Low-power ammonia production system using nitrate reduction and hydrazine oxidation

Abstract

A low-power ammonia production system utilizing nitrate reduction and hydrazine oxidation is disclosed. More specifically, a nanowire composite is provided comprising: a plurality of longitudinally aligned tungsten oxide nanowires; and a tungsten phosphide layer formed on part or all of the surface of the tungsten oxide nanowires and comprising tungsten phosphide. The present invention may provide an electrochemical catalyst that exhibits simultaneous activity in the nitrate reduction reaction and the hydrazine reaction.

Description

Technology Field

[0001] The present invention relates to a low-power ammonia production system using nitrate reduction and hydrazine oxidation. Background Technology

[0002] Ammonia (NH3 or NH4), one of the most widely produced and utilized chemicals. + NH3 is an indispensable feedstock for nitrogen-based fertilizers and is recently considered an ideal carbon-neutral fuel or hydrogen carrier due to its very high hydrogen density. Unfortunately, current NH3 production relies primarily on the Haber-Bosch process, which is energy-intensive (1.0–2.0% of global energy production) and waste-intensive (1.5% of global carbon emissions).

[0003] However, the Haber-Bosch process requires high temperature and high pressure conditions and has problems such as high carbon dioxide emissions and high energy consumption during the process.

[0004] Therefore, research on ammonia production technology that does not generate carbon dioxide is necessary. The problem to be solved

[0005] The objective of the present invention is to provide an ammonia production system that does not generate carbon dioxide during the ammonia production process.

[0006] Another objective of the present invention is to provide a tungsten-based electrochemical catalyst that exhibits simultaneous activity in nitrate reduction and hydrazine reactions.

[0007] Another objective of the present invention is to provide an ammonia production system capable of producing ammonia using only a single solar cell, as it enables small-scale production by electrochemically producing ammonia and allows for ammonia production with low power. means of solving the problem

[0008] According to one aspect of the present invention, a nanowire composite is provided comprising: a plurality of longitudinally aligned tungsten oxide nanowires; and a tungsten phosphide layer formed on part or all of the surface of the tungsten oxide nanowires and comprising tungsten phosphide.

[0009] In addition, the nanowire composite may further include a substrate, and the plurality of tungsten oxide nanowires may be formed vertically on one surface of the substrate.

[0010] In addition, the substrate may include nickel foam.

[0011] In addition, the tungsten oxide nanowire may have one or more shapes selected from the group consisting of nanowires, nanotubes, and nanorods.

[0012] In addition, the tungsten oxide nanowire may be a tungsten oxide nanowire.

[0013] In addition, the tungsten oxide nanowire may include one or more types selected from the group consisting of WO2 and WO3.

[0014] In addition, the tungsten oxide nanowire may contain WO3.

[0015] In addition, the tungsten phosphide layer may include one or more selected from the group consisting of W2P, WP, W3P4, W3P5, and WP2.

[0016] In addition, the tungsten phosphide layer may contain WP.

[0017] In addition, the average length of the tungsten oxide nanowire may be 50 to 300 μm.

[0018] According to another aspect of the present invention, a catalyst for use in ammonia production is provided, comprising the nanowire complex.

[0019] In addition, the above catalyst can be used to reduce nitrates to produce ammonia, and at the same time, to oxidize hydrazine to produce nitrogen.

[0020] According to another aspect of the present invention, an ammonia production system is provided comprising: an oxidation electrode comprising the catalyst; a reduction electrode comprising the catalyst; a separator located between the reduction electrode and the oxidation electrode; and an electrolyte.

[0021] In addition, the ammonia production system may further include a battery, and the battery may be connected to the reduction electrode and the oxidation electrode, respectively, to supply electrical energy.

[0022] In addition, the above battery may include a solar cell.

[0023] In addition, the oxidation electrode receives hydrazine (N2H4) and oxidizes it to produce nitrogen (N2) through a reaction (HzOR), and the reduction electrode performs a reaction (HzOR) through nitrate (NO3 - ) supplied and reduced to ammonium ions (NH4 + It can perform a reaction (NO3RR) that produces ).

[0024] In addition, when operating the ammonia production system, the current density is 20 to 30 mAcm -2 It could be.

[0025] In addition, the above ammonia production system can be driven by a voltage of 0 to 1 V to oxidize hydrazine to produce nitrogen and reduce nitrate to produce ammonium ions.

[0026] According to another aspect of the present invention, the ammonia production system is used to oxidize hydrazine (N2H4) to produce nitrogen (N2) and nitrate (NO3 - By reducing ) ammonium ions (NH4 + A method for producing ammonia is provided, comprising the step of producing ). Effects of the invention

[0027] The present invention can provide an electrochemical catalyst that exhibits simultaneous activity in nitrate reduction reactions and hydrazine reactions.

[0028] In addition, by combining the two reactions of nitrate reduction and hydrazine, an electrochemical ammonia production system capable of operating at low energy can be constructed.

[0029] In addition, due to its low-energy operation capability, it can be powered by solar cells, which ultimately enables self-driving green ammonia production and allows for environmentally friendly ammonia production without carbon dioxide emissions. Brief explanation of the drawing

[0030] These drawings are for reference to explain exemplary embodiments of the present invention, and therefore, the technical concept of the present invention should not be interpreted as being limited to the attached drawings. Figures 1a and 1e show SEM images of WO and WP NW. Figures 1c and 1g show low-resolution TEM images of WO and WP NW. Figures 1b and 1f show the EDS element mapping of WO and WP NW. Figures 1d and 1h show HRTEM images of WO and WP NW and their corresponding diffraction patterns (inset images). Figure 2a shows the XRD spectra of Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and Example of the present invention (WP / NF). FIGS. 2b to 2d show XPS profiles for Comparative Example 1 (WO / NF) and an embodiment of the present invention (WP / NF). Figure 3a shows the LSV curves for the nitrate reduction reaction (NO3RR) of Comparative Example 1 (WO / NF) and Example of the present invention (WP / NF) in a neutral electrolyte. FIG. 3b shows the Faraday efficiency at each applied potential of Comparative Example 1 (WO / NF) and Example of the present invention (WP / NF) in a neutral electrolyte. FIG. 3c shows the ammonia yield at each applied potential of Comparative Example 1 (WO / NF) and Example of the present invention (WP / NF) in a neutral electrolyte. Figure 3d shows the LSV curves for NO3RR of Comparative Example 1 (WO / NF) and Example of the present invention (WP / NF) in a basic electrolyte. Figure 3e shows the Faraday efficiency at each applied potential of Comparative Example 1 (WO / NF) and Example of the present invention (WP / NF) in a basic electrolyte. Figure 3f shows the ammonia yield at each applied potential of Comparative Example 1 (WO / NF) and Example of the present invention (WP / NF) in a basic electrolyte. Figure 3g is in a basic electrolyte 14 N-KNO3 and 15 Example (WP / NF) of the present invention obtained using N-KNO3 1 This shows the H-NMR results. Figure 3h shows the results confirming that ammonia is produced from nitrate by comparing Faraday efficiency based on isotope NMR tests and colorimetric indophenol tests with and without nitrate. Figure 3i shows a stability test for NO3RR of an embodiment of the present invention in a basic electrolyte. FIG. 4a shows the calculated adsorption energies of nitrate (ΔGads(NO3)) for Comparative Example 1 (WO3) and Example of the present invention (WP). - It represents )) FIG. 4b shows the charge transferred to nitrate on the surface of Comparative Example 1 (WO3) and Example of the present invention (WP). FIG. 5a shows the LSV curves of the oxygen evolution reaction (OER) for Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and an embodiment of the present invention (WP / NF). FIG. 5b shows the corresponding Tafel plots for Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and the embodiment of the present invention (WP / NF). FIG. 5c shows the OER of 10 mA cm⁻¹ for an embodiment (WP / NF) of the present invention. -2 This shows the time potential difference analysis at. The drawing inserted in FIG. 5c shows the CV curve over 1,000 cycles of OER for an embodiment (WP / NF) of the present invention. FIG. 5d shows the LSV curves of the urea oxidation reaction (UOR) for Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and an embodiment of the present invention (WP / NF). FIG. 5e shows the corresponding Tafel plots for Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and the embodiment of the present invention (WP / NF). FIG. 5f shows the UOR of an embodiment (WP / NF) of the present invention at 10 mA cm⁻¹. -2 This shows the time potential difference analysis at. The drawing inserted in FIG. 5f shows the CV curve of UOR over 1,000 cycles for an embodiment (WP / NF) of the present invention. FIG. 5g shows the LSV curves of the hydrazine oxidation reaction (HzOR) for Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and the embodiment of the present invention (WP / NF). FIG. 5h shows the corresponding Tafel plots for Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and the embodiment of the present invention (WP / NF). FIG. 5i shows 10 mA cm⁻¹ for HzOR of an embodiment (WP / NF) of the present invention. -2This shows the time potential difference analysis at. The drawing inserted in FIG. 5i shows the CV curve over 1,000 cycles for an embodiment (WP / NF) of the present invention. Figure 6a shows a schematic diagram of NO3RR-OER, NO3RR-UOR, and NO3RR-HzOR. FIG. 6b shows the LSV curves for NO3RR-OER, NO3RR-UOR, and NO3RR-HzOR by configuring an embodiment of the present invention (WP / NF) with two electrodes. Figure 6c shows the potential profiles for the cathodic and anode reactions of NO3RR-HzOR and NO3RR-OER. Figure 6d compares the Faraday efficiency and energy consumption of various electrochemical ammonia production methods. Figure 7a shows the IV curves of WP / NF(NO3RR)-WP / NF(HzOR) for a two-electrode configuration and a perovskite solar cell. Here, the junction point represents the ideal operating current. Figure 7b shows the time potential difference of an unbiased PV-EC system combining WP / NF(NO3RR)-WP / NF(HzOR) and a perovskite solar cell. Figure 7c shows a schematic diagram of a cyclic electrochemical system equipped with a PV cell for ammonia production based on a NO3RR-HzOR system. Specific details for implementing the invention

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention.

[0032] However, the following description is not intended to limit the present invention to specific embodiments, and detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions could obscure the essence of the present invention.

[0033] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, actions, components, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, or combinations thereof.

[0034] Additionally, terms including ordinal numbers, such as "first," "second," etc., used below may be used to describe various components, but said components are not limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0035] Furthermore, when it is stated that a component is "formed" or "laminated" on another component, it should be understood that while it may be formed or laminated by being directly attached to the entire surface or one surface of the other component, there may also be other components present in between.

[0036] Hereinafter, a low-power ammonia production system utilizing nitrate reduction and hydrazine oxidation according to the present invention will be described in detail. However, this is presented as an example and is not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0037] The present invention provides a nanowire composite comprising: a plurality of tungsten oxide nanowires aligned in the longitudinal direction; and a tungsten phosphide layer formed on part or all of the surface of the tungsten oxide nanowires and comprising tungsten phosphide.

[0038] In addition, the nanowire composite may further include a substrate, and the plurality of tungsten oxide nanowires may be formed vertically on one surface of the substrate.

[0039] In addition, the substrate may include nickel foam.

[0040] In addition, the tungsten oxide nanowire may have one or more shapes selected from the group consisting of nanowires, nanotubes, and nanorods.

[0041] In addition, the tungsten oxide nanowire may be a tungsten oxide nanowire.

[0042] In addition, the tungsten oxide nanowire may include one or more types selected from the group consisting of WO2 and WO3.

[0043] In addition, the tungsten oxide nanowire may contain WO3.

[0044] In addition, the tungsten phosphide layer may include one or more selected from the group consisting of W2P, WP, W3P4, W3P5, and WP2.

[0045] In addition, the tungsten phosphide layer may contain WP.

[0046] In addition, the average length of the tungsten oxide nanowire may be 50 to 300 μm. If the average length is less than 50 μm, the specific surface area becomes smaller and is undesirable, and if it exceeds 300 μm, stability decreases and is undesirable.

[0047] According to another aspect of the present invention, a method for manufacturing a metal hydroxide layer / tungsten phosphide nanowire composite is provided, comprising: (a) introducing a substrate and a tungsten precursor to grow a plurality of tungsten oxide nanowires aligned along a direction perpendicular to the substrate; and (b) introducing a phosphide precursor onto the tungsten oxide nanowires and heat-treating under an inert atmosphere to convert the tungsten oxide nanowires into tungsten phosphide nanowires.

[0048] In addition, in step (a) above, the growth of the tungsten oxide nanowire can be performed by thermal evaporation.

[0049] In addition, the above thermal deposition method can be performed by heating to a temperature of 1000 to 1200 ℃ for 30 minutes to 2 hours at a heating rate of 5 to 15 ℃ / min. If the heating rate is less than 5 ℃ / min, over-deposition occurs, which is undesirable, and if it exceeds 15 ℃ / min, temperature control is not suitable, which is undesirable. If the thermal deposition temperature is performed at less than 1000 ℃, nanowires are not formed, which is undesirable, and if it exceeds 1200 ℃, structural stability is compromised, which is undesirable.

[0050] Additionally, the above step (a) can be performed under vacuum.

[0051] Additionally, in step (b) above, the phosphide precursor is NaH2PO 2· It may include one or more selected from the group consisting of H2O, phosphine, and phosphorous.

[0052] In addition, in step (b), the inert gas may include one or more selected from the group consisting of Ar, N2, and He.

[0053] In addition, in step (b) above, the step of converting tungsten oxide nanowires into tungsten phosphide nanowires may be performed by heat treatment selected from one or more methods from the group consisting of thermal evaporation, chemical vapor deposition, or sputtering.

[0054] In addition, the step of converting the tungsten oxide nanowire into a tungsten phosphide nanowire can be performed by chemical vapor deposition.

[0055] In addition, the chemical vapor deposition method described above can perform a first heat treatment and a second heat treatment.

[0056] The above first heat treatment and second heat treatment are each performed in a two-zone furnace divided into two zones, and the phosphide precursor is heated to 300 ℃ in the zone where the first heat treatment is performed, and the reactant (WO) is heated to 800 ℃ in the zone where the second heat treatment is performed.

[0057] In addition, the first heat treatment can be performed at a temperature of 100 to 500 ℃, and the second heat treatment can be performed at a temperature of 500 to 1000 ℃, preferably 700 to 900 ℃, and more preferably 800 ℃.

[0058] In addition, it can be phosphorylated into tungsten phosphide by performing the above heat treatment.

[0059] Figure 7a shows the IV curve of WP / NF(NO3RR)-WP / NF(HzOR) for a two-electrode configuration and a perovskite solar cell, Figure 7b shows the time potential difference of an unbiased PV-EC system combining WP / NF(NO3RR)-WP / NF(HzOR) and a perovskite solar cell, and Figure 7c shows a schematic diagram of a cyclic electrochemical system equipped with a PV cell for ammonia production based on a NO3RR-HzOR system.

[0060] Referring to FIG. 7, a catalyst for use in ammonia production is provided, comprising the nanowire composite.

[0061] In addition, the above catalyst can be used to reduce nitrates to produce ammonia, and at the same time, to oxidize hydrazine to produce nitrogen.

[0062] According to another aspect of the present invention, an ammonia production system is provided comprising: an oxidation electrode comprising the catalyst; a reduction electrode comprising the catalyst; a separator located between the reduction electrode and the oxidation electrode; and an electrolyte.

[0063] In addition, the ammonia production system may further include a battery, and the battery may be connected to the reduction electrode and the oxidation electrode, respectively, to supply electrical energy.

[0064] In addition, the above battery may include a solar cell.

[0065] In addition, the oxidation electrode receives hydrazine (N2H4) and oxidizes it to produce nitrogen (N2) through a reaction (HzOR), and the reduction electrode performs a reaction (HzOR) through nitrate (NO3 - ) supplied and reduced to ammonium ions (NH4 + It can perform a reaction (NO3RR) that produces ).

[0066] In addition, when operating the ammonia production system, the current density is 20 to 30 mAcm -2, preferably 23 to 24 mAcm -2 It may be. Here, the ammonia production system may be driven by a voltage of 0 to 1 V, preferably 0.2 to 0.4 V, to oxidize hydrazine to produce nitrogen and reduce nitrate to produce ammonium ions. If the ammonia production system is driven by a voltage of less than 0 V, it deviates from the solar cell driving conditions and is undesirable, and if it exceeds 1 V, more power is consumed and is undesirable.

[0067] In addition, the current density during the operation of the ammonia production system is 10 mAcm -2 It may be possible. Here, the ammonia production system can be driven by a voltage of 0.24 V to oxidize hydrazine to produce nitrogen and reduce nitrate to produce ammonium ions.

[0068] According to another aspect of the present invention, the ammonia production system is used to oxidize hydrazine (N2H4) to produce nitrogen (N2) and nitrate (NO3 - By reducing ) ammonium ions (NH4 + A method for producing ammonia is provided, comprising the step of producing ).

[0069] [Example]

[0070] Hereinafter, preferred embodiments of the present invention will be described. However, this is for illustrative purposes only and does not limit the scope of the present invention.

[0071] Example: WP NW (WP / NF) Synthesis

[0072] WP NW (Tungsten phosphide nanowire) was synthesized in a tube furnace through a two-step process of thermal evaporation and chemical vapor deposition.

[0073] First, tungsten oxide (WO) NWs were grown directly on Ni foam (NF) by thermal evaporation at 1050°C (WO3 heating temperature) under vacuum. Then, 1 g of NaH2PO 2· The surface portion of the WO NW, excluding the center, was converted to WP by additional chemical vapor deposition of WO NW using H2O. The tube furnace was purged with Ar gas and heated in a 2-zone furnace for 1 hour at 300°C in the first heat treatment zone and at 800°C in the second heat treatment zone to produce the final WP NW (WP / NF).

[0074] Comparative Example 1: WO / NF

[0075] WO / NF was prepared in the same manner as in the example, except that chemical vapor deposition was not performed using NaH2PO2·H2O, instead of converting to WP NW by chemical vapor deposition using NaH2PO2·H2O.

[0076] Comparative Example 2: bare NF

[0077] I prepared untreated nickel foam.

[0078] Device Example

[0079] Device Example 1: Self-powered PV-Electrolysis (EC) System

[0080] NO 3 RR-HzOR System Construction

[0081] The NO3RR-HzOR system was fabricated by utilizing WP NWs deposited by a chemical vapor phase method as a catalyst for the positive electrode, injecting nitrate, a reactant of the NO3RR reaction, into the negative electrode and hydrazine, a reactant of the HzOR reaction, into the positive electrode.

[0082] Perovskite solar cell fabrication

[0083] Perovskite solar cells were fabricated on glass substrates coated with fluorine-doped tin oxide (FTO). Zinc powder and hydrochloric acid were used to etch the FTO-coated glass substrates. The etched FTO-coated glass substrates were cleaned by ultrasonic treatment. After adding detergent, deionized water, ethanol, acetone, and isopropyl alcohol, they were dried overnight in an oven. 0.11 M SnCl 2 ·A dense tin oxide (SnO2) layer was prepared by the sol-gel method, in which a solution of 2H2O dissolved in ethanol was spin-coated at 4000 rpm for 30 seconds, followed by annealing at 190 °C for 60 minutes. Prior to spin-coating the SnO2 layer, the substrate was treated with UV-ozone for 15 minutes. After depositing the SnO2 layer, the substrate was treated with UV-ozone for 15 minutes, spin-coated with 3-(1-pyridinio)-1-propanesulfonate dissolved in methanol at 5000 rpm for 40 seconds, and then annealed at 110 °C for 5 minutes. After cooling the substrate to room temperature, it was transferred to a drying box (approx. 25% RH at 25 °C). The perovskite precursor solution was prepared from a mixture of formamidinium iodide. N,N-dimethylformamide (1.4M), methylammonium bromide (0.04M), lead(II) iodide (1.4M), lead(II) bromide (0.04M), and methylammonium chloride (0.5M):dimethyl sulfoxide = 8:1 (v:v) were used, and spin coating was performed using a two-step program of 1000 rpm and 5000 rpm for 10 and 20 seconds. In the second step, 800 μL of diethyl ether was poured onto the substrate 5 seconds before the program ended. Then, the substrate was annealed at 150°C for 15 minutes. After annealing, an n-octylammonium bromide solution dissolved in chloroform was spin-coated at 3000 rpm for 30 seconds, followed by annealing at 105°C for 5 minutes. A hole transport material solution (72.3 mg Spiro-OMeTAD in 1 mL chlorobenzene, 27.8 μL 4-tert-butylpyridine, 17.8 μL lithium bis(trifluoromethanesulfonyl)imide (520 mg / mL in acetonitrile)) was spin-coated at 5000 rpm for 30 seconds. Finally, a perovskite solar cell was fabricated by depositing a gold electrode (80 nm) by thermal evaporation under high vacuum conditions.

[0084] Production of Self-powered PV-Electrolysis (EC) System

[0085] A self-powered PV-electrolysis (EC) system was fabricated by connecting the NO3RR-HzOR system prepared above to the negative electrode (electron emission) of the solar cell and the negative reaction of the NO3RR-HzOR system, NO3RR, and connecting the positive electrode (hole emission) of the solar cell and the positive reaction of the NO3RR-HzOR system, HzOR. At this time, to verify the amount of current generated, a measuring device was connected between the positive electrode of the solar cell and the positive reaction of the NO3RR-HzOR system.

[0086] [Test Example]

[0087] Test Example 1: Confirmation of Synthesis of WP NW (WP / NF) Catalyst

[0088] Test Example 1-1: Confirmation of SEM and TEM Images

[0089] Figures 1a and 1e show SEM images of WO and WP NWs, Figures 1c and 1g show low-resolution TEM images of WO and WP NWs, Figures 1b and 1f show EDS element mapping of WO and WP NWs, and Figures 1d and 1h show HRTEM images of WO and WP NWs and their corresponding diffraction patterns (inset images).

[0090] Table 1 summarizes the Faraday efficiency and ammonia yield of the embodiments of the present invention prepared at various phosphorylation temperatures of -0.1V and RHE with 0.1M KNO3 added to 1M KOH after 1 hour of NO3RR.

[0091] catalyst FE(%) Ammonia yield(mg cm -2 h -1 ) Example of secondary heat treatment at 700 ℃ 12.38±1.39 0.61±0.19 Example of secondary heat treatment at 800 ℃ 85.1±5.89 1.97±0.35 Example of secondary heat treatment at 900 ℃ 67.32±2.93 0.85±0.13

[0092] Referring to Figure 1 and Table 1, secondary heat treatment (phosphorylation) temperatures of 700 to 900 °C were tested to obtain optimal samples. Samples synthesized at 700 °C were not fully phosphorylated, and the proportion of phosphorus was low in the EDS elemental mapping results. On the other hand, it was confirmed that synthesis at 900 °C caused partial surface structure collapse. Additionally, referring to Table 1, the catalyst phosphorylated at 800 °C exhibited the highest Faraday efficiency of 85.1 ± 5.89% and a value of 1.97 ± 0.35 mg cm⁻¹. -2 h -1 It exhibited the highest ammonia yield. In contrast, the catalyst phosphorylated at 700 °C showed significantly lower Faraday efficiency (12.38 ± 1.39%) and ammonia yield (0.61 ± 0.19 mg cm⁻¹). -2 h -1 The catalyst phosphorylated at 900 ℃ showed an efficiency of 67.32 ± 2.93%, but still 0.85 ± 0.13 mg cm⁻¹. -2 h -1 It was confirmed that it exhibited a low ammonia yield.

[0093] Test Example 1-2: XRD / XPS Verification

[0094] FIG. 2a shows the XRD spectra of Comparative Example 1 (WO / NF), Comparative Example 2 (NF), and Example of the present invention (WP / NF), and FIG. 2b to 2d show the XPS profiles for Comparative Example 1 (WO / WF) and Example of the present invention (WP / NF).

[0095] Referring to Fig. 2, W 18 O 49 The determination of was observed in Comparative Example 1 (WO / NF) after the WO3 powder thermal evaporation process. The most intense peak observed at 23.6° was W 18 O 49 (010) corresponds to. W after phosphorylation 18 O 49The peak disappeared and a new diffraction peak appeared, which matched the peak of the WP reference well. The most intense peak observed at 31.2° originated from WP (101).

[0096] X-ray Photoelectron Spectroscopy (XPS) analysis was performed to confirm the chemical bonding state of Comparative Example 1 (WO / NF) and Example (WP / NF). The tungsten peaks of Comparative Example 1 (WO / NF) and Example (WP / NF) of the present invention were W 4f 7 / 2 , W 4f 5 / 2 and W 5p 3 / 2 It was deconvolved with respect to . The main peak of Comparative Example 1 (WO / NF) is W 6+ W 5+ It showed the double bond state of. In contrast, the embodiment of the present invention (WP / NF) showed an additional WP bond peak at 31.6 eV. The phosphorus peak of the embodiment of the present invention (WP / NF) clearly indicated the presence of a phosphate (PO) bond at 134.5 eV and a metal phosphide (PM) bond at 130.6 and 129.6 eV, confirming the successful synthesis of the WP sample. No phosphorus peak was observed in the profile of Comparative Example 1 (WO / NF). The O 1s spectrum of Comparative Example 1 (WO / NF) showed a major lattice oxygen state (WO) with a hydroxyl bond, whereas the profile of the embodiment of the present invention (WP / NF) showed the presence of a PO bond at 533.1 eV, confirming the successful synthesis of the WP sample.

[0097] Test Example 2: NO of WP NW 3 RR activity analysis (electrocatalytic cathodic reaction)

[0098] FIG. 3a shows the LSV curves for the nitrate reduction reaction (NO3RR) of Comparative Example 1 (WO / WF) and the Example of the present invention (WF / NF) in a neutral electrolyte; FIG. 3b shows the Faraday efficiency at each applied potential of Comparative Example 1 (WO / WF) and the Example of the present invention (WF / NF) in a neutral electrolyte; FIG. 3c shows the ammonia yield at each applied potential of Comparative Example 1 (WO / WF) and the Example of the present invention (WF / NF) in a neutral electrolyte; FIG. 3d shows the LSV curves for NO3RR of Comparative Example 1 (WO / WF) and the Example of the present invention (WF / NF) in a basic electrolyte; FIG. 3e shows the Faraday efficiency at each applied potential of Comparative Example 1 (WO / WF) and the Example of the present invention (WF / NF) in a basic electrolyte; and FIG. 3f shows Comparative Example 1 (WO / WF) and in a basic electrolyte Figure 3g shows the ammonia yield at each applied potential of an embodiment (WF / NF) of the present invention, and in a basic electrolyte 14 N-KNO3 and 15 Example (WF / NF) of the present invention obtained using N-KNO3 1 Figure 3h shows the H-NMR results and confirms that ammonia is produced from nitrate by comparing the Faraday efficiency based on the isotope NMR test and the colorimetric indophenol test with and without nitrate.

[0099] Referring to FIG. 3, it is shown that the current density generated by the embodiment of the present invention (WP / NF) under both neutral and basic conditions is higher than the current density generated by Comparative Example 1 (WO / NF), indicating that the catalytic activity of the embodiment of the present invention (WP / NF) for NO3RR is higher than that of Comparative Example 1 (WO / NF). The current density recorded in 1 M KOH is significantly higher than the current density recorded in 0.45 M K2SO4, indicating that the basic electrolyte provides higher ionic conductivity and more concentrated ions to promote the electrochemical reaction compared to the neutral electrolyte. To evaluate NO3RR performance, the Faraday efficiency (FE) and the ammonia production rate (NH4 + Two parameters of yield were compared. Time-amplitude (It) analysis, which measures the current generated when a fixed voltage is applied, was performed for one hour at each voltage. FE was calculated based on the ammonia concentration.

[0100] Referring to FIG. 3b, under neutral conditions, the embodiment of the present invention (WP / NF) produced 93±3.0% FE at -0.5V compared to RHE, whereas Comparative Example 1 (WO / NF) produced a relatively low FE of 76.8±8.1% at -0.4V compared to RHE.

[0101] Referring to Figures 3c, 3e, and 3f, under basic conditions, WP achieved 85.1±5.9% relative to RHE at -0.1V, while WO produced a lower efficiency of 75.3±2.2% relative to RHE at -0.1V. Ammonia yield per unit time and per unit area was calculated at each voltage under both neutral and basic conditions based on the measured concentration of the generated ammonia. In both cases, the ammonia yield increased as the applied potential increased, and the yield of the embodiment of the present invention (WP / NF) was higher than the yield of Comparative Example 1 (WO / NF).

[0102] Referring to Fig. 3g, isotope experiments were performed to exclude the influence of contamination from other sources on ammonia quantification. 14 When N-KNO3 was used as the nitrate source, three peaks between 7.0 and 7.3 ppm were observed in the nuclear magnetic resonance (NMR) spectrum at 55 Hz intervals. These peaks 14 NH4 + It can be assigned to.

[0103] Referring to Fig. 3h, 15 When the same experiment was performed using N-KNO3, two peaks were detected at a 73 Hz interval between the three previously observed peaks. These two peaks are 15 NH4 + This corresponds to... This result confirmed that nitrate is the sole source of ammonia production in the current experiment. A control experiment conducted without nitrate further confirmed that no ammonia production occurs in the absence of nitrate.

[0104] Colorless indophenol and 1 H-NMR testing confirmed that ammonia was detected only when a nitrate source was applied. For more rigorous quantitative analysis, ammonia production was quantified using isotopic nitrate. The calibration curve representing the area ratio of maleic acid to the concentration used is 1 It showed excellent linearity in the H-NMR results. 5 In the case of N ammonia production, measured by the colorimetric method 14 Compared to N ammonia production 1 The H-NMR value was within the acceptable error range.

[0105] Referring to Fig. 3i, an initial current drop was repeatedly observed during the initial phase of each run in the cycle test. This trend is consistent with NO3, as previously reported. -This can be explained by the decrease in concentration and the change in electrolyte pH due to ammonia generation. However, the current density showed a trend similar to the initial value upon recharging the electrolyte, indicating good catalyst stability.

[0106] Test Example 3: NO 3 Theoretical analysis of RR activity (comparison of adsorption reactions)

[0107] FIG. 4a shows the calculated adsorption energies of nitrate (ΔGads(NO3)) for Comparative Example 1 (WO3) and Example of the present invention (WP). - Figure 4b shows the charge transferred to nitrate on the surface of Comparative Example 1 (WO3) and Example of the present invention (WP).

[0108] Referring to Fig. 4, ΔGads (NO3) at -0.1V relative to RHE - It was predicted that ) is 0.94 eV at WO3(001) and -1.60 eV at WP(010). Negative values ​​indicate that the adsorption is energetically stable because it is an exothermic reaction.

[0109] Also, NO3 - It was confirmed that it can exhibit stronger adsorption on the WP(010) surface. Charge transfer analysis based on Bader charge also NO3 - It was confirmed that it can have a stronger interaction with WP (010) than with WO3 (001). NO3 on the surface - The amount of charge transferred is 0.77e in the case of WP(010). - and for WO3(001), 0.60e - am.

[0110] Through this, it can be inferred that the embodiment of the present invention (WP / NF) has a stronger nitrate adsorption capacity, which is advantageous for multiple electron reactions. Consequently, it was confirmed that the embodiment of the present invention (WP / NF) exhibits higher efficiency in producing ammonia with an improved yield requiring the participation of 8 electrons.

[0111] Test Example 4: Electrocatalytic Anode Reaction: Comparison of OER, UOR, and HzOR

[0112] FIG. 5a shows the LSV curves of the oxygen evolution reaction (OER) for Comparative Example 1, Comparative Example 2 and the embodiment of the present invention, FIG. 5b shows the corresponding Tafel plots for Comparative Example 1, Comparative Example 2 and the embodiment of the present invention, and FIG. 5c shows the OER of the embodiment of the present invention (WF / NF) at 10 mA cm⁻¹. -2 This shows the time potential difference analysis at, the figure inserted in Fig. 5c shows the CV curve of the OER over 1,000 cycles for an embodiment of the present invention, Fig. 5d shows the LSV curve of the urea oxidation reaction (UOR) for Comparative Example 1, Comparative Example 2 and an embodiment of the present invention, Fig. 5e shows the corresponding Tafel plots for Comparative Example 1, Comparative Example 2 and an embodiment of the present invention, and Fig. 5f shows the 10 mA cm⁻¹ for the UOR of an embodiment (WF / NF) of the present invention. -2 This shows the time potential difference analysis at, the figure inserted in Fig. 5f shows the CV curve of UOR over 1000 cycles for an embodiment of the present invention, Fig. 5g shows the LSV curve of the hydrazine oxidation reaction (HzOR) for Comparative Example 1, Comparative Example 2 and an embodiment of the present invention, Fig. 5h shows the corresponding Tafel plots for Comparative Example 1, Comparative Example 2 and an embodiment of the present invention, and Fig. 5i shows 10 mA cm⁻¹ for HzOR of an embodiment (WF / NF) of the present invention -2 This shows the time potential difference analysis in, and the figure inserted in Fig. 5i shows the CV curve over 1,000 cycles for an embodiment of the present invention.

[0113] Referring to Figures 5a, 5b, and 5c, the OER catalytic activity was evaluated by measuring the LSV curves in 1M KOH (basic electrolyte) for samples of NF, Comparative Example 1 (WO / NF), and Example of the present invention (WP / NF).

[0114] Referring to Fig. 5a, 10 mA cm -2 When comparing the required potentials, the embodiment of the present invention (WP / NF) showed the lowest value at 1.535V, whereas Comparative Example 1 (WO / NF) showed a higher potential at 1.634V and NF at 1.628V.

[0115] Referring to FIG. 5b, when comparing Tafel slopes to evaluate the kinetic energy of OER, the embodiment of the present invention (WP / NF) has the lowest Tafel slope (50.7 mV dec -1 ...represented. For Comparative Example 1 (WO / NF) and Comparative Example 2 (NF), the Tafel slope values ​​were 73.1 and 74.1 mV dec, respectively. -1 The EIS Nyquist plot of the embodiment (WP / NF) of the present invention shows a smaller radius than that of Comparative Example 1 (WO / NF) and Comparative Example 2 (NF), indicating that the RCT of WP / WP is lower. The OER stability of the embodiment (WP / NF) of the present invention was tested through cyclic voltammetry (CV) and time potential difference (Vt) analysis. The potential was 10 mA cm⁻¹ for 20 hours during the Vt test. -2 It showed a constant value.

[0116] Referring to FIGS. 5d through 5f, the highest ECSA of the embodiment of the present invention (WP / NF) can be attributed to the large reaction surface area resulting from the large number of active sites exposed to the NW structure. Electrooxidation of the urea was performed in an alkaline electrolyte using a typical human urine concentration (0.33 M urea).

[0117] Referring to FIG. 5d, the UOR catalytic activity of NF, Comparative Example 1 (WO / NF), and the Example of the present invention (WP / NF) was compared. Compared to Comparative Example 2 (Bare NF) and Comparative Example 1 (WO / NF), the Example of the present invention (WP / NF) showed 10 mA cm⁻¹. -2 It showed enhanced activity with a low potential requirement of 1.384V required to generate it. Comparative Example 2 (NF) and Comparative Example 1 (WO / NF) showed higher potentials of 1.404V and 1.486V, respectively.

[0118] Referring to FIG. 5e, the Tafel slope of the embodiment (WP / NF) of the present invention is 15.0 mV dec -1 Represents the lowest value of. For Comparative Example 1 (WO / NF) and Comparative Example 2 (NF), 229.7 and 46.1 mV dec, respectively. -1 I obtained.

[0119] Referring to FIG. 5f, the UOR stability of an embodiment (WP / NF) of the present invention was tested, and after 1000 cycles of CV testing, it showed a very stable 10 mA cm² for more than 20 hours (Vt test) with nearly identical curves. -2 It showed the current density.

[0120] Referring to Figures 5g to 5i, electro-oxidation of hydrazine was performed using 0.1M hydrazine in an alkaline electrolyte.

[0121] Referring to FIG. 5g, the HzOR catalytic activity of Comparative Example 2 (NF), Comparative Example 1 (WO / NF), and the embodiment of the present invention (WP / NF) is shown. 10 mA cm⁻¹ -2 The required potential is 0.024 V in the case of the embodiment of the present invention (WP / NF), which is lower than that of Comparative Example 1 (WO / NF) (0.092 V) and NF (0.183 V). In particular, this required potential is much lower than that of OER and UOR.

[0122] Referring to FIG. 5h, the Tafel slope of the embodiment of the present invention (WP / NF) is compared to Comparative Example 1 (WO / NF) (54.0 mV dec -1 ) and Comparative Example 2 (NF) (97.9mV dec -1 Lower value (35.7mV dec) compared to ) -1 It represents ).

[0123] Referring to FIG. 5i, the HzOR stability of an embodiment (WP / NF) of the present invention was tested through CV testing and Vt analysis, which indicates high durability.

[0124] Test Example 5: Total reaction system NO 3 RR-OER, NO 3 RR-UOR and NO 3 RR-HzOR comparison

[0125] Figure 6a shows schematic diagrams of NO3RR-OER, NO3RR-UOR, and NO3RR-HzOR; Figure 6b shows LSV curves for NO3RR-OER, NO3RR-UOR, and NO3RR-HzOR configured with two electrodes in an embodiment of the present invention; Figure 6c shows potential profiles for the cathodic and anode reactions of NO3RR-HzOR and NO3RR-OER; and Figure 6d compares the Faraday efficiency and energy consumption of various electrochemical ammonia production methods.

[0126] Referring to Fig. 6, the two-electrode total reaction system of the H cell was tested by combining NO3RR with OER, UOR, and HzOR.

[0127] Referring to Fig. 6a, the reaction mechanisms of the three systems NO3RR-OER, NO3RR-UOR, and NO3RR-HzOR are schematically shown. 10 mA cm⁻¹ -2 The cell potential of the embodiment of the present invention (WP / NF) required to generate is lower than that of Comparative Example 1 (WO / NF) and NF of each system.

[0128] Referring to FIG. 6b, the LSV curves for an embodiment of the present invention (WP / NF) with a two-electrode configuration using NO3RR-OER, NO3RR-UOR, and NO3RR-HzOR are directly compared. NO3RR-HzOR requires a much lower operating potential than NO3RR-UOR and NO3RR-OER. 20 mA cm -2 The potential required to generate it is 0.34V for NO3RR-HzOR, which is lower than that of NO3RR-UOR (1.37V) and NO3RR-OER (1.60V). Another advantage of this system is that it decomposes pollutants for water treatment while simultaneously generating ammonia.

[0129] Referring to Fig. 6c, the potential profile for NO3RR-HzOR was monitored to evaluate the power required to operate the entire reaction system. The cathode-anode potential was measured as NO3RR-HzOR 20 mA cm⁻¹. -2 It generates a constant current. The electrodes of the embodiment (WP / NF) of the present invention were applied equally to both the cathodic and anode reactions of the two systems. The cathodic potential of NO3RR was similar for both NO3RR-HzOR and NO3RR-OER. However, regarding the anode potential, a clear difference of ~0.1V (HzOR) and 1.5V (OER) was observed for Ag / AgCl. These results provide a significant difference in cell potential requirements for NO3RR-HzOR (1.1V) and NO3RR-OER (2.4V).

[0130] Referring to Fig. 6d, the energy consumption (kW hr kg) of various electrochemical ammonia production methods -1We compare NH3) and FE (%). Energy consumption is closely related to the cost of ammonia production and is an important factor in evaluating electrochemical ammonia synthesis as an environmentally friendly alternative to the traditional Haber-Bosch process. Compared to nitrogen reduction reactions (NRR) via aqueous or Li-mediated reactions, NO3RR exhibits higher FE and lower energy consumption. This is because nitrates have higher reactivity than nitrogen gas as a N source material. In particular, it was confirmed that the NO3RR-HzOR of the present invention recorded the lowest energy consumption among NO3RR results with a similar FE, although it still showed slight deviation from the commercial Haber-Bosch process.

[0131] Test Example 6: Self-powered ammonia production system: Combined with perovskite solar cells

[0132] Figure 7a shows the IV curve of WP / NF(NO3RR)-WP / NF(HzOR) for a two-electrode configuration and a perovskite solar cell, Figure 7b shows the time potential difference of an unbiased PV-EC system combining WP / NF(NO3RR)-WP / NF(HzOR) and a perovskite solar cell, and Figure 7c shows a schematic diagram of a cyclic electrochemical system equipped with a PV cell for ammonia production based on a NO3RR-HzOR system.

[0133] Referring to Fig. 7, the IV curves of the PSC and WP / NF(NO3RR)-WP / NF(HzOR) systems are shown. The theoretical operating point of the NO3RR-HzOR and PSC combination device is 0.36 V, 23.8 mA cm⁻¹ -2 It was calculated from. The actual operating point of the PV-EC system is 23 mA cm⁻¹. -2 It generates a current density, which indicates that energy loss is minimized when converting electricity into ammonia.

[0134] Referring to Fig. 7c, the electrochemical NO3RR-HzOR system connected to the PV cell can circulate both energy and chemicals. This cycle begins with nitrates and hydrazines discharged as wastewater from factories and farms. These can be supplied as reactants to the electrocatalytic NO3RR-HzOR system. Electrochemical ammonia synthesis is carried out by nitrate reduction along with hydrazine oxidation driven by the PV cell. The ammonia generated by the self-generating system can be supplied as a basic chemical and energy source for industrial applications and can also be used as a raw material for agricultural fertilizers. Groundwater discharged from industries and farms contains nitrates and hydrazines, which can be recovered and used as raw materials.

[0135] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A catalyst comprising a nanowire complex, used for reducing nitrate to produce ammonia and simultaneously oxidizing hydrazine to produce nitrogen, wherein the nanowire complex comprises a plurality of longitudinally aligned tungsten oxide nanowires; and a tungsten phosphide layer formed on part or all of the surface of the tungsten oxide nanowires and comprising tungsten phosphide; wherein the tungsten oxide nanowires comprise WO3. Claim 2 A catalyst according to claim 1, characterized in that the nanowire composite further comprises a substrate, and the plurality of tungsten oxide nanowires are formed vertically on one surface of the substrate. Claim 3 A catalyst according to paragraph 2, characterized in that the substrate comprises nickel foam. Claim 4 A catalyst according to claim 2, characterized in that the tungsten oxide nanowire has one or more shapes selected from the group consisting of nanowires, nanotubes, and nanorods. Claim 5 A catalyst according to claim 4, characterized in that the tungsten oxide nanowire is a tungsten oxide nanowire. Claim 6 delete Claim 7 delete Claim 8 A catalyst according to claim 1, characterized in that the tungsten phosphide layer comprises one or more types selected from the group consisting of W2P, WP, W3P4, W3P5, and WP2. Claim 9 A catalyst according to claim 8, characterized in that the tungsten phosphide layer comprises WP. Claim 10 A catalyst according to claim 1, characterized in that the average length of the tungsten oxide nanowire is 50 to 300 μm. Claim 11 delete Claim 12 delete Claim 13 An ammonia production system comprising: an oxidation electrode comprising a catalyst according to claim 1; a reduction electrode comprising a catalyst according to claim 1; a separator located between the reduction electrode and the oxidation electrode; and an electrolyte. Claim 14 An ammonia production system according to claim 13, wherein the ammonia production system further comprises a battery, and the battery is connected to the reduction electrode and the oxidation electrode, respectively, to supply electrical energy. Claim 15 An ammonia production system according to claim 14, characterized in that the above-mentioned battery includes a solar cell. Claim 16 In paragraph 13, the oxidation electrode receives hydrazine (N2H4) and oxidizes it to produce nitrogen (N2) through a reaction (HzOR), and the reduction electrode performs nitrate (NO3 - ) supplied and reduced to ammonium ions (NH4 + An ammonia production system characterized by performing a reaction (NO3RR) that produces ). Claim 17 In paragraph 13, the current density when the ammonia production system is operated is 20 to 30 mAcm -2 Ammonia production system characterized by the following. Claim 18 An ammonia production system according to claim 17, characterized in that the ammonia production system is driven by a voltage of 0 to 1 V to oxidize hydrazine to produce nitrogen and reduce nitrate to produce ammonium ions. Claim 19 Using an ammonia production system according to paragraph 13, hydrazine (N2H4) is oxidized to produce nitrogen (N2) and nitrate (NO3 - By reducing ) ammonium ions (NH4 + A method for producing ammonia comprising the step of producing ).

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