Manganese anolyte and preparation method and application thereof

Abstract

The invention provides manganese anolyte as well as a preparation method and application thereof. The manganese anolyte comprises divalent manganese ions, a stabilizer and supporting electrolyte, the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid, and the stabilizer is one or more of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, sodium phosphate, sodium metaphosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium pyrophosphate. According to the manganese anolyte, the stabilizer is added, so that the problem of disproportionation and precipitation of trivalent manganese in the electrolysis process is solved, and stable electrolysis is realized. The manganese anode electrolyte can be used for capacity recovery of the iron-chromium flow battery, and the recovery process is stable, pollution-free, economical and feasible. The manganese anode electrolyte can also be used for cathode reduction of a vanadium solution, vanadium can be reduced to below pentavalent vanadium, and the problem that low-concentration anode pentavalent vanadium cannot be reduced is solved. The manganese anode electrolyte has good application prospects and large-scale popularization potential in the field of flow batteries.

Description

Technical Field

[0001] The invention relates to a manganese anode electrolyte, and relates to a manganese anode electrolyte, a preparation method and application thereof. Background Art

[0002] Iron-chromium flow batteries appeared in the 1980s. They have received widespread attention due to their abundant reserves of iron and chromium elements, simple extraction, low cost, huge output, and broad application prospects.

[0003] However, until today, iron-chromium flow batteries have not been widely used because of the low activity of chromium. In addition, since its standard electrode potential in aqueous solution is -0.41V, which is much lower than the hydrogen evolution potential, the hydrogen evolution rate of the negative electrode solution after charging is high. Therefore, the flow battery using chromium as the negative electrode active material decays quickly, which is manifested as a continuous increase in the ion valence in the electrolyte, which leads to a gradual decrease in the concentration of active ions that can play a role in the battery. The rapid decay problem seriously limits the commercial application of iron-chromium flow batteries.

[0004] The recovery methods of iron-chromium flow batteries that have been reported so far include: (1) using a solution containing ferrous ions as the anode and the positive or negative electrode in the iron-chromium battery as the cathode, and reducing the valence state of the electrolyte of the iron-chromium battery by electrolysis to achieve the purpose of recovery. In essence, this is to replace the trivalent ferrous ions in the iron-chromium battery with new ferrous ions, thereby achieving battery recovery. Therefore, it is not economical in the industrialization process. Because the recovery process will produce a large amount of trivalent ferrous solution, it cannot be processed on site at the project site. (2) Using the electrolyte of the vanadium battery as the anode and the electrolyte of the iron-chromium battery as the cathode, reducing the valence state of the iron-chromium electrolyte by electrolysis, and then adding a reducing agent to the oxidized vanadium electrolyte to restore it to its initial state. Although this method can achieve the recovery of the iron-chromium electrolyte and can be continuously cycled, the price of vanadium is relatively high, and during the electrolysis process, vanadium ions will continue to migrate through the diaphragm of the electrolytic cell into the iron-chromium electrolyte, resulting in vanadium loss and high cost. It can be seen that the publicly available recovery methods of iron-chromium flow batteries all have certain problems and cannot meet the requirements of their commercial applications.

[0005] All-vanadium liquid flow batteries appeared in the 1990s and are currently the best liquid flow batteries for commercial applications. In the early stages of vanadium battery development, high-purity vanadium products were commonly used, which were dissolved and reduced to make electrolytes. With the commercialization of vanadium batteries, there is an urgent need to reduce costs and increase efficiency to improve their competitiveness in the market. Using the extraction process, bypassing the high-purity vanadium process, in the wet extraction process of vanadium, the extraction process can be used to extract vanadium from the solution, separate it from impurities, and directly produce vanadium electrolyte, which can significantly reduce costs. For low-content vanadium raw materials, such as stone coal and steel slag, this process can not only enrich the concentration, but also greatly shorten the production process and reduce production costs.

[0006] Different extractants can extract vanadium ions of different valence states, for example, N235 and N263 can extract pentavalent vanadium ions, and P204 can extract tetravalent vanadium ions. Among them, pentavalent vanadium ions have strong oxidizing properties in acidic solutions and will slowly destroy the extractant. Moreover, the extraction of pentavalent vanadium is an anion exchange process, in which the extractant, pentavalent vanadium, sulfate ions and other ions are very easy to form a gel together, which is difficult to separate, resulting in low production efficiency and high cost. The extraction process of tetravalent vanadium ions is simple, and the operation process is stable and reliable.

[0007] Whether extracting pentavalent vanadium or tetravalent vanadium ions, in order to prepare electrolytes that can be used in vanadium batteries, vanadium ions need to be reduced. Using chemical reduction, such as sulfur dioxide, vanadium can be reduced to tetravalent, but sulfur dioxide is toxic and has great environmental hazards. At the same time, the introduction of sulfur dioxide will lead to an increase in the sulfate concentration in the system, which has low practicality for low-sulfur electrolyte systems.

[0008] The cathode reduction of vanadium by electrolysis using oxygen evolution electrolysis as the anode requires the use of precious metals as oxygen evolution catalysts, but the stability of precious metals is poor, and their calendar life is only about 2000 hours, the production efficiency is low, and the cost is extremely high. The cathode reduction of vanadium using vanadium solution as the anode requires a higher anode vanadium concentration, otherwise, during the anode recovery process after the electrolysis is completed, when the chemical reagent is added, the reaction of pentavalent vanadium and the chemical reagent is not sufficient, the residual amount of the chemical reagent is large, and the cost is high. If the vanadium concentration is too high, it will gradually migrate to the cathode, resulting in an inability to stabilize the electrolysis.

[0009] On the other hand, the redox potential of divalent manganese ions is relatively high. After oxidation, they form trivalent manganese ions, which are unstable in aqueous solution and are prone to further disproportionation reaction to form divalent manganese and MnO2 precipitates. If the divalent manganese ion aqueous solution is used as the anode, disproportionation reaction will occur during the electrolysis process to form precipitates, which will cause blockage of the battery stack and attachment of carbon felt precipitates, causing electrode polarization, damaging or even burning the battery stack, and making it impossible to complete electrolysis recovery. Summary of the invention

[0010] The purpose of the present invention is to propose a manganese anode electrolyte in view of the above problems. By adding a stabilizer, the problem of trivalent manganese disproportionation precipitation in the electrolysis process is solved, and stable electrolysis is achieved; the manganese anode electrolyte can be used for capacity recovery of iron-chromium liquid flow batteries, and the recovery process is smooth, pollution-free, and economically feasible; the manganese anode electrolyte can also be used for cathode reduction of vanadium solution. After the electrolytic reduction is completed, the manganese anode electrolyte can be reduced to the initial state by adding chemical reagents, and the anode is reused, which solves the problem that pentavalent vanadium is difficult to reduce and the vanadium anode liquid cannot be recycled when low-concentration vanadium is used as the anode; the method has good application prospects and large-scale promotion potential in the field of liquid flow batteries.

[0011] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0012] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a manganese anode electrolyte, comprising: divalent manganese ions, a stabilizer and an electrolyte; the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid, and the stabilizer is one or more of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, sodium phosphate, sodium metaphosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium pyrophosphate.

[0013] Furthermore, the divalent manganese ion (Mn 2+ ) is sourced from one or more of manganese sulfate, manganese carbonate, manganese oxide, manganese hydroxide, manganese carbonate and metallic manganese.

[0014] Furthermore, the concentration of divalent manganese ions in the manganese anode electrolyte is 0.2M to 3M, preferably 0.5M to 2M; more preferably 1M to 2M.

[0015] Furthermore, the supporting electrolyte in the manganese anode electrolyte is measured in terms of hydrogen ions, with a concentration of 0.1 to 3M, preferably 0.3 to 2M.

[0016] Furthermore, the concentration of the stabilizer in the manganese anode electrolyte is 0.1-1M, preferably 0.4-0.8M.

[0017] Another object of the present invention is to disclose a method for preparing a manganese anolyte, comprising the following steps: mixing a divalent manganese ion source, a supporting electrolyte and a stabilizer to obtain a manganese anolyte.

[0018] Another object of the present invention is to disclose an application of a manganese anode electrolyte in the field of capacity recovery of iron-chromium liquid flow batteries or the field of cathode reduction of vanadium.

[0019] Another object of the present invention is to disclose a recovery method of an iron-chromium flow battery (also called a cathode reduction recovery method of an iron-chromium flow battery), comprising the following steps:

[0020] Step 1, using the divalent manganese ion solution as the anode solution and the iron-chromium battery electrolyte as the cathode solution to construct an electrolytic cell;

[0021] Step 2, applying power to electrolyze to reduce the active ions (iron ions and chromium ions) in the iron-chromium battery electrolyte, and restore the iron-chromium battery electrolyte to its initial capacity, while the divalent manganese ions in the anode liquid are oxidized to trivalent manganese ions;

[0022] A stabilizer is added to the anode solution, and the addition of the stabilizer allows trivalent manganese ions to exist stably in the anode solution, thereby achieving stable operation of electrolysis;

[0023] Step 3: After the electrolysis recovery is completed, a reducing agent is added to the anode solution to reduce the trivalent manganese ions to divalent manganese ions, so that the anode solution returns to its initial state.

[0024] Furthermore, when the unbalanced capacity of the iron-chromium flow battery decays to 70-90% (preferably 80%) of the initial capacity, recovery begins, that is, the iron-chromium battery electrolyte with decayed capacity is used as the cathode solution.

[0025] Furthermore, the iron-chromium battery electrolyte is an iron-chromium battery negative electrode electrolyte or an iron-chromium battery positive electrode electrolyte.

[0026] Furthermore, the iron-chromium battery electrolyte includes iron ions, chromium ions and a supporting electrolyte.

[0027] Furthermore, the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid, wherein the concentration is 0.1 to 3M, preferably 0.3 to 2M, measured as hydrogen ions.

[0028] Furthermore, the concentration of iron ions in the iron-chromium battery electrolyte is 0.5-2M, and the concentration of chromium ions is 0.5-2M.

[0029] Furthermore, the average current density is 10-300 mA / cm 2 , preferably 50 to 200 mA / cm 2 .

[0030] Furthermore, the reducing agent is one or more of formaldehyde, formic acid, acetic acid, glucose, fructose, citric acid, tartaric acid and vitamin C.

[0031] Furthermore, the amount of the reducing agent added is 1 to 1.5 times the required stoichiometric amount, preferably 1.1 to 1.2 times.

[0032] Take fructose as an example:

[0033] Using standard potassium permanganate solution, fructose is titrated in an acidic solution, and the reduction capacity it can provide is 0.1 mol electrons / g. When the battery capacity is restored to 1Ah, the amount of manganese ions oxidized in the anode is 1Ah. The required recovery dose is calculated as follows:

[0034] 1Ah / 26.8(Ah / mol) / 0.1(mol / g)=0.373g

[0035] Furthermore, a reducing agent is added to the anode solution, and the reaction temperature is 40-65°C and the reaction time is 1-24 hours. Preferably, the reaction temperature is 50-65°C and the reaction time is 6-20 hours.

[0036] Furthermore, the electrolytic cell structure includes: an anode electrode, a diaphragm, a cathode electrode, storage tanks required for the positive and negative electrodes, and a liquid circulation system.

[0037] Furthermore, the membrane is a cation exchange membrane or an anion exchange membrane.

[0038] Furthermore, the separator is a porous membrane.

[0039] The method for recovering the electrolyte of the iron-chromium liquid flow battery of the present invention has the following advantages compared with the prior art:

[0040] 1) The recovery method of the iron-chromium flow battery of the present invention uses a solution containing low-valent manganese ions as an anode solution, and does not use a solution containing vanadium ions as an anode solution, which is low in price;

[0041] 2) The recovery method of the iron-chromium liquid flow battery electrolyte of the present invention can construct a stable electrolytic reduction reaction by adding a stabilizer to stabilize the trivalent manganese ions, thereby achieving a smooth operation of the recovery process;

[0042] 3) The method for recovering the electrolyte of the iron-chromium flow battery of the present invention separates the reducing agent from the iron-chromium flow battery to prevent the reducing agent from contaminating the electrolyte of the iron-chromium flow battery. The method for recovering the electrolyte of the iron-chromium flow battery of the present invention has good application prospects and large-scale promotion potential in the field of flow batteries.

[0043] Another object of the present invention is to disclose a cathode reduction method of vanadium (also known as a cathode electrochemical reduction method of vanadium ions), comprising the following steps:

[0044] S1, using the manganese anode electrolyte as the anode solution and the vanadium-containing acidic solution as the cathode solution to construct an electrolytic cell;

[0045] S2, applying power to electrolyze to reduce vanadium ions in the vanadium-containing solution, and at the same time, divalent manganese ions in the anolyte are oxidized to trivalent manganese ions;

[0046] S3. After the electrolytic reduction is completed, a reducing agent is added to the anode solution to reduce the trivalent manganese ions to divalent manganese ions, so that the anode solution returns to its initial state.

[0047] Furthermore, the vanadium concentration in the vanadium-containing acidic solution is 0.1-3M, preferably 0.5-2M, and the hydrogen ion concentration is 0.1-2M, preferably 0.5-2M.

[0048] Furthermore, the vanadium-containing acidic solution is a stone coal leachate, a vanadium slag leachate of vanadium-titanium magnetite, a steel slag leachate, a petroleum ash leachate, or a pre-extraction solution in a vanadium extraction process or a stripping solution obtained by stripping, and the acid (leaching agent) is one or more of sulfuric acid, hydrochloric acid and phosphoric acid.

[0049] Furthermore, the average current density is 10-300 mA / cm 2 , preferably 50 to 200 mA / cm 2 .

[0050] Furthermore, the reducing agent is one or more of formaldehyde, formic acid, acetic acid, glucose, fructose, citric acid, tartaric acid and vitamin C.

[0051] Furthermore, the amount of the reducing agent added is 1 to 1.5 times the required stoichiometric amount, preferably 1.1 to 1.2 times.

[0052] Furthermore, a reducing agent is added to the anode solution, and the reaction temperature is 40-65°C and the reaction time is 1-24 hours. Preferably, the reaction temperature is 50-65°C and the reaction time is 6-12 hours.

[0053] Furthermore, the electrolytic cell structure includes: an anode electrode, a diaphragm, a cathode electrode, storage tanks required for the positive and negative electrodes, and a liquid circulation system.

[0054] Furthermore, the membrane is a cation exchange membrane or an anion exchange membrane.

[0055] Furthermore, the separator is a porous membrane.

[0056] The cathode reduction method of vanadium of the present invention has the following advantages compared with the prior art:

[0057] 1) The cathode reduction method of the present invention uses a solution containing low-valent manganese ions as an anode solution, and does not use a solution containing vanadium ions as an anode solution, which is low in price;

[0058] 2) The cathode reduction method of the present invention can construct a stable electrolytic reduction reaction by adding a stabilizer to stabilize the trivalent manganese ions, thereby achieving a smooth operation of the recovery process;

[0059] 3) The cathode reduction method of the present invention separates the reducing agent from the cathode solution to avoid the reducing agent from contaminating the solution to be reduced, and the reducing agent can be used to reduce trivalent manganese, so that the anode solution can be reused.

[0060] The cathode reduction method of the present invention has good application prospects and large-scale promotion potential in the field of liquid flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Schematic diagram of the structure of the electrolytic cell.

[0062] Figure 2 This is the voltage curve of cathode reduction of vanadium solution. DETAILED DESCRIPTION

[0063] The present invention is further described below with reference to the examples. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0064] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0065] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0066] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0067] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0068] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0069] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-35°C.

[0070] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0071] The electrolytic cell structure used in the present invention is as follows Figure 1As shown, the structure of the electrolytic cell is similar to that of the all-vanadium liquid flow battery, including: an anode storage tank, a battery, a cathode storage tank, a positive electrode pump and a circulation pipeline, a negative electrode pump and a circulation pipeline. The anode storage tank and the cathode storage tank are used to store the anode solution and the cathode solution, respectively. The battery is a single cell or a battery stack, and the battery includes an anode electrode, a diaphragm and a cathode electrode; the diaphragm is located in the battery housing to isolate the anode solution and the cathode solution; the anode electrode is located in the anode solution, and the cathode electrode is located in the cathode solution. The anode storage tank is connected to the anode solution in the battery housing through the positive electrode pump and the circulation pipeline, and the cathode storage tank is connected to the cathode solution in the battery housing through the negative electrode pump and the circulation pipeline.

[0072] The working process of the electrolytic cell structure is as follows: the anode solution in the anode storage tank is pressed into the side of the battery shell where the anode electrode is provided by the positive electrode pump, and power is turned on to oxidize the anode solution, and then the oxidized anode solution returns to the anode storage tank; at the same time, the cathode solution in the cathode storage tank is pressed into the side of the battery shell where the cathode electrode is provided by the negative electrode pump, and power is turned on to reduce the cathode solution, and then the reduced cathode solution returns to the cathode storage tank.

[0073] Example 1

[0074] This embodiment discloses a recovery method of an iron-chromium flow battery, comprising the following steps:

[0075] For a 10Ah iron-chromium flow battery, when the capacity decays to 8Ah, electrolysis recovery is performed after discharge. The electrolytic cell structure used for electrolysis recovery is as follows: Figure 1 shown.

[0076] Step 1, using a divalent manganese ion solution as an anode solution and an iron-chromium battery electrolyte as a cathode solution to construct an electrolytic cell;

[0077] The divalent manganese ion solution comprises:

[0078] Manganese sulfate 1M, sulfuric acid 1.5M, phosphoric acid 0.5M;

[0079] Carbon felt is used as electrode and 212 membrane is used as diaphragm;

[0080] The negative electrode solution of the iron-chromium flow battery is used as the cathode;

[0081] Step 2: Use 100mA / cm 2 The current density is set to 2Ah with constant current charging, and the electrolysis is terminated; the negative electrode solution of the iron-chromium liquid flow battery is transferred back to the iron-chromium liquid flow battery, and the battery is restored to its initial capacity; at the same time, the divalent manganese ions in the anode solution are oxidized to trivalent manganese ions; phosphoric acid is added to the anode solution, and the addition of phosphoric acid allows the trivalent manganese ions to exist stably in the anode solution, thereby achieving stable operation of the electrolysis;

[0082] Step 3: After the electrolysis recovery is completed, 0.6 g of glucose is added to the anode solution, maintained at 55°C, and stirred for 8 hours to restore the trivalent manganese ions to divalent manganese ions and restore the anode solution to its initial state.

[0083] The amount of glucose added is calculated from the number of Ah lost, the amount of glucose added is:

[0084] 2Ah / 26.8(Ah / mol) / 24(mol / mol)*180.14(g / mol)×1.072=0.6g.

[0085] Reactions occurring at the anode during electrolysis:

[0086] Mn 2+ =Mn 3+ +e+1.5V

[0087] The reaction at the cathode is:

[0088] Cr 3+ +e=Cr 2+ -0.41V

[0089] Example 2

[0090] This embodiment discloses a recovery method of an iron-chromium flow battery, comprising the following steps:

[0091] For a 14Ah iron-chromium flow battery, when the capacity decays to 11Ah, electrolysis recovery is performed after discharge;

[0092] Step 1, using a divalent manganese ion solution as an anode solution and an iron-chromium battery electrolyte as a cathode solution to construct an electrolytic cell;

[0093] The divalent manganese ion solution composition: Mn 2+ 0.6M, sulfuric acid 1M, pyrophosphate 0.3M, phosphoric acid 0.1M;

[0094] Carbon felt is used as electrode and anion exchange membrane (AEM) is used as diaphragm;

[0095] The positive electrode solution of the iron-chromium flow battery is used as the cathode;

[0096] Step 2: Use 50mA / cm 2 The current density is set to 3 Ah with constant current charging, and the electrolysis is terminated. The positive electrode solution of the iron-chromium flow battery is transferred back to the iron-chromium flow battery, and the battery is restored to its initial capacity.

[0097] Step 3: After the electrolysis recovery is completed, 1.31 g of anhydrous citric acid is added to the manganese anode solution. The calculation process is as follows:

[0098] 3Ah / 26.8(Ah / mol) / 18(mol / mol)×192.14(g / mol)×1.1=1.31g;

[0099] The solution temperature was maintained at 65°C and the reaction was stirred for 10 hours to restore the trivalent manganese ions to divalent manganese ions and restore the anode solution to its initial state.

[0100] Reactions occurring at the anode during electrolysis:

[0101] Mn 2+ =Mn 3+ +e+1.5V

[0102] The reaction at the cathode is:

[0103] Fe 3+ +e=Fe 2+ +0.77V

[0104] Example 3

[0105] This embodiment discloses a cathode reduction method for a vanadium leaching solution, comprising the following steps:

[0106] The electrolytic cell used for cathode reduction of vanadium leaching solution includes: anode storage tank, anode electrode, diaphragm, cathode electrode, cathode storage tank, positive electrode pump and circulation pipeline, negative electrode pump and circulation pipeline. The specific structure is as follows Figure 1 shown.

[0107] Step 1, using 1 liter of divalent manganese ion solution as an anode solution, 1 liter of vanadium leaching solution as a cathode solution, using carbon felt as an electrode and 115 membrane as a diaphragm to construct an electrolytic cell;

[0108] The manganese anolyte composition:

[0109] Mn 2+ 0.5M, sulfate 1M, sodium pyrophosphate 0.5M;

[0110] 1L pentavalent vanadium leaching solution, vanadium concentration is 0.4M, pH 1;

[0111] Step 2: Use 180mA / cm 2 Current density, constant current charging to the cut-off voltage of 1.1V, end the electrolysis;

[0112] The divalent manganese ions in the anode solution are partially oxidized to trivalent manganese ions; sodium pyrophosphate is added to the anode solution, and its presence enables the trivalent manganese ions to exist stably in the anode solution, thereby achieving stable operation of electrolysis;

[0113] Step 3: After the electrolysis recovery is completed, add 3.6 g of fructose to the anode solution, maintain 60° C., and stir the reaction for 18 hours to restore the trivalent manganese ions to divalent manganese ions and restore the anode solution to its initial state.

[0114] The amount of fructose added is calculated based on the amount of vanadium and the reducing power of fructose. The amount of fructose added is:

[0115] 0.4mol / 24(mol / mol)*180(g / mol)×1.2=3.6g.

[0116] Reactions occurring at the anode during electrolysis:

[0117] Mn 2+ =Mn 3+ +e+1.5V

[0118] The reaction at the cathode is:

[0119] VO2 + +2H + +e=H2O+VO 2+ +1V

[0120] The standard electrode potential difference of the above two reactions is 1.5V-1V=0.5V

[0121] After the electrolysis is completed, the vanadium is reduced to tetravalent state and can be further extracted and separated from impurities.

[0122] Figure 2 It is the voltage and current curve of the electrolysis process. The voltage in the figure gradually increases from below 0.4V to 0.8V and then rises rapidly. This change process corresponds to the change of the potential difference of the above two reactions. The voltage is lower than the standard potential difference in the initial stage because the concentration of the substance in the solution is lower than the standard state. The reduction reaction at the cathode corresponds to the reduction of pentavalent vanadium to tetravalent vanadium. Since the manganese in the anode solution is excessive, at the end of the reaction, the pentavalent vanadium at the cathode is completely reduced, and the tetravalent vanadium ion is reduced to the trivalent vanadium ion (+0.34V). The cathode potential continues to decrease, which is manifested as a sharp increase in the electrolysis voltage.

[0123] Example 4

[0124] This embodiment discloses a cathode reduction production method for vanadium electrolyte, comprising the following steps:

[0125] The electrolytic cell used for electrolysis recovery includes: a cell body for accommodating an anode solution, an anode electrode, a diaphragm, a cathode electrode, a cell body for accommodating a cathode solution, a positive electrode pump and a circulation pipeline, a negative electrode pump and a circulation pipeline. The cell body for accommodating an anode solution and the cell body for accommodating a cathode solution are separated by a diaphragm, and the anode electrode and the cathode electrode are respectively placed in the cell body for accommodating an anode solution and the cell body for accommodating a cathode solution;

[0126] Step 1, using 1 liter of divalent manganese ion solution as an anode solution, 1 liter of vanadium solution as a cathode solution, using carbon felt as an electrode and 117 membrane as a diaphragm to construct an electrolytic cell;

[0127] The manganese anolyte composition:

[0128] Mn 2+ 1.5M, sulfate 2M, metaphosphoric acid 0.8M;

[0129] Vanadium solution, volume 1L, initially tetravalent vanadium solution, concentration 1.5M, sulfuric acid 2M;

[0130] Step 2: Use 200mA / cm 2 Current density, constant current charging,

[0131] Since the purpose of this embodiment is to produce a 3.5-valent vanadium electrolyte, that is, half of the vanadium needs to be reduced, the required electrolysis power can be calculated based on the vanadium concentration and the change in vanadium valence:

[0132] 1L×1.5M / 2*26.8Ah / mol=20.1Ah

[0133] Start the power supply and charge to 20.1Ah, then end the electrolysis;

[0134] Step 3: After the electrolysis recovery is completed, vitamin C (VC) is added to the anode solution, the temperature is maintained at 55°C, and the reaction is stirred for 15 hours to restore the trivalent manganese ions to divalent manganese ions and restore the anode solution to its initial state.

[0135] The amount of VC added is calculated from the charge during electrolysis and the reducing power of VC:

[0136] 20.1Ah / 26.8(Ah / mol) / 20(mol / mol)*176.12(g / mol)×1.05=6.94g.

[0137] Reactions occurring at the anode during electrolysis:

[0138] Mn 2+ =Mn 3+ +e+1.5V

[0139] The reaction at the cathode is:

[0140] VO 2+ +2H + +e=H2O+V 3+ +0.34V

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A manganese anolyte, characterized in that: The invention comprises divalent manganese ions, a stabilizer and a supporting electrolyte; the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid, and the stabilizer is one or more of phosphoric acid, pyrophosphoric acid, metaphosphoric acid, sodium phosphate, sodium metaphosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium pyrophosphate.

2. The manganese anolyte according to claim 1, characterized in that: The source of the divalent manganese ions is one or more of manganese sulfate, manganese phosphate, manganese oxide, manganese carbonate and metallic manganese.

3. The manganese anolyte according to claim 1, characterized in that: The divalent manganese ion concentration is 0.2M to 3M; and / or, the supporting electrolyte is measured in hydrogen ions with a concentration of 0.1 to 3 M; And / or, the stabilizer concentration is 0.1-1M.

4. A method for preparing the manganese anolyte according to any one of claims 1 to 3, characterized in that: The following steps are involved: A divalent manganese ion source, a supporting electrolyte and a stabilizer are mixed to obtain a manganese anolyte.

5. A capacity recovery method for an iron-chromium flow battery, characterized in that: The following steps are involved: Step 1, using the manganese anode electrolyte described in any one of claims 1 to 3 as the anode solution and the iron-chromium battery electrolyte as the cathode solution to construct an electrolytic cell; Step 2, applying power to electrolyze to reduce the active ions in the iron-chromium battery electrolyte, and restore the iron-chromium battery electrolyte to its initial capacity, while the divalent manganese ions in the anode liquid are oxidized to trivalent manganese ions; Step 3: After the electrolysis recovery is completed, a reducing agent is added to the anode solution to reduce the trivalent manganese ions to divalent manganese ions, so that the anode solution returns to its initial state.

6. The capacity recovery method of the iron-chromium flow battery according to claim 5, characterized in that: The iron-chromium battery electrolyte is an iron-chromium battery cathode electrolyte or an iron-chromium battery cathode electrolyte; And / or, the iron-chromium battery electrolyte comprises iron ions, chromium ions and a supporting electrolyte; and / or, the supporting electrolyte is one or more of hydrochloric acid, sulfuric acid and phosphoric acid, wherein the concentration is 0.1 to 3 M as measured by hydrogen ions; And / or, the concentration of iron ions in the iron-chromium battery electrolyte is 0.5-2M, and the concentration of chromium ions is 0.5-2M.

7. The capacity recovery method of the iron-chromium flow battery according to claim 5, characterized in that: When the unbalanced capacity of the iron-chromium flow battery decays to 70-90% of the initial capacity, it begins to recover; And / or, the average current density is 10-300 mA / cm 2 ; and / or, the reducing agent is one or more of formaldehyde, formic acid, acetic acid, glucose, fructose, citric acid, tartaric acid and vitamin C; and / or, the amount of the reducing agent added is 1 to 1.5 times the required stoichiometric amount; And / or, a reducing agent is added to the anode solution, the reaction temperature is 40 to 65° C., and the reaction time is 1 to 24 hours.

8. A method for cathode reduction of vanadium, characterized in that: The following steps are involved: S1. Using the manganese anode electrolyte according to any one of claims 1 to 3 as the anode solution and the vanadium-containing acidic solution as the cathode solution to construct an electrolytic cell; S2, applying power to electrolyze to reduce vanadium ions in the vanadium-containing solution, and at the same time, divalent manganese ions in the anolyte are oxidized to trivalent manganese ions; S3. After the electrolytic reduction is completed, a reducing agent is added to the anode solution to reduce the trivalent manganese ions to divalent manganese ions, so that the anode solution returns to its initial state.

9. The cathode reduction method of vanadium according to claim 8, characterized in that: The vanadium concentration in the vanadium-containing acidic solution is 0.1-3M, and the hydrogen ion concentration is 0.1-2M.

10. The cathode reduction method of vanadium according to claim 8, characterized in that: The average current density of the current is 10-300 mA / cm 2 ; and / or, the reducing agent is one or more of formaldehyde, formic acid, acetic acid, glucose, fructose, citric acid, tartaric acid and vitamin C; and / or, the amount of the reducing agent added is 1 to 1.5 times the required stoichiometric amount; And or, adding a reducing agent to the anode solution, the reaction temperature is 40-65°C; the reaction time is 1-24h.

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