Determination of vanadium ion content in vanadium electrolyte by potentiometric titration

Abstract

The invention belongs to the field of new energy, and specifically relates to a method for determining the content of vanadium ions in a vanadium electrolyte by a potentiometric titration method. The method comprises: a pretreatment step, wherein the concentration of the electrolyte to be tested is adjusted to obtain a test sample, wherein the chloride ion content in the test sample is less than 10 mol / L; a step of adding a chloride ion complexing agent, wherein the chloride ion complexing agent is added to make the initial potential in the test sample less than 430 mv; and a titration step, wherein a titration reagent containing an oxidant of known concentration is dripped into the test sample containing the chloride ion complexing agent, and the volume of the titration reagent consumed at the potential jump point is recorded, wherein in the step of adding the chloride ion complexing agent, the chloride ion complexing agent is a mercury salt, and the initial potential is obtained based on a three-electrode system.

Description

Technical Field

[0001] The present invention belongs to the field of new energy, and specifically relates to a method for detecting a liquid flow battery electrolyte, and more specifically to a method for measuring vanadium ions in a vanadium-containing liquid flow battery electrolyte, which is obtained based on an improvement of a titration method. Background Art

[0002] Liquid flow battery refers to a type of battery in which both the positive and negative active materials are in liquid form. It differs from other electrochemical systems mainly in that the main energy source of the battery is the positive and negative active materials in liquid form, rather than solid materials in the general sense. The positive and negative active material solutions are stored in two containers respectively. When working, the active material solutions enter the battery stack through the circulation pump respectively, and a battery reaction occurs, converting chemical energy into electrical energy.

[0003] At present, vanadium flow batteries, especially all-vanadium flow batteries, have great application prospects in the fields of solar energy and wind energy storage, as well as grid peak regulation, power supply systems in remote areas, uninterruptible power supplies, etc., due to their advantages of no pollution, long life, high stability of energy conversion efficiency and simple maintenance. They are a very important energy storage method for the development of new energy. Moreover, compared with traditional batteries, the positive and negative electrodes of vanadium flow batteries, especially all-vanadium flow batteries, are vanadium ion reactions, which reduces cross-interference and capacity loss.

[0004] As a carrier of active substances, the electrolyte is one of the most important components of (all) vanadium flow batteries. The concentration of the electrolyte directly affects the energy density of the battery. How to obtain high-performance vanadium electrolyte has become a hot topic for researchers from all over the world.

[0005] The preparation methods of electrolyte, especially vanadium electrolyte, generally include chemical synthesis method, electrolysis method, etc. The quality control of electrolyte usually includes the control of impurities and ion state. For example, in some existing technical solutions for detecting the state of electrolyte, the valence state or content of the corresponding metal element in the electrolyte can be determined by methods such as spectrophotometry, titration, ICP (inductively coupled plasma), etc.

[0006] For the detection method based on spectrophotometry, it is necessary to make a corresponding standard curve, and then compare the test results with the standard curve to determine the ion state in the detection object. For the titration method, the corresponding ion state is determined by adding chemical reagents and measuring the potential jump in the system. For the ICP method, detection is carried out with the help of electromagnetic fields.

[0007] Since spectrophotometry is based on a fitted standard curve, it is generally considered an indirect detection method, but it requires the preparation of standard samples of different concentrations, the testing process is cumbersome, and the error is large when measuring high-concentration vanadium ions; and it is impossible to accurately measure the concentrations of two vanadium ions when they coexist; the detection equipment of the ICP (inductively coupled plasma) method is expensive, and it is impossible to accurately measure the concentrations of two vanadium ions when they coexist.

[0008] Titration is based on the potential change caused by the ion state, so it is generally considered to be a direct detection method, and it can also be used for direct detection of multiple ion systems. For example, for sulfuric acid-based vanadium flow battery electrolytes, suitable reagents can be used to titrate sulfuric acid-based electrolytes.

[0009] Reference 1 discloses a method for quantitatively determining the vanadium ion concentration in the negative electrode electrolyte solution of an all-vanadium liquid flow battery. In an oxygen-free environment, a volume V1 of the negative electrode vanadium electrolyte solution of the all-vanadium liquid flow battery is taken and diluted with a sulfuric acid-phosphate buffer solution. At a certain temperature, a redox titration is performed with a potassium permanganate solution KMnO4 of a calibrated concentration. When the redox titration potential has two jumps (a, b), the second jump is the titration end point. The volume of potassium permanganate consumed during the first jump and the second jump is V. a 、V b , calculate the concentration C of divalent and trivalent vanadium in the electrolyte solution V(Ⅱ) , C V(Ⅲ) And the total vanadium concentration C V .

[0010] References:

[0011] Reference 1: CN104713923A Summary of the invention

[0012] Problem that the invention aims to solve

[0013] There are usually two adjacent valence states of vanadium ions in the electrolyte solution of vanadium flow batteries. When using the existing titration method for detection, potassium permanganate is usually used as an oxidant, and the redox reaction between it and low-valent vanadium is the basis. For example, in a phosphate buffer solution, a potassium permanganate standard titration solution is used to titrate the electrolyte sample to gradually oxidize the low-valent vanadium ions until they are pentavalent. Each potential jump corresponds to a change in the vanadium valence state. According to the consumed volume of the potassium permanganate standard solution corresponding to the potential jump point, the content of vanadium ions in each valence state and total vanadium is calculated.

[0014] The above-mentioned titration method has no obvious problem in the detection of sulfuric acid-based electrolytes. For example, the detection is also completed by this mechanism in Reference 1.

[0015] However, in current industrial practice, it has been found that if the above detection is performed for hydrochloric acid-based electrolytes, satisfactory detection results cannot be obtained. The main reason is that the chloride ions in the electrolyte to be detected may consume a part of the titration reagent when the titration reagent is added, or in the titration, due to the instantaneous reaction with the titration reagent, the irregular jump of the detection potential may occur, which may make it difficult to determine or be unable to determine the potential jump point or the titration end point. Therefore, for hydrochloric acid-based electrolytes, it is currently difficult to directly detect the vanadium ion concentration by a simple and accurate titration method.

[0016] In view of the problems existing in the detection of hydrochloric acid-based vanadium flow battery electrolyte, the present invention provides a new titration method for detecting hydrochloric acid-based vanadium flow battery electrolyte. In this method, a chloride ion complexing agent is added to stabilize the chloride ions so that they do not react with the titration reagent and do not cause changes in the potential baseline. Overall, the potential jumps from trivalent to tetravalent and from tetravalent to pentavalent vanadium ions are obviously retained and do not cause other potential jumps or instability. Therefore, the concentration of vanadium ions in the hydrochloric acid-based vanadium flow battery electrolyte can be successfully determined.

[0017] Solutions for solving problems

[0018] [1] The present invention provides a method for detecting the concentration of vanadium ions in a vanadium flow battery electrolyte, wherein the method comprises:

[0019] A pre-treatment step of adjusting the concentration of the electrolyte to be tested to obtain a test sample, wherein the chloride ion content in the test sample is less than 10 mol / L;

[0020] The step of adding a chloride ion complexing agent, wherein the chloride ion complexing agent is added to reduce the initial potential in the test sample to below 430 mv;

[0021] The titration step comprises dripping a titration reagent containing an oxidant of known concentration into the test sample containing the chloride ion complexing agent, and recording the volume of the titration reagent consumed at the potential jump point.

[0022] Wherein, in the step of adding the chloride ion complexing agent, the chloride ion complexing agent is a mercury salt, and the initial potential is obtained based on a three-electrode system.

[0023] [2] The detection method according to [1], wherein in the pretreatment step, water or sulfuric acid solution is used to adjust the concentration.

[0024] [3] The detection method according to [1] or [2], wherein after the pretreatment step, the chloride ion content in the detection sample is 0.5 to 8 mol / L.

[0025] [4] The detection method according to any one of [1] to [3], wherein phosphoric acid has been added to the detection sample before using the chloride ion complexing agent.

[0026] [5] The detection method according to any one of [1] to [4], wherein the chloride ion complexing agent is mercuric sulfate.

[0027] [6] The detection method according to any one of [1] to [5], wherein in the titration step, the oxidant comprises a salt of a transition metal acid.

[0028] [7] The detection method according to any one of [1] to [6], wherein the titration step is performed under stirring conditions.

[0029] [8]. The detection method according to any one of [1] to [7], wherein in the titration step, two potential jump points appear, and the volumes of the titration reagent consumed are V1 and V2 in the order in which the jump points appear, and the following calculation is performed.

[0030] C (V-III） = C (O) V1 / Vρ

[0031] C (V全） = C (O) (V2-V1) / Vρ

[0032] C (V-IV） =C (V全） - C (V-III）

[0033] Among them, C (V-III） Indicates the concentration of trivalent vanadium ions in the test sample, C (O) Indicates the concentration of the oxidant in the titration reagent, C (V全） Indicates the concentration of all vanadium ions in the test sample, C (V-IV） represents the concentration of tetravalent vanadium ions in the test sample, V represents the volume of the test sample, and ρ represents the difference in valence of the oxidizing element before and after the oxidant is reduced.

[0034] [9] The detection method according to any one of [1] to [8], wherein the oxidant is permanganate and ρ is 5.

[0035]

[10] The detection method according to any one of [1] to [9], wherein the vanadium redox flow battery electrolyte is an all-vanadium redox flow battery electrolyte.

[0036] Effects of the Invention

[0037] By implementing the above technical solution, the present invention can achieve the following technical effects:

[0038] 1) The present invention provides a new testing method, which makes it possible to use the titration detection method that could not be used in hydrochloric acid-based vanadium liquid flow battery electrolyte in the past;

[0039] 2) The chloride ion complexing agent used in the present invention can successfully bind the chloride ions in the test sample and prevent them from reacting with the oxidant in the titration reagent, thereby shielding the influence of the chloride ions on the titration reaction;

[0040] 3) The chloride ion complexing agent selected in the present invention, when added to the test sample, can not cause instability of the potential baseline in the test, and does not affect the potential jump caused by the change of the valence of vanadium ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 :A flow chart of the detection method of the present invention

[0042] Figure 2 : Titration potential curve in Example 1

[0043] Figure 3 : Titration potential curve in Comparative Example 1

[0044] Figure 4 : Titration potential curve in Comparative Example 2 DETAILED DESCRIPTION

[0045] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0046] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoint numerical values ​​A and B.

[0047] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0048] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0049] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0050] In this specification, the term "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2°C", and unless otherwise specified, the "viscosity" of the present invention refers to the viscosity at this temperature.

[0051] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used indicates weight or mass percentage.

[0052] In the present specification, the use of “substantially” or “essentially” means that the standard deviation from a theoretical model or theoretical data is within a numerical range of 2%, preferably 1%, and more preferably 0.8%.

[0053] In this specification, when the terms “include” and / or “comprise” are used, they indicate the existence of features, steps, operations, devices, components and / or their combinations.

[0054] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0055] The present invention mainly provides a detection method for hydrochloric acid-based vanadium liquid flow battery electrolyte. The method of the present invention overcomes the problem that the original detection method for hydrochloric acid-based vanadium liquid flow battery electrolyte cannot be tested by potentiometric titration. By adding a specific chloride ion complexing agent, it is possible to successfully detect the vanadium ion concentration in the sample through a specific potential jump without affecting the detection potential characteristics.

[0056] Specifically, the present invention is mainly obtained through the following insights:

[0057] As mentioned above, in view of the problem that hydrochloric acid-based vanadium electrolyte could not be tested by titration in the past, the starting point of the present invention is how to shield the influence of chloride ions, so various methods have been tried. Through continuous attempts, it has been found that when a chloride ion complexing agent containing mercury salt is used, the chloride ions in the test sample can be well bound, and its addition affects the stability of the potential baseline during titration detection, and retains the obvious potential jump when the valence of the vanadium ion changes. Therefore, it makes it possible to detect hydrochloric acid-based vanadium electrolyte by potentiometric titration.

[0058] Specifically, the present invention provides a method for detecting the concentration of vanadium ions in a vanadium flow battery electrolyte, the method comprising:

[0059] A pre-treatment step of adjusting the concentration of the electrolyte to be tested to obtain a test sample, wherein the chloride ion content in the test sample is less than 10 mol / L;

[0060] The step of adding a chloride ion complexing agent, wherein the chloride ion complexing agent is added to reduce the initial potential in the test sample to below 430 mv;

[0061] The titration step comprises dripping a titration reagent containing an oxidant of known concentration into the test sample containing the chloride ion complexing agent, and recording the volume of the titration reagent consumed at the potential jump point.

[0062] Wherein, in the step of adding the chloride ion complexing agent, the chloride ion complexing agent is a mercury salt, and the initial potential is obtained based on a three-electrode system.

[0063] (Electrolyte to be tested / vanadium flow battery electrolyte)

[0064] In principle, there is no particular limitation on the vanadium flow battery electrolyte to be tested in the present invention, as long as it contains vanadium ions.

[0065] In some preferred embodiments, the vanadium flow battery electrolyte of the present invention can be an all-vanadium flow battery electrolyte. Further, the type of the electrolyte of the present invention is a hydrochloric acid-based all-vanadium flow battery electrolyte as described above, that is, the vanadium ions therein are mainly present in the form of chloride, or substantially all in the form of chloride.

[0066] The all-vanadium liquid flow battery electrolyte of the present invention can be an unused finished product electrolyte, a positive electrode electrolyte or a negative electrode electrolyte in any state during the operation of the liquid flow battery.

[0067] The finished electrolyte of the present invention is not particularly limited in the present invention, and can be any electrolyte produced in the art that can be used in liquid flow batteries.

[0068] In some specific embodiments, the finished electrolyte can be those electrolytes that are allowed to be directly used for filling of liquid flow batteries, and the indicators such as metal ion content, system pH value, electrolyte concentration, impurity content, etc. can fully meet the use requirements.

[0069] In some other specific embodiments, the finished electrolyte may also be those electrolytes that need to be further adjusted in composition, content, etc. before being used for filling liquid flow battery equipment.

[0070] There is no particular limitation on the positive or negative electrode electrolyte in any state during the operation of the present invention, and it can be the electrolyte directly obtained from the positive electrode or the negative electrode at any SOC state.

[0071] In principle, there is no particular limitation on the preparation method of the electrolyte for vanadium-containing redox flow batteries. In some specific embodiments, the oxide may be dissolved in a hydrochloric acid solvent, and, optionally, impurities may be removed by various impurity removal or purification means to obtain an electrolyte. In addition, in any desired case, various reducing agents may be used in the above method after the hydrochloric acid solvent is dissolved to adjust the overall valence of the metal ions in the system.

[0072] In some typical embodiments, for the above-mentioned oxide route, vanadium oxide mainly comprising V2O5 can be obtained by sintering or the like (for example, sintering ammonium metavanadate, etc.), and further, the oxide is dissolved in a hydrochloric acid solvent, and optionally, various heavy metal impurities therein can be removed by impurity removal.

[0073] In principle, there is no particular limitation on the concentration of the hydrochloric acid solvent that can be used. The conventional concentration of the hydrochloric acid solvent for preparing electrolyte in the art can be used. In some specific embodiments of the present invention, dilute hydrochloric acid with a mass concentration of 37% by mass or less can be listed. Preferably, the concentration of the hydrochloric acid can be 20-37% by mass, and more preferably 30-37% by mass.

[0074] Further, the reductant that can be used may include solids, gases, etc. with reducing properties. Preferably, one or more solid organic compounds and inorganic compounds with reducing properties may be used. In some specific embodiments of the present invention, the reductant that can be listed in the present invention includes one or more of oxalic acid, citric acid, sulfites, diethyldithiocarbamic acid, hydrogen, ammonia, methane, hydrogen sulfide, sulfur dioxide, etc. Preferably, the reductant is selected from one or more of oxalic acid, sulfites, and diethyldithiocarbamic acid.

[0075] (Three-electrode system)

[0076] The electrode potentials described below in the present invention, such as potential baseline and potential jump, are tested by a three-electrode system.

[0077] In principle, there is no particular limitation on the three-electrode system, and a three-electrode system commonly used in the art can be used, which includes a reference electrode, a working electrode, and a counter electrode.

[0078] In some preferred embodiments of the present invention, the reference electrode may be a saturated calomel electrode, and the working electrode is preferably a platinum electrode.

[0079] When the above three-electrode system is used for testing, preferably, the effective detection parts of the three electrodes can be extended to 2 to 3 cm below the detection liquid surface.

[0080] (Pre-processing steps)

[0081] In the pre-treatment step of the present invention, the chloride ion concentration in the above-mentioned electrolyte to be tested is mainly adjusted to obtain a test sample with a suitable chloride ion concentration.

[0082] The present invention finds that if the chloride ion concentration in the test sample is too high, it will be difficult to completely bind the chloride ions even if the chloride ion stabilizer described below is used subsequently. As a result, the baseline of the test unit will be unstable or the jump will become irregular or abnormal.

[0083] The appropriate chloride ion concentration may be below 10 mol / L. In some preferred embodiments, the chloride ion concentration in the test sample may be adjusted to 0.5 to 8 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, etc.

[0084] There is no particular limitation on the method for adjusting the chloride ion concentration. For example, pure water or an acid solvent may be added. As for the acid solvent that can be used, sulfuric acid may be preferably used.

[0085] In addition, in the pre-treatment step of the present invention, in addition to adjusting the chloride ion concentration, in some preferred embodiments, a suitable buffering substance, typically phosphoric acid, may be added. There is no particular limitation on the use of such a buffering substance in principle, and it may be used with reference to the conventional use rules in titration tests in the art.

[0086] (Steps for adding a chloride ion complexing agent)

[0087] The main function of the chloride ion complexing agent used in the present invention is to bind chloride ions and prevent them from reacting with the oxidant in the titration reagent. On the other hand, the main requirement for the use of the chloride ion complexing agent is that its use will not cause instability in potential detection (such as baseline, etc.), and the substance after complexing with chlorine will not affect the potential detection, that is, neither the chloride ion itself nor the reaction product with chloride ions will affect the observation and determination of the potential jump in the potentiometric titration.

[0088] Therefore, from the above-mentioned purpose, the chloride ion complexing agent used in the present invention can include a mercuric salt, which can be an acid-soluble or water-soluble mercuric salt. In some preferred embodiments, the mercuric salt can be mercuric sulfate. For mercuric sulfate, it can form a mercury-chlorine system after being added to the test sample.

[0089] In principle, the amount of mercuric sulfate added can be enough to bind the chloride ions, for example, an amount of more than 0.5 times the molar number of chloride ions can be added by estimation or other auxiliary detection means (determining the chloride ion concentration). In addition, for the use form of mercuric sulfate, it is preferably used in the form of sulfuric acid solution.

[0090] In some other specific embodiments, by adding the above-mentioned chloride ion complexing agent, the initial potential of the system is made to be below 430 mv, preferably below 400 mv.

[0091] Furthermore, after the chloride ion complexing agent is added to the test sample, stirring or other means may be used to make it combine more fully with the chloride ions.

[0092] (Titration steps)

[0093] In principle, there is no particular limitation on the titration steps of the present invention, and the titration steps can be performed by referring to the existing titration methods in the art, while monitoring the potential changes.

[0094] In the titration step, the titration reagent used may be a titration reagent containing an oxidant, and the type and concentration of the oxidant are not particularly limited in principle, for example, it may be a salt of a transition metal acid, etc. In some preferred embodiments of the present invention, the oxidant may be a permanganate, such as potassium permanganate, etc.

[0095] In the titration step, after the titration reagent is added to the test sample, the oxidant in the titration reagent first reacts with the trivalent vanadium ions to convert the trivalent vanadium ions into tetravalent vanadium ions. When the trivalent vanadium ions are all converted into tetravalent vanadium ions, an obvious jump will appear in the electrode potential curve of the test; further, the titration is continued. At this time, the oxidant in the titration reagent will react with the tetravalent vanadium ions to oxidize the tetravalent vanadium ions into pentavalent vanadium ions. When the tetravalent vanadium ions are all converted into pentavalent vanadium ions, an obvious jump will appear in the electrode potential curve of the test, which can indicate the titration endpoint.

[0096] In addition, the “jump” described in the present invention is, in principle, consistent with the conventional method for determining the jump point of a curve in the art. Typically, the “jump” point can be determined by the tangent of the curve.

[0097] Therefore, in the titration step, two potential jump points appear, and the volumes of the consumed titration reagents are V1 and V2 according to the time sequence of the jump points. In principle, there is no particular limitation on the specific calculation process, and it can be processed in a conventional manner in the art.

[0098] In some specific implementation schemes, the calculation can be performed as follows:

[0099] C (V-III） = C (O) V1 / Vρ

[0100] C (V全） = C (O) (V2-V1) / Vρ

[0101] C (V-IV） =C (V全） - C (V-III）

[0102] Among them, C (V-III） Indicates the concentration of trivalent vanadium ions in the test sample, C (O) Indicates the concentration of the oxidant in the titration reagent, C (V全） Indicates the concentration of all vanadium ions in the test sample, C (V-IV） represents the concentration of tetravalent vanadium ions in the test sample, V represents the volume of the test sample, and ρ represents the difference in the valence of the oxidizing element before and after the oxidant is reduced. Further, the corresponding ion concentration in the electrolyte to be tested can be calculated by inverse calculation based on the ion concentration in the test sample.

[0103] In some specific embodiments, when the oxidant in the titration reagent is potassium permanganate, the above ρ represents 5, that is, the above calculation process can be:

[0104] C (V-III） = C (KMnO4) V1 / 5V

[0105] C (V全） = C (KMnO4) (V2-V1) / 5V

[0106] C (V-IV） =C (V全） - C (V-III）

[0107] In addition, the titration can be carried out under stirring to ensure that the reaction is fully carried out. In principle, there is no particular limitation on other auxiliary measures that can be used, and they can be carried out with reference to the specific methods of potentiometric titration in the art.

[0108] Example

[0109] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0110] Embodiment 1:

[0111] Prepare the electrolyte for the all-vanadium redox flow battery, and pre-determine the chloride ion content in the electrolyte. Dilute the electrolyte according to the chloride ion content, so that the chloride ion content of the electrolyte sample is less than 10 mol / L and the total V is less than 2.5 mol / L. Specifically, accurately transfer 5.00 mL of electrolyte into a 100 mL volumetric flask, dilute to volume with water, and shake well.

[0112] Furthermore, 10 mL of phosphoric acid was added to a 250 mL beaker, and water was added to 150 mL, and a mercuric sulfate solution was added (the mercuric sulfate complexing agent was prepared by dissolving 24 g of solid mercuric sulfate in 10% sulfuric acid solution and adjusting the volume to 1 L, i.e., the concentration was preferably 24 g / L).

[0113] Accurately transfer 20.00 mL of the diluted electrolyte into the above 250 mL beaker, rinse the beaker wall with a small amount of water, place it on the potentiometric titration instrument and start stirring until the initial measured potential is below 430 mv.

[0114] Use potassium permanganate standard titration solution and a potentiometric titration device to rinse the liquid inlet pipe 4 times.

[0115] After rinsing, put the prepared sample to be tested into the titration area, extend the electrode 2 cm below the liquid surface, and start stirring.

[0116] Titrate until two sudden end points appear successively (see Figure 2 )

[0117] According to the time sequence of the sudden end point, the corresponding volumes of potassium permanganate standard titration solution consumed are V1 and V2, and the corresponding vanadium ion concentration is calculated.

[0118] The final test results are:

[0119] Concentration of trivalent vanadium ions in electrolyte = 1.020 mol / L

[0120] Concentration of tetravalent vanadium ions in the electrolyte =1.008mol / L

[0121] Comparative Example 1:

[0122] Same as Example 1, except that mercuric sulfate solution is not used, the titration potential curve is shown in Figure 3 .

[0123] Comparative Example 2:

[0124] Same as Example 1, except that the initial measurement point was adjusted to 500 mv, the titration potential curve is shown in Figure 4 .

[0125] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0126] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for detecting the concentration of vanadium ions in a vanadium flow battery electrolyte, characterized in that: The method comprises: In the pretreatment step, the concentration of the electrolyte to be tested is adjusted to obtain a test sample, wherein the chloride ion content of the test sample is 2 to 10 mol / L; The step of adding a chloride ion complexing agent, wherein the chloride ion complexing agent is added to reduce the initial potential in the test sample to less than 400 mv; The titration step comprises dripping a titration reagent containing an oxidant of known concentration into the test sample containing the chloride ion complexing agent, and recording the volume of the titration reagent consumed at the potential jump point. Wherein, in the step of adding the chloride ion complexing agent, the chloride ion complexing agent is mercuric sulfate, the mercuric sulfate is used in the form of sulfuric acid solution, and the initial potential is obtained based on a three-electrode system, In the titration step, two potential jump points appear. According to the time sequence of the jump points, the volumes of the corresponding consumed titration reagents are V1 and V2, and the following calculation is performed: C (V-III） = C (O) V1 / Vρ C (V全） = C (O) (V2-V1) / Vρ C (V-IV） =C (V全） - C (V-III） Among them, C (V-III） Indicates the concentration of trivalent vanadium ions in the test sample, C (O) Indicates the concentration of the oxidant in the titration reagent, C (V全） Indicates the concentration of all vanadium ions in the test sample, C (V-IV） represents the concentration of tetravalent vanadium ions in the test sample, V represents the volume of the test sample, and ρ represents the difference in valence of the oxidizing element before and after the oxidant is reduced.

2. The detection method according to claim 1, characterized in that: In the pretreatment step, water or sulfuric acid solution is used to adjust the concentration.

3. The detection method according to claim 1 or 2, characterized in that: After the pretreatment step, the chloride ion content in the test sample is 2-8 mol / L.

4. The detection method according to claim 1 or 2, characterized in that: Before using the chloride ion complexing agent, phosphoric acid has been added to the test sample.

5. The detection method according to claim 1 or 2, characterized in that: In the titration step, the oxidizing agent comprises a salt of a transition metal acid.

6. The detection method according to claim 1 or 2, characterized in that: The titration step is carried out under stirring conditions.

7. The detection method according to claim 1, characterized in that: The oxidant is permanganate, and the p is 5.

8. The detection method according to claim 1 or 2, characterized in that: The vanadium redox flow battery electrolyte is an all-vanadium redox flow battery electrolyte.

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