Process for lithium-mediated synthesis of ammonia using a cyclophosphazene-based electron-deficient aryl layer material

Abstract

The application relates to the technical field of electrochemical synthesis, and discloses a method for synthesizing ammonia by lithium mediation, which comprises a solvent, lithium bis-trifluoromethanesulfonimide, a cyclotriphosphazene source, a fluorine-containing aromatic hydrocarbon synergist and a boron-based anion acceptor. The method comprises the following steps: first, in an inert atmosphere, a pulse voltage is used to induce in-situ co-deposition of components to form an organic-inorganic hybrid interface layer containing anion anchoring centers; then, a proton source is introduced and switched to nitrogen for electrolysis. The electrostatic potential complementary effect of the cyclotriphosphazene and the fluorine-containing aromatic hydrocarbon is utilized to construct a dense hydrophobic network, which effectively blocks the penetration of the proton source to inhibit the hydrogen evolution side reaction; meanwhile, the boron-based acceptor in-situ captures halogen anions to construct a single-ion conductor, thereby reducing the driving force of dendrite growth. The step-by-step process avoids the complexation of active sites by the proton source, and significantly improves the faradic efficiency and long-term stability of lithium-mediated synthesis of ammonia.

Description

Technical Field

[0001] This invention relates to the field of electrochemical synthesis technology, specifically to a method for using cyclotriphosphazene-based electron-deficient aromatic materials for lithium-mediated ammonia synthesis. Background Technology

[0002] Ammonia is a crucial raw material in modern chemical systems, playing a central role in agricultural fertilizer production and industrial chemical manufacturing. It is also considered a highly promising carbon-free energy carrier. While the traditional Haber-Bosch process for ammonia synthesis is mature, it requires operation under high temperature and pressure conditions, resulting in enormous energy consumption and significant carbon dioxide emissions. In contrast, the electrochemical nitrogen reduction reaction (NRR) can synthesize ammonia from nitrogen and water (or a proton source) using renewable electricity at ambient temperature and pressure, providing a feasible alternative for green, distributed ammonia production.

[0003] Among the numerous electrochemical ammonia synthesis strategies, the lithium-mediated nitrogen reduction route has attracted considerable attention due to its unique reaction mechanism. This mechanism utilizes the extremely high reducing power of lithium metal, where active lithium generated through electrodeposition instantly dissociates the N≡N triple bond of nitrogen molecules to form a lithium nitride intermediate, which is then protonated to generate ammonia. However, the practical application of this system faces severe challenges, with the core contradiction being the competitive reaction between the active lithium and the proton source. To ensure the protonation step proceeds, proton carriers such as ethanol must be added to the electrolyte. However, these polar molecules readily diffuse to the negative electrode surface under an electric field, undergoing a violent hydrogen evolution reaction (HER) with the highly reactive lithium metal. This not only leads to a significant reduction in current efficiency but also accelerates the non-productive consumption of active lithium.

[0004] To suppress hydrogen evolution side reactions, existing technologies typically rely on a solid electrolyte interphase (SEI) film formed on the electrode surface by electrolyte decomposition products to achieve physical barrier. However, conventional SEI films are mainly composed of microcrystals of inorganic lithium salts (such as lithium fluoride and lithium carbonate). This structure usually has grain boundary defects and exhibits high mechanical modulus but insufficient toughness. During lithium-mediated reactions, metallic lithium undergoes repeated deposition and stripping, leading to drastic changes in electrode volume. The brittle inorganic SEI film is unable to adapt to this deformation and breaks. The electrolyte then permeates through the cracks, re-contacting the fresh lithium surface and triggering side reactions, resulting in a continuous decline in coulombic efficiency. Furthermore, SEI films composed solely of inorganic components have weak lithium-ion conductivity, easily causing concentration polarization at the interface, inducing lithium dendrite growth, and ultimately forming a loose layer mainly composed of dead lithium, severely hindering the continuous progress of the reaction.

[0005] To improve the properties of interfacial membranes, researchers have attempted to introduce various organic additives to construct flexible interfaces. While some fluorine- or phosphorus-containing additives can enhance the hydrophobicity of the membrane, single additives often struggle to balance ionic conductivity and physical barrier properties. For example, organic layers formed solely through physical adsorption or simple electrochemical decomposition lack ordered ion transport channels, leading to a significant increase in overpotential. On the other hand, Lewis acidic anion acceptors (such as borane compounds) introduced to improve ionic conductivity face chemical compatibility issues in proton-rich ammonia synthesis electrolytes. Since proton sources are typically Lewis basic, improper mixing processes can cause Lewis acidic sites to preferentially complex with the proton source and become inactive, losing their function of regulating interfacial ion transport. Therefore, how to construct an interfacial protective layer with high hydrophobicity, high mechanical stability, and single-ion conductivity in situ in a proton-rich environment is a key technological bottleneck for improving the efficiency of lithium-mediated ammonia synthesis. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for using cyclotriphosphazene-based electron-deficient aromatic materials in lithium-mediated ammonia synthesis. This method solves the problem in lithium-mediated electrochemical ammonia synthesis technology where the proton source easily penetrates the solid electrolyte interface film and reacts directly with active lithium, resulting in hydrogen evolution side reactions and reduced Faraday efficiency. Furthermore, conventional inorganic interface films formed by phosphorus and fluorine additives have low ionic conductivity, easily leading to the accumulation of dead lithium and electrode passivation, making it impossible to maintain stable synthesis over long periods.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a composition of a cyclotriphosphazene-based electron-deficient aromatic layer material, employing the following technical solution:

[0009] A composition of a cyclotriphosphazene-based electron-deficient aromatic material, comprising a solvent and a solute dissolved in the solvent at the following concentrations: lithium bis(trifluoromethanesulfonylimide): 0.8–1.2 mol / L; cyclotriphosphazene source: 0.05–0.20 mol / L; fluorinated aromatic synergist: 0.10–0.30 mol / L; boron-based anion acceptor: 0.02–0.08 mol / L.

[0010] By employing the above technical solution, this invention utilizes the synergistic effect between the components to construct an interfacial precursor system with ion sieving and conduction functions: the electron-rich PN framework of the cyclotriphosphazene source and the electron-deficient aromatic ring of the fluorinated aromatic synergist have complementary electrostatic potential characteristics. In the solvent, the two form locally ordered supramolecular aggregates through non-covalent interactions. These aggregates serve as templates for interfacial film formation, providing a structural basis for the subsequent construction of a dense, hydrophobic organic-inorganic hybrid framework. Simultaneously, the boron-based anion acceptor dispersed in the system, as a strong Lewis acid component, can specifically capture the halide anions released by the reduction and decomposition of the cyclotriphosphazene source during subsequent film formation, blocking the disordered accumulation of high-resistivity inorganic salts, thereby improving the ion transport performance of the interface.

[0011] Preferably, the concentration of the solute is: lithium bis(trifluoromethanesulfonyl)imide 1.0 mol / L, cyclotriphosphazene source 0.1 mol / L, fluorinated aromatic synergist 0.2 mol / L, and boron-based anion acceptor 0.05 mol / L. By adopting the above technical solution, this ratio can promote the orderly stacking between the cyclotriphosphazene source and the fluorinated aromatic synergist, and the amount of boron-based anion acceptor is sufficient to capture the anions generated by decomposition without causing changes to the bulk properties of the electrolyte, thereby obtaining an interface layer with both high ionic conductivity and high mechanical stability.

[0012] Preferably, the cyclotriphosphazene source is selected from hexachlorocyclotriphosphazene or hexafluorocyclotriphosphazene; the fluorinated aromatic synergist is selected from hexafluorobenzene, decafluorobiphenyl, or octafluorotoluene; and the boron-based anion acceptor is tris(pentafluorophenyl)borane. By adopting the above technical solution, the selected perfluoroaromatic hydrocarbon exhibits significant quadrupole moment characteristics and can form stable reactions with cyclotriphosphazene. - Stacked structure; Tris(pentafluorophenyl)borane has large steric hindrance and strong electron-withdrawing ability, which can form a large-volume weakly coordinated anionic complex, which is beneficial for realizing single-ion conduction properties.

[0013] Preferably, the solvent is anhydrous tetrahydrofuran; the composition is a clear solution prepared in an inert atmosphere with both water and oxygen content below 0.1 ppm. By adopting the above technical solution, the interference of water and oxygen on the activity of boron-based anion acceptors is eliminated, ensuring the chemical stability of each component before film formation.

[0014] Secondly, the present invention provides a method for using cyclotriphosphazene-based electron-deficient aromatic materials in lithium-mediated ammonia synthesis, employing the following technical solution:

[0015] A method for lithium-mediated ammonia synthesis using cyclotriphosphazene-based electron-deficient aromatic layer materials, employing the composition described in the first aspect as the film-forming base solution, comprises the following steps: S1, interface assembly and pulse deposition: under an inert atmosphere, a working electrode is placed in the composition, and a pulse voltage is applied for in-situ electrochemical deposition to form an organic-inorganic hybrid interface layer containing anion anchoring centers on the surface of the working electrode; S2, proton source introduction and gas switching: after deposition, a proton source is introduced into the composition, and the inert gas flow is stopped, and nitrogen gas is switched to flow until saturation; S3, electrochemical synthesis: under continuous nitrogen gas flow, a constant current is applied to the working electrode to carry out an electrolytic reaction, and the product ammonia is collected.

[0016] By employing the above technical solution, this method solves the problem of incompatibility between Lewis acidic additives and proton sources through a stepwise process, and achieves the regulation of interfacial ion transport and barrier functions: First, in step S1, pulsed voltage induces the co-deposition of cyclotriphosphazene source and fluorinated aromatic synergist to form a hybrid network with physical confinement effect; boron-based anion acceptor captures halide ions generated by reduction decomposition in situ, generating a large-volume anion complex; due to the volume effect and the physical confinement of the hybrid network, this large-volume anion is fixed within the interfacial film, constructing a fixed negative electric field, which transforms the interfacial layer into a single-ion conductor with a high lithium-ion mobility number, reducing the lithium-ion penetration barrier and inhibiting the formation of the space charge layer and dendrite growth. Second, the formed fluorinated aromatic network has strong hydrophobicity, which can effectively repel direct contact between polar solvents and subsequently added proton sources and the metallic lithium surface, thereby inhibiting the occurrence of hydrogen evolution side reactions. Finally, by adopting a process sequence of first forming the film and then adding the proton source, it was ensured that the boron-based anion acceptor had completed the coordination and capture of halide ions before contacting the proton source, thus avoiding catalyst deactivation caused by the direct complexation of Lewis acid with the proton source as a Lewis base, and ensuring the effectiveness of the anchoring mechanism.

[0017] Preferably, in step S1, before applying the pulse voltage, the working electrode is allowed to stand at an open-circuit potential for 15-40 minutes. By employing the above technical solution, the standing process allows the cyclotriphosphazene source and the fluorinated aromatic synergist to pre-form an adsorbed double layer at the electrode-electrolyte interface based on the principle of electrostatic potential complementarity, providing conditions for the subsequent pulse deposition to form a dense and uniform film structure.

[0018] Preferably, in step S1, the parameters of the pulse voltage are controlled as follows: substrate cathode potential is -0.3V to -0.8V (vs. Li / Li⁺); pulse amplitude is 20mV to 80mV; pulse frequency is 50Hz to 200Hz; duty cycle is 40% to 60%; and deposition time is 20 to 45 minutes. By adopting the above technical solution, the pulse potential is within the reduction potential range of cyclotriphosphazene, ensuring its ring-opening decomposition and participation in film formation; the high-frequency pulse is beneficial for refining the deposited grains and eliminating concentration polarization, thereby forming a dense interface layer and improving its physical barrier properties.

[0019] Preferably, in step S2, the proton source is anhydrous ethanol; the specific operation of introducing the proton source is as follows: injecting a replenishing solution containing ethanol into the composition treated in step S1, so that the final volume percentage of ethanol in the system is 0.5 vol% to 2.0 vol%. By adopting the above technical solution, controlling the ethanol concentration at a low level can not only provide the protons required for nitrogen reduction, but also, in conjunction with the sieving effect of the interface layer, control the hydrogen evolution side reaction at a low level.

[0020] Preferably, in step S3, the current density of the constant current is -0.5 mA / cm² to -5.0 mA / cm²; the flow rate of the nitrogen gas is controlled at 20 sccm. By adopting the above technical solution, while ensuring the ammonia production rate, excessive current density is avoided to prevent interface film rupture or lithium dendrite piercing, thus maintaining a long-term stable reaction environment.

[0021] This invention provides a method for using cyclotriphosphazene-based electron-deficient aromatic materials in lithium-mediated ammonia synthesis. It offers the following advantages:

[0022] 1. This invention utilizes the complementary electrostatic potential between the electron-rich skeleton of the cyclotriphosphazene source and the electron-deficient aromatic ring of the fluorinated aromatic synergist to construct a dense organic-inorganic hybrid interface layer in situ on the electrode surface. Due to the significant hydrophobic properties of the fluorinated aromatic network, this interface layer can effectively block the penetration of polar solvents and proton sources (such as ethanol) into the lithium metal surface, thereby significantly suppressing the competition of hydrogen evolution side reactions in the lithium-mediated process at the physical level and improving the Faraday efficiency of the ammonia synthesis reaction.

[0023] 2. This invention introduces a boron-based anion acceptor, which utilizes its strong Lewis acidity to capture halide anions generated by the decomposition of cyclotriphosphazene sources in situ, generating a large-volume weakly coordinated anion complex. Due to the physical confinement effect of the hybrid network, these large-volume anions are fixed inside the interface film, making the interface layer transform into a single-ion conductor with a high lithium-ion transference number. This regulation of ion transport characteristics effectively eliminates the anion concentration gradient at the interface, inhibits the formation of the space charge layer, and reduces the driving force for lithium dendrite growth from a kinetic perspective.

[0024] 3. This invention employs a process strategy that combines pulsed electrochemical deposition with stepwise introduction of proton sources, resolving the contradiction between interfacial film density and active site protection. High-frequency pulsed deposition eliminates concentration polarization, inducing the formation of a uniform film layer free of pores and defects, enabling it to adapt to volume deformation during the lithium metal deposition and stripping process. Furthermore, the sequence of film formation followed by proton source addition avoids the premature complexation and deactivation of Lewis acid sites by the proton source, ensuring the long-term stability of the interfacial modification layer and thus maintaining a high ammonia yield during long-term electrolysis operation. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see the appendix Figure 1 This invention provides a method for using cyclotriphosphazene-based electron-deficient aromatic materials in lithium-mediated ammonia synthesis, comprising:

[0028] raw material:

[0029] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0030] Tetrahydrofuran (CAS No. 109-99-9), anhydrous ethanol (CAS No. 64-17-5), and lithium bis(trifluoromethanesulfonyl)imide (CAS No. 90076-65-6) are all commercially available battery-grade or anhydrous products. The solvents and lithium salts are treated with molecular sieves or vacuum dried to remove trace amounts of moisture before use. Hexachlorocyclotriphosphazene (CAS No. 940-71-6) and hexafluorocyclotriphosphazene (CAS No. 15599-91-4) are both crystalline powders with a purity greater than 99%. Hexafluorobenzene (CAS No. 392-56-3), decafluorobiphenyl (CAS No. 434-90-2), and octafluorotoluene (CAS No. 434-64-0) are all fluorinated aromatic hydrocarbon reagents with a purity greater than 99%. Tris(pentafluorophenyl)borane (CAS No. 1109-15-5) is a Lewis acid powder with a purity greater than 98%, and is stored and used entirely in an argon-filled glove box.

[0031] Preparation Example 1: This preparation example provides a film-forming basic electrolyte for lithium-mediated ammonia synthesis, comprising the following steps: In an argon atmosphere glove box with water and oxygen content both below 0.1 ppm, anhydrous tetrahydrofuran is measured as a solvent, and lithium bis(trifluoromethanesulfonyl)imide, hexachlorocyclotriphosphazene, hexafluorobenzene, and tris(pentafluorophenyl)borane are added sequentially; the mixture is magnetically stirred at room temperature for 30 minutes until all solids are completely dissolved, resulting in a clear and transparent electrolyte; wherein the concentration of lithium bis(trifluoromethanesulfonyl)imide is 1.0 mol / L, the concentration of hexachlorocyclotriphosphazene is 0.1 mol / L, the concentration of hexafluorobenzene is 0.2 mol / L, and the concentration of tris(pentafluorophenyl)borane is 0.05 mol / L.

[0032] Preparation Example 2: This preparation example provides a film-forming basic electrolyte for lithium-mediated ammonia synthesis, comprising the following steps: In an argon atmosphere glove box with water and oxygen content both below 0.1 ppm, anhydrous tetrahydrofuran is measured as a solvent, and lithium bis(trifluoromethanesulfonyl)imide, hexachlorocyclotriphosphazene, hexafluorobenzene, and tris(pentafluorophenyl)borane are added sequentially; the mixture is magnetically stirred at room temperature for 30 minutes until all solids are completely dissolved, resulting in a clear and transparent electrolyte; wherein the concentration of lithium bis(trifluoromethanesulfonyl)imide is 0.8 mol / L, the concentration of hexachlorocyclotriphosphazene is 0.05 mol / L, the concentration of hexafluorobenzene is 0.10 mol / L, and the concentration of tris(pentafluorophenyl)borane is 0.02 mol / L.

[0033] Preparation Example 3: This preparation example provides a film-forming basic electrolyte for lithium-mediated ammonia synthesis, comprising the following steps: In an argon atmosphere glove box with water and oxygen content both below 0.1 ppm, anhydrous tetrahydrofuran is measured as a solvent, and lithium bis(trifluoromethanesulfonyl)imide, hexachlorocyclotriphosphazene, hexafluorobenzene, and tris(pentafluorophenyl)borane are added sequentially; the mixture is magnetically stirred at room temperature for 45 minutes until all solids are completely dissolved, resulting in a clear and transparent electrolyte; wherein the concentration of lithium bis(trifluoromethanesulfonyl)imide is 1.2 mol / L, the concentration of hexachlorocyclotriphosphazene is 0.20 mol / L, the concentration of hexafluorobenzene is 0.30 mol / L, and the concentration of tris(pentafluorophenyl)borane is 0.08 mol / L.

[0034] Preparation Example 4: This preparation example provides a film-forming basic electrolyte for lithium-mediated ammonia synthesis. The preparation steps are basically the same as those in Preparation Example 1, except that hexafluorocyclotriphosphazene is used instead of hexachlorocyclotriphosphazene, and decafluorobiphenyl is used instead of hexafluorobenzene. The concentration of lithium bis(trifluoromethanesulfonylimide) is 1.0 mol / L, the concentration of hexafluorocyclotriphosphazene is 0.1 mol / L, the concentration of decafluorobiphenyl is 0.2 mol / L, and the concentration of tris(pentafluorophenyl)borane is 0.05 mol / L.

[0035] Preparation Example 5: This preparation example provides a film-forming basic electrolyte for lithium-mediated ammonia synthesis. The preparation steps are basically the same as those in Preparation Example 1, except that octafluorotoluene is used instead of hexafluorobenzene. The concentration of lithium bis(trifluoromethanesulfonylimide) is 1.0 mol / L, the concentration of hexachlorocyclotriphosphazene is 0.1 mol / L, the concentration of octafluorotoluene is 0.2 mol / L, and the concentration of tris(pentafluorophenyl)borane is 0.05 mol / L.

[0036] The following are specific embodiments designed based on the aforementioned preparation examples and process range. These embodiments cover endpoint and intermediate values ​​of key parameters such as pulse frequency, duty cycle, deposition potential, deposition time, and synthesis current density to fully support the scope of protection of the claims.

[0037] Example 1: This example provides a quasi-solid-state interface lithium-mediated ammonia synthesis method based on anion acceptor anchoring and electrostatic potential complementarity. It uses the film-forming electrolyte obtained in Example 1 and includes the following steps:

[0038] (1) Interface assembly and pulse deposition: In an argon-filled glove box, the copper foil working electrode, lithium foil counter electrode and lithium foil reference electrode were assembled into an electrolytic cell and injected with the film-forming base electrolyte obtained in Preparation Example 1; static self-assembly was performed by standing at the open circuit potential for 20 minutes; then, a pulse voltage was applied for in-situ deposition, and the pulse parameters were set as follows: substrate cathode potential -0.5V (vs. Li / Li+), pulse amplitude 50mV, frequency 100Hz, duty cycle 50%, and deposition time 30 minutes;

[0039] (2) Proton source introduction and gas switching: After the deposition is completed, a supplementary solution containing 10 vol% anhydrous ethanol is injected into the electrolytic cell to make the final concentration of ethanol in the system 1.0 vol%; then the argon gas is stopped and high-purity nitrogen is switched to purge continuously at a flow rate of 20 sccm for 20 minutes until saturation.

[0040] (3) Electrochemical synthesis: Under the condition of continuous nitrogen gas, a constant current density of -2.0 mA / cm² is applied to the working electrode to carry out the electrolysis reaction. The reaction lasts for 2 hours, and the tail gas is passed into the dilute sulfuric acid absorption liquid to collect the product.

[0041] Example 2: This example provides a quasi-solid-state interface lithium-mediated ammonia synthesis method based on anion acceptor anchoring and electrostatic potential complementarity. The film-forming electrolyte obtained in Example 2 is used. The process parameters are mainly used to verify low-frequency and low-potential boundary conditions, including the following steps:

[0042] (1) Interface assembly and pulse deposition: The system assembly method is the same as in Example 1. The film-forming base electrolyte obtained in Preparation Example 2 is injected; it is left to stand at the open circuit potential for 15 minutes; then a pulse voltage is applied with the following parameters: substrate cathode potential -0.3V (vs. Li / Li+), pulse amplitude 20mV, frequency 50Hz, duty cycle 40%, and deposition time 20 minutes.

[0043] (2) Proton source introduction and gas switching: inject supplementary liquid into the electrolytic cell to make the final concentration of ethanol in the system 0.5 vol%; switch to high-purity nitrogen purging;

[0044] (3) Electrochemical synthesis: Under the condition of continuous nitrogen gas flow, a constant current density of -0.5mA / cm² is applied to the working electrode to carry out the electrolytic reaction, and the reaction duration is 4 hours.

[0045] Example 3: This example provides a quasi-solid-state interface lithium-mediated ammonia synthesis method based on anion acceptor anchoring and electrostatic potential complementarity. The film-forming electrolyte obtained in Example 3 is used, and the process parameters are mainly used to verify high-frequency and high-potential boundary conditions. The method includes the following steps:

[0046] (1) Interface assembly and pulse deposition: The system assembly method is the same as in Example 1. The film-forming base electrolyte obtained in Preparation Example 3 is injected; it is left to stand at the open circuit potential for 40 minutes; then a pulse voltage is applied with the following parameters: substrate cathode potential -0.8V (vs. Li / Li+), pulse amplitude 80mV, frequency 200Hz, duty cycle 60%, and deposition time 45 minutes.

[0047] (2) Proton source introduction and gas switching: inject supplementary liquid into the electrolytic cell to make the final concentration of ethanol in the system 2.0 vol%; switch to high-purity nitrogen purging;

[0048] (3) Electrochemical synthesis: Under the condition of continuous nitrogen gas flow, a constant current density of -5.0 mA / cm² is applied to the working electrode to carry out the electrolytic reaction, and the reaction duration is 1 hour.

[0049] Example 4: This example provides a quasi-solid-state interface lithium-mediated ammonia synthesis method based on anion acceptor anchoring and electrostatic potential complementarity. The film-forming electrolyte obtained in Example 4 (containing hexafluorocyclotriphosphazene and decafluorobiphenyl) was used to verify the applicability of different frameworks and networking agents, including the following steps:

[0050] (1) Interface assembly and pulse deposition: The system assembly method is the same as in Example 1. The film-forming base electrolyte obtained in Preparation Example 4 is injected; it is left to stand at the open circuit potential for 30 minutes; then a pulse voltage is applied with the following parameters: substrate cathode potential -0.6V (vs. Li / Li+), pulse amplitude 40mV, frequency 150Hz, duty cycle 50%, and deposition time 35 minutes.

[0051] (2) Proton source introduction and gas switching: inject supplementary liquid into the electrolytic cell to make the final concentration of ethanol in the system 1.5 vol%; switch to high-purity nitrogen purging;

[0052] (3) Electrochemical synthesis: Under the condition of continuous nitrogen gas flow, a constant current density of -3.0 mA / cm² is applied to the working electrode to carry out the electrolytic reaction, and the reaction duration is 2 hours.

[0053] Example 5: This example provides a quasi-solid-state interface lithium-mediated ammonia synthesis method based on anion acceptor anchoring and electrostatic potential complementarity, using the film-forming basic electrolyte (containing octafluorotoluene) obtained in Example 5, and includes the following steps:

[0054] (1) Interface assembly and pulse deposition: The system assembly method is the same as in Example 1. The film-forming base electrolyte obtained in Preparation Example 5 is injected; it is left to stand at the open circuit potential for 25 minutes; then a pulse voltage is applied with the following parameters: substrate cathode potential -0.4V (vs. Li / Li+), pulse amplitude 60mV, frequency 80Hz, duty cycle 45%, and deposition time 25 minutes.

[0055] (2) Proton source introduction and gas switching: inject supplementary liquid into the electrolytic cell to make the final concentration of ethanol in the system 1.0 vol%; switch to high-purity nitrogen purging;

[0056] (3) Electrochemical synthesis: Under the condition of continuous nitrogen gas supply, a constant current density of -1.5mA / cm² is applied to the working electrode to carry out the electrolysis reaction, and the reaction duration is 3 hours.

[0057] The following are comparative examples, which aim to comprehensively demonstrate the necessity and inventiveness of the three-component synergistic effect (skeleton + network + anchoring) and the specific process flow (film formation before proton source addition) in this invention through "default experiment" and "condition change experiment".

[0058] Comparative Example 1 (Blank Control): Compared with Example 1, the difference is that the film-forming electrolyte does not contain hexachlorocyclotriphosphazene, hexafluorobenzene, and tris(pentafluorophenyl)borane, but only a 1.0 mol / L lithium bis(trifluoromethanesulfonyl)imide / tetrahydrofuran solution; all other steps and parameters are the same. (Purpose: To demonstrate that the basic system without any additives cannot effectively suppress hydrogen evolution and has low ammonia production efficiency, thus establishing a performance baseline).

[0059] Comparative Example 2 (Lacking Networking and Anchoring Agents - Prior Art): Compared with Example 1, the difference is that the electrolyte for film formation does not contain hexafluorobenzene (component B) and tris(pentafluorophenyl)borane (component C), but only contains 1.0 mol / L lithium bis(trifluoromethanesulfonylimide) and 0.1 mol / L hexachlorocyclotriphosphazene; all other steps and parameters are the same. (Purpose: To simulate the case of using only cyclotriphosphazene to construct SEI membranes in the prior art, and to demonstrate that a single inorganic framework lacks hydrophobicity and ion conduction advantages, and cannot solve the proton penetration problem).

[0060] Comparative Example 3 (Missing Key Anchoring Agent - Verification of TFPB Function): Compared to Example 1, the difference is that the base electrolyte for film formation does not contain tris(pentafluorophenyl)borane (component C), but only lithium bis(trifluoromethanesulfonylimide), hexachlorocyclotriphosphazene, and hexafluorobenzene; all other steps and parameters are the same. (Objective: Core comparative example. To demonstrate that although a hydrophobic network is formed, the lack of Lewis acid anchoring for halide anions leads to excessively high interfacial film impedance (dead lithium problem) and a lack of selective permeability as a single-ion conductor.)

[0061] Comparative Example 4 (Lacking Synergistic Networking Agent - Verification of HFB Function): The difference from Example 1 is that the film-forming electrolyte does not contain hexafluorobenzene (component B), but only lithium bis(trifluoromethanesulfonylimide), hexachlorocyclotriphosphazene, and tris(pentafluorophenyl)borane; all other steps and parameters are the same. (Objective: To demonstrate that the absence of perfluoroaromatics provides...) - Stacked physical confinement networks cannot fix large-volume anions at the interface, resulting in unstable membrane structures.

[0062] Comparative Example 5 (Incorrect Process Sequence - Verification of the Necessity of the Step-by-Step Method): Compared with Example 1, the difference is that the timing of the introduction of the proton source is changed. Specifically, when preparing the basic electrolyte for film formation, 1.0 vol% anhydrous ethanol is added directly, and then the mixed solution is used directly for pulse deposition and subsequent electrolysis, omitting the replenishment operation in step (2); all other parameters are the same. (Purpose: Key comparative example. To prove that if the process of "film formation first and then ethanol addition" is not adopted, Lewis acid (TPFPB) will preferentially complex with ethanol and fail, resulting in the inability to form the expected functionalized interface).

[0063] Comparative Example 6 (Different film formation methods - verifying the necessity of pulse induction): Compared with Example 1, the difference is that the "pulse potential induced deposition" process in step (1) is omitted. After standing adsorption at open circuit potential for 30 minutes, the process directly proceeds to step (2) to add a proton source and start constant current synthesis; all other parameters are the same. (Purpose: to prove that a dense hybrid interface layer cannot be formed by physical adsorption alone, and electrochemical reduction-induced co-deposition is necessary).

[0064] Test Example 1: Electrochemical Impedance Spectroscopy (EIS) Interface Characterization

[0065] Experimental Procedure: The working electrodes from Examples 1-5 and Comparative Examples 1-6, after interface assembly and pulse deposition, were used as test objects. Testing was conducted before the introduction of a proton source and the start of the nitrogen reduction reaction to eliminate interference from reaction products on the interfacial membrane impedance. The tests were performed in an argon-filled glove box using freshly prepared 1.0M LiTFSI / THF electrolyte, free of any additives and proton sources. After assembling a symmetrical cell or a three-electrode system, AC impedance testing was performed using an electrochemical workstation. Test parameters were set with a frequency range of 100kHz to 0.1Hz, a perturbation voltage amplitude of 10mV, and a temperature control of 25±1℃. Testing was performed after the open-circuit potential stabilized. The obtained data were fitted using an equivalent circuit model, which consisted of a parallel circuit of solution resistance (Rs), interfacial membrane resistance (Rsei), a constant phase angle element (CPE1), and a series circuit of charge transfer resistance (Rct) and double-layer capacitance (CPE2).

[0066] Experimental data: The impedance fitting parameters obtained from each group of experiments are shown in the table below.

[0067] Table 1. Fitting results of electrode interface impedance parameters for each embodiment and comparative example.

[0068] Experimental group Solution resistance ( ) Interfacial film resistor ( ) Charge transfer resistance ( ) Lithium-ion diffusion coefficient ( (Estimation level) Example 1 5.23 28.4 86.7 Example 2 5.31 35.6 102.1 Example 3 5.18 24.9 91.5 Example 4 5.29 31.2 98.4 Example 5 5.25 29.8 94.3 Comparative Example 1 5.15 8.2 452.6 Comparative Example 2 5.22 168.5 315.4 Comparative Example 3 5.46 412.3 689.1 Comparative Example 4 5.33 115.7 288.9 Comparative Example 5 5.89 287.4 512.8 Comparative Example 6 5.27 12.6 398.5

[0069] Conclusions and Mechanism Analysis: Table 1 shows that the electrode interface impedance characteristics differ among different systems. Comparing Example 1 and Comparative Example 3, the interface film resistance Rsei and charge transfer resistance Rct are higher when tris(pentafluorophenyl)borane is missing, indicating that the interface film formed solely by hexachlorocyclotriphosphazene and hexafluorobenzene lacks regulation of halide ions, and the disordered accumulation of decomposition products increases the resistance to lithium-ion transport. In Example 1, the resistance value decreases after the introduction of boron-based acceptors, indicating that Lewis acid sites capture the anions released during film formation. The generated large-volume weakly coordinated anions are confined within the perfluoroaromatic network, constructing a negatively charged framework that facilitates lithium-ion passage and lowers the lithium-ion desolvation barrier.

[0070] Comparing Example 1 with Comparative Examples 2 and 4, the interfacial membrane constructed with only inorganic components in Comparative Example 2 showed a higher Rsei value. Comparative Example 4, although containing a boron-based acceptor, lacked hexafluorobenzene, and its Rsei and Rct values ​​were both higher than those of Example 1. These results indicate that without the physical confinement network provided by hexafluorobenzene, large-volume anion complexes cannot exist stably on the electrode surface. The electrostatic potential complementarity structure formed by hexafluorobenzene and cyclotriphosphazene is the basis for achieving stable anion anchoring.

[0071] For Comparative Example 5, the one-pot mixing method resulted in Rsei and Rct values ​​close to those of Comparative Example 3, indicating that the presence of ethanol deactivates Lewis acidic sites. Tris(pentafluorophenyl)borane preferentially complexes with ethanol rather than trapping interfacial halide ions, highlighting the necessity of a stepwise process for maintaining the function of active sites. Comparative Example 6, which omitted the pulse deposition step, had a lower Rsei value but a higher Rct, indicating that an effective protective layer was not formed on the electrode surface, leading to poor kinetic performance due to direct exposure to the electrolyte. The pulse process in Example 1 promoted co-deposition and densification between components, maintaining necessary physical coverage while ensuring ion transport.

[0072] Test Example 2: Hydrogen Evolution Suppression Performance Test by Linear Scan Voltammetry (LSV)

[0073] Experimental Procedure: The working electrodes from Examples 1-5 and Comparative Examples 1-6, after interface assembly and pulse deposition, were used as the research objects. A three-electrode system was employed for testing, with lithium sheets serving as both the counter and reference electrodes. The electrolyte was a 1.0 M LiTFSI / THF solution containing 1.0 vol% anhydrous ethanol to simulate the reaction environment. The working electrodes were immersed in the electrolyte and allowed to stand until the open-circuit potential stabilized. Linear sweep voltammetry was then performed, with the scan range from the open-circuit potential to -3.0 V (vs. Li / Li+) in the negative direction, at a scan rate of 5 mV / s. The change in current density with voltage was recorded, and the potential at which the current density reached -0.5 mA / cm² was taken as the hydrogen evolution initiation potential. Simultaneously, the current density at -2.0 V was also recorded.

[0074] Experimental data: The hydrogen evolution initiation potential (defined as the potential when the current density reaches -0.5 mA / cm²) and the current density at -2.0 V are shown in Table 2 for each group of experiments.

[0075] Table 2. Test data on the hydrogen evolution reaction suppression performance of electrodes in each embodiment and comparative example.

[0076] Experimental group Hydrogen evolution initiation potential (Vvs). ) Current density at -2.0V (mA / cm²) Example 1 -2.45 -0.12 Example 2 -2.38 -0.18 Example 3 -2.41 -0.15 Example 4 -2.33 -0.21 Example 5 -2.29 -0.24 Comparative Example 1 -1.15 -15.63 Comparative Example 2 -1.68 -6.45 Comparative Example 3 -1.82 -4.12 Comparative Example 4 -1.74 -5.89 Comparative Example 5 -1.58 -8.76 Comparative Example 6 -1.42 -11.20

[0077] Conclusions and Mechanism Analysis: Table 2 shows the differences in electrochemical behavior at different electrode interfaces. Comparative Example 1 exhibits a hydrogen evolution current at -1.15 V, with a current density of -15.63 mA / cm² at -2.0 V, indicating that ethanol molecules diffuse to the lithium surface and undergo reduction at low overpotentials in the absence of an interfacial film. In Example 1, the hydrogen evolution onset potential shifts negatively to -2.45 V, with a current density of -0.12 mA / cm² at -2.0 V, indicating that this interfacial layer blocks the permeation of the proton source.

[0078] Compared to Comparative Example 2, the interface layer initiation potential containing only hexachlorocyclotriphosphazene was -1.68V. The inorganic decomposition products lacked hydrophobic groups, and grain boundary defects provided diffusion channels, resulting in limited blocking effect. In Example 1, the introduction of hexafluorobenzene and tris(pentafluorophenyl)borane created a hydrophobic environment within the perfluoroaromatic skeleton. Combined with the dense network formed by complementary electrostatic potentials, this shielded the contact between polar ethanol molecules and the lithium surface.

[0079] Comparative Example 3, lacking an anion anchoring agent, had an onset potential of -1.82V and a higher current density than Example 1. This indicates that when Lewis acid sites are missing to immobilize large-volume anions, the interfacial layer cannot screen polar molecules through electrostatic repulsion. In Comparative Example 5, due to the preparation process, the Lewis acid sites contacted ethanol before the film formation process, resulting in the occupation of active sites and a decrease in hydrogen evolution inhibition performance to near the level without an anchoring agent. Comparative Example 6, without pulse induction, had a loose physical adsorption layer structure, allowing ethanol molecules to easily penetrate, leading to a higher current density. Example 1 utilized a hybrid interfacial layer formed by pulse electrochemical deposition, combining the physical shielding of the hydrophobic framework with the electrostatic repulsion of immobilized anions, thus suppressing the occurrence of competitive reactions.

[0080] Test Example 3: Determination of Ammonia Yield and Faraday Efficiency

[0081] Experimental Procedure: The electrochemical systems prepared in Examples 1-5 and Comparative Examples 1-6 were used for testing. After completing interface assembly and introducing the proton source, the electrolytic cell was placed in a constant temperature environment of 25°C. High-purity nitrogen gas was introduced into the cathode chamber at a flow rate of 20 sccm while stirring was started. Electrolysis was performed using an electrochemical workstation with a constant current of -2.0 mA / cm² applied to the working electrode for 2 hours. The gas generated during electrolysis was introduced into an absorption bottle containing 50 mL of 0.05 M sulfuric acid solution. After the reaction, the absorption solution and part of the electrolyte were mixed and measured using the indophenol blue colorimetric method. Phenol-sodium nitroprusside solution and sodium hypochlorite-sodium hydroxide solution were added to the test solution, and the mixture was incubated in the dark for 1 hour. The absorbance was measured at 655 nm using a UV-Vis spectrophotometer, the ammonia yield was calculated, and the Faraday efficiency (FE) was calculated based on the charge.

[0082] Experimental data: The ammonia synthesis performance data of each experimental group under the same electrolysis conditions are shown in Table 3.

[0083] Table 3. Electrochemical ammonia synthesis performance test results for each example and comparative example.

[0084] Experimental group ammonia yield ( ) Faraday efficiency (FE,%) Example 1 28.43 46.21 Example 2 25.17 41.58 Example 3 27.89 44.92 Example 4 26.54 43.15 Example 5 24.92 40.87 Comparative Example 1 0.85 1.34 Comparative Example 2 4.12 6.89 Comparative Example 3 11.23 18.45 Comparative Example 4 8.56 13.72 Comparative Example 5 9.45 15.21 Comparative Example 6 5.38 8.64

[0085] Conclusions and Mechanism Analysis: Table 3 shows that the ammonia synthesis performance varies among different systems. The Faraday efficiency of Comparative Example 1 is 1.34%, indicating that without interfacial membrane protection, protons are directly reduced at the electrode surface, and the current is mainly consumed in the hydrogen evolution side reaction. The ammonia yield in Example 1 reached 28.43%. The Faraday efficiency is 46.21%. This performance is due to the hydrophobic network formed by hexafluorobenzene and cyclotriphosphazene, which blocks the permeation of ethanol molecules and inhibits the hydrogen evolution reaction; at the same time, tris(pentafluorophenyl)borane captures halide ions to form fixed anion centers, giving the interface layer the characteristics of a single-ion conductor, increasing the lithium ion transference number, ensuring the supply of active lithium on the electrode surface, and promoting nitrogen fixation.

[0086] Compared with Comparative Example 1 and Comparative Example 3 (FE 18.45%), the lack of a boron-based anchoring agent led to a decrease in efficiency. Although Comparative Example 3 was hydrophobic, it lacked an anion immobilization mechanism, resulting in impaired ion transport at the interface and a lack of cation selectivity. Part of the protonated solvent penetrated the interface, consuming the active lithium. Comparative Example 5 (FE 15.21%) lost its ability to capture halide ions due to the preferential complexation of tris(pentafluorophenyl)borane with ethanol, and thus could not form a single-ion conductor structure; its performance was close to that of Comparative Example 3 without the anchoring agent. Comparative Example 6 (FE 8.64%) was not pulsed densified, resulting in a loose adsorption layer structure that could not maintain effective protection during the reaction. The data confirm that constructing an electrostatic potential complementary network containing anion anchoring centers through a pulsed process effectively blocked the proton source and enhanced lithium-ion transport.

[0087] Test Example 4: Long-term stability test of electrochemical ammonia synthesis

[0088] Experimental Procedure: The electrochemical systems of Examples 1-5 and Comparative Examples 1-6 were placed in a constant temperature environment of 25°C and tested under a nitrogen flow of 20 sccm. A constant current of -2.0 mA / cm² was applied to the working electrode for continuous electrolysis for a total duration of 10 hours. The absorbent was replaced every 2 hours during the experiment. The ammonia yield was determined using the indophenol blue method during this time period, and the Faraday efficiency was calculated. The data were recorded to evaluate the stability of the interfacial layer under long-term operating conditions.

[0089] The changes in Faraday efficiency (FE,%) at different time points during the 10-hour continuous electrolysis process for each experimental group are shown in Table 4.

[0090] Table 4. Faraday efficiency retention during the long-term electrolysis process of each embodiment and comparative example.

[0091] Experimental group 2h(%) 4h(%) 6h(%) 8h(%) 10h(%) Efficiency retention rate (10h / 2h) Example 1 46.21 45.89 45.12 44.35 43.18 93.4% Example 2 41.58 41.02 40.55 39.12 38.05 91.5% Example 3 44.92 43.65 42.18 41.09 39.88 88.8% Example 4 43.15 42.78 42.10 41.56 40.23 93.2% Example 5 40.87 39.56 38.12 36.45 34.89 85.4% Comparative Example 1 1.34 0.82 0.45 0.12 0.05 3.7% Comparative Example 2 6.89 5.12 3.45 1.88 0.92 13.4% Comparative Example 3 18.45 15.23 12.56 9.78 7.45 40.4% Comparative Example 4 13.72 10.45 8.12 6.34 4.12 30.0% Comparative Example 5 15.21 12.89 10.56 8.23 6.45 42.4% Comparative Example 6 8.64 6.12 4.56 2.34 1.12 13.0%

[0092] Conclusions and Mechanism Analysis: Table 4 shows that the Faraday efficiency changes varied among the groups during long-term electrolysis. Example 1 maintained an efficiency of 93.4% after 10 hours of operation, demonstrating high stability. Comparative Example 2 (containing only the inorganic framework) showed a significant decrease in efficiency from the initial 6.89% to 0.92%. This decrease is attributed to the lack of flexibility of the inorganic interface film (mainly LiF / LiCl), which makes it difficult to adapt to the volume changes during lithium deposition and stripping, leading to film rupture and exposure of fresh lithium surfaces, triggering continuous side reactions and dead lithium accumulation.

[0093] Although Comparative Example 3 contained an organic network, its efficiency retention was only 40.4% due to the lack of an anchoring agent. In the interface lacking single-ion conductor properties, bidirectional migration of anions and cations led to concentration polarization on the electrode surface, and uneven local electric field distribution induced lithium dendrite growth. Dendrites pierced the interfacial film, disrupting the physical barrier and exacerbating electrolyte decomposition.

[0094] The stability of Example 1 stems from the single-ion conductor properties of tris(pentafluorophenyl)borane, which captures anions, eliminating the interfacial ion concentration gradient, suppressing the formation of the space charge layer and the driving force for dendrite growth, and achieving uniform lithium deposition. Simultaneously, the hybrid network formed by hexafluorobenzene and cyclotriphosphazene possesses flexibility, capable of adapting to the volume deformation of metallic lithium and maintaining the integrity of the interfacial film. Comparative Example 5, due to the fabrication process, experienced anchoring effect failure, exhibiting a degradation trend consistent with Comparative Example 3, confirming the impact of the anion anchoring mechanism on long-term operation.

[0095] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A composition of a cyclotriphosphazene-based electron-deficient aromatic layer material, characterized in that, include: The composition comprises a solvent and a solute dissolved in the solvent at the following concentrations: lithium bis(trifluoromethanesulfonylimide): 0.8–1.2 mol / L; cyclotriphosphazene source: 0.05–0.20 mol / L; fluorinated aromatic synergist: 0.10–0.30 mol / L; boron-based anion acceptor: 0.02–0.08 mol / L.

2. The composition of the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 1, characterized in that, The concentrations of the solutes are as follows: lithium bis(trifluoromethanesulfonyl)imide: 1.0 mol / L; cyclotriphosphazene source: 0.1 mol / L; fluorinated aromatic synergist: 0.2 mol / L; boron-based anion acceptor: 0.05 mol / L.

3. The composition of the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 1, characterized in that, The specific selection of the solute must meet the following conditions: The cyclotriphosphazene source is selected from hexachlorocyclotriphosphazene or hexafluorocyclotriphosphazene; The fluorinated aromatic synergist is selected from hexafluorobenzene, decafluorobiphenyl, or octafluorotoluene; The boron-based anion acceptor is tris(pentafluorophenyl)borane.

4. The composition of the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 1, characterized in that, The solvent is anhydrous tetrahydrofuran; the composition is a clear solution prepared in an inert atmosphere with both water and oxygen content below 0.1 ppm.

5. A method for using cyclotriphosphazene-based electron-deficient aromatic materials in lithium-mediated ammonia synthesis, characterized in that, Using the composition according to any one of claims 1-4 as the film-forming base liquid, the method includes the following steps: S1. Interface assembly and pulse deposition: Under an inert atmosphere, the working electrode is placed in the composition, and a pulse voltage is applied to perform in-situ electrochemical deposition to form an organic-inorganic hybrid interface layer containing anion anchoring centers on the surface of the working electrode. S2. Proton source introduction and gas switching: After deposition, a proton source is introduced into the composition, and the inert gas is stopped and nitrogen gas is switched to be introduced until saturation. S3. Electrochemical Synthesis: Under the condition of continuous nitrogen gas flow, a constant current is applied to the working electrode to carry out the electrolysis reaction, and the product ammonia is collected.

6. The method for using the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 5 for lithium-mediated ammonia synthesis, characterized in that, In step S1, before applying the pulse voltage, the working electrode is placed at an open circuit potential for 15 to 40 minutes to perform static self-assembly.

7. The method for using the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 5 for lithium-mediated ammonia synthesis, characterized in that, In step S1, the parameters of the pulse voltage are controlled as follows: the substrate cathode potential is -0.3V to -0.8V (vs. Li / Li⁺); the pulse amplitude is 20mV to 80mV; the pulse frequency is 50Hz to 200Hz; the duty cycle is 40% to 60%; and the deposition time is 20 to 45 minutes.

8. The method for using the cyclotriphosphazene-based electron-deficient aromatic material according to claim 5 for lithium-mediated ammonia synthesis, characterized in that, In step S2, the proton source is anhydrous ethanol; the specific operation of introducing the proton source is as follows: inject a replenishing solution containing ethanol into the composition after step S1, so that the final concentration volume percentage of ethanol in the system is 0.5 vol%~2.0 vol.

9. The method for using the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 5 for lithium-mediated ammonia synthesis, characterized in that, In step S3, the current density of the constant current is -0.5 mA / cm² to -5.0 mA / cm²; the flow rate of the nitrogen gas is controlled at 20 sccm.

10. The method for using the cyclotriphosphazene-based electron-deficient aromatic layer material according to claim 5 for lithium-mediated ammonia synthesis, characterized in that, In step S1, the working electrode is made of copper foil; the inert atmosphere is argon; and the tail gas generated in step S3 is collected by passing it into an acidic absorption liquid.

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