Electrolyte for lithium-mediated conductive chemical synthesis of ammonia as well as preparation method and application of electrolyte

Abstract

The invention provides an electrolyte for lithium-mediated conductive chemical synthesis of ammonia, and a preparation method and application thereof, and belongs to the technical field of synthesis of ammonia. The electrolyte comprises a lithium salt, an organic solvent, a proton source and an additive, wherein the additive is any one of zinc salt, copper salt and silver salt. An organic solvent is adopted to form an organic system, dissolution of nitrogen and separation of a product ammonia are more facilitated, secondly, a metal inorganic salt additive is introduced into the electrolyte, a lithium-phobic R-lithium-loving LiF heterojunction (R is metal) is formed, the lithium-phobic R can accelerate diffusion of Li < + > in a solid electrolyte interface film (SEI) and avoid high-concentration polarization, and the lithium-phobic R-lithium-loving LiF heterojunction is formed. And the lithium-philic LiF ensures uniform nucleation of diffused Li < + > and participation in subsequent reaction, so that the electrochemical performance of the lithium-mediated conductive chemical synthesis ammonia is remarkably improved, the ammonia yield and the Faraday efficiency are further improved, and the reaction energy consumption is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic ammonia, and in particular relates to an electrolyte for lithium-mediated electrochemical synthesis of ammonia, and a preparation method and application thereof. Background Art

[0002] At present, most of the world's ammonia is synthesized through a century-old Harper-Bosch process, which usually uses hydrogen produced by fossil fuels and nitrogen obtained by deep-cold separation of air as raw materials to prepare ammonia under high temperature, high pressure and catalyst. This method has harsh reaction conditions, requires high temperature (300-500℃) and high pressure (100-200 bar), high energy consumption and large carbon dioxide emissions.

[0003] At present, aqueous electrolytes (such as KOH, Na 2 SO 4 Aqueous solution, etc.) is the most commonly used electrolyte for synthesizing ammonia. 2 The molecule is reduced to the target product NH by a six-electron, six-proton transfer process. 3 (N 2 +6H + +6e - →2NH 3 ). However, the nitrogen reduction reaction in aqueous solution to synthesize ammonia has the problems of poor nitrogen solubility, low ammonia current density, and low Farad efficiency. Summary of the invention

[0004] The present disclosure aims to solve at least one of the technical problems existing in the prior art and to provide an electrolyte for lithium-mediated electrochemical synthesis of ammonia and a preparation method and application thereof.

[0005] In one aspect of the present disclosure, an electrolyte for lithium-mediated electrochemical synthesis of ammonia is provided, the electrolyte comprising:

[0006] Lithium salts;

[0007] Organic solvents;

[0008] Proton source;

[0009] Metallic inorganic salt additives.

[0010] Optionally, the metal inorganic salt additive is any one of zinc salt, copper salt and silver salt.

[0011] Optionally, the concentration of the metal inorganic salt additive is 0.1-3.0wt%;

[0012] The concentration of the lithium salt in the organic solvent is 0.1-3M;

[0013] The volume fraction of the proton source is 0.1-10 vol%;

[0014] The volume fraction of the solvent is 90-99.9 vol%.

[0015] Optionally, the lithium salt is any one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenide.

[0016] Optionally, the solvent is any one of tetrahydrofuran, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and dioxolane.

[0017] Optionally, the proton source is any one of methanol, ethanol, propanol and butanol.

[0018] Another aspect of the present disclosure provides a method for preparing the electrolyte described above, the method comprising:

[0019] Dehydrating the lithium salt, the proton source and the solvent;

[0020] The treated lithium salt is mixed with a proton source, a solvent and a metal inorganic salt additive to form an electrolyte.

[0021] Optionally, the dehydration treatment of the lithium salt, the proton source and the solvent comprises:

[0022] The lithium salt is dried at 100-130° C.;

[0023] The zeolite molecular sieve is washed and dried, and the treated zeolite molecular sieve is used to dehydrate the solvent and the proton source.

[0024] Another aspect of the present disclosure provides an application of an electrolyte in lithium-mediated electrochemical synthesis of ammonia, comprising the following steps:

[0025] Sulfuric acid, potassium hydroxide and tetrahydrofuran pretreatment solutions are sequentially placed near the outlet of the nitrogen bottle;

[0026] The electrolysis device is provided with a gas diffusion working electrode, a counter electrode, a reference electrode, a bubbler and a gas outlet, wherein the bubbler is located close to the working electrode;

[0027] The electrolyte described in claims 1 to 6 is injected into the electrolysis device, and nitrogen is introduced for purging, and a current of a certain density is introduced to synthesize ammonia through an electrochemical nitrogen reduction reaction.

[0028] Optionally, the nitrogen purge time is 1-60 min, and the current density is 1-50 mA·cm -2 and / or,

[0029] The volume of the electrolyte injected is 10-100 mL.

[0030] The present disclosure proposes an electrolyte for lithium-mediated electrochemical synthesis of ammonia, a preparation method, and an application. The electrolyte includes: a lithium salt, an organic solvent, a proton source, and an additive; wherein the additive is any one of a zinc salt, a copper salt, and a silver salt. The present disclosure uses an organic solvent to form an organic system, which is more conducive to the dissolution of nitrogen and the separation of the product ammonia. Secondly, by introducing a metal inorganic salt additive into the electrolyte, a lithium-phobic R-lithiophilic LiF heterojunction (R is a metal) is formed, wherein the lithium-phobic R can accelerate the Li + The lithium-philic LiF ensures the diffusion of Li + The uniform nucleation of lithium and its participation in subsequent reactions can significantly improve the electrochemical performance of lithium-mediated electrochemical synthesis of ammonia, further increase the ammonia yield and Faraday efficiency, and reduce the reaction energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flowchart of a method for preparing an electrolyte according to a specific embodiment of the present disclosure;

[0032] Figure 2 It is a flowchart of the electrolyte application process of the specific embodiment of the present disclosure;

[0033] Figure 3 Schematic diagram of a three-electrode device, a gas purification process, and a lithium-nitrogen reduction test according to a specific embodiment of the present disclosure;

[0034] Figure 4 The linear sweep voltammetric curves of Example 1 and Comparative Example 1 of the present disclosure;

[0035] Figure 5 Activation energy curves for passing through SEI of Example 1 and Comparative Example 1 of the present disclosure. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0037] In one aspect of the present disclosure, an electrolyte for lithium-mediated electrochemical synthesis of ammonia is provided, the electrolyte comprising: a lithium salt, an organic solvent, a proton source and an additive; wherein the additive is any one of a zinc salt, a copper salt and a silver salt.

[0038] In this embodiment, an organic solvent is used to form an organic system, which is more conducive to the dissolution of nitrogen and the separation of product ammonia. Secondly, by introducing a metal inorganic salt additive into the electrolyte, a lithium-phobic R-lithiophilic LiF heterojunction (R is a metal) is formed, wherein the lithium-phobic R can accelerate the Li + The lithium-philic LiF ensures the diffusion of Li + The uniform nucleation of lithium and its participation in subsequent reactions can significantly improve the electrochemical performance of lithium-mediated electrochemical synthesis of ammonia, further increase the ammonia yield and Faraday efficiency, and reduce the reaction energy consumption.

[0039] In some preferred embodiments, the metal inorganic salt additive is any one of zinc salt, copper salt, and silver salt. For example, zinc salt may be preferred. When zinc salt is used, the inorganic metal Zn 2+ The introduction of Zn forms a lithium-phobic Zn-lithiophilic LiF heterojunction, and the lithium-phobic Zn accelerates the Li + diffusion within the SEI and avoid high concentration polarization, while the lithiophilic LiF ensures the diffusion of Li + In addition, the concentration of the metal inorganic salt additive is 0.1-3.0wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, etc., which is conducive to the formation of Li + The structure of the transmission accelerates Li + Diffusion within SEI avoids polarization, improves ion transfer efficiency, and promotes nitrogen reduction reaction.

[0040] In other preferred embodiments, the lithium salt is any one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenide, without specific limitation. In addition, the concentration of the lithium salt in the organic solvent is 0.1-3M, for example, preferably 0.1M, 0.5M, 1M, 2M, 3M, etc. This concentration range can ensure that the electrolyte has good ionic conductivity, maintain the stability of the electrolyte and electrode interface, and is conducive to improving the selectivity of the reaction.

[0041] In other preferred embodiments, the proton source is any one of methanol, ethanol, propanol, and butanol. In addition, the volume fraction of the proton source is 0.1-10 vol%, for example, preferably 0.1 vol%, 1 vol%, 2 vol%, 3 vol%, 5 vol%, 7 vol%, 10 vol%, etc. The proton source within this volume fraction range can provide a sufficient number of protons to meet the reaction requirements, accelerate the reaction rate, and promote the reduction of nitrogen to ammonia.

[0042] In other preferred embodiments, the solvent is any one of tetrahydrofuran, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and dioxolane. And the volume fraction of the solvent is 90-99.9 vol%, for example, preferably 90 vol%, 95 vol%, 99.9 vol%, etc.

[0043] like Figure 1 As shown, another aspect of the present disclosure provides a method S100 for preparing the electrolyte described above, the method comprising the following steps S110 to S120:

[0044] S110, dehydrating the lithium salt, the proton source and the solvent.

[0045] Specifically, the lithium salt is placed in a vacuum drying oven at 100-130°C overnight to remove moisture. After dehydration, the lithium salt can be more fully dissociated into lithium ions and corresponding anions, improving the ionic conductivity of the electrolyte and making the lithium ions transfer more smoothly in the electrolyte, thereby improving the battery's charge and discharge efficiency. At the same time, reducing moisture can avoid side reactions between water and electrode materials or other active substances, ensuring that the reaction on the electrode surface is mainly the insertion and extraction of lithium ions, and improving the reversibility and stability of the electrode reaction.

[0046] Furthermore, the zeolite molecular sieve was washed alternately with ethanol and acetone for 3*30 minutes in an ultrasonic (40kHz, 120W) water bath, and then dried in a 120°C vacuum drying oven for 12 hours, and the treated zeolite molecular sieve was used to dehydrate the solvent and the proton source for one day. The dehydration treatment can avoid unnecessary reaction between the proton source and water, ensure that the proton source can exist in a stable form and play its role in the synthetic ammonia reaction, reduce the occurrence of side reactions, and improve the selectivity and efficiency of the reaction.

[0047] S120, mixing the treated lithium salt with a proton source, a solvent and a metal inorganic salt additive to form an electrolyte.

[0048] Specifically, lithium salt and a solvent with a volume fraction of 90-99.9 vol% are mixed to form a lithium salt solution with a concentration of 0.1-3 M, and then mixed with a proton source with a volume fraction of 0.1-10 vol% and a metal inorganic salt additive with a mass fraction of 0.1-3 wt% and fully dissolved to form an electrolyte.

[0049] like Figure 2 and Figure 3 As shown, another aspect of the present disclosure provides an application of an electrolyte in lithium-mediated electrochemical synthesis of ammonia S200, comprising the following steps S210-S230:

[0050] S210. A sulfuric acid pretreatment solution, a potassium hydroxide pretreatment solution and a tetrahydrofuran pretreatment solution are sequentially arranged near the outlet of the nitrogen bottle. This step is equivalent to setting the gas path of the electrolysis device so that the upstream gas flowing out of the nitrogen bottle passes through sulfuric acid, potassium hydroxide and a certain volume of tetrahydrofuran in sequence before entering the electrolytic cell. This can remove impurity gases such as alkalinity and acidity that may exist in the upstream gas, ensure relatively pure nitrogen for the electrolytic cell, and reduce the interference of impurity gases on the electrolysis reaction.

[0051] In some preferred embodiments, the concentration of sulfuric acid may be preferably 0.04-0.06 M, for example, 0.05 M, etc. The concentration of potassium hydroxide may be preferably 0.05-0.15 M, for example, 0.1 M, etc.

[0052] Of course, in other preferred embodiments, sulfuric acid may be arranged at the downstream position of the outflow after the reaction, so that the downstream gas passes through 0.05M sulfuric acid and is discharged into the air.

[0053] S220, the electrolysis device is provided with a gas diffusion working electrode, a counter electrode, a reference electrode, a bubbler and a gas outlet, and the bubbler is located near the working electrode.

[0054] It should be noted that the present embodiment does not specifically limit the electrolysis device, for example, a single-chamber electrolysis cell, an H-type electrolysis cell, a flow cell, etc. Of course, other electrolysis cells may also be used.

[0055] It should be further explained that the material of the gas diffusion electrode can be stainless steel, and the working area is 1cm 2 The counter electrode can be a platinum sheet or a carbon rod, etc., and the reference electrode can be silver / silver chloride, calomel electrode, mercury / mercury oxide electrode, silver electrode, platinum electrode, etc.

[0056] It should still be noted that the bubbler of this embodiment can be inserted through an adapter and its position can be adjusted to a position very close to the working electrode, so as to maintain a higher nitrogen concentration near the working electrode. In addition, the electrolysis device should also have a gas outlet to discharge the reaction gas.

[0057] It should be noted that steps S210 and S220 of this embodiment are for configuring the electrolysis device, and their order is not limited. On the premise that the electrolysis device has been assembled, the above steps can be omitted and the electrolyte can be directly injected into it. Of course, the electrolysis device can also be boiled in ultrapure water before use and dried in air at 60°C overnight to remove impurities.

[0058] S230, injecting electrolyte into the electrolysis device, passing nitrogen gas for purging, passing a current of a certain density, and synthesizing ammonia through electrochemical nitrogen reduction reaction.

[0059] In some preferred embodiments, the nitrogen purge time is 1-60 min, and the current density is 1-50 mA·cm -2 ; The volume of the injected electrolyte is 10-100mL.

[0060] Specifically, in the electrochemical reduction process, the electrochemical performance of lithium-mediated electrochemical synthesis of ammonia can be improved by introducing metal inorganic salts as additives. 2+ The introduction of R-lithiophilic LiF heterojunction forms a lithium-phobic R-lithiophilic LiF heterojunction, in which the lithium-phobic R accelerates the Li + diffusion within the SEI and avoid high concentration polarization, while the lithiophilic LiF ensures the diffusion of Li + Uniform nucleation and its participation in subsequent reactions.

[0061] The electrolyte and its application will be further described below in conjunction with specific embodiments:

[0062] Example 1

[0063] The electrolysis device of this embodiment is an H-type electrolytic cell. As shown in Table 1, the electrolyte composition is a 1M tetrahydrofuran solution of lithium tetrafluoroborate, and contains 1% by volume of ethanol and 1.0% by mass of zinc nitrate. At a current density of 10 mA cm -2 The electrolysis lasted for 1350 s, and the ammonia yield was 11.8 nmol·s -1 cm -2 , the Faradaic efficiency (FE) is 32.07%.

[0064] like Figure 4 As shown, when N is introduced into the pure electrolyte 2 When the current density is much lower than that of the 1.0wt% Zn 2+ This indicates that the deposited Zn enhances the intrinsic activity of Li-NRR. 2 After, containing 1.0wt% Zn 2+ The current density of the electrolyte system is greatly reduced, which further verifies the above conclusion that the deposition of Zn enhances the intrinsic activity of Li-NRR.

[0065] In order to further understand the additive engineering and pure electrolyte derived SEI electrode process kinetics, the impedance diagrams of the two-electrolyte system without and with metal inorganic salt additives at -20℃ to 35℃ were tested, such as Figure 5 As shown in Figure 2, the activation energy calculated according to the Arrhenius formula shows that the electrolyte system containing metal inorganic salt additives requires less energy to pass through the SEI membrane, which is only about 1 / 2 of that in the pure electrolyte system. This shows that the lithium-philic-lithium-phobic heterojunction generated by the metal inorganic salt additive accelerates the reactants to pass through the SEI and speeds up the reaction rate.

[0066] Example 2

[0067] The electrolysis device of this embodiment is an H-type electrolytic cell. As shown in Table 1, the electrolyte composition is a 1M tetrahydrofuran solution of lithium tetrafluoroborate, and contains 1% by volume of ethanol and 2.0% by mass of zinc nitrate. At a current density of 10 mA cm -2 Electrolysis was performed for 1350 s, and the ammonia yield was 3.36 nmol·s -1 cm -2 , FE is 9.72%.

[0068] Example 3

[0069] The electrolysis device of this embodiment is an H-type electrolytic cell. The electrolyte composition is a 1M tetrahydrofuran solution of lithium tetrafluoroborate, and contains 1% by volume of ethanol and 1.0% by mass of zinc nitrate. At a current density of 20 mA cm -2 The electrolysis was carried out for 675 s, and the ammonia yield was 11.60 nmol·s -1 cm -2 , FE is 16.79%.

[0070] Compared with Example 1, increasing the current density and shortening the electrolysis time have little effect on the ammonia yield and reduce the FE.

[0071] Example 4

[0072] The electrolysis device of this embodiment is an H-type electrolytic cell. The electrolyte composition is a 1M tetrahydrofuran solution of lithium tetrafluoroborate, and contains 1% by volume of ethanol and 1.0% by mass of zinc nitrate. At a current density of 10 mA cm -2 The electrolysis was carried out for 5400 s, and the ammonia yield was 4.17 nmol·s -1 cm -2 , FE is 12.07%.

[0073] Compared with Example 1, increasing the electrolysis time leads to a decrease in both ammonia yield and FE.

[0074] It should be noted that the above embodiments are all described by taking zinc nitrate as an example. In other preferred embodiments, other zinc salts or other copper salts, such as copper nitrate, can also be selected. It should be noted that since copper ions are blue, the detection of NH 3 The concentration has a certain interference, so the product test needs to be quantitatively analyzed by liquid chromatography and nuclear magnetic resonance. Of course, silver salts can also be selected, such as silver nitrate. Since silver nitrate has low solubility in organic solvents, silver salts such as silver perchlorate can be preferred, and they are not listed one by one here.

[0075] Comparative Example 1

[0076] The electrolysis device of this comparative example 1 is an H-type electrolytic cell, the electrolyte composition is a 1M tetrahydrofuran solution of lithium tetrafluoroborate and contains 1% by volume of ethanol, and the current density is 10 mA cm -2 Electrolysis was performed for 1350 s, and the ammonia yield was 1.36 nmol·s -1 cm -2 , FE is 7.87%.

[0077] Compared with Example 1, without adding the inorganic metal additive, the ammonia yield and FE are both reduced, which shows that the metal inorganic salt additive helps to improve the ammonia production efficiency.

[0078] like Figure 4 As shown, when N is introduced into the pure electrolyte 2 The corresponding current density is much lower than that of Example 1 containing 1.0 wt% Zn 2+ This suggests that the deposited Zn enhances the intrinsic activity of Li-NRR.

[0079] like Figure 5 As shown, the activation energy calculated according to the Arrhenius formula shows that, compared with Example 1, the pure electrolyte system requires more energy to pass through the SEI membrane. It should be understood that in chemical kinetics, the lower the activation energy, the easier the reaction occurs, which means that Zn 2+ The presence of can accelerate the reactants through SEI, lower the energy threshold required for the reaction, and speed up the reaction rate.

[0080] Table 1 Ammonia production performance results

[0081]

[0082] The present disclosure provides an electrolyte for lithium-mediated electrochemical synthesis of ammonia, a preparation method, and an application thereof, which have the following beneficial effects compared with the prior art:

[0083] First, compared with the electrolyte system without adding metal inorganic salt additives, the metal inorganic salt additives disclosed in the present invention can enhance the intrinsic activity of the nitrogen reduction reaction, so that a solid electrolyte interphase (SEI) with a lithium-phobic and lithium-philic Zn-LiF inhibition structure is spontaneously formed during the reaction, thereby improving the Faraday efficiency and ammonia yield. In addition, the impedance of the electrolyte reaction system disclosed in the present invention and the activation energy of passing through the solid electrolyte membrane are significantly reduced, which helps to reduce energy consumption.

[0084] Second, the present invention can improve the Faraday efficiency and ammonia yield by optimizing the types of additives, proton sources, lithium salts, and solvents, and by controlling variables such as charge amount and electrolysis time, achieving an 8-fold increase in ammonia production selectivity compared to a system without additives.

[0085] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. An electrolyte for lithium-mediated electrochemical synthesis of ammonia, characterized in that: The electrolyte comprises: Lithium salts; Organic solvents; Proton source; Metallic inorganic salt additives.

2. The electrolyte according to claim 1, characterized in that The metal inorganic salt additive is any one of zinc salt, copper salt and silver salt.

3. The electrolyte according to claim 1, characterized in that The concentration of the metal inorganic salt additive is 0.1-3.0wt%; The concentration of the lithium salt in the organic solvent is 0.1-3M; The volume fraction of the proton source is 0.1-10 vol%; The volume fraction of the solvent is 90-99.9 vol%.

4. The electrolyte according to claim 1, characterized in that The lithium salt is any one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenide.

5. The electrolyte according to claim 1, characterized in that The solvent is any one of tetrahydrofuran, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and dioxolane.

6. The electrolyte according to claim 1, characterized in that The proton source is any one of methanol, ethanol, propanol and butanol.

7. A method for preparing the electrolyte according to any one of claims 1 to 6, characterized in that: The preparation method comprises: Dehydrating the lithium salt, the proton source and the solvent; The treated lithium salt is mixed with a proton source, a solvent and a metal inorganic salt additive to form an electrolyte.

8. The preparation method according to claim 7, characterized in that: The dehydration treatment of the lithium salt, the proton source and the solvent comprises: The lithium salt is dried at 100-130° C.; The zeolite molecular sieve is washed and dried, and the treated zeolite molecular sieve is used to dehydrate the solvent and the proton source.

9. Use of an electrolyte in lithium-mediated electrochemical synthesis of ammonia, characterized in that: The steps include: Sulfuric acid, potassium hydroxide and tetrahydrofuran pretreatment solutions are sequentially placed near the outlet of the nitrogen bottle; The electrolysis device is provided with a gas diffusion working electrode, a counter electrode, a reference electrode, a bubbler and a gas outlet, wherein the bubbler is located near the working electrode; The electrolyte according to any one of claims 1 to 6 is injected into the electrolysis device, and nitrogen is introduced for purging, and a current of a certain density is introduced to synthesize ammonia through an electrochemical nitrogen reduction reaction.

10. The use according to claim 9, characterized in that: The nitrogen purge time is 1-60 min, and the current density is 1-50 mA·cm -2 and / or, The volume of the electrolyte injected is 10-100 mL.

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