Methods for determining and/or adjusting redox-active element concentrations in redox flow batteries
09846116 · 2017-12-19
Assignee
Inventors
Cpc classification
H01M8/04447
ELECTRICITY
H01M8/04455
ELECTRICITY
Y02E60/50
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
H01M8/18
ELECTRICITY
Abstract
Methods of determining concentrations and/or amounts of redox-active elements at each valence state in an electrolyte solution of a redox flow battery are provided. Once determined, the concentrations and/or amounts of the redox-active elements at each valence state can be used to determine side-reactions, make chemical adjustments, periodically monitor battery capacity, adjust performance, or to otherwise determine a baseline concentration of the redox-active ions for any purpose.
Claims
1. A method of determining a vanadium ion concentration in a vanadium redox flow battery, comprising: step (a), or a combination of steps (b) and (c), wherein step (a): providing an electrolyte solution comprising V.sup.3+ and V.sup.4+; converting the V.sup.3+ to V.sup.4+; determining a concentration of each of V.sup.3+ and V.sup.4+ in the electrolyte solution, and determining an amount of V.sup.3+ and V.sup.4+ based on the concentration of each of V.sup.3+ and V.sup.4+ and a volume of the electrolyte solution; step (b): providing a catholyte solution comprising V.sup.4+ and V.sup.5+, converting the V.sup.5+ to V.sup.4+; determining a concentration of each of V.sup.5+ and V.sup.4+ in the catholyte solution, and determining an amount of V.sup.4+ and V.sup.5+ based on the concentration of each of V.sup.4+ and V.sup.5+ and a volume of the catholyte solution; and step (c): providing an anolyte solution comprising V.sup.2+, V.sup.3+, or both V.sup.2+ and V.sup.3+; converting each of the V.sup.2+ and V.sup.3+, when present, to V.sup.4+ by exposing each of the V.sup.2+ and V.sup.3+ to a first solution containing known concentrations of V.sup.5+ and V.sup.4+; determining a concentration of each of V.sup.2+ and V.sup.3+, when present in the anolyte solution; and determining an amount of V.sup.2+, V.sup.3+, or both V.sup.2+ and V.sup.3+ based on the concentration of each of V.sup.2+, V.sup.3+, when present, and a volume of the anolyte solution.
2. The method of claim 1, wherein in step (a), converting the V.sup.3+ to V.sup.4+ comprises exposing the V.sup.3+ to an oxidizing agent comprising a second solution containing known concentrations of V.sup.5+ and V.sup.4+.
3. The method of claim 1, wherein in step (a) further comprises using optical absorption spectroscopy to determine the concentration of each of V.sup.3+ and V.sup.4+ in the electrolyte solution.
4. The method of claim 1, wherein in step (b), converting the V.sup.5+ to V.sup.4+ comprises exposing the V.sup.5+ to a reducing agent selected from the group consisting of Sn.sup.2+, Fe.sup.2+, sulfites, phosphites, hypophosphites, phosphorous acid, metal hydrides, metals, metal amalgams, and diboranes.
5. The method of claim 1, wherein in step (b), converting the V.sup.5+ to V.sup.4+ comprises exposing the V.sup.5+ to a sulfite.
6. The method of claim 1, wherein in step (b), converting the V.sup.5+ to V.sup.4+ comprises exposing the V.sup.5+ to a reducing agent selected from the group consisting of sugars, alcohols, organic acids, oils, and hydrocarbons.
7. The method of claim 1, wherein step (b) further comprises using optical absorption spectroscopy to determine the concentration of each of V.sup.5+ and V.sup.4+ in the catholyte solution and step (c) further comprises using optical absorption spectroscopy to determine the concentration of each of V.sup.2+ and V.sup.3+, when present, in the anolyte solution.
Description
DESCRIPTION OF THE DRAWINGS
(1) The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
(2)
(3)
(4)
(5)
(6)
(7)
DETAILED DESCRIPTION
(8) The present disclosure is generally directed to methods for determining a concentration of a given redox-active element at a given valence state in a redox flow battery. Once known, the concentration of the given redox-active element at a given valence state, together with a volume of an electrolyte that includes the given redox-active element, can allow for adjustments of a redox flow battery's performance. Adjustment of a redox flow battery's performance can be carried out, for example, to improve battery efficiency, energy utilization, and/or to provide information to supervisory and/or control systems. A known concentration of a given redox-active element at a given valence state can provide a basis for adjusting the concentration and/or amount of redox-active elements at various valence states in an electrolyte solution to meet a predetermined redox flow battery operating performance parameter, such as a baseline concentration and/or amount of the redox-active elements at each valence state.
(9) Redox Flow Battery
(10) A schematic illustration of a representative redox flow battery is shown in
(11) While a single electrochemical cell 100 is illustrated in
(12) During operation, catholyte 20 and anolyte 30 are delivered to electrochemical cell 100 from storage tanks 15 and 25, respectively. During battery charge, a power element 50 operates as a power source, providing electrical energy that is stored as chemical potential in the catholyte 20 and anolyte 30. Thus, anode redox-active ions are reduced on the negative electrode 42, while cathode redox-active ions are oxidized on the positive electrode 40. The power source can be any power source known to generate electrical power, including, but not limited to, renewable power sources, such as wind, solar, and hydroelectric. Traditional power sources, such as combustion, can also be used.
(13) During battery discharge, redox flow battery 10 is operated to transform the chemical potential stored in the catholyte 20 and anolyte 30 into electrical energy that is then discharged at the power element 50, which acts as an electrical load.
(14) As discussed above, redox flow batteries include redox-active elements. Examples of redox-active elements include V, Br, S, Zn, Ce, Fe, Mn, and Ti.
(15) During operation, a redox flow battery can have certain characteristics that can cause operating inefficiencies. For example, at an initial state, the charge capacity of each of the anolyte and catholyte reservoirs can initially be identical. However, as the battery is operated over extended periods of time under certain conditions, side reactions (e.g., oxidation, reduction, precipitation, and/or decomposition) can occur to cause a chemical imbalance between the anolyte and catholyte solutions, causing asymmetric capacity loss between the anolyte and the catholyte. This chemical imbalance can be corrected to adjust performance of the battery.
(16) As a non-limiting example, in a vanadium flow redox battery prior to charging, the initial anolyte solution and catholyte solution each include identical concentrations of V.sup.3+ and V.sup.4+. Upon charge, the vanadium ions in the anolyte solution are reduced to V.sup.2+/V.sup.3+ while the vanadium ions in the catholyte solution are oxidized to V.sup.4+/V.sup.5+.
(17) Over time, side reactions can occur in the vanadium battery as the anolyte is susceptible to V.sup.2+ oxidation by atmospheric oxygen (thereby decreasing the amount and/or concentration of V.sup.2+), V.sup.2+ can also be oxidized by H.sup.+ if hydrogen is evolved at the anode (thereby decreasing the amount and/or concentration of V.sup.2+). Furthermore, precipitation of V.sup.5+ as V.sub.2O.sub.5 can occur in the catholyte (thereby decreasing the amount and/or the concentration and amount of V.sup.5+). Because of these side reactions, the vanadium flow redox battery can lose capacity as its catholyte and anolyte become chemically imbalanced. The reduced capacity of one of the electrolyte tanks can limit battery performance. The chemical imbalance can be corrected to increase battery efficiency.
(18) Expressed mathematically, for a vanadium redox flow battery with the same quantities of electrochemically available vanadium ions at the anolyte and the catholyte (i.e., a chemically balanced vanadium redox flow battery), the concentrations of the redox-active vanadium ions in the anolyte and the catholyte can be represented by:
[V.sup.2+]/([V.sup.2+]+[V.sup.3+]) at anolyte=[VO.sub.2.sup.+]/([VO.sup.2+]+[VO.sub.2.sup.+]) at catholyte.
However, if the vanadium redox flow battery is chemically imbalanced, then:
[V.sup.2+]/([V.sup.2+]+[V.sup.3+]) at anolyte≠[VO.sub.2.sup.+]/([VO.sup.2+]+[VO.sub.2.sup.+]) at catholyte.
(19) While restoration of a chemically imbalanced redox flow battery to a chemically balanced redox flow battery is described above, in some embodiments, a redox flow battery can desirably be chemically imbalanced. The chemical imbalance can be predetermined and can be desirable, for example, to compensate for or to minimize possible side-reactions in a redox flow battery, and/or to reduce or prevent the likelihood of active species transfer across the separator. Correction of the chemical imbalance in this embodiment restores the amounts and/or the concentrations of the redox-active elements at various valence states to the desired predetermined imbalanced amounts and/or concentrations.
(20) Thus, the efficiency of operation for a redox flow battery can be monitored by providing the concentrations and/or amounts of redox-active elements at various valence states in the electrolytes. The concentrations and/or amounts of redox-active elements at various valence states can provide a basis for adjusting concentrations of the redox-active elements at various valence states to achieve a predetermined battery operating parameter, which can include a battery at a chemically balanced state or a battery at a desired predetermined chemically imbalanced state. In some embodiments, the concentrations and/or amounts of redox-active elements at various valence states are used by battery operating algorithms, for example, to start or stop charge/discharge, to determine allowable charge/discharge rates, and/or to determine how much charge is left to support a particular application.
(21) Existing methods used to determine the concentrations and/or amounts of redox-active elements at various valence states in the electrolytes are often time-consuming, inconsistent, inaccurate, or require the use of a laboratory. Thus, a method of analysis that can reliably, consistently, accurately, and rapidly determine the concentrations of redox-active elements at various valence states in a redox flow battery is needed. Such a method can be amenable to field-deployment using standardized chemicals and equipment.
(22) Methods are provided herein for determining the concentrations and/or amounts of redox-active elements at various valence states in a redox flow battery, and using the concentrations and/or amounts of redox-active elements at various valence states to adjust battery performance by, for example, adjusting the concentrations and/or amounts of redox-active elements in various valence states to meet a battery operating performance parameter. The determination methods for the concentrations and/or amounts of redox-active elements at various valence states are rapid, reliable, consistent, accurate, and can be easily implemented using available analytical methods. The determination methods can be implemented in an automated or semi-automated manner (e.g., with a computer-controlled system) and the analytical methods can be externally to a housing for the redox flow battery, or internally within a housing for the redox flow battery.
(23) Redox-Active Element Concentration and Amount Determinations
(24) Methods to determine concentrations and/or amounts of redox-active elements at each valence state in a redox flow battery are provided. In general, the methods include (1) providing (e.g., withdrawing) a given electrolyte sample (e.g., a catholyte sample, an anolyte sample, an electrolyte sample prior to an initial charging process, or an electrolyte sample that is a mixture of a catholyte and an anolyte); (2) converting a redox-active element having one or more valence states in the sample to a single predetermined valence state, using an oxidizing agent and/or a reducing agent; (3) determining the concentration of the redox-active element at the single predetermined valence state in the original sample and after conversion; and (4) determining the concentration of the redox-active element at each valence state in the sample from the concentration of the converted single valence state redox-active element. The concentration of the redox-active element can be determined by mathematical calculation from the total concentration of the redox-active element in the sample (which can be determined by obtaining the concentration of the redox-active element at the single valence state, once all the redox-active element having one or more valence states have been converted), the concentration of oxidizing and/or reducing agent used to convert the redox-active element to a single valence state, and the concentration of any redox-active active element at the single predetermined valence state in the original sample. The amount of the redox-active elements at each valence state can then be determined based on the concentration of the redox-active elements at each valence state and the volume of the given electrolyte solution (e.g., by multiplying the concentration and the volume).
(25) For example, to determine the concentrations of redox-active elements at various valence states in a catholyte of a redox flow battery, an amount of a catholyte solution including a cathode redox-active element at one or more valence states is withdrawn from a redox flow battery; the cathode redox-active element at each valence state is converted to a first predetermined valence state; and a concentration of the cathode redox-active element at each valence state is determined based on the concentration of the converted cathode redox-active element at the first predetermined valence state. The amount of redox-active elements at various valence states in the catholyte is then determined, based on the concentration of the cathode redox-active element at each valence state and the volume of the catholyte solution (e.g., by multiplying the concentration and the volume).
(26) Similarly, to determine the concentrations of redox-active elements at various valence states in an anolyte of a redox flow battery, an amount of an anolyte solution including an anode redox-active element having one or more valence states is withdrawn from a redox flow battery, the anode redox-active element at each valence state is converted to a second predetermined valence state; and a concentration of the anode redox-active element at each valence state is determined based on the concentration of the converted anode redox-active element at the second predetermined valence state. The amount of redox-active elements at various valence states of the anolyte is then determined, based on the concentration of the anode redox-active element at each valence state and the volume of the anolyte solution (e.g., by multiplying the concentration and the volume).
(27) In some embodiments, a baseline concentration of a redox-active element (e.g., a cathode redox-active element, an anode redox-active element, or a redox-active element in an electrolyte solution prior to an initial charging process) at each valence state is determined for comparison with a measured concentration of redox-active elements at various valence states of a battery (e.g., during operation or maintenance). The baseline concentration of the redox-active element can be determined by (1) providing a catholyte or anolyte solution after an initial charge of a redox flow battery, or providing an electrolyte solution prior to an initial charging process; (2) converting the redox active element at each valence state in each electrolyte solution to a predetermined valence state; (3) determining the concentration of the redox-active element at the single predetermined valence state in the original electrolyte solution and after conversion; (4) and determining the concentration of the redox-active element in the electrolyte solution at each valence state, as described above. The based amount of the redox-active elements at each valence state can then be determined based on the base concentration of the redox-active elements at each valence state and the volume of the given electrolyte solution (e.g., by multiplying the concentration and the volume).
(28) In some embodiments, withdrawing an amount of catholyte and/or anolyte includes taking an amount of the catholyte or anolyte prior to or after electrolyte flow into the cathode or the anode, respectively, or directly from the catholyte or anolyte tanks. The withdrawal can occur periodically during battery maintenance, or at any time during battery operation. In some embodiments, withdrawing an amount of an initial electrolyte includes taking an amount of electrolyte from either of the anolyte or catholyte tank, prior to initial charging of the battery. In some embodiments, withdrawing an amount of a mixed electrolyte solution includes taking a sample from the catholyte tank, a sample from the anolyte tank, mixing the two samples, and allowing the redox-active element at various valence states to equilibrate. Withdrawing an amount of a mixed electrolyte solution can occur after discharge of a redox flow battery. The amount of the given electrolyte (e.g., the catholyte, the anolyte, an initial electrolyte solution, or a mixed electrolyte solution) that is withdrawn can be relatively little, for example, about 10 mL, 20 mL, or 30 mL.
(29) The predetermined valence state can be a valence state that can afford a detectable signal with minimal background noise or interference from other chemical species in the electrolyte, using a given analytical method. When the cathode redox-active element and the anode redox-active element are the same, the predetermined valence states to which the cathode and/or anode redox-active element at each valence state are converted to can be the same.
(30) In some embodiments, converting a cathode redox-active element having one or more valence states to a predetermined valence state includes exposing a cathode redox-active element to a reducing agent. The concentration of the reducing agent can be predetermined. Non-limiting examples of reducing agents include Sn.sup.2+, Fe.sup.2+, sulfites, phosphites, hypophosphites, phosphorous acid, metal hydrides, metals, metal amalgams, diboranes, sugars, alcohols, organic acids, oils, and/or hydrocarbons. In some embodiments, the reducing agent is sulfite. In some embodiments, the reducing agent can be a redox-active species that can form an electrochemical pair with the cathode redox-active element to be reduced and that has a lower standard potential than the cathode redox-active element to be reduced. For example, the reducing agent can be the same redox-active element at a lower valence state than the valence state of cathode redox-active element to be reduced, such as an anolyte solution of the redox flow battery being tested.
(31) In some embodiments, converting an anode redox-active element having one or more valence states to a predetermined valence state includes oxidizing an anode redox-active element with an oxidizing agent. The concentration of the oxidizing agent can be predetermined. Non-limiting examples of oxidizing agents include oxygen, air, ozone, hydrogen peroxide, and permanganates. In some embodiments, the oxidizing agent can be a redox-active species that can form an electrochemical pair with the anode redox-active element to be reduced and that has a higher standard potential than the anode redox-active element to be reduced. For example, the oxidizing agent can be the same redox-active element at a higher valence state than the valence state of the anode redox-active element to be oxidized, such as a catholyte solution of the redox flow battery being tested.
(32) The electrolyte solution (e.g., a catholyte, anolyte, or a mixed electrolyte solution) can be subjected to an analytical method, which can provide measurement of a detectable signal that can be correlated to the concentration of a given redox-active element at the predetermined valence state in the electrolyte solution. In some embodiments, determining the concentration of a given redox-active element (e.g., a cathode redox-active element, or an anode redox-active element) further includes determining a standard concentration calibration curve for the given redox-active element, at the same predetermined valence state to which the given redox-active element at each valence state is converted, at defined concentrations, using the analytical method. Determining the concentration of a given redox-active element can include matching a magnitude of a detectable signal in the electrolyte solution to a standard concentration calibration curve at the same magnitude of the detectable signal to determine the corresponding concentration.
(33) Redox-Active Element Concentration and/or Amount Adjustment
(34) After the concentrations and/or amounts of redox-active elements at various valence states are determined, (1) the concentration and/or amount of the cathode redox-active element at each valence state in the catholyte solution can be adjusted, (2) the concentration and/or amount of the anode redox-active element at each valence state in the anolyte solution can be adjusted, or (3) the concentration and/or amount of an initial or mixed electrolyte solution can be adjusted, to meet a predetermined redox flow battery operating performance parameter.
(35) Representative predetermined redox flow battery operating performance parameters include, for example, energy capacity, power capacity, and power ramping rates. In some embodiments, the predetermined redox flow battery operating performance parameter includes a baseline concentration and/or amount of the cathode redox active element at each valence state in the catholyte solution, a baseline concentration and/or amount of the anode redox active element at each valence state in the anolyte solution, or a baseline concentration and/or amount of the redox-active element at each valence state in an electrolyte solution prior to an initial charging process. Upon determining the concentration and/or amount of the cathode redox-active element at each valence state, the concentration and/or amount of the cathode redox-active element at each valence state in the catholyte solution is compared to the baseline concentration and/or amount of the cathode redox active element at each valence state; and the concentration and/or amount of the cathode redox-active element at each valence state in the catholyte solution is restored to the baseline concentration and/or amount of the cathode redox-active element at each valence state. Similarly, upon determining the concentration and/or amount of the anode redox-active element at each valence state, the concentration and/or amount of the anode redox-active element at each valence state in the anolyte solution is compared to the baseline concentration and/or amount of the anode redox active element at each valence state; and the concentration and/or amount of the anode redox-active element at each valence state in the anolyte solution is restored to the baseline concentration and/or amount of the anode redox-active element at each valence state. A similar adjustment process can be carried out for redox-active elements at each valence state in an electrolyte solution prior to an initial charging process or in a mixed electrolyte solution, by comparing and restoring the concentration and/or amount of said electrolyte solution to a baseline concentration and/or amount of a reference electrolyte solution, prior to an initial charge.
(36) To adjust the concentration and/or amount of the redox active element in a given electrolyte solution (e.g., a catholyte, an anolyte, an initial electrolyte solution, or a mixed electrolyte solution), an oxidizing agent or a reducing agent can be added to the given electrolyte solution to meet a predetermined redox flow battery operating performance parameter. In some embodiments, an amount of solvent (e.g., water, acid) can be added to adjust the concentration of the redox-active element. In some embodiments, adjusting the amount of redox-active element in a given electrolyte solution includes adding or removing a quantity of the given electrolyte solution.
(37) Non-limiting examples of reducing agents and oxidizing agents for adjusting the concentration of a given electrolyte are as provided above.
(38) Analytical Method
(39) As noted above, an analytical method is used to measure of a detectable signal in a given electrolyte solution. The nature of analytical method is not critical so long as the method can accurately determine the concentration of a redox-active element to be analyzed. In some embodiments, the analytical method is optical absorption spectroscopy, such that absorbance of a given sample can be measured and correlated to the concentration of a redox-active element at a predetermined valence state. Optical absorption spectroscopy can be beneficial as it can be portable, easily implemented, and simple to operate. In some embodiments, the analytical method is a conventional method for directly detecting redox-active ions, such as potentiometric titration, inductively coupled plasma atomic emission spectrometry, or ion chromatography.
(40) Vanadium Redox Flow Battery
(41) In some embodiments, the redox flow battery is a vanadium flow redox flow battery, where the anolyte includes a mixture of V.sup.2+ and V.sup.3+, and the catholyte includes a mixture of V.sup.4+ and V.sup.5+. Thus, the redox-active element in both the anolyte and the catholyte is vanadium. When determining the concentration of vanadium at each valence state in the vanadium flow redox battery, the predetermined valence state to which the cathode redox-active ions are reduced and to which the anode redox-active ions are oxidized can be V.sup.4+. In some embodiments, before determining the concentration of the cathode redox-active element and the anode redox-active element, a standard concentration calibration curve of a detectable signal vs. the concentration of V.sup.4+ in a standard V.sup.4+ solution is determined, for example, using optical absorption spectroscopy.
(42) Oxidizing the anode redox-active element includes exposing the anode redox-active element vanadium at valence states 2+ and 3+ to an oxidizing agent, such as a solution of known concentrations of V.sup.4+ and V.sup.5+, to generate a solution of V.sup.4+. Reducing the cathode redox-active element vanadium at a valence state of 5+ can include exposing the cathode redox-active element to a reducing agent, such as Sn.sup.2+, Fe.sup.2+, sulfites, phosphites, hypophosphites, phosphorous acid, metal hydrides, metals, metal amalgams, diboranes, sugars, alcohols, organic acids, oils, and/or hydrocarbons, to generate a solution of V.sup.4+. In some embodiments, the reducing agent is sulfites, which exhibits minimal background signal when subjected to an analytical method, such as optical absorption spectroscopy.
(43) Once the vanadium at each valence state is converted to V.sup.4+, the concentration of V.sup.4+ and V.sup.5+ in the catholyte solution and the concentration of the V.sup.2+ and V.sup.3+ in the anolyte solution can be calculated from the amount of reducing agent and oxidizing agent used, respectively, the total concentration of vanadium in each electrolyte solution, and the concentration of V.sup.4+ in each solution (which can be determined by comparing a detectable signal for V.sup.4+ vs. the standard concentration calibration curve). Knowing the concentration of vanadium at each valence state and volume of each of the catholyte and anolyte solutions, the amount of vanadium at each valence state in the redox flow battery can be calculated.
(44) In some embodiments, instead of a catholyte solution including V.sup.4+ and V.sup.5+ or an anolyte solution including V.sup.2+ and V.sup.3+, the electrolyte solution includes V.sup.3+ and V.sup.4+. The electrolyte solution can be an initial electrolyte solution that is loaded into a vanadium redox flow battery prior to any charging process. In some embodiments, the electrolyte solution is an electrolyte solution post-battery discharge, once the anolyte and the catholyte solutions have been mixed and allowed to equilibrate for a period of time.
(45) To determine the concentrations of V.sup.3+ and V.sup.4+ in the electrolyte solution, V.sup.3+ is converted to V.sup.4+ by exposure to an oxidizing agent, such as a solution containing known concentrations of V.sup.5+ and V.sup.4+. The total V.sup.4+ concentration of the solution can be determined by comparing a detectable signal against the standard concentration calibration curve for V.sup.4+, and the concentration of each of V.sup.3+ and V.sup.4+ in the initial V.sup.3+/V.sup.4+ solution can be calculated from the total vanadium concentration and the known amount of V.sup.5+ used to oxidize V.sup.3+. Knowing the concentration of V.sup.3+ and V.sup.4+ and volume of the electrolyte solution, the amount of vanadium at each valence state in the electrolyte solution can be calculated.
(46) The analytical method can be optical absorption spectroscopy and the detectable signal can be an absorbance at a predetermined wavelength. The predetermined wavelength can be one at which V.sup.4+ absorbs while being substantially free of interfering absorbance values.
(47) While the above describes methods for determining concentrations and amounts of redox-active vanadium ions for a vanadium redox flow battery, it is understood that the methods can be generalized for mixed redox-active element redox flow batteries.
(48) Evaluation of sulfite as a non-interfering reducing agent is described in Example 1. Determination of suitable concentrations for measuring VO.sup.2+ absorbance is described in Example 2. A protocol for standard concentration calibration curve for VO.sup.2+ is described in Example 3. Protocols and mathematical calculations for determining concentrations of electrolyte solutions in an exemplary vanadium flow battery are described in Examples 4-7.
(49) The following examples are provided for the purpose of illustrating, not limiting, the invention.
Example 1
Sodium Sulfite as a Reducing Agent for Vanadium Ion Analysis
(50) The suitability of sodium sulfite (0.5 mol/L) as a reducing agent for analysis of vanadium ion concentration was investigated. The reducing agent should meet the requirement of no signal interference with VO.sup.2+ ions analysis. Here, no absorption at the wavelength of 765 nm was observed in an optical absorption spectrum of the aqueous sodium sulfite solution.
(51) Excess sodium sulfite solution (0.5 mol/L) is added to a VO.sub.2.sup.+/VO.sup.2+ solution (C.sub.vanadium=0.03 mol/L) to reduce VO.sub.2.sup.+ ions to VO.sup.2+ ions. The following reaction takes place: 2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2 VO.sup.2++SO.sub.4.sup.2−+H.sub.2O. Referring to
Example 2
Absorbance Vs. VO2+ Concentration in VO2+/VO2+ Solution
(52) The concentrations at which VO.sup.2+ and VO.sub.2.sup.+ exist as independent species were investigated. It is believed that VO.sup.2+ and VO.sub.2.sup.+ can form complexes in solution. However, diluting a VO.sup.2+/VO.sub.2.sup.+ solution could reduce the VO.sup.2+−VO.sub.2.sup.+ complex formation. Referring to
Example 3
Standard Concentration Curve Calibration
(53) A standard concentration calibration curve for VO.sup.2+ was determined. 1 mL, 3 mL, 6 mL, 10 mL and 12 mL of VO.sup.2+ standard solutions (0.19585 mol/L) (purchased from Sigma Aldrich, USA) were individually placed in 50 mL volumetric flasks. Then, excess sodium sulfite solution (0.5 mol/L) was added and the mixed solutions were each heated at 40° C. for 3 minutes.
(54) After diluting with deionized water to 50 mL, the solutions were measured by optical absorption spectroscopy at a wavelength of 765 nm.
(55) The standard concentration calibration curve was plotted as shown in
Example 4
Vanadium Ion Analysis—General Procedures
(56) Procedures for analysis of vanadium ions at valence states 2+, 3+, 4+ and 5+ are described.
(57) (A) VO.sup.2+ and VO.sub.2.sup.+ Ions:
(58) 1.0 mL of VO.sup.2+/VO.sub.2.sup.+ solution was added into a 100 mL volumetric flask. After diluting with DI water to 100 mL, the solution was analyzed by optical absorption spectroscopy. Referring to
(59) The other 100 mL volumetric flask with 1.0 mL of VO.sup.2+/VO.sub.2.sup.+ solution was prepared, and excess sodium sulfite (0.5 mol/L) was added to reduce VO.sub.2.sup.+ to VO.sup.2+. Then, the mixed solution was heated at 40° C. for 3 minutes. The following reaction takes place:
2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2VO.sup.2++SO.sub.4.sup.2−+H.sub.2O
(60) After diluting with deionized water to 100 mL, the solution was analyzed by optical absorption spectroscopy. Referring again to
(61) The concentration of VO.sub.2.sup.+ (C.sub.V(V)) in the sample could be calculated by subtracting VO.sup.2+ concentration from total vanadium concentration (C.sub.Vtot): C.sub.V(V)=C.sub.Vtot−C.sub.V(IV)
(62) (B) V.sup.3+ and VO.sup.2+ Ions:
(63) One VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared. The procedure of vanadium concentration analysis was conducted as discussed in (A). The VO.sup.2+ and VO.sub.2.sup.+ concentrations in the solution were measured as C.sub.1 and C.sub.2 (C.sub.2≧C.sub.1, C.sub.1+C.sub.2=2.0˜3.0 mol/L), respectively.
(64) 2 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was added into a 250 mL volumetric flask. Then, 1 mL of V.sup.3+/VO.sup.2+ solution was added into the flask. The following reaction took place:
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
(65) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at the wavelength of 765 nm. Then the VO.sup.2+ concentration (C.sub.3) in this solution was calculated from the standard curve shown in
(66) The other 250 mL volumetric flask with 2 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared, and 1.0 mL of V.sup.3+/VO.sub.2.sup.+ solution was added. Then, excess sodium sulfite (0.5 mol/L) was added to reduce VO.sub.2.sup.+ to VO.sup.2+, and the mixed solution was heated at 40° C. for 3 minutes. The following reactions took place:
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2VO.sup.2++SO.sub.4.sup.2−+H.sub.2O
(67) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at the wavelength of 765 nm. Then the total vanadium concentration (C.sub.4) in this solution was calculated from the standard concentration calibration curve shown in
(68) The V.sup.3+ concentration in the V.sup.3+/VO.sup.2+ sample could calculated by the following equation: C.sub.V(III)=2C.sub.2−3(C.sub.4−C.sub.3).
(69) The VO.sup.2+ concentration in the V.sup.3+/VO.sup.2+ sample could be calculated by the following equation: C.sub.V(IV)=3C.sub.3−2C.sub.1−2C.sub.V(III).
(70) (C) V.sup.2+ and V.sup.3+ Ions:
(71) One VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared. The procedure of vanadium concentration analysis was conducted as discussed in (A). The VO.sup.2+ and VO.sub.2.sup.+ concentrations in the solution were measured as C.sub.1 and C.sub.2 (C.sub.2≧C.sub.1, C.sub.1+C.sub.2=2.0˜3.0 mol/L), respectively.
(72) 3 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was added into a 250 mL volumetric flask and purged with argon gas for 2 minutes. Then, 1 mL of V.sup.2+/V.sup.3+ solution was added into the flask and mixed quickly. The following reactions took place:
V.sup.2++VO.sub.2.sup.++2H+.fwdarw.V.sup.3++VO.sup.2++H.sub.2O
V.sup.2++VO.sup.2++2H.sup.+.fwdarw.2V.sup.3++H.sub.2O
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
(73) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at a wavelength of 765 nm. Then the VO.sup.2+ concentration (C.sub.5) in this solution was calculated from the standard concentration calibration curve shown in
(74) The other 250 mL volumetric flask with 3 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared and purged with argon gas for 2 minutes. Then, 1.0 mL of V.sup.2+/V.sup.3+ solution was added and mixed quickly. After that, excess sodium sulfite (0.5 mol/L) was added to reduce VO.sub.2.sup.+ to VO.sup.2+, and the mixed solution was heated at 40° C. for 3 minutes. The following reactions take place:
V.sup.2++VO.sub.2.sup.++2H.sup.+.fwdarw.V.sup.3++VO.sup.2++H.sub.2O
V.sup.2++VO.sup.2++2H.sup.+.fwdarw.2V.sup.3++H.sub.2O
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2VO.sup.2++SO.sub.4.sup.2−+H.sub.2O
(75) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at 765 nm. Then the total vanadium concentration (C.sub.6) in this solution was calculated from the standard concentration calibration curve shown in
(76) The V.sup.2+ concentration in the V.sup.2+/V.sup.3+ sample could be calculated by the following equation:
C.sub.V(II)=3(C.sub.1+2C.sub.2)−4(2C.sub.6−C.sub.5).
(77) The V.sup.3+ concentration in the V.sup.2+/V.sup.3+ sample could be calculated by the following equation:
C.sub.V(III)=3C.sub.2−4(C.sub.6−C.sub.5)−2C.sub.V(II).
Example 5
Determination of V4+ and V5+ Concentrations
(78) The concentrations of vanadium ions at valence states 4+ and 5+ were determined in a V.sup.4+/V.sup.5+ electrolyte solution.
(79) 1.0 mL of VO.sup.2+/VO.sub.2.sup.+ solution (Sample 1) was added into a 100 mL volumetric flask. After diluting with deionized water to 100 mL, the solution was measured by optical absorption spectroscopy at the wavelength of 765 nm. The absorbance of the solution was measured as A.sup.u.sub.765nm=0.262. Then the VO.sup.2+ concentration (C.sub.V(IV)) in Sample 1 was calculated by standard concentration calibration curve, shown in
(80) The other 100 mL volumetric flask with 1.0 mL of VO.sup.2+/VO.sub.2.sup.+ solution (Sample 1) was prepared, and excess sodium sulfite (0.5 mol/L) was added to reduce VO.sub.2.sup.+ to VO.sup.2+. Then, the mixed solution was heated at 40° C. for 3 minutes. The following reaction takes place:
2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2VO.sup.2++SO.sub.4.sup.2−+H.sub.2O
(81) After diluting with deionized water to 100 mL, the solution was measured by optical absorption spectroscopy at the wavelength of 765 nm. The absorbance of the solution is measured as A.sup.u.sub.765nm=0.303. Then, the total vanadium concentration in Sample 1 was calculated (C.sub.Vtot) from the standard concentration calibration curve shown in
(82) The concentration of VO.sub.2.sup.+ (C.sub.V(V)) in Sample 1 was calculated by subtracting VO.sup.2+ concentration from total vanadium concentration: C.sub.V(V)=C.sub.Vtot−C.sub.V(V)=1.685−1.457=0.228 (mol/L)
(83) TABLE-US-00001 TABLE 1 Comparison of concentrations of vanadium ions in Sample 1 using different analysis methods Sample 1 Method VO.sup.2+ VO.sub.2.sup.+ V.sub.tot Optical Absorption Spectroscopy 1.457 0.228 1.685 Potentiometric Titration 1.419 0.233 1.652 Inductively Coupled Plasma — — 1.670 Relative Error (%) 2.68 2.15 2.00 (Optical absorption spectroscopy compared with potentiometric titration)
Example 6
Determination of V3+ and V4+ Concentrations
(84) The concentrations of vanadium ions at valence states 3+ and 4+ were determined in a V.sup.3+/V.sup.4+ electrolyte solution.
(85) One VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared. The procedure of vanadium concentration analysis was conducted as the Example 4A. The VO.sup.2+ and VO.sub.2.sup.+ concentrations in the solution were measured as C.sub.1=1.064 mol/L and C.sub.2=1.106 mol/L, respectively.
(86) 2 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was added into a 250 mL volumetric flask. Then, 1 mL of V.sup.3+/VO.sup.2+ solution (Sample 2) was added into the flask. The following reaction takes place:
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
(87) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at 765 nm. The absorbance of this solution was measured as A.sup.u.sub.765nm=0.390. Then the VO.sup.2+ concentration (C.sub.3) in this solution was calculated from the standard concentration calibration curve as shown in
(88) The other 250 mL volumetric flask with 2 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared, and 1.0 mL of V.sup.3+/VO.sup.2+ solution (Sample 2) was added. Then, excess sodium sulfite (0.5 mol/L) was added to reduce VO.sub.2.sup.+ to VO.sup.2+, and the mixed solution was heated at 40° C. for 3 minutes. The following reactions take place:
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2VO.sup.2++SO.sub.4.sup.2−+H.sub.2O
(89) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at 765 nm. The absorbance of this solution was measured as A.sup.u.sub.765nm=0.472. Then the total vanadium concentration (C.sub.4) in this solution was calculated from the standard concentration calibration curve as shown in
(90) The V.sup.3+ concentration in Sample 2 can be calculated by the following equation.
C.sub.V(III)=2C.sub.2−3(C.sub.4−C.sub.3)=2×1.106−3×(2.186−1.807)=1.075 (mol/L)
(91) The VO.sup.2+ concentration in Sample 2 can be calculated by the following equation.
C.sub.V(IV)=3C.sub.3−2C.sub.1−2C.sub.V(III)=3×1.807−2×1.064−2×1.075=1.143 (mol/L)
(92) TABLE-US-00002 TABLE 2 Comparison of the measurements of Sample 2 using different analysis methods Sample 2 Method V.sup.3+ VO.sup.2+ V.sub.tot Optical Absorption Spectroscopy 1.075 1.143 2.218 Potentiometric Titration 1.10 1.15 2.25 Inductively Coupled Plasma — — 2.102 Relative Error (%) 2.27 0.61 1.42 (optical absorption spectroscopy compared with potentiometric titration)
Example 7
Determination of V2+ and V3+ Concentrations
(93) The concentrations of vanadium ions at valence states 2+ and 3+ were determined in a V.sup.2+/V.sup.3+ electrolyte solution.
(94) One VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared. The procedure of vanadium concentration analysis was conducted as in Example 4(A). The VO.sup.2+ and VO.sub.2.sup.+ concentrations in the solution were measured as C.sub.1=1.064 mol/L and C.sub.2=1.106 mol/L, respectively.
(95) 3 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was added into a 250 mL volumetric flask and purged with argon gas for 2 minutes. Then, 1 mL of V.sup.2+/V.sup.3+ solution (Sample 3) was added into the flask and mixed quickly. The following reactions take place:
V.sup.2++VO.sub.2.sup.++2H.sup.+.fwdarw.V.sup.3++VO.sup.2++H.sub.2O
V.sup.2++VO.sup.2++2H.sup.+.fwdarw.2V.sup.3++H.sub.2O
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
(96) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at 765 nm. The absorbance of this solution was measured as A.sup.u.sub.765nm=0.547. Then the VO.sup.2+ concentration (C.sub.5) in this solution can be calculated by standard concentration calibration curve (
(97) The other 250 mL volumetric flask with 3 mL of VO.sup.2+/VO.sub.2.sup.+ standard solution was prepared and purged with argon gas for 2 minutes. Then, 1.0 mL of V.sup.2+/V.sup.3+ solution (Sample 3) was added and mixed quickly. After that, excess sodium sulfite (0.5 mol/L) was added to reduce VO.sub.2.sup.+ to VO.sup.2+, and the mixed solution was heated at 40° C. for 3 minutes. The following reactions take place:
V.sup.2++VO.sub.2.sup.++2H.sup.+.fwdarw.V.sup.3++VO.sup.2++H.sub.2O
V.sup.2++VO.sup.2++2H.sup.+.fwdarw.2V.sup.3++H.sub.2O
V.sup.3++VO.sub.2.sup.+.fwdarw.2VO.sup.2+
2VO.sub.2.sup.++SO.sub.3.sup.2−+2H.sup.+.fwdarw.2VO.sup.2++SO.sub.4.sup.2−+H.sub.2O
(98) After diluting with deionized water to 250 mL, the solution was measured by optical absorption spectroscopy at 765 nm. The absorbance of this solution was measured as A.sup.u.sub.765nm=0.585. Then the total vanadium concentration (C.sub.6) in this solution was calculated from the standard concentration calibration curve as shown in
(99) The V.sup.2+ concentration in the Sample 3 was calculated by the following equation.
C.sub.V(II)=3(C.sub.1+2C.sub.2)−4(2C.sub.6−C.sub.5)=3×(1.064+2×1.106)−4×(2×2.032−1.900)=1.172 (mol/L)
(100) The V.sup.3+ concentration in Sample 3 can be calculated by the following equation.
C.sub.V(III)=3C.sub.2−4(C.sub.6−C.sub.5)−2C.sub.V(II)=3×1.106−4×(2.032−1.900)−2×1.172=0.446 (mol/L)
(101) TABLE-US-00003 TABLE 3 Comparison of the measurements of Sample 3 using different analysis methods Sample 3 Method V.sup.2+ V.sup.3+ V.sub.tot Optical Absorption Spectroscopy 1.172 0.446 1.618 Potentiometric Titration 1.165 0.457 1.622 Inductively Coupled Plasma — — 1.602 Relative Error (%) 0.60 2.41 0.25 (optical absorption spectroscopy compared with potentiometric titration)
(102) Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
(103) While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the disclosure.