Electrochemical nitrate conversion ammonia production catalyst using cuprous oxide surface substitution doping and method for manufacturing same

Abstract

According to the disclosure, an ammonia production catalyst including cuprous oxide and bismuth is provided. An ammonia production catalyst according to an embodiment of the disclosure has excellent ammonia conversion efficiency and has an effect of high stability even after reaction.

Description

BACKGROUND

[0001] The disclosure relates to an ammonia production catalyst, and more particularly, to an ammonia production catalyst based on cuprous oxide.

[0002] Ammonia is receiving much attention as a nitrogen-based raw material essential for fertilizer, pharmaceutical, and chemical industries, and as a carbon-free energy storage medium that can replace hydrogen. However, conventional ammonia production technology is carried out through the Habor-Bosch process, which causes a large amount of energy consumption and greenhouse gas emissions, so an eco-friendly electrochemical ammonia production method that can replace it is required.

[0003] The existing electrochemical ammonia production method using reduction of gaseous nitrogen (N2) can utilize nitrogen that exists in large quantities in the atmosphere, but it must overcome low solubility and strong triple bonds of nitrogen, and stability issues have been pointed out due to poisoning by nitrogen atoms. Therefore, the ammonia production method using reduction of nitrate (NO3−), which exists stably in nature, has high solubility compared to gaseous nitrogen, and is easy to convert to other forms, is receiving much attention.

[0004] Accordingly, copper-based materials with excellent adsorption properties for nitrates have been studied extensively to avoid the initial adsorption competition by the water reduction hydrogen evolution reaction (HER), a competitive reaction in aqueous electrolytes. In order to achieve high-efficiency ammonia production, the introduction of uneconomical precious metals such as Pd, Ru, Rh, Ag, and Au has been mainly studied. Recently, the introduction of transition metals such as Fe, Ni, and Co has been studied, but the conversion efficiency and stability are not up to the commercialization level.RELATED ART DOCUMENTPatent Document(Patent document 0001) Publication of Patent Publication No. 10-2024-0086159SUMMARY

[0006] An aspect of the disclosure provides a high-performance ammonia production catalyst capable of converting nitrate into high value-added ammonia in an environmentally friendly and efficient manner.

[0007] The aspect of the disclosure is not limited to that mentioned above, and other aspects not mentioned will be clearly understood by those skilled in the art from the description below.

[0008] An embodiment of the disclosure provides an ammonia production catalyst.

[0009] An ammonia production catalyst according to an embodiment of the disclosure includes: cuprous oxide (Cu2O); and bismuth doped on the surface of the cuprous oxide.

[0010] In an embodiment of the disclosure, the cuprous oxide may have a cuboctahedral morphology and cubic structure.

[0011] In an embodiment of the disclosure, the bismuth may be partially substitutionally doped on the surface of the cuprous oxide.

[0012] Another embodiment of the disclosure provides an ammonia production catalyst manufacturing method.

[0013] An ammonia production catalyst manufacturing method according to an embodiment of the disclosure is characterized by mixing and reacting a precursor containing copper, a reducing agent, and a bismuth precursor.

[0014] An ammonia production catalyst manufacturing method according to an embodiment of the disclosure may include: forming cuprous oxide by stirring and reacting a first solution containing a reducing agent and a precursor containing copper; and adding a bismuth precursor during the reaction to obtain a catalyst in which bismuth is partially substitutionally doped on the surface of cuprous oxide.

[0015] According to an embodiment of the disclosure, it is possible to provide a highly efficient catalyst material selective for ammonia production, and the manufactured catalyst can be applied as a nitrate reduction electrode in a neutral electrolyte to secure a conversion efficiency (Faraday efficiency) close to 100% and long-term operation stability.

[0016] The effects of the disclosure are not limited to the effects described above, and should be understood to include all effects that are inferable from the configuration of the disclosure described in the detailed description or claims of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0018] FIG. 1 is a schematic view showing an improved mechanism of an ammonia production catalyst according to an embodiment of the disclosure;

[0019] FIG. 2 is a schematic view showing a manufacturing process of an ammonia production catalyst according to an embodiment of the disclosure;

[0020] FIG. 3A is a schematic view showing an ammonia production reaction occurring on the surface of an ammonia production catalyst (Bi / Cu2O, embodiment 1) according to an embodiment of the disclosure;

[0021] FIG. 3B is an SEM image of cuprous oxide (Cu2O, comparative example 1) and a lattice spacing analysis view using HR-TEM;

[0022] FIG. 3C is an SEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0023] FIG. 3D is a BF-STEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0024] FIG. 3E is an HR-TEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0025] FIG. 3F is a view showing the elemental distribution measurement using EDS of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0026] FIG. 4A is a view showing the SEM image and particle size distribution of cuprous oxide (Cu2O);

[0027] FIG. 4B is a view showing the EDS element-specific distribution of cuprous oxide (Cu2O);

[0028] FIG. 5A is an SEM image of a comparative example (d-Bi / Cu2O, comparative example 2) in which the bismuth precursor was added at the beginning of Cu2O formation;

[0029] FIG. 5B is an HR-TEM image of d-Bi / Cu2O;

[0030] FIG. 5C is a view showing the EDS element-specific distribution of d-Bi / Cu2O;

[0031] FIG. 6A is a view showing the XRD diffraction patterns for Cu2O and Bi / Cu2O;

[0032] FIG. 6B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and Bi / Cu2O;

[0033] FIG. 6C is a view showing the high-resolution Bi 4f XPS spectra for a comparative example (Bi catalyst, comparative example 3) synthesized using HS-40 silica instead of Cu2O as a support and Bi / Cu2O;

[0034] FIG. 6D is a view showing the high-resolution O 1s XPS spectra for Cu2O and Bi / Cu2O;

[0035] FIG. 6E is a view showing the EPR spectra for Cu2O and Bi / Cu2O;

[0036] FIG. 6F is a view showing the FT-IR spectra for Cu2O and Bi / Cu2O;

[0037] FIG. 7A is a view showing the XRD diffraction patterns for Cu2O and d-Bi / Cu2O;

[0038] FIG. 7B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and d-Bi / Cu2O;

[0039] FIG. 7C is a view showing the high-resolution Bi 4f XPS spectra for Cu2O and d-Bi / Cu2O;

[0040] FIG. 7D is a view showing the high-resolution O 1s XPS spectra for Cu2O and d-Bi / Cu2O;

[0041] FIG. 7E is a view showing the EPR spectra for Cu2O and d-Bi / Cu2O;

[0042] FIG. 7F is a view showing FT-IR spectra for Cu2O and d-Bi / Cu2O;

[0043] FIG. 8A is a view showing current density (J)-voltage (V) graphs for nitrate reduction on Bi / Cu2O according to the amount of Bi introduced by linear scanning voltammetry (LSV);

[0044] FIG. 8B is a view showing ammonia production rates for Bi / Cu2O (embodiments 1-4) according to the amount of Bi introduced;

[0045] FIG. 9A is a current density-voltage graphs for nitrite reduction compared to nitrate for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV);

[0046] FIG. 9B is a current density-voltage graphs for water reduction compared to nitrate for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV);

[0047] FIG. 10A is a view showing ammonia production rates for electrochemical nitrate reduction according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0048] FIG. 10B is a view showing the electrochemical nitrate reduction to ammonia conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0049] FIG. 10C is a view showing the electrochemical nitrate reduction to nitrite production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0050] FIG. 10D is a view showing the electrochemical nitrate reduction to nitrite conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0051] FIG. 10E is a view showing the electrochemical nitrate reduction to hydrogen production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0052] FIG. 10F is a view showing the electrochemical nitrate reduction to hydrogen conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0053] FIG. 11A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1;

[0054] FIG. 11B is a view showing Nyquist plots from electrochemical impedance spectroscopy (EIS) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1;

[0055] FIG. 11C is a view showing ammonia production rates for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1;

[0056] FIG. 12A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for nitrate / nitrite / water reduction reactions for comparative example 3;

[0057] FIG. 12B is a view showing the nitrate reduction ammonia production rates according to the applied voltage for comparative example 3;

[0058] FIG. 12C is a view showing the nitrate reduction nitrite production rates according to the applied voltage for comparative example 3;

[0059] FIG. 13 is a view showing the nitrite reduction ammonia production rates according to the applied voltage for comparative example 3;

[0060] FIG. 14A is a view showing the electrochemical nitrite reduction ammonia production rates according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0061] FIG. 14B is a view showing the electrochemical nitrite reduction ammonia conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0062] FIG. 14C is a view showing the electrochemical nitrite reduction hydrogen production rates according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0063] FIG. 14D is a view showing the electrochemical nitrite reduction hydrogen conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0064] FIG. 15 is Nyquist plots from EIS analysis of the electrochemical nitrate reduction reaction for comparative examples 1-2 and embodiment 1;

[0065] FIG. 16 is a view comparing the electrochemical nitrate reduction ammonia production rates for embodiment 1 according to the presence and absence of a surface proton desorption material (adsorbed proton trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO));

[0066] FIG. 17A is a view showing the ammonia production rates and conversion efficiencies according to the nitrate concentration for embodiment 1;

[0067] FIG. 17B is a view showing the ammonia production rates and conversion efficiencies according to the electrolyte pH for embodiment 1;

[0068] FIG. 17C is a view showing the reactant / intermediate / product concentrations according to the reaction time for embodiment 1;

[0069] FIG. 17D is a view showing the ammonia production rates and conversion efficiencies according to the reaction time for embodiment 1;

[0070] FIG. 17E is a view showing the ammonia production rates and conversion efficiencies according to the number of repeated measurements for embodiment 1;

[0071] FIG. 18A is a view showing the hydrogen production rates according to the electrolyte pH for embodiment 1;

[0072] FIG. 18B is a view showing the hydrogen conversion efficiencies according to the electrolyte pH for embodiment 1;

[0073] FIG. 19A is a view showing the ammonia production rate change according to time at electrolyte pH 2 for embodiment 1;

[0074] FIG. 19B is a view showing the ammonia production rate change according to time at electrolyte pH 13 for embodiment 1;

[0075] FIG. 19C is a view showing the current density changes according to time at each pH for embodiment 1;

[0076] FIG. 20 is a view showing the current density change during 10 repeated activity evaluation measurements for embodiment 1;

[0077] FIG. 21A is an HR-TEM image of embodiment 1 after a long-term operation for stability evaluation;

[0078] FIG. 21B is XRD patterns of embodiment 1-coated electrodes before and after a long-term operation for stability evaluation;

[0079] FIG. 21C is a BF-STEM view of embodiment 1 after a long-term operation for stability evaluation;

[0080] FIG. 21D is an element distribution measurement view using EDS of embodiment 1 after a long-term operation for stability evaluation;

[0081] FIG. 22A is a view showing the XPS spectrum (Cu 2p) for embodiment 1-coated electrode after the long-term operation;

[0082] FIG. 22B is a view showing the XPS spectrum (Bi 4f) for embodiment 1-coated electrode after the long-term operation; and

[0083] FIG. 22C is a view showing the XPS spectrum (O 1s) for embodiment 1-coated electrode after the long-term operation.DETAILED DESCRIPTION

[0084] Hereinafter, the disclosure will be described with reference to the accompanying drawings. However, the disclosure may be implemented in various different forms and therefore is not limited to the embodiments described herein. In addition, in order to clearly describe the disclosure in the drawings, parts that are not related to the description are omitted, and similar parts are given similar drawing reference numerals throughout the specification.

[0085] In the entire specification, when a part is said to be “connected (linked, contacted, coupled)” to another part, this includes not only the case where it is “directly connected” but also the case where it is “indirectly connected” with another member in between. In addition, when a part is said to “include” a component, this does not mean that it excludes other components, unless otherwise specifically stated, but rather that it may include other components.

[0086] The terms used in this specification are used only to describe specific embodiments and are not intended to limit the disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, the terms “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood as not excluding in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0087] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

[0088] The electrochemical nitrate reduction reaction has two major reaction paths depending on the product, either nitrogen (N2) or ammonia (NH3), and the step in which the initial nitrate (NO3−) is converted to nitrite (NO2−) is known as the rate determining step.

[0089] In the disclosure, by introducing bismuth to the surface of a cuprous oxide material with excellent nitrate adsorption characteristics but low selectivity for ammonia, an effective protonation was induced, so that developed was a transition metal-based high-efficiency and high-selectivity nitrate reduction ammonia production electrocatalyst material.

[0090] Existing cuprous oxide-based materials with excellent nitrate adsorption characteristics had a limitation in that the selectivity for the target product, ammonia, was low due to poor catalytic characteristics in the subsequent reduction step after nitrite. Various metal doping strategies have been implemented to modify these surface catalyst properties, but noble metal dopants have been pointed out to have low economic efficiency compared to high activity, and previously studied transition metal dopants have relatively low conversion efficiency and stability.

[0091] FIG. 1 is a schematic view showing an improved mechanism of an ammonia production catalyst according to an embodiment of the disclosure; in this invention, bismuth, a p-orbital transition metal rather than a conventional d-orbital noble metal or transition metal, is applied as a dopant to induce bismuth doping locally concentrated on the surface of cuprous oxide through an in-situ doping method added during the hydrothermal synthesis of cuprous oxide. As shown in FIG. 1, the ammonia production efficiency, which was previously identified as a limitation of cuprous oxide due to poor protonation characteristics after conversion of nitrate to nitrite, was overcome through the introduction of bismuth, and the ammonia production efficiency was maximized by suppressing the hydrogen evolution reaction, which is a competitive reaction, and promoting the protonation of the adsorbed nitrogen intermediate.

[0092] Hereinafter, an ammonia production catalyst according to an embodiment of the disclosure will be described.

[0093] An ammonia production catalyst according to an embodiment of the disclosure is characterized by including cuprous oxide (Cu2O) and bismuth (Bi) doped on the surface of the cuprous oxide.

[0094] At this time, the cuprous oxide may have a cuboctrahedral morphology and cubic structure.

[0095] In an embodiment of the disclosure, the bismuth may be incorporated by injecting a bismuth precursor during the hydrothermal synthesis of the cuprous oxide. At this time, since the catalyst is manufactured in a manner in which the precursor is injected during the hydrothermal synthesis of the cuprous oxide as described above, the bismuth may not be doped on the entire cuprous oxide structure of the catalyst, but may be formed by surface-limited substitution doping in which it is concentrated and substituted on a portion of the surface.

[0096] If bismuth is introduced from the beginning of the synthesis of the catalyst, the bismuth dopant may contribute to the formation of Cu2O structure, which may cause the crystal structure to collapse and the crystallinity to deteriorate. On the other hand, when introduced at the terminal period of the synthesisterminal period, bismuth may be formed as a dopant limited to the surface. Therefore, a structure in which bismuth is limited to a portion of the surface and is doped by substitution is appropriate, and this may be formed by introducing a bismuth precursor during the hydrothermal synthesis process of cuprous oxide.

[0097] At this time, the mass ratio of bismuth to cuprous oxide may be 0.1 to 3.0 wt %, preferably 0.4 to 2.0 wt %.

[0098] In addition, the catalyst may be a structure that includes a thin film layer composed of the cuprous oxide and bismuth and uses this as an active point. The catalyst may be utilized as a cathode in a neutral electrolyte containing nitrate.

[0099] Next, an ammonia production catalyst manufacturing method according to an embodiment of the disclosure will be described.

[0100] In the disclosure, it is possible to manufacture a highly efficient catalyst material selective for ammonia production by inducing substitutional doping of bismuth (Bi) on the surface of cuprous oxide (Cu2O), which has been used as a conventional electrochemical nitrate conversion catalyst, through hydrothermal synthesis.

[0101] Therefore, the manufacturing method of the disclosure includes mixing and reacting a precursor containing copper, a reducing agent, and a bismuth precursor.

[0102] Preferably, in the manufacturing method, stirring and reacting a first solution containing the precursor containing copper and the reducing agent may be performed, wherein a bismuth precursor may be added during the reaction.

[0103] When manufacturing a bismuth-doped cuprous oxide catalyst based on a mixed solution in which the bismuth precursor, the precursor containing copper, and the reducing agent are all mixed at first, bismuth may contribute to the formation of Cu2O structure, which may cause structural collapse and deterioration of crystallinity. In addition, the obtained catalyst forms a catalyst having a doped structure throughout the cuprous oxide structure. As a result, the performance of the catalyst may be poor.

[0104] Therefore, during the reacting of cuprous oxide using a copper precursor and a reducing agent, a bismuth precursor is added to manufacture an ammonia production catalyst partially doped with bismuth.

[0105] First, a solution containing a copper precursor and a reducing agent is manufactured.

[0106] At this time, the copper precursor may be CuC4H4O6 (copper tartate) manufactured by mixing CuSO4 and C4H4O6KNa. In addition, the reducing agent may be glucose. However, that is not limited to the types of copper precursor and reducing agent selected as the above example, and a known copper precursor and reducing agent capable of forming cuprous oxide may be used.

[0107] When manufacturing a solution containing a copper precursor and a reducing agent, it is preferable to adjust the pH of the solution to an appropriate range by adding a KOH solution. At this time, the pH range may be 11.5 to 12.

[0108] Next, the solution is stirred.

[0109] Cuprous oxide may be formed through the stirring process at a temperature controlled within an appropriate range. At this time, the temperature may be 75° C.

[0110] During the process of forming cuprous oxide through stirring, a bismuth precursor may be added. For example, the bismuth precursor may be Bi(NO3)3·5H2O. When bismuth doping is completed, a catalyst may be obtained through centrifugation and vacuum drying.

[0111] Hereinafter, the disclosure will be described in more detail through manufacturing examples, comparative examples, and experimental examples. However, the disclosure is not limited to the following manufacturing examples and experimental examples.

[0112] The electrochemical system for verifying the effect of the disclosure was performed in a 0.5 M K2SO4 neutral electrolyte containing 1000 ppm NO3− unless otherwise specified, and was measured using a Ag / AgCl as a reference electrode and a Pt plate as a counter electrode.

[0113] In addition, the concentrations of ammonia as a product, nitrite as an responsive intermediate, and nitrate as a reactant were quantified using an ultraviolet-visible spectrometer and a calibration curve, and hydrogen as a byproduct was quantified using a gas chromatography.Examples 1-4: Bismuth-Doped Cuprous Oxide Catalyst (Bi—Cu2O)

[0114] Embodiments and comparative examples of the disclosure were produced through a hydrothermal method.

[0115] FIG. 2 is a schematic view showing a manufacturing process of an ammonia production catalyst according to an embodiment of the disclosure.

[0116] Hereinafter, referring to FIG. 2 above, a manufacturing process of an ammonia production catalyst according to an embodiment of the disclosure will be described.

[0117] After manufacturing 240 mL of a copper tartrate complex solution containing 1.4 mM CuSO4 and 8.9 mM C4H4O6KNa, 0.33 mL of 10 M KOH was added to adjust the pH to 11.5-12.

[0118] Subsequently, 10 mL of 0.25 M glucose was added and stirred at 300 rpm for 10 minutes.

[0119] The mixed solution was continuously stirred in a silicone oil bath at 75° C. for 2.5 hours, 10 mL of 0.85 mg / mL Bi(NO3)3·5H2O was added, and the reaction was performed for an additional 1 hour at 75° C., followed by several centrifugation steps using ultrapure water and ethanol, and vacuum drying steps to produce embodiment 1 (Bi / Cu2O).

[0120] In addition, embodiments 2 to 4 (Bi doping concentrations of 0.5, 1.5, and 2 times that of embodiment 1, respectively) were produced according to the change in Bi introduction amount. In each embodiment, the bismuth / cuprous oxide mass % ratio was 0.8 for embodiment 1, 0.4 for embodiment 2, 1.2 for embodiment 3, and 1.5 for embodiment 4.Comparative Examples: Pure Cu2O (Comparative Example 1), d-Bi / Cu2O (Comparative Example 2), Bi-Catalyst (Comparative Example 3)

[0121] In comparative example 1, pure Cu2O without Bi doping effect was produced by omitting the Bi(NO3)3·5H2O solution injection step during the same synthesis process as embodiment 1.

[0122] In comparative example 2, a sample (d-Bi / Cu2O) was produced by inducing full-structure doping rather than surface-limited substitution doping by injecting Bi(NO3)3·5H2O solution from the beginning of Cu2O synthesis.

[0123] In comparative example 3, HS-40 colloidal silica nanoparticles were used instead of Cu2O to analyze the effect of pure Bi(Bi-catalyst).Experimental Example 1: Changes in Structure and Composition Due to Introduction of Bismuth

[0124] FIG. 3A is a schematic view showing an ammonia production reaction occurring on the surface of an ammonia production catalyst (Bi / Cu2O, embodiment 1) according to an embodiment of the disclosure.

[0125] FIG. 3B is an SEM image of cuprous oxide (Cu2O, comparative example 1) and a lattice spacing analysis view using HR-TEM.

[0126] FIG. 3C is an SEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0127] FIG. 3D is an BF-STEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0128] FIG. 3E is an HR-TEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0129] FIG. 3F is a view showing the elemental distribution measurement using EDS of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0130] FIG. 4A is a view showing the SEM image and particle size distribution of cuprous oxide (Cu2O).

[0131] FIG. 4B is a view showing the EDS element-specific distribution of cuprous oxide (Cu2O).

[0132] FIG. 5A is an SEM image of a comparative example (d-Bi / Cu2O, comparative example 2) in which the bismuth precursor was added at the beginning of Cu2O synthesis.

[0133] FIG. 5B is an HR-TEM image of d-Bi / Cu2O.

[0134] FIG. 5C is a view showing the EDS element-specific distribution of d-Bi / Cu2O.

[0135] FIG. 6A is a view showing the XRD diffraction patterns for Cu2O and Bi / Cu2O.

[0136] FIG. 6B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and Bi / Cu2O.

[0137] FIG. 6C is a view showing the high-resolution Bi 4f XPS spectra for a comparative example (Bi catalyst, comparative example 3) synthesized using HS-40 silica instead of Cu2O as a support and Bi / Cu2O.

[0138] FIG. 6D is a view showing the high-resolution O 1s XPS spectra for Cu2O and Bi / Cu2O.

[0139] FIG. 6E is a view showing the EPR spectra for Cu2O and Bi / Cu2O.

[0140] FIG. 6F is a view showing the FT-IR spectra for Cu2O and Bi / Cu2O.

[0141] FIG. 7A is a view showing the XRD diffraction patterns for Cu2O and d-Bi / Cu2O.

[0142] FIG. 7B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and d-Bi / Cu2O.

[0143] FIG. 7C is a view showing the high-resolution Bi 4f XPS spectra for Cu2O and d-Bi / Cu2O.

[0144] FIG. 7D is a view showing the high-resolution O 1s XPS spectra for Cu2O and d-Bi / Cu2O.

[0145] FIG. 7E is a view showing the EPR spectra for Cu2O and d-Bi / Cu2O.

[0146] FIG. 7F is a view showing FT-IR spectra for Cu2O and d-Bi / Cu2O.

[0147] SEM, TEM, and XRD analyses were performed on embodiment 1 and comparative examples 1-2.

[0148] As a result, compared to comparative example 1 and embodiment 1, phenomena such as structural collapse, crystallinity deterioration, and overall Bi distribution in the structure were found in comparative example 2 (FIGS. 5A to 5C, FIG. 7).

[0149] On the other hand, in embodiment 1 and comparative example 1, which show similar shapes and crystal structures, it is possible to confirm the difference in roughness of specific surfaces in SEM and HR-TEM images and the difference in the formation of Bi introduction layers concentrated on the surface through EDS mapping.

[0150] This is because Bi, a dopant, contributes to the formation of Cu2O structure when introduced from the beginning of the Cu2O synthesis, and is formed in a form limited to the surface as a dopant when introduced at the end of the synthesis, depending on the timing of Bi introduction during the Cu2O synthesis process.

[0151] In addition, in the case of embodiment 1 where Bi was introduced at the terminal period of Cu2O synthesis, the Cu2+ peak representing the second copper oxide (CuO) of Cu 2p and the oxygen vacancy site (Ov) peak of O Is were significantly reduced in XPS analysis, and this phenomenon was also observed in the EPR spectrum, confirming that the introduction of Bi at the terminal period of Cu2O synthesis occurred along with a chemical state change on the surface of Cu2O.

[0152] On the other hand, in the case of comparative example 2, the oxygen vacancy significantly increased, and it showed a large structural and morphological change, so the introduction of Bi in the early stage of the synthesis affected the structure formation of Cu2O, forming a significantly etched cuboctahedral structure.Experimental Example 2: Electrochemical Nitrate Reduction Ammonia Production Catalyst Activity and Mechanism Analysis

[0153] An analysis of the catalytic activity was performed on the synthesized embodiment and comparative example.

[0154] FIG. 8A is a view showing current density (J)-voltage (V) graphs for Bi / Cu2O according to the amount of Bi introduced by linear scanning voltammetry (LSV).

[0155] FIG. 8B is a view showing ammonia production rates for Bi / Cu2O (embodiments 1-4) according to the amount of Bi introduced.

[0156] FIG. 9A is a current density-voltage graphs for nitrite reduction compared to nitrate reduction for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV).

[0157] FIG. 9B is a current density-voltage graphs for water reduction compared to nitrate reduction for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV).

[0158] FIG. 10A is a view showing ammonia production rates for electrochemical nitrate reduction according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0159] FIG. 10B is a view showing the electrochemical nitrate reduction to ammonia conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0160] FIG. 10C is a view showing the electrochemical nitrate reduction to nitrite production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0161] FIG. 10D is a view showing the electrochemical nitrate reduction to nitrite conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0162] FIG. 10E is a view showing the electrochemical nitrate reduction to hydrogen production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0163] FIG. 10F is a view showing the electrochemical nitrate reduction to hydrogen conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0164] FIG. 11A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1.

[0165] FIG. 11B is a view showing Nyquist plots from electrochemical impedance spectroscopy (EIS) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1.

[0166] FIG. 11C is a view showing ammonia production rates for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1.

[0167] FIG. 12A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for nitrate / nitrite / water reduction reactions for comparative example 3.

[0168] FIG. 12B is a view showing the nitrate reduction ammonia production rate according to the applied voltage for comparative example 3.

[0169] FIG. 12C is a view showing the nitrate reduction nitrite production rates according to the applied voltage for comparative example 3.

[0170] FIG. 13 is a view showing the nitrite reduction ammonia production rates according to the applied voltage for comparative example 3.

[0171] FIG. 14A is a view showing the electrochemical nitrite reduction ammonia production rates according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0172] FIG. 14B is a view showing the electrochemical nitrite reduction ammonia conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0173] FIG. 14C is a view showing the electrochemical nitrite reduction hydrogen production rates according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0174] FIG. 14D is a view showing the electrochemical nitrite reduction hydrogen conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0175] FIG. 15 is Nyquist plots from EIS analysis of the electrochemical nitrate reduction reaction for comparative examples 1-2 and embodiment 1.

[0176] FIG. 16 is a view comparing the electrochemical nitrate reduction ammonia production rates for embodiment 1 according to the presence and absence of a surface proton desorption material (adsorbed proton trapping, agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)).

[0177] FIG. 17A is a view showing the ammonia production rates and conversion efficiencies according to the nitrate concentration for embodiment 1.

[0178] FIG. 17B is a view showing the ammonia production rates and conversion efficiencies according to the electrolyte pH for embodiment 1.

[0179] FIG. 17C is a view showing the reactant / intermediate / product concentrations according to the reaction time for embodiment 1.

[0180] FIG. 17D is a view showing the ammonia production rates and conversion efficiencies according to the reaction time for embodiment 1.

[0181] FIG. 17E is a view showing the ammonia production rates and conversion efficiencies according to the number of repeated measurements for embodiment 1.

[0182] FIG. 18A is a view showing the hydrogen production rates according to the electrolyte pH for embodiment 1.

[0183] FIG. 18B is a view showing the hydrogen conversion efficiencies according to the electrolyte pH for embodiment 1.

[0184] FIG. 19A is a view showing the ammonia production rate change according to time at electrolyte pH 2 for embodiment 1.

[0185] FIG. 19B is a view showing the ammonia production rate change according to time at electrolyte pH 13 for embodiment 1.

[0186] FIG. 19C is a view showing the current density changes according to time at each pH for embodiment 1.

[0187] As a result, the electrochemical nitrate reduction ammonia conversion efficiency of up to 99.2% was shown at the −0.8 V vs. RHE for embodiment 1 of the disclosure.

[0188] For the sample optimization and mechanism analysis, the linear scanning voltage (LSV) and ammonia production were compared. In addition, the reaction was identified as a reaction dominated by mass transportation through the difference in the supporting electrolyte concentration, electrochemical impedance spectroscopy (EIS), and the plateau region on the LSV.

[0189] In addition, a comparative analysis was conducted for the embodiment and comparative examples according to the applied voltage, electrolyte pH, reaction time, and adsorbed proton trapping agent, and the reactant of nitrate or nitrite.

[0190] Accordingly, it was confirmed that the reaction rate is determined by the two-dimensional diffusion-controlled model, and that the poor protonation process after the conversion of nitrate to nitrite, which was a limitation of the existing Cu2O, occurs smoothly in Bi / Cu2O with Bi introduced.Experimental Example 3: Stability Evaluation of Electrochemical Nitrate Reduction Ammonia Production Catalyst

[0191] FIG. 20 is a view showing the current density change during 10 repeated activity evaluation measurements for embodiment 1.

[0192] FIG. 21A is an HR-TEM image of embodiment 1 after a long-term operation for stability evaluation.

[0193] FIG. 21B is XRD patterns of embodiment 1-coated electrode before and after the long-term operation.

[0194] FIG. 21C is a BF-STEM view of embodiment 1 after the long-term operation.

[0195] FIG. 21D is an element distribution measurement view using EDS of embodiment 1 after the long-term operation.

[0196] FIG. 22A is a view showing the XPS spectrum (Cu 2p) for embodiment 1-coated electrode after the long-term operation for stability evaluation.

[0197] FIG. 22B is a view showing the XPS spectrum (Bi 4f) for embodiment 1-coated electrode after the long-term operation.

[0198] FIG. 22C is a view showing the XPS spectrum (O 1s) for embodiment 1-coated electrode after the long-term operation.

[0199] As a result of performing 10 repeated measurements on embodiment 1 synthesized above, it was confirmed that continuously excellent conversion efficiency was exhibited, and excellent stability was ensured also for TEM, XRD, and XPS after the reaction.

[0200] The description of the disclosure is for illustrative purposes, and those skilled in the art will understand that it can be easily modified into other specific forms without changing the technical idea or essential features of the disclosure. Therefore, the embodiments described above should be understood as being exemplary in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and likewise, components described as distributed may be implemented in a combined form.

[0201] The scope of the disclosure is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the disclosure.

Examples

experimental example 1

Changes in Structure and Composition Due to Introduction of Bismuth

[0124]FIG. 3A is a schematic view showing an ammonia production reaction occurring on the surface of an ammonia production catalyst (Bi / Cu2O, embodiment 1) according to an embodiment of the disclosure.

[0125]FIG. 3B is an SEM image of cuprous oxide (Cu2O, comparative example 1) and a lattice spacing analysis view using HR-TEM.

[0126]FIG. 3C is an SEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0127]FIG. 3D is an BF-STEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0128]FIG. 3E is an HR-TEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0129]FIG. 3F is a view showing the elemental distribution measurement using EDS of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0130]FIG. 4A is a view showing the SEM image and particle size distr...

experimental example 3

Stability Evaluation of Electrochemical Nitrate Reduction Ammonia Production Catalyst

[0191]FIG. 20 is a view showing the current density change during 10 repeated activity evaluation measurements for embodiment 1.

[0192]FIG. 21A is an HR-TEM image of embodiment 1 after a long-term operation for stability evaluation.

[0193]FIG. 21B is XRD patterns of embodiment 1-coated electrode before and after the long-term operation.

[0194]FIG. 21C is a BF-STEM view of embodiment 1 after the long-term operation.

[0195]FIG. 21D is an element distribution measurement view using EDS of embodiment 1 after the long-term operation.

[0196]FIG. 22A is a view showing the XPS spectrum (Cu 2p) for embodiment 1-coated electrode after the long-term operation for stability evaluation.

[0197]FIG. 22B is a view showing the XPS spectrum (Bi 4f) for embodiment 1-coated electrode after the long-term operation.

[0198]FIG. 22C is a view showing the XPS spectrum (O 1s) for embodiment 1-coated electrode after the long-term op...

BACKGROUND

[0001] The disclosure relates to an ammonia production catalyst, and more particularly, to an ammonia production catalyst based on cuprous oxide.

[0002] Ammonia is receiving much attention as a nitrogen-based raw material essential for fertilizer, pharmaceutical, and chemical industries, and as a carbon-free energy storage medium that can replace hydrogen. However, conventional ammonia production technology is carried out through the Habor-Bosch process, which causes a large amount of energy consumption and greenhouse gas emissions, so an eco-friendly electrochemical ammonia production method that can replace it is required.

[0003] The existing electrochemical ammonia production method using reduction of gaseous nitrogen (N2) can utilize nitrogen that exists in large quantities in the atmosphere, but it must overcome low solubility and strong triple bonds of nitrogen, and stability issues have been pointed out due to poisoning by nitrogen atoms. Therefore, the ammonia production method using reduction of nitrate (NO3−), which exists stably in nature, has high solubility compared to gaseous nitrogen, and is easy to convert to other forms, is receiving much attention.

[0004] Accordingly, copper-based materials with excellent adsorption properties for nitrates have been studied extensively to avoid the initial adsorption competition by the water reduction hydrogen evolution reaction (HER), a competitive reaction in aqueous electrolytes. In order to achieve high-efficiency ammonia production, the introduction of uneconomical precious metals such as Pd, Ru, Rh, Ag, and Au has been mainly studied. Recently, the introduction of transition metals such as Fe, Ni, and Co has been studied, but the conversion efficiency and stability are not up to the commercialization level.RELATED ART DOCUMENTPatent Document(Patent document 0001) Publication of Patent Publication No. 10-2024-0086159SUMMARY

[0006] An aspect of the disclosure provides a high-performance ammonia production catalyst capable of converting nitrate into high value-added ammonia in an environmentally friendly and efficient manner.

[0007] The aspect of the disclosure is not limited to that mentioned above, and other aspects not mentioned will be clearly understood by those skilled in the art from the description below.

[0008] An embodiment of the disclosure provides an ammonia production catalyst.

[0009] An ammonia production catalyst according to an embodiment of the disclosure includes: cuprous oxide (Cu2O); and bismuth doped on the surface of the cuprous oxide.

[0010] In an embodiment of the disclosure, the cuprous oxide may have a cuboctahedral morphology and cubic structure.

[0011] In an embodiment of the disclosure, the bismuth may be partially substitutionally doped on the surface of the cuprous oxide.

[0012] Another embodiment of the disclosure provides an ammonia production catalyst manufacturing method.

[0013] An ammonia production catalyst manufacturing method according to an embodiment of the disclosure is characterized by mixing and reacting a precursor containing copper, a reducing agent, and a bismuth precursor.

[0014] An ammonia production catalyst manufacturing method according to an embodiment of the disclosure may include: forming cuprous oxide by stirring and reacting a first solution containing a reducing agent and a precursor containing copper; and adding a bismuth precursor during the reaction to obtain a catalyst in which bismuth is partially substitutionally doped on the surface of cuprous oxide.

[0015] According to an embodiment of the disclosure, it is possible to provide a highly efficient catalyst material selective for ammonia production, and the manufactured catalyst can be applied as a nitrate reduction electrode in a neutral electrolyte to secure a conversion efficiency (Faraday efficiency) close to 100% and long-term operation stability.

[0016] The effects of the disclosure are not limited to the effects described above, and should be understood to include all effects that are inferable from the configuration of the disclosure described in the detailed description or claims of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0018] FIG. 1 is a schematic view showing an improved mechanism of an ammonia production catalyst according to an embodiment of the disclosure;

[0019] FIG. 2 is a schematic view showing a manufacturing process of an ammonia production catalyst according to an embodiment of the disclosure;

[0020] FIG. 3A is a schematic view showing an ammonia production reaction occurring on the surface of an ammonia production catalyst (Bi / Cu2O, embodiment 1) according to an embodiment of the disclosure;

[0021] FIG. 3B is an SEM image of cuprous oxide (Cu2O, comparative example 1) and a lattice spacing analysis view using HR-TEM;

[0022] FIG. 3C is an SEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0023] FIG. 3D is a BF-STEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0024] FIG. 3E is an HR-TEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0025] FIG. 3F is a view showing the elemental distribution measurement using EDS of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure;

[0026] FIG. 4A is a view showing the SEM image and particle size distribution of cuprous oxide (Cu2O);

[0027] FIG. 4B is a view showing the EDS element-specific distribution of cuprous oxide (Cu2O);

[0028] FIG. 5A is an SEM image of a comparative example (d-Bi / Cu2O, comparative example 2) in which the bismuth precursor was added at the beginning of Cu2O formation;

[0029] FIG. 5B is an HR-TEM image of d-Bi / Cu2O;

[0030] FIG. 5C is a view showing the EDS element-specific distribution of d-Bi / Cu2O;

[0031] FIG. 6A is a view showing the XRD diffraction patterns for Cu2O and Bi / Cu2O;

[0032] FIG. 6B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and Bi / Cu2O;

[0033] FIG. 6C is a view showing the high-resolution Bi 4f XPS spectra for a comparative example (Bi catalyst, comparative example 3) synthesized using HS-40 silica instead of Cu2O as a support and Bi / Cu2O;

[0034] FIG. 6D is a view showing the high-resolution O 1s XPS spectra for Cu2O and Bi / Cu2O;

[0035] FIG. 6E is a view showing the EPR spectra for Cu2O and Bi / Cu2O;

[0036] FIG. 6F is a view showing the FT-IR spectra for Cu2O and Bi / Cu2O;

[0037] FIG. 7A is a view showing the XRD diffraction patterns for Cu2O and d-Bi / Cu2O;

[0038] FIG. 7B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and d-Bi / Cu2O;

[0039] FIG. 7C is a view showing the high-resolution Bi 4f XPS spectra for Cu2O and d-Bi / Cu2O;

[0040] FIG. 7D is a view showing the high-resolution O 1s XPS spectra for Cu2O and d-Bi / Cu2O;

[0041] FIG. 7E is a view showing the EPR spectra for Cu2O and d-Bi / Cu2O;

[0042] FIG. 7F is a view showing FT-IR spectra for Cu2O and d-Bi / Cu2O;

[0043] FIG. 8A is a view showing current density (J)-voltage (V) graphs for nitrate reduction on Bi / Cu2O according to the amount of Bi introduced by linear scanning voltammetry (LSV);

[0044] FIG. 8B is a view showing ammonia production rates for Bi / Cu2O (embodiments 1-4) according to the amount of Bi introduced;

[0045] FIG. 9A is a current density-voltage graphs for nitrite reduction compared to nitrate for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV);

[0046] FIG. 9B is a current density-voltage graphs for water reduction compared to nitrate for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV);

[0047] FIG. 10A is a view showing ammonia production rates for electrochemical nitrate reduction according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0048] FIG. 10B is a view showing the electrochemical nitrate reduction to ammonia conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0049] FIG. 10C is a view showing the electrochemical nitrate reduction to nitrite production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0050] FIG. 10D is a view showing the electrochemical nitrate reduction to nitrite conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0051] FIG. 10E is a view showing the electrochemical nitrate reduction to hydrogen production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0052] FIG. 10F is a view showing the electrochemical nitrate reduction to hydrogen conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1;

[0053] FIG. 11A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1;

[0054] FIG. 11B is a view showing Nyquist plots from electrochemical impedance spectroscopy (EIS) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1;

[0055] FIG. 11C is a view showing ammonia production rates for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1;

[0056] FIG. 12A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for nitrate / nitrite / water reduction reactions for comparative example 3;

[0057] FIG. 12B is a view showing the nitrate reduction ammonia production rates according to the applied voltage for comparative example 3;

[0058] FIG. 12C is a view showing the nitrate reduction nitrite production rates according to the applied voltage for comparative example 3;

[0059] FIG. 13 is a view showing the nitrite reduction ammonia production rates according to the applied voltage for comparative example 3;

[0060] FIG. 14A is a view showing the electrochemical nitrite reduction ammonia production rates according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0061] FIG. 14B is a view showing the electrochemical nitrite reduction ammonia conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0062] FIG. 14C is a view showing the electrochemical nitrite reduction hydrogen production rates according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0063] FIG. 14D is a view showing the electrochemical nitrite reduction hydrogen conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1;

[0064] FIG. 15 is Nyquist plots from EIS analysis of the electrochemical nitrate reduction reaction for comparative examples 1-2 and embodiment 1;

[0065] FIG. 16 is a view comparing the electrochemical nitrate reduction ammonia production rates for embodiment 1 according to the presence and absence of a surface proton desorption material (adsorbed proton trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO));

[0066] FIG. 17A is a view showing the ammonia production rates and conversion efficiencies according to the nitrate concentration for embodiment 1;

[0067] FIG. 17B is a view showing the ammonia production rates and conversion efficiencies according to the electrolyte pH for embodiment 1;

[0068] FIG. 17C is a view showing the reactant / intermediate / product concentrations according to the reaction time for embodiment 1;

[0069] FIG. 17D is a view showing the ammonia production rates and conversion efficiencies according to the reaction time for embodiment 1;

[0070] FIG. 17E is a view showing the ammonia production rates and conversion efficiencies according to the number of repeated measurements for embodiment 1;

[0071] FIG. 18A is a view showing the hydrogen production rates according to the electrolyte pH for embodiment 1;

[0072] FIG. 18B is a view showing the hydrogen conversion efficiencies according to the electrolyte pH for embodiment 1;

[0073] FIG. 19A is a view showing the ammonia production rate change according to time at electrolyte pH 2 for embodiment 1;

[0074] FIG. 19B is a view showing the ammonia production rate change according to time at electrolyte pH 13 for embodiment 1;

[0075] FIG. 19C is a view showing the current density changes according to time at each pH for embodiment 1;

[0076] FIG. 20 is a view showing the current density change during 10 repeated activity evaluation measurements for embodiment 1;

[0077] FIG. 21A is an HR-TEM image of embodiment 1 after a long-term operation for stability evaluation;

[0078] FIG. 21B is XRD patterns of embodiment 1-coated electrodes before and after a long-term operation for stability evaluation;

[0079] FIG. 21C is a BF-STEM view of embodiment 1 after a long-term operation for stability evaluation;

[0080] FIG. 21D is an element distribution measurement view using EDS of embodiment 1 after a long-term operation for stability evaluation;

[0081] FIG. 22A is a view showing the XPS spectrum (Cu 2p) for embodiment 1-coated electrode after the long-term operation;

[0082] FIG. 22B is a view showing the XPS spectrum (Bi 4f) for embodiment 1-coated electrode after the long-term operation; and

[0083] FIG. 22C is a view showing the XPS spectrum (O 1s) for embodiment 1-coated electrode after the long-term operation.DETAILED DESCRIPTION

[0084] Hereinafter, the disclosure will be described with reference to the accompanying drawings. However, the disclosure may be implemented in various different forms and therefore is not limited to the embodiments described herein. In addition, in order to clearly describe the disclosure in the drawings, parts that are not related to the description are omitted, and similar parts are given similar drawing reference numerals throughout the specification.

[0085] In the entire specification, when a part is said to be “connected (linked, contacted, coupled)” to another part, this includes not only the case where it is “directly connected” but also the case where it is “indirectly connected” with another member in between. In addition, when a part is said to “include” a component, this does not mean that it excludes other components, unless otherwise specifically stated, but rather that it may include other components.

[0086] The terms used in this specification are used only to describe specific embodiments and are not intended to limit the disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, the terms “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood as not excluding in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0087] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

[0088] The electrochemical nitrate reduction reaction has two major reaction paths depending on the product, either nitrogen (N2) or ammonia (NH3), and the step in which the initial nitrate (NO3−) is converted to nitrite (NO2−) is known as the rate determining step.

[0089] In the disclosure, by introducing bismuth to the surface of a cuprous oxide material with excellent nitrate adsorption characteristics but low selectivity for ammonia, an effective protonation was induced, so that developed was a transition metal-based high-efficiency and high-selectivity nitrate reduction ammonia production electrocatalyst material.

[0090] Existing cuprous oxide-based materials with excellent nitrate adsorption characteristics had a limitation in that the selectivity for the target product, ammonia, was low due to poor catalytic characteristics in the subsequent reduction step after nitrite. Various metal doping strategies have been implemented to modify these surface catalyst properties, but noble metal dopants have been pointed out to have low economic efficiency compared to high activity, and previously studied transition metal dopants have relatively low conversion efficiency and stability.

[0091] FIG. 1 is a schematic view showing an improved mechanism of an ammonia production catalyst according to an embodiment of the disclosure; in this invention, bismuth, a p-orbital transition metal rather than a conventional d-orbital noble metal or transition metal, is applied as a dopant to induce bismuth doping locally concentrated on the surface of cuprous oxide through an in-situ doping method added during the hydrothermal synthesis of cuprous oxide. As shown in FIG. 1, the ammonia production efficiency, which was previously identified as a limitation of cuprous oxide due to poor protonation characteristics after conversion of nitrate to nitrite, was overcome through the introduction of bismuth, and the ammonia production efficiency was maximized by suppressing the hydrogen evolution reaction, which is a competitive reaction, and promoting the protonation of the adsorbed nitrogen intermediate.

[0092] Hereinafter, an ammonia production catalyst according to an embodiment of the disclosure will be described.

[0093] An ammonia production catalyst according to an embodiment of the disclosure is characterized by including cuprous oxide (Cu2O) and bismuth (Bi) doped on the surface of the cuprous oxide.

[0094] At this time, the cuprous oxide may have a cuboctrahedral morphology and cubic structure.

[0095] In an embodiment of the disclosure, the bismuth may be incorporated by injecting a bismuth precursor during the hydrothermal synthesis of the cuprous oxide. At this time, since the catalyst is manufactured in a manner in which the precursor is injected during the hydrothermal synthesis of the cuprous oxide as described above, the bismuth may not be doped on the entire cuprous oxide structure of the catalyst, but may be formed by surface-limited substitution doping in which it is concentrated and substituted on a portion of the surface.

[0096] If bismuth is introduced from the beginning of the synthesis of the catalyst, the bismuth dopant may contribute to the formation of Cu2O structure, which may cause the crystal structure to collapse and the crystallinity to deteriorate. On the other hand, when introduced at the terminal period of the synthesisterminal period, bismuth may be formed as a dopant limited to the surface. Therefore, a structure in which bismuth is limited to a portion of the surface and is doped by substitution is appropriate, and this may be formed by introducing a bismuth precursor during the hydrothermal synthesis process of cuprous oxide.

[0097] At this time, the mass ratio of bismuth to cuprous oxide may be 0.1 to 3.0 wt %, preferably 0.4 to 2.0 wt %.

[0098] In addition, the catalyst may be a structure that includes a thin film layer composed of the cuprous oxide and bismuth and uses this as an active point. The catalyst may be utilized as a cathode in a neutral electrolyte containing nitrate.

[0099] Next, an ammonia production catalyst manufacturing method according to an embodiment of the disclosure will be described.

[0100] In the disclosure, it is possible to manufacture a highly efficient catalyst material selective for ammonia production by inducing substitutional doping of bismuth (Bi) on the surface of cuprous oxide (Cu2O), which has been used as a conventional electrochemical nitrate conversion catalyst, through hydrothermal synthesis.

[0101] Therefore, the manufacturing method of the disclosure includes mixing and reacting a precursor containing copper, a reducing agent, and a bismuth precursor.

[0102] Preferably, in the manufacturing method, stirring and reacting a first solution containing the precursor containing copper and the reducing agent may be performed, wherein a bismuth precursor may be added during the reaction.

[0103] When manufacturing a bismuth-doped cuprous oxide catalyst based on a mixed solution in which the bismuth precursor, the precursor containing copper, and the reducing agent are all mixed at first, bismuth may contribute to the formation of Cu2O structure, which may cause structural collapse and deterioration of crystallinity. In addition, the obtained catalyst forms a catalyst having a doped structure throughout the cuprous oxide structure. As a result, the performance of the catalyst may be poor.

[0104] Therefore, during the reacting of cuprous oxide using a copper precursor and a reducing agent, a bismuth precursor is added to manufacture an ammonia production catalyst partially doped with bismuth.

[0105] First, a solution containing a copper precursor and a reducing agent is manufactured.

[0106] At this time, the copper precursor may be CuC4H4O6 (copper tartate) manufactured by mixing CuSO4 and C4H4O6KNa. In addition, the reducing agent may be glucose. However, that is not limited to the types of copper precursor and reducing agent selected as the above example, and a known copper precursor and reducing agent capable of forming cuprous oxide may be used.

[0107] When manufacturing a solution containing a copper precursor and a reducing agent, it is preferable to adjust the pH of the solution to an appropriate range by adding a KOH solution. At this time, the pH range may be 11.5 to 12.

[0108] Next, the solution is stirred.

[0109] Cuprous oxide may be formed through the stirring process at a temperature controlled within an appropriate range. At this time, the temperature may be 75° C.

[0110] During the process of forming cuprous oxide through stirring, a bismuth precursor may be added. For example, the bismuth precursor may be Bi(NO3)3·5H2O. When bismuth doping is completed, a catalyst may be obtained through centrifugation and vacuum drying.

[0111] Hereinafter, the disclosure will be described in more detail through manufacturing examples, comparative examples, and experimental examples. However, the disclosure is not limited to the following manufacturing examples and experimental examples.

[0112] The electrochemical system for verifying the effect of the disclosure was performed in a 0.5 M K2SO4 neutral electrolyte containing 1000 ppm NO3− unless otherwise specified, and was measured using a Ag / AgCl as a reference electrode and a Pt plate as a counter electrode.

[0113] In addition, the concentrations of ammonia as a product, nitrite as an responsive intermediate, and nitrate as a reactant were quantified using an ultraviolet-visible spectrometer and a calibration curve, and hydrogen as a byproduct was quantified using a gas chromatography.Examples 1-4: Bismuth-Doped Cuprous Oxide Catalyst (Bi—Cu2O)

[0114] Embodiments and comparative examples of the disclosure were produced through a hydrothermal method.

[0115] FIG. 2 is a schematic view showing a manufacturing process of an ammonia production catalyst according to an embodiment of the disclosure.

[0116] Hereinafter, referring to FIG. 2 above, a manufacturing process of an ammonia production catalyst according to an embodiment of the disclosure will be described.

[0117] After manufacturing 240 mL of a copper tartrate complex solution containing 1.4 mM CuSO4 and 8.9 mM C4H4O6KNa, 0.33 mL of 10 M KOH was added to adjust the pH to 11.5-12.

[0118] Subsequently, 10 mL of 0.25 M glucose was added and stirred at 300 rpm for 10 minutes.

[0119] The mixed solution was continuously stirred in a silicone oil bath at 75° C. for 2.5 hours, 10 mL of 0.85 mg / mL Bi(NO3)3·5H2O was added, and the reaction was performed for an additional 1 hour at 75° C., followed by several centrifugation steps using ultrapure water and ethanol, and vacuum drying steps to produce embodiment 1 (Bi / Cu2O).

[0120] In addition, embodiments 2 to 4 (Bi doping concentrations of 0.5, 1.5, and 2 times that of embodiment 1, respectively) were produced according to the change in Bi introduction amount. In each embodiment, the bismuth / cuprous oxide mass % ratio was 0.8 for embodiment 1, 0.4 for embodiment 2, 1.2 for embodiment 3, and 1.5 for embodiment 4.Comparative Examples: Pure Cu2O (Comparative Example 1), d-Bi / Cu2O (Comparative Example 2), Bi-Catalyst (Comparative Example 3)

[0121] In comparative example 1, pure Cu2O without Bi doping effect was produced by omitting the Bi(NO3)3·5H2O solution injection step during the same synthesis process as embodiment 1.

[0122] In comparative example 2, a sample (d-Bi / Cu2O) was produced by inducing full-structure doping rather than surface-limited substitution doping by injecting Bi(NO3)3·5H2O solution from the beginning of Cu2O synthesis.

[0123] In comparative example 3, HS-40 colloidal silica nanoparticles were used instead of Cu2O to analyze the effect of pure Bi(Bi-catalyst).Experimental Example 1: Changes in Structure and Composition Due to Introduction of Bismuth

[0124] FIG. 3A is a schematic view showing an ammonia production reaction occurring on the surface of an ammonia production catalyst (Bi / Cu2O, embodiment 1) according to an embodiment of the disclosure.

[0125] FIG. 3B is an SEM image of cuprous oxide (Cu2O, comparative example 1) and a lattice spacing analysis view using HR-TEM.

[0126] FIG. 3C is an SEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0127] FIG. 3D is an BF-STEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0128] FIG. 3E is an HR-TEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0129] FIG. 3F is a view showing the elemental distribution measurement using EDS of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0130] FIG. 4A is a view showing the SEM image and particle size distribution of cuprous oxide (Cu2O).

[0131] FIG. 4B is a view showing the EDS element-specific distribution of cuprous oxide (Cu2O).

[0132] FIG. 5A is an SEM image of a comparative example (d-Bi / Cu2O, comparative example 2) in which the bismuth precursor was added at the beginning of Cu2O synthesis.

[0133] FIG. 5B is an HR-TEM image of d-Bi / Cu2O.

[0134] FIG. 5C is a view showing the EDS element-specific distribution of d-Bi / Cu2O.

[0135] FIG. 6A is a view showing the XRD diffraction patterns for Cu2O and Bi / Cu2O.

[0136] FIG. 6B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and Bi / Cu2O.

[0137] FIG. 6C is a view showing the high-resolution Bi 4f XPS spectra for a comparative example (Bi catalyst, comparative example 3) synthesized using HS-40 silica instead of Cu2O as a support and Bi / Cu2O.

[0138] FIG. 6D is a view showing the high-resolution O 1s XPS spectra for Cu2O and Bi / Cu2O.

[0139] FIG. 6E is a view showing the EPR spectra for Cu2O and Bi / Cu2O.

[0140] FIG. 6F is a view showing the FT-IR spectra for Cu2O and Bi / Cu2O.

[0141] FIG. 7A is a view showing the XRD diffraction patterns for Cu2O and d-Bi / Cu2O.

[0142] FIG. 7B is a view showing the high-resolution Cu 2p XPS spectra for Cu2O and d-Bi / Cu2O.

[0143] FIG. 7C is a view showing the high-resolution Bi 4f XPS spectra for Cu2O and d-Bi / Cu2O.

[0144] FIG. 7D is a view showing the high-resolution O 1s XPS spectra for Cu2O and d-Bi / Cu2O.

[0145] FIG. 7E is a view showing the EPR spectra for Cu2O and d-Bi / Cu2O.

[0146] FIG. 7F is a view showing FT-IR spectra for Cu2O and d-Bi / Cu2O.

[0147] SEM, TEM, and XRD analyses were performed on embodiment 1 and comparative examples 1-2.

[0148] As a result, compared to comparative example 1 and embodiment 1, phenomena such as structural collapse, crystallinity deterioration, and overall Bi distribution in the structure were found in comparative example 2 (FIGS. 5A to 5C, FIG. 7).

[0149] On the other hand, in embodiment 1 and comparative example 1, which show similar shapes and crystal structures, it is possible to confirm the difference in roughness of specific surfaces in SEM and HR-TEM images and the difference in the formation of Bi introduction layers concentrated on the surface through EDS mapping.

[0150] This is because Bi, a dopant, contributes to the formation of Cu2O structure when introduced from the beginning of the Cu2O synthesis, and is formed in a form limited to the surface as a dopant when introduced at the end of the synthesis, depending on the timing of Bi introduction during the Cu2O synthesis process.

[0151] In addition, in the case of embodiment 1 where Bi was introduced at the terminal period of Cu2O synthesis, the Cu2+ peak representing the second copper oxide (CuO) of Cu 2p and the oxygen vacancy site (Ov) peak of O Is were significantly reduced in XPS analysis, and this phenomenon was also observed in the EPR spectrum, confirming that the introduction of Bi at the terminal period of Cu2O synthesis occurred along with a chemical state change on the surface of Cu2O.

[0152] On the other hand, in the case of comparative example 2, the oxygen vacancy significantly increased, and it showed a large structural and morphological change, so the introduction of Bi in the early stage of the synthesis affected the structure formation of Cu2O, forming a significantly etched cuboctahedral structure.Experimental Example 2: Electrochemical Nitrate Reduction Ammonia Production Catalyst Activity and Mechanism Analysis

[0153] An analysis of the catalytic activity was performed on the synthesized embodiment and comparative example.

[0154] FIG. 8A is a view showing current density (J)-voltage (V) graphs for Bi / Cu2O according to the amount of Bi introduced by linear scanning voltammetry (LSV).

[0155] FIG. 8B is a view showing ammonia production rates for Bi / Cu2O (embodiments 1-4) according to the amount of Bi introduced.

[0156] FIG. 9A is a current density-voltage graphs for nitrite reduction compared to nitrate reduction for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV).

[0157] FIG. 9B is a current density-voltage graphs for water reduction compared to nitrate reduction for comparative examples 1 and 2 and embodiment 1 by linear scanning voltammetry (LSV).

[0158] FIG. 10A is a view showing ammonia production rates for electrochemical nitrate reduction according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0159] FIG. 10B is a view showing the electrochemical nitrate reduction to ammonia conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0160] FIG. 10C is a view showing the electrochemical nitrate reduction to nitrite production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0161] FIG. 10D is a view showing the electrochemical nitrate reduction to nitrite conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0162] FIG. 10E is a view showing the electrochemical nitrate reduction to hydrogen production rates according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0163] FIG. 10F is a view showing the electrochemical nitrate reduction to hydrogen conversion efficiencies according to the applied voltage for comparative examples 1 and 2 and embodiment 1.

[0164] FIG. 11A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1.

[0165] FIG. 11B is a view showing Nyquist plots from electrochemical impedance spectroscopy (EIS) for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1.

[0166] FIG. 11C is a view showing ammonia production rates for different concentrations of supporting electrolyte (K2SO4) for a fixed NO3 concentration (1000 ppm) based on embodiment 1.

[0167] FIG. 12A is a view showing a current density-voltage graphs using linear scanning voltammetry (LSV) for nitrate / nitrite / water reduction reactions for comparative example 3.

[0168] FIG. 12B is a view showing the nitrate reduction ammonia production rate according to the applied voltage for comparative example 3.

[0169] FIG. 12C is a view showing the nitrate reduction nitrite production rates according to the applied voltage for comparative example 3.

[0170] FIG. 13 is a view showing the nitrite reduction ammonia production rates according to the applied voltage for comparative example 3.

[0171] FIG. 14A is a view showing the electrochemical nitrite reduction ammonia production rates according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0172] FIG. 14B is a view showing the electrochemical nitrite reduction ammonia conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0173] FIG. 14C is a view showing the electrochemical nitrite reduction hydrogen production rates according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0174] FIG. 14D is a view showing the electrochemical nitrite reduction hydrogen conversion efficiencies according to the applied voltage for comparative examples 1-2 and embodiment 1.

[0175] FIG. 15 is Nyquist plots from EIS analysis of the electrochemical nitrate reduction reaction for comparative examples 1-2 and embodiment 1.

[0176] FIG. 16 is a view comparing the electrochemical nitrate reduction ammonia production rates for embodiment 1 according to the presence and absence of a surface proton desorption material (adsorbed proton trapping, agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)).

[0177] FIG. 17A is a view showing the ammonia production rates and conversion efficiencies according to the nitrate concentration for embodiment 1.

[0178] FIG. 17B is a view showing the ammonia production rates and conversion efficiencies according to the electrolyte pH for embodiment 1.

[0179] FIG. 17C is a view showing the reactant / intermediate / product concentrations according to the reaction time for embodiment 1.

[0180] FIG. 17D is a view showing the ammonia production rates and conversion efficiencies according to the reaction time for embodiment 1.

[0181] FIG. 17E is a view showing the ammonia production rates and conversion efficiencies according to the number of repeated measurements for embodiment 1.

[0182] FIG. 18A is a view showing the hydrogen production rates according to the electrolyte pH for embodiment 1.

[0183] FIG. 18B is a view showing the hydrogen conversion efficiencies according to the electrolyte pH for embodiment 1.

[0184] FIG. 19A is a view showing the ammonia production rate change according to time at electrolyte pH 2 for embodiment 1.

[0185] FIG. 19B is a view showing the ammonia production rate change according to time at electrolyte pH 13 for embodiment 1.

[0186] FIG. 19C is a view showing the current density changes according to time at each pH for embodiment 1.

[0187] As a result, the electrochemical nitrate reduction ammonia conversion efficiency of up to 99.2% was shown at the −0.8 V vs. RHE for embodiment 1 of the disclosure.

[0188] For the sample optimization and mechanism analysis, the linear scanning voltage (LSV) and ammonia production were compared. In addition, the reaction was identified as a reaction dominated by mass transportation through the difference in the supporting electrolyte concentration, electrochemical impedance spectroscopy (EIS), and the plateau region on the LSV.

[0189] In addition, a comparative analysis was conducted for the embodiment and comparative examples according to the applied voltage, electrolyte pH, reaction time, and adsorbed proton trapping agent, and the reactant of nitrate or nitrite.

[0190] Accordingly, it was confirmed that the reaction rate is determined by the two-dimensional diffusion-controlled model, and that the poor protonation process after the conversion of nitrate to nitrite, which was a limitation of the existing Cu2O, occurs smoothly in Bi / Cu2O with Bi introduced.Experimental Example 3: Stability Evaluation of Electrochemical Nitrate Reduction Ammonia Production Catalyst

[0191] FIG. 20 is a view showing the current density change during 10 repeated activity evaluation measurements for embodiment 1.

[0192] FIG. 21A is an HR-TEM image of embodiment 1 after a long-term operation for stability evaluation.

[0193] FIG. 21B is XRD patterns of embodiment 1-coated electrode before and after the long-term operation.

[0194] FIG. 21C is a BF-STEM view of embodiment 1 after the long-term operation.

[0195] FIG. 21D is an element distribution measurement view using EDS of embodiment 1 after the long-term operation.

[0196] FIG. 22A is a view showing the XPS spectrum (Cu 2p) for embodiment 1-coated electrode after the long-term operation for stability evaluation.

[0197] FIG. 22B is a view showing the XPS spectrum (Bi 4f) for embodiment 1-coated electrode after the long-term operation.

[0198] FIG. 22C is a view showing the XPS spectrum (O 1s) for embodiment 1-coated electrode after the long-term operation.

[0199] As a result of performing 10 repeated measurements on embodiment 1 synthesized above, it was confirmed that continuously excellent conversion efficiency was exhibited, and excellent stability was ensured also for TEM, XRD, and XPS after the reaction.

[0200] The description of the disclosure is for illustrative purposes, and those skilled in the art will understand that it can be easily modified into other specific forms without changing the technical idea or essential features of the disclosure. Therefore, the embodiments described above should be understood as being exemplary in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and likewise, components described as distributed may be implemented in a combined form.

[0201] The scope of the disclosure is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the disclosure.

Examples

experimental example 1

Changes in Structure and Composition Due to Introduction of Bismuth

[0124]FIG. 3A is a schematic view showing an ammonia production reaction occurring on the surface of an ammonia production catalyst (Bi / Cu2O, embodiment 1) according to an embodiment of the disclosure.

[0125]FIG. 3B is an SEM image of cuprous oxide (Cu2O, comparative example 1) and a lattice spacing analysis view using HR-TEM.

[0126]FIG. 3C is an SEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0127]FIG. 3D is an BF-STEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0128]FIG. 3E is an HR-TEM image of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0129]FIG. 3F is a view showing the elemental distribution measurement using EDS of an ammonia production catalyst (Bi / Cu2O) according to an embodiment of the disclosure.

[0130]FIG. 4A is a view showing the SEM image and particle size distr...

experimental example 3

Stability Evaluation of Electrochemical Nitrate Reduction Ammonia Production Catalyst

[0191]FIG. 20 is a view showing the current density change during 10 repeated activity evaluation measurements for embodiment 1.

[0192]FIG. 21A is an HR-TEM image of embodiment 1 after a long-term operation for stability evaluation.

[0193]FIG. 21B is XRD patterns of embodiment 1-coated electrode before and after the long-term operation.

[0194]FIG. 21C is a BF-STEM view of embodiment 1 after the long-term operation.

[0195]FIG. 21D is an element distribution measurement view using EDS of embodiment 1 after the long-term operation.

[0196]FIG. 22A is a view showing the XPS spectrum (Cu 2p) for embodiment 1-coated electrode after the long-term operation for stability evaluation.

[0197]FIG. 22B is a view showing the XPS spectrum (Bi 4f) for embodiment 1-coated electrode after the long-term operation.

[0198]FIG. 22C is a view showing the XPS spectrum (O 1s) for embodiment 1-coated electrode after the long-term op...

Claims

1. An ammonia production catalyst, comprising:cuprous oxide (Cu2O); andbismuth doped on the surface of the cuprous oxide.

2. The ammonia production catalyst of claim 1, wherein the cuprous oxide has a cuboctahedral morphology and cubic structure.

3. The ammonia production catalyst of claim 1, wherein the bismuth is partially substitutionally doped on the surface of the cuprous oxide.

4. The ammonia production catalyst of claim 1, wherein a mass ratio of the bismuth to the cuprous oxide is 0.1 to 3.0 (bismuth / cuprous oxide).

5. An ammonia production catalyst manufacturing method characterized by mixing and reacting a precursor containing copper, a reducing agent, and a bismuth precursor.

6. The ammonia production catalyst manufacturing method of claim 5, comprising:forming cuprous oxide by stirring and reacting a first solution containing a reducing agent and a precursor containing copper; andadding a bismuth precursor during the reaction to obtain a catalyst in which bismuth is partially substitutionally doped on the surface of cuprous oxide.

7. The ammonia production catalyst manufacturing method of claim 5, wherein the reaction is performed through hydrothermal synthesis.

8. The ammonia production catalyst manufacturing method of claim 5, wherein the copper precursor is copper tartate (CuC4H4O6), a complex of CuSO4 and C4H4O6KNa.

9. The ammonia production catalyst manufacturing method of claim 5, wherein the reducing agent is glucose.

10. An ammonia production catalyst manufactured by the ammonia production catalyst manufacturing method of claim 5.

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