AMMONIA PRODUCTION METHOD

Description

FIELD OF INVENTION

The present invention relates to a high-efficiency green ammonia production method of electrochemical energy conversion technology, particularly to a green ammonia production system and method for carrying out a nitrogen reduction reaction (NRR) under ambient temperature and pressure.

BACKGROUND OF THE INVENTION

Ammonia (NH₃) is one of the most critical raw materials in modern chemical industry. Its main applications cover fertilizer synthesis, bioenergy utilization, fine chemical production, and pharmaceutical intermediates. In addition, due to its high volumetric energy density, ease of liquefaction under ambient conditions, and convenient storage and transportation, ammonia is regarded as a highly promising hydrogen carrier in the hydrogen economy. A complete infrastructure for ammonia transport and storage has already been established worldwide, allowing ammonia to play an important role in energy transition and renewable energy utilization. Particularly in the development of zero-carbon fuels, ammonia can be directly applied in power generation or as a marine fuel, becoming a crucial option for energy diversification.

However, currently more than 90% of global ammonia still relies on the Haber-Bosch process. This method requires extremely high temperature and pressure conditions, and the hydrogen feedstock typically originates from fossil-fuel-based steam reforming. Such harsh conditions lead to enormous energy consumption, making it one of the major challenges for global carbon neutrality and energy transition. Furthermore, because this process heavily depends on centralized large-scale chemical plants, it lacks the flexibility of distributed production, which is unfavorable for the promotion of future green energy applications.

Electrochemical nitrogen reduction reaction (electrochemical NRR, e-NRR) is considered an important alternative to the Haber-Bosch process. This method directly reduces nitrogen molecules to ammonia using external electrical energy, theoretically feasible under room temperature and atmospheric pressure, and can be coupled with renewable energy such as solar or wind power to realize low-carbon or even zero-carbon ammonia production. However, current e-NRR technologies still face major challenges. First, the triple bond in nitrogen molecules is extremely stable and difficult to activate, resulting in slow reaction rates. Second, the hydrogen evolution reaction (HER) often competes with NRR for electrons and protons, leading to low ammonia generation efficiency and difficulty in obtaining high purity and high selectivity products. In addition, common electrolytes or solvents in existing technologies often lack sufficient stability, resulting in system instability during long-term operation and thereby affecting yield and purity.

In recent years, many improvements have been proposed worldwide in terms of new catalysts and reaction designs. For example, transition metal complexes such as molybdenum or ruthenium coordination compounds have been used as catalysts to enhance nitrogen activation efficiency through molecular design. Rare earth metal-carbon based binders have also been introduced into cathode structures to improve electron transport. However, these designs often still rely on complex solid-state catalytic materials and fail to fully meet practical application needs in terms of energy efficiency and durability. Therefore, how to realize efficient electrochemical ammonia synthesis under ambient temperature and pressure, while maintaining stability, modularity, and low-carbon features, has become a pressing global technical challenge. It is eager to have a solution that will overcome or substantially ameliorate at least one or more of the deficiencies of a prior art, or to at least provide an alternative solution to the problems. It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art.

SUMMARY OF THE INVENTION

To overcome the disadvantages of the Haber-Bosch process such as high energy consumption, poor stability, insufficient yield, and low purity, the present invention proposes combining aromatic mediators with metal salts capable of participating in electrochemical reactions and organic solvents, forming soluble electron transfer mediators, and employing a dual-cell electrolytic design where hydrogen oxidation provides a stable proton source. This design overcomes the shortcomings of conventional electrochemical nitrogen reduction reaction and opens up new opportunities for green ammonia technology.

The present invention provides a ammonia production method, achieved by means of an electrochemical reaction device. The electrochemical device contains an electrolyte and is divided into a cathode reaction chamber and an anode reaction chamber by a proton-conductive/exchange membrane. A cathode is disposed in the cathode chamber and immersed in the electrolyte, and an anode is disposed in the anode chamber and immersed in the electrolyte. The cathode and the anode are electrically connected.

The method comprises the following steps:

• • Step S1: Introducing nitrogen gas into the cathode reaction chamber, where it contacts the electrolyte. The electrolyte comprises a metal salt (M salt) capable of participating in electrochemical reactions, an organic solvent, and an aromatic mediator.
  • Step S2: When external electric energy/voltage is applied, a reduction deposition reaction occurs at the surface of the cathode, reducing the M salt to its corresponding metal (M) and depositing it. Reaction formula (1):

• • Step S3: The deposited metal then reacts with the aromatic mediator in the electrolyte to generate a soluble metal-aromatic complex intermediate, as shown in formula (2):

M+X→MX  formula (2); where X is the aromatic mediator;

• • Step S4: The soluble metal-aromatic complex intermediate further reacts with the nitrogen introduced in Step 1, activating nitrogen and forming a metal nitride (MN), as shown in formula (3):

MX+N₂→MN+X  formula (3); where X is also the aromatic mediator;

• • Step S5: The metal nitride then acquires protons to produce ammonia, as shown in formula (4):

• • Step S6: Hydrogen gas is oxidized at the anode to generate protons and electrons as shown in formula (5), which subsequently pass through the proton-conductive/permeable membrane to the cathode reaction chamber to participate in the aforementioned reaction.

In accordance, the present invention has the following advantages:

1. High-efficiency ammonia production under ambient temperature and pressure, reducing energy consumption and carbon emissions.

High-efficiency ammonia production under ambient temperature and pressure, reducing energy consumption and carbon emissions.

The conventional Haber-Bosch process must be operated at extremely high temperatures and high pressures, resulting in tremendous energy demand, and it often relies on hydrogen produced by fossil-fuel steam reforming, which further causes substantial carbon dioxide emissions. The present invention, through an electrochemically metal-mediated nitrogen reduction reaction combined with an aromatic mediator serving as an electron-transfer carrier, enables nitrogen to be effectively activated and reduced to ammonia under ambient temperature and pressure, completely avoiding the need for high-pressure vessels and high-temperature reactors inherent to traditional processes. This feature not only significantly reduces energy consumption but also makes the system safer and more convenient to operate. More importantly, because the invention can optionally be directly coupled to renewable power sources such as solar energy or wind energy, its ammonia-production process is virtually zero-carbon, helping to meet global net-zero and energy-transition trends and providing a practical, deployable green alternative.

2. Adoption of an aromatic mediator in combination with electrochemically reactive metal salts to enhance reaction selectivity and stability.

In existing electrochemical ammonia-synthesis research, the hydrogen evolution reaction (HER) often competes with the nitrogen reduction reaction (NRR) for electrons and protons, resulting in low ammonia generation efficiency and difficulty meeting industrial application requirements. The present invention employs an aromatic mediator (such as naphthalene, anthracene, or pyrene) to form a stable, soluble intermediate with electrochemically reactive metal ions, thereby, through a stepwise mechanism of electron transfer and protonation, effectively enhancing the activation efficiency of nitrogen and avoiding sacrificial-solvent or metal-ion side reactions. In addition, this mediator mechanism can stabilize the electrochemically deposited metal and the metal nitride compound formed by its reaction with nitrogen, ensuring that the reaction proceeds continuously and stably without reductions in performance caused by solvent decomposition or catalyst deactivation. This design not only strengthens reaction selectivity but also greatly improves system durability, enabling long-term continuous operation consistent with the needs of the energy-chemistry industry.

3. Potential for modular design and broad applicability.

Compared with the centralized, large-scale chemical plants used for the Haber-Bosch process, the system proposed by the present invention can adopt a dual-cell electrolytic structure and achieve effective separation of reactions via a proton-conductive/exchange membrane. In this way, not only can the nitrogen reduction and hydrogen oxidation reactions proceed in independent environments, but the overall apparatus also gains modular potential and can be stacked or combined according to the required scale. Relative to traditional industrial production, the present invention offers greater flexibility and portability, can reduce construction and transportation costs, and enhances local energy autonomy. This modular and distributed application model will allow ammonia energy to deliver broader value in future energy markets and become a crucial hub linking renewable energy with the hydrogen economy.

Many of the attendant features and advantages of the present invention will become better understood with reference to the following detailed description considered in connection with the accompanying figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The steps and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings.

FIGS. 1A and 1B are two preferred embodiment of schematic diagrams of the system of the present invention.

FIG. 2 is a flow chart of the method steps of the present invention.

FIG. 3 and FIG. 4 are ultraviolet-visible absorption spectra (UV-Vis) detection and quantitative analysis diagrams of preferred embodiments of the present invention and comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. It is not intended to limit the method by the exemplary embodiments described herein. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to attain a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. As used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” may include reference to the plural unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the terms “comprise or comprising”, “include or including”, “have or having”, “contain or containing” and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

Referring to FIG. 1A, the system employed in the high-efficiency green ammonia production method based on proton source from hydrogen oxidation is illustrated.

The method of the present invention is implemented by an electrochemical reaction device 100. The electrochemical reaction device 100 contains an electrolyte 10 and is divided by a proton-conductive/exchange membrane 20 into a cathode reaction chamber 30 and an anode reaction chamber 40. The separation of the two chambers allows the reactions to proceed independently, avoiding interference from side reactions and ensuring that the resulting ammonia has high selectivity and purity. A cathode 31 is disposed in the cathode chamber 30 and immersed in the electrolyte 10, and an anode 41 is disposed in the anode chamber 40 and immersed in the electrolyte 10. The cathode 31 and the anode 41 are electrically connected. The cathode chamber 30 has a cathode gas inlet 32 on its bottom side and a cathode gas outlet 33 on its top side. The anode chamber 40 has an anode gas inlet 42 on its bottom side and an anode gas outlet 43 on its top side.

The proton-conductive/exchange membrane 20 preferably comprises a sulfonic acid resin membrane, a high-temperature proton exchange membrane (PEM), an inorganic composite membrane (Composite Membrane, including silicon-containing or aluminum-containing composite membranes), or an alkaline/anionic exchange membrane (AEM). The sulfonic acid resin membrane includes a perfluorosulfonic acid resin membrane (Nafion membrane) or a partially fluorinated sulfonic acid resin membrane.

As shown in FIG. 1B, a second preferred embodiment of the electrochemical reaction device 100 is generally the same as the aforementioned first embodiment, except that the anode 41 is directly attached to the proton-conductive/exchange membrane 20, forming an integrated electrode-membrane structure that replaces the conventional anode chamber requiring a liquid electrolyte environment. In this structure, the anode 41 adheres to the surface of the proton-conductive/exchange membrane 20 and performs a dry or wet oxidation reaction to generate protons and electrons. The generated protons are directly transmitted through the proton-conductive/exchange membrane to the cathode reaction chamber. The membrane possesses both high proton conductivity and gas-blocking properties, enabling the anode region to perform electrochemical reactions without being filled with liquid electrolyte.

Furthermore, the integrated structure of the anode 41 and the membrane provides multiple engineering advantages. First, the liquid-free anode chamber 40 effectively prevents variations in electrolyte composition that occur during long-term operation due to oxidation or evaporation in conventional liquid anode environments. Second, the overall system becomes more compact, reducing the size and weight of the device by eliminating bulky liquid chambers and pipelines. Third, the absence of liquid electrolyte prevents the back-diffusion of reaction products or membrane contamination, thereby extending the service life of the proton-conductive/exchange membrane 20. This configuration can also be directly connected to a hydrogen source without requiring additional electrolyte maintenance or replacement procedures.

Referring to FIG. 2, the method steps of the present invention comprise:

Step S1: Nitrogen gas (N₂) is introduced from the cathode gas inlet 32 into the cathode reaction chamber 30, where it contacts the electrolyte 10. The electrolyte 10 includes a metal salt capable of participating in electrochemical reactions, an organic solvent, and an aromatic mediator.

The preferred metal salts capable of participating in electrochemical reactions include Group 1A or Group 2A metal salts possessing high solubility and stability. The Group 1A salts include, but are not limited to, lithium salts, potassium salts, or sodium salts, such as lithium perchlorate (LiClO₄), lithium tetrafluoroborate (LiBF₄), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(oxalato) borate (LiBOB). The Group 2A salts include calcium salts.

The solvent comprises tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), acetone, diethylene glycol dimethyl ether (Diglyme), propylene carbonate, dimethylformamide (DMF), 1,2-dimethoxyethane (DME), 1,4-dioxane, 2-methyltetrahydrofuran (2-MeTHF), N,N-diethylacetamide, N-methylformamide, N,N-diethylformamide, glymes, γ-butyrolactone, acetonitrile, diethyl ether, trimethyl phosphate, ethylene sulfite, diethylene glycol dimethyl ether (DEGDME), a THF/n-hexane mixed solvent, or combinations thereof.

The aromatic mediators include naphthalene, anthracene, phenanthrene, pyrene, fullerene (C₆₀), biphenyl, fluorene, benzoquinone, benzophenone, or a combination thereof, among which naphthalene is particularly preferred due to its stable π-conjugated structure. The organic solvent may include water, alcohol, or acetone. The benzoquinone may include, for example, 1,4-benzoquinone, and the biphenyl may include 4,4′-di-tert-butylbiphenyl (DTBB).

The cathode 31 is preferably selected from structures having high porosity, large surface area, and good electrical conductivity, such as foams, meshes, cloths, sheets, or plates made of carbon, copper, nickel, silver, stainless steel, or molybdenum. Copper foam or stainless steel mesh are preferred due to their combination of high mechanical strength and low cost.

Step S2: When external electric energy/voltage is applied, the metal ions (M⁺) of the metal salt in the electrolyte undergo a reduction deposition reaction at the surface of the cathode 31, forming metal (M), as shown in formula (1):

Step S3: The deposited metal then reacts with the aromatic mediator (X, e.g., naphthalene) in the electrolyte 10, generating a soluble metal-aromatic complex intermediate (MX), as shown in formula (2):

Step S4: The soluble metal-aromatic complex intermediate further reacts with the nitrogen molecules introduced in Step S1, activating nitrogen and generating a metal nitride (MN), as shown in formula (3):

Step S5: The metal nitride then acquires protons to generate high-purity ammonia, which can be discharged and collected from the cathode gas outlet 33, as shown in formula (4):

During the aforementioned reaction process, the lithium-aromatic complex intermediate formed from the lithium salts and the aromatic mediator remains in the electrolyte after completion of the nitrogen reduction reaction and is not permanently consumed. The intermediate can be reactivated through a subsequent electrochemical regeneration process, converting it back into a reactive state and allowing it to participate again in the lithium deposition and nitrogen activation processes in the next cycle. This reversible cycling mechanism enables the overall system to maintain stable reaction efficiency during long-term operation without frequent replenishment of lithium salts or aromatic mediators. Moreover, such recyclability significantly reduces raw material consumption and operational costs, while preventing variations in electrolyte composition that could affect reaction reproducibility. Through this reversible electron transfer mechanism of the lithium-aromatic complex intermediate, the present invention not only exhibits high selectivity and energy efficiency but also demonstrates a sustainable feature of resource reusability in green chemical processes, thereby enhancing the economic feasibility and environmental compatibility of the system in practical industrial applications.

Step S6: Hydrogen gas is introduced from the anode gas inlet 42. Hydrogen undergoes oxidation at the anode 41, generating protons and electrons, which permeate through the proton-conductive/exchange membrane 20 into the cathode chamber 30 to participate in the aforementioned reaction. The hydrogen is subsequently reduced back to molecular hydrogen and discharged from the anode gas outlet 43, where it can be recycled. The reaction is shown in formula (5):

The anode chamber 40 continuously supplies hydrogen gas (H₂), and the anode 41 employs high catalytic activity materials to perform the hydrogen oxidation reaction (HOR). Preferably, the material of the anode 41 comprises platinum, platinum-modified titanium, a platinum, platinum-modified titanium, platinum-modified stainless steel, or a platinum-gold alloy in the form of a foam, mesh, cloth, sheet, or plate.

The protons generated at the anode 41 are transmitted through the proton-conductive/exchange membrane 20 to the cathode chamber 30, participating in the protonation reaction of lithium nitride, thereby completing the cycle of high-purity ammonia (NH₃) generation. The invention ensures stable proton sources during electrochemical reactions and avoids the instability issues of sacrificial solvents in traditional electrolytes. The proton-conductive/exchange membrane 20 has excellent proton conductivity and chemical stability, ensuring effective proton transmission and preventing gas crossover. With the above design, the system can operate stably under room temperature and atmospheric pressure conditions, and the generated ammonia can be directly discharged without additional gas separation processes. Compared with the conventional Haber-Bosch process, the invention significantly reduces energy consumption and realizes a green ammonia production system.

Preferred Embodiment 1

In a preferred embodiment, the electrochemically active metal salt comprises a lithium salt. The corresponding reaction equations are as follows:

At the Cathode chamber 30:

At Anode chamber 40:

Preferably, this embodiment is carried out under ambient temperature and pressure conditions. The operating voltage range is set between 2.5 V and 4.5 V, corresponding to a cathodic potential range of approximately −2.5 V to −3.5 V (relative to a reference electrode), while the anodic potential lies within the range of 0 to 1.5 V. The current is controlled within a range of 5 mA to 20 mA to ensure both stability and energy efficiency during the reaction process.

<Verification Test>

To verify the feasibility of the green electrochemical ammonia production system of the present invention and its capability to generate ammonia under ambient conditions, UV-Vis absorption spectroscopy detection and quantitative analysis were carried out.

To verify the feasibility of the green electrochemical ammonia production system of the present invention and its capability to generate ammonia under ambient conditions, UV-Vis absorption spectroscopy detection and quantitative analysis were carried out.

FIG. 3 and FIG. 4 show the spectral signals obtained under identical operating conditions for both the embodiment of the present invention—where hydrogen gas and nitrogen gas are simultaneously introduced with the addition of the aromatic mediator naphthalene—and the comparative example without the addition of the aromatic mediator. It can be observed that, after the reaction, the solution exhibits a distinct absorption peak around 420 nm, whose intensity corresponds to that of the standard ammonia solution calibration curve. This result confirms that the present invention successfully reduces nitrogen to ammonia under ambient temperature and pressure. The absorption signal not only matches the characteristic spectrum of standard ammonia but also demonstrates that the aromatic mediator effectively participates in electron transfer during the reaction process, thereby facilitating nitrogen activation and subsequent ammonia formation.

Please refer to Table 2 below, which compares the preferred embodiment of the present invention with the comparative example (without the aromatic mediator).

Therefore, the above verification confirms that the technical solution of the invention is feasible and has significant effects. Through spectroscopic analysis, the system is shown to stably produce ammonia, with yields that can be accurately quantified, further highlighting its advantage over the conventional energy-intensive Haber-Bosch process as a green production method.

The above specification, examples, and data provide a complete description of the present disclosure and use of exemplary embodiments. Although various embodiments of the present disclosure have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those with ordinary skill in the art could make numerous alterations or modifications to the disclosed embodiments without departing from the spirit or scope of this disclosure.