CN115128026B - Method for testing balance degree of iron-chromium flow battery system - Google Patents
Method for testing balance degree of iron-chromium flow battery system Download PDFInfo
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Abstract
The invention relates to a method for testing the balance degree of a ferro-chromium flow battery system. The method of the invention is realized by mixing the positive electrolyte and the negative electrolyteTesting the mixed solution for Fe 2+ And then adding a reducing agent to the mixed solution to obtain the iron ion concentration, and calculating the equilibrium degree therefrom. The test method of the invention only needs to use a single wavelength spectrometer to test Fe 2+ The concentration and the obtained result are accurate, the operation is simple and convenient, and the method has wide applicability.
Description
Technical Field
The invention relates to a method for testing the balance degree of a ferro-chromium flow battery system, in particular to a method for detecting by adopting a portable device so as to obtain electrolyte balance data, and belongs to the technical field of electrolyte detection of ferro-chromium flow batteries.
Background
The flow battery technology has natural advantages of large-scale energy storage: the size of the electric storage quantity is linearly proportional to the volume of the electrolyte, and the charging and discharging power is determined by the size and the quantity of the galvanic pile, so that the flow battery with different charging and discharging powers from kW to MW level and different energy storage quantities from 1 hour to several days of sustainable discharging can be designed according to the requirements. The electrolyte based on common inorganic acid and inorganic salt has stable chemical components, convenient storage, little influence on environment, extremely low self-discharge coefficient and suitability for long-term electric energy storage. The reaction temperature of the battery is normal temperature and normal pressure, the flowing process of the electrolyte is a natural water-based circulating heat dissipation system, the safety performance is extremely high, and the accident influence is far lower than that of other large-scale energy storage schemes. There is no upper limit to the theoretical number of charge and discharge cycles due to its stable and reliable charge and discharge cycles.
Among the flow batteries, iron-chromium flow batteries are receiving attention due to their abundant iron-chromium resources, low cost, high cycle times, long life, low toxicity and corrosivity, easy modular design, etc.
The electrolyte balance degree is an important index for the operation of the flow battery system. The electrolyte of the whole flow battery system can be unbalanced due to various reasons, a means with high speed, accuracy and repeatability is needed, the electrolyte balance degree is monitored constantly, the normal and stable operation of the system is ensured, side reactions are not frequently generated, and the failure or capacity attenuation of the whole system is caused.
The balance degree detection method is particularly important for the iron-chromium flow battery. Unlike all-vanadium flow batteries, iron-chromium flow batteries do not solve the problem of hydrogen evolution at the negative electrode well. This problem causes the balance of the iron-chromium electrolyte to shift to the unbalance direction continuously. This can result in a significant and sustained decay in the capacity of the system and result in more severe hydrogen evolution from the negative electrode and even a severe impact on the overall safety of the ferrochrome flow battery system.
Reference 1 discloses a method for determining the degree of electrolyte imbalance in a ferrochrome flow battery, which comprises: introducing a first liquid electrolyte into a first compartment of a test cell; introducing a second liquid electrolyte into a second compartment of the test cell; measuring a voltage of the test cell; measuring an elapsed time from the test cell reaching a first voltage until a voltage test endpoint is reached; and determining a concentration indicative of one reactant in the first and second liquid electrolytes based on the elapsed time.
As can be seen from the above, the method and the test apparatus disclosed in reference 1 are complicated and cannot be monitored quickly, accurately, and conveniently from time to time.
Cited document 1: CN103534858A.
Disclosure of Invention
Problems to be solved by the invention
Although the method capable of determining the degree of imbalance of the electrolyte in the ferrochrome flow battery is disclosed in the above cited document 1, there is a large error in determining the voltage test end point in the method, and therefore, the accuracy of the method is to be improved. In addition, the method needs to additionally use a test battery, so that the equipment is complex and not convenient enough.
In addition, the present inventors have found that Cr 2+ Is sensitive to environment, and can be quickly oxidized by oxygen in the environment to change the valence state under the common storage condition. Such a phenomenon increases as the sampling-detection interval becomes longer, so that the test result tends to deviate.
Aiming at the problems of insufficient accuracy and convenience of a detection method in the prior art, the invention provides a method for testing the balance degree of a ferrochrome flow battery system, which only needs to use a single wavelength spectrometer to measureTest Fe 2+ The concentration, the obtained result are accurate, and the operation is simple and convenient.
Means for solving the problems
Through long-term research by the inventor of the present invention, it is found that the technical problems can be solved through implementation of the following technical scheme:
the invention provides a method for testing the balance degree of a ferro-chromium flow battery system, which is characterized by comprising the following steps:
a standard working curve making step: preparing a series of ferrous ion standard solutions with known concentration, and obtaining an absorbance-concentration standard working curve under a specified wavelength by adopting an ultraviolet-visible spectrophotometry;
electrolyte mixing step: the obtained volume is V 1 Is directly added to the obtained cathode electrolyte with the volume V 2 To obtain a volume of V 0 Mixed electrolyte solution A of (1), wherein V 1 And V 2 Substantially of equal volume;
concentration C 1 An acquisition step: testing Fe in the mixed electrolyte A at the specified wavelength 2+ The absorbance of the mixed electrolyte A is matched with the standard working curve to obtain Fe in the mixed electrolyte A 2+ Concentration C of 1 ；
Concentration C 2 An acquisition step: adding a reducing agent into the mixed electrolyte A to obtain a mixed electrolyte B,
testing Fe in the mixed electrolyte B at the specified wavelength at intervals of unit time in the adding process by taking the moment of adding the reducing agent as a starting point 2+ Until the absorbance reaches the maximum value, the volume V of the mixed electrolyte B at that time was recorded 3 And matching the standard working curve to obtain the Fe at the moment 2+ Concentration C of 2 ；
Total iron concentration C 3 A calculation step: calculating Fe in the mixed electrolyte A according to the following formula (1) 2+ And Fe 3+ Total concentration of (C) 3 ：
C 3 =C 2 ×V 3 /V 0 （1）；
And a balance degree calculation step: calculating the balance k of the iron-chromium flow battery system based on the following formula (2):
k=(C 3 -C 1 )×2/C 3 ×100%（2）。
the method of testing as described above, characterized in that samples are taken from the positive system and from the negative system of the flow battery at any state of charge SOC, preferably at a state of charge SOC of 0.
The test method as described above, characterized in that the mixed electrolyte is trivalent chromium ions Cr 3+ Divalent iron ion Fe 2+ And ferric ion Fe 3+ The mixed solution of (1).
The test method described above, wherein the predetermined wavelength is in a range of 900 to 1100 nm.
The method according to the above, wherein the electrolyte mixing step is performed after the mixed electrolyte A reaches an oxidation-reduction equilibrium at the concentration C 1 And (5) obtaining.
The test method as described above, characterized in that the concentration C 1 In the step of obtaining, the mixed electrolyte A is diluted and then tested for Fe 2+ Absorbance of (b).
The test method as described above, characterized in that the unit time is 3s-5min, preferably 5s-3min.
The test method as described above, wherein the reducing agent comprises an inorganic reducing agent and an organic reducing agent.
The test method as described above, wherein the inorganic reducing agent includes a negative electrode electrolyte, fe, zn, cu, cr 2+ 、S、SO 2 One or more of (a).
The test method as described above, wherein the organic reducing agent comprises CH 4 N 2 S、CH 3 CSNH 2 、N 2 H 4 ·H 2 O、NH 2 NH 2 2HCl, ethylene glycol, oxalic acid, glycerolOne or more of (a).
ADVANTAGEOUS EFFECTS OF INVENTION
1) The method for testing the electrolyte balance degree of the iron-chromium flow battery is convenient and quick to operate, and only a single wavelength spectrometer is needed to measure Fe 2+ The concentration of the detection reagent is low in requirement on detection equipment, and the detection reagent has wider applicability and convenience;
2) In the detection process of the invention, cr can be reduced or avoided 2+ The test accuracy is reduced due to the oxidation, and the accuracy of the detection method is further improved.
Detailed Description
The present invention will be described in detail below. The technical features described below are explained based on typical 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:
in the present specification, the numerical range represented by "numerical value a to numerical value B" means a range including the end points of numerical values a and B.
In the present specification, the numerical ranges indicated by "above" or "below" refer to numerical ranges including the number.
In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.
In the present specification, the use of "optional" or "optional" means that certain materials, components, performance steps, application conditions, and the like are used or not used.
In the present specification, "normal temperature" used means an operating environment temperature of "25 ℃.
In the present specification, the unit names used are all international standard unit names, and the "%" used means weight or mass% content, if not specifically stated.
In the present specification, the term "substantially" is used to indicate that the standard deviation from the theoretical model or theoretical data is within a range of 2%, preferably 1%, and more preferably 0.5%.
In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.
The invention provides a method for testing the electrolyte balance degree of a ferrochrome flow battery, which is quick and convenient to operate. The test method of the present invention is completed mainly based on the following findings.
Generally, to some extent, chromium ions are present in divalent and trivalent forms in the negative electrolyte and iron ions are present in divalent and trivalent forms in the positive electrolyte of a flow battery. When equal volumes of the negative electrolyte and the positive electrolyte are mixed in almost the same time, the Cr in the mixed electrolyte solution reaches the oxidation-reduction balance under normal conditions 3+ And Fe 2+ The ratio of (A) to (B) should be 1. However, the side reaction of hydrogen evolution which is continuously generated in the negative electrode causes Cr 3+ :Fe 2+ The ratio of (a) may be constantly shifted in a direction deviating from 1. That is, therefore, it is necessary to monitor the degree of balance of the iron-chromium electrolyte from time to time. The inventor has found through research that Fe can be tested only 2+ The concentration of the iron-chromium electrolyte can be accurately, conveniently and quickly measured.
The method for testing the balance degree of the iron-chromium flow battery system comprises the following steps: standard working curve making step, electrolyte mixing step and concentration C 1 Acquisition step, concentration C 2 Obtaining step, total iron concentration C 3 A calculating step and a balance calculating step. The respective steps will be described in detail below.
Standard working curve making step
In the standard working curve making step, a series of ferrous ion standard solutions with known concentration are required to be configured, and an absorbance-concentration standard working curve under specified wavelength is obtained by adopting an ultraviolet-visible spectrophotometry.
The method for preparing the standard solution is not particularly limited, and the method can be performed according to a method generally used in the art. Meanwhile, the number of samples of the standard solution should be appropriate, and it is understood that the number of samples of the standard is important for the accuracy of drawing the standard working curve, and thus, standard solutions of different concentrations can be obtained more frequently as conditions allow.
The concentration range of the standard working curve obtained in this step should also be appropriate, and in some cases, it is desirable that such concentration range be as wide as possible and the intervals between different concentrations be as small as possible in order to obtain the final absorption peak intensity-Fe 2+ A curve with good continuity of ion concentration.
The above-mentioned predetermined wavelength and Fe 2+ The characteristic absorption of (c). In the present invention, the predetermined wavelength may be in the range of 900 to 1100nm, preferably in the range of 950 to 1000nm, and more preferably in the range of 960 to 980nm.
In some preferred embodiments, the standard working curve generation step can be performed in advance and stored in the optical instrument for detection, in order to ensure the accuracy and convenience of detection. In some preferred embodiments of the invention, the same instrument is used throughout the test method, thereby ensuring that the detection is not affected by the instrument, the test environment, or time.
The present invention is not particularly limited to an optical instrument used in the test, as long as it can emit light of the above-specified wavelength. In some specific embodiments, the optical instrument may have an emission spectrum in the wavelength range of 200 to 1200nm. In some preferred embodiments, the optical instrument is a single wavelength spectrometer.
Electrolyte mixing step
In this step, it first involves taking a sample from the flow battery. In the invention, the sampling is required to be respectively carried out from the positive and negative liquid storage tanks of the redox flow battery. The sampling method is not limited, and may be determined according to the actual equipment. For the working state of the flow battery during sampling, the method provided by the invention can be used for sampling in the working period of the flow battery and can also be used for sampling in the non-working period as long as the safe operation condition is met.
Specifically, in some embodiments of the present invention, sampling and testing can be performed at any state of charge SOC of the operation of the ferrochrome flow battery, so that the electrolyte balance testing method provided by the present invention can monitor the balance problem of the positive and negative electrolytes of the ferrochrome flow battery at any time. The sampling is preferably performed at a state of charge SOC of 0, in which case the accuracy of the test method can be further increased.
Fe is stored in a positive liquid storage tank of the iron-chromium flow battery 2+ /Fe 3+ A mixed liquid, in which Cr is stored in a negative liquid storage tank of the flow battery 2+ /Cr 3+ And (4) mixing the solution. In the electrolyte mixing step, the volume obtained from the negative electrode system is V 1 Is directly added to the volume V already obtained from the positive system 2 To obtain a volume of V 0 Mixed electrolyte solution a of (4). In the present invention, the volume V 1 And V 2 Are substantially equal.
The iron-chromium electrolyte according to the present invention is not limited to the positive electrode electrolyte containing Fe 2+ /Fe 3 + Mixed solution, negative electrode electrolyte is Cr 2+ /Cr 3+ The condition of the mixed solution also comprises that the initial electrolytes of the anode and the cathode are all Cr 3+ /Fe 2 + In the case of a mixed solution, that is, after the start of charge and discharge, the positive electrode electrolyte is Fe 2+ /Fe 3+ /Cr 3+ Mixed solution, negative electrode electrolyte is Cr 2 + /Cr 3+ /Fe 2+ The case of a mixed solution. In both cases, the ratio of the chromium concentration to the iron concentration, i.e., cr/Fe, in the initial electrolyte is not limited to 1, but includes both cases where the ratio is greater than 1 and less than 1.
As previously described, after sampling from the negative electrode electrolyteThe cathode electrolyte is exposed to the atmosphere for at least part of the time (especially considering that flow batteries are typically placed in large open fields, and therefore, exposure time can be difficult to control), with Cr therein 2+ Is highly susceptible to oxidation by oxygen and the like, resulting in final test variations.
Therefore, the invention considers that the sampling from the anode system can be carried out firstly, and then the electrolyte with basically equal volume taken out from the cathode system is directly added into the taken-out anode electrolyte, so as to avoid or reduce Cr caused by the sampling 2+ The oxidation of (a) causes test result deviation. The anode system and the cathode system comprise any position of an anode and a cathode and any position of a positive electrolyte storage tank and a negative electrolyte storage tank.
By "direct addition" it is meant herein that the continuity and continuity of the necessary actions during operation, i.e. without significant disturbance of unnecessary actions or discontinuities, is such as to avoid as much as possible the presence of Cr in the obtained anolyte 2+ Unnecessary oxidation occurs.
The volume sampled from the positive electrode system and the negative electrode system is not particularly limited as long as it is substantially equal in volume, and for example, the volume V sampled from the negative electrode system 1 And sampling volume V from positive electrode system 2 May be 0.1 to 100mL, preferably 0.5 to 80mL, more preferably 1 to 60mL.
For the mixed electrolyte A after sampling and mixing, the oxidation-reduction reaction, namely Fe, occurs basically instantaneously 3+ And Cr 2+ Obtaining Fe after reaction 2+ And Cr 3+ . In some embodiments, the mixing operation may be assisted by shaking or the like, in view of uniform mixing and promotion of sufficient and rapid progress of the oxidation-reduction reaction.
As described above, in an ideal state, cr in the mixed electrolyte solution is present after the mixed electrolyte solution reaches the oxidation-reduction equilibrium 3+ And Fe 2+ The ratio of (c) should be 1. However, the negative electrode causes a hydrogen evolution side reaction, which results in Cr in the actual mixed solution 2+ Is always lower than Fe 3+ To C, thereby Cr 2+ Will be totally oxidized into Cr 3+ Thereby making Cr 3+ :Fe 2+ The ratio of (a) may be constantly shifted in a direction deviating from 1. Because of this, the operating state of the flow battery can be judged by the balance k described below.
In some embodiments of the invention, cr is present in the sample 2+ Is totally oxidized into Cr 3+ Thus the mixed electrolyte A is trivalent chromium ion Cr 3+ Fe, a divalent iron ion 2+ And ferric ion Fe 3+ The mixed solution of (1).
It should be noted that initial Cr was considered due to the hydrogen evolution characteristics of the ferrochrome flow battery itself 3+ Concentration and Fe 2+ Concentration ratio of (i) Cr 3+ /Fe 2+ The electrolyte system is 1, and after the battery starts to operate, cr appears in positive and negative isometric mixed liquid 3+ /Fe 2+ /Fe 3+ Without the occurrence of Cr 2+ /Cr 3+ /Fe 2+ The case of the mixed liquid of (4). If Cr happens to occur 3+ /Fe 2+ The mixed solution of (3) shows that the degree of balance is not changed at all as in the initial state, but this possibility is almost zero. For initial Cr 3+ Concentration and Fe 2+ Concentration ratio of more than 1 (i.e. Cr) 3+ /Fe 2+ >1) The electrolyte system of (1), if Cr appears in the mixed liquid of positive and negative electrodes with equal volume 2+ /Cr 3+ /Fe 2+ The condition of the mixed liquid of (2) indicates that the electrolyte is in a negative equilibrium state, namely a safe equilibrium state; if Cr happens to occur 3+ /Fe 2+ The mixed liquid indicates that the equilibrium degree is shifted from a negative equilibrium state to a positive equilibrium state, and the system hydrogen evolution condition needs to be observed. If Cr appears 3+ /Fe 2+ /Fe 3+ The mixed liquid of (2) indicates that the electrolyte has been greatly shifted from the initial negative equilibrium state to the positive equilibrium state, and the equilibrium state of the electrolyte needs to be adjusted as soon as possible to avoid aggravation of the hydrogen evolution condition of the system.
In the present invention, at the time of sampling, except that the volume obtained for obtaining the mixed electrolyte A is V as described above 1 Sample of negative electrode electrolyte and volume V 2 Positive electrode electrolyte sample ofBesides, a certain volume of the cathode electrolyte can be independently sampled and used for follow-up needs.
1 Concentration C obtaining step
After the mixed electrolyte a is substantially completed or oxidation-reduction equilibrium is reached, the concentration of divalent iron ions in the mixed electrolyte a may be tested. In some preferred embodiments of the present invention, the mixed electrolyte a may be diluted and then tested, and the diluent may be diluted hydrochloric acid, diluted sulfuric acid, or a mixture thereof.
When the concentration of the ferrous ion was measured, the above-mentioned optical instrument was used to measure Fe in the mixed electrolyte A at the same wavelength as the predetermined wavelength in the standard working curve preparation step 2+ The absorbance of the mixed electrolyte A is matched with the standard working curve to obtain Fe in the mixed electrolyte A 2+ Concentration C of 1 。
In some preferred embodiments, the standard working curve is stored in the optical instrument as Fe 2+ The concentration of (b) can be directly obtained along with the completion of the detection.
2 Concentration C obtaining step
Obtaining Fe in the mixed electrolyte A 2+ Concentration C of 1 Then, gradually adding a reducing agent into the mixed electrolyte A to obtain a mixed electrolyte B, wherein the reducing agent and Fe in the mixed solution are added in the process of adding 3+ Further reaction to produce Fe 2+ . Therefore, fe in the mixed electrolyte B was monitored during the dropping 2+ Concentration until the highest value is monitored.
Specifically, the mixed electrolyte B was tested for Fe at the prescribed wavelength mentioned above at intervals of unit time during the addition, starting from the time of addition of the reducing agent 2+ Until the absorbance reaches the maximum value, the volume V of the mixed electrolyte B at that time was recorded 3 Matching the standard working curve to obtain the Fe at the moment 2+ Concentration C of 2 。
In some embodiments of the present invention, the unit time is 3s to 5min, preferably 5s to 3min, and more preferably 30s to 2min.
It should be noted that if the mixed electrolyte A is tested for Fe after dilution 2+ The concentration of the negative electrode electrolyte added dropwise was also diluted by the same factor.
In some embodiments of the invention, the reducing agent comprises an inorganic reducing agent and an organic reducing agent. Examples of the inorganic reducing agent may include a negative electrode electrolyte, fe, zn, cu, cr 2+ 、S、SO 2 One or more of (a). Examples of the organic reducing agent may include CH 4 N 2 S、CH 3 CSNH 2 、N 2 H 4 ·H 2 O、NH 2 NH 2 2HCl, ethylene glycol, oxalic acid, glycerol.
In a preferred embodiment of the present invention, the reducing agent uses an anode electrolyte. In this case, no other chemical reagents are needed, but only the electrolyte in the ferrochrome flow battery is used. Therefore, the method is more convenient.
3 Calculating the total concentration C of iron
In the measurement of Fe 2+ Concentration C of 2 Then, fe in the mixed electrolyte A can be calculated according to the following formula (1) 2+ And Fe 3+ Total concentration of C 3 ：
C 3 =C 2 ×V 3 /V 0 （1）。
The total concentration C 3 I.e. the total concentration of iron ions in the positive electrolyte.
From the above, when V 3 Is equal to V 0 That is, when the volume of the mixed electrolyte B is not changed from that of the mixed electrolyte A by the addition of the reducing agent, the concentration C is 2 Namely the total concentration of iron ions in the electrolyte of the positive electrode.
Calculating the balance：
After the above steps, the balance k of the ferrochrome flow battery system can be calculated based on the following formula (2):
k=(C 3 -C 1 )×2/C 3 ×100%（2）。
wherein, C 3 The total concentration of iron ions in the mixed electrolyte of the positive electrode and the negative electrode is (C) 3 -C 1 ) Namely the concentration of ferric ions in the mixed electrolyte of the positive electrode and the negative electrode.
In other specific embodiments, the flow battery can be considered to be operated in a balanced state when the balance k is less than or equal to 10% in relation to the operation requirement of the flow battery. When the value is greater than 10%, the whole flow battery electrolyte is considered to be shifted to the positive electrode, and certain measures are needed to maintain and manage the flow battery electrolyte.
When it is estimated by the above method of the present invention that the electrolyte of the flow battery is shifted to the positive electrode at the detection time point, such a shift can be adjusted by means conventional in the art, such as adding a reducing agent, an oxidizing agent or supplementing a desired ion at a corresponding position.
The electrolyte balance testing method provided by the invention has the advantages of reasonable design, convenience in operation, accurate detection and small error, can provide a guiding function for maintenance and management work of the long-term running iron-chromium flow battery electrolyte, and ensures safe and stable running of a galvanic pile. More importantly, the present invention requires only a single wavelength spectrometer for Fe determination 2+ The concentration detection is convenient and accurate, and has wider applicability.
Examples
Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Example 1
Certain iron-chromium battery system with Fe as positive electrode electrolyte 2+ /Fe 3+ Mixed solution, negative electrode electrolyte is Cr 2+ /Cr 3+ And (3) mixing the solution, wherein the concentration ratio of Cr/Fe is 1.05. Taking 1ml of the mixed solution, and performing UV test at 970nm according to Fe 2+ The intensity of the UV absorption peak can obtain Fe 2+ The concentration of (A) is 0.89M; then 1ml of positive and negative electrode mixed liquid is taken, and 1ml of 1M CrCl is added 2 Solution, mixed solution was subjected to UV test according to Fe 2+ The intensity of the UV absorption peak and the volume of the mixed liquid can obtain Fe in the mixed liquid 2+ The concentration of (2) was 1.06M. Thus obtaining Fe in the original anode-cathode mixed liquid 2+ In a concentration of 0.89M 3+ Is 1.06-0.89=0.17m. The results show that the balance degree of the iron-chromium battery system shifts to the positive balance, and the balance degree is +32.6%, namely the balance degree is far more than +10%, and the balance degree of the electrolyte of the system needs to be adjusted, so that the balance degree of the system is reduced to be less than +10%, even to be in a negative balance state.
To verify the stability of the method, 1ml of electrolyte was taken every 5 minutes after mixing the initial positive and negative electrolytes, and the above operations were repeated until 30min, and the corresponding balance data was calculated, the results are shown in table 1 below.
TABLE 1
Comparative example 1
For comparison, 10ml of each electrolyte was taken from the positive electrode and the negative electrode, respectively, and stored in the same iron-chromium battery system. Every 5 minutes, respectively taking 0.5ml from the positive and negative electrolyte samples and mixing to obtain a mixed solution, and obtaining Fe by utilizing UV of the mixed solution 2+ Concentration data; then 1ml of positive and negative mixed solution is mixed with 1ml of 1M CrCl 2 Mixing the solutions to obtain Fe in the positive and negative electrode mixed solution 2+ +Fe 3+ To the total concentration of (c). And calculating to obtain the balance degree of the system. The results are shown in table 2 below.
TABLE 2
As can be seen from the above table, in the process of the subsequent mixing test with the reducing agent, the balance data is very stable as the time interval is lengthened for the pre-mixed positive and negative electrolytes, and no large deviation occurs within 30 minutes; for the electrolytes respectively stored in the anode and the cathode, cr in the cathode 2+ The oxygen-containing gas is easy to oxidize, and the balance data can be greatly shifted to the positive direction, so that the test data is seriously distorted within 30 minutes.
Industrial applicability
The test method is simple, convenient and quick, has accurate result and convenient operation, and is suitable for field detection of the actual operation place of the iron-chromium flow battery.
Claims (4)
1. A method for testing the balance degree of a ferro-chromium flow battery system is characterized by comprising the following steps:
and (3) standard working curve making: preparing a series of ferrous ion standard solutions with known concentration, and obtaining an absorbance-concentration standard working curve under a specified wavelength by adopting an ultraviolet-visible spectrophotometry;
electrolyte mixing: first obtaining a volume V 2 And then the obtained volume is V 1 Is directly added to the obtained positive electrolyte to obtain a volume V 0 Mixed electrolyte A of (1), wherein V 1 And V 2 Substantially of equal volume;
concentration C 1 An acquisition step: testing Fe in the mixed electrolyte A at the specified wavelength 2+ The absorbance of the mixed electrolyte A is matched with the standard working curve to obtain Fe in the mixed electrolyte A 2+ Concentration C of 1 ；
Concentration C 2 An acquisition step: adding a reducing agent into the mixed electrolyte A to obtain a mixed electrolyte B,
starting from the moment of addition of the reducing agent atTesting Fe in the mixed electrolyte B at the specified wavelength at intervals of unit time during the addition 2+ Until the absorbance reaches the maximum value, the volume V of the mixed electrolyte B at that time was recorded 3 Matching the standard working curve to obtain the Fe at the moment 2+ Concentration C of 2 ；
Total concentration of iron C 3 A calculation step: calculating Fe in the mixed electrolyte A according to the following formula (1) 2+ And Fe 3+ Total concentration of (C) 3 ：
C 3 ＝C 2 ×V 3 /V 0 (1)；
And a balance degree calculation step: calculating the balance k of the iron-chromium flow battery system based on the following formula (2):
k＝(C 3 -C 1 )×2/C 3 ×100％ (2)，
the prescribed wavelength is in the range of 900 to 1100nm,
wherein the positive electrolyte is Fe 2+ /Fe 3+ The mixed solution and the negative electrode electrolyte are Cr 2+ /Cr 3+ The mixed solution is selected from the group consisting of Fe, cu, ni, and Cu 2+ /Fe 3+ /Cr 3+ The mixed solution and the negative electrode electrolyte are Cr 2+ /Cr 3+ /Fe 2+ The mixed solution is mixed with the raw materials,
the mixed electrolyte A is trivalent chromium ion Cr 3+ Fe, a divalent iron ion 2+ And ferric ion Fe 3+ The mixed solution of (a) and (b),
samples were taken from the positive system and from the negative system of the flow battery at any state of charge SOC,
in the electrolyte mixing step, the concentration C is performed after the mixed electrolyte A reaches an oxidation-reduction equilibrium 1 And (5) obtaining.
2. The test method according to claim 1, wherein the concentration C is 1 In the obtaining step, the mixed electrolyte A is diluted and then the Fe is tested 2+ Absorbance of (b).
3. A test method according to claim 1 or 2, characterized in that the unit time is 3s-5min.
4. The test method according to claim 1 or 2, wherein the reducing agent comprises an inorganic reducing agent and an organic reducing agent.
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