source is a tungsten lamp or an LED light source; The optical path length b of the flow-through detection cell is 0.05~0.2 cm; The spectral detection unit is a fiber optic spectrometer with a wavelength range of 300~1000 nm.

[0012] Specifically, the inlet of the flow-through detection cell is connected to the upstream porous electrode via a flow-through detection cell inlet pipe, and the outlet of the flow-through detection cell is connected to the downstream porous electrode, thereby connecting the flow-through detection cell in series into the detection battery circuit. The detection system also includes an electrically controlled on / off valve on the electrolyte inlet pipe of the detection battery, used to precisely control the timing and amount of electrolyte replenishment in the detection system, ensuring the accuracy and stability of electrolyte supply during the detection process.

[0013] Furthermore, the in-situ online detection method for the total Cr concentration in the iron-chromium redox flow battery electrolyte includes the following steps: S1. The electrolyte to be tested is introduced into the detection system to detect the Cr content in the electrolyte. 2+ The concentrations specifically include: S11. Open the electronically controlled opening and closing valve, introduce the electrolyte to be tested into the detection system, and close the electronically controlled opening and closing valve after it flows through the porous electrode downstream of the detection battery. This moment is recorded as t0. S12. The absorption spectrum of the electrolyte in the flow-through detection cell at time t0 in the 300~1000 nm wavelength range is acquired by the spectral detection unit, and the absorbance of the electrolyte at wavelengths of 480 nm and 800 nm is recorded, respectively denoted as . and Then, according to Equation 1, the Cr content in the electrolyte at time t0 is calculated. 2+ concentration : (Equation 1) In the formula, Fe in the negative electrode liquid 2+ actual concentration or nominal concentration (If the actual concentration is known or measurable, it should be used preferentially to improve detection accuracy.) The unit is mol·L. -1 ; For Fe 2+ Actual or nominal molar absorbance at 800 nm wavelength (0.3 L·mol) -1 ·cm-1 (Unit: L·mol) -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of the molar absorbance at 800 nm (the nominal value is 7.5 L·mol⁻¹). -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm.

[0014] S2. Reduce the electrolyte to a high-charge state and detect the Cr content. 3+ The concentrations specifically include: S21. At time t0, at a rate of 5~50 mA·cm -2 The low current density is used to detect battery charging, where the upstream porous electrode acts as the negative electrode and the downstream porous electrode acts as the positive electrode (this charging process removes Cr from the electrolyte in the negative electrode). 3+ Ions reduced to Cr 2+ ions, and in Cr 3+ During the final stage of charging, when the ion concentration decreases significantly, a significant hydrogen evolution reaction occurs. The generated hydrogen gas pushes the electrolyte in the inlet tube of the negative electrode and the flow-through detection cell, causing the electrolyte in the inlet tube of the flow-through detection cell to flow through the flow-through detection cell. The absorption spectrum in the 300–1000 nm wavelength range is continuously monitored until the absorbance at 480 nm is measured. Below At this point, the electrolyte reduced in the negative electrode of the detection battery (hereinafter referred to as: negative electrode electrolyte) begins to flow through the flow-through detection cell (indicating that the volume of hydrogen gas evolved at this time is the volume of the inlet tube of the flow-through detection cell), and charging stops. This moment is recorded as t1. Subsequently, the amount of hydrogen gas evolved is calculated according to Equation 2: (Equation 2) In the formula, t0 represents the amount of hydrogen gas produced during the period from t0 to t1, in mol; p represents the pressure inside the detection battery, in Pa. The volume of the inlet pipe of the flow-through detection pool is expressed in cubic meters (m³). 3 R is the universal gas constant, 8.314 J·mol⁻¹ -1 ·K -1 T represents the temperature inside the battery, measured in Kelvin (K). During the S22 and t0 to t1 periods, the cumulative charge corresponds to the total effect of chromium ion reduction and hydrogen evolution at the negative electrode (i.e., the upstream porous electrode). Therefore, Cr is calculated according to Equation 3. 2+ Generation amount: (Equation 3) In the formula, For the upstream porous electrode during the time period from t0 to t1, Cr 2+ The amount produced is expressed in mol; i is the charging current density, expressed in A·m. -2 ; The area of ​​the upstream porous electrode is expressed in m². 2 F is the Faraday constant, F = 96485 C·mol⁻¹ -1 ; S23. At time t2 after charging is completed, open the electronically controlled on / off valve to introduce new electrolyte into the detection system. Simultaneously, push the highly charged negative electrode electrolyte (i.e., the upstream porous electrode) and the inlet tube of the flow-through detection cell downstream (this negative electrode electrolyte first flows through the flow-through detection cell). Monitor and synchronously collect the absorption spectrum of the negative electrode electrolyte during the period when it flows through the flow-through detection cell. Measure the absorbance at 480 nm wavelength. Higher than At time t3, it indicates that the newly introduced electrolyte has flowed through the flow-through detection cell, completing the spectral acquisition of the high-charge state negative electrode electrolyte. Based on Equation 4, the residual Cr in the negative electrode electrolyte flowing through the flow-through detection cell from time t2 to t3 is calculated. 3+ Total amount : (Equation 4) In the formula, The real-time absorbance at a wavelength of 407 nm during the time period from t2 to t3; The area of ​​the upstream electrode is expressed in dm². 2 ; The thickness of the upstream electrode is expressed in dm. The porosity of the upstream electrode; The volume of the upstream porous electrode is expressed in liters (L). The molar absorbance of trivalent chromium hexahydrate is 16.1 L·mol⁻¹. -1 ·cm -1 .

[0015] S3. Based on the detection results of steps S1 and S2, calculate the total Cr concentration of the electrolyte to be tested, specifically including: The total chromium concentration of the electrolyte in the upstream porous electrode at time t0 is calculated according to Equation 5: (Equation 5) In the formula, For the upstream electrode during the time period from t0 to t1, Cr 2+ The amount produced, in mol; The area of ​​the upstream electrode is expressed in dm². 2 ; The thickness of the upstream electrode is expressed in dm. The porosity of the upstream electrode; This represents the volume of the upstream electrode, expressed in liters (L).

[0016] This method was used to perform in-situ online real-time detection of total Cr concentration in the electrolyte during the operation of an iron-chromium redox flow battery.

[0017] Specifically, it includes any of the following detection modes: (1) Online real-time monitoring: The detection system is connected to the pipeline of the flow battery system, and the electrolyte is extracted using the Venturi effect for online real-time monitoring; or (2) In-situ sampling and detection: The detection system is connected to the side wall or pipeline of the electrolyte storage tank, and the electrolyte is driven by a pump to form a closed loop for sampling and detection.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) Fully enclosed testing to completely avoid sampling leakage, contamination and oxidation errors. The flow-through detection cell in the system's spectral detection module is directly connected in series with the electrolyte circulation pipeline embedded in the battery, forming a fully enclosed flow path. During detection, the light source and spectrometer are fixed outside the optical windows on both sides of the flow-through detection cell, achieving non-contact measurement. This method fundamentally eliminates electrolyte leakage and contamination caused by opening the battery cap for sampling, and in particular avoids Cr... 2+ The oxidation problem caused by contact with air significantly improves the authenticity and reliability of the measurement results.

[0019] (2) Achieve low-interference, in-situ, online, and real-time detection The inlet and outlet of the detection system are fully sealed and fixedly connected to the pipeline or storage tank of the system under test through a sealed interface, without requiring changes to the main system circulation or interruption of operation. This structure enables low-interference, in-situ, online, and continuous detection of the flow battery system, ensuring the real-time nature and representativeness of the data.

[0020] (3) Low-cost in-situ regulation of state of charge simplifies the detection process and improves detection accuracy. This invention utilizes the built-in detection battery module of the detection system to restore the electrolyte to a high-charge state without the need to introduce or remove other auxiliary electrolytes, which greatly simplifies the system structure and detection process and significantly improves the universality of the method.

[0021] This invention establishes a mapping model between absorbance and ion concentration by screening characteristic wavelengths of 407 nm and 800 nm, and combines this with benchmark concentration calibration under high state of charge (SOC) to accurately analyze the concentration changes of total Cr in the electrolyte. Specifically, it first obtains the Cr concentration based on the absorbance at 800 nm. 2+The initial concentration was determined; subsequently, the electrolyte was reduced to a high-charge state, and spectral signal changes were monitored simultaneously to determine the charging termination conditions and hydrogen evolution amount; the Cr content during charging was calculated based on the charging coulomb number and hydrogen evolution amount. 2+ The concentration increment was obtained, and Cr was also obtained based on the absorption spectrum at 407 nm wavelength under high charge state. 3+ Concentration; finally, by combining the above data, the concentration data of total Cr in the electrolyte is obtained.

[0022] The detection system of this invention includes a battery detection module, an online spectral detection module, and a data processing and control module, which can be flexibly adapted to different application scenarios: online measurement is achieved by connecting a venturi tube in series to the electrolyte pipeline under test, or in-situ detection is achieved by connecting a liquid sampling and return pipe installed on the side wall to the electrolyte storage tank or pipeline, truly realizing non-invasive online detection. This method overcomes the limitations of traditional offline detection, such as cumbersome operation, long time consumption, and inability to continuously monitor, and achieves rapid response detection of total Cr concentration, effectively avoiding ion mutual interference and Cr in the electrolyte system. 3+ The measurement errors caused by complex and variable hydration states provide accurate data support for monitoring total Cr content in the electrolyte, correlation analysis of state of charge (SOC), and electrolyte rebalancing control, making it suitable for intelligent operation and maintenance management of megawatt-level iron-chromium redox flow battery energy storage systems.

[0023] (4) Reduce operation and maintenance costs and empower intelligent battery management The system of this invention automates the entire process from spectral acquisition and data analysis to result storage, significantly reducing manual intervention, human error, and labor costs. The system provides ion concentration data with second-level response, laying a data foundation for battery management (such as SOC / SOH) and fault diagnosis. Real-time and accurate ion concentration data directly guides the initiation and optimization of electrolyte rebalancing strategies, mitigating capacity decay. It also supports predictive maintenance, reducing unplanned downtime, extending lifespan, and improving the economy and reliability of energy storage systems. It is suitable for intelligent operation and maintenance of megawatt-level iron-chromium redox flow batteries. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the basic components and principle of the in-situ online detection system for total Cr concentration in the electrolyte of an iron-chromium redox flow battery according to an embodiment of the present invention. Figure 2 In order to be in Figure 1 A schematic diagram of the structure of the detection system of this invention after adding a Venturi tube suction and supply device; Figure 3 In order to be in Figure 1 A schematic diagram of the structure of the detection system of this invention after adding a sampling return system and connecting it to the sampling port of the iron-chromium flow battery electrolyte storage tank; The attached figures are labeled as follows: 1-1 Battery for testing, 1-2 Charge / discharge detector, 1-3 Battery inlet for testing, 1-4 Electrically controlled on / off valve, 1-5 Upstream porous electrode, 1-6 Flow-through detection cell inlet, 1-7 Flow-through detection cell outlet, 1-8 Downstream porous electrode, 1-9 Battery outlet for testing, 1-10 Flow-through detection cell inlet front pipe, 2-1 Light source, 2-2 Incident optical fiber, 2-3 Flow-through detection cell, 2-4 Outgoing optical fiber, 2-5 Spectroscopic detection unit, 3-1 Data processing and control unit, 4-1 Venturi tube, 4-2 Venturi tube inlet flange, 4-3 Venturi tube outlet flange, 4-4 Inlet sampling pipe, 4-5 Return pipe port, 5-1 Electrolyte storage tank, 5-2 Sampling return pipe, 5-3 Sampling return pipe flange, 5-4 Sampling return pipe inlet, 5-5 Sampling return pipe return port, 5-6 Sampling return pump. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, all raw materials and equipment used in this invention are commercially available products.

[0027] An in-situ online detection system for total Cr concentration in the electrolyte of an iron-chromium flow battery, such as... Figure 1 As shown, it includes a battery detection module, an online spectral detection module, and a data processing and control unit 3-1; The battery testing module includes a testing battery 1-1 and a charge / discharge tester 1-2. The testing battery 1-1, along the electrolyte flow direction, is sequentially equipped with a testing battery inlet 1-3, an electronically controlled on / off valve 1-4, an upstream porous electrode 1-5, a flow-through testing cell inlet pipe 1-10, a flow-through testing cell inlet 1-6, a flow-through testing cell outlet 1-7, a downstream porous electrode 1-8, and a testing battery outlet 1-9. The upstream porous electrode 1-5 has a thickness of 1.0~3.5 mm and a porosity >0.6, while the downstream porous electrode 1-8 has a thickness not less than twice the thickness of the upstream porous electrode 1-5 and a porosity >0.6. The volume of the flow-through testing cell inlet pipe 1-10 is... The volume is 5-50% of the upstream porous electrode (1-5); the charge / discharge detector 1-2 is electrically connected to the two porous electrodes and is used to regulate the charge / discharge state of the detection battery.

[0028] The online spectral detection module is built based on the UV-Vis absorption spectroscopy principle and includes a light source 2-1, an incident fiber optic cable 2-2, an exiting fiber optic cable 2-4, a flow-through detection cell 2-3, and a spectral detection unit 2-5. The optical path length of the flow-through detection cell 2-3 is 0.05~0.2 cm. The spectral detection unit 2-5 is a fiber optic spectrometer with a wavelength range of 300~1000 nm. The light source 2-1 is either a tungsten lamp or an LED light source. The two ends of the flow-through detection cell 2-3 are sealed to the inlet 1-6 and outlet 1-7 of the detection cell 1-1, respectively, to achieve a closed-loop flow path for the electrolyte. Simultaneously, the light incident end of the flow-through detection cell 2-3 is connected to the light source 2-1 via the incident fiber optic cable 2-2, and its light exit end is connected to the spectral detection unit 2-5 via the exiting fiber optic cable 2-4.

[0029] The data processing and control unit 3-1 is electrically connected to the charge and discharge detector 1-2, the spectral detection unit 2-5, and the electronically controlled on / off valve 1-4, respectively. It synchronously acquires the charge and discharge parameters of the test battery, collects and processes spectral data, and controls the start and stop, working mode switching and operation status monitoring of the test battery 1-1 by controlling the opening and closing state of the electronically controlled on / off valve 1-4, thereby realizing the overall control of the entire test system operation process.

[0030] Example 1 Online monitoring of total chromium concentration in electrolyte of negative electrode pipeline in iron-chromium flow battery This embodiment addresses the need for online real-time monitoring of the total chromium ion concentration in the electrolyte of the negative electrode pipeline during the operation of an iron-chromium redox flow battery energy storage system. Based on the Venturi tube suction supply principle, it realizes the pumpless layout and installation of the detection system.

[0031] Figure 2 This is a schematic diagram showing the detection system of the present invention equipped with a Venturi tube suction and liquid supply device. The components and markings of the detection system are shown below. Figure 1 Same. In this embodiment, the effective reaction area of ​​the detection battery is 20 cm². 2 The upstream porous electrode 1-5 has a thickness of 3 mm (porosity of 0.9), and the downstream porous electrode 1-8 has a thickness of 9 mm (porosity of 0.9). The inlet tube 1-10 of the flow-through detection cell has a volume of 1.5 mL. The optical path of the flow-through detection cell 2-3 is 0.1 cm. The spectral detection unit 2-5 uses a fiber optic spectrometer (model: SPEC-CMS 960, manufacturer: Linax (Shenzhen) Technology Co., Ltd.). The data processing and control unit 3-1 uses a SmartSoft 2.5.8 processing unit (manufacturer: Linax (Shenzhen) Technology Co., Ltd.), which is responsible for spectral data acquisition, processing and system operation control.

[0032] Figure 2The newly added components are described as follows: 4-1 is a Venturi tube (throat inner diameter D1 = 4.9 cm), connected in series to the test pipeline with inner diameter D0 = 9 cm via Venturi tube inlet flange 4-2 and Venturi tube outlet flange 4-3; 4-4 is the liquid inlet sampling tube, used to lead out the electrolyte to be tested; 4-5 is the liquid return port, used to return the tested electrolyte to the test pipeline. When the flow rate of the electrolyte in the test pipeline is 10 L·s... -1 At this time, the pressure difference between the inlet sampling tube 4-4 and the return tube 4-5 is approximately 16 kPa; under this pressure difference, when the electrically controlled on / off valve 1-4 is opened, the electrolyte flow rate through the detection system is approximately 0.5 mL / s. -1 .

[0033] Taking an iron-chromium redox flow battery system with an initial electrolyte formulation of 1 M FeCl2·4H2O + 1 M CrCl3·6H2O + 3 M HCl as an example, the specific steps for detecting the total chromium ion concentration are as follows: S1. Detecting the Cr content in the electrolyte to be tested. 2+ Concentration: (1) Open the electrically controlled on / off valve 1-4, and use the pressure difference to guide the electrolyte to be tested from the inlet sampling tube 4-4 of the venturi tube 4-1 at a rate of approximately 0.5 mL·s. -1 The flow rate flows into the detection system from the detection battery inlet 1-3, passes sequentially through the upstream porous electrode 1-5, the inlet pipe 1-10 of the flow-through detection cell, the flow-through detection cell 2-3, and the downstream porous electrode 1-8, and returns from the return outlet 1-9. The process takes about 1 minute. After completion, the electronically controlled on / off valve 1-4 is closed. This moment is recorded as t0, at which point the battery reaches stability.

[0034] (2) The absorption spectrum of the electrolyte in the flow-through detection cell 2-3 at time t0 in the 300~1000 nm band was collected by the spectral detection unit 2-5, and the absorbance of the electrolyte at a wavelength of 480 nm was recorded. and absorbance at 800 nm wavelength Then, according to Equation 1, the Cr content in the electrolyte (i.e., the sampled electrolyte) at time t0 is calculated. 2+ concentration : (Equation 1) In the formula, Fe in the negative electrode liquid 2+ actual concentration or nominal concentration (If the actual concentration is known or measurable, it should be used preferentially to improve detection accuracy.) The unit is mol·L. -1 ; For Fe 2+Actual or nominal molar absorbance at 800 nm wavelength (0.3 L·mol) -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of the molar absorbance at 800 nm (the nominal value is 7.5 L·mol⁻¹). -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm.

[0035] S2. Reduce the electrolyte to a high-charge state and detect the Cr content. 3+ Concentration: (1) At time t0, with a speed of 20 mA·cm -2 The low current density is used to charge the detection battery 1-1, where the upstream porous electrode 1-5 serves as the negative electrode and the downstream porous electrode 1-8 serves as the positive electrode; the absorption spectrum in the 300~1000 nm wavelength range is continuously monitored until the absorbance at 480 nm is measured. Below At time t1, charging is stopped, and then the amount of hydrogen released is calculated according to Equation 2: (Equation 2) In the formula, t0 represents the amount of hydrogen gas produced during the period from t0 to t1, in mol; p represents the pressure inside the detection battery, in Pa. The volume of inlet pipes 1-10 of the flow-through detection pool is expressed in cubic meters (m³). 3 R is the universal gas constant, 8.314 J·mol⁻¹ -1 ·K -1 T represents the temperature inside the battery, measured in Kelvin (K). (2) During the period from t0 to t1, the cumulative charge corresponds to the total effect of chromium ion reduction and hydrogen evolution at the negative electrode (i.e., the upstream porous electrode). Therefore, the Cr is calculated according to Equation 3. 2+ Generation amount: (Equation 3) In the formula, For the upstream porous electrodes 1-5 during the time period from t0 to t1, Cr 2+ The amount produced is expressed in mol; i is the charging current density, expressed in A·m. -2 ; The area of ​​the upstream porous electrodes 1-5 is in m².2 F is the Faraday constant, F = 96485 C·mol⁻¹ -1 ; (3) At time t2 after charging is completed, open the electronically controlled on / off valve 1-4 to introduce new electrolyte into the detection system. The new electrolyte flows in from the inlet 1-3 of the detection battery, pushing the negative electrode electrolyte in the upstream porous electrode 1-5 and the inlet tube 1-10 of the flow-through detection cell, which is in a high-charge state, through the flow-through detection cell 2-3. Monitor and collect the full-band absorption spectrum of the negative electrode electrolyte during the time it flows through the flow-through detection cell 2-3 in real time. The absorbance at 480 nm wavelength is then measured. Higher than The time is recorded as t3, indicating that the newly introduced electrolyte has flowed through the flow-through detection cell, completing the spectral acquisition of the high-charge state negative electrode electrolyte. Based on Equation 4, the residual Cr in the negative electrode electrolyte flowing through flow-through detection cell 2-3 during the period from t2 to t3 is calculated. 3+ Total amount : (Equation 4) In the formula, The real-time absorbance at a wavelength of 407 nm during the time period from t2 to t3; The volume of the upstream porous electrodes 1-5 is expressed in liters (L). The molar absorbance of trivalent chromium hexahydrate is 16.1 L·mol⁻¹. -1 ·cm -1 .

[0036] S3. Close the electrically controlled on / off valve 1-4 to complete this measurement sampling. Based on the detection results of steps S1 and S2, calculate the total chromium concentration of the electrolyte (i.e., the sampling electrolyte) in the upstream porous electrode 1-5 at time t0 according to Equation 5: (Equation 5) In the formula, For the upstream porous electrodes 1-5 during the time period from t0 to t1, Cr 2+ The amount produced, in mol; The volume of the upstream porous electrodes 1-5 is expressed in liters (L).

[0037] Example 2 In-situ monitoring of total chromium concentration in the electrolyte of the negative electrode storage tank of an iron-chromium flow battery This embodiment addresses the need for in-situ monitoring of the total chromium ion concentration in the electrolyte of the negative electrode tank during the operation of an iron-chromium redox flow battery energy storage system. The detection system is equipped with a sampling return pump to achieve a closed-loop circulation of electrolyte extraction, internal circulation of the detection system, and return.

[0038] Figure 3This is a schematic diagram of the in-situ monitoring of the detection system of the present invention, which is connected to the electrolyte storage tank 5-1 (a negative electrode liquid storage tank in this embodiment) via the sampling return pipe 5-2. The components and markings of the detection system are as follows: Figure 1 Same. In this embodiment, the effective reaction area of ​​the detection battery is 20 cm². 2 The upstream porous electrode 1-5 has a thickness of 3 mm (porosity of 0.9), and the downstream porous electrode 1-8 has a thickness of 9 mm (porosity of 0.9). The inlet tube 1-10 of the flow-through detection cell has a volume of 1.5 mL. The optical path of the flow-through detection cell 2-3 is 0.1 cm. The spectral detection unit 2-5 uses a fiber optic spectrometer (model: SPEC-CMS 960, manufacturer: Linax (Shenzhen) Technology Co., Ltd.). The data processing and control unit 3-1 uses a SmartSoft 2.5.8 processing unit (manufacturer: Linax (Shenzhen) Technology Co., Ltd.) to handle spectral data acquisition and processing.

[0039] Figure 3 The newly added components are described as follows: 5-1 is the electrolyte storage tank, which stores the negative electrode liquid; 5-2 is the sampling return pipe, used for sampling and reflux of the electrolyte; 5-3 is the sampling return pipe flange, which achieves a sealed connection between the sampling return pipe 5-2 and the electrolyte storage tank 5-1; 5-4 is the sampling return pipe inlet, which is located far from the tank wall and can be flexibly adjusted to ensure that the electrolyte is collected in a uniformly mixed manner; 5-5 is the sampling return pipe return port, which is arranged close to the tank wall to reduce the interference of the refluxed electrolyte on the concentration distribution of the electrolyte in the tank; 5-6 is the sampling return pump (in this embodiment, a magnetically coupled centrifugal pump is used, with a flow rate adjustable range of 0.25~2.5 mL·s). -1 (with a pumping pressure differential of not less than 50 kPa), providing stable power for the flow of electrolyte in a closed-loop circulation.

[0040] Taking an iron-chromium redox flow battery system with an initial electrolyte formulation of 1 M FeCl2·4H2O + 1 M CrCl3·6H2O + 3 M HCl as an example, the specific steps for detecting the total chromium ion concentration are as follows: S1. Detecting the Cr content in the electrolyte to be tested. 2+ Concentration: (1) Keep the electrically controlled on / off valve 1-4 in the open state, start the sampling return pump 5-6, drive the electrolyte to be drawn in from the sampling return pipe inlet 5-4, flow through the upstream porous electrode 1-5, the inlet pipe 1-10 of the flow-through detection cell, the flow-through detection cell 2-3, and the downstream porous electrode 1-8 in sequence, and finally return to the electrolyte storage tank 5-1 through the sampling return pipe return port 5-5; set the circulation flow rate to 1 mL·s -1After about 30 seconds, the battery injection is completed. Then, the sampling return pump 5-6 and the electronically controlled on / off valve 1-4 are closed in sequence. This moment is recorded as t0. At this time, the battery reaches stability.

[0041] (2) The absorption spectrum of the electrolyte in the flow-through detection cell 2-3 at time t0 in the 300~1000 nm band was collected by the spectral detection unit 2-5, and the absorbance of the electrolyte at a wavelength of 480 nm was recorded. and absorbance at 800 nm wavelength Then, according to Equation 1, the Cr content in the electrolyte (i.e., the sampled electrolyte) at time t0 is calculated. 2+ concentration : (Equation 1) In the formula, Fe in the negative electrode liquid 2+ actual concentration or nominal concentration (If the actual concentration is known or measurable, it should be used preferentially to improve detection accuracy.) The unit is mol·L. -1 ; For Fe 2+ Actual or nominal molar absorbance at 800 nm wavelength (0.3 L·mol) -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of the molar absorbance at 800 nm (the nominal value is 7.5 L·mol⁻¹). -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm.

[0042] S2. Reduce the electrolyte to a high-charge state and detect the Cr content. 3+ Concentration: (1) At time t0, with a speed of 20 mA·cm -2 The low current density is used to charge the detection battery 1-1, where the upstream porous electrode 1-5 serves as the negative electrode and the downstream porous electrode 1-8 serves as the positive electrode; the absorption spectrum in the 300~1000 nm wavelength range is continuously monitored until the absorbance at 480 nm is measured. Below At time t1, charging is stopped, and then the amount of hydrogen released is calculated according to Equation 2: (Equation 2) In the formula, t0 represents the amount of hydrogen gas produced during the period from t0 to t1, in mol; p represents the pressure inside the detection battery, in Pa. The volume of inlet pipes 1-10 of the flow-through detection pool is expressed in cubic meters (m³). 3 R is the universal gas constant, 8.314 J·mol⁻¹ -1 ·K -1 T represents the temperature inside the battery, measured in Kelvin (K). (2) During the period from t0 to t1, the cumulative charge corresponds to the total effect of chromium ion reduction and hydrogen evolution at the negative electrode (i.e., the upstream porous electrode). Therefore, the Cr is calculated according to Equation 3. 2+ Generation amount: (Equation 3) In the formula, For the upstream porous electrodes 1-5 during the time period from t0 to t1, Cr 2+ The amount produced is expressed in mol; i is the charging current density, expressed in A·m. -2 ; The area of ​​the upstream porous electrodes 1-5 is in m². 2 F is the Faraday constant, F = 96485 C·mol⁻¹ -1 ; (3) At time t2 after charging is completed, open the electronically controlled on / off valve 1-4 to introduce new electrolyte into the detection system. The new electrolyte flows in from the inlet 1-3 of the detection battery, pushing the negative electrode electrolyte in the upstream porous electrode 1-5 and the inlet tube 1-10 of the flow-through detection cell, which is in a high-charge state, through the flow-through detection cell 2-3. Monitor and collect the full-band absorption spectrum of the negative electrode electrolyte during the time it flows through the flow-through detection cell 2-3 in real time. The absorbance at 480 nm wavelength is then measured. Higher than The time is recorded as t3, indicating that the newly introduced electrolyte has flowed through the flow-through detection cell, completing the spectral acquisition of the high-charge state negative electrode electrolyte. Based on Equation 4, the residual Cr in the negative electrode electrolyte flowing through flow-through detection cell 2-3 during the period from t2 to t3 is calculated. 3+ Total amount : (Equation 4) In the formula, The real-time absorbance at a wavelength of 407 nm during the time period from t2 to t3; The volume of the upstream porous electrodes 1-5 is expressed in liters (L). The molar absorbance of trivalent chromium hexahydrate is 16.1 L·mol⁻¹. -1 ·cm -1 .

[0043] S3. Sequentially close the sampling return pump 5-6 and the electrically controlled on / off valve 1-4 to complete this measurement sampling. Based on the detection results of steps S1 and S2, calculate the total chromium concentration of the electrolyte (i.e., the sampling electrolyte) in the upstream porous electrode 1-5 at time t0 according to Equation 5: (Equation 5) In the formula, For the upstream porous electrodes 1-5 during the time period from t0 to t1, Cr 2+ The amount produced, in mol; The volume of the upstream porous electrodes 1-5 is expressed in liters (L).

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An in-situ online detection method for total Cr concentration in an iron-chromium flow battery electrolyte, characterized in that, Includes the following steps: S1. The electrolyte to be tested is introduced into the detection cell (1-1). A flow-through detection cell (2-3) is connected in series between the upstream and downstream electrodes of the detection cell (1-1). The Cr in the electrolyte in the flow-through detection cell (2-3) is detected by the spectroscopic detection unit (2-5). 2+ concentration; S2. Charge the test battery (1-1). This charging process will remove Cr from the electrolyte in the negative electrode. 3+ Ions reduced to Cr 2+ Ions; During the final stage of charging, a hydrogen evolution reaction occurs, and the generated hydrogen gas pushes the electrolyte in the inlet tube (1-10) of the flow-through detection cell through the flow-through detection cell (2-3). Simultaneously, the spectroscopic detection unit (2-5) collects the spectrum of the electrolyte flowing through it to obtain Cr. 2+ The amount of Cr generated; after charging, new electrolyte is introduced, and the reduced electrolyte is pushed through the flow-through detection cell (2-3). The spectrum of the electrolyte flowing through the cell is collected again by the spectroscopic detection unit (2-5) to obtain the Cr content in the reduced electrolyte. 3+ concentration; S3. Based on the detection results of steps S1 and S2, the total Cr concentration of the electrolyte to be tested is obtained.

2. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium flow battery according to claim 1, characterized in that, The spectral detection unit (2-5) is a fiber optic spectrometer with a wavelength range of 300~1000 nm.

3. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium redox flow battery according to claim 1, characterized in that, In step S1, the Cr in the electrolyte is detected. 2+ Concentration, the specific process is as follows: S11. The electrolyte to be tested is introduced into the detection battery (1-1) and flows sequentially through the upstream electrode of the detection battery (1-1), the flow-through detection cell (2-3) and the downstream electrode of the detection battery (1-1) before the introduction is stopped. This is recorded as time t0. S12. The absorption spectrum of the electrolyte in the flow-through detection cell (2-3) at time t0 in the 300~1000 nm wavelength range is collected by the spectral detection unit (2-5), and the absorbance of the electrolyte at wavelengths of 480 nm and 800 nm is recorded, respectively. and Then, according to Equation 1, the Cr in the electrolyte at time t0 is calculated. 2+ Concentration: (Equation 1) In the formula, Fe, the negative electrode liquid 2+ The concentration, in mol·L -1 ; For Fe 2+ The molar absorbance at 800 nm, expressed in L·mol⁻¹. -1 ·cm -1 ; For Cr 2+ The molar absorbance at 800 nm, expressed in L·mol⁻¹. -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm.

4. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium flow battery according to claim 3, characterized in that, The optical path length b of the flow-through detection cell (2-3) is 0.05~0.2 cm.

5. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium redox flow battery according to claim 1, characterized in that, In step S2, Cr 2+ The amount generated is obtained through the following steps: S21. At time t0, charge the detection battery (1-1); continuously monitor the absorption spectrum in the 300~1000 nm band, and wait for the absorbance at the 480 nm wavelength. Below When charging stops, this time is recorded as t1; then the amount of hydrogen released is calculated according to Equation 2: (Equation 2) In the formula, t0 represents the amount of hydrogen gas produced during the period from t0 to t1, in mol; p represents the pressure inside the detection battery, in Pa. The volume of the inlet pipe (1-10) of the flow-through detection pool is expressed in cubic meters (m³). 3 R is the universal gas constant; T is the temperature inside the battery being tested, in K. S22, Calculate Cr according to Equation 3 2+ Generation amount: (Equation 3) In the formula, For Cr in the upstream electrodes (1-5) during the time period from t0 to t1 2+ The amount produced is expressed in mol; i is the charging current density, expressed in A·m. -2 ; The area of ​​the upstream electrode, in meters. 2 F is the Faraday constant, with units of C·mol⁻¹. -1 ; This represents the amount of hydrogen gas produced during the period from t0 to t1, expressed in mol.

6. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium flow battery according to claim 5, characterized in that, In step S21, the detection battery (1-1) is charged, with its upstream electrode serving as the negative electrode during the charging process; the charging current density used is 5~50 mA·cm. -2 .

7. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium redox flow battery according to claim 5, characterized in that, The flow-through detection cell (2-3) is connected to the upstream electrode through the inlet pipe (1-10); the volume of the inlet pipe (1-10) is... It is 5-50% of the volume of the upstream electrode.

8. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium redox flow battery according to claim 1, characterized in that, In step S2, the Cr in the reduced electrolyte 3+ The concentration is obtained through the following steps: At time t2 after charging is completed, new electrolyte is introduced into the detection system, and the absorption spectrum of the highly charged negative electrode electrolyte flowing through the flow-through detection cell (2-3) is simultaneously collected. The absorbance at 480 nm wavelength is then measured. Higher than The time is recorded as t3, and the data collection is completed. The residual Cr in the electrolyte flowing through the flow-through detection cell (2-3) during the period from t2 to t3 is calculated according to the following formula. 3+ Total amount : (Equation 4) In the formula, The real-time absorbance at a wavelength of 407 nm during the time period from t2 to t3; The area of ​​the upstream electrode is expressed in dm². 2 ; The thickness of the upstream electrode is expressed in dm. The porosity of the upstream electrode; This refers to the volume of the upstream electrode, in liters (L). The molar absorbance of trivalent chromium hexahydrate is 16.1 L·mol⁻¹. -1 ·cm -1 .

9. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium redox flow battery according to claim 1, characterized in that, The specific process for calculating the total Cr concentration of the electrolyte in step S3 is as follows: The total chromium concentration of the electrolyte in the upstream electrode at time t0 is calculated according to Equation 5: (Equation 5) In the formula, For the upstream electrode during the time period from t0 to t1, Cr 2+ The amount produced, in mol; The area of ​​the upstream electrode is expressed in dm². 2 ; The thickness of the upstream electrode is expressed in dm. The porosity of the upstream electrode; This represents the volume of the upstream electrode, expressed in liters (L).

10. The in-situ online detection method for total Cr concentration in the electrolyte of an iron-chromium flow battery according to any one of claims 1-9, characterized in that, Both the upstream and downstream electrodes are porous electrodes; the thickness of the upstream electrode... Porosity is 1.0~5.0 mm. >0.6; the thickness of the downstream electrode Porosity >0.6.

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