Method for detecting concentration of vanadium ions in vanadium battery electrolyte

Abstract

The invention discloses a method for detecting the concentration of vanadium ions in a 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; dropwise adding a reducing agent standard solution 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 the moment; the oxidant solution is dropwise added into the solution b to be detected, then the reducing agent standard solution is dropwise added, the concentration c2 of the vanadium ions is calculated according to the volume of the reducing agent standard solution consumed at the moment, the concentration of the pentavalent vanadium ions in the vanadium electrolyte containing the mixture of tetravalent vanadium and pentavalent vanadium is c1, and the concentration of the tetravalent vanadium ions is c2-c1. According to the method, the vanadium ion concentration in the electrolyte containing the mixture of tetravalent vanadium and pentavalent vanadium can be rapidly and conveniently detected, professional detection equipment is not needed, and the operation is simple.

Description

Technical Field

[0001] The invention relates to a method for detecting the concentration of vanadium ions in a vanadium battery electrolyte, belonging to the technical field of vanadium battery electrolyte detection. Background Art

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

[0003] At present, the main methods for detecting vanadium ion concentration are: redox titration, ultraviolet-visible spectroscopy, inductively coupled plasma (ICP) method, etc., and these methods require the use of professional detection equipment, which limits the detection of electrolyte in all-vanadium liquid flow battery systems. Therefore, it is particularly important to develop and design a rapid detection method for vanadium ion concentration.

[0004] NB / T 42006-2013 discloses the electrolyte test method for all-vanadium redox flow batteries. In this standard, sulfuric acid buffer solution is used as the medium, and potassium permanganate standard solution is used for titration until a potential jump occurs. The corresponding electrolyte volume is obtained based on the potential jump, and the corresponding vanadium ion concentration is calculated. However, this method requires the use of professional testing equipment, which limits the electrolyte testing in all-vanadium redox flow battery systems.

[0005] CN116256463A discloses a method for rapidly determining the concentration of vanadium ions in vanadium battery electrolyte. The method is to take a certain amount of trivalent, tetravalent or mixture of vanadium electrolyte to be tested, add an appropriate amount of oxidant, completely oxidize the trivalent vanadium ions that may exist in the test solution into tetravalent vanadium ions, and then drip a potassium permanganate solution of known concentration into the test solution until the solution appears light pink or light red, and calculate the concentration of vanadium ions in the electrolyte according to the volume of potassium permanganate consumed at this time. However, the method only lists the detection method of vanadium electrolyte of trivalent vanadium, or vanadium electrolyte of tetravalent vanadium, or vanadium electrolyte of a mixture of trivalent vanadium and tetravalent vanadium, and does not detect the vanadium 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 uses an online monitoring sensor to measure the vanadium ion concentration through the change in the redox potential of the positive electrolyte caused by the change in the valence state of the vanadium ions. However, this method requires the establishment of a potential-vanadium ion concentration relationship curve each time, and the measurement is inaccurate due to changes in working conditions during engineering applications.

[0007] Therefore, the existing methods for detecting the vanadium ion concentration in the electrolyte of vanadium batteries have the following problems: the operation process is complicated, professional detection equipment is required, and there is a lack of a fast and convenient detection method for the vanadium ion concentration in the electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium. Summary of the invention

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

[0009] In order to achieve the above object, the present invention provides a method for detecting the concentration of vanadium ions in a vanadium battery electrolyte, which comprises the following steps:

[0010] (1) dividing a vanadium electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium into two parts, namely, a test solution a and a test solution b;

[0011] (2) adding a reducing agent standard solution to the test solution a until the color of the test solution a changes to bright blue or blue, and then stopping the adding of the reducing agent standard solution; calculating the concentration c1 of the vanadium ion according to the volume of the reducing agent standard solution consumed at this time by using the following formula I: c1=n×c×V1÷V Formula I; wherein n is the reaction coefficient, which has no unit 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, in mol / L; V1 is the volume of the reducing agent standard solution consumed at this time, in L; and V is the volume of the test solution a, in L;

[0012] (3) adding an oxidant solution to the test solution b until the color of the test solution b changes to bright yellow or yellow, then stopping the addition of the oxidant solution to obtain a mixed solution; then adding a reducing agent standard solution to the mixed solution until the color of the mixed solution changes to bright blue or blue, then stopping the addition of the reducing agent standard solution; calculating the concentration c2 of vanadium ions according to the volume of the reducing agent standard solution consumed at this time using the following formula II: c2=n×c×V2÷V'Formula II; wherein n is a reaction coefficient, which has no unit and 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, in mol / L; V2 is the volume of the reducing agent standard solution consumed at this time, in L; and 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.

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

[0014] According to a specific embodiment of the present invention, preferably, in Formula I and Formula II, n is 1, 2 or 18. Specifically, if the reducing agent standard solution is an ammonium ferrous sulfate standard solution, n is 1; if the reducing agent standard solution is a citric acid standard solution, n is 18; if the reducing agent standard solution is an oxalic acid standard solution, n is 2.

[0015] According to a specific embodiment of the present invention, 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, further preferably 0.02-0.1 mol / L, and most preferably 0.1 mol / L.

[0016] According to a specific embodiment of the present invention, preferably, the dropping speed of adding the reducing agent standard solution to the test solution a is 1 mL / min-3 mL / min.

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

[0018] According to a specific embodiment of the present invention, 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 a specific embodiment of the present invention, preferably, the dropping speed of adding the oxidant solution to the test solution b is 1 mL / min-3 mL / min, and the dropping speed of adding the reducing agent standard solution to the mixed solution is 1 mL / min-3 mL / min.

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

[0021] The present invention can quickly and conveniently detect the vanadium ion concentration in the electrolyte of an all-vanadium liquid flow battery containing a mixture of tetravalent vanadium and pentavalent vanadium, does not require professional detection equipment, is simple to operate, and has no stringent requirements on the detection environment. At the same time, it has high accuracy and can meet the rapid detection needs of the all-vanadium liquid flow battery system on site. DETAILED DESCRIPTION

[0022] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the present invention is now described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0023] Example 1

[0024] The positive electrode electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

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

[0026] (2) Add a 0.100 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 7.7 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration of vanadium ions c1 is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; and V is the volume of the test solution a, in L. It is calculated that c1=0.77 mol / L;

[0027] (3) Add a 10% potassium persulfate aqueous solution to the test solution b at a rate of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the potassium persulfate aqueous solution to obtain a mixed solution; then add a 0.100 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a rate of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 15.5 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; c2=1.55 mol / L is calculated;

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

[0029] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.7766 mol / L, and the tetravalent vanadium ion concentration was 0.7831 mol / L.

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

[0031] Example 2

[0032] The positive electrode electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

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

[0034] (2) Add a 0.100 mol / L oxalic acid standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and then stop adding the oxalic acid standard solution; the volume of the oxalic acid standard solution consumed at this time is 3.4 mL. According to the volume of the oxalic acid standard solution consumed at this time, the concentration c1 of the vanadium ion is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 2; c is the concentration of the oxalic acid standard solution, in mol / L; V1 is the volume of the oxalic acid standard solution consumed at this time, in L; and V is the volume of the test solution a, in L. It is calculated that c1=0.68 mol / L;

[0035] (3) adding a 10% potassium persulfate aqueous solution to the test solution b at a rate of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stopping the addition of the potassium persulfate aqueous solution to obtain a mixed solution; then adding a 0.100 mol / L oxalic acid standard solution to the mixed solution at a rate of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stopping the addition of the oxalic acid standard solution; the volume of the oxalic acid standard solution consumed at this time is 7.9 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the oxalic acid standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 2; c is the concentration of the oxalic acid standard solution, in mol / L; V2 is the volume of the oxalic acid standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; and c2=1.58 mol / L is calculated;

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

[0037] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.6838 mol / L, and the tetravalent vanadium ion concentration was 0.8939 mol / L.

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

[0039] Example 3

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

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

[0042] (2) Add a 0.100 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 7.9 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration c1 of the vanadium ion is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; and V is the volume of the test solution a, in L. It is calculated that c1=0.79 mol / L;

[0043] (3) Add 10% lead dioxide acetic acid solution to the test solution b at a dropping speed of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the lead dioxide acetic acid solution to obtain a mixed solution; then add 0.100 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a dropping speed of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 16.8 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; c2=1.68 mol / L is calculated;

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

[0045] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.7937 mol / L, and the tetravalent vanadium ion concentration was 0.8883 mol / L.

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

[0047] Example 4

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

[0049] (1) Divide the sample to be tested into two parts, namely, solution a and solution b, and the volume of solution a and solution b are both 1.000 mL;

[0050] (2) Add a 0.800 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 1.1 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration c1 of the vanadium ion is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V is the volume of the test solution a, in L; and c1=0.88 mol / L is calculated;

[0051] (3) Add a 10% potassium persulfate aqueous solution to the test solution b at a dropping speed of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the potassium persulfate aqueous solution to obtain a mixed solution; then add a 0.800 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a dropping speed of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 2.0 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; c2=1.60 mol / L is calculated;

[0052] The concentration of pentavalent vanadium ions in the sample to be tested is c1, that is, 0.88 mol / L; the concentration of tetravalent vanadium ions is c2-c1, that is, 0.72 mol / L.

[0053] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.8524 mol / L, and the tetravalent vanadium ion concentration was 0.7531 mol / L.

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

[0055] Example 5

[0056] The positive electrode electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

[0057] (1) Divide the sample to be tested into two parts, namely, solution a and solution b, and the volume of solution a and solution b are both 1.000 mL;

[0058] (2) Add a 4.000 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 0.2 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration c1 of the vanadium ion is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V is the volume of the test solution a, in L; and c1=0.80 mol / L is calculated;

[0059] (3) Add a 10% potassium persulfate aqueous solution to the test solution b at a rate of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the potassium persulfate aqueous solution to obtain a mixed solution; then add a 4.000 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a rate of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 0.4 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; c2=1.60 mol / L is calculated;

[0060] Then the concentration of pentavalent vanadium ions in the sample to be tested is c1, that is, 0.80 mol / L; the concentration of tetravalent vanadium ions is c2-c1, that is, 0.80 mol / L.

[0061] The same sample to be tested was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.7312 mol / L, and the tetravalent vanadium ion concentration was 0.8727 mol / L.

[0062] It can be seen that, compared with the method in the above standard, the detection errors of the pentavalent vanadium ion concentration and the tetravalent vanadium ion concentration of the method in this embodiment are 9.41% and 8.33% respectively.

[0063] Example 6

[0064] The positive electrode electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

[0065] (1) Divide the sample to be tested into two parts, namely, solution a and solution b, and the volume of solution a and solution b are both 1.000 mL;

[0066] (2) Add a 0.020 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 22.6 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration of vanadium ions c1 is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V is the volume of the test solution a, in L; and c1=0.452 mol / L is calculated;

[0067] (3) Add a 10% potassium persulfate aqueous solution to the test solution b at a rate of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the potassium persulfate aqueous solution to obtain a mixed solution; then add a 0.020 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a rate of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 78.4 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; c2=1.568 mol / L is calculated;

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

[0069] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.4503 mol / L, and the tetravalent vanadium ion concentration was 1.1191 mol / L.

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

[0071] Example 7

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

[0073] (1) Divide the sample to be tested into two parts, namely, solution a and solution b, and the volume of solution a and solution b are both 1.000 mL;

[0074] (2) Add a 0.500 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 1.43 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration c1 of the vanadium ion is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; and V is the volume of the test solution a, in L. It is calculated that c1=0.715 mol / L;

[0075] (3) Add a 10% potassium persulfate aqueous solution to the test solution b at a dropping speed of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the potassium persulfate aqueous solution to obtain a mixed solution; then add a 0.500 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a dropping speed of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 3.18 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; c2=1.59 mol / L is calculated;

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

[0077] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.7282 mol / L, and the tetravalent vanadium ion concentration was 0.8887 mol / L.

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

[0079] Comparative Example 1

[0080] The positive electrode electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

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

[0082] (2) Add a 0.100 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 7.7 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration of vanadium ions c1 is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; and V is the volume of the test solution a, in L. It is calculated that c1=0.77 mol / L;

[0083] (3) A 10% potassium persulfate aqueous solution (molar concentration of 0.37 mol / L) was added dropwise to the test solution b at a rate of 2 mL / min until the color of the test solution b changed to bright yellow or yellow, and the addition of the potassium persulfate aqueous solution was stopped; the volume of the potassium persulfate aqueous solution consumed at this time was 2.2 mL. According to the volume of the potassium persulfate aqueous solution consumed at this time, the concentration of vanadium ions c2 was calculated using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the potassium persulfate aqueous solution, in mol / L; V2 is the volume of the potassium persulfate aqueous solution consumed at this time, in L; V' is the volume of the test solution b, in L; and c2=0.814_mol / L was calculated;

[0084] The concentration of pentavalent vanadium ions in the sample to be tested is c1, i.e. 0.77 mol / L; the concentration of tetravalent vanadium ions is c2, i.e. 0.814 mol / L.

[0085] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.7738 mol / L, and the tetravalent vanadium ion concentration was 0.8364 mol / L.

[0086] It can be seen that compared with the method in the above standard, the detection errors of the pentavalent vanadium ion concentration and the tetravalent vanadium ion concentration of the method in this comparative example are 0.49% and 2.68% respectively.

[0087] Comparative Example 2

[0088] The positive electrode electrolyte in the all-vanadium liquid flow battery was taken as the sample to be tested, and the sample was dark blue.

[0089] (1) Divide the sample to be tested into two parts, namely, solution a and solution b, and the volume of solution a and solution b are both 1.000 mL;

[0090] (2) Add a 0.100 mol / L ammonium ferrous sulfate standard solution to the test solution a at a dropping speed of 2 mL / min until the color of the test solution a changes to bright blue or blue, and stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 7.7 mL. According to the volume of the ammonium ferrous sulfate standard solution consumed at this time, the concentration of vanadium ions c1 is calculated using the following formula: c1=n×c×V1÷V; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V1 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; and V is the volume of the test solution a, in L. It is calculated that c1=0.77 mol / L;

[0091] (3) Add a 5% potassium permanganate aqueous solution to the test solution b at a rate of 2 mL / min until the color of the test solution b changes to bright yellow or yellow, then stop adding the potassium permanganate aqueous solution to obtain a mixed solution; then add a 0.100 mol / L ammonium ferrous sulfate standard solution to the mixed solution at a rate of 2 mL / min until the color of the mixed solution changes to bright blue or blue, then stop adding the ammonium ferrous sulfate standard solution; the volume of the ammonium ferrous sulfate standard solution consumed at this time is 15.4 mL, and the concentration c2 of the vanadium ion is calculated according to the volume of the ammonium ferrous sulfate standard solution consumed at this time using the following formula: c2=n×c×V2÷V'; wherein n is the reaction coefficient, which has no unit and is taken as 1; c is the concentration of the ammonium ferrous sulfate standard solution, in mol / L; V2 is the volume of the ammonium ferrous sulfate standard solution consumed at this time, in L; V' is the volume of the test solution b, in L; and c2=1.54 mol / L is calculated;

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

[0093] The same sample was taken and the vanadium ion concentration was detected according to the potentiometric titration method described in NB / T 42006-2013. The test results were: the pentavalent vanadium ion concentration was 0.7766 mol / L, and the tetravalent vanadium ion concentration was 0.7831 mol / L.

[0094] It can be seen that compared with the method in the above standard, the detection errors of the pentavalent vanadium ion concentration and the tetravalent vanadium ion concentration of the method in this comparative example are 0.44% and 1.67% respectively.

[0095] It can be seen from the above embodiments and comparative examples that the embodiments of the present invention can quickly and conveniently detect the vanadium ion concentration in the electrolyte of the all-vanadium flow battery containing a mixture of tetravalent vanadium and pentavalent vanadium, without the need for professional detection equipment, and the operation is simple, and there is no harsh requirement for the detection environment, and at the same time, it has high accuracy, and can meet the rapid detection requirements of the all-vanadium flow battery system on site. Moreover, the embodiments of the present invention use a standard solution of ammonium ferrous sulfate with a concentration of 0.02-0.5mol / L, especially 0.1mol / L, as a standard solution of reducing agent, so that the accuracy of the detection result is high; while the use of a standard solution of ammonium ferrous sulfate with a concentration that is too high, such as 0.800mol / L in Example 4 and 4.000mol / L in Example 5, reduces the accuracy. At the same time, it can be seen from the comparison of Example 1 of the present invention and Comparative Example 1 that the embodiment of the present invention calculates the concentration c2 of vanadium ions according to the volume of the reducing agent standard solution by dripping an oxidant solution and then dripping a reducing agent standard solution, and then determines the concentration of tetravalent vanadium ions, which has higher accuracy than the method of Comparative Example 1. In addition, it can be seen from the comparison between Example 1 of the present invention and Comparative Example 2 that the oxidant solution used in the present invention has higher accuracy than 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) dividing a vanadium electrolyte containing a mixture of tetravalent vanadium and pentavalent vanadium into two parts, namely, a test solution a and a test solution b; (2) adding a reducing agent standard solution to the test solution a until the color of the test solution a changes to bright blue or blue, and then stopping the adding of the reducing agent standard solution; according to the volume of the reducing agent standard solution consumed at this time, the concentration c1 of the vanadium ion is calculated using the following formula I: c1=n×c×V1÷V Formula I; wherein n is the reaction coefficient, which has no unit 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, in mol / L; V1 is the volume of the reducing agent standard solution consumed at this time, in L; and V is the volume of the test solution a, in L; (3) adding an oxidant solution to the test solution b until the color of the test solution b changes to bright yellow or yellow, then stopping the addition of the oxidant solution to obtain a mixed solution; then adding a reducing agent standard solution to the mixed solution until the color of the mixed solution changes to bright blue or blue, then stopping the addition of the reducing agent standard solution; calculating the concentration c2 of vanadium ions according to the volume of the reducing agent standard solution consumed at this time using the following formula II: c2=n×c×V2÷V'Formula II; wherein n is a reaction coefficient, which has no unit and 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, in mol / L; V2 is the volume of the reducing agent standard solution consumed at this time, in L; and 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.

2. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: The reducing agent standard solution includes one or more of a ferrous ammonium sulfate standard solution, a citric acid standard solution and an oxalic acid standard solution; Preferably, the reducing agent standard solution is ammonium ferrous sulfate standard solution.

3. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: In Formula I and Formula II, n is 1, 2 or 18; Preferably, if the reducing agent standard solution is ammonium ferrous sulfate standard solution, then the value of n is 1; if the reducing agent standard solution is citric acid standard solution, then the value of n is 18; if the reducing agent standard solution is oxalic acid standard solution, then the value of n is 2.

4. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: The concentration of the reducing agent standard solution is 0.01-4 mol / L.

5. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 4, wherein: The concentration of the reducing agent standard solution is 0.02-0.5 mol / L.

6. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: The dropping speed of adding the reducing agent standard solution to the test solution a is 1 mL / min-3 mL / min.

7. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: The oxidant solution includes one or more of an acetic acid solution of lead dioxide, an aqueous solution of potassium persulfate, an aqueous solution of sodium persulfate, an aqueous solution of ammonium persulfate, and an aqueous solution of elemental bromine.

8. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: The mass concentration of the oxidant solution is 3%-30%.

9. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 8, wherein: The mass concentration of the oxidant solution is 8%-12%.

10. The method for detecting the concentration of vanadium ions in a vanadium battery electrolyte according to claim 1, wherein: The oxidant solution is added to the test solution b at a dropping speed of 1 mL / min-3 mL / min, and the reducing agent standard solution is added to the mixed solution at a dropping speed of 1 mL / min-3 mL / min.