Method for continuous electrochemical reduction of nitrogen molecules

Abstract

A method of continuously electrochemically reducing a nitrogen molecule to produce ammonia, the method comprising: supplying a nitrogen molecule to an electrochemical cell comprising an electrolyte in contact with at least a cathode; introducing protons into the electrolyte by anodic oxidation of a hydrogen-containing species; and cathodically reducing the nitrogen molecule in the presence of a metal selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminium and vanadium to produce ammonia, wherein the electrolyte comprises a cationic proton carrier capable of reversible deprotonation to form a neutral proton acceptor, wherein the neutral proton acceptor is a silyl hydride.

Description

Technical Field

[0001] This invention relates to a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia. The method includes supplying nitrogen molecules to an electrochemical cell comprising an electrolyte in contact with at least a cathode, introducing protons into the electrolyte via anodic oxidation of a hydrogen-containing substance, and reducing the nitrogen molecules at the cathode in the presence of certain metals to prepare ammonia. The electrolyte comprises a cationic proton carrier capable of reversibly deprotonating to form a ylide proton acceptor. The invention also relates to a liquid electrolyte for electrochemical reduction reactions, its use in reduction reactions in an electrochemical cell, and a system for continuous electrochemical reduction reactions in an electrochemical cell including the electrolyte. Background of the Invention

[0003] Providing sufficient food and energy to meet the needs of the world’s growing population remains a persistent challenge for humanity. New technologies for fixing nitrogen molecules (N2) to form ammonia (NH3) offer potential solutions to both challenges: the synthesis of ammonia-based fertilizers is already crucial for global food production, while the high energy density of NH3 makes it a promising candidate as a transportable fuel or a carrier of renewable energy.

[0004] The invention of the Haber-Bosch process in the 20th century provided the first industrial route for the large-scale production of synthetic ammonia. However, due to the special stability of the nitrogen molecule's triple bond (N≡N, 942 kJ molar), [the process is challenging]. 1 The Haber-Bosch process requires extreme reaction conditions of high pressure (150 atm to 350 atm) and high temperature (400°C to 550°C), as well as a pure H2 supply typically derived from natural gas steam reforming. Therefore, this process consumes approximately 2% of the global energy supply and contributes about 1.5% of global greenhouse gas emissions. Consequently, there is an urgent need for technologies that utilize renewable resources to power the conversion of N2 to NH3.

[0005] The successful development of an electrochemical nitrogen reduction reaction (NRR) process will enable the direct conversion of renewable electricity into NH3 in a simple electrolytic cell. The cathode half-reaction of NRR is shown in equation (1):

[0006] N2+6H + +6e - →2NH3 (1)

[0007] Without relying on steam reforming, the protons required for NRR can be provided by the anodic oxidation of water (oxygen evolution reaction) or by H2 generated from a sustainable water separation process. Unfortunately, 6e- and 6H- are also present. + NRR is kinetically slow, and therefore electrochemically milder than the 2e- and 2H- shown in equation (2). +The hydrogen evolution reaction (HER) is at a disadvantage compared to NH3. Due to competition from HER, many reported electrochemical synthesis of NH3 suffers from very low Faraday efficiency and / or low NH3 yield.

[0008] 2H + +2e - →H2 (2)

[0009] DE102018210304 discloses a method for solving this problem, which uses suitable metals, including lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium, to form the corresponding nitrides. First, the metal is formed in its metallic form, preferably in a liquid state by electrolyzing a molten salt containing metal ions at high temperature, and then reacting it with N2 to form a metal nitride. Once the nitride formation is complete, it is separated and introduced into the anode chamber of an electrochemical cell that generates protons, ultimately producing ammonia. Because the metal nitride needs to be manipulated between different process environments, a complex multi-step process is generated, which is capital-intensive in terms of equipment and inefficient in terms of energy.

[0010] Another previously developed method, such as that reported by Tsuneto et al., Chemistry Letters 1993 851-854, is lithium-mediated continuous electrochemical ammonia synthesis. In typical Li-mediated continuous electrochemical NH3 synthesis reactions, the electrolyte system includes a Li salt, such as lithium trifluoromethanesulfonate (LiOtf), lithium perchlorate (LiClO4), or lithium tetrafluoroborate (LiBF4), and a proton carrier (or proton donor) in an organic solvent such as tetrahydrofuran. For the case where the proton source is anodic H2 oxidation, the proposed mechanism of the reaction is as follows: Figure 1 As shown. At the negative electrode 102, lithium ions (Li... + The lithium cation is reduced to metallic lithium (Li), which spontaneously reacts with nitrogen molecules (N2) to form lithium nitride (Li3N). Li3N is then protonated by a proton carrier (BH) present in the electrolyte to produce ammonia and a deprotonated proton carrier (B), thus regenerating lithium cations. At the anode 104, protons (H2) are generated through anodic oxidation with H2. + These protons protonate B in the electrolyte to regenerate the proton carrier (BH), thus completing the reaction cycle. Since protons only participate indirectly in the nitrogen reduction reaction, competition from HER is expected to be minimized.

[0011] The proton carrier molecule (BH) should react with Li3N to generate NH3, but ideally it should only be weakly acidic to reduce the rate of competitive reduction of protons to hydrogen molecules and / or hydrides. Currently, the most common proton carriers used in this process are ethanol and similar alcohols (e.g., methanol, isopropanol). Therefore, the proton carrier (BH) is typically a neutral substance such as CH3CH2OH, while its deprotonated form B is an anionic substance such as CH3CH2O-. Water is generally unsuitable as a proton carrier because of its high acidity and its lower acidity compared to Li3N. + It is reduced to H2 at the corrected potential of Li.

[0012] A major challenge in lithium-mediated electrochemical synthesis is the efficient regeneration of ethanol or other alcohol proton carriers, which has never been experimentally confirmed. If alcohols, which are typically more expensive than ammonia, are not fully recovered, they are uneconomically consumed as proton sources during synthesis. Anodic decomposition of alcohols is considered a parasitic process that exacerbates ethanol consumption in the battery.

[0013] Another problem is the formation of insoluble byproducts after the proton carrier is deprotonated at the cathode. These byproducts react with Li through anionic substances. + Precipitation forms as insoluble salts. The deposition of these materials leads to a rapid increase in the battery's internal resistance, thereby increasing the battery voltage required to drive the desired reaction. The anions generated by the deprotonation of alcohols such as ethanol are very strong bases and will react with Li... + Cations interact strongly to form salts with low solubility.

[0014] Therefore, there is a continued need for new methods for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, methods that at least partially address one or more of the aforementioned drawbacks, or provide useful alternatives.

[0015] References to patent documents or other matters given as prior art in this document should not be construed as an admission that such document or matter was known at the priority date of any claim or that the information contained therein is part of common general knowledge. Summary of the Invention

[0016] According to a first aspect, the present invention provides a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, the method comprising: supplying nitrogen molecules to an electrochemical cell comprising an electrolyte in contact with at least a cathode; introducing protons into the electrolyte by anodic oxidation of a hydrogen-containing substance; and reducing nitrogen molecules at the cathode to prepare ammonia in the presence of a metal selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium, wherein the electrolyte comprises a cationic proton carrier capable of reversibly deprotonating to form a neutral proton acceptor, wherein the neutral proton acceptor is a ylidene.

[0017] In some embodiments, cathodic reduction of nitrogen molecules involves reacting nitrogen molecules with a cationic proton carrier to prepare ammonia and form a neutral proton acceptor. The cationic proton carrier can then be regenerated in an electrolyte by protonating the neutral proton acceptor.

[0018] Reacting nitrogen molecules with a cationic proton carrier may include (i) reacting nitrogen molecules with a metal to form a metal nitride; and (ii) reacting the metal nitride with a cationic proton carrier to prepare ammonia and form a neutral proton acceptor.

[0019] In some implementations, the metal exists in the electrolyte as a metal cation.

[0020] In some implementations, the metal is lithium.

[0021] In some embodiments, the ylide contains a carbanion adjacent to a cation heteroatom selected from phosphorus, nitrogen, sulfur and oxygen.

[0022] In some implementations, the neutral proton acceptor is selected from... Yelid and Sulfond. In some implementations, the neutral proton acceptor is Ye Lide.

[0023] In some embodiments, the cationic proton carrier is selected from alkyl groups. Cations and alkylsulfonium cations. In some embodiments, the cation proton carrier is an alkyl group. Cation. Alkyl group. The cation can be tetraalkyl Cations, such as [PR 6 R 7 R 8 R 9 ] + Form, where R 6 R 7 R 8 and R 9 Independently selected from C1-C 20 n-alkyl group.

[0024] In some implementations, when contacted with lithium nitride, the cationic proton carrier can be deprotonated to form a neutral proton acceptor.

[0025] In some embodiments, the electrolyte is a non-aqueous liquid electrolyte. The non-aqueous liquid electrolyte may contain one or more molecular solvents. The molecular solvent may be selected from ethers, methylated polyethers, methylated glycol ethers, fluorinated ethers, fluorinated alkyl compounds, fluorinated cycloalkyl compounds, carbonates, sulfolane, and dimethyl sulfoxide. Alternatively or additionally, the non-aqueous liquid electrolyte may contain a room-temperature ionic liquid solvent, for example, in an amount of at least 50% by weight of the total solvent in the electrolyte.

[0026] In some implementations, the cationic proton carrier and the neutral proton acceptor are soluble in electrolytes.

[0027] In some embodiments, the cationic proton carrier is charged in the electrolyte by one or more electrochemically stable anions. One or more electrochemically stable anions may be selected from tetrafluoroborate, hexafluorophosphate, chloride, perchlorate, fluoroalkyl phosphates such as tris(pentafluoroethyl)trifluorophosphate, fluoroarylborates such as tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and tetrakis(pentafluorophenyl)borate, fluoroalkylborates such as tetrakis[hexafluoroisopropyl]borate, fluorinated bis(sulfonyl)imide such as bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide and (fluorosulfonyl)-(trifluoromethanesulfonyl)imide, and fluorinated sulfonates such as trifluoromethanesulfonate and other perfluoroalkyl sulfonates.

[0028] In some embodiments, the cationic proton carrier and the neutral proton acceptor are present in the electrolyte at a combined concentration of greater than 0.001 mol / L, or greater than 0.01 mol / L, or from 0.1 mol / L to 4 mol / L.

[0029] In some implementations, the hydrogen-containing substance is selected from hydrogen molecules and water.

[0030] In some embodiments, the method includes supplying nitrogen molecules to the electrochemical cell at a partial pressure greater than 1 bar, or greater than 5 bar, or preferably greater than 10 bar.

[0031] In some implementations, when the cathode reduces nitrogen molecules, the cathode potential is lower (more negative) than -2.0V vs Ag / Ag. + The potential can be lower than the reduction potential of the metal, that is, the potential from its cation to its metallic form.

[0032] According to a second aspect, the present invention provides a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, the method comprising: supplying nitrogen molecules to an electrochemical cell comprising an electrolyte in contact with at least a cathode; introducing protons into the electrolyte by anodic oxidation of a hydrogen-containing substance; and reducing nitrogen molecules at the cathode in the presence of lithium to prepare ammonia, wherein the electrolyte comprises a cationic proton carrier capable of reversibly deprotonating to form a neutral proton acceptor, wherein the cationic proton carrier is... Cations, neutral proton acceptors are Ye Lide.

[0033] According to a third aspect, the present invention provides a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, the method comprising: supplying nitrogen molecules to an electrochemical cell comprising an electrolyte in at least contact with a cathode; introducing protons into the electrolyte by anodic oxidation of a hydrogen-containing substance; and reducing nitrogen molecules at the cathode to prepare ammonia in the presence of a metal selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium, wherein the electrolyte comprises an alkyl group. At least one of a cation and an alkylsulfonium cation.

[0034] In some embodiments, the electrolyte comprises alkyl groups. Cation. Alkyl group. The cation can be tetraalkyl Cations, such as [PR 6 R 7 R 8 R 9 ] + Form, where R 6 R 7 R 8 and R 9 Independently selected from C1-C 20 n-alkyl group. In some embodiments, when in contact with lithium nitride, the alkyl group... Cations can be deprotonated to form ylides.

[0035] The relevant features relating to the first aspect of the invention also apply to the second and third aspects.

[0036] According to a fourth aspect, the present invention provides a liquid electrolyte for electrochemical reduction reactions, comprising: (i) a neutral proton acceptor, which is a ylidene; (ii) a cationic proton carrier capable of reversibly deprotonating to form a neutral proton acceptor; and (iii) a non-aqueous solvent.

[0037] In some embodiments, the liquid electrolyte further comprises: (iv) a metal cation selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum and vanadium.

[0038] In some embodiments, the ylide contains a carbanion adjacent to a cation heteroatom selected from phosphorus, nitrogen, sulfur and oxygen.

[0039] In some implementations, the neutral proton acceptor is selected from... Yelid and Sulfond. In some implementations, the neutral proton acceptor is Ye Lide.

[0040] In some embodiments, the cationic proton carrier is selected from alkyl groups. Cations and alkylsulfonium cations. In some embodiments, the cation proton carrier is an alkyl group. Cation. Alkyl group. The cation can be tetraalkyl Cations, such as [PR 6 R 7 R 8 R 9 ] + Form, where R 6 R 7 R 8 and R 9 Independently selected from C1-C 20 n-alkyl group.

[0041] In some embodiments, the cationic proton carrier is charged in a liquid electrolyte by one or more electrochemically stable anions. The one or more electrochemically stable anions may be selected from tetrafluoroborate, hexafluorophosphate, chloride, perchlorate, fluoroalkyl phosphates such as tris(pentafluoroethyl)trifluorophosphate, fluoroarylborates such as tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and tetra(pentafluorophenyl)borate, fluoroalkylborates such as tetrakis[hexafluoroisopropyl]borate, fluorinated bis(sulfonyl)imide such as bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide and (fluorosulfonyl)-(trifluoromethanesulfonyl)imide, and fluorinated sulfonates such as trifluoromethanesulfonate and other perfluoroalkyl sulfonates.

[0042] In some implementations, the liquid electrolyte is essentially water-free.

[0043] In some embodiments, the non-aqueous solvent comprises one or more molecular solvents. The molecular solvent may be selected from ethers, methylated polyethers, methylated glycol ethers, fluorinated ethers, fluorinated alkyl compounds, fluorinated cycloalkyl compounds, carbonates, sulfolane, and dimethyl sulfoxide.

[0044] In some embodiments, the non-aqueous solvent comprises a room-temperature ionic liquid solvent, for example, in an amount of at least 20% by weight or at least 50% by weight of the total non-aqueous solvent in the electrolyte.

[0045] In some implementations, when contacted with lithium nitride, the cationic proton carrier can be deprotonated to form a neutral proton acceptor.

[0046] According to a fifth aspect, the present invention provides a liquid electrolyte for electrochemical reduction reactions, comprising: (i) a neutral proton acceptor, which is... Ye Lide; (ii) cationic proton carrier, which is (iii) A cation, wherein the cationic proton carrier is reversibly deprotonated to form a neutral proton acceptor; and (iii) a non-aqueous solvent.

[0047] The relevant features relating to the fourth aspect of the invention also apply to the fifth aspect.

[0048] According to a sixth aspect, the present invention provides the use of a liquid electrolyte according to any embodiment of the third or fourth aspect for a reduction reaction in an electrochemical cell.

[0049] In some implementations, the neutral proton acceptor is protonated by protons generated by the anodic oxidation of a hydrogen-containing substance in an electrochemical cell to form a cationic proton acceptor, and the cationic proton acceptor is deprotonated in a reduction reaction to reform the neutral proton acceptor.

[0050] In some implementations, the reduction reaction is a continuous electrochemical reduction of nitrogen molecules mediated by a metal selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium.

[0051] According to a seventh aspect, the present invention provides a system for a continuous electrochemical reduction reaction, comprising an electrochemical cell including a cathode, an anode, and a power source for applying a voltage between the cathode and the anode; and a liquid electrolyte according to any embodiment of the third or fourth aspect, in contact with at least the cathode.

[0052] When the terms “comprising” or “including” are used in the specification (including the claims), they should be interpreted as specifying the said feature, integer, step or component, but do not exclude the presence of one or more other features, integers, steps or components or combinations thereof.

[0053] Other aspects of the invention are described below in the detailed embodiments. Attached Figure Description

[0054] This document will illustrate embodiments of the invention by way of example only with reference to the accompanying drawings, wherein:

[0055] Figure 1 A proposed mechanism for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia is schematically described.

[0056] Figure 2 A single-chamber electrochemical cell using H2 as a hydrogen-containing substance for continuous electrochemical reduction of nitrogen molecules according to an embodiment of the present invention is illustrated schematically.

[0057] Figure 3 A dual-chamber electrochemical cell for membrane separation using H2O as a hydrogen-containing substance for continuous electrochemical reduction of nitrogen molecules, according to an embodiment of the present invention, is described.

[0058] Figure 4 Example 2 illustrates the reaction of 0.2 M LiBF4 and 0.1 M [P] under N2 pressure. 666,14The results of cyclic voltammetry tests on the electrolyte of tetrahydrofuran (THF) solution [eFAP] were compared with those of the electrolyte of THF solution containing 0.2 M LiBF4 and 0.17 M ethanol.

[0059] Figure 5 In Example 3, the voltage was between -0.15V and -1.05V compared to Li / Li. + Using 0.2M LiBF4 and 0.1M [P] under N2 pressure 666,14 The graphs of ammonia yield and Faraday efficiency obtained from a series of chronoamperochemical experiments using [eFAP] as the electrolyte in THF solution are shown.

[0060] Figure 6 Example 4 illustrates the use of lithium trifluoromethanesulfonate (LiOTf) containing 0.2 M and 0.1 M [P] 666,14 The electrolyte of the THF solution of [eFAP] was subjected to N2 and H2 pressures at 4 mA / cm. -2 The battery stability results were obtained from a chronopotential electrochemical experiment with a constant applied current and compared with the results of an electrolyte containing a THF solution of 0.2 M LiOTf and 0.17 M ethanol.

[0061] Figure 7 A series of examples obtained in Example 5 are shown. 31 P NMR spectra proved [P 666,14 ] + The cation was deprotonated sequentially with lithium nitride and then reprotonated by a weak acid at 0.2 M [P]. 666,14 Reversible deprotonation of [eFAP] in THF solution.

[0062] Figure 8 In Example 9, 0.2 M LiBF4 and 0.1 M [P] were used. 666,14 [eFAP] electrolyte in THF solution at -0.75V vs Li / Li + The graph shows the ammonia yield and Faraday efficiency obtained from a series of time-ampere electrochemical experiments conducted at N2 pressures ranging from 2 bar to 20 bar. Detailed Implementation

[0063] Method for preparing ammonia by continuous electrochemical reduction of nitrogen molecules

[0064] This invention relates to a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, typically carried out in an electrochemical cell comprising a cathode, an anode, and a power source for applying a voltage between the cathode and the anode. The electrolyte in the electrochemical cell, at least in contact with the cathode, comprises a cationic proton carrier. The cationic proton carrier is reversibly deprotonated to form a neutral proton acceptor for ylide molecules. The method includes supplying nitrogen molecules to the electrochemical cell for the reaction; introducing protons into the electrolyte by anodic oxidation of a hydrogen-containing substance; and reducing nitrogen molecules at the cathode to prepare ammonia in the presence of a metal selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium. The metal may be present in the electrolyte and / or on the cathode surface. The cationic proton carrier provides protons for the preparation of ammonia and can therefore be deprotonated to form a neutral proton acceptor.

[0065] Without being bound by any theory, the ammonia synthesis reaction of this invention is proposed to proceed via a mechanism of lithium-mediated continuous ammonia synthesis as generally understood. According to this proposal, metal cations are reduced at the cathode to form the corresponding metal atoms, nitrogen molecules react with the metal atoms to form the corresponding metal nitride, and the metal nitride is then protonated by a cation proton carrier to prepare ammonia, forming a neutral proton acceptor and regenerating the metal cation. The cation proton carrier is continuously regenerated in the electrolyte by protonating the neutral proton acceptor, wherein protons are introduced into the electrolyte by oxidizing hydrogen-containing substances at the anode.

[0066] A key difference from conventional lithium-mediated ammonia synthesis is the use of cationic proton carriers and their corresponding neutral proton acceptors, particularly cationic proton carriers deprotonated to form ylide proton acceptors. This has been found to offer numerous advantages over neutral proton carriers, such as alcohols, which are deprotonated to form anionic proton acceptors.

[0067] These advantages can include lower initial cell resistance and increased cell stability. Furthermore, excellent Faraday efficiency and high reaction rates can be achieved. It has been suggested that the improved performance is at least partly due to the absence of any anionic substances in the reaction sequence. Indeed, in the synthesis of NH3, the only anion that must be present in the system is an intentionally introduced anion, particularly a counterion that serves as a proton donor for metal cations and / or cationic cations. These anions can be selected based on their cathode and anodic stability under electrochemical reaction conditions and their solubility in the electrolyte, thereby avoiding or minimizing anion degradation pathways.

[0068] The performance improvement may also be due to the tendency of cationic substances to be electrostatically attracted to the negative electrode. Therefore, cationic proton donors may be enriched in the electrolyte layer closest to the cathode, thereby improving their availability in protonation reactions on or near the cathode surface.

[0069] Continuous electrochemical reduction of nitrogen molecules can be distinguished from sequential electrochemical processes, in which nitrogen molecules are converted into ammonia in a series of temporally and / or spatially separated process steps, such as separate batches used in lithium electrolysis, lithium nitride formation, and ammonia production. As mentioned above, it has been proposed that continuous reduction involves one or more substances, including metallic substances and / or proton carrier substances, cycling between different forms in a single process step of synthesis.

[0070] Metal

[0071] The continuous electrochemical reduction of nitrogen molecules is mediated or catalyzed by a metal. It has been proposed that this synthesis involves metal nitride intermediates in a reaction cycle. Therefore, a range of metals capable of forming metal nitrides from nitrogen molecules under electrochemical reaction conditions can be used in this invention. Here, "metal" refers to a metallic element and does not imply a specific reduced state or substance. When the zero-oxidation-state metallic form of a metal is specifically identified, for example in the context of the proposed reaction mechanism, this will be referred to as its "metallic form" or "metal atom".

[0072] According to the previously proposed mechanism, the electrochemical reduction of metal cations produces metal atoms at the cathode, which then spontaneously react with N₂ to produce the corresponding metal nitride. Therefore, under the conditions of ammonia electrosynthesis, the latter reaction should be thermodynamically favorable (generally speaking). The negative Gibbs energy). Based on the list of thermodynamic data (e.g., LBPankratz et al., Thermodynamic Data for Mineral Technology, Washington D.C., 1984; John R. Rumble, CRC Handbook of Chemistry and Physics 101st Edition, 2020), published theoretical calculations (e.g. According to [Authors' names], in Energy Environ. Sci., 2017, 10, 1621-1630 and experimental reports (e.g. DE102018210304), suitable metals include lithium, magnesium, calcium, strontium, barium, zinc, aluminum and vanadium.

[0073] In some implementations, the metal comprises or is composed of lithium. Lithium is considered particularly suitable because it has been shown to activate nitrogen molecules at ambient temperatures.

[0074] During reduction, metals can exist as metal cations dissolved in the electrolyte, such as Li. +As mentioned above, we believe the reaction cycle involves the reduction of metal cations from the electrolyte, the formation of metal atoms on the cathode, and the regeneration of the metal cations as the final step in the cycle. However, it is also thought that the cycle may occur through a continuous reaction between the metal and solid matter (e.g., metal nitrides and metal atoms) on the cathode surface, without soluble metal cations as intermediates. Therefore, in the case of lithium, the cathode reaction mechanism may in principle involve (i) the chemical reaction of lithium atoms with nitrogen molecules on the cathode to form lithium nitride, and (ii) the direct electrochemical reduction of lithium nitride in the presence of a proton donor, directly regenerating lithium atoms and producing ammonia (i.e., Li3N + 3HB + 3e). - =NH3 + 3Li(0) + 3B - ).

[0075] The concentration of the metal cation in the electrolyte can be greater than 0.001 mol / L, or greater than 0.01 mol / L, or greater than 0.1 mol / L. The upper limit of the concentration is considered to be limited only by the solubility of the precursor metal salt in the electrolyte medium. In some embodiments, the concentration of the metal cation in the electrolyte is from 0.1 mol / L to 4 mol / L, for example, about 0.2 mol / L.

[0076] Metals are most conveniently introduced into electrochemical cells in the form of cations, for example, by dissolving a suitable metal salt in the electrolyte. However, the introduction of metals as metal nitrides or even in their metallic form is not excluded. Assuming that metal cations participate in the reaction cycle, they can be generated in situ from these substances in the electrolyte.

[0077] Cation proton carrier - Yelide proton acceptor

[0078] The electrolyte also contains a cationic proton carrier capable of reversible deprotonation to form a neutral proton acceptor. Both the proton carrier and the proton acceptor are typically organic substances. As used herein, reversible deprotonation means that the cationic proton carrier can be deprotonated to form a neutral proton acceptor, and the neutral proton acceptor can be reprotonated to regenerate the cationic proton carrier.

[0079] Consistent with the proposed mechanism, cationic proton carriers can be deprotonated to neutral proton acceptors via reaction with metal nitrides such as Li3N, preferably in solution at room temperature. Neutral proton acceptors can be protonated to form cationic proton carriers via reaction with free protons and / or organic acids, preferably in solution at room temperature. The inventors have found that such reactions can be a convenient way to evaluate cationic proton carrier-neutral proton acceptor candidates.

[0080] The neutral proton acceptor molecule is the ylide, which is a neutral dipole molecule containing an atom with a formal negative charge directly attached to a heteroatom with a formal positive charge. Therefore, the ylide is a zwitterion.

[0081] Unwilling to be bound by any theory, it is believed that a suitable ylide can reversibly interconvert with a proton donor via protonation and deprotonation reactions as needed, since the negatively charged electrons partially share the empty orbitals at the positive center. This is thought to provide the protonated form with the acidity within the weak acid range required for the proton donor in metal-mediated continuous ammonia synthesis.

[0082] In some embodiments, the ylide contains a carbanion adjacent to a positively charged heteroatom. Therefore, the proton-carrying site on the molecule is a carbon atom that transitions between a deprotonated carbanion and a protonated CH covalent bond. The positively charged (or cation) heteroatom of the ylide can be selected from phosphorus, nitrogen, sulfur, and oxygen.

[0083] In some implementations, the cation proton donor is Cations or sulfonium cations, neutral proton acceptors are the corresponding Yelide or sulfonium yelide. In some embodiments, the proton donor is... Cations, neutral proton acceptors are the corresponding Ye Lide.

[0084] In some implementations, the cationic proton carrier is an alkyl group. Cations or alkylsulfonium cations, with neutral proton acceptors being the corresponding... Yelide or sulfonium yelide. As used herein, alkyl A cationic or alkylsulfonium cationic refers to a cation containing at least one optionally substituted alkyl group. Cation or sulfonium cation. In some embodiments, the cation proton donor is an alkyl group. Cations, neutral proton acceptors are the corresponding Ye Lide. Alkyl Cations can typically be deprotonated to form Carbon anion ylide (R')3P + –C - Any such substance of (R”)2, wherein each R’ and R” organic alkyl group may be the same or different.

[0085] alkyl The deprotonation of cations to form ylides is known in synthetic organic chemistry, where ylides are commonly referred to as Wittig reagents. In many synthetic reaction schemes, Carbanion ylides can be used as nucleophiles. For example, in the Wittig reaction, Yerlide reacts with carbonyl groups via a [2+2] cycloaddition to form oxophosphorus heterocyclic butanes, which are then eliminated to generate alkenes and phosphine oxides. Synthetic reactions with yerlide reagents are typically driven by the irreversible conversion of reactive yerlides to stable substances such as phosphine oxides.

[0086] In contrast, the embodiments of the present invention use Yelide, as a reversible proton shuttle, intercepts protons in the electrolyte and transports them for protonation reactions with nitrogen to form ammonia.

[0087] Many alkyl groups are considered Cations are suitable for this invention, provided they are readily and reversibly deprotonated into ylide proton acceptors, as shown in Scheme 1, for example. Therefore, alkyl groups... Cations can have the structure of Formula I, and the corresponding ylides have the structure of Formula II:

[0088]

[0089] Option 1

[0090] In some implementation schemes, R 1 R 2 R 3 Independently selected from alkyl groups (e.g., C1 to C2). 20 (n-alkyl) and aryl (e.g., phenyl), R 4 Choose brain hydrogen, alkyl (e.g., C1 to C2) 20 (n-alkyl) and aryl (e.g., phenyl), R 5 Selected from hydrogen, alkyl (e.g., C1 to C1) 19 Alkyl), cycloalkyl (e.g., C3 to C6 cycloalkyl), alkyl (e.g., C1 to C6 cycloalkyl) 19 Alkyl groups or cycloalkyl groups substituted with halogens, ether groups, ester groups, acyl groups, amino groups, and cyano groups; aryl groups (e.g., phenyl groups containing -C6F5); ester groups (e.g., -C(=O)O (C1 to C6 alkyl); amide groups (e.g., C(=O)NHC6F5, C(=O)N(Me)OMe); cyano groups (-CN); halogens; ether groups (e.g., -O (C1 to C6 alkyl); thioether groups (e.g., -S (C1 to C5 alkyl), SC6F5); -PR 10 R 11 and -P(=O)R 12 R 13 , where R 10 To R 13 Independently alkyl (e.g., C1 to C6) alkyl and aryl (e.g., -C6F5). R 1 To R 4 The alkyl and aryl groups in any one of them may be unsubstituted or substituted with substituents such as halogens, ethers, hydroxyl groups, esters, acyl groups, amino groups, and cyano groups, and R1 To R 4 Any two of them can be connected to form a ring structure.

[0091] As those skilled in the art will recognize, the group R can be selected. 1 To R 5 Especially R 5 To control alkyl The acidity of the cation controls its proton-donating ability.

[0092] In some implementation schemes, R 1 R 2 and R 3 Independently selected from C1 to C 20 n-alkyl and phenyl, R 4 It is hydrogen, R 5 Selected from hydrogen and C1 to C 19 n-alkyl group.

[0093] In some implementations, alkyl The cation is an ionic liquid cation, meaning that when paired with a suitable counterion, it is capable of forming an ionic liquid, such as a room-temperature ionic liquid. As used herein, ionic liquids are salts with a melting temperature below 100°C, while room-temperature ionic liquids have a melting temperature below approximately 25°C. Such cations are preferred due to their high solubility / miscibility with other solvents and salts in electrolytes, as well as their high conductivity. A series of general formulas I... Cations (including tetra-alkyl) Cations and counterions such as BF4 - PF6 - Fluoroalkyl phosphates, including tris(pentafluoroethyl)trifluorophosphate (eFAP), fluoroalkyl borates such as tetra[hexafluoroisopropyl]borate, fluorinated bis(sulfonyl)imides including bis(fluorosulfonyl)imides and bis(trifluoromethanesulfonyl)imides (TFSI) and (fluorosulfonyl)-(trifluoromethanesulfonyl)imides, and fluorinated sulfonates including trifluoromethanesulfonates, combined with other perfluoroalkyl sulfonates, form ionic liquids. In the prior art, this type of ionic liquid has been used for nitrogen reduction without dissolving metal cations (e.g., MacFarlane et al., WO2017 / 132721A1); however, at the cathode potentials disclosed in the prior art, these ionic liquids do not show any tendency to deprotonate. At the more pronounced negative potentials required for the invention, such as -2.0 V to Ag / Ag... + More negative, in order to achieve the formation of metal nitrides, these ionic liquids can become active proton donors.

[0094] In some implementations, the cationic proton carrier is an alkyl group. Cation. Tetraalkyl Cations can have [PR] 6 R 7 R 8 R 9 ] + The structure, where R 6 R 7 R 8 and R 9 Independently selected from C1 to C 20 n-alkyl. In some embodiments, R 6 R 7 R 8 and R 9 The total number of carbon atoms is at least 7, at least 13, or at least 16. As those skilled in the art will understand, tetra-alkyl... Increasing the chain length of a cation typically increases its solubility in organic media, lowers the melting point of its salt, and reduces its tendency to absorb or dissolve water. In some embodiments, R 6 R 7 and R 8 Independently selected from C4 to C 20 n-alkyl, R 9 C1 to C 20 n-alkyl group.

[0095] During continuous NH3 synthesis, especially under steady-state or near-steady-state operating conditions, the electrolyte typically comprises a mixture of cationic proton carriers and ylide proton acceptors. If other materials (e.g., Li, Li3N, LiH) do not accumulate, a continuously operating cell will reach a stable relative concentration of the two substances when proton production at the anode is perfectly matched with proton consumption at the cathode (as desired NH3 or byproducts such as H2). In fact, the presence of both substances in the electrolyte is understood to produce the desired buffering effect. This buffering allows the proton carrier to absorb excess protons produced at the anode during start-up and / or intermittently driven current variations. Furthermore, the use of a significant concentration of ylide proton acceptors in the electrolyte ensures that a high proportion of protons are intercepted and consumed by the ylide before they could participate in undesirable cathode reactions such as HER.

[0096] In some embodiments, the proton carrier system is introduced into the chemical cell in its cationic form, for example, by dissolving a suitable salt of the cationic proton carrier material in the electrolyte. However, it should be understood that a cationic proton donor or a corresponding ylide proton acceptor can be supplied to the electrochemical cell to facilitate the NH3 synthesis reaction; a mixture of the two substances can be formed in situ in both of the aforementioned cases.

[0097] The combined concentration of the cationic proton donor and its corresponding Yeride proton acceptor in the electrolyte can be greater than 0.001 mol / L, or greater than 0.01 mol / L, or greater than 0.05 mol / L. In some embodiments, for example when the electrolyte solvent is primarily a molecular organic solvent, the combined concentration is from 0.05 mol / L to 1 mol / L, for example, about 0.1 mol / L. In other embodiments, for example, in a solution based on… When the ionic liquid constitutes a significant proportion in the electrolyte solvent, the combined concentration of the cation proton donor and its corresponding ylide proton acceptor can be significantly higher.

[0098] Given the proposed reaction mechanism, it is understood that the total concentration of the metal cation and the cationic proton carrier is expected to remain constant during the electrochemical synthesis of NH3, although the ratio of these two substances may vary under different steady-state conditions. In some embodiments, the concentrations of the metal cation and the cationic proton carrier present in the electrolyte may be greater than 0.001 mol / L, or greater than 0.01 mol / L, or greater than 0.1 mol / L. The combined concentration may be from 0.1 mol / L to 4 mol / L, or from 0.1 mol / L to 1 mol / L, for example, about 0.3 mol / L.

[0099] Electrochemically stable anions

[0100] The electrolyte contains one or more anions to balance the cationic substances present in the electrolyte, including metal cations and cationic proton carriers. Preferably, the anion is an electrochemically stable anion. As used herein, an electrochemically stable anion is an anion that exhibits acceptable stability to the cathodic or anodic reaction under conditions of continuous electrochemical reduction of nitrogen molecules, or is not significantly affected by it.

[0101] As already mentioned, significant advantages are believed to be achieved in the method of the present invention because anionic substances do not participate in the reaction pathway. Therefore, anions present in the electrolyte, including anions required for charge-balancing metal cations and cationic proton carriers, can be selected due to their cathode and anodic stability under electrochemical reaction conditions and their solubility in the electrolyte, thereby avoiding or minimizing anionic degradation pathways.

[0102] In the fields of electrochemical synthesis and ionic liquids, a variety of electrochemically stable anions are known, and any such anion or combination thereof is considered suitable for the methods of the present invention. Non-limiting examples of suitable anions include tetrafluoroborate, hexafluorophosphate, perchlorate, fluoroalkyl phosphates such as tris(pentafluoroethyl)trifluorophosphate, fluoroarylborates such as tetra[3,5-bis(trifluoromethyl)phenyl]borate and tetra(pentafluorophenyl)borate, fluoroalkylborates such as tetra[hexafluoroisopropyl]borate, fluorinated bis(sulfonyl)imides such as bis(fluorosulfonyl)imides and bis(trifluoromethanesulfonyl)imides and (fluorosulfonyl)-(trifluoromethanesulfonyl)imides, and fluorinated sulfonates such as trifluoromethanesulfonates and other perfluoroalkyl sulfonates (e.g., perfluorohexanesulfonates). In some embodiments, such as when the anodic reaction is H2, chloride ions are considered sufficiently stable for anodic oxidation and can therefore also be used.

[0103] Electrochemically stable anions can be introduced into electrolytes along with metal cations, i.e., as metal salts, or along with proton donors, or both.

[0104] solvent

[0105] The electrolyte is typically a non-aqueous liquid electrolyte and therefore may contain one or more non-aqueous solvents. Suitable non-aqueous solvents are typically aprotic solvents and may include aprotic molecular solvents and ionic solvents, such as room-temperature ionic liquids. Preferably, the solvent is stable under the reaction conditions, or degrades to a very small extent at most.

[0106] Ideally, non-aqueous solvents are good solvents for key substances participating in the reaction cycle, including metal cations, cationic proton carriers, and ylide proton acceptors. It should be noted that the solubility of cationic substances in a particular solvent can be increased by the judicious selection of counterions and by designing the cationic proton carrier systems disclosed herein. Therefore, many aprotic solvents may be suitable in embodiments of the invention.

[0107] In some embodiments, the non-aqueous liquid electrolyte comprises one or more molecular solvents selected from ethers, methylated polyethers, methylated ethylene glycol ethers such as tetraethylene glycol, fluorinated ethers, fluorinated alkyl compounds, fluorinated cycloalkyl compounds, carbonates, sulfolane, and dimethyl sulfoxide.

[0108] In some embodiments, the non-aqueous ionic electrolyte comprises a room-temperature ionic liquid solvent, for example, in an amount of at least 20% by weight or at least 50% by weight of the total non-aqueous solvent in the electrolyte. A variety of room-temperature ionic liquids are considered suitable solvents for electrochemical synthesis, such as those disclosed in WO2017 / 132721, and such solvents are generally applicable to the methods currently disclosed.

[0109] Therefore, in some embodiments, the room-temperature ionic liquid solvent includes:

[0110] (i) at least one selected from PR 1-4 NR 1-4 (tetraalkylammonium), C4H8NR2 (pyrrolidine) The cation of ), wherein each R group is independently linear, branched, or cyclic, and preferably contains 1 to 18 carbon atoms, optionally partially or completely halogenated, optionally containing heteroatoms, optionally containing functional groups selected from ether, hydroxyl, carbonyl (acetate), mercapto, thioyl, sulfonic acid, amino, azo, or cyano groups, and wherein two R groups may be linked to form a monocyclic or heterocyclic ring; and

[0111] (ii) at least one selected from (R'O) x PF 6-x (phosphate), (R'O) x BF 4-x (Borate), R'SO2NSO2R' (imine), R'SO2C(SO2R')(SO2R') (methyl compound), FSO2NSO2F, C2O4BF2, C2O4PF4, RC2O4BF2, RC2O4PF4, CF3SO3 (trifluoromethanesulfonate), R'SO3 (sulfonate), R'CO2 (carboxylate), CF3COO (trifluoroacetate), R' X PF 6-x (FAP), R' x BF 4-x The anion, wherein each R' group is independently linear, branched, or cyclic, and preferably contains 1 to 18 carbon atoms, optionally partially or fully fluorinated, and optionally contains a functional group selected from ether, hydroxyl, carbonyl (acetate), mercapto, thioyl, sulfonic acid, amino, azo, or cyano groups, and wherein two R' groups may be linked to form a monocyclic or heterocyclic ring. In each case, x is zero to the maximum possible number of covalent bonds at the central atom.

[0112] In some implementations, the ionic liquid solvent is stable under the conditions of electrochemical NH3 synthesis, i.e., it is essentially unreacted.

[0113] In other embodiments, at least one cation of the ionic liquid solvent is a cationic proton carrier material capable of reversible deprotonation to form a ylide proton acceptor. Examples of such ionic liquids are those with tetra-alkyl groups as disclosed herein. Those that are cations. Based on the principles disclosed herein, it is envisioned that... The ionic liquid solvent can facilitate the metal-mediated continuous electrochemical reduction of nitrogen molecules to ammonia in the absence of water. The electrolyte solvent can consist of an ionic liquid solvent with reactive cations. Alternatively, an ionic liquid solvent with a mixture of reactive and stable cations, or a mixture of reactive ionic liquids and stable molecular solvents, can be used.

[0114] The electrolyte is preferably substantially anhydrous, meaning that the amount of water is zero or sufficiently low to avoid significantly interfering with the reaction cycle of the metal-mediated continuous electrochemical NH3 synthesis reaction as disclosed herein. For example, the electrolyte may contain no more than 1000 ppm, preferably less than 100 ppm, and most preferably less than 20 ppm of water.

[0115] The electrolyte can have a sufficiently low or acceptablely low viscosity to avoid mass transfer limitations. In some embodiments, the non-aqueous electrolyte has a viscosity of less than 50 MPa s, or less than 20 MPa s, or less than 15 MPa s at 25 °C. This viscosity can be measured using a Lovis 2000M Anton Paar viscometer (Lovis angle 30°) according to ISO 12058.

[0116] Supply nitrogen molecules to reduce to ammonia

[0117] The method of the present invention includes supplying nitrogen molecules to an electrochemical cell containing an electrolyte in contact with at least the cathode, and reducing the nitrogen molecules at the cathode in the presence of a metal to prepare ammonia.

[0118] It should be understood that, as used herein, “cathodic reduction” does not imply any specific mechanism, specify any intermediate substances involved in the reaction cycle, or suggest where such substances react (e.g., at the cathode surface or in the bulk electrolyte). However, it is not intended to impose any theoretical constraints, but rather to suggest that the terms used herein are appropriate. Figure 1 The disclosed mechanism reduces nitrogen molecules to ammonia at the cathode. As generally disclosed herein, in this invention, a proton donor ( Figure 1 BH in the text is a cationic proton carrier (YH). + ), proton acceptor ( Figure 1 B) is the corresponding neutral ylide molecule (Y). Therefore, the entire cathode nitrogen reduction reaction is considered to be as shown in equation (3):

[0119] N2+6Y-H + +6e - →2NH3+6Y (3)

[0120] Therefore, the cathode can be positioned at a potential suitable for driving the cathode reaction. In particular, the potential can be lower (more negative) than the reduction potential of the corresponding reduced form of the metal cation, such as the metallic form and / or metal nitride (e.g., Li).+ / Li reduction potential). This reduction potential can be determined as the apparent reduction potential of a metal cation in a non-aqueous electrolyte under nitrogen molecule reduction conditions, as measured by cross-point measurement in cyclic voltammetry.

[0121] In some embodiments, the cathode potential is lower (more negative) than -0.2V or -0.4V relative to the apparent reduction potential of the metal cation in the non-aqueous electrolyte. Excellent yields and Faraday efficiencies can be obtained at such potentials. However, in some embodiments, the cathode potential is higher (corrected) than -1V or -0.8V relative to the apparent reduction potential of the metal cation in the non-aqueous electrolyte.

[0122] Nitrogen molecules can be supplied to the electrochemical cell at partial pressures greater than 1 bar, or greater than 5 bar, or greater than 10 bar. In some embodiments, nitrogen molecules are supplied at partial pressures of 0.7 bar to 100 bar, or 2 bar to 30 bar, or 5 bar to 20 bar. Increasing the partial pressure of N2 in the cell can improve the Faraday efficiency of ammonia synthesis by increasing the concentration of N2 dissolved in the electrolyte. This is believed to favor the desired reaction between N2 and the metal to form metal nitrides.

[0123] By contacting the electrolyte with nitrogen molecules, thereby dissolving the nitrogen molecules in the electrolyte, nitrogen molecules can be supplied to the electrochemical cell for cathode reduction. In some embodiments, nitrogen molecules are predominantly or entirely present in the solution phase when exposed to the cathode. Additionally, nitrogen gas can pass through the cathode, forming a three-phase interface between the electrode, gas, and electrolyte.

[0124] The electrolyte can be maintained at a suitable temperature to promote ammonia synthesis. This temperature can range from -35°C to 200°C, for example, from 15°C to 100°C.

[0125] The product ammonia is expected to be in the electrolyte as NH3 instead of NH4. + It appears in the form of ammonium cations because ammonium cations are more readily accepted than the cationic proton carriers of this invention (such as alkyl groups). A stronger acid. However, if an excess of protons is produced, the possibility of generating some NH4+ cannot be ruled out. + Ammonia in various forms.

[0126] Anodizing

[0127] The method of this invention involves introducing protons into an electrolyte via the anodization of a hydrogen-containing substance. Based on the principles disclosed herein, it is anticipated that the protons will react with a ylide proton acceptor in the electrolyte to regenerate the cation proton carrier. It is believed that the ylide, rather than the proton itself, is the primary protonating agent involved in the nitrogen reduction reaction.

[0128] Protons can be generated at the anode of an electrochemical cell by oxidizing any suitable hydrogen-containing substance, including hydrogen molecules (H2) and water (H2O). The anodic half-reactions of these reactants are shown in equations (4) and (5), respectively.

[0129] H2→2H + +2e - (4)

[0130] 2H₂O→O₂+4H + +4e - (5)

[0131] Therefore, in order to balance equation (3), the entire anodic regeneration process of the proton carrier can be shown as in equation (6) or equation (7), where Y is the ylide proton acceptor, YH + It is a cationic proton carrier:

[0132] 3H2 + 6Y → 6Y - H + +6e - (6)

[0133] 3H₂O + 6Y → 3 / 2O₂ + 6Y-H + -6e - (7)

[0134] In cases where H2 is oxidized to produce protons, an electrolyte containing a proton carrier can be contacted with both the cathode and anode. Therefore, protons are directly introduced into the electrolyte as they form at the anode. H2 can be obtained from any source, including water electrolysis using renewable energy sources. Optionally, the water electrolysis cell can be integrated with a nitrogen reduction cell to supply H2 directly from electrolysis to nitrogen reduction.

[0135] Water is a particularly desirable proton source in electrochemical synthesis due to its low cost, but it is known to interfere with metal-mediated sequential electrochemical reduction. Therefore, in cases where H₂O is oxidized to produce protons, indirect transfer of protons from the anode to an electrolyte containing a cationic proton carrier may be preferred. This can help to acceptably limit or avoid the presence of water in the electrolyte where nitrogen reduction occurs. For example, an electrochemical cell may comprise two electrolytes: a cathode electrolyte containing a cationic proton carrier (as generally disclosed herein) and an anolyte (liquid, solid, or solid-liquid mixture) in contact with the anode, where water is oxidized. The electrochemical cell is configured to allow proton transfer from the anolyte to the cathode electrolyte but substantially limit or avoid water transfer. Various arrangements for achieving this are known in the field of electrochemical synthesis, which will be explained in more detail below.

[0136] Due to competition from the HER at the cathode, H2 is typically an important byproduct of the nitrogen reduction reaction. The H2 byproduct can optionally be recycled for cathode oxidation, supplementing the feed of selected hydrogen-containing substances. This results in reduced energy consumption per unit of ammonia produced, as there are no other energy-intensive byproducts.

[0137] Electrochemical batteries

[0138] The method of the present invention is typically carried out in an electrochemical cell comprising a cathode, an anode, and a power source connected to the cathode and anode. The power source is configured to apply a voltage between the cathode and anode sufficient to drive electrochemical ammonia synthesis.

[0139] The cathode can typically be any conductive electrode that is stable at the desired reduction potential, such as the metal electrode used in previously reported lithium-mediated continuous electrochemical synthesis (e.g., Tsuneto et al., Chemistry Letters 1993, 851-854), or other methods involving the reduction of metal cations to their metallic form. Non-limiting examples of suitable metals may include Ni, Nb, Ti, Mo, Fe, Cu, Ag, and Zn, and alloys thereof. In some embodiments, a copper (Cu) cathode is used. In other embodiments, the metal of the cathode comprises or consists of a metal used in the mediated ammonia synthesis.

[0140] The cathode can be cylindrical, disk-shaped, plate-shaped, or other shapes suitable for the battery design. The cathode can also be porous, for example, achieved through etching, or constructed as a foam or compressed granular mass, or through an inverse opal structure. The desired dielectric metal can also be coated onto the underlying structure, providing optimal roughness and porosity, for example, by electrodeposition or chemical deposition. The cathode can also be formed by depositing metal nanoparticles into other inert structures.

[0141] Suitable anodes for oxidizing hydrogen-containing substances (such as H2O or H2) to form protons are well known in the field of electrochemistry. In some embodiments, the anode is a platinum electrode.

[0142] The power source can be any conventional power source used in electrolysis systems, such as a DC power source. Optionally, the power source may include photovoltaic solar cells. A particular advantage of the invention is considered to be that ammonia can be produced from electricity, particularly renewable electricity. For example, the invention is contemplated to allow the production of ammonia-based fertilizers using solar or wind power when needed; this could be especially valuable for high-value agricultural applications (such as hydroponics) or for minimizing the logistical challenges of transporting fertilizers to remote areas.

[0143] Figure 2An embodiment of an electrochemical cell for implementing embodiments of the present invention is schematically depicted. Cell 200 includes a copper cathode 210 in a cell chamber 211. Cell 200 also includes a platinum anode 212 and an optional conventional type reference electrode 213, such as Ag / Ag. + The three electrodes are immersed in the same non-aqueous liquid electrolyte 214, as generally disclosed herein, comprising lithium cations and cationic proton carriers. Optionally, a stirrer or other means for mixing or circulating the electrolyte may be included to provide enhanced mass transfer in the cell chamber 211. The electrodes are connected to a power source (not shown) capable of applying a voltage between the cathode 210 and the anode 212, and the reduction potential of the cathode is controlled (or measured) relative to a reference electrode.

[0144] The battery 200 also includes a gas inlet 215 for introducing a gas mixture 218 containing nitrogen molecules (N2) and hydrogen molecules (H2) into the chamber 211. The battery may include a gas outlet 216 for removing gas 219 from the top space of the chamber, an electrolyte inlet 220 for replenishing electrolyte with electrolyte feed 222, and an electrolyte outlet 221 for recovering electrolyte 214. Preferably, the battery is configured to operate under elevated pressure.

[0145] In use, the gas mixture 218 is pressurized into chamber 211 via feed inlet 215, and an application sufficient to establish a pressure below (more negative) Li at cathode 210 is applied between the cathode and anode. + The voltage of the reduction potential of / Li. The partial pressure of nitrogen molecules in cell 211 can be greater than 10 bar, while the partial pressure of hydrogen molecules is greater than 1 bar. According to the principles disclosed herein, the current generated by the cell causes the nitrogen molecules to be electrochemically reduced to ammonia. The ammonia product can be continuously or periodically removed from cell 211 through gas outlet 216 in gas 219 and / or through electrolyte outlet 221 in electrolyte 214.

[0146] In some embodiments, the battery operates in a steady state by continuously venting one or both of these streams and continuously replenishing gaseous reactants (N2 and H2) and / or electrolytes as needed by introducing gas mixture 218 and / or electrolyte feed 222. Ammonia can be separated from the vented gas stream 219 and / or electrolyte 214, and residual gas and electrolyte can be recycled back to battery chamber 211 as part of gas mixture 218 and electrolyte feed 222, respectively. A portion of the electrolyte 214 vented through electrolyte outlet 221 can be discarded (or regenerated) and replaced with fresh electrolyte in feed 222, thereby maintaining the target electrolyte residence time in the battery.

[0147] In one embodiment of the point-of-use fertilizer generation battery, the exhaust gas stream 219 passes through an aqueous sulfuric acid solution or an aqueous phosphoric acid solution to absorb ammonium (NH4).+ Ammonia is produced in the form of ammonium salts of the acid used, such as ammonium sulfate solution, which can be applied directly as a fertilizer solution. In hydroponics or commercial greenhouses, the battery can be controlled to continuously supply fertilizer to the plants' water supply.

[0148] Figure 3 Another embodiment of an electrochemical cell for implementing embodiments of the present invention is schematically depicted. Cell 300 includes a cathode chamber 311 and an anode chamber 331, separated by a proton-permeable membrane separator 333, such as a membrane made of a sulfonated poly(tetrafluoroethylene) ionomer like Nafion. A copper cathode 310 is disposed in the cathode chamber 311. A reference electrode 313 of a conventional type is also disposed in the cathode chamber. A platinum anode 312 is disposed in the anode chamber 331. The electrodes are connected to a power source (not shown) capable of applying a voltage between the cathode 310 and the anode 312, and the reduction potential of the cathode is controlled (or measured) relative to the reference electrode.

[0149] Cathode 310 and reference electrode 313 are immersed in cathode electrolyte 314, while anode 312 is immersed in anode electrolyte 334. Cathode electrolyte 314 is a non-aqueous liquid electrolyte comprising lithium cations and cationic proton carriers as generally disclosed herein, and is substantially free of water. Anode electrolyte 334 contains water for oxidation at the anode, but may otherwise be the same as or different from the composition of cathode electrolyte 314. Membrane separator 333 inhibits or substantially prevents the transport of substances other than protons between the cathode and anode reaction chambers.

[0150] The battery 300 also includes a gas feed inlet 315 for introducing nitrogen molecule feed 318 into the cathode chamber 311. The battery may include a cathode gas outlet 316 for removing gas 319 from the top space of the cathode chamber, a cathode electrolyte inlet 324 for replenishing the cathode electrolyte with cathode electrolyte feed 325, and a cathode electrolyte outlet 321 for discharging the cathode electrolyte. The battery 300 may include an anode inlet 340 for introducing or replenishing anode electrolyte 334, and optionally also for introducing one or more hydrogen-containing substances into the anode chamber 331 (e.g., H2O and / or H2 as liquids or vapors). An anode electrolyte outlet 341 is provided for discharging the anode electrolyte 334, and an anode gas outlet 344 is provided for discharging gas 345 from the top space of the anode chamber.

[0151] In operation, nitrogen molecules 318 are pressurized into the cathode chamber 311 via the gas feed inlet 315. The partial pressure of nitrogen molecules in the cathode chamber 311 can be greater than 10 bar. Water may initially be present in the anolyte 344 and / or fed into the anode chamber via the anode inlet 340. An application sufficient to establish a pressure below (more negative than) Li at the cathode 310 is applied between the cathode and anode. +The voltage of the reduction potential of / Li. According to the principle disclosed herein, the current generated by the battery causes nitrogen molecules to be electrochemically reduced to ammonia in the cathode chamber 311.

[0152] In battery 300, unlike battery 200, water is oxidized at cathode 312 to produce protons in anolyte 334 according to equation (5). Protons migrate through membrane separator 333 to maintain charge neutrality in the battery, where they enter cathode electrolyte 314 and regenerate the cation proton carrier by protonating the neutral proton acceptor. However, through membrane separator 333, water and other unwanted substances are excluded or inhibited from migrating from anolyte 334 to cathode electrolyte 314.

[0153] Ammonia products can be continuously or periodically removed from the cathode chamber 311 via gas outlet 316 in gas 319 and / or via electrolyte outlet 221 in electrolyte 314. After the removal of ammonia and other byproducts, the battery can operate continuously, and the electrolyte and gas removed from the battery can be recycled in a manner similar to that described for battery 200. Hydrogen molecules generated as byproducts in the cathode chamber 311 can be recovered and recycled to the anode chamber 331 for oxidation.

[0154] In one variation, hydrogen molecules can be introduced into the battery 300 as the only hydrogen-containing substance oxidized at the anode 312. In this case, both the cathode electrolyte 314 and the anode electrolyte 334 can be substantially water-free.

[0155] The arrangement shown in battery 300 is merely one embodiment of an electrochemical cell configured to allow water to be oxidized at the cathode, and the resulting protons selectively transported to a substantially anhydrous electrolyte to participate in a water-sensitive cathode reaction. In another reported method, a separator is positioned near a porous anode (e.g., a gas diffusion electrode). A gas flow containing some water (e.g., humid air) is directed across the outer surface of the anode, and the separator impedes convective mixing. The electrolyte is sufficiently hydrophobic so that very little water is absorbed by the gas flow. If the hydrophobicity of the electrolyte and the humidity of the gas flow are adequately regulated, the separator may not require proton selectivity to maintain a low water content in a large volume of electrolyte.

[0156] In another reported method, the hydrophobic organic cathode electrolyte and the polar (e.g., aqueous) anode electrolyte are immiscible, and protons transfer at the phase boundary between them. This arrangement also allows for satisfactory proton transfer while sufficiently suppressing water transport into the cathode electrolyte. To maintain a stable phase boundary, a separator can be used as the location of the boundary.

[0157] Liquid electrolytes, applications of electrolytes, and systems that include electrolytes.

[0158] The present invention also relates to a liquid electrolyte for electrochemical reduction reactions. The electrolyte comprises: (i) a neutral proton acceptor, which is a ylidene; (ii) a cationic proton carrier capable of reversible deprotonation to form a neutral proton acceptor; and (iii) a non-aqueous solvent. The liquid electrolyte is preferably substantially free of water. For example, it may contain less than 1000 ppm, preferably less than 100 ppm, and most preferably less than 20 ppm of water.

[0159] The present invention also relates to the use of such electrolyte in reduction reactions in electrochemical cells.

[0160] The cationic proton carrier, its corresponding neutral ylide proton acceptor, the electrochemically stable anion that balances the charge of the cationic substance in the electrolyte, the concentration of the above substances, and the non-aqueous solvent are generally as disclosed herein in the context of a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia.

[0161] The inventors have recognized that electrolytes containing both cationic proton donors and ylide proton acceptors can provide advantages for a range of electrochemical reductions. Of particular interest are cathodic reductions that require anodic oxidation to generate protons, but in which: (a) the direct reduction of protons or water to H2 at the cathode competes with the desired reduction process; (b) non-aqueous conditions are required in the electrolyte; and / or (c) anionic organic intermediates in the reaction sequence are prone to precipitation, decomposition, or other degradation pathways.

[0162] According to the principles disclosed herein, a cation proton donor provides protons to the cathodic reduction reaction, while the corresponding ylide proton acceptor intercepts protons introduced into the electrolyte via anodic oxidation of a hydrogen-containing substance (suitably H2 or H2O) at the anode. It has been found that certain ylides, including... -Carbon anion ylides can repeatedly cycle between protonated and deprotonated forms without substantial degradation or precipitation, thus achieving a high flip number. Furthermore, the presence of both substances in the electrolyte buffers the entire reduction reaction, absorbing excess reaction intermediates (including protons) generated or accumulated during startup or online intermittent processes, and ensuring a high proportion of anodic protons are intercepted and consumed before participating in undesirable cathodic reactions (such as HER).

[0163] In some embodiments, as described in detail in this disclosure, the reduction reaction in the electrochemical cell is a continuous electrochemical reduction of nitrogen molecules mediated by a metal selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium. In such embodiments, the electrolyte may include these metal cations. However, it should be understood that the metal cation is a specific requirement for this particular reduction reaction, and the metal cation component may therefore be absent in other embodiments.

[0164] The present invention also relates to a system for a continuous electrochemical reduction reaction. The system includes an electrochemical cell comprising a cathode, an anode, and a power source for applying a voltage between the cathode and the anode; and a liquid electrolyte in contact with at least the cathode, as described herein. The electrochemical cell can generally be as described in the context of a method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia.

[0165] Example

[0166] The present invention is described with reference to the following embodiments. It should be understood that these embodiments are illustrative of the invention described herein and not limiting.

[0167] Materials and methods

[0168] Tetrahydrofuran (THF), stabilized with butylated hydroxytoluene (BHT), was purchased from Chem-Supply. The received THF was subjected to [further treatment] prior to electrolyte preparation. The molecular sieves were further dried for 24 hours or until the detected water content (by Karl Fischer titration) was less than 5 ppm. LiBF4, lithium trifluoromethanesulfonate (LiOTf), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were purchased from commercial suppliers, including ACROS Organics (LiBF4 98% purity, anhydrous). The salts were further dried under vacuum at 120 °C for 12 hours before use in electrolyte preparation. Salts and matte salts: tri(pentafluoroethyl)trifluorophosphate trihexyl(tetradecyl) ([P 666,14 [eFAP]), Tri(pentafluoroethyl)trifluorophosphate tributyl(octyl) ([P 444,8 [eFAP]), tri(pentafluoroethyl)trifluorophosphate triethyl(methyl) ([P 1222 [eFAP]), Trihexyl(tetradecyl) perfluorohexanesulfonate ([P 666,14 [PFHS]) and bis(trifluoromethanesulfonyl)imine triethyl sulfonium (Et3S-TFSI) were synthesized according to previously disclosed methods.

[0169] Electrochemical measurements were performed in a single-chamber, three-electrode pressure cell with an internal volume of 75 mL. A consistent electrolyte volume of 5 mL was used for each experiment. The working electrode (WE) used was a 1.25 mm diameter Cu disk electrode. Pt sheet electrodes separated from a glass melt were used as electrode pairs (CE, geometrical surface area, GSA = 1 cm²). 2Electrodes and Ag quasi-reference electrodes (REs) were used. Prior to each experiment, the electrode polishing pads (Buehler) were polished with a mixture of alumina slurries (0.3 μm and 0.05 μm). The polished electrode was then rinsed with deionized (DI) water to remove residual alumina particles and further polished on a clean polishing pad (alumina-free) to obtain the original surface, followed by a further rinse with acetone. For the CE, the electrodes were ignited with a butane flame until a bright red glow was observed, followed by a rinse with acetone. After cleaning, all electrodes and pressure cell assemblies were dried under vacuum at 80 °C for at least 4 hours. The electrochemical cells were then assembled and filled with electrolyte inside an Ar glove box. The cells were then pressurized to the target pressure outside the Ar glove box using ultra-high purity N2 (99.999% purity).

[0170] Electrochemical measurements were performed using a Biologic VMP XXX instrument. Chronoamperometry (CA) measurements were then performed following a series of electrochemical measurements. After the cell was pressurized, electrochemical impedance spectroscopy (EIS) was performed, followed by open-circuit potential (OCP) measurements until a stable potential reading was observed. Cyclic voltammetry experiments were then performed after OCP to determine the corresponding Li / Li ratio. + The cross potential. In the following CA experiments, this potential value is used as an internal standard to determine the applied working electrode (WE) potential (vs Li / Li). + ).

[0171] Following the procedure in ACS Energy Lett 2020, 5, 736-741, ammonia generated during the CA experiment was measured using Berthelot (indophenol blue) spectrophotometry and the internal standard addition method. After the electrochemical measurement, the electrolyte was taken and diluted with 50 mL of M H₂SO₄ aqueous solution. Subsequently, four different test tubes were filled with 100 μL of diluted sample aliquots, 400 μL of deionized water, and 400 μL of internal standard sample (10 μM, 20 μM, and 50 μM), respectively, to prepare four different calibration points. In addition, a tube containing 0.5 mL of deionized water was prepared as a blank control. 0.4 mL of a solution containing 1 M NaOH (containing 5 wt% salicylic acid and 5 wt% sodium citrate), 100 μL of 10 vol% NaClO solution, and 30 μL of 1 wt% C₅FeN₆Na₂O (sodium nitroferricyanide) was added to each of the five tubes. The mixture was then incubated for 2 hours to allow color development. After incubation, the absorbance of the five sample solutions was measured at 655 nm using a UV-Vis spectrometer, and curves were plotted to determine the amount of ammonia in the original electrolyte.

[0172] Example 1. Preparation of electrolytes

[0173] In typical electrolyte preparation, a batch of 25 mL electrolyte is prepared in an Ar glove box to minimize the potential accumulation of any possible contaminants. One electrolyte contains 0.2 M LiBF4 and 0.1 M [P] 666,14 The electrolyte is a THF solution containing [eFAP]. To prepare this electrolyte, 2.3 g ± 0.1 g of [P] was used. 666,14 [eFAP] was added to a 25 mL volumetric flask, then 0.47 g ± 0.05 g LiBF4 was added to the flask, and then dissolved in THF to form a 25 mL solution. The water content of the final electrolyte was further tested by Karl Fischer titration; only batches with a water content <20 ppm were used for electrochemical testing.

[0174] Similar electrolytes are prepared in the following proportions:

[0175] • 0.2M lithium trifluoromethanesulfonate (LiOtf) and 0.1M [P 666,14 [eFAP] in THF solution;

[0176] 0.2M LiBF4 and 0.1M [P 444,8 [eFAP] in THF solution;

[0177] 0.2M LiBF4 and 0.1M [P 666,14 [PFHS] THF solution;

[0178] ·0.2M LiOTf / 0.1M[P 444,8 Cl in THF solution;

[0179] 0.2M LiBF4 / 0.1M[P 4444 [BF4] in THF solution;

[0180] • 2.0M LiTFSI / 0.1M MEt3S-TFSI THF solution;

[0181] 0.2M LiBF4 / 0.1M[P 4444 [BF4] in THF solution;

[0182] ·0.2M LiOTf / 0.1M[P 666,14 [eFAP] in dimethoxyethane (DME) solution;

[0183] ·2.0M LiTFSI / 0.1M[P 666,14 [eFAP] sulfolane solution;

[0184] ·0.2M LiOTf / 0.1M[P 666,14 [TFSI] THF solution.

[0185] Example 2. Study on Cyclic Voltammetry

[0186] Using 0.2M LiBF4 / 0.1M [P 666,14 The compatibility of the [eFAP] / THF electrolyte molecules with lithium electrochemistry was analyzed, and preliminary cyclic voltammetry experiments were conducted to study its role as a proton carrier. Electrochemical properties of the cation. Comparisons were made with typical electrolytes used in previously reported lithium-mediated continuous electrochemical systems, this electrolyte consisting of a 0.2 M LiOtf / 0.17 M ethanol THF solution. Cyclic voltammetry experiments were conducted at varying N2 pressures up to 20 bar.

[0187] Figure 4 Cyclic voltammetry results for two proton carrier systems are shown. It is clear that [P] 666,14 The presence of [eFAP] does not interfere with Li electrochemistry. Conversely, [P] 666,14 [eFAP] is itself a salt, which increases the ionic conductivity of the electrolyte. As a result, significantly higher electrochemical reaction rates can be inferred from higher current densities. For example, it has been observed that in electrolytes containing [P]... 666,14 In the [eFAP] system, at 0.22V vs Li / Li + The current at the Li oxidation peak is 8.5 mA cm⁻¹. -2 This value is higher than the value observed in the standard ethanol system (0.35 mA cm). -2 It is 24 times higher.

[0188] Example 3. Preparation of ammonium by chronoamperometry

[0189] For further evaluation cation / The ability of the Ylide system as a proton carrier to prepare ammonia in lithium-mediated nitrogen reduction was demonstrated using 0.2 M LiBF4 / 0.1 M [P 666,14 A series of CA experiments were conducted on the [eFAP] / THF electrolyte, with an applied potential of -0.15V versus Li / Li. + to -1.05V vs Li / Li + The experiment was conducted for 2 hours under 20 bar N2. To avoid any contribution of H2 reduction to LiH during the cathode process, no hydrogen was introduced into the cell. In the absence of H2, the anodic reaction that forms protons is the oxidation of THF. Figure 5 The results show that ammonia was successfully formed at a high Faraday efficiency (FE). The maximum FE for ammonia preparation was 82% ± 12% at an applied voltage of -0.75 V vs Li / Li+. At this potential, the ammonia yield was 77 nmol / cm³.-2 s -1 ±16 nmol cm -2 s -1 Within the tested potential range, the yield of ammonia preparation was observed to increase with increasing applied overpotential. The error bar at -0.75V reflects the standard deviation of the results for n=4 (four repeated experiments), while the other error bars reflect the standard deviation for n=2.

[0190] Example 4. Stability Test of Chronopotential Battery

[0191] In the chronopotential (CP) experiment, cations The cathode potential stability of the proton carrier system was compared with that of the ethanol proton carrier system. Therefore, in each case, at 27 mA cm⁻¹ -2 Under a constant applied current, 0.2M lithium trifluoromethanesulfonate (LiOTf) / 0.1M [P] 666,14 The [eFAP] / THF electrolyte was compared with 0.2M lithium trifluoromethanesulfonate (LiOTf) / 0.17M ethanol / THF electrolyte. The experiment was conducted under 19.5 bar N2 and 0.5 bar H2 in the case of ethanol, and under 20 bar N2 in the case of ethanol (in the latter case, the results were the same with and without H2). The results are as follows. Figure 6 As shown, the inset is a magnified view of the first few minutes of the experiment. The results indicate that from the start of the CP experiment, the ethanol-based system is affected by an immediate increase in the required cathode voltage. Within just 20 minutes, the working electrode potential exceeds -6V vs. Li / Li. + This can lead to potential overload of the electrochemical system. In contrast, based on The proton carrier system exhibited significantly higher stability, providing extended voltage stability over 20 hours. During the experiment, The cathode potential of the proton carrier remains below -2Vvs Li / Li + This is also Higher energy efficiency is achieved in proton carrier systems.

[0192] Over the entire 20-hour experiment, 40% FE was obtained, with a yield of 5.5 nmol / cm³. -2 s -1 In a similar experiment lasting only 1.5 hours, 67% FE and 9.0 nmol cm⁻¹ were obtained. -2 s -1 The yield. It has been suggested that the performance degradation after 6 hours may be at least partly attributable to the decomposition of the THF solvent.

[0193] The working electrode (WE) was checked after each CP experiment. After 20 hours of experimentation with the proton carrier system, the Cu surface remained glossy. In contrast, after 8 hours of experimentation using only the ethanol proton carrier system, a strongly adherent white deposit was observed on the WE surface. This material is thought to be due to the insolubility and / or instability of the deprotonated carrier (i.e., EtOLi), with the accumulation of insoluble material leading to the gradual passivation of WE. This is consistent with previous recommendations that the increase in cell potential during Li-mediated ammonia synthesis leads to the decomposition of the alcohol electrolyte component.

[0194] Example 5. Ye Lide's Regeneration Research

[0195] To study alkyl The substance acts as a renewable proton carrier in the electrochemical lithium-mediated ammonia synthesis process, using [P] 666,14 [eFAP] conducted a series of experiments and through 31 Monitoring is performed using P NMR spectroscopy, such as Figure 7 As shown. All reactions were carried out using dry materials in an inert atmosphere (O2 and H2O < 0.5 ppm) in an argon glove box. Recordings were performed in THF using an external capillary with PPh3 as a reference. 31 P-NMR spectra, calibrated to 0 ppm according to this axis.

[0196] In the first step, [P] is prepared. 666,14 [eFAP] in 0.2M THF solution, and record. 31 pNMR spectrum. For example... Figure 7 As shown, the spectral characteristics are one 31 The P NMR signal corresponds to 39.3 ppm. Cations [P] 666,14 [ ], and a set of signals from -131 ppm to -151 ppm, corresponding to [eFAP] anions. In the second step, excess Li3N is added to [P 666,14 The mixture was added to a 0.2 M solution of [eFAP] and stirred for 24 hours. Visually, no change was observed in the mixture: it remained colorless, transparent, and without any visible precipitate. Results were recorded after 24 hours. 31 P NMR spectrum ( Figure 7 The intermediate spectrum shows that the peak at 39.3 ppm has completely disappeared, and a new peak appears at 15.7 ppm. This peak corresponds to the reaction with Li3N... Cation deprotonation forms zwitterions in near-quantitative yields. NMR data and The formation of ylide was consistent. In the third step, 0.2 ml of 0.1 M acetic acid solution was added to 0.5 ml of the solution containing ylide, and the results were recorded. 31P NMR spectrum ( Figure 7 (The bottom spectrum in the image). The spectrum shows... The quantitative recovery rate of cations was 39.3 ppm (peak value).

[0197] Confirmed using mass spectrometry (MS) Cation recovery: The mass spectra of stages 1 and 3 are identical, showing only one corresponding to [P]. 666,14 The signal of the cation (m / z = 483).

[0198] For others Salt: [P] 1222 [eFAP], [P] 4448 [eFAP] and triphenylmethyl tetrafluoroborate ([PPh3Me][BF4]) Repeat the stepwise reaction process as follows. All 31 P-NMR spectroscopy revealed the formation of ylide compounds upon reaction with Li3N, and the subsequent addition of acetic acid. Regeneration of cations. This indicates a series of alkyl groups. Cations are suitable proton carriers, and stepwise reaction assays can be used as a screening method for potential proton carriers.

[0199] Example 6. Other alkyl groups Salt assessment

[0200] Using (a) 0.2M LiBF4 / 0.1M [P] 444,8 [eFAP] / THF electrolyte, (b) 0.2M LiBF4 / 0.1M [P 666,14 [PFHS] / THF electrolyte, or (c) 0.2M LiOTf / 0.1M [ P666,14 Cl / THF electrolytes, with an applied voltage of -0.45V for each electrolyte vs. Li / Li + , lasting 8 hours; and (d)0.2M LiBF4 / 0.1M[P 4444 [BF4] / THF electrolyte and e)0.2M LiOTf / 0.1M [P 666,14 [TFSI] / THF electrolytes, each with an applied voltage of -0.75V vs. Li / Li + The study lasted two hours and evaluated other alkyl groups in a series of CA experiments. Salt. The experiment was conducted under 20 bar N2 (without H2). The results are shown in Table 1 below.

[0201] Table 1

[0202]

[0203] Use [P] 444,8 The productivity and selectivity obtained by [eFAP] are the same as those obtained by using [P] at the same potential. 666,14 The productivity and selectivity obtained by the [eFAP] proton carrier are comparable (see Example 3), indicating that various alkyl groups... The structure is appropriate. [P] 666,14 [TFSI] achieved excellent performance, but [P] 666,14 [PFHS] and [P] 666,14 Cl yielded a slightly lower productivity, attributed to the lower conductivity of the electrolytes containing these salts. However, the results demonstrated the applicability of a range of electrochemically stable counterions. In this case, chloride ions were stable enough for use in the H2 anodic reaction.

[0204] Example 7. Evaluation of H2 as a hydrogen-containing substance in anodizing

[0205] In continuous ammonia synthesis, H2 is used as the proton source for the electrolyte, employing 0.2M LiBF4 / 0.1M [P] 666,14 The [eFAP] / THF electrolyte was used in a carbon-based electrochemical cell (CA) experiment at an applied voltage of -0.45 V vs. Li / Li+. Hydrogen (H2) was thus supplied to the pressurized electrochemical cell. Four measurements were performed at a total cell pressure of 20 bar, including 15 bar of N2 and 5 bar of H2. The average yield of NH3 was 22 nmol / cm³ at a Faraday efficiency (FE) of 65% ± 22%. -2 s -1 ±11 nmol cm -2 s -1 .

[0206] Example 8. Replacing N2 with Ar of Control experiment

[0207] To demonstrate that the NH3 produced in Examples 2 to 7 originated from the supplied N2 gas, 0.2M LiBF4 / 0.1M [P] was used at an Ar pressure of 20 bar. 666,14 [eFAP] / THF electrolyte at -0.45V vs Li / Li + The CA experiment was conducted under the applied voltage. After charging at 2.5C, only 6 nmol of NH3 was detected in total. This contrasts with the 3479 nmol detected in the equivalent experiment under N2 (through a charge of 1.5C), proving that the generated NH3 originated from the electrochemical reduction of N2.

[0208] Example 9. Effect of N2 pressure

[0209] To investigate the effect of N2 pressure, 0.2M LiBF4 / 0.1M [P] was used. 666,14 [eFAP] / THF electrolyte at -0.75V vs Li / Li + A series of CA experiments were conducted under the applied potential. The experiments were carried out for 2 hours at N2 pressures ranging from 2 bar to 20 bar. Figure 8 The results shown indicate that higher pressures improve yield and Faraday efficiency.

[0210] Example 10. Evaluation of other solvents

[0211] Solubility studies were conducted to identify other potentially suitable non-aqueous solvents for lithium-mediated ammonia electrosynthesis, due to the undesirable polymerization of THF caused by lithium electrodeposition. Solubility was evaluated at a concentration of 0.2 M salt in specified solvents. The results are shown in Table 2.

[0212] Table 2

[0213]

[0214] LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide; DME: Dimethoxyethane; FPEE: 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether; HFCP: 1H,1H,2H-heptafluorocyclopentane; TFT: Trifluorotoluene.

[0215] *To 0.1M[P 666,14 Add 350 μL of DME to a 5 mL mixture of [eFAP] and 0.2 M salt HFCP.

[0216] # 375 μL of DME is required to dissolve 0.2 M LiOtf in 5 mL of 0.1 M [P] 666,14 In the TFT solution of the mixture of [eFAP]

[0217] Then, in the CA experiment, 0.2M LiOTf / 0.1M [P] was used. 666,14 Solvent evaluation of [eFAP] / DME electrolyte for dimethoxyethane (DME) was performed with an applied potential of -0.45V versus Li / Li. + The experiment was conducted for 1.3 hours under 20 bar N2.

[0218] The results are shown in Table 3.

[0219] In the CA experiment, 2.0M LiTFSI / 0.1M [P] was used. 666,14 [eFAP] / sulfolane electrolyte (applied voltage -0.25V vs Li / Li) +The study also evaluated sulfolane as a solvent. The experiments were conducted at 20 bar N2 and 60 °C for 2 hours. The results are shown in Table 3 below.

[0220] Table 3

[0221]

[0222] Example 11. Evaluation of alkyl sulfonium salts as cationic proton carriers

[0223] Alkyl sulfonium salts were evaluated in a series of CA experiments using an electrolyte containing 2M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.1M triethyl bis(trifluoromethanesulfonyl)imide (Et3S-TFSI) in THF, with a nickel wire cathode (0.15 cm). 2 In a single-chamber cell with a surface area of ​​0.55V, a voltage of 0.55V is applied compared to Li / Li. + The experiment was conducted for 6 hours under 15 bar N2 (no H2), with the electrolyte stirred at 600 rpm. 71 nmol s was obtained. -1 cm -2 The NH3 yield and 30% Faraday efficiency.

[0224] These results are consistent with [P] 666，14 The results for the [eFAP] proton carriers at the same potential are comparable (see Example 3). The results indicate that sulfonium-type cations are suitable as proton carriers in lithium-mediated NRR.

[0225] Those skilled in the art will understand that the invention described herein is susceptible to variations and modifications other than those specifically described. It should be understood that the invention includes all such variations and modifications falling within the spirit and scope of the invention.

Claims

1. A method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, the method comprising: Nitrogen molecules are supplied to an electrochemical cell containing an electrolyte that is at least in contact with the cathode; Protons are introduced into the electrolyte through the anodic oxidation of hydrogen-containing substances; and Ammonia is prepared by cathode reduction of nitrogen molecules in the presence of metals selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium. The electrolyte contains a cationic proton carrier capable of reversible deprotonation to form a neutral proton acceptor. The neutral proton acceptor is Yerde, and The cathode reduction of nitrogen molecules involves reacting nitrogen molecules with a cationic proton carrier to prepare ammonia and form a neutral proton acceptor.

2. The method of claim 1, wherein the cationic proton carrier is regenerated in the electrolyte by protonating the neutral proton acceptor.

3. The method according to claim 1 or 2, wherein reacting nitrogen molecules with a cationic proton carrier comprises (i) reacting nitrogen molecules with the metal to form a metal nitride; and (ii) reacting the metal nitride with a cationic proton carrier to prepare ammonia and form a neutral proton acceptor.

4. The method according to any one of claims 1 to 3, wherein the metal exists in the electrolyte in the form of a metal cation.

5. The method according to any one of claims 1 to 4, wherein the metal is lithium.

6. The method according to any one of claims 1 to 5, wherein the ylide comprises a carbanion adjacent to a cation heteroatom selected from phosphorus, nitrogen, sulfur and oxygen.

7. The method according to any one of claims 1 to 6, wherein the neutral proton acceptor is selected from phosphonium ylide and sulfonium ylide.

8. The method according to any one of claims 1 to 6, wherein the neutral proton acceptor is a phosphonium ellide.

9. The method according to any one of claims 1 to 8, wherein the cationic proton carrier is selected from alkylphosphonium cations and alkylsulfonium cations.

10. The method according to any one of claims 1 to 9, wherein the cationic proton carrier is an alkylphosphonium cation.

11. The method according to any one of claims 1 to 10, wherein the cationic proton carrier is a tetraalkylphosphonium cation.

12. The method according to any one of claims 1 to 11, wherein the electrolyte is a non-aqueous liquid electrolyte.

13. The method of claim 12, wherein the non-aqueous liquid electrolyte comprises one or more molecular solvents selected from ethers, fluorinated alkyl compounds, fluorinated cycloalkyl compounds, carbonates, sulfolane, and dimethyl sulfoxide.

14. The method of claim 12, wherein the non-aqueous liquid electrolyte comprises an ether selected from methylated polyethers, methylated glycol ethers, and fluorinated ethers.

15. The method of claim 12 or 13, wherein the non-aqueous liquid electrolyte comprises a room-temperature ionic liquid solvent.

16. The method according to any one of claims 1 to 15, wherein the cationic proton carrier and the neutral proton acceptor are soluble in the electrolyte.

17. The method according to any one of claims 1 to 16, wherein the cationic proton carrier is charged in the electrolyte by one or more anions selected from tetrafluoroborate, hexafluorophosphate, perchlorate, fluoroalkyl phosphate, fluoroarylborate, fluoroalkylborate, fluorinated bis(sulfonyl)imide, and fluorinated sulfonate.

18. The method according to any one of claims 1 to 17, wherein the cationic proton carrier and the neutral proton acceptor are present in the electrolyte at a combined concentration greater than 0.001 mol / L.

19. The method according to any one of claims 1 to 18, wherein the hydrogen-containing substance is selected from hydrogen molecules and water.

20. The method according to any one of claims 1 to 19, comprising supplying nitrogen molecules to the electrochemical cell at a partial pressure greater than 1 bar.

21. The method according to any one of claims 1 to 20, wherein when the cathode reduces nitrogen molecules, the cathode potential is more negative than the apparent reduction potential of the metal cation in the non-aqueous electrolyte under nitrogen molecule reduction conditions, as measured by the crossover point in cyclic voltammetry.

22. The method according to any one of claims 1 to 21, wherein the metal is lithium and wherein the lithium cation is dissolved in the electrolyte at a concentration greater than 0.1 mol / L.

23. A method for the continuous electrochemical reduction of nitrogen molecules to prepare ammonia, the method comprising: Nitrogen molecules are supplied to an electrochemical cell containing an electrolyte in contact with at least the cathode; Protons are introduced into the electrolyte through the anodic oxidation of hydrogen-containing substances; and Ammonia is prepared by cathode reduction of nitrogen molecules in the presence of metals selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium. The electrolyte contains at least one selected from alkylphosphonium cations and alkylsulfonium cations, and The cathode reduction of nitrogen molecules to prepare ammonia includes deprotonating a cationic proton donor to form a ylide.

24. A liquid electrolyte for electrochemical reduction reactions, comprising: (i) The proton receptor is a ylide; (ii) A cationic proton carrier capable of reversible deprotonation to form a neutral proton acceptor; (iii) Non-aqueous solvents; and (iv) Metal cations selected from lithium, magnesium, calcium, strontium, barium, zinc, aluminum, and vanadium. The cationic proton carrier is charged in a liquid electrolyte by one or more anions, wherein the anions are selected from tetrafluoroborate, hexafluorophosphate, perchlorate, fluoroalkyl phosphate, fluoroarylborate, fluoroalkylborate, fluorinated bis(sulfonyl)imide, and fluorinated sulfonate.

25. The liquid electrolyte of claim 24, wherein the ylide comprises a carbanion adjacent to a cation heteroatom selected from phosphorus, nitrogen, sulfur and oxygen.

26. The liquid electrolyte according to claim 24 or 25, wherein the neutral proton acceptor is selected from phosphonium ylide and sulfonium ylide.

27. The liquid electrolyte according to any one of claims 24 to 26, wherein the cationic proton carrier is selected from alkylphosphonium cations and alkylsulfonium cations.

28. The liquid electrolyte according to any one of claims 24 to 27, wherein the cationic proton carrier is a tetraalkylphosphonium cation.

29. The liquid electrolyte according to any one of claims 24 to 28, which is substantially free of water.

30. The liquid electrolyte according to any one of claims 24 to 29, wherein the non-aqueous solvent comprises one or more molecular solvents selected from ethers, fluorinated alkyl compounds, fluorinated cycloalkyl compounds, carbonates, sulfolane, and dimethyl sulfoxide.

31. The liquid electrolyte according to any one of claims 24 to 30, wherein the non-aqueous solvent comprises a room-temperature ionic liquid solvent.

32. The liquid electrolyte according to any one of claims 24 to 31, wherein the cationic proton carrier is deprotonated upon contact with lithium nitride to form a neutral proton acceptor.

33. The liquid electrolyte according to any one of claims 24 to 32, wherein the metal cation is a lithium cation and wherein the lithium cation is dissolved in the electrolyte at a concentration greater than 0.1 mol / L.

34. A system for continuous electrochemical reduction reactions, comprising: An electrochemical cell includes a cathode, an anode, and a power source for applying a voltage between the cathode and the anode; and At least the liquid electrolyte according to any one of claims 24 to 33 in contact with the cathode.

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