Patent Application
20220042185
This application claims the priority of Korean Patent Application No. 10-2020-0098505 filed on Aug. 6, 2020, and all the benefits accruing therefrom under 35 U.S.C. § 119, the contents of which in its entirety are herein incorporated by reference.
The present disclosure relates to a catalyst for electrochemical synthesis of ammonia, which includes a metal sulfide, a method for preparing the same and a method for regenerating the same.
Ammonia (NH3) is a very important chemical in various applications, including plastics, textile industry, agriculture and food production. In addition, it draws attentions as a hydrogen carrier that can be transported easily. As of 2017, the total production of NH3 worldwide exceeded 150 million ton, and the demand for NH3 is increasing consistently. At present, most of industrial production of ammonia depends on the traditional Haber-Bosch process whereby ammonia is produced from high-quality nitrogen and hydrogen gases at high temperature (300-500° C.) and pressure (150-300 atm). This process has the problems of a lot of natural gas consumption and severe environmental problems such as a large quantity of CO2 emission. In order to resolve the problems of the Haber-Bosch process, a new ammonia synthesis method which is environment-friendly and consumes less energy is necessary.
Nowadays, electrochemical nitrogen reduction reaction (eNRR) has been proposed as an alternative method for producing NH3 from N2 and H2O under ambient conditions. Although this NH3 production method is environment-friendly and renewable, about 941 kJmol−1 of energy is necessary to break the strong triple bond of the N2 molecule. Therefore, eNRR has the problems of low FE efficiency and ammonia production yield. To solve this disadvantage, an electrocatalyst with high activity is necessary for renewable and environment-friendly conversion from N2 to NH3.
Meanwhile, although various eNRR catalysts have been investigated for improved eNRR performance, including noble metal, transition metal oxide, nitride, carbide, sulfide and metal-free catalysts, researches on the regeneration of catalysts for renewable eNRR with high yield has never been reported.
In an aspect, the present disclosure is directed to providing a metal sulfide-based catalyst which exhibits remarkable NRR activity and overcomes weak durability.
In another aspect, the present disclosure is directed to providing a method for preparing a metal sulfide-based catalyst convenient via a thermal heating process and a solid-state reaction.
In another aspect, the present disclosure is directed to providing a method for achieving remarkable eNRR reaction by using an electrochemical regeneration process between continuous eNRR reactions.
In an aspect, the present disclosure provides a catalyst for electrochemical synthesis of ammonia, which includes a copper-sulfur compound and N-doped carbon.
In another aspect, the present disclosure provides an electrode for ammonia synthesis, which includes the catalyst for ammonia synthesis described above.
In another aspect, the present disclosure provides a method for preparing a catalyst for ammonia synthesis, which includes a step of preparing a mixture of a copper precursor containing N and a sulfur precursor containing C and N; and a step of heat-treating the mixture.
In another aspect, the present disclosure provides a method for regenerating the catalyst for ammonia synthesis described above, which includes a step of synthesizing ammonia by electrochemical nitrogen reduction reaction (eNRR) in the presence of a catalyst for electrochemical synthesis of ammonia; and a step of regenerating the catalyst for electrochemical synthesis of ammonia after the step of synthesizing ammonia using Na2S.
According to an aspect of the present disclosure, there is provided an electrochemical regeneration method providing remarkably superior ammonia synthesis activity as compared to the existing single metal or metal oxide catalyst and being applicable to continuous NRR. The method may be used to improve the production yield and synthesis speed of a catalyst in an environment-friendly way.
Hereinafter, specific exemplary embodiments of the present disclosure are described in detail referring to the attached drawings.
The described exemplary embodiments of the present disclosure are provided for the purpose of illustration only. The exemplary embodiments of the present disclosure may also be embodied into other various forms, without being limited to the described exemplary embodiments.
The present disclosure may be changed variously and may have various exemplary embodiments. The exemplary embodiments are not intended to limit the present disclosure, and should be understood to include all changes, equivalents and substitutes included in the technical idea and scope of the present disclosure.
In the present disclosure, when a portion is described to “include” a certain element, it does not mean that another element is excluded but means that another element can be included unless specially stated otherwise.
Catalyst for Electrochemical Synthesis of Ammonia
In exemplary embodiments of the present disclosure, there is provided a catalyst for electrochemical synthesis of ammonia, which includes a copper-sulfur compound and N-doped carbon.
The present disclosure discloses a copper-sulfur compound/NC (N-doped carbon) composite which exhibits superior NRR activity and is prepared by a thermal heating process and a solid-state reaction under an Ar atmosphere.
In an exemplary embodiment, the copper-sulfur compound may be represented by the chemical formula CuxSy (wherein x is 1.7-1.8 when y is 1).
In an exemplary embodiment, the copper-sulfur compound may be represented by the chemical formula CuxSy (wherein x is 8.5-9 when y is 5).
In an exemplary embodiment, the copper-sulfur compound may be represented by the chemical formula of Cu9S5. The actual structure of the copper-sulfur compound may be the same as (1) in
In an exemplary embodiment, the copper-sulfur compound and the N-doped carbon may be complexed with each other and dispersed throughout the catalyst.
Referring to
In an exemplary embodiment, a mass ratio of the copper-sulfur compound may be 65-85% based on the total mass of the catalyst. If the mass ratio is lower than 65%, the apparent activity of an electrode may be low due to insufficient catalyst loading. And, if it exceeds 85%, the mass activity of the catalyst may decrease due to aggregation of excess catalyst and it may be difficult to achieve an NRR electron transfer effect due to low NC content.
In an exemplary embodiment, the catalyst may have a size of 0.1-10 μm.
In an exemplary embodiment, the catalyst may have a specific surface area (SSA) of 5-20 m2g−1.
In an exemplary embodiment, the catalyst may have a total pore volume of 0.001-0.15 cm3g−1.
In an exemplary embodiment, the catalyst may have an ammonia production yield of 600 nmol/hcm2 or higher at −0.5 VRHE.
In an exemplary embodiment, the catalyst may be regenerated using Na2S.
Another exemplary embodiment of the present disclosure provides an electrode for ammonia synthesis including the catalyst for ammonia synthesis.
Method for Preparing Catalyst for Electrochemical Synthesis of Ammonia
Another exemplary embodiment of the present disclosure provides a method for preparing a catalyst for electrochemical synthesis of ammonia, which includes: a step of preparing a mixture of a copper precursor comprising N and a sulfur precursor comprising C and N; and a step of heat-treating the mixture (see
In an exemplary embodiment, the copper precursor may be Cu(NO3)2.6H2O and the sulfur precursor may be CH4N2S.
The copper precursor is a hydrate Cu(NO3)2.H2O and the sulfur precursor is thiourea (CH4N2S). As Cu9S5 is formed from the S of the sulfur precursor and the Cu of the copper precursor under a high-temperature condition, and N-doped carbon is synthesized from the remaining C and N sources.
In an exemplary embodiment, in the step of preparing the mixture, the copper precursor and the sulfur precursor may be pulverized and mixed.
In an exemplary embodiment, the step of heat-treating the mixture may be performed by a solid-state reaction.
In an exemplary embodiment, the step of heat-treating the mixture may be performed at 400-600° C. for 1-5 hours.
In an exemplary embodiment, the step of heat-treating the mixture may be performed under Ar atmosphere.
Method for Regenerating Catalyst for Electrochemical Synthesis of Ammonia
Another exemplary embodiment of the present disclosure provides a method for regenerating a catalyst for ammonia synthesis, which includes: a step of synthesizing ammonia by electrochemical nitrogen reduction reaction (eNRR) in the presence of a catalyst for electrochemical synthesis of ammonia; and a step of regenerating the catalyst for electrochemical synthesis of ammonia after the step of synthesizing ammonia using Na2S.
Despite the simple synthesis process and remarkable NRR activity of the catalyst for ammonia synthesis described above, the catalyst experiences composition change to Cu2O during NRR due to the weak durability of the metal sulfide/NC (N-doped carbon). In order to overcome the disadvantage of the metal sulfide-based catalyst, the deteriorated of the catalyst such as Cu9S5/NC, i.e., Cu2O, may be regenerated by an electrochemical regeneration process in between the continuous eNRR reaction. During the electrochemical metal oxide/sulfide redox regeneration cycle, NH3 and H2 are produced from dissolved N2 and H2O through repeated N2 fixation reactions.
Until now, electrochemical NH3 production using a catalyst regenerated by oxide/sulfide redox cycles mimicking the natural regeneration of a N2 fixation catalyst has not been reported yet. This unprecedented method for achieving remarkable eNRR reaction provides an insight for an electrochemical N2 reduction mechanism on the metal sulfide surface. Accordingly, it is expected that regeneration redox cycle of the eNRR catalyst provided in the present disclosure will provide a new method for preparing a material for an effective eNRR catalyst.
In an exemplary embodiment, the step of regenerating the catalyst for electrochemical synthesis of ammonia may be performed by immersing the catalyst for electrochemical synthesis of ammonia in an aqueous solution containing Na2S and an electrolyte.
In an exemplary embodiment, the step of regenerating the catalyst for electrochemical synthesis of ammonia may be performed at a potential of 0.05-1 VRHE for 30 minutes to 5 hours.
In an exemplary embodiment, after the step of regenerating the catalyst for electrochemical synthesis of ammonia, the step of synthesizing ammonia may be repeated using the regenerated catalyst.
Hereinafter, the present disclosure will be described in more detail through examples.
However, the following examples are for illustrating the present disclosure in more detail, and it will be obvious to those having ordinary skill in the art that the scope and contents of the present disclosure are not reduced or limited by the examples. In addition, it is also obvious that those having ordinary skill in the art that can easily carry out the present disclosure based on the disclosure of the present disclosure even for the matters experimental data of which are not presented and such changes and modifications belong to the scope of the appended claims.
Experimental Methods
Reagents and Chemicals
CuCl2.2H2O (Sigma-Aldrich), Cu(NO3)2.2.5H2O (Sigma-Aldrich), ethylene glycol (99.8%, Sigma-Aldrich), Na2S (99%, Sigma-Aldrich), p-dimethylaminobenzaldehyde (99%, Sigma-Aldrich), thiourea (99%, Junsei), ethanol (95%, Daejung), Nafion resin solution (5 wt %, Sigma-Aldrich) and isopropyl alcohol (99.5%, Duksan) were used. All chemicals were of analytical grade and used without further purification.
Synthesis of Cu9S5/NC (Catalyst for Electrochemical Synthesis of Ammonia)
A Cu9S5/NC catalyst was prepared by pulverizing Cu(NO3)2.2.5H2O and CH4N2S powders and then heat-treating the same in a crucible (
Specifically, Cu(NO3)2.2.5H2O (0.8 g) and thiourea (1.2 g) were mixed as follows. The precursors were mixed well physically in an agate mortar by agitating for about 5 minutes.
After transferring to a ceramic crucible, the mixture was heated in a tube furnace at 773 K (500° C.) for 1 hour with a heating rate of 8.3 K/min under Ar gas atmosphere. The prepared catalyst was washed 4 times with deionized water.
Synthesis of Cu9S5
CuCl2.2H2O (1 g) and thiourea (1 g) were added to ethylene glycol (40 mL). After stirring for 30 minutes, the precursors were heated in an oven controlled to 150° C. (423 K) for 4 hours under an autoclave condition. Then, the prepared catalyst was washed several times with deionized water and ethanol.
NRR Measurement
For preparation of a working electrode, the wet-dispersed Cu9S5/NC or Cu9S5 catalyst was sprayed manually onto carbon paper (2.5 cm×2.5 cm, Toray T-120) and then dried in a desiccator at ambient temperature. The loading amount of the catalyst coated on the electrode was set to 1 mg/cm2. A catalyst ink was prepared by mixing 10 mg of the catalyst powder with 1 mL of an IPA solution. Prior to starting experiment, the working electrode was rinsed with 0.5 M Na2SO4 (pH 7) to remove water-soluble pollutants attached to the surface. As an electrolyte for eNRR, 0.5 M Na2SO4 (99%, aqueous solution) was used. 10 mM H2SO4 was used to trap NH3 in the electrolysis chamber. The cathode and anode chambers of H-cell were separated using an anion exchange membrane (FAA-3, Fumatech), which were pretreated with 1 M KOH for 24 hours prior to the test, and then further pretreated with DI water for 1 hour. The Bio-Logic SP-300 potentiostat was used for all electrochemical experiments. Electrochemical experiments were conducted at room temperature under atmospheric pressure. For a 3-electrode system, a standard calomel electrode (SCE) and a graphite rod were used as a reference electrode and a counter electrode, respectively, and carbon paper covered with the catalyst powder was used as a working electrode. All potentials were referenced to the reversible hydrogen electrode scale. The activity of electrochemical ammonia synthesis was measured by chronoamperometry (CA) for different potentials from −0.4 to −0.8 VRHE for an hour. For NRR, 14N2 (99.999%, Sinyang) and 15N2 (98 atom %, Sigma) were bubbled for about 20 minutes prior to measurement and then purged into the cathode compartment at a flow rate of 250 ccm and 5 ccm, respectively, during the experiment. The redox characteristics of the catalyst loaded onto a glossy carbon (GC) electrode were investigated in different electrolytes by cyclic voltammetry (CV) at a scan rate of 50 mV/s.
Regeneration of Metal Chalcogenide Electrode
During the NRR measurement, the Cu9S5/NC electrode was decomposed in an aqueous solution (0.5 M Na2SO4) to Cu20/NC at −0.5 VRHE. The electrode was regenerated by oxidizing and restoring to Cu9S5 via an electrochemical regeneration process. For regeneration, the used electrode was treated for 1 hour at a constant potential of 0.1 VRHE in an aqueous solution containing 5 mM Na2S and 0.5 M Na2SO4. After completely washing the regenerated electrode with deionized (DI) water, NRR was measured at −0.5 to −0.7 VRHE as described above. After repeating N2 reduction and electrochemical sulfurization processes several times, the produced NH3 was quantified by the indophenol method.
Physical Properties
X-ray diffraction (XRD) patterns were obtained on MiniFlex-2 (Rigaku) equipped with Cu Kα radiation (λ=1.5406 Å). Scanning electron microscopy (SEM) images were obtained using the Inspect F50 microscope with an acceleration voltage of 10 kV. TEM images were recorded using a transmission electron microscope (Talos F200X), and X-ray photoelectron spectroscopy (XPS) spectra were measured using the PHI VersaProbe system with a 100-W ALK α X-ray source.
Low-temperature nitrogen adsorption-desorption isotherms were measured at 77 K (−196° C.) using the volumetric adsorption analyzer BEL (BEL, Inc., Japan). Prior to the measurement, all the samples were deaerated at 173 K (100° C.) for 12 hours under a constant-volume condition in vacuo. Specific surface area was measured from the nitrogen adsorption isotherms by the Brunnauer-Emmet-Teller (BET) method in the relative pressure (P/P0) range of 0.05-0.20. Pore size distribution (PSD) was measured by the Barrett-Joyner-Halenda (BJH) method. Total pore volume was determined at P/P0 of 0.99. Temperature-programmed desorption (TPD) was performed on Micromeritics AutoChem II 2920 TPR/TPD.
Thermogravimetric analysis (TGA) was conducted on SDT Q600 (TA Instruments Inc., New Castle, De, USA).
NH3 Detection
The concentration of the produced ammonia was measured by the indophenol blue method. First, 1 mL of a sample solution was added to an electrochemical cathode reactor. Then, 1 mL of a phenol solution (0.64 M C6H5OH, 0.38 M NaOH and 1.3 mM C5FEN6Na2O) and 1 mL of a hypochlorite solution (55 mM NaOCl and 0.75 M NaOH) were added. After reaction at room temperature for 2 hours, the absorbance of the sample was analyzed at 900-350 nm by UV-vis spectroscopy. UV-Vis spectra were obtained using the Cary UV-vis 100 spectrophotometer (Agilent). Absorbance peaks at 633 nm were calibrated by subtracting the background absorbance measured at 875 nm. In the UV-Vis spectra, the background absorbance means the absorbance of the bulk electrolyte solution at 0 ppm (NH3). In addition, the production of NH3 was confirmed from the 14N and 15N spectra acquired by 1H NMR (nuclear magnetic resonance) using Bruker Avance III HD 400 MHz.
N2H4 Detection
The quantity of the byproduct, N2H4, produced during the electrochemical NH3 production was measured by the Watt and Chrisp method. A mixture of p-dimethylaminobenzaldehyde) (6 g), HCl (37%, 30 mL) and ethanol (300 mL) was used as an indicator. Measurement was performed after mixing 2 mL of an electrolyte and 2 mL of the indicator solution for 5 minutes. For measurement of the hydrazine, a standard curve was plotted from a series of N2H4.H2O solutions of different concentrations, diluted with 0.5 M Na2SO4. The absorbance of N2H4 was measured at 455 nm.
Calculation of Faradaic Efficiency (FE) and NH3 Yield
Assuming that three electrons are required to produce one NH3, FE is calculated as follows.
FE=(3F×V×CNH3)/(mNH3×Q)
In the above equation, F is the Faraday constant (96485 C mol−1), V is the volume (mL) of an electrolyte, CNH3 is the concentration (g/mL) of NH3 determined 1 hour after CA for UV-Vis measurement, mNH3 is the molar mass of NH3 (17 g/mol), and Q is the total charge (C) accumulated for 1 hour during CA.
The NH3 yield is calculated as follows.
(1) Production speed of NH3 normalized to the mass of catalyst, rmass=(CNH3×V)/(mNH3×mCat)
(2) Production speed of NH3 per time, normalized to geometrical area, rarea=(CNH3×V)/(mNH3×A)
In the above equations, CNH3 is the concentration (g/mL) of determined 1 hour after CA for UV-Vis measurement, V is the volume (mL) of an electrolyte in the cathode chamber, mNH3 is the molar mass of NH3 (17 g/mol), mCat is the mass (mg) of the cathode catalyst, and A is the geometrical area of the electrode (6.25 cm2).
Observation of Synthesized Catalyst
The XRD pattern of the prepared catalyst is shown in
As a result of energy-dispersive X-ray spectroscopy (EDX) mapping, it was confirmed that Cu, S, C and N were distribute uniformly throughout the entire structure of the Cu9S5/NC catalyst (
The conductive support, i.e., NC, was used in Cu9S5/NC to improve the active surface area of the catalyst. For characterization of the catalyst, the textural property of Cu9S5/NC and Cu9S5 was investigated by N2 adsorption analysis. From the N2 adsorption-desorption isotherms, the specific surface area (SSA) and total pore volume of Cu9S5/NC and Cu9S5 were determined to be 12 m2g−1 and 0.084 cm3g−1, and 8 m2g−1 and 0.051 cm3g−1, respectively (
As expected, the BJH plots revealed that Cu9S5/NC had mesoporosity with a size 2-8 nm larger than Cu9S5 (
Electrochemical NRR Activity
The NRR performance of Cu9S5/NC was investigated in a N2-saturated 0.5 M Na2SO4 electrolyte using a H-cell under an ambient condition (
In order to measure the NRR activity of the Cu9S5/NC and Cu9S5 catalysts, chronoamperometry (CA) was conducted in a N2-saturated 0.5 M Na2SO4 electrolyte at different potentials in the range from −0.4 to −0.8 VRHE (
Additional controlled CA experiment was conducted to confirm the electrochemical NRR result obtained with the Cu9S5/NC catalyst. The conditions of the controlled experiment are as follows: (1) Cu9S5/NC-free carbon paper under N2 atmosphere, (2) Cu9S5/NC electrode under N2 atmosphere, open-circuit potential with no voltage applied, and (3) Cu9S5/NC, −0.5 VRHE in an Ar-saturated 0.5 M Na2SO4 electrolyte solution (
Degradation and Regeneration of Catalyst
In general, the electrochemical reaction rate (i.e., current) is improved with increased overpotential. The exponential increase of current at applied overpotential is explained by the Butler-Volmer equation using two simple variables of transfer coefficient and overpotential. The NRR and FE of Cu9S5/NC decreased greatly at higher negative potentials (see Table 2,
The NH3 production rate was decreased from 645 to 22 nmol/hcm2 as the applied potential was increased from −0.5 to −0.7 VRHE, and then to 0.37 μg/hcm2 at a potential of 11 VRHE. The inverse relationship between the NRR activity and the overpotential may be derived from two possible effects: (i) N2 adsorption may be interrupted on more negative surface, and proton adsorption and reduction may dominate the reduction reaction, or (ii) the catalyst activity may be lost as the surface is actually changed or electrochemically degraded at potential. Although the decrease in reaction rate with increased overpotential was proposed in the inverted Marcus region for electrochemical reactions, it was not considered in the present disclosure. The decrease in NRR activity at higher overpotential for Cu9S5/NC was observed as decreased current density, which is commensurate with both HER and NRR in extended CA experiments under N2 atmosphere (
Referring to
10Cu1.8S+10H2O+2e−→9Cu2O+10H2S+O2−
Although the faradaic peak current associated with the reductive degradation of Cu9S5 was not clearly observed in CV, the structural change and activity loss at more negative potentials than −0.5 VRHE strongly suggests the electrochemical degradation of the catalyst.
The inventors of the present disclosure hypothesized that the Cu—S bond is cleaved during NRR and the restoration of the Cu—S bond will recover NRR activity. Therefore, in order to mimic the unstable chemistry of the sulfhydryl group of the FeMo cofactor and restore NRR activity, ex-situ electrochemical sulfurization reaction was used to restore the Cu—S bond on the Cu9S5/NC surface. Specifically, a degraded Cu9S5/NC electrode was re-oxidized by CA in 5 mM Na2S and 0.5 M Na2SO4 aqueous solutions for 1 hour at a potential in the range from −0.9 to 0.1 VRHE (
However, the Cu9S5/NC composite structure shown in
9Cu2O+10Na2S+11H2O→10Cu1.8S+20NaOH+2H++2e−
It is reported that a Cu substrate is oxidized in an electrolyte solution in the presence of a sulfide at more positive potentials than approximately −0.8 VRHE to form CuxS (Cu2S and Cu9S5). In a previous study, a small bumpy current was recorded at about −0.8 VRHE in CV for forming CuxS from a Cu substrate. In addition, a large oxidation current was not detected at a potential around −0.8 VRHE from CV in 5 mM Na2S using a degraded Cu9S5 electrode (
The increased NRR activity of the regenerated Cu9S5/NC electrode and its crystal structure strongly suggest that the Cu—S bond is regenerated by the electrochemical treatment. The result also suggests that the metal-sulfur bond is very important in the electrochemical NRR process. The Cu—S bond was broken in the NRR process only and was not affected in an aqueous solution in the absence of N2. In the FeMo cofactor of nitrogenase, the Fe center provides an adsorption site for N2 adsorption. The Fe—S bond is broken during the N2 adsorption process, and the atomic hydrogen transferred to the cofactor approaches Fe—N2 and forms a sulfhydryl group. Then, the sulfhydryl group is involved in hydrogenation processes including reductive removal of H2 molecules. A similar adsorption mechanism was proposed in the electrochemical N2 reduction reaction. The N2Hx intermediate on the electrocatalyst surface was observed through in-situ IR measurement, which supports the related adsorption mechanism under ambient condition. The NRR activity of the metal sulfide catalyst was also reported. However, the role of sulfur in the electrochemical NRR process has not been elucidated yet. The NRR activity observed on the Cu9S5/NC surface disappears when the metal-sulfur bond is broken. Importantly, the catalyst activity is recovered through sequential NH3 production and catalyst regeneration cycles. These results mean that the metal-sulfur bond is important in the electrochemical production of NH3 and is actively involved in the electrochemical N2 reduction process.
In summary, the use of the Cu9S5/NC catalyst as a NRR catalyst resulted in significant NH3 production, activity and selectivity (11.0 μg/h cm2, 645 nmol/h cm2 and 35%, respectively). Importantly, the Cu9S5 catalyst was degraded to Cu2O during the NRR process and the catalyst activity was decreased. Subsequently, the Cu9S5 surface was reconstructed from the degraded electrode through an electrochemical sulfurization process. The importance of the metal-sulfur bond in NRR was demonstrated by the recovered NH3 production yield of the recovered Cu9S5/NC surface. The degradation and regeneration processes of the metal chalcogenide catalyst for electrochemical NH3 production are similar to the enzymatic N2 fixation process discovered in the FeMo cofactor of nitrogenase. In addition, this result strongly suggests that, in order to achieve effective electrochemical NH3 production under ambient condition, a powerful catalyst that provides an unstable sulfhydryl functional group favored by the metal center for N2 adsorption is necessary.
To conclude, in the present disclosure, Cu9S5/NC was prepared by a thermal heating reaction using the solid-state method, and an FE of 35% and a yield of 11.0 μg/hcm2 (or 645 nmol/hcm2) was achieved in a 0.5 M Na2SO4 electrolyte at −0.5 VRHE for electrochemical NH3 production. However, the crystal structure of Cu9S5/NC was degraded to Cu2O during the NRR reaction. The regeneration redox cycle of metal sulfide was first demonstrated in the present disclosure. The Cu9S5 surface was reconstructed in a 5 mM Na2S electrolyte via an electrochemical sulfurization process.
The NRR activity of Cu9S5/NC was recovered in the reconstructed electrode, and NH3 production was activated through repeated NRR and regeneration processes. The important of the metal-sulfur bond in NRR can be explained with the NH3 yield on the recovered Cu9S5/NC surface. The degradation and regeneration processes of the metal chalcogenide catalyst for electrochemical NH3 production show a mechanism similar to the enzymatic N2 fixation process discovered for the FeMo cofactor of nitrogenase. The result suggests that, in order to achieve effective electrochemical NH3 production under ambient condition, a powerful catalyst that provides an unstable sulfhydryl functional group favored by the metal center for N2 adsorption is necessary. Accordingly, the present disclosure provides a new electrochemical regeneration method for a low-durability catalyst used in continuous NRR.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2020-0098505 | Aug 2020 | KR | national |
This research was supervised by the Korea Institute of Science and Technology and supported by the Ministry of Science and ICT. Research project is Future materials discovery (R&D) and Research title is Development of structural alchemy technology for preparation of fractal catalyst (project ID: 1711105282).
