Method for measuring content of ferric ions in electrolyte of iron-chromium flow battery

Abstract

The invention discloses a method for measuring the content of ferric ions in an iron-chromium flow battery electrolyte, which comprises the following steps: before the content of the ferric ions is measured, pretreating the electrolyte to be measured to remove the influence of Cr ions and other impurity ions in the electrolyte on an experimental result, and then titrating with a sodium thiosulfate standard solution; the method has the advantages that the method is suitable for directly measuring the content of the ferric ions under the coexistence condition of a large amount of ferrous ions, the problems that in the prior art, when a large amount of ferrous ions and a trace amount of ferric ions coexist, the error is large, and the accuracy is low are solved, and a technical guarantee is provided for capacity recovery and efficiency improvement of the electrolyte of the flow battery.

Description

Technical Field

[0001] The present invention relates to a method for determining the ion content of a liquid flow battery, specifically a method for determining the ferric ion content of an electrolyte of an iron-chromium liquid flow battery, and in particular to a method for directly determining the ferric ion content in the presence of a large amount of divalent iron ions. The invention belongs to the field of liquid flow batteries. Background Art

[0002] Against the backdrop of the digital and intelligent transformation of traditional industries, the traditional energy system, primarily based on non-renewable energy sources such as coal and oil, is gradually transitioning to a new power system based on new energy sources such as wind, solar, and geothermal energy, combined with energy storage. Currently, the mainstream energy storage technology is electrochemical energy storage. Among them, Fe / Cr flow batteries are widely used for buffering, storage, and output of renewable energy sources such as solar and wind energy due to their low cost, long cycle life, excellent high-current rapid discharge capability, wide temperature range, good safety, and scalable design. These advantages enhance stability. Fe / Cr flow batteries can also be used in large-scale energy storage systems for peak shaving and valley filling in power grids. Imbalances in the concentrations of ferrous and ferric ions in the cathode electrolyte, caused by hydrogen evolution and irreversible electrochemical side reactions, are a major factor in the reduced capacity and efficiency of Fe / Cr flow batteries. Regarding the detection of the content of divalent iron ions and trivalent iron ions in the electrolyte, the current conventional potassium dichromate method is suitable for the detection of extremely high content of divalent iron ions, but for the detection of the content of trivalent iron ions in the electrolyte, the experimental error is slightly large and the test accuracy is slightly low. Summary of the Invention

[0003] The purpose of the present invention is to design a method for determining the trivalent iron ion content of the iron-chromium liquid flow battery electrolyte, which is suitable for directly determining the trivalent iron ion content in the presence of a large amount of divalent iron ions, with low error and high accuracy.

[0004] The technical solution of the present invention is:

[0005] A method for determining the ferric ion content of an iron-chromium flow battery electrolyte comprises: before determining the ferric ion content, pre-treating the electrolyte to be tested to remove the influence of Cr ions and other impurity ions in the electrolyte on the experimental results, and then titrating with a sodium thiosulfate standard solution;

[0006] The specific operation process is as follows:

[0007] (1) Pipette the electrolyte solution V0 to be tested into a volumetric flask, dilute with high-purity water, make up to volume, and mix well;

[0008] (2) Pipette V1 from the electrolyte obtained after the treatment in step (1) into a conical flask, add a number of glass beads, and then add perchloric acid; heat the mixed solution in the conical flask, and after the mixed solution stops smoking, cool it to room temperature, add concentrated nitric acid, dilute it with water, and then heat and boil it to dissolve the ions in the electrolyte and the salts formed with the added perchloric acid and concentrated nitric acid.

[0009] (3) adding a portion of concentrated ammonia water to the mixed solution obtained after the treatment in step (2) until iron precipitation appears, then adding another portion of excess concentrated ammonia water, then heating to boil, letting it stand, filtering with filter paper while hot, and then washing the conical flask and filter paper with hot dilute ammonia water until the chromium ions are completely separated and the washing liquid is colorless;

[0010] (4) The iron precipitate obtained by filtration in step (3) is placed back into the original conical flask together with the filter paper, and then nitric acid and perchloric acid are added. The resulting mixture is heated until the smoke stops. After cooling to room temperature, concentrated hydrochloric acid is added, and then diluted with water. The mixture is heated to a boil to fully dissolve the iron salt. After cooling, the volume is adjusted to V2;

[0011] (5) Take the volume of the electrolyte to be tested as V3, add excess potassium iodide, stir, and then add starch solution as an indicator until the electrolyte turns blue;

[0012] (6) Using a concentration of C S The electrolyte obtained in step (5) is titrated with a sodium thiosulfate standard solution until the blue color of the solution disappears, and the volume of sodium thiosulfate standard solution consumed is V S ;

[0013] (7) Calculate the ferric iron content in the electrolyte to be tested according to the formula:

[0014] C Fe 3+ =5*(55.85*(C S *V S ) / V3)*(V2 / V1)

[0015] Among them, C Fe is the ferric iron content in the electrolyte to be tested, in g / L;

[0016] C S is the concentration of sodium thiosulfate standard solution, in mo / L;

[0017] V S is the volume of sodium thiosulfate standard solution consumed, in ml;

[0018] V1 is the volume of electrolyte removed after 10-fold dilution;

[0019] V2 is the volume of the iron salt after dissolution and cooling;

[0020] V3 is the volume of the electrolyte to be tested, in ml.

[0021] The purpose of dilution in step (1) is to reduce the acidity to avoid the occurrence of side reactions in the strongly acidic solution. The dilution ratio is 2-10 times, preferably 5 times, and other dilution ratios may also be used. The 5-fold dilution ratio is adopted in combination with the common concentration of the iron-chromium flow battery electrolyte, the constant volume in the subsequent process, the concentration of the sodium thiosulfate standard solution drop, and other conditions to obtain a more appropriate titrant consumption volume, thereby accurately determining the trivalent iron ion content.

[0022] In the step (2), the mass fraction of perchloric acid is 70-72%, the mass fraction of concentrated nitric acid is 65-68%, and the added amounts of perchloric acid and concentrated nitric acid are both within the range of 2-10 ml.

[0023] The mass fraction of the concentrated ammonia water in step (3) is 22-25%. The first addition amount is the amount of concentrated ammonia water consumed when iron precipitation occurs in the solution, and the second excess amount is 5-15 ml.

[0024] The filter paper used for filtering in step (3) is slow quantitative filter paper.

[0025] The temperature of the dilute ammonia water in step (3) is about 40-50° C., and the mass fraction thereof is 9.5%-10.5%.

[0026] In the step (4), the amount of perchloric acid added is 5-15 ml, and the amount of concentrated nitric acid added is 5-15 ml.

[0027] In step (4), 5-15 ml of concentrated hydrochloric acid is added to a concentration of 12 mol / L.

[0028] The purpose of adding water to dilute in step (4) is to reduce the acidity of hydrochloric acid when dissolving iron salt and avoid side reactions. The amount of water added is 20 ml.

[0029] The mass fraction of the starch solution in step (5) is 0.1%.

[0030] The principle of the method for determining the content of ferric ions in the electrolyte of the present invention is: after potassium iodide is added to the electrolyte, the chemical reaction that occurs is:

[0031] 2Fe 3+ +2I - =2Fe 2+ +I2

[0032] This step of the reaction reduces the trivalent iron ions to produce iodine. Then, an appropriate amount of starch solution is added. The iodine turns blue when it encounters the starch solution and is then titrated with a standard solution. The chemical reaction that occurs is:

[0033] 2Na2S2O3+I2=Na2S4O6+2NaI

[0034] The amount of Na2S2O3 standard solution consumed can be used to calculate the content of elemental iodine in the solution, and then the content of trivalent iron ions in the test solution can be converted.

[0035] The beneficial effects of the present invention are: it is suitable for directly measuring the content of trivalent iron ions in the presence of a large amount of divalent iron ions, solving the problem of large errors and low accuracy when a large amount of divalent iron and a trace amount of trivalent iron coexist in the prior art, and providing technical support for the recovery of electrolyte capacity and improvement of efficiency of liquid flow batteries.

[0036] The present invention will be further described below with reference to the embodiments. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0038] Example 1

[0039] The electrolyte used in this embodiment is prepared by mixing ferrous chloride, chromium chloride, ferric chloride and analytical grade hydrochloric acid in a certain proportion, wherein Fe 2+ Concentration 1.2 mol / L, Fe 3+ Concentration 0.1mol / L, Cr 3+ 1.2mol / L:

[0040] The method for determining the content of trivalent ferrous ions in the electrolyte of the present invention is used to detect the concentration of trivalent ferrous ions in the electrolyte to be tested. The detection method comprises the following steps:

[0041] 1. Electrolyte pretreatment

[0042] Pipette the electrolyte solution (10 ml) V0 to be tested into a volumetric flask, dilute it with high-purity water at a dilution factor of 5, make up to volume (50 ml), and mix evenly;

[0043] Pipette (10 ml) of the evenly mixed electrolyte solution of V1 into a conical flask, add several glass beads, and add 3 ml of perchloric acid. Heat the mixed solution in the conical flask. After the mixed solution stops smoking, cool it to room temperature, add 5 ml of concentrated nitric acid, and dilute it with 20 ml of water. Then heat and boil to dissolve the salts formed by the ions in the electrolyte and the added perchloric acid and concentrated nitric acid.

[0044] Add concentrated ammonia until iron precipitates in the solution, then add 5 ml of excess concentrated ammonia, boil, let stand, filter while hot, then wash the conical flask and filter paper with hot dilute ammonia until the washing liquid becomes colorless;

[0045] Put the iron precipitate and filter paper back into the original conical flask, then add 5 ml of concentrated nitric acid and 5 ml of perchloric acid, heat the mixture until the smoke stops, cool to room temperature, add 5 ml of concentrated hydrochloric acid, and then dilute with 20 ml of water, heat to boil, so that the iron salt is fully dissolved, and adjust the volume to (50 ml) V2 after cooling.

[0046] 2. Titration

[0047] Take the pre-treated electrolyte (10ml) V3, add 50-100ml of high-purity water and shake well, then add excess potassium iodide and stir:

[0048] Add 0.1% starch solution as an indicator and the solution turns blue;

[0049] Then titrate with a sodium thiosulfate standard solution with a concentration of 0.0101 mol / L until the blue color of the solution disappears. The volume of sodium thiosulfate standard solution consumed is (3.94 ml)V S ;

[0050] Calculate the ferric iron content in the electrolyte to be tested using the following formula:

[0051] The calculation formula is: C Fe 3+ =5*(55.85*((C S *V S ) / V3)*(V2 / V1))

[0052] =5*(55.85*(0.0101*3.94) / 10)*(50 / 10)

[0053] =5.56g / L

[0054] 3. Results Analysis

[0055] The Fe 3+ Compared with the originally prepared solution, the error of the content is -0.025 g / / L, and the error rate is 0.45%. It can be seen that the detection result of the method of the present invention is highly accurate.

Claims

1. A method for determining the ferric ion content of an iron-chromium flow battery electrolyte, characterized in that: The method comprises the following steps: before determining the content of trivalent iron ions, pre-treating the electrolyte to be tested to remove the influence of Cr ions and other impurity ions in the electrolyte on the experimental results, and then titrating with a sodium thiosulfate standard solution; The specific operation process is as follows: (1) Pipette the electrolyte solution V0 to be tested into a volumetric flask, dilute with high-purity water, make up to volume, and mix well; (2) Pipette V1 from the electrolyte obtained after the treatment in step (1) into a conical flask, add a number of glass beads, and then add perchloric acid; heat the mixed solution in the conical flask, and after the mixed solution stops smoking, cool it to room temperature, add concentrated nitric acid, dilute it with water, and then heat and boil it to dissolve the ions in the electrolyte and the salts formed with the added perchloric acid and concentrated nitric acid. (3) adding a portion of concentrated ammonia water to the mixed solution obtained after the treatment in step (2) until iron precipitation appears, then adding another portion of excess concentrated ammonia water, then heating to boil, letting it stand, filtering with filter paper while hot, and then washing the conical flask and filter paper with hot dilute ammonia water until the chromium ions are completely separated and the washing liquid is colorless; (4) The iron precipitate obtained by filtration in step (3) is placed back into the original conical flask together with the filter paper, and then nitric acid and perchloric acid are added. The resulting mixture is heated until the smoke stops. After cooling to room temperature, concentrated hydrochloric acid is added, and then diluted with water. The mixture is heated to a boil to fully dissolve the iron salt. After cooling, the volume is adjusted to V2; (5) Take the volume of the electrolyte to be tested as V3, add excess potassium iodide, stir, and then add starch solution as an indicator until the electrolyte turns blue; (6) Using a concentration of C S The electrolyte obtained in step (5) is titrated with a sodium thiosulfate standard solution until the blue color of the solution disappears, and the volume of sodium thiosulfate standard solution consumed is V S ; (7) Calculate the ferric iron content in the electrolyte to be tested according to the formula: C Fe 3+ =10*(55.85*(C S *V S ) / V3)*(V2 / V1) Among them, C Fe is the ferric iron content in the electrolyte to be tested, in g / L; C S is the concentration of sodium thiosulfate standard solution, in mo / L; V S is the volume of sodium thiosulfate standard solution consumed, in ml; V1 is the volume of electrolyte removed after 10-fold dilution; V2 is the volume of the iron salt after dissolution and cooling; V3 is the volume of the electrolyte to be tested, in ml.

2. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: The dilution ratio in step (1) is 2-10 times.

3. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: In the step (2), the mass fraction of perchloric acid is 70-72%, the mass fraction of concentrated nitric acid is 65-68%, and the added amounts of perchloric acid and concentrated nitric acid are both within the range of 2-10 ml.

4. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: The mass fraction of the concentrated ammonia water in step (3) is 22-25%. The first addition amount is the amount of concentrated ammonia water consumed when iron precipitation occurs in the solution, and the second excess amount is 5-15 ml.

5. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: The filter paper used for filtering in step (3) is slow quantitative filter paper.

6. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: The temperature of the dilute ammonia water in step (3) is about 40-50° C., and the mass fraction thereof is 9.5%-10.5%.

7. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: In the step (4), the amount of perchloric acid added is 5-15 ml, and the amount of concentrated nitric acid added is 5-15 ml.

8. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: In step (4), 5-15 ml of concentrated hydrochloric acid is added to a concentration of 12 mol / L.

9. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: The amount of water added in step (4) is 20 ml.

10. The method for determining the ferric ion content in an iron-chromium flow battery electrolyte according to claim 1, wherein: The mass fraction of the starch solution in step (5) is 0.1%.