Modified ammonia electrooxidation electrolyte and application thereof

Abstract

This invention relates to the field of electrochemical energy conversion and electrosynthesis technology, specifically to a modified ammonia electro-oxidation electrolyte and its applications. The modified ammonia electro-oxidation electrolyte of this invention comprises an anhydrous organic solvent, a supporting electrolyte, and 1,8-diazabicyclo[5.4.0]undec-7-ene. This invention introduces 1,8-diazabicyclo[5.4.0]undec-7-ene as a functional additive into a conventional non-aqueous ammonia oxidation electrolyte, utilizing its strong basicity as a highly efficient proton scavenger to rapidly capture protons generated during the ammonia oxidation dehydrogenation step, reducing the dehydrogenation energy barrier, and simultaneously regulating the electrode / electrolyte interface microenvironment. Compared with existing technologies, this invention can significantly reduce the overpotential of the ammonia oxidation reaction, increase the current density and nitrogen Faradaic efficiency, and has good catalyst universality, making it applicable to the fields of ammonia electrolysis for hydrogen production, direct ammonia fuel cells, and the electrosynthesis of nitrogen-containing chemicals.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy conversion and electrosynthesis technology, specifically to a modified ammonia electro-oxidation electrolyte and its application. Background Technology

[0002] Ammonia (NH3), due to its high hydrogen content (approximately 17.6% by mass), ease of liquefaction and storage, and mature synthesis and transportation infrastructure, is considered a highly promising carbon-free energy storage carrier and key chemical raw material. Its electrochemical oxidation reaction (ammonia oxidation, AOR) can be used not only in direct ammonia fuel cells and electrocatalytic hydrogen production, but also demonstrates significant application value in the electrosynthesis of high-value-added nitrogen-containing chemicals and the treatment of ammonia-containing wastewater. However, traditional aqueous electrolytes suffer from several inherent defects, severely limiting the economic efficiency and energy efficiency of the entire system. Specifically: First, the thermodynamic potential for water splitting (1.23V vs. SHE) is lower than the theoretical potential for ammonia oxidation (approximately 0.077V), causing the oxygen evolution reaction (OER) to become the main competing side reaction, significantly reducing Faraday efficiency and energy conversion efficiency; second, the nitrogen oxides (NOx) generated during the reaction... x Intermediates such as ammonia molecules are easily adsorbed onto the electrode surface, causing poisoning and leading to electrolyte contamination and catalyst deactivation, resulting in generally poor long-term stability. Thirdly, the solubility of ammonia molecules in aqueous media is limited, and protons are mainly provided by water dissociation, which fails to fully utilize the advantages of ammonia as a high-density hydrogen storage carrier. Mass transfer of reactants is limited, and the overall current density and energy efficiency are difficult to improve.

[0003] To circumvent the inherent limitations of aqueous systems, researchers have gradually shifted towards anhydrous organic electrolyte systems. These electrolytes typically have a wider electrochemical stability window (usually >1.5V), effectively suppressing oxygen evolution side reactions and providing a wider operable potential range for AOR (Aqueous Ortho-Or ... Although this system avoids oxygen evolution competition reactions in a non-aqueous environment, the ammonia oxidation reaction still exhibits a high overpotential and limited current response; especially in the low potential range, the reaction start-up is slow and the utilization rate of active sites on the catalyst surface is low. The root cause is that the electrolyte's ability to regulate the ammonia deprotonation process is insufficient, resulting in a high energy barrier for the ammonia dehydrogenation step and limited interfacial charge transfer kinetics. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a modified ammonia electro-oxidation electrolyte and its application, comprising an anhydrous organic solvent, a supporting electrolyte, and 1,8-diazabicyclo[5.4.0]undec-7-ene. The anhydrous organic solvent serves as the base medium, supporting the electrolyte and providing an ion-conducting environment. DBU acts as a proton transfer regulator, interacting with protons in the system, reactants at the interface, and electrolyte ions to optimize the overall reaction kinetics from the electrolyte side without altering the catalyst itself. Therefore, the electrolyte of this invention can directly regulate the proton transfer process and the interfacial reaction microenvironment, significantly reducing the overpotential of the ammonia oxidation reaction and increasing the current density, thereby solving the problems of slow reaction kinetics, high overpotential, and limited current density caused by insufficient proton management capabilities in existing non-aqueous electrolytes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a modified ammonia electro-oxidation electrolyte, comprising an anhydrous organic solvent, a supporting electrolyte, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU); wherein the concentration of DBU is 0.1 mol / L to 0.5 mol / L, which acts as a proton transfer regulator to promote the proton transfer process in the electrolyte, thereby reducing the overpotential of the ammonia electro-oxidation reaction and increasing the current density. In the above modified ammonia electro-oxidation electrolyte, the anhydrous organic solvent serves as the continuous phase and basic medium, used to dissolve ammonia, support the electrolyte and DBU, and provide a stable non-aqueous medium environment for the electrochemical reaction; the supporting electrolyte is dissolved in the above anhydrous organic solvent, taking ammonium benzenesulfonate as an example, its main functions include: (1) providing ammonium ions (NH4+) + ), serving as a storage and transport carrier for protons in the reaction system, and through NH4 + / NH3 balances the ammonia species required for the reaction; (2) participates in the interfacial charge transport under the action of an electric field, ensuring the ionic conductivity of the electrolyte; (3) its benzenesulfonate anion has good electrochemical stability and solvent compatibility, which helps to maintain the long-term stable operation of the electrolyte system.

[0006] Preferably, the concentration of 1,8-diazabicyclo[5.4.0]undec-7-ene in the modified ammonia electro-oxidation electrolyte is 0.25 mol / L. Below this concentration, the proton capture and interface regulation capabilities of the DBU are not fully utilized; above this concentration, the negative effects of mass transfer resistance and interfacial competitive adsorption will outweigh its positive promoting effect, leading to a decline in overall performance.

[0007] Preferably, the concentration of the electrolyte in the electrolyte solution is 0.01 mol / L to 2.0 mol / L.

[0008] Preferably, the supporting electrolyte is selected from at least one of ammonium benzenesulfonate, tetrabutylammonium salt, lithium perchlorate, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0009] Preferably, the anhydrous organic solvent is selected from at least one of dimethylformamide, acetonitrile, dimethyl sulfoxide, N,N-dimethylacetamide, and propylene carbonate.

[0010] Preferably, the anhydrous organic solvent is a mixture of dimethylformamide and acetonitrile, and the volume ratio of dimethylformamide to acetonitrile is 1:9 to 9:1.

[0011] The second objective of this invention is to provide an application of the above-mentioned modified ammonia electro-oxidation electrolyte in the electrocatalytic ammonia oxidation reaction, as detailed below: A three-electrode system was constructed using a glassy carbon electrode supported on a catalyst as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The working electrode, counter electrode, and reference electrode were placed in the modified ammonia electro-oxidation electrolyte. Ammonia gas or ammonia-containing feed gas was continuously introduced into the modified ammonia electro-oxidation electrolyte to dissolve the ammonia in the electrolyte until saturation. A potential was applied between the working electrode and the counter electrode using linear sweep voltammetry or cyclic voltammetry to cause the ammonia to undergo an electrochemical oxidation reaction on the working electrode to generate nitrogen gas.

[0012] Preferably, the conditions for the electrochemical oxidation reaction are: voltage of 0V vs. Ag / AgCl to 1.5V vs. Ag / AgCl, temperature of -20℃ to 80℃, and scan rate of 5mV / s to 50mV / s.

[0013] Preferably, the catalyst supported on the working electrode is selected from platinum-carbon catalysts, samarium oxide catalysts, nickel-based oxide catalysts, or nickel-iron layered double hydroxide catalysts.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a modified ammonia electro-oxidation electrolyte, comprising an anhydrous organic solvent, a supporting electrolyte, and 1,8-diazabicyclo[5.4.0]undec-7-ene; wherein the concentration of DBU is 0.1 mol / L to 0.5 mol / L. Without altering the catalyst, the modified ammonia electro-oxidation electrolyte of this invention allows DBU to directly regulate the proton transfer process and interfacial reaction microenvironment in the electrolyte through interaction with protons, interfacial reactive species, and electrolyte ions in the system. This significantly reduces the reaction overpotential and increases the current density, thereby solving the shortcomings of existing non-aqueous electrolytes in proton management and reaction kinetics promotion, which still result in high overpotential and limited current density in overall performance.

[0015] In this system, anhydrous organic solvents form the basic framework of the reaction, supporting the dissolution of electrolytes as reactants and charge transport carriers; DBU, as a key additive, does not act directly as a reactant, but rather performs the following core functions through its molecular structure (strong basicity, large steric hindrance, bicyclic structure): (a) Highly efficient proton acceptor: rapidly capturing ammonia oxidative dehydrogenation steps (such as NH3→NH2+H) + +e - (a) The protons generated in the reaction drive the equilibrium to shift to the right, lowering the dehydrogenation energy barrier; (b) the interfacial microenvironment modifier: adsorbed or distributed near the electrode surface, forming a local alkaline or specific polar microenvironment, which is conducive to NH3 adsorption and intermediate stability; (c) the medium-stable ligand: the lone pair electrons on its nitrogen atom interact weakly with the reaction intermediate (such as NH2), guiding it to couple towards the direction of N2 formation, and inhibiting side reactions.

[0016] 2. The modified ammonia electro-oxidation electrolyte of the present invention is a novel electrolyte or electrolyte system that can significantly improve the performance of ammonia oxidation reaction in anhydrous systems. It has the characteristics of high ammonia solubility, high ionic conductivity, wide electrochemical window, good interfacial compatibility and high stability. It can also work synergistically with efficient and inexpensive non-precious metal catalysts to reduce the reaction energy barrier and increase the current density. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the mechanism by which DBU regulates the non-aqueous ammonia oxidation reaction.

[0018] Figure 2 The graph shows the LSV test results of the modified ammonia electro-oxidation electrolyte of Example 1 and the ammonia electro-oxidation electrolyte of Comparative Example 1, where a represents the condition without NH3 introduction and b represents the condition with saturated NH3.

[0019] Figure 3 The graph shows the LSV test results of the modified ammonia electro-oxidation electrolytes of Examples 1 to 4 under saturated NH3 conditions.

[0020] Figure 4 The graph shows the EIS test results of the modified ammonia electro-oxidation electrolytes of Examples 1 to 4 and the ammonia electro-oxidation electrolyte of Comparative Example 1 under saturated NH3 conditions.

[0021] Figure 5 The graph shows the LSV test results of the modified ammonia electro-oxidation electrolyte of Example 8 and the ammonia electro-oxidation electrolyte of Comparative Example 1 under saturated NH3 conditions.

[0022] Figure 6 The graph shows the LSV test results of the modified ammonia electro-oxidation electrolytes of Examples 6 to 9 under saturated NH3 conditions.

[0023] Figure 7The graph shows the EIS test results of the modified ammonia electro-oxidation electrolytes of Examples 6 to 9 and the ammonia electro-oxidation electrolyte of Comparative Example 1 under saturated NH3 conditions.

[0024] Figure 8 The graph shows the LSV test results of the modified ammonia electro-oxidation electrolyte of Comparative Example 2 under conditions of no NH3 introduction and saturated NH3. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased on the market or prepared by existing methods.

[0027] Although previous studies have improved the activity of ammonia oxidation by introducing catalysts with specific structures into non-aqueous electrolytes, performance breakthroughs still mainly rely on the optimization of the catalytic material interface, failing to actively regulate the proton transfer environment and reaction micro-interface from the electrolyte side. Therefore, the following key issues remain unresolved: insufficient proton transfer efficiency constrains reaction kinetics. In electrolytes composed of pure organic solvents and ammonium benzenesulfonate, the protons released from ammonia dehydrogenation (NH bond breaking) lack efficient acceptors or rapid transfer channels, relying mainly on solvent molecule-mediated or slow interfacial diffusion. This makes the proton-coupled electron transfer step the rate-controlling step, leading to an increased activation barrier, increased overpotential, and difficulty in further increasing the current density.

[0028] This invention, after clarifying that the core bottleneck of existing non-aqueous systems lies in insufficient proton transfer efficiency, establishes a design criterion of introducing highly efficient proton traps to break the thermodynamic limitations of the dehydrogenation step and drive the reaction equilibrium to shift forward. Based on this criterion, a variety of candidate additives possessing strong basicity, non-nucleophilicity, and good organic solubility were systematically screened, including amidines (DBU, DBN), guanidines (TBD, TMG), phosphazene bases (t-Bu-P4), conventional organic amines (triethylamine, diisopropylethylamine), and imidazole ionic liquids (such as 1-ethyl-3-methylimidazolium acetate). Comparative electrochemical tests in the same basic electrolyte (0.05 mol / L ammonium benzenesulfonate / DMF) showed that most candidate additives either failed to significantly reduce the onset potential due to insufficient basicity (such as triethylamine), or caused side reactions and deteriorated the current response due to instability under the anodic window (such as imidazole salts). Even some strong bases (such as t-Bu-P4) experienced severe mass transfer obstruction due to a dramatic increase in viscosity. DBU is the only additive that can significantly reduce overpotential while maintaining stable current gain and good system compatibility. Its bridged ring structure provides moderate basicity, large steric hindrance brings non-nucleophilic properties, and bicyclic conjugated stable protonation form, making it the only ideal additive that simultaneously meets the triple conditions of "strongly promoting proton transfer, not interfering with catalyst active sites, and being electrochemically stable".

[0029] (1) Proton affinity level matching. The initial dehydrogenation step of the ammonia oxidation reaction (NH3→NH2+H) + +e - In non-aqueous systems, DBU faces a high activation energy barrier, essentially due to the lack of efficient acceptors for the released protons, leading to NH bond breaking and becoming a kinetic bottleneck. The pK of DBU in acetonitrile... a The pK of DBN in DMF is 24.3, and approximately 23.5, which falls within the golden window of effectively capturing protons to drive dehydrogenation equilibrium, but not so strongly as to irreversibly consume intermediates or cause excessive interfacial basicization. Meanwhile, the pK of DBN in DMF... a The free energy of DBN is about 0.5 to 0.8 log units lower than that of DBU. According to the Hammett-type linear free energy relationship, this difference means that DBN has insufficient thermodynamic driving force for the protons released during the oxidative dehydrogenation of ammonia. At the same potential, it cannot effectively pull the NH bond breaking equilibrium, and its promoting effect on the overall reaction rate is extremely limited.

[0030] (2) Thermodynamic stability of the protonated form. The stability of the cation species formed after the additive captures protons determines the reversibility of the capture step and the cycle efficiency of subsequent proton transfer and additive regeneration. The protonated product of DBU [DBU-H] + It possesses a unique bicyclic conjugated system, where positive charges can be effectively dispersed through transcyclic delocalization, endowing it with extremely high thermodynamic stability and preventing interfacial reactions from being hindered by cation accumulation; simultaneously, [DBU-H] +Capable of rapidly transferring protons to benzenesulfonate anions (PhSO3). - (or DMF solvent molecules) enable the regeneration of the DBU and long-range transport of protons, forming a complete proton shuttle cycle. DBN-H + Because the rigidity of the pentagonal ring restricts the optimal orientation of the conjugated system, the degree of positive charge delocalization is not as high as that of [DBU-H]. + This leads to two negative effects: firstly, the reverse reaction (deprotonation) of DBN capturing protons has a faster rate, weakening its pulling effect on the dehydrogenation step; secondly, DBN-H + The prolonged residence time at the electrode interface makes it easier to form a space charge layer, which hinders the diffusion and adsorption of ammonia molecules to the active site.

[0031] (3) Electrochemical tolerance window. The oxidation initiation potential of DBU in the DMF system is higher than +1.5V (vs. Ag / Ag). + The effective operating potential range for ammonia oxidation is typically +0.8 to +1.4 V. DBU remains within its electrochemically stable window throughout this range, not participating in electrode reactions but regulating the reaction microenvironment solely through intermolecular interactions. The oxidation initiation potential of DBN in the DMF system is advanced to approximately +1.0 V (vs. Ag / Ag). + The anodic oxidation potential (APO) overlaps with the optimal reaction potential range for ammonia oxidation, resulting in irreversible anodic degradation upon application of an anodic potential. This side reaction not only directly consumes charge and reduces Faraday efficiency, but its degradation products can also adsorb onto the catalyst surface, covering active sites and further inhibiting ammonia adsorption and activation. This electrochemical instability is the root cause of the observed phenomenon in experiments where DBN "is itself electro-oxidized" and "cannot significantly enhance ammonia oxidation activity."

[0032] (4) Interfacial structure-activity relationship. The spatial behavior of additives at the electrode / electrolyte interface has a decisive influence on their function, including adsorption orientation, interfacial coverage, ability to modulate the double layer structure, and non-covalent interactions with reaction intermediates. The [5.4.0] bicyclic skeleton of DBU contains a seven-membered ring and a six-membered ring, and has a moderate molecular size (Vander Waals volume approximately 180 Å). 3The seven-membered ring provides the molecule with good conformational flexibility, allowing it to undergo weak adsorption in various orientations on the electrode surface (such as lying flat, tilting, or standing upright). This effectively regulates the interfacial electric double layer structure and reduces the interfacial proton transport barrier without blocking ammonia molecules from approaching the active site. At the same time, the hydrophobic properties of the DBU framework help to repel trace amounts of water and maintain a strictly anhydrous microenvironment at the interface. In contrast, the [4.3.0] framework of DBN contains a five-membered ring and a six-membered ring. The rigidity of the five-membered ring restricts the molecular conformational freedom, making its adsorption orientation at the interface tend to be singular and fixed, leading to two adverse consequences: on the one hand, the arrangement of DBN molecules at the interface may be too dense or poorly oriented, occupying the adsorption space of ammonia molecules and generating a competitive steric hindrance effect; on the other hand, it cannot adjust its conformation according to the instantaneous spatial requirements of reaction intermediates, weakening its stabilizing effect on key intermediates such as NH2.

[0033] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will provide a detailed description in conjunction with specific embodiments: Example 1 A method for preparing a modified ammonia electro-oxidation electrolyte includes the following steps: In an argon-atmosphere-protected glove box, 0.856 g of ammonium benzenesulfonate was added to 50 mL of thoroughly dried DMF solvent. The solution was magnetically stirred at 500 rpm at room temperature until completely dissolved, yielding a clear 0.05 mol / L ammonium benzenesulfonate / DMF electrolyte (Comparative Example 1). Subsequently, under continuous stirring, 3.8 g of DBU was added dropwise to the ammonia electro-oxidation electrolyte (Comparative Example 1), and stirring continued for 60 min until homogeneous, ensuring uniform dispersion of DBU and sufficient interaction with the system, resulting in a modified ammonia electro-oxidation electrolyte. The concentration of DBU in the modified ammonia electro-oxidation electrolyte was 0.25 mol / L.

[0034] Example 2 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 1, except that the concentration of DBU in the modified ammonia electro-oxidation electrolyte is replaced from 0.25 mol / L to 0.1 mol / L to obtain the modified ammonia electro-oxidation electrolyte.

[0035] Example 3 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 1, except that the concentration of DBU in the modified ammonia electro-oxidation electrolyte is replaced from 0.25 mol / L to 0.15 mol / L to obtain the modified ammonia electro-oxidation electrolyte.

[0036] Example 4 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 1, except that the concentration of DBU in the modified ammonia electro-oxidation electrolyte is replaced from 0.25 mol / L to 0.2 mol / L to obtain the modified ammonia electro-oxidation electrolyte.

[0037] Example 5 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 1, except that the concentration of DBU in the modified ammonia electro-oxidation electrolyte is replaced from 0.25 mol / L to 0.3 mol / L to obtain the modified ammonia electro-oxidation electrolyte.

[0038] Example 6 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 2, except that the anhydrous organic solvent is replaced by acetonitrile instead of DMF to obtain the modified ammonia electro-oxidation electrolyte.

[0039] Example 7 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 3, except that the anhydrous organic solvent is replaced by acetonitrile instead of DMF to obtain the modified ammonia electro-oxidation electrolyte.

[0040] Example 8 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 4, except that the anhydrous organic solvent is replaced by acetonitrile instead of DMF to obtain the modified ammonia electro-oxidation electrolyte.

[0041] Example 9 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as that in Example 1, except that the anhydrous organic solvent is replaced by acetonitrile instead of DMF to obtain the modified ammonia electro-oxidation electrolyte.

[0042] Comparative Example 1 A method for preparing an ammonia electro-oxidation electrolyte includes the following steps: In an argon-filled glove box, weigh 0.856 g of ammonium benzenesulfonate and add it to 50 mL of thoroughly dried DMF solvent. Stir at room temperature with magnetic stirring (e.g., 500 rpm) until the ammonium benzenesulfonate is completely dissolved to obtain a clear 0.05 mol / L ammonium benzenesulfonate / DMF comparative example 1 ammonia electro-oxidation electrolyte, i.e., ammonia electro-oxidation electrolyte.

[0043] Comparative Example 2 A method for preparing a modified ammonia electro-oxidation electrolyte is the same as the method in Example 1, except that DBU is replaced with DBN to obtain the modified ammonia electro-oxidation electrolyte.

[0044] application: To quantitatively evaluate the effect of the functional additive DBU on the kinetics of ammonia electro-oxidation, the modified ammonia electro-oxidation electrolytes of Examples 1 to 9 and the ammonia electro-oxidation electrolyte of Comparative Example 1 were used as electrolytes, and a glassy carbon electrode with a catalyst supported on a diameter of 5 mm was used as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode to construct a three-electrode electrochemical testing system.

[0045] The preparation of the catalyst-supported glassy carbon electrode is as follows: 5 mg of Ce2MgCu2 catalyst is dispersed in a mixed solution consisting of 900 μL of anhydrous ethanol and 50 μL of Nafion, and ultrasonically treated for 45 min to obtain a catalyst slurry; 10 μL of the catalyst slurry is coated on the surface of the glassy carbon electrode and air-dried at room temperature to obtain the catalyst-supported glassy carbon electrode.

[0046] Before testing, cyclic voltammetry (CV) was performed at a scan rate of 50 mV / s within a potential window of 0 V to 1.5 V (vs. Ag / AgCl) without ammonia gas introduction. The background current was recorded to confirm the electrochemical stability of the electrolyte and working electrode within this window. Subsequently, high-purity anhydrous ammonia gas was continuously introduced into the electrolyte at a flow rate of 50 mL / min for at least 15 min to saturate the electrolyte with ammonia. Under continuous ammonia gas introduction, linear sweep voltammetry (LSV) tests were performed within the same potential window at scan rates of 5 mV / s to 50 mV / s.

[0047] like Figure 2 As shown in Figure a, without the introduction of NH3, the addition of DBU did not cause a significant change in the background current. The two curves basically overlapped throughout the entire scan potential range, and the background current density remained at a low level (<0.5 mA / cm²). 2 This result demonstrates that within the potential window (0–1.5 V vs. Ag / AgCl) involved in this invention, DBU molecules do not undergo any significant electrochemical oxidation reaction, exhibiting good electrochemical inertness. These properties ensure that DBU plays only a chemical regulatory role within the operating potential range of the ammonia oxidation reaction, without participating in direct charge transfer processes, and without introducing side reactions or generating toxic species due to its own electrochemical decomposition.

[0048] like Figure 2 As shown in b, under NH3 saturation conditions, the introduction of DBU significantly promoted the electrochemical response of ammonia oxidation. At a potential of 1.1 V, the anolyte current density in the modified ammonia electrooxidation electrolyte reached 30.6 mA / cm². 2 In contrast, the current density of the ammonia electro-oxidation electrolyte in Comparative Example 1 was only 15.2 mA / cm² at the same potential. 2This represents an increase of approximately 2.0 times. These results indicate that the addition of DBU significantly accelerates the kinetic rate of the ammonia oxidation reaction. More importantly, the addition of DBU also causes a significant negative shift in the onset oxidation potential. (At a current density of 0.5 mA / cm²) 2 The potential corresponding to this point is defined as the initiation potential. The initiation potential of ammonia oxidation in the modified ammonia electro-oxidation electrolyte is 0.41V, which is approximately 90mV negatively shifted compared to the initiation potential (0.50V) of the ammonia electro-oxidation electrolyte in Comparative Example 1. This significant reduction in initiation potential directly indicates that DBU effectively lowers the electrochemical overpotential of the ammonia oxidation reaction, enabling the reaction to initiate under lower anodic polarization conditions. This phenomenon is highly consistent with the functional positioning of DBU as a highly efficient proton scavenger, namely, by rapidly capturing protons released during the ammonia dehydrogenation step, it lowers the activation barrier of the NH bond breaking step, thereby promoting the initial excitation of the reaction at both thermodynamic and kinetic levels.

[0049] This invention systematically investigated the ammonia oxidation reactivity of a modified ammonia electro-oxidation electrolyte under saturated NH3 conditions at DBU concentrations of 0.15 mol / L, 0.20 mol / L, 0.25 mol / L, and 0.30 mol / L. The test results are as follows: Figure 3 As shown.

[0050] Depend on Figure 3 It was found that the promoting effect of DBU on the ammonia oxidation reaction showed a significant non-monotonic dependence: when its concentration increased from 0.15 mol / L to 0.25 mol / L, the anolyte current density continued to increase with the increase of concentration, indicating that the proton capture and interface regulation function of DBU was enhanced with the increase of the number of available molecules in this range; however, when its concentration was further increased to 0.30 mol / L, the current density dropped significantly, indicating that the excess DBU had an inhibitory effect on the reaction. This phenomenon is mainly attributed to: (1) high concentration of DBU leads to an increase in electrolyte viscosity, a decrease in the diffusion coefficient of ammonia molecules and reaction intermediates, and a limitation of mass transfer process; (2) excess DBU forms a dense adsorption layer on the electrode surface, occupies catalytic active sites, and hinders the adsorption and activation of ammonia molecules; (3) excessively high concentration of DBU changes the double layer structure, increases the interfacial resistance, and weakens the charge transfer efficiency.

[0051] There is an optimal range for the promoting effect of DBU concentration on the ammonia oxidation reaction; under the experimental conditions of this invention, 0.25 mol / L is the optimal addition concentration. These results indicate that the function of DBU depends on its concentration balance in the bulk solution and at the interface, and an appropriate concentration is key to achieving the best promoting effect.

[0052] The AC impedance response of this powder was determined in pure DMF solvent and in modified ammonia electro-oxidation electrolytes containing 0.05 mol / L ammonium benzenesulfonate and DBU concentrations of 0.15 mol / L, 0.20 mol / L, 0.25 mol / L, and 0.30 mol / L. The charge transfer impedance (Rct) values ​​for each system were obtained by equivalent circuit fitting, and the results are as follows: Figure 4 As shown.

[0053] Depend on Figure 4 The Rct of the pure DMF system was found to be 76.5 Ω. With the introduction of DBU, Rct decreased significantly: to 56.4 Ω at 0.15 mol / L, 55.8 Ω at 0.20 mol / L, and a minimum of 47.1 Ω at 0.25 mol / L, a reduction of approximately 38.4% compared to the pure DMF system. This trend indicates that DBU effectively lowers the charge transfer barrier at the electrode / electrolyte interface, accelerating interfacial electron transfer, which is highly consistent with the results of LSV testing showing an increase in current density with increasing DBU concentration (0.15 mol / L~0.25 mol / L). When the DBU concentration was further increased to 0.30 mol / L, Rct rebounded to 48.2 Ω. This inflection point confirms... Figure 3 The performance degradation caused by excessive DBU is mainly attributed to the increase in electrolyte viscosity, decrease in mass transfer coefficient and densification of the interfacial adsorption layer caused by high concentration of DBU, which partially offsets its positive contribution to promoting proton transfer.

[0054] Combining the EIS and LSV results, the effect of DBU concentration on ammonia oxidation performance shows a clear "volcano-like" relationship: 0.25 mol / L is the optimal addition concentration under the experimental conditions. At this concentration, DBU has the greatest promoting effect on interfacial charge transfer, while avoiding the negative effects of mass transfer and interfacial competitive adsorption caused by high concentration.

[0055] Figure 5 This study demonstrates the universality of the promoting effect of DBU on ammonia oxidation in an acetonitrile system. At 1.1V, the anolyte current density of the basic electrolyte is only 1.75 mA / cm². 2 The DBU-modified electrolyte increased to 4.58 mA / cm² at the same potential. 2 The increase was approximately 2.6 times. This improvement is roughly equivalent to that of the DMF system (approximately 2.0 times), indicating that the accelerating effect of DBU on the kinetics of ammonia oxidation can be effectively exerted in various non-aqueous solvents.

[0056] The addition of DBU also caused a negative shift in the onset oxidation potential: the onset potential of the base electrolyte was 0.79V, which shifted negatively to 0.69V in the DBU-modified electrolyte, a decrease of approximately 100mV. This result further confirms that the mechanism by which DBU acts as a proton scavenger to reduce the overpotential of ammonia oxidation is solvent-universal and does not depend on any specific organic solvent.

[0057] comprehensive Figure 2 and Figure 5 The results show that, regardless of whether DMF or acetonitrile is used as the solvent, the introduction of DBU significantly increases the current density and markedly shifts the onset potential of the ammonia oxidation reaction without altering its electrochemical stability. This solvent substitution experiment fully verifies the solvent universality of the DBU-modified electrolyte strategy. Its core mechanism—DBU-mediated proton transfer promotion and interfacial microenvironment regulation—provides experimental support for the widespread application of this invention's technical solution in different electrolyte systems.

[0058] Depend on Figure 6 It was found that the promoting effect of DBU concentration on the ammonia oxidation reaction was also non-monotonic in the acetonitrile system, but the optimal concentration window differed from that in the DMF system. When the DBU concentration increased from 0.10 mol / L to 0.20 mol / L, the anolyte current density continued to increase, indicating that the proton capture function of DBU was fully utilized and the interfacial charge transfer efficiency gradually improved; however, when the concentration was further increased to 0.25 mol / L, the current density dropped significantly, indicating that the excess DBU had an inhibitory effect on the reaction. This inflection point was mainly due to: (1) the high concentration of DBU in the acetonitrile system led to an increase in electrolyte viscosity, a decrease in the diffusion coefficient of ammonia molecules and reaction intermediates, and limited mass transfer; (2) the excess DBU formed a dense adsorption layer on the electrode surface, occupying catalytic active sites and inhibiting the adsorption and activation of ammonia molecules; (3) the interfacial double layer structure was changed due to the excess additive, the interfacial impedance increased, and the charge transfer efficiency was weakened.

[0059] comprehensive Figure 5 and Figure 6 The results showed that DBU also exhibited a significant promoting effect in the acetonitrile system, but its optimal addition concentration was 0.20 mol / L, lower than the 0.25 mol / L in the DMF system. This difference may stem from the different dielectric constants, donor numbers, and solvation capabilities of the two solvents, which in turn affected the aggregation state, diffusion behavior, and effective concentration distribution of DBU at the interface in the bulk solution. Nevertheless, DBU exhibited a clear "volcano-like" concentration dependence in various non-aqueous solvent systems, verifying its general applicability as a functional additive, while also indicating that fine optimization of DBU concentration is necessary for specific solvent systems in practical applications.

[0060] Figure 7The results show that the charge transfer impedance of the pure acetonitrile system is 149.0 Ω, significantly higher than that of the DMF system (76.5 Ω), reflecting the fundamental differences between the two solvents in terms of dielectric properties, donor number, and ion solvation ability. With the introduction of DBU, Rct exhibits a "volcano-shaped" change, first decreasing and then increasing: it drops to 55.5 Ω at 0.10 mol / L, a decrease of 62.8%; it further decreases to 54.1 Ω at 0.15 mol / L; and reaches its lowest value of 53.1 Ω at 0.20 mol / L, where the interfacial charge transfer efficiency is optimal. When the concentration continues to increase to 0.25 mol / L, Rct rebounds to 60.7 Ω. This inflection point... Figure 6 The results from LSV are in complete agreement, indicating that the increase in viscosity caused by excessive DBU and the densification of the interfacial adsorption layer lead to an increase in mass transfer resistance, which partially offsets its positive contribution to promoting proton transfer.

[0061] Based on the combined EIS and LSV results, the optimal concentration of DBU in the acetonitrile system is 0.20 mol / L. This concentration is lower than that in the DMF system, mainly due to the lower dielectric constant (ε=37.5) and weaker Lewis basicity (donor number DN=14.1) of acetonitrile, which reduces its affinity for DBU molecules and [DBU-H]. + The solvation ability of cations is weaker than that of DMF (ε=38.3, DN=26.6), which makes it easier for DBU to reach effective concentration saturation at the interface in acetonitrile, thus achieving optimal interface control at a lower bulk concentration. Nevertheless, DBU exhibits a clear "volcano-like" concentration dependence and a significant reduction in charge transfer impedance in both solvent systems, verifying its solvent versatility as a functional additive for ammonia oxidation.

[0062] Figure 8 The results showed that, even without the introduction of NH3, the DBN-modified electrolyte exhibited a significant oxidation current response during the anodic scan, with a background current density significantly higher than that of the DBU system. Figure 2 (a) This oxidation current indicates that DBN underwent an electrochemical oxidation reaction within the investigated potential window. Its own oxidation initiation potential is lower than or close to the ammonia oxidation initiation potential, leading to preferential irreversible degradation when the anodic potential is applied. Under NH3 saturation conditions, although the apparent current density of the DBN-modified electrolyte increased, the increase was limited, and the contribution of the ammonia oxidation reaction to the DBN's own oxidation current could not be distinguished. This means that even if an ammonia oxidation reaction occurs, its signal is significantly interfered with by the DBN oxidation current. This phenomenon corroborates that DBN does not possess sufficient electrochemical stability within the ammonia oxidation working potential range; its own oxidation side reactions and the target reaction superimpose each other, severely affecting the reliability of the test results.

[0063] contrast Figure 8 and Figure 2The results show that DBN cannot serve as an effective functional additive for non-aqueous ammonia oxidation systems due to insufficient electrochemical stability. Its premature oxidation within the operating potential range not only fails to provide effective proton capture and interface regulation functions, but also introduces additional side reaction currents and potential electrode poisoning effects. This result further confirms the irreplaceable nature of DBU in the system of this invention: only DBU, possessing both an appropriate proton affinity level and a sufficiently broad electrochemical stability window, can maintain its electrochemical inertness and functional stability while promoting the ammonia oxidation reaction.

[0064] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A modified ammonia electro-oxidation electrolyte, characterized in that, The modified ammonia electro-oxidation electrolyte comprises an anhydrous organic solvent, a supporting electrolyte, and 1,8-diazabicyclo[5.4.0]undec-7-ene; The concentration of 1,8-diazabicyclo[5.4.0]undec-7-ene is 0.1 mol / L to 0.5 mol / L.

2. The modified ammonia electro-oxidation electrolyte according to claim 1, characterized in that, In the modified ammonia electro-oxidation electrolyte, the concentration of 1,8-diazabicyclo[5.4.0]undec-7-ene is 0.25 mol / L.

3. The modified ammonia electro-oxidation electrolyte according to claim 1, characterized in that, The supported electrolyte concentration is 0.01 mol / L to 2.0 mol / L.

4. The modified ammonia electro-oxidation electrolyte according to claim 1, characterized in that, The supporting electrolyte is selected from at least one of ammonium benzenesulfonate, tetrabutylammonium salt, lithium perchlorate, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide.

5. The modified ammonia electro-oxidation electrolyte according to claim 1, characterized in that, The anhydrous organic solvent is selected from at least one of dimethylformamide, acetonitrile, dimethyl sulfoxide, N,N-dimethylacetamide, and propylene carbonate.

6. The modified ammonia electro-oxidation electrolyte according to claim 5, characterized in that, The anhydrous organic solvent is a mixture of dimethylformamide and acetonitrile, with a volume ratio of dimethylformamide to acetonitrile of 1:9 to 9:

1.

7. The application of the modified ammonia electro-oxidation electrolyte according to any one of claims 1 to 6 in the electrocatalytic ammonia oxidation reaction, characterized in that, Specifically as follows: A three-electrode system was constructed using a glassy carbon electrode supported on a catalyst as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode; the working electrode, counter electrode, and reference electrode were respectively placed in the modified ammonia electro-oxidation electrolyte; Ammonia gas or ammonia-containing raw material gas is continuously introduced into the modified ammonia electro-oxidation electrolyte to dissolve the ammonia in the modified ammonia electro-oxidation electrolyte until it reaches saturation. A potential is applied between the working electrode and the counter electrode using linear sweep voltammetry or cyclic voltammetry, causing ammonia to undergo an electrochemical oxidation reaction on the working electrode to generate nitrogen gas.

8. The application according to claim 7, characterized in that, The conditions for the electrochemical oxidation reaction are: voltage 0V vs. Ag / AgCl ~ 1.5V vs. Ag / AgCl, temperature -20℃ ~ 80℃, and scan rate 5mV / s ~ 50mV / s.

9. The application according to claim 7, characterized in that, The catalyst supported on the working electrode is selected from platinum-carbon catalysts, samarium oxide catalysts, nickel-based oxide catalysts, or nickel-iron layered double hydroxide catalysts.

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