Method for detecting concentration of vanadium ions in electrolyte of vanadium battery

Abstract

The application discloses a method for detecting the concentration of vanadium ions in vanadium battery electrolyte. The method comprises the following steps: dividing the vanadium electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium into a to-be-detected solution a and a to-be-detected solution b; adding a reducing agent standard solution dropwise into the to-be-detected solution a, and calculating the concentration c1 of vanadium ions according to the volume of the reducing agent standard solution consumed at this time; adding an oxidizing agent solution dropwise into the to-be-detected solution b first, and then adding a reducing agent standard solution dropwise, and calculating the concentration c2 of vanadium ions according to the volume of the reducing agent standard solution consumed at this time; and the concentration of pentavalent vanadium ions in the vanadium electrolyte containing the mixture of tetravalent vanadium and pentavalent vanadium is c1, and the concentration of tetravalent vanadium ions is c2-c1. The application can quickly and conveniently detect the concentration of vanadium ions in the electrolyte containing the mixture of tetravalent vanadium and pentavalent vanadium, does not need professional detection equipment, and is simple to operate.

Description

TECHNICAL FIELD

[0001] The application relates to a method for detecting the concentration of vanadium ions in vanadium battery electrolyte and belongs to the technical field of vanadium battery electrolyte detection. BACKGROUND

[0002] A full vanadium redox flow battery is a new type of electrochemical energy storage system. Compared with traditional batteries, it has the characteristics of fast, large-capacity charging and discharging, low self-discharge rate and simple battery structure, and shows great advantages in the application of fixed energy storage devices for renewable energy. The positive and negative electrolytes of the vanadium battery are sulfuric acid solutions containing V(V) / V(IV) and V(III) / V(II) vanadium compounds. It is not only a conductive medium, but also an electroactive material for energy storage, which is the core of vanadium battery energy storage and energy conversion. Through the change of the valence state of vanadium ions, the mutual conversion of electrical energy and chemical energy is realized. Therefore, whether the concentration of vanadium ions in the positive and negative electrolytes is high or low and whether the valence state is balanced determines the energy storage capacity of the full vanadium flow battery. Therefore, it is necessary to regularly detect the concentration of vanadium ions in the electrolyte of the full vanadium flow battery system to ensure that the electrolyte remains in good condition.

[0003] At present, the detection methods of vanadium ion concentration mainly include oxidation-reduction titration, ultraviolet-visible spectroscopy, inductively coupled plasma (ICP) method, etc. However, these methods all need to use professional detection equipment, which limits the detection of electrolyte in the full vanadium flow battery system. Therefore, it is particularly important to develop a rapid detection method for the concentration of vanadium ions.

[0004] NB / T 42006-2013 discloses a test method for electrolyte of a full vanadium flow battery. In this standard, a sulfur-phosphorus acid buffer solution is used as a medium, and a standard potassium permanganate solution is used for titration until a potential jump occurs. The corresponding electrolyte volume is obtained according to the potential jump, and the corresponding vanadium ion concentration is calculated. However, this method needs to use professional detection equipment, which limits the detection of electrolyte in the full vanadium flow battery system.

[0005] CN116256463A discloses a rapid determination method for the concentration of vanadium ions in vanadium battery electrolyte. The method takes a certain amount of vanadium electrolyte containing trivalent, tetravalent or their mixture, adds an appropriate amount of oxidizing agent to completely oxidize the possible trivalent vanadium ions in the test solution to tetravalent vanadium ions, then drops a known concentration of potassium permanganate solution into the test solution until a light pink or light red color appears in the solution. According to the volume of potassium permanganate consumed at this time, the concentration of vanadium ions in the electrolyte is calculated. However, this method only lists the detection methods for trivalent vanadium electrolyte, or tetravalent vanadium electrolyte, or a mixture of trivalent vanadium and tetravalent vanadium electrolyte, and does not detect the electrolyte of a mixture of tetravalent vanadium and pentavalent vanadium.

[0006] There is also an online in-situ detection method in the prior art, which measures the concentration of vanadium ions by using an online monitoring sensor and the change of the positive electrolyte redox potential caused by the change of the valence state of vanadium ions. However, this method needs to establish a potential-vanadium ion concentration relationship curve each time, and the measurement is not accurate due to the change of working conditions in engineering application.

[0007] Therefore, the detection method of the concentration of vanadium ions in the vanadium battery electrolyte in the prior art has problems such as complicated operation process, need for professional detection equipment, lack of quick and convenient detection method for the concentration of vanadium ions in the electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium, etc. SUMMARY

[0008] To solve at least one of the above technical problems, the purpose of the present application is to provide a detection method of the concentration of vanadium ions in the vanadium battery electrolyte. The present application can quickly and conveniently detect the concentration of vanadium ions in the electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium, without the need for professional detection equipment and with simple operation.

[0009] To achieve the above purpose, the present application provides a detection method of the concentration of vanadium ions in the vanadium battery electrolyte, which comprises the following steps:

[0010] (1) The vanadium electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium is divided into two parts, which are the test solution a and the test solution b, respectively;

[0011] (2) A reducing agent standard solution is added dropwise to the test solution a until the color of the test solution a becomes bright blue or blue, and the addition of the reducing agent standard solution is stopped; according to the volume of the reducing agent standard solution consumed at this time, the concentration c1 of vanadium ions is calculated by using the following formula I: c1=n×c×V1÷V formula I; wherein n is the reaction coefficient, unitless, which is determined according to the chemical reaction equation of pentavalent vanadium ions and the reducing agent standard solution; c is the concentration of the reducing agent standard solution, unit: mol / L; V1 is the volume of the reducing agent standard solution consumed at this time, unit: L; V is the volume of the test solution a, unit: L;

[0012] (3) adding the oxidant solution to the to-be-tested solution b dropwise until the color of the to-be-tested solution b becomes bright yellow or yellow, stopping the dropwise addition of the oxidant solution, obtaining a mixed solution; then adding the reducing agent standard solution to the mixed solution dropwise until the color of the mixed solution becomes bright blue or blue, stopping the dropwise addition of the reducing agent standard solution; according to the volume of the reducing agent standard solution consumed at this time, the concentration c2 of the vanadium ion is calculated by using the following formula II: c2 = n x c x V2 ÷ V' formula II; wherein n is a reaction coefficient, unitless, and is determined according to the chemical reaction equation of the pentavalent vanadium ion and the reducing agent standard solution; c is the concentration of the reducing agent standard solution, unit: mol / L; V2 is the volume of the reducing agent standard solution consumed at this time, unit: L; V' is the volume of the to-be-tested solution b, unit: L; then the concentration of the pentavalent vanadium ion in the vanadium electrolyte containing the mixture of the tetravalent vanadium and the pentavalent vanadium is c1, and the concentration of the tetravalent vanadium ion is c2-c1.

[0013] According to the specific embodiment of the present application, preferably, the reducing agent standard solution includes one or two or more of the ferrous ammonium sulfate standard solution, the citric acid standard solution, and the oxalic acid standard solution. More preferably, the reducing agent standard solution is the ferrous ammonium sulfate standard solution.

[0014] According to the specific embodiment of the present application, preferably, in the formula I and the formula II, n takes the value of 1, 2 or 18. Specifically, the reducing agent standard solution is the ferrous ammonium sulfate standard solution, and n takes the value of 1; the reducing agent standard solution is the citric acid standard solution, and n takes the value of 18; the reducing agent standard solution is the oxalic acid standard solution, and n takes the value of 2.

[0015] According to the specific embodiment of the present application, preferably, the concentration of the reducing agent standard solution is 0.01-4 mol / L, more preferably 0.01-1 mol / L, further preferably 0.02-0.5 mol / L, more further preferably 0.02-0.1 mol / L, and most preferably 0.1 mol / L.

[0016] According to the specific embodiment of the present application, preferably, the dropwise addition speed of the reducing agent standard solution to the to-be-tested solution a is 1 mL / min-3 mL / min.

[0017] According to the specific embodiment of the present application, preferably, the oxidant solution includes one or two or more of the lead dioxide acetic acid solution, the potassium persulfate aqueous solution, the sodium persulfate aqueous solution, the ammonium persulfate aqueous solution, and the elemental bromine aqueous solution.

[0018] According to the specific embodiment of the present application, preferably, the mass concentration of the oxidant solution is 3%-30%, more preferably 5%-15%, further preferably 8%-12%, and most preferably 10%.

[0019] According to the specific embodiment of the present application, preferably, the dropping speed of the oxidizing agent solution to the to-be-tested solution b is 1 mL / min-3 mL / min, and the dropping speed of the reducing agent standard solution to the mixed solution is 1 mL / min-3 mL / min.

[0020] The present application has at least the following beneficial effects:

[0021] The present application can quickly and conveniently detect the vanadium ion concentration in the electrolyte of the all-vanadium redox flow battery containing a mixture of tetravalent vanadium and pentavalent vanadium, without the need for professional detection equipment, and the operation is simple, and the detection environment is not harsh, and has high accuracy, and can meet the rapid detection needs of the all-vanadium redox flow battery system on site. DETAILED DESCRIPTION

[0022] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the present application will be described in detail below, but it cannot be understood as limiting the scope of the present application.

[0023] Example 1

[0024] Take the positive electrolyte in the all-vanadium redox flow battery as the to-be-tested sample, and the sample is dark blue.

[0025] (1) Divide the to-be-tested sample into two parts, which are to-be-tested solution a and to-be-tested solution b, and the volume of to-be-tested solution a and to-be-tested solution b is 1.000 mL;

[0026] (2) Add the ferrous ammonium sulfate standard solution with a concentration of 0.100 mol / L to the to-be-tested solution a, and the dropping speed is 2 mL / min, until the color of the to-be-tested solution a becomes bright blue or blue, and stop adding the ferrous ammonium sulfate standard solution; at this time, the volume of the consumed ferrous ammonium sulfate standard solution is 7.7 mL, and according to the volume of the consumed ferrous ammonium sulfate standard solution, the concentration c1 of vanadium ions is calculated by the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V1 is the volume of the consumed ferrous ammonium sulfate standard solution at this time, unit: L; V is the volume of the to-be-tested solution a, unit: L; and the calculation gives c1=0.77 mol / L;

[0027] (3) to the to-be-tested solution b, drop 10% mass concentration of potassium persulfate aqueous solution, the drop rate is 2 mL / min, until the color of the to-be-tested solution b becomes bright yellow or yellow, stop dropping the potassium persulfate aqueous solution, to obtain a mixed solution; then drop 0.100 mol / L concentration of ferrous ammonium sulfate standard solution into the mixed solution, the drop rate is 2 mL / min, until the color of the mixed solution becomes bright blue or blue, stop dropping the ferrous ammonium sulfate standard solution; at this time, the volume of the consumed ferrous ammonium sulfate standard solution is 15.5 mL, according to the volume of the consumed ferrous ammonium sulfate standard solution at this time, the concentration c2 of vanadium ions is calculated by the following formula: c2 = n x c x V2 ÷ V'; wherein, n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V2 is the volume of the consumed ferrous ammonium sulfate standard solution at this time, unit: L; V' is the volume of the to-be-tested solution b, unit: L; it is calculated that c2 = 1.55 mol / L;

[0028] Therefore, the concentration of pentavalent vanadium ions in the to-be-tested sample is c1, that is, 0.77 mol / L; the concentration of tetravalent vanadium ions is c2-c1, that is, 0.78 mol / L.

[0029] Take the same to-be-tested sample, detect the concentration of vanadium ions according to the potentiometric titration method recorded in NB / T 42006-2013, the detection result is: the concentration of pentavalent vanadium ions is 0.7766 mol / L, and the concentration of tetravalent vanadium ions is 0.7831 mol / L.

[0030] It can be seen that compared with the method in the above standard, the detection errors of the concentrations of pentavalent vanadium ions and tetravalent vanadium ions in the method of the embodiment are 0.44% and 0.40% respectively.

[0031] Example 2

[0032] Take the positive electrolyte in the all-vanadium liquid flow battery as the to-be-tested sample, and the sample is dark blue.

[0033] (1) Divide the to-be-tested sample into two parts, to-be-tested solution a and to-be-tested solution b, and the volume of the to-be-tested solution a and the to-be-tested solution b is 1.000 mL;

[0034] (2) to the to-be-tested solution a, drop 0.100 mol / L oxalic acid standard solution at a speed of 2 mL / min until the color of the to-be-tested solution a becomes bright blue or blue, and stop dropping the oxalic acid standard solution; at this time, the volume of the consumed oxalic acid standard solution is 3.4 mL, and the concentration c1 of vanadium ions is calculated according to the volume of the consumed oxalic acid standard solution at this time by using the following formula: c1 = n x c x V1 ÷ V; wherein n is a reaction coefficient, unitless, and is 2; c is the concentration of the oxalic acid standard solution, unit: mol / L; V1 is the volume of the consumed oxalic acid standard solution at this time, unit: L; V is the volume of the to-be-tested solution a, unit: L; and the calculation result is c1 = 0.68 mol / L;

[0035] (3) to the to-be-tested solution b, drop 10% potassium persulfate aqueous solution at a speed of 2 mL / min until the color of the to-be-tested solution b becomes bright yellow or yellow, and stop dropping the potassium persulfate aqueous solution to obtain a mixed solution; then to the mixed solution, drop 0.100 mol / L oxalic acid standard solution at a speed of 2 mL / min until the color of the mixed solution becomes bright blue or blue, and stop dropping the oxalic acid standard solution; at this time, the volume of the consumed oxalic acid standard solution is 7.9 mL, and the concentration c2 of vanadium ions is calculated according to the volume of the consumed oxalic acid standard solution at this time by using the following formula: c2 = n x c x V2 ÷ V'; wherein n is a reaction coefficient, unitless, and is 2; c is the concentration of the oxalic acid standard solution, unit: mol / L; V2 is the volume of the consumed oxalic acid standard solution at this time, unit: L; V' is the volume of the to-be-tested solution b, unit: L; and the calculation result is c2 = 1.58 mol / L;

[0036] Therefore, the concentration of pentavalent vanadium ions in the to-be-tested sample is c1, that is, 0.68 mol / L; and the concentration of tetravalent vanadium ions is c2-c1, that is, 0.90 mol / L.

[0037] The same to-be-tested sample is taken, and the concentration of vanadium ions is detected by using the potentiometric titration method recorded in NB / T 42006-2013, and the detection result is that the concentration of pentavalent vanadium ions is 0.6838 mol / L, and the concentration of tetravalent vanadium ions is 0.8939 mol / L.

[0038] It can be seen that, compared with the method in the above standard, the detection errors of the concentrations of pentavalent vanadium ions and tetravalent vanadium ions in the method of the embodiment are 0.56% and 0.68%, respectively.

[0039] Example 3

[0040] The positive electrolyte in the all-vanadium liquid flow battery is taken as a to-be-tested sample, and the sample is dark blue.

[0041] (1) The sample to be tested is divided into two parts, namely, a solution to be tested a and a solution to be tested b, and the volume of the solution to be tested a and the solution to be tested b is 1.000 mL;

[0042] (2) The ferrous ammonium sulfate standard solution with a concentration of 0.100 mol / L is added dropwise into the solution to be tested a at a speed of 2 mL / min until the color of the solution to be tested a becomes bright blue or blue, and the addition of the ferrous ammonium sulfate standard solution is stopped. At this time, the volume of the ferrous ammonium sulfate standard solution consumed is 7.9 mL. According to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c1 of vanadium ions is calculated by using the following formula: c1 = n x c x V1 ÷ V; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V1 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V is the volume of the solution to be tested a, unit: L; and it is calculated that c1 = 0.79 mol / L.

[0043] (3) The lead dioxide acetic acid solution with a mass concentration of 10% is added dropwise into the solution to be tested b at a speed of 2 mL / min until the color of the solution to be tested b becomes bright yellow or yellow, and the addition of the lead dioxide acetic acid solution is stopped to obtain a mixed solution. Then, the ferrous ammonium sulfate standard solution with a concentration of 0.100 mol / L is added dropwise into the mixed solution at a speed of 2 mL / min until the color of the mixed solution becomes bright blue or blue, and the addition of the ferrous ammonium sulfate standard solution is stopped. At this time, the volume of the ferrous ammonium sulfate standard solution consumed is 16.8 mL. According to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c2 of vanadium ions is calculated by using the following formula: c2 = n x c x V2 ÷ V'; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V2 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V' is the volume of the solution to be tested b, unit: L; and it is calculated that c2 = 1.68 mol / L.

[0044] Therefore, the concentration of the pentavalent vanadium ions in the sample to be tested is c1, that is, 0.79 mol / L; and the concentration of the tetravalent vanadium ions is c2-c1, that is, 0.89 mol / L.

[0045] The same sample to be tested is taken, and the concentration of vanadium ions is detected by using the potentiometric titration method recorded in NB / T 42006-2013, and the detection result is that the concentration of pentavalent vanadium ions is 0.7937 mol / L, and the concentration of tetravalent vanadium ions is 0.8883 mol / L.

[0046] It can be seen that, compared with the method in the above standard, the detection errors of the concentrations of pentavalent vanadium ions and tetravalent vanadium ions in the method of the present embodiment are 0.47% and 0.19%, respectively.

[0047] Example 4

[0048] The positive electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

[0049] (1) The sample to be tested was divided into two parts, namely, sample solution a and sample solution b, and the volume of each was 1.000 mL;

[0050] (2) The sample solution a was added dropwise with a standard solution of ferrous ammonium sulfate with a concentration of 0.800 mol / L at a rate of 2 mL / min until the color of the sample solution a changed to bright blue or blue, and the dropwise addition of the standard solution of ferrous ammonium sulfate was stopped. At this time, the volume of the standard solution of ferrous ammonium sulfate consumed was 1.1 mL. According to the volume of the standard solution of ferrous ammonium sulfate consumed at this time, the concentration c1 of vanadium ions was calculated by the following formula: c1 = n x c x V1 ÷ V; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the standard solution of ferrous ammonium sulfate, unit: mol / L; V1 is the volume of the standard solution of ferrous ammonium sulfate consumed at this time, unit: L; V is the volume of the sample solution a, unit: L; and the calculation gave c1 = 0.88 mol / L.

[0051] (3) The sample solution b was added dropwise with a potassium persulfate aqueous solution with a mass concentration of 10% at a rate of 2 mL / min until the color of the sample solution b changed to bright yellow or yellow, and the dropwise addition of the potassium persulfate aqueous solution was stopped to obtain a mixed solution. Then, the mixed solution was added dropwise with a standard solution of ferrous ammonium sulfate with a concentration of 0.800 mol / L at a rate of 2 mL / min until the color of the mixed solution changed to bright blue or blue, and the dropwise addition of the standard solution of ferrous ammonium sulfate was stopped. At this time, the volume of the standard solution of ferrous ammonium sulfate consumed was 2.0 mL. According to the volume of the standard solution of ferrous ammonium sulfate consumed at this time, the concentration c2 of vanadium ions was calculated by the following formula: c2 = n x c x V2 ÷ V'; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the standard solution of ferrous ammonium sulfate, unit: mol / L; V2 is the volume of the standard solution of ferrous ammonium sulfate consumed at this time, unit: L; V' is the volume of the sample solution b, unit: L; and the calculation gave c2 = 1.60 mol / L.

[0052] Therefore, the concentration of pentavalent vanadium ions in the sample to be tested was c1, i.e., 0.88 mol / L, and the concentration of tetravalent vanadium ions was c2-c1, i.e., 0.72 mol / L.

[0053] The same sample to be tested was taken, and the concentration of vanadium ions was detected by the potential titration method recorded in NB / T 42006-2013, and the detection results were as follows: the concentration of pentavalent vanadium ions was 0.8524 mol / L, and the concentration of tetravalent vanadium ions was 0.7531 mol / L.

[0054] It can be seen that the detection errors of the concentration of pentavalent vanadium ions and the concentration of tetravalent vanadium ions are 3.24% and 4.40% respectively compared with the method in the above standard.

[0055] Example 5

[0056] The positive electrolyte in the full-vanadium flow battery was taken as the sample to be measured, and the sample was dark blue.

[0057] (1) The sample to be measured was divided into two parts, namely sample solution a and sample solution b, and the volume of each was 1.000 mL;

[0058] (2) The sample solution a was added dropwise with ferrous ammonium sulfate standard solution with a concentration of 4.000 mol / L at a speed of 2 mL / min until the color of the sample solution a changed to bright blue or blue, and the dropwise addition of the ferrous ammonium sulfate standard solution was stopped. At this time, the volume of the ferrous ammonium sulfate standard solution consumed was 0.2 mL. According to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c1 of vanadium ions was calculated by the following formula: c1 = n x c x V1 ÷ V; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V1 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V is the volume of the sample solution a, unit: L; and the calculation showed that c1 = 0.80 mol / L;

[0059] (3) The sample solution b was added dropwise with potassium persulfate aqueous solution with a mass concentration of 10% at a speed of 2 mL / min until the color of the sample solution b changed to bright yellow or yellow, and the dropwise addition of the potassium persulfate aqueous solution was stopped to obtain a mixed solution. Then the mixed solution was added dropwise with ferrous ammonium sulfate standard solution with a concentration of 4.000 mol / L at a speed of 2 mL / min until the color of the mixed solution changed to bright blue or blue, and the dropwise addition of the ferrous ammonium sulfate standard solution was stopped. At this time, the volume of the ferrous ammonium sulfate standard solution consumed was 0.4 mL. According to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c2 of vanadium ions was calculated by the following formula: c2 = n x c x V2 ÷ V'; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V2 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V' is the volume of the sample solution b, unit: L; and the calculation showed that c2 = 1.60 mol / L;

[0060] Therefore, the concentration of pentavalent vanadium ions in the sample to be measured is c1, i.e. 0.80 mol / L; and the concentration of tetravalent vanadium ions is c2-c1, i.e. 0.80 mol / L.

[0061] Take the same sample to be tested, according to the potential titration method described in NB / T 42006-2013 to detect the concentration of vanadium ions, the detection results are: the concentration of pentavalent vanadium ions is 0.7312mol / L, the concentration of tetravalent vanadium ions is 0.8727mol / L.

[0062] It can be seen that the detection error of the method of the embodiment compared with the method in the above standard is 9.41% and 8.33% respectively for the concentration of pentavalent vanadium ions and tetravalent vanadium ions.

[0063] Example 6

[0064] Take the positive electrolyte in the all-vanadium liquid flow battery as the sample to be tested, and the sample is dark blue.

[0065] (1) The sample to be tested is divided into two parts, which are respectively the test solution a and the test solution b, and the volume of the test solution a and the test solution b is 1.000mL;

[0066] (2) Add the ferrous ammonium sulfate standard solution with a concentration of 0.020mol / L to the test solution a at a speed of 2mL / min until the color of the test solution a becomes bright blue or blue, stop adding the ferrous ammonium sulfate standard solution; At this time, the volume of the ferrous ammonium sulfate standard solution consumed is 22.6mL, according to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c1 of vanadium ions is calculated by the following formula: c1=n×c×V1÷V; Wherein, n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V1 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V is the volume of the test solution a, unit: L; It is calculated that c1=0.452mol / L;

[0067] (3) Add the potassium persulfate aqueous solution with a mass concentration of 10% to the test solution b at a speed of 2mL / min until the color of the test solution b becomes bright yellow or yellow, stop adding the potassium persulfate aqueous solution, and obtain a mixed solution; Then add the ferrous ammonium sulfate standard solution with a concentration of 0.020mol / L to the mixed solution at a speed of 2mL / min until the color of the mixed solution becomes bright blue or blue, stop adding the ferrous ammonium sulfate standard solution; At this time, the volume of the ferrous ammonium sulfate standard solution consumed is 78.4mL, according to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c2 of vanadium ions is calculated by the following formula: c2=n×c×V2÷V'; Wherein, n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V2 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V' is the volume of the test solution b, unit: L; It is calculated that c2=1.568mol / L;

[0068] The concentration of pentavalent vanadium ions in the sample to be tested is c1, i.e. 0.452 mol / L; and the concentration of tetravalent vanadium ions is c2-c1, i.e. 1.116 mol / L.

[0069] The same sample to be tested was taken, and the concentration of vanadium ions was detected by the potential titration method described in NB / T 42006-2013. The detection results were as follows: the concentration of pentavalent vanadium ions was 0.4503 mol / L, and the concentration of tetravalent vanadium ions was 1.1191 mol / L.

[0070] It can be seen that, compared with the method in the above standard, the detection errors of the concentrations of pentavalent vanadium ions and tetravalent vanadium ions in the method of the present embodiment are 0.38% and 0.28%, respectively.

[0071] Example 7

[0072] The positive electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

[0073] (1) The sample to be tested was divided into two parts, which were sample solution a and sample solution b, and the volume of each was 1.000 mL;

[0074] (2) Ammonium ferrous sulfate standard solution with a concentration of 0.500 mol / L was added dropwise to sample solution a at a rate of 2 mL / min until the color of sample solution a changed to bright blue or blue, and the addition of ammonium ferrous sulfate standard solution was stopped. At this time, the volume of ammonium ferrous sulfate standard solution consumed was 1.43 mL. According to the volume of ammonium ferrous sulfate standard solution consumed at this time, the concentration c1 of vanadium ions was calculated by the following formula: c1 = n x c x V1 ÷ V; wherein n is the reaction coefficient, which is unitless and takes a value of 1; c is the concentration of ammonium ferrous sulfate standard solution, in units of mol / L; V1 is the volume of ammonium ferrous sulfate standard solution consumed at this time, in units of L; and V is the volume of sample solution a, in units of L. It was calculated that c1 = 0.715 mol / L;

[0075] (3) to the to-be-tested solution b, drop 10% mass concentration of potassium persulfate aqueous solution, the drop rate is 2 mL / min, until the color of the to-be-tested solution b becomes bright yellow or yellow, stop dropping the potassium persulfate aqueous solution, to obtain a mixed solution; then drop 0.500 mol / L concentration of ferrous ammonium sulfate standard solution into the mixed solution, the drop rate is 2 mL / min, until the color of the mixed solution becomes bright blue or blue, stop dropping the ferrous ammonium sulfate standard solution; at this time, the volume of the consumed ferrous ammonium sulfate standard solution is 3.18 mL, according to the volume of the consumed ferrous ammonium sulfate standard solution at this time, the concentration c2 of vanadium ions is calculated by the following formula: c2 = n x c x V2 ÷ V'; wherein, n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V2 is the volume of the consumed ferrous ammonium sulfate standard solution at this time, unit: L; V' is the volume of the to-be-tested solution b, unit: L; it is calculated that c2 = 1.59 mol / L;

[0076] Therefore, the concentration of pentavalent vanadium ions in the to-be-tested sample is c1, that is, 0.715 mol / L; the concentration of tetravalent vanadium ions is c2-c1, that is, 0.875 mol / L.

[0077] Take the same to-be-tested sample, detect the concentration of vanadium ions according to the potentiometric titration method recorded in NB / T 42006-2013, the detection result is: the concentration of pentavalent vanadium ions is 0.7282 mol / L, and the concentration of tetravalent vanadium ions is 0.8887 mol / L.

[0078] It can be seen that, compared with the method in the above standard, the detection errors of the concentrations of pentavalent vanadium ions and tetravalent vanadium ions in the method of the embodiment are 1.81% and 1.54% respectively.

[0079] Comparative Example 1

[0080] Take the positive electrolyte in the all-vanadium liquid flow battery as the to-be-tested sample, and the sample is dark blue.

[0081] (1) Divide the to-be-tested sample into two parts, to-be-tested solution a and to-be-tested solution b, and the volume of the to-be-tested solution a and the to-be-tested solution b is 1.000 mL;

[0082] (2) to the to-be-measured solution a, drop 0.100 mol / L ferrous ammonium sulfate standard solution at a speed of 2 mL / min until the color of the to-be-measured solution a becomes bright blue or blue, stop dropping the ferrous ammonium sulfate standard solution; at this time, the volume of the ferrous ammonium sulfate standard solution consumed is 7.7 mL, according to the volume of the ferrous ammonium sulfate standard solution consumed at this time, the concentration c1 of vanadium ions is calculated by the following formula: c1 = n x c x V1 ÷ V; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V1 is the volume of the ferrous ammonium sulfate standard solution consumed at this time, unit: L; V is the volume of the to-be-measured solution a, unit: L; it is calculated that c1 = 0.77 mol / L;

[0083] (3) to the to-be-measured solution b, drop 10% potassium persulfate aqueous solution (molar concentration is 0.37 mol / L) at a speed of 2 mL / min until the color of the to-be-measured solution b becomes bright yellow or yellow, stop dropping the potassium persulfate aqueous solution; at this time, the volume of the potassium persulfate aqueous solution consumed is 2.2 mL, according to the volume of the potassium persulfate aqueous solution consumed at this time, the concentration c2 of vanadium ions is calculated by the following formula: c2 = n x c x V2 ÷ V'; wherein n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the potassium persulfate aqueous solution, unit: mol / L; V2 is the volume of the potassium persulfate aqueous solution consumed at this time, unit: L; V' is the volume of the to-be-measured solution b, unit: L; it is calculated that c2 = 0.814 mol / L;

[0084] Therefore, the concentration of pentavalent vanadium ions in the to-be-measured sample is c1, that is, 0.77 mol / L; the concentration of tetravalent vanadium ions is c2, that is, 0.814 mol / L.

[0085] Take the same to-be-measured sample, detect the concentration of vanadium ions according to the potentiometric titration method recorded in NB / T 42006-2013, and the detection results are: the concentration of pentavalent vanadium ions is 0.7738 mol / L, and the concentration of tetravalent vanadium ions is 0.8364 mol / L.

[0086] It can be seen that the detection error of the method of the present comparative example compared with the method in the above standard is 0.49% and 2.68% respectively for the concentration of pentavalent vanadium ions and the concentration of tetravalent vanadium ions.

[0087] Comparative Example 2

[0088] Take the positive electrolyte in the all-vanadium liquid flow battery as the to-be-measured sample, and the sample is dark blue.

[0089] (1) Divide the to-be-measured sample into two parts, to-be-measured solution a and to-be-measured solution b, and the volume of to-be-measured solution a and to-be-measured solution b is 1.000 mL;

[0090] (2) drop the concentration of 0.100 mol / L ferrous ammonium sulfate standard solution into the to-be-measured solution a, the drop rate is 2 mL / min, until the color of the to-be-measured solution a becomes bright blue or blue, stop dropping the ferrous ammonium sulfate standard solution; at this time, the volume of the consumed ferrous ammonium sulfate standard solution is 7.7 mL, according to the volume of the consumed ferrous ammonium sulfate standard solution at this time, the concentration c1 of vanadium ions is calculated by the following formula: c1 = n x c x V1 ÷ V; wherein, n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V1 is the volume of the consumed ferrous ammonium sulfate standard solution at this time, unit: L; V is the volume of the to-be-measured solution a, unit: L; it is calculated that c1 = 0.77 mol / L;

[0091] (3) drop the mass concentration of 5% potassium permanganate aqueous solution into the to-be-measured solution b, the drop rate is 2 mL / min, until the color of the to-be-measured solution b becomes bright yellow or yellow, stop dropping the potassium permanganate aqueous solution, to obtain a mixed solution; then drop the concentration of 0.100 mol / L ferrous ammonium sulfate standard solution into the mixed solution, the drop rate is 2 mL / min, until the color of the mixed solution becomes bright blue or blue, stop dropping the ferrous ammonium sulfate standard solution; at this time, the volume of the consumed ferrous ammonium sulfate standard solution is 15.4 mL, according to the volume of the consumed ferrous ammonium sulfate standard solution at this time, the concentration c2 of vanadium ions is calculated by the following formula: c2 = n x c x V2 ÷ V'; wherein, n is the reaction coefficient, unitless, and the value is 1; c is the concentration of the ferrous ammonium sulfate standard solution, unit: mol / L; V2 is the volume of the consumed ferrous ammonium sulfate standard solution at this time, unit: L; V' is the volume of the to-be-measured solution b, unit: L; it is calculated that c2 = 1.54 mol / L;

[0092] Therefore, the concentration of pentavalent vanadium ions in the to-be-measured sample is c1, that is, 0.77 mol / L; the concentration of tetravalent vanadium ions is c2-c1, that is, 0.77 mol / L.

[0093] Take the same to-be-measured sample, detect the concentration of vanadium ions according to the potentiometric titration method recorded in NB / T 42006-2013, the detection result is: the concentration of pentavalent vanadium ions is 0.7766 mol / L, and the concentration of tetravalent vanadium ions is 0.7831 mol / L.

[0094] It can be seen that the detection error of the method of the present comparative example and the method in the above standard is 0.44% and 1.67% respectively for the concentration of pentavalent vanadium ions and the concentration of tetravalent vanadium ions.

[0095] As can be seen from the above examples and comparative examples, the vanadium ion concentration in the all-vanadium redox flow battery electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium can be quickly and conveniently detected by the embodiments of the present application, without the need for professional detection equipment, and the operation is simple, and the detection environment is not harsh, and has high accuracy, and can meet the rapid detection needs of the all-vanadium redox flow battery system site. Moreover, by using the ferrous ammonium sulfate standard solution with a concentration of 0.02-0.5mol / L, especially 0.1mol / L, as the reducing agent standard solution, the accuracy of the detection result is higher; and the use of a ferrous ammonium sulfate standard solution with a too high concentration, such as 0.800mol / L in Example 4 and 4.000mol / L in Example 5, reduces the accuracy. At the same time, as can be seen from the comparison between Example 1 and Comparative Example 1 of the present application, by the method of adding the oxidizing agent solution and then adding the reducing agent standard solution, the concentration c2 of the vanadium ion is calculated according to the volume of the reducing agent standard solution, and then the tetravalent vanadium ion concentration is determined, which has higher accuracy compared with the method of Comparative Example 1. In addition, as can be seen from the comparison between Example 1 and Comparative Example 2 of the present application, the oxidizing agent solution used in the present application has higher accuracy compared with the potassium permanganate solution.

Claims

1. A method for detecting the concentration of vanadium ions in a vanadium battery electrolyte, comprising the following steps: (1) Divide the vanadium electrolyte containing a mixture of tetravalent and pentavalent vanadium into two portions, namely solution a and solution b to be tested; (2) Add the reducing agent standard solution to the test solution a until the color of the test solution a turns bright blue or blue, then stop adding the reducing agent standard solution; calculate the concentration c1 of vanadium ions using the following formula I based on the volume of reducing agent standard solution consumed at this time: c1 = n × c × V1 ÷ V Formula I; where n is the reaction coefficient, which has no unit and is determined according to the chemical reaction equation of pentavalent vanadium ions and reducing agent standard solution; c is the concentration of reducing agent standard solution, in mol / L; V1 is the volume of reducing agent standard solution consumed at this time, in L; V is the volume of test solution a, in L; (3) Add an oxidizing agent solution to the test solution b until the color of the test solution b turns bright yellow or yellow, then stop adding the oxidizing agent solution to obtain a mixed solution; then add a reducing agent standard solution to the mixed solution until the color of the mixed solution turns bright blue or blue, then stop adding the reducing agent standard solution; based on the volume of the reducing agent standard solution consumed at this time, calculate the concentration c2 of vanadium ions using the following formula II: c2=n×c×V2÷V' Formula II; where n is the reaction coefficient, which has no unit and is determined according to the chemical reaction equation of pentavalent vanadium ions and reducing agent standard solution; c is the concentration of reducing agent standard solution, in mol / L; V2 is the volume of reducing agent standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; then the concentration of pentavalent vanadium ions in the vanadium electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium is c1, and the concentration of tetravalent vanadium ions is c2-c1; The reducing agent standard solution is selected from either ferrous ammonium sulfate standard solution or oxalic acid standard solution; The concentration of the reducing agent standard solution is 0.02-0.1 mol / L; The oxidant solution is selected from one of the following: an acetic acid solution of lead dioxide, an aqueous solution of potassium persulfate, and an aqueous solution of sodium persulfate; The mass concentration of the oxidant solution is 10%.

2. The method for detecting vanadium ion concentration in vanadium battery electrolyte according to claim 1, wherein, In Formula I and Formula II, n takes the value 1 or 2.

3. The method for detecting vanadium ion concentration in vanadium battery electrolyte according to claim 2, wherein, If the reducing agent standard solution is ferrous ammonium sulfate standard solution, then n is 1; if the reducing agent standard solution is oxalic acid standard solution, then n is 2.

4. The method for detecting vanadium ion concentration in vanadium battery electrolyte according to claim 1, wherein, The standard solution of reducing agent is added to the test solution a at a rate of 1 mL / min to 3 mL / min.

5. The method for detecting vanadium ion concentration in vanadium battery electrolyte according to claim 1, wherein, The oxidant solution is added to the test solution b at a rate of 1 mL / min to 3 mL / min, and the reducing agent standard solution is added to the mixed solution at a rate of 1 mL / min to 3 mL / min.