Patent Application
20230318003
The present invention relates to a redox flow battery and an aqueous-based solution.
Society faces a large challenge in transitioning to sustainably generating electricity from renewable energy sources such as wind and solar. One of the biggest obstacles to this transition is the intermittence of the sources, leading to a mismatch of supply and demand, a problem most commonly solved by installing large-scale energy storage.
The flow battery has existed for roughly 50 years already, but has been employing metals such as Iron, Chromium and Vanadium, which have serious inherent problems relating to either performance, procurement or toxicity.
Also, organic molecules have been considered for use in flow battery systems, and flow battery systems which are based on different quinones such as anthraquinone and benzoquinone, are known. For example, WO2017170944A1 which relates to an aqueous secondary cell for which at least one of the positive electrode and the negative electrode contains a compound having a naphthalene diimide structure or a perylene diimide structure as an active material. Further, WO18162851A1 which relates to the use of a bis(pyridinium)-naphthalene diimide redox ionic compound used as an active electrode material for an aqueous electrolyte battery.
An energy storage technology, that has the potential to surpass current technology in both performance, cost and environmental benignity, is aqueous organic redox flow batteries. Thus, there is a need for high-performing aqueous organic redox flow battery systems to meet the demands.
According to a first aspect of the present invention, a redox flow battery is provided.
The redox flow battery comprising:
The positive compartment may be referred to as the positive side of the battery and the negative compartment may be referred to as the negative side of the battery.
According to at least one example embodiment, the positive compartment contains a positive electrode in contact with a first aqueous-based electrolyte solution comprising a positive electrolyte dissolved in a first aqueous-based solvent.
According to at least one example embodiment, the negative compartment contains a negative electrode in contact with a second aqueous-based electrolyte solution comprising a negative electrolyte being an organic redox-active molecule dissolved in a second aqueous-based solvent.
According to at least one example embodiment, the negative electrolyte has a more negative redox potential than the positive electrolyte. According to at least one example embodiment, the negative electrolyte comprises an organic redox-active molecule that has a more negative redox potential than the positive electrolyte, e.g. compared to a corresponding molecule in the positive electrolyte. The difference in reduction potential between the positive electrolyte and the negative electrolyte typically determines the open-circuit voltage.
Further, the redox flow battery also comprises means capable of (i.e., having design features for) establishing flow of the first aqueous-based electrolyte solution and the second aqueous-based electrolyte solution past, or through, said positive and negative electrodes, respectively. Such means may e.g. be a pump or other means resulting in a flow or pressure difference.
During discharge of the redox flow battery, the first aqueous-based electrolyte solution and the second aqueous-based electrolyte solution are, upon operation, pumped through the positive electrode and the negative electrode, respectively, in a fuel cell-like reactor, which involves an electrochemical cell. The negative electrode, for example being a porous electrode, and the positive electrode, e.g. being a porous electrode, are separated by the separator component, e.g. an ion-selective membrane.
Suitable negative electrodes and positive electrodes comprise, e.g. any suitable material/s, for example, woven or non-woven graphite, or other porous carbonaceous materials.
The first and/or second aqueous-based electrolyte solutions may be, for example, water, or water in admixture with water-soluble co-solvent/s and/or supporting electrolytes. Some examples of protic organic solvents, which may be used as a water-soluble co-solvent in the aqueous-based electrolyte solutions, according to the present invention, include the alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, t-butanol, n-pentanol, isopentanol, 3-pentanol, neopentyl alcohol, n-hexanol, 2-hexanol, 3-hexanol, 3-methyl-1-pentanol, 3,3-dimethyl-1-butanol, isohexanol, and cyclohexanol. The protic organic solvent, which may be used as a water-soluble co-solvent in the aqueous-based electrolyte solutions, according to the present invention, may alternatively be or include a carboxylic acid, such as acetic acid, propionic acid, butyric acid, or a salt thereof. Some examples of polar aprotic solvents, which may be used as a water-soluble co-solvent in the aqueous-based electrolyte solutions, according to the present invention, include nitrile solvents (e.g., acetonitrile, propionitrile, and butyronitrile), sulfoxide solvents (e.g., dimethyl sulfoxide, ethyl methyl sulfoxide, diethyl sulfoxide, methyl propyl sulfoxide, and ethyl propyl sulfoxide), sulfone solvents (e.g., methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone, propyl sulfone, butyl sulfone, tetramethylene sulfone, i.e., sulfolane), amide solvents (e.g., N,N-dimethylformamide, N,N-diethylformamide, acetamide, dimethylacetamide, and N-methylpyrrolidone), ether solvents (e.g., diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, and tetrahydrofuran), carbonate solvents (e.g., propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluorocarbonate solvents, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate), organochloride solvents (e.g., methylene chloride, chloroform, 1,1,-trichloroethane), ketone solvents (e.g., acetone and 2-butanone), and ester solvents (e.g., 1,4-butyrolactone, ethylacetate, methylpropionate, ethylpropionate, and the formates, such as methyl formate and ethyl formate). The polar aprotic solvent may also be or include, for example, hexamethylphosphoramide (HMPA), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), or propylene glycol monomethyl ether acetate (PGMEA).
The first and/or second aqueous-based electrolyte solutions may according to at least one example embodiment comprise a supporting electrolyte/s, serving to make the aqueous-based electrolyte solutions ionically conductive and provide the system with mobile charge carriers. According to at least one example embodiment, the supporting electrolyte of at least one of the first and second aqueous-based electrolyte solutions comprises the previously mentioned ammonium-based salt. According to at least one example embodiment, the supporting electrolyte of the other one of the first and second aqueous-based electrolytes (i.e. in embodiments in which only one of the first and second aqueous-based electrolytes is based on the ammonium-based salt) comprises varying concentrations of neat, or mixtures of, solutions of sulfuric acid, hydrobromic acid, chloric acid, perchloric acid, hydrochloric acid, citric acid, carbonic acid, phosphonic acid, phosphoric acid, formic acid, acetic acid, chloride salts of sodium, potassium, magnesium, calcium and ammonium, as well as sodium, potassium, calcium and magnesium salts of carbonate, bicarbonate, phosphate, biphosphate, sulfate, bisulfate, nitrate, citrate, chlorate and perchlorate. According to at least one example embodiment, the supportive electrolyte of both the first and second aqueous-based electrolyte solutions are based on an ammonium-based salt.
According to at least one example embodiment, the second aqueous-based electrolyte solution, or the supporting electrolyte of the same, is based on an ammonium-based salt. According to at least one example embodiment, the first aqueous-based electrolyte solution, or the supporting electrolyte of the same, is not based on an ammonium-based salt.
According to at least one example embodiment, the ammonium-based salt is, or comprises at least, one of the following: ammonium chloride, ammonium phosphate. Additionally or alternatively, the ammonium-based salt is, or comprises at least, one of the following: ammonium sulphate, ammonium nitrate. That is, according to at least one example embodiment, the ammonium-based salt is, or comprises at least, one of the following: ammonium chloride, ammonium phosphate, ammonium sulphate, ammonium nitrate. According to at least one example embodiment, the ammonium-based salt is, or comprises ammonium chloride. According to at least one example embodiment, the ammonium-based salt is, or comprises ammonium phosphate. According to at least one example embodiment, the ammonium-based salt is, or comprises ammonium sulphate. According to at least one example embodiment, the ammonium-based salt is, or comprises ammonium nitrate. When stating that at least one of the first and second aqueous-based electrolytes is based on an ammonium-based salt, the first and/or second aqueous-based electrolytes is formed from the ammonium-based salt, or comprises the ammonium-based salt.
The redox flow battery, according to the present invention, comprises electrical conductive means for establishing electrical conduction between said positive electrode and said negative electrode in order to permit the redox flow battery, according to the present invention, to be charged and discharged. In a particular embodiment, the electrical conduction means include wiring means, i.e., the presence of wiring and associated bonding pads and the like sufficient for establishing electrical conduction. However, the electrical conductive means for establishing electrical conduction do not necessarily have to be in the form of wiring.
For example, electrical conduction may be established by assembling multiple electrodes and multiple flow channels in a stacked bipolar configuration so that electrical connections need only be made to the first and last electrodes.
The redox flow battery, according to the present invention, comprises external load for directing electrical energy into or out of the redox flow battery. For example, the load has a dual function of accepting electrical energy from an electrical source during a charging phase of the redox flow battery, according to the present invention, and also accepting electrical energy from the redox flow battery during a discharging phase of the redox flow battery. According to at least one example embodiment, the load functions only to accept electrical energy from the redox flow battery, according to the present invention, during a discharging phase of the redox flow battery, and a separate source is included for sourcing electrical energy during a charging phase of the redox flow battery. Generally, switching means are included in order to operate the redox flow battery, according to the present invention, in either a charging or discharging mode. For example, when operating in a charging mode, a first switch establishing connection between positive and negative electrodes and an external load is disengaged (i.e., open) while a second switch establishing connection between a source and positive and negative electrodes is engaged (i.e., closed); and in the discharging mode, the first switch establishing circuitry between positive and negative electrodes and an external load is engaged while the second switch establishing circuitry between a source and positive and negative electrodes is disengaged.
In accordance with the present invention the redox flow battery, as described herein, has outstanding voltage and stability. The aqueous-based electrolyte solutions, according to an example embodiment of the present invention, are aqueous-based comprising metal-free electrolytes, and are safe and non-toxic. The organic redox-active molecules, according to the present invention, are manufactured using extremely “green” synthesis routes, including synthesis routes with few steps and one-step synthesis routes.
The redox flow battery, according to the present invention, is thus an especially perfect candidate for large-scale energy storage such as this, also since the production cost typically does not depend on any rare earth metals, like it does for competing technologies. Furthermore, since the redox-active materials, i.e. the aqueous-based electrolyte solutions, may be stored in tanks and pumped through electrochemical cells upon operation, the power/capacity ratio can be scaled up based on what is desired for the specific application.
Apart from the opportunity in storage of solar energy, there are also opportunities for the redox flow battery, according to the present invention, in load levelling, peak shaving, district housing and residential energy storage, wind power, farms, densely populated cities where the cost of installing power transmission is very expensive, amongst others.
Further, the redox flow battery, according an example embodiment of the present invention, also does have the features of enabling decoupled power and capacity, large scale and long term energy storage, that every component is replaceable during maintenance, and/or that it is safe due to the aqueous-based electrolyte solutions.
According to at least one example embodiment, the organic redox-active molecule has a solubility at room temperature of at least 0.4 M in the second aqueous-based electrolyte solution. According to at least one example embodiment, buffer or acid is added to the solution or respective aqueous based electrolyte to increase the solubility.
According to at least one example embodiment, the organic redox-active molecule is a naphthalene diimide, abbreviated NDI, or a modified NDI.
Thus, according to at least one example embodiment the organic redox-active molecule is a modified NDI, or modified naphthalene diimide (NDI) having a solubility at room temperature of at least 0.4 M in the aqueous-based electrolyte solution. According to at least one example embodiment the organic redox-active molecule is a naphthalene diimide (NDI) having a solubility at room temperature of at least 0.4 M in the aqueous-based electrolyte solution.
According to at least one example embodiment all the utilized oxidation states of the organic redox-active molecule is a modified naphthalene diimide (NDI) having a solubility at room temperature of at least 0.4 M in the aqueous-based electrolyte solution.
The solubility of species, the organic redox-active molecule/s, directly influences the energy density of electrolyte solutions, and in extension, battery systems as a whole. A redox flow battery utilizing NDI, or a modified NDI, with a solubility exceeding 0.4 M will offer relatively higher energy densities and will allow higher charge/discharge current densities.
Further, the present invention does also relate to a redox flow battery, as described herein, wherein the organic redox-active molecule is a naphthalene diimide (NDI) and at least one, e.g. one to two, for example one, modified naphthalene diimide (NDI), as described herein, or at least two, e.g. two to three, for example two, modified naphthalene diimide (NDI), as described herein.
According to at least one example embodiment, the aqueous-based electrolyte solution comprises at least two different organic redox-active molecules dissolved in the second aqueous-based solvent, a first organic redox-active molecule being NDI as described above, and a second organic redox-active molecule being, modified naphthalene diimide NDI, as described above.
In further embodiments of the redox flow battery according to the present invention, as described herein, the first aqueous-based solvent and the second aqueous-based solvent are the same.
In further embodiments of the redox flow battery according to the present invention, as described herein, the modified NDI having a solubility at room temperature of at least 0.5 M, at least 0.6 M, at least 0.7 M, at least 0.75 M, at least 0.8 M, at least 0.9 M, or, alternatively, at least 1.0 M, in the aqueous-based electrolyte solution.
In even further embodiments of the redox flow battery according to the present invention, as described herein, the modified NDI has a water solubility at room temperature of at least 0.5 M, at least 0.6 M, at least 0.7 M, at least 0.75 M, at least 0.8 M, at least 0.9 M, or, alternatively, at least 1.0 M.
In further embodiments of the redox flow battery according to the present invention, as described herein, the modified NDI has a solubility of at most 10 M, at most 9.0 M, at most 8.0 M, at most 7.0 M, at most 6.0 M, at most 5.0 M, at most 4.0 M, at most 3.0 M, at most 2.5 M, at most 2.0 M, or, alternatively, at most 1.5 M in the aqueous-based electrolyte solution at room temperature.
In still further embodiments of the redox flow battery according to the present invention, as described herein, the modified NDI has a water solubility at room temperature of at most 10 M, at most 9.0 M, at most 8.0 M, at most 7.0 M, at most 6.0 M, at most 5.0 M, at most 4.0 M, at most 3.0 M, at most 2.5 M, at most 2.0 M, or, alternatively, at most 1.5 M.
In a further embodiment of the present invention, a redox flow battery, as described herein, is disclosed, wherein the modified NDI, is a substituted NDI, e.g. a core-aminated NDI.
According to at least one example embodiment, the modified NDI comprises an amino group. In a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has a structure according to formula I
wherein each, of R1, R2, R3, R4, R5 and R6, is independently selected from:
According to at least one example embodiment, R1 and R4 comprises tertiary or quaternary amines, and/or sulfonate groups.
According to at least one example embodiment, at least one of R2, R3, R5 and R6 is a group or molecule comprising more than a hydrogen atom, or is different to a hydrogen atom, e.g. another atom or molecule. That is, at least one of R2, R3, R5 and R6 is not solely hydrogen. This may e.g. improve the aqueous solubility and/or electronic properties of the molecule.
According to at least one example embodiment, the modified NDI, comprises an amino group and/or cyano group on at least one of R2, R3, R5 and R6. R2, R3, R5 and R6 are typically referred to as core substituents or core group, as they are associated with the core of the NDI, or modified NDI, molecule. This may e.g. improve the aqueous solubility and/or electronic properties of the molecule.
According to at least one example embodiment, R2, R3, R5 and R6 comprises at least two amino groups and/or two cyano groups, with hydrogen present on any remaining two core groups. For example, the two amino groups and/or the two cyano groups may be arranged mirrored, i.e. on R2 and R5, or arranged on R3 and R6. This may e.g. improve the aqueous solubility and/or electronic properties of the molecule.
It should be understood that the embodiments related to the chemical structure of the modified NDI above are also applicable to the NDI having a structure according to formula II as described below. In such cases, R21, R22, R23, R24, R25 and R26 correspond to R1 R2, R3, R4, R5 and R6 respectively, wherein R22, R23, R25 and R26 are the core substituents or core groups.
Redox flow batteries utilizing an NDI, or a modified NDI, as described herein, as a redox-active molecule in the electrolyte solution/s offer multiple advantages over analogous aqueous organic redox flow battery systems. In choosing R1 and R4, or R21 and R24, as described herein, to be quaternary amines (or tertiary amines which will be protonated upon solution), or sulfonate groups connected to the imide nitrogen by a hydrocarbyl linker, the aqueous solubility of the molecule is promoted, while at the same time two permanent charges are introduced to the structure, without affecting the electronic properties of the NDI, or the modified NDI, as described herein. The permanent charges, apart from giving a solubilizing effect, hinder the NDI, or the modified NDI, as described herein, from crossing over the ion-exchange membrane due to coulombic repulsion.
As seen in
As seen in
In choosing R2, R3, R5 and R6, or R22, R23, R25 and R26, as described herein, to be electron-withdrawing or electron-donating groups, the reduction potential of the NDI and the modified NDI, as described herein, can be tuned for the specific application, potentially maximizing the operating voltage of the battery. Due to the less negative reduction potentials of the modified NDI, it can be used in conjunction with NDI, resulting in a battery system that has a fast-charge part, characterized by the reduction of the modified NDI, suitable for when there is demand for high power output, and a slow-charge part, characterized by the reduction of NDI, suitable for long-term energy storage.
In still a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, and wherein each, of R1, R2, R3, R4, R5 and R6, is independently selected from:
In even a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, wherein, three or less, of R1, R2, R3, R4, R5 and R6, are hydrogen.
In a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, wherein R2 and R5 are both hydrogen.
In still a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, wherein each, of R1, R3, R4 and R6, is independently selected from:
In even a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, wherein each, of R1, R3, R4 and R6, is independently selected from:
In still a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, wherein each, of R3 and R6, is independently selected from:
In even a further embodiment of the redox flow battery according to the present invention, as described herein, the modified NDI has the structure according to formula I, wherein each, of R1 and R4, is independently selected from:
According to at least one example embodiment, the battery is configured such that the NDI, or modified NDI, is reduced with two electrons in the negative compartment, creating reducedNDl in the form of an NDI dianion, NDI− or hydroNDI, NDIH2. Hereby, an improved battery is provided. According to at least one example embodiment, the reduced NDI is an original reduced NDI having a first structure, and the battery is configured such that the original reduced NDI is restructured into a restructured reduced NDI having a second structure different from said first structure, the restructured reduced NDI having a different reduction potential compared to the original reduced NDI. The difference in reduction potential between the original reduced NDI and the restructured reduced NDI may determine the voltage of the battery.
Such configuration of the battery may e.g. comprise adapting the pH of the electrolyte. For example, the pH at the negative compartment may be lower compared to the positive compartment with at least a value of pH 2. Such configuration may additionally or alternatively comprise changing electrolyte (e.g. NaCl instead of KCl), setting suitable temperature, and/or adapting the substituents of the NDI molecule.
According to at least one example embodiment, the pH is adjusted during cycling due to the proton-coupled electron transfer of NDI.
Thus, depending on pH and substituent of the NDI, the reduction may include the reaction of NDI+2e−+2H+→NDIH2. Here, as two protons are assimilated, pH will increase automatically, in response to a well balanced concentration of NDI and buffer capacity of the solution.
In embodiments of the present invention, a redox flow battery, as described herein, is disclosed, wherein also the positive electrolyte is a NDI, e.g. the same as the negative electrolyte, or a redox flow battery, as described herein, is disclosed, wherein also the positive electrolyte is an organic redox-active molecule being a modified NDI, as described herein, e.g. the same as the negative electrolyte.
In other words, according to at least one example embodiment, the positive electrolyte is the same as the negative electrolyte, forming a symmetrical redox flow battery.
In embodiments of the present invention, a redox flow battery, as described herein, is disclosed, wherein also the positive electrolyte is an organic redox-active molecule being NDI or a modified NDI as described herein.
In further embodiments of the present invention, a redox flow battery, as described herein, is disclosed, wherein the positive electrolyte and the negative electrolyte are the same modified NDI as described herein.
In the embodiments of the present invention, where a redox flow battery, as described herein, is disclosed, wherein also the positive electrolyte is a NDI, e.g. the same as the negative electrolyte, or a redox flow battery, as described herein, is disclosed, wherein also the positive electrolyte is an organic redox-active molecule being a modified NDI, as described herein, e.g. the same as the negative electrolyte, the cost of production for the NDI and/or the modified NDI will be drastically reduced, due to the double scale. Further, in keeping the amount of different substances in the electrolyte solutions to a minimum, the range of possible degradation mechanisms are also decreased. Further, in utilizing the same molecule, i.e. the same organic redox-active molecule, as both the negative and positive redox-active material, any capacity decay due to species permeating the membrane will be reversible through electrolyte remixing, greatly enhancing the cycling lifetime of the system.
According to at least one example embodiment of the symmetrical redox flow battery, charging of the battery results in the following reactions:
According to at least one example embodiment of the symmetrical redox flow battery, charging of the battery results in the following reactions:
According to a second aspect of the present invention, an aqueous solution is provided. The aqeuous solution comprises the NDI, or modified NDI, as described in relation to the first aspect of the invention, and an aqueous-based electrolyte based on an ammonium-based salt, e.g. ammonium chloride or ammonium phosphate. The ammonium salt is preferably making up a supporting electrolyte in a redox flow battery.
According to at least one example embodiment, the ammonium-based salt is, or comprises at least, one of the following: ammonium chloride, ammonium phosphate. Additionally, or alternatively, the ammonium-based salt is, or comprises at least, one of the following: ammonium sulphate, ammonium nitrate.
In the aqueous solution, the modified NDI may have a structure according to formula
wherein R22 and R25 are both hydrogen atom, and each, of R21, R23, R24 and R26, is independently selected from:
The modified NDI as described herein, e.g. the modified NDI having a structure according to formula II, has a high chemical stability, easy and green synthesis, high aqueous solubility and attractive electronic properties. This makes the modified NDI valuable for use in various aqueous electrochemical applications such as electrocatalysis or sensoring.
In a further embodiment of the present invention, the modified NDI, as described herein, is disclosed, wherein each of R21 and R24, is independently selected from:
A further embodiment of the modified NDI according to the present invention, as described herein, is provided wherein the modified NDI has the structure according to formula II, and wherein R23 and R26, is independently selected from:
An even further embodiment of the modified NDI according to the present invention, as described herein, is provided wherein the modified NDI has the structure according to formula II, and wherein R21 and R24, is independently selected from:
A further embodiment of the modified NDI according to the present invention, as described herein, is provided wherein the modified NDI has the structure according to formula II, and each, of R21 and R24, is independently selected from:
In still a further embodiment of the modified NDI according to the present invention, as described herein, the modified NDI has the structure according to formula II, wherein R21 and R24 are, e.g. the same, selected from:
In a further embodiment of the modified NDI according to the present invention, as described herein, the modified NDI has the structure according to formula II, wherein each, of R23 and R26, is independently selected from:
In still a further embodiment of the modified NDI according to the present invention, as described herein, the modified NDI has the structure according to formula II, wherein each, of R21 and R24, is independently selected from:
In further embodiments of the redox flow battery, according to the present invention, as described herein, the modified NDI has the structure according to formula II, as described herein. That is, according to a third aspect of the present invention, a redox flow battery according to the first aspect of the invention, with an aqueous solution according to the second aspect of the invention is provided.
In a further embodiment according to the present invention, a redox flow battery, as described herein, is disclosed wherein the modified NDI has a structure according to formula II, as described herein, wherein R22 and R25 are both hydrogen atom, R21 and R24 are both a hydrocarbyl group having one to six, for example one to three, e.g. three carbon atoms, each hydrocarbyl group substituted by one amino group —NR28R29R30, wherein R30 is present when the amino group is quaternized, and wherein R28 and R29 are both a hydrocarbyl group having one to four carbon atoms, for example one to three, e.g. one, carbon atoms, and R30, if R30 present, is a hydrogen or a hydrocarbyl group having one to four carbon atoms, for example one to three, e.g. one, carbon atoms and
R23 and R26 are both an amino group —NR28R29, wherein R28 and R29 are both a hydrocarbyl group having one to four carbon atoms, for example one to three carbon atoms, e.g. one carbon atom.
In a still further embodiment according to the present invention, a redox flow battery, as described herein, is disclosed wherein the modified NDI is the free base or the protonated amine form of either:
In a further embodiment according to the present invention, a redox flow battery, as described herein, is disclosed wherein the modified NDI has a structure according to formula II, as described herein, wherein R22 and R25 are both hydrogen atom, R21 and R24 are both a hydrocarbyl group having one to six, for example one to three, e.g. three carbon atoms, each hydrocarbyl group substituted by one amino group —NR28R29R30, wherein R30 is present when the amino group is quaternized, and wherein R28 and R29 are both a hydrocarbyl group having one to four carbon atoms, for example one to three, e.g. one, carbon atoms, and R30, if R30 present, is a hydrogen or a hydrocarbyl group having one to four carbon atoms, for example one to three, e.g. one, carbon atoms and R23 and R26 are both cyano group (CN) or, alternatively, R23 and R26 are both sulfonate (—S(O)2OH or —S(O)2O−).
According to at least one example embodiment, the sulfonate group (—S(O)2OH or —S(O)2O−), for NDI or modified NDI, may be replaced with a carboxylate group (—COOH or or CO)—), applicable to both the first and second aspects of the invention.
The present invention further relates to a method for producing a redox flow battery as described herein.
The present invention also relates to a method for producing a modified NDI having the structure according to formula II as described herein.
The invention will be described in greater detail in the following, with reference to the embodiments that are shownin the attached drawings, in which:
The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way intended to limit the scope of the protection provided by the patent claims.
NDI was synthesized in 30 g scale according to Sissi, C. et al, Bioorg. Med. Chem. 2007, 15, (1), 555-62, in a facile and green manner with high yields and water as the only byproduct, and the quaternization, if necessary, simply by bubbling chloromethane through a chloroform solution of the tertiary NDI, whereupon the pure product is precipitated, see Scheme.
The quaternization is only necessary if the molecule is to be examined at higher pH values, since the tertiary amine sidechains are protonated for pH values less than about 8 (pKa≈8.1) as shown by the titration curve in
The electrochemistry of NDI was examined by CV at a range of different pH values, to gain understanding of the electron transfer reaction mechanism.
A plot of the reduction potentials for NDI at different pHs is seen in
It should be remarked that the reduction potential of NDI is outstandingly low, and if used in a redox flow battery, it would possibly yield an operating voltage among the highest of the previously reported structures in aqueous solutions. Indeed, more negative potentials are not beneficial, due to the parasitic hydrogen evolution reactions eventually taking precedence.
Further, rotating disk electrode (RDE) voltammetry was coupled with diffusion NMR to assess the accessible concentration of NDI in a neutral buffered solution, and tested whether it corresponded to dimerization. The diffusion coefficients from diffusion NMR were found to be 2.57 and 2.34×10−6 cm2 s−1 for the acid and neutral solutions respectively. From the slope in
Based on this relationship and reasoning, the reduction scheme in Scheme 2 is proposed for acidic solutions as follows.
As work on 9,10-Anthraquinone-2,7-disulfonic acid (AQDS) has shown the impact of dimerization on its electrochemical properties, it was prudent to examine whether the same behavior could be seen for NDI. Since NDI has a large aromatic core, and it is known to self-associate quite readily, it was imagined that the effect could be quite strong, despite the flexible positively charged sidechains.
A solution of 25 mM NDI in pH 6.4 sodium phosphate buffer was cycled in a bulk electrolysis cell, where all of the material is reduced, as opposed to CV and RDE, where only a small fraction of the material is probed. A galvanostatic BE setting was used, where a constant current of 40 mA was applied. The electrolysis was intermittently paused, allowing for CVs to be collected to be able to quantify the amount of NDI that has been reduced. The peak heights from the CVs were correlated to the passed current, and it was seen that the complete capacity of NDI could be accessed using bulk electrolysis. See here
After the initial sweep, continuous cycling at a current of 15 mA was performed for twelve cycles. A CV was collected after the cycling had finished, roughly a week after starting. The CV was compared to the initial, untouched solution, and it was seen that they overlapped perfectly, indicating no or little material degradation over the course of the experiment, showing the exceptional stability of NDI. See here
The cost and performance of the aqueous redox flow battery depends very strongly on the redox-active material employed. The starting material for the synthesis of NDI, 1,4,5,8-naphthalene tetracarboxylic acid dianhyride is easily synthezied from naphthalene—a very cheap and abundant compound. The combination of having a very low reduction potential, high aqueous solubility, high chemical stability, low membrane permeability, environmental benignity, possibility for use at neutral pH, and potential for manufacture at very low costs, is a set of criteria that is not easily fulfilled. NDI achieves a fulfillment of these criteria to a far higher extent than competing technologies. Thus, a flow battery employing NDI has a superior cost-performance relationship than competing technologies, without compromising on environmental impact or operational safety.
A 250 ml round-bottom flask charged with 1,4,5,8-naphthalene tetracarboxylic acid dianhydride (NDA) (4.00 g, 14.92 mmol) and sulfuric acid (98%, 100 ml) was subjected to stirring at 50° C. for an hour to enhance dissolution. To the resulting solution was added by portions dibromoisocyanuric acid (DBI) (6.46 g, 22.51 mmol) and stirred at ambient temperature for 30 minutes. The reaction temperature was then adjusted and maintained at 120° C. for 45 hours.
Upon heating, reddish-brown fumes evolved which were trapped in a solution of sodium thiosulphate. The reaction mixture was cooled to room temperature, remaining reddish fumes were removed with a gentle stream of nitrogen gas and then poured into crushed ice. The precipitate formed was filtered, washed with copious amount of distilled water and then methanol. Br,Br-NDA was obtained as a yellowish-green solid and vacuum-dried at 40° C. overnight to afford approximately 78% yield. This was used without any further purification.
The nuclear magnetic resonance (NMR) spectroscopy for 2,6-dibromonaphtalene-1,4,5,8-tetracarboxylic dianhydride is: 1H NMR (400 MHz, DMSO-d6) δ 8.77 (s, 2H); 13C NMR (101 MHz, DMSO-d6) δ 158.39, 156.89, 137.97, 129.87, 127.85, 124.72, 123.87.
2,6-dibromonaphtalene-1,4,5,8-tetracarboxylic dianhydride from Example 2 (5.01 g, 11.76 mmol) and 50 ml of glacial acetic acid were charged into a two-necked round-bottom flask under stirring. To the system was added 3-(dimethylamino)-1-propylamine (3.61 g, 4.45 ml, 35.33 mmol, 3 eq). The mixture was stirred at 120° C., and after 30 minutes of reaction, cooled to room temperature, quenched in ice, neutralized with sodium carbonate and extracted three times with chloroform. The organic layer was dried under vacuum to give an orange crude, which was purified by column chromatography (CHCl3:MeOH, 9:1) to obtain approximately 20% yield. The silica stationary phase was pretreated with triethylamine.
The nuclear magnetic resonance (NMR) spectroscopy for 4,9-dibromo-2,7-bis(3-(dimethylamino)propyl)benzo[Imn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone is: 1H NMR (400 MHz, Chloroform-d) δ 8.98 (s, 2H), 4.31-4.22 (m, 4H), 2.45 (t, J=7.0 Hz, 4H), 2.24 (s, 12H), 1.99-1.85 (m, 4H); 13C NMR (101 MHz, Chloroform-d) δ 160.79, 160.75, 138.99, 128.28, 127.70, 125.32, 124.10, 57.06, 45.23, 39.90, 25.54.
A 100 ml round-bottom flask was charged at each reaction with 50 mg of either NDI or Br,Br-NDI for the synthesis of compound of Example 4a and compound of Example 4b, respectively. To the system was added 10-15 ml of chloroform and subjected to heating in an oil bath at 50° C. while stirring. Chloromethane gas was bubbled through the content of the flask three times for at most a minute each time. Precipitates were observed to form after an hour of stirring. The system was left to stir for 12 hours. The reaction was cooled to room temperature, filtered and dried under vacuum to afford a quantitative yield.
The compound of Example 4a was obtained as an off-white solid, and the nuclear magnetic resonance (NMR) spectroscopy for Benzo[Imn][3,8]phenanthroline-2,7-dipropanaminium, 1,3,6,8-tetrahydro-N, N, N,N′,N′, N′-hexamethyl-1,3,6,8-tetraoxo-, dichloride is:
1H NMR (400 MHz, Deuterium Oxide) δ 8.41 (s, 4H), 4.09 (t, J=7.0 Hz, 4H), 3.44-3.35 (m, 4H), 3.02 (s, 18H), 2.20-2.07 (m, 4H); 13C NMR (101 MHz, Deuterium Oxide) δ 163.88, 130.96, 125.86, 125.81, 64.00, 52.88, 37.63, 21.34.
The compound of Example 4b was obtained as an orange-red solid and the nuclear magnetic resonance (NMR) spectroscopy for 3,3′-(4,9-dibromo-1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[Imn][3,8]phenanthroline-2,7-diyl)bis(N,N,N-trimethylpropan-1-aminium) chloride is:
1H NMR (400 MHz, Deuterium Oxide) δ 8.56 (s, 2H), 4.07 (t, J=7.0 Hz, 4H), 3.44-3.36 (m, 4H), 3.02 (s, 18H), 2.15-2.06 (m, 4H). 13C NMR (101 MHz, Deuterium Oxide) δ 161.21, 138.48, 128.22, 126.52, 124.31, 123.31, 63.85, 63.82, 63.79, 55.15, 52.95, 52.91, 52.87, 42.74, 38.33, 21.14.
A saturated solution of about 500 μl each of the targeted molecules, i.e the compounds obtained in Examples 3, 4a and 4b, in milli-Q water containing undissolved particles were prepared at ambient temperature. The solutions were centrifuged at 12,500 rpm for 30 minutes. 100 μl of the supernatant were pipetted in triplicates from each of the solution into separate empty vials of known weights. The content of these vails were left to dry in a vacuum oven overnight. The final weights of the vials were determined and the amount of each of the compounds calculated from the weight difference. Solubility in mmol/L for each compound was finally determined. The results obtained are presented in Table 1, where “Compound 1” is the compound obtained in Example 3, “Compound 2” is the compound obtained in Example 4a and “Compound 3” is the compound obtained in Example 4b. It should be noted that the solubility may be increased by adding a buffer or acid. For example, by adding a buffer or acid to compound 1, the solubility is increased above 0.4 M.
Solubility of the compound obtained in Example 3 which is a base NDI is lower than those of the compounds obtained in Examples 4a and 4b which are quaternary ammonium NDI salts. This is due to the differences in intermolecular interactions of the individual compounds. The compound obtained in Example 3 contains soluble amines both at the imide positions and the naphthalene core eventually affects the solubility at the molecular level. Adversely, a long range intermolecular π-π stacking effect of the molecules in solution could not be hindered, therefore limiting their solubility. Since the compounds obtained in Examples 4a and 4b exist as salts, they could dissolve more easily in water due to electrostatic interactions of their resulting ions. This could limit the π-π stacking of the NDI to an extent of permitting higher solubilities than compound 1. The difference in the solubilities of the compounds obtained in Examples 4a and 4b is resulting from the insoluble bromine substituent on the naphthalene core. If the structure obtained in Example 3 was to be added to a slightly acidic solution, the amines would become protonated and the solubility would increase significantly. The structures of the compounds obtained in Examples 3, 4a and 4b are shown in Scheme 3.
All CV measurements were carried out in a custom built 10 ml three-electrode electrochemical cell. The lower part of the cell holds the electrolyte of interest. In the upper part are ports to hold the working electrode, reference electrode and auxiliary electrode as well as inlet and outlet for N2 gas. 1 mM solutions of compounds, i.e the compounds obtained in Examples 3, 4a and 4b, each in either 1 M sulfuric acid or 0.5 M sodium phosphate buffer of pH 7 electrolytes. Cyclic voltammograms were recorded at scan rates of 10 mVs−1, 20 mVs−1, 50 mVs−1, 100 mVs−1 and 250 mVs−1 at room temperature. Prior to measurements, the electrolyte was de-aerated by continuously purging with N2 gas for 10-15 minutes and maintaining a N2 flow-blanket throughout the experiment to minimize any environmental contamination. Also, 80% of the ohmic drop was compensated for during the experiment using a positive feedback-loop.
The CVs for the compounds obtained in Examples 4a and 4b revealed two pseudo-reversible redox processes in both the acidic and neutral electrolytes, see CVs for the compounds obtained in Example 4b displayed in
The CVs of “the compound obtained in Example 4a” in the acidic electrolyte at 1 mM concentration appeared to give a single but broad reduction and reverse oxidation peaks (CVs not shown). Further investigations were conducted by running CVs for 10 mM and 25 mM concentration of the compound in the acid electrolyte. These then revealed CV waves with two pairs of peaks almost merged together which is characteristic of two separate electron transfer steps with similar redox potentials. When “the compound obtained in Example 4a” was examined in the neutral electrolyte, the resolution of these pairs of peaks become more pronounced (CVs not shown). In the acidic electrolyte, the redox potential, E0′, was approximated to be −0.32 V vs. Ag/AgCl. In the neutral electrolyte, the two observed redox processes could be approximated to occur at potentials, E0′, −0.30 V vs. Ag/AgCl and −0.63 V vs. Ag/AgCl.
The compound obtained in Example 4b gave the most complicated CVs. Two observable pairs of peaks appeared at approximated potentials −0.13 V vs. Ag/AgCl and −0.38 V vs. Ag/AgCl in the acidic electrolyte. In the neutral electrolyte, the redox processes were observed at −0.05 V vs. Ag/AgCl and −0.65 V vs. Ag/AgCl. The broad cathodic and anodic peaks appearing respectively in the first and second redox processes coupled with the high capacitance made it difficult to evaluate peak-to-peak potential separations. Although the voltammograms are complex the systems are in total reversible.
Electrochemical Behaviour of the Target NDIs i.e. “Compound Obtained in Example 3”, “Compound Obtained in Example 4a”, and “Compound Obtained in Example 4b”
Different electrochemical behaviours were observed for the synthesized NDIs i.e. “compound obtained in Example 3”, “compound obtained in Example 4a”, and “compound obtained in Example 4b” in the acidic and neutral electrolytes. The redox potential of each compound showed dependency on pH. All compounds except for “the compound obtained in Example 3” displayed two redox waves characteristic of two separate electron transfer processes. “The compound obtained in Example 3” showing only one redox wave may be that the two-electron transfer processes occur simultaneously at similar potentials at a relatively fast rate. Effects of the different NDI core-substituents and the different background electrolytes can be seen by the shift of the redox potentials. Although the second redox processes for “compounds obtained in Examples 4a and 4b” appear to occur at the same potential, it is clear that the influences of the core substitutions are pronounced on the first redox process. The potential gap between the first and second redox waves narrows down by pushing the former wave to a more negative redox potential when moving from the electron withdrawing bromo-substituents on “compound obtained in Example 4b” to the electron donating amino-groups on “compound obtained in Example 3”. By comparing the compounds in the acidic electrolytes (red CV waves), “the compound obtained in Example 3” shows a redox potential which is more positive than that of “the compound obtained in Example 4a” but almost at the same potential as the first redox wave of the “compound obtained in Example 4b”. This is because in the acidic electrolyte, the amino substituents at the core of “the compound obtained in Example 3” are protonated causing a switch from their usual electron donating properties to electron withdrawing and eventually leading to a facile shift of the redox wave to a more positive potential than that of “the compound obtained in Example 4a”. In the neutral electrolyte (blue CV waves), the potential gap between the first and second redox processes for “the compounds obtained in Examples 4a and 4b” becomes relatively wider compared to their respective behaviours in the acidic electrolyte. The electron withdrawing bromo-substituents on “the compound obtained in Example 4b” influences the first redox wave to appear at a more positive potential than that of “the compound obtained in Example 4a” as a result of an inductive effect of the bromides.
Further, in
During discharge, the electrolyte solutions are pumped through an electrochemical cell consisting of two porous electrodes, which are separated by an ion-selective membrane. The molecules in the positive electrolyte, once they reach the surface of the porous electrode, get oxidized and give off electrons which are conducted through an external circuit and used as electricity. At the same time, the negative electrolyte receives electrons from the porous electrode on the cathodic side, and thus gets reduced. Since electrons have effectively been transported from one side of the cell to the other, a charge imbalance has arisen. To negate this, cation or a proton migrates through the membrane from the anodic (positive) to the cathodic (negative) chamber of the electrochemical cell. Thus,
The NDI may e.g. be dissolved in an acidic electrolyte, for example 1 M sulfuric acid.
The four different redox flow batteries were assembled according to table 4 below. For all four redox flow batteries, the negative electrolyte was based on NDI (denoted NDI-1) or modified NDI (denoted NDI-2) in a potassium chloride (KCl)-potassium phosphate (KPh) solution or NDI-1 and NDI-2 in an ammonium chloride (AmCl)-ammonium phosphate (AmPh) solution, while the positive electrolyte was based on BTMAP-Fc in a KCl-KPh solution and BTMAP-Fc in an AmCl-AmPh solution. NDI-1 and NDI-2 had the general structure according to formula III with the below listed specification:
The BTMAP-Fc had a structure according to formula IV:
NDI-1 had the specific formula: 2,7-bis(3-(dimethylamino)propyl)benzo[Imn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone and NDI-2 had the specific formula: 4,9-bis(dimethylamino)-2,7-bis(3-(dimethylamino)propyl)benzo[Imn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone. The first and second redox flow batteries had NDI-1 and the second and third redox flow batteries had NDI-2. The details of the composition of the first, second, third and fourth redox flow batteries are given in table 4 (the negative aqueous-based electrolyte corresponds to the second aqueous-based electrolyte and the positive aqueous-based electrolyte corresponds to the first aqueous-based electrolyte).
For each one of the four redox flow batteries, 10 ml of the negative electrolyte, and 20 ml of the positive electrolyte was used, to balance the capacities, and the concentration of the redox active materials (BTMAP-Fc, NDI-1 and NDI-2) was 50 mM for all the four redox flow batteries. Each one of the redox flow batteries were cycled (100 cycles) with a current density of 10 mA cm−2, and each cycle took between 1.5 and 2 hours.
The capacity utilizations of the four redox flow batteries shown in
As seen in
In summary, a significant capacity loss is observed for redox flow batteries number 1 and 3 over 100 cycles, while redox flow batteries number 2 and 4 instead show a slow capacity increase. Thus, the impact of the ammonium cation on the cycling stability is apparent for both NDI-1 and NDI-2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2050965-9 | Aug 2020 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2021/050814 | 8/19/2021 | WO |
