WO2020169848A1 - Electrocatalytic reduction of nitrogen to ammonia - Google Patents

Electrocatalytic reduction of nitrogen to ammonia Download PDF

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Publication number
WO2020169848A1
WO2020169848A1 PCT/EP2020/054788 EP2020054788W WO2020169848A1 WO 2020169848 A1 WO2020169848 A1 WO 2020169848A1 EP 2020054788 W EP2020054788 W EP 2020054788W WO 2020169848 A1 WO2020169848 A1 WO 2020169848A1
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Prior art keywords
iron
electrocatalyst
boron
oxygen
previous
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PCT/EP2020/054788
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French (fr)
Inventor
Johan Hofkens
Maarten Roeffaers
Yansong ZHOU
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Katholieke Universiteit Leuven
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Priority claimed from GBGB1902456.1A external-priority patent/GB201902456D0/en
Application filed by Katholieke Universiteit Leuven filed Critical Katholieke Universiteit Leuven
Publication of WO2020169848A1 publication Critical patent/WO2020169848A1/en

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material

Definitions

  • This invention relates generally to novel noble-metal-free materials for highly efficient NtE electrosynthesis from nitrogen, such as dinitrogen (N 2 ) and water (H 2 O).
  • the invention further relates to iron-boron-oxygen catalyst for the conversion of N 2 into ammonia (Nt3 ⁇ 4) under ambient conditions.
  • This iron-boron-oxygen material drives electrocatalytic reduction of nitrogen, such as N 2 to NtE, preferably at ambient conditions.
  • the invention further relates to an electrochemical apparatus and method for the conversion of N 2 into NFE by use of such iron-boron-oxygen electrocatalysts comprised in or on an electrode, for instance such electrode comprising iron-boron-oxygen in a composite with a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, for instance Naflion ( C 7 HF 13 O 5 S . C 2 F 4 ) on the cathode of a N 2 reduction reactor for electrocatalytic reduction of N 2 to NtE .
  • an electrode for instance such electrode comprising iron-boron-oxygen in a composite with a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, for instance Naflion ( C 7 HF 13 O 5 S . C 2 F 4 ) on the cathode of a N 2 reduction reactor for electrocatalytic reduction of N 2 to NtE .
  • Ammonia as one of the most important chemicals of industrial production, is generally used for pharmaceutical, synthetic fiber, and fertilizer production, as well as for energy conversion.
  • conventional ammonia synthesis mainly relies on the high-cost Haber-Bosch process, which converts N 2 and 3 ⁇ 4 to N3 ⁇ 4 at high operating pressures (150-250 bar) and temperatures (350-550 °C).
  • electrochemical ammonia synthesis can provide an alternative pathway to the Haber-Bosch process at mild conditions, because the electrochemical nitrogen reduction reaction (NRR) enables the decentralized production of NH 3 at ambient conditions from N 2 , H 2 O, and electricity.
  • NRR electrochemical nitrogen reduction reaction
  • the present invention solves the problems of the related art by providing a novel noble-metal- free iron-boron-oxygen (Fe-B-O) material as a highly efficient electrocatalyst to drive NH 3 electrosynthesis from N 2 and H 2 O at ambient conditions.
  • Fe-B-O noble-metal- free iron-boron-oxygen
  • the Fe-B-0 samples are synthesized through facile wet-chemical method at ambient conditions using only the low- cost iron salts and metal borate as precursors, suggesting the fast and low-cost massive production of the material. Therefore, the noble-metal-free Fe-B-0 material can be achieved in a very cost-effective way. Further application of this Fe-B-0 demonstrates its great advantages when used as an electrocatalyst for NH 3 electrosynthesis from N 2 and H 2 O at ambient conditions.
  • the Fe-B-0 sample showed superior high selectivity for N3 ⁇ 4 at a low overpotential, resulting in the promising energy conversion efficiency. All these indicate the great potential of the Fe-B-0 as an efficient electrocatalyst for NH 3 synthesis for piratical applications.
  • a material synthesized according to the first particular embodiment, whereby the material comprises Fe, B, O, and Na.
  • concentrations of the iron(III) salt precursor solution in the range from 15 to 30 mM.
  • a material synthesized according to the first particular embodiment can be used as an electrocatalyst for NRR application.
  • a material synthesized according to the first particular embodiment for NRR application whereby the applied potentials range from -0.4 to 0.2 V vs RHE.
  • the current collector is glassy carbon, carbon paper or carbon cloth.
  • material that is synthesized using borates and iron(III) salts as precursors, 'cc whereby borates are NaiE ⁇ Cb or K2B4O7, iron(III) salts are FeCh, Fe2(SC>4)3 or Fe(N03)3.
  • a material synthesized according to the second particular embodiments can be used as an electrocatalyst for NRR application.
  • the current collector is glassy carbon, carbon paper or carbon cloth.
  • a N2 reduction electrocatalyst comprising iron-boron-oxygen (Fe-B-O) or a N2 reduction electrocatalyst essentially consisting of iron-boron-oxygen (Fe-B-O).
  • the electrocatalyst can be any of the following an iron-boron-oxygen (Fe-B-O) is amorphous, an iron-boron-oxygen (Fe-B-O) is doped with an alkali metal, an iron-boron-oxygen (Fe-B-O) is doped with an alkali metal of the group consisting of lithium (Li), sodium (Na) and potassium (K), an iron-boron-oxygen (Fe-B-O) is amorphous and the amorphous iron-boron-oxygen (Fe-B-O) comprising crystallites, an iron-boron-oxygen (Fe-B-O) is amorphous and the amorphous iron-boron- oxygen (Fe-B-O) comprising crystallites at an amount less than 1 % of the iron-boron-oxygen (Fe-B-O) material, that iron-boron-oxygen (Fe-B-O) is comprised in a composite material,
  • This embodiment of the invention advantageously comprises that the electrocatalyst is a selective N2 reduction electrocatalyst.
  • a further disadvantageous aspect is also that the electrocatalyst is a selective N2 reduction into N3 ⁇ 4 electrocatalyst at a low overpotential.
  • the iron-boron-oxygen (Fe-B-O) is produced from an iron(III) salt precursor solution in the range from 15 to 30 mM.
  • the iron- boron-oxygen (Fe-B-O) can be produced from a precursor whereby the Fe/B ratios in precursors range from 0.04 to 0.07, for instance the iron-boron-oxygen (Fe-B-O) is formed directly by adding iron(III) salts solution into the borates solution with stirring, the iron- boron-oxygen (Fe-B-O) can be synthesized using borates and iron(III) salts as precursors, whereby borates are the group consisting of Na 2 B 4 0 7 and K2B4O7 and whereby the iron(III) salts are FeCh, Fe2(S04)3 or Fe(N03)3, the iron-boron-oxygen (Fe-B-O) can be synthesized or formed according to the claims 20 - 23 and whereby the stirring
  • a method for the electrochemical reduction of dinitrogen to ammonia comprising the steps of: (1) contacting a cathodic working electrode comprising an electrocatalyst of present with an electrolyte and (2) introducing dinitrogen to the electrolyte, wherein the dinitrogen is reduced to ammonia at the cathodic working electrode and for instance whereby the electrolyte further comprises comprising (a) one or more liquid salts optionally in combination and supporting high ionic conductivity, whereby the electrolyte comprises a product of the group consisting of alkali (NaOH or KOH) and lithum salts (L12SO4, LiOH and LiCICri) a combination thereof or whereby the electrolyte is a product of the group consisting of alkali (NaOH or KOH) and lithum salts (LESCE, LiOH and LiClCE) a combination thereof.
  • Preferred embodiments of said method for the electrochemical reduction of dinitrogen to ammonia concerns the use of the electrolyte concentrations range from 0.05 to 0.5 M.
  • Preferred embodiments of said method for the electrochemical reduction of dinitrogen to ammonia concerns applying potentials range from -0.1 to 0.4 V vs RHE.
  • the current collector is glassy carbon, carbon paper or carbon cloth.
  • Yet another aspect of present invention is a cell for electrochemical reduction of dinitrogen to ammonia, the cell comprising: a cathodic working electrode comprising a the electrocatalyst of present invention here above described in detail and an electrolyte according of present invention here above described in detail for reduction of dinitrogen and a counter electrode, wherein dinitrogen introduced to the cell is reduced to ammonia at the cathodic working electrode in the presence of a source of hydrogen, for instance H2O.
  • a source of hydrogen for instance H2O.
  • Naflion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, in particular CVHFI 05S . C2F4
  • the Fe-B-0 sample is synthesized via a wet-chemical method at ambient conditions. 2.0 g sodium borate is dispersed into 50 mL water with the assistance of a sonic bath for 5 min. Subsequently, 50 mL water with 1 mmol FeCF is poured into the sodium borate solution under stirring (1000 rpm). After 2 minutes, the big particles are removed by centrifugation (8000 rpm, 1 min). Then, equal volume of acetone is added into the supernatant to form the precipitation. Subsequently, the precipitation is repeatedly washed with 500 mL the mixture of water and acetone for 5 times. Then the solid obtained is sonically dispersed into 1 mL water or ethanol (10 mg/mL).
  • the catalyst ink To prepare the catalyst ink, 0.5 mL ethanol and 10 pL Nafion solution (5%) were added into 0.5 ml of the sample dispersion. After that, the mixture was ultrasonically treated for 30 min. Subsequently, 5 pL of the as-prepared ink was drop coated on the glassy carbon electrode with a surface area of 0.079 cm 2 . The electrode was then dried slowly for the subsequent electrochemical testing experiments.
  • the sample synthesized from the previous procedure is in the amorphous phase, which is demonstrated by the X-ray powder diffraction results ( Figure 1). Taking the XRD spectrum of Fe 2 0 3 as a reference, it’s found that the as-synthesized sample is not in the Fe oxide phase. To further confirm the phase information, the Raman spectrum was collected ( Figure 2). The peak attributed to OH group around 3000 cm 1 is not shown, suggesting the sample is not Fe hydroxide. To check the composition information, EDX was carried out ( Figure 3). The sample is composed of Fe, O, B and a little amount of Na. The TG-DSC analysis further reveal the glass-like properties of the as-synthesized Fe-B-0 sample ( Figure 4). Therefore, the sample is an amorphous Fe-B-0 compound.
  • the sample has a dendritic morphology, possible due to the aggregation of the nanoparticles during the sample washing process. No obvious lattice was observed in the HRTEM image, in accordance with the XRD results. Further analyses the particle size of the individual particles shows the diameters range from 2 to 5 nm. It can be concluded that the as- synthesized sample shows a dendritic morphology with nanostructured features on the scale of 2-5 nm.
  • the magnetic properties of the as-synthesized sample were studied using EPR.
  • There is only a single broad resonance line centered at about g 2.0 is found in the spectrum of Fe-B-0 sample.
  • the EPR spectra of Fe-B-0 sample at different temperatures ranging from 142 to 363 K were collected. An increase in its linewidth (DH RR ) with a decrease in temperature is shown.
  • the shifting and broadening observed for the two main features can be correlated to the superparamagnetic behavior of the sample, which is possible due to its nanostructured nature.
  • the NRR performance of the Fe-B-0 sample was investigated.
  • the Fe-B-0 sample showed a superior high Faradaic efficiency in the range of 61-65% at 0.2 V vs RHE (Figure 7 shows an example of 63%), which is even much higher than the highest value over the noble metal- based NRR electrocatalyst (35.9% over Au).
  • High Faradaic efficiency of 53% can also be achieved after six cycles, suggesting the great advantages as NRR catalyst of these noble- metal free Fe-B-0 material.
  • FIG. 1 XRD patterns of the as-synthesized Fe-B-0 and FeiCb.
  • FIG. 2 Raman spectrum of the as-synthesized Fe-B-O.
  • FIG. 3 EDS spectrum of the as-synthesized Fe-B-0
  • FIG. 4 TG-DSC curves of the as-synthesized Fe-B-0
  • FIG. 5 TEM images of the as-synthesized Fe-B-0
  • FIG. 6 EPR spectra of (a) Fe 2 0 3 and Fe-B-0 sample, and (b) Fe-B-0 sample at different temperatures.
  • FIG. 7 NRR performance of Fe-B-0 sample (a) Faradaic efficiency at different applied potentials (b) Cycle performance at 0.2 V vs RHE.

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  • Chemical Kinetics & Catalysis (AREA)
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Abstract

Present invention concerns the development of noble-metal-free Fe-B-O materials for highly efficient NH3 electrosynthesis from N2 and H2O at ambient conditions.

Description

ELECTROCATALYTIC REDUCTION OF NITROGEN TO AMMONIA
Background and Summary
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates generally to novel noble-metal-free materials for highly efficient NtE electrosynthesis from nitrogen, such as dinitrogen (N2) and water (H2O). The invention further relates to iron-boron-oxygen catalyst for the conversion of N2 into ammonia (Nt¾) under ambient conditions. This iron-boron-oxygen material drives electrocatalytic reduction of nitrogen, such as N2 to NtE, preferably at ambient conditions. The invention further relates to an electrochemical apparatus and method for the conversion of N2 into NFE by use of such iron-boron-oxygen electrocatalysts comprised in or on an electrode, for instance such electrode comprising iron-boron-oxygen in a composite with a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, for instance Naflion ( C7HF13O5S . C2F4) on the cathode of a N2 reduction reactor for electrocatalytic reduction of N2 to NtE.
B. Description of the Related Art
Ammonia, as one of the most important chemicals of industrial production, is generally used for pharmaceutical, synthetic fiber, and fertilizer production, as well as for energy conversion. However, conventional ammonia synthesis mainly relies on the high-cost Haber-Bosch process, which converts N2 and ¾ to N¾ at high operating pressures (150-250 bar) and temperatures (350-550 °C). It has been demonstrated that electrochemical ammonia synthesis can provide an alternative pathway to the Haber-Bosch process at mild conditions, because the electrochemical nitrogen reduction reaction (NRR) enables the decentralized production of NH3 at ambient conditions from N2, H2O, and electricity.
Nonetheless, most of the current materials have shown low electrocatalytic activity and selectivity for N¾ production mainly due to the high energy required for N ºN cleavage and due to the competition with the hydrogen evolution reaction (HER). Noble metals including Au and Ru show high selectivity for NH3 electrosynthesis, but their scarce availability and high cost seriously restrict their widespread applications. In addition, the low NH3 yield rate over noble metals is also a major problem for further practical applications. Recently, compared to noble metals catalyst, noble-metal-free materials such as M02N, N-doped carbon have shown much higher NH3 yield. However, higher overpotentials are required to drive the formation of NH3. Furthermore, the selectivity (Faradaic efficiency) of NH3 is usually very low over the noble-metal-free materials due to the dramatically HER side reaction at the high negative applied potentials. As a result, the energy conversion efficiency values reported are lower than 15%.
There is a need in the art to develop a novel noble-metal free catalyst to drive NH3 electrosynthesis from N2 and H2O with low overpotential and high selectivity at ambient conditions.
SUMMARY OF THE INVENTION
The present invention solves the problems of the related art by providing a novel noble-metal- free iron-boron-oxygen (Fe-B-O) material as a highly efficient electrocatalyst to drive NH3 electrosynthesis from N2 and H2O at ambient conditions. In this example, the Fe-B-0 samples are synthesized through facile wet-chemical method at ambient conditions using only the low- cost iron salts and metal borate as precursors, suggesting the fast and low-cost massive production of the material. Therefore, the noble-metal-free Fe-B-0 material can be achieved in a very cost-effective way. Further application of this Fe-B-0 demonstrates its great advantages when used as an electrocatalyst for NH3 electrosynthesis from N2 and H2O at ambient conditions. The Fe-B-0 sample showed superior high selectivity for N¾ at a low overpotential, resulting in the promising energy conversion efficiency. All these indicate the great potential of the Fe-B-0 as an efficient electrocatalyst for NH3 synthesis for piratical applications.
According to an particular first embodiment of the present invention there is provided a material that is formed directly adding iron(III) salts solution into the borates solution with stirring.
A material synthesized according to the first particular embodiment, whereby the stirrig rates range from 800-12000 rpm.
A material synthesized according to the first particular embodiment, whereby the material comprises Fe, B, O, and Na. A material synthesized according to the first particular embodiment, whereby the Fe/B ratios in precursors range from 0.04 to 0.07.
A material synthesized according to the first particular embodiment, whereby the
concentrations of the iron(III) salt precursor solution in the range from 15 to 30 mM.
A material synthesized according to the first particular embodiment, whereby the materials formed at temperatures ranging from 293 to 323 K.
A material synthesized according to the first particular embodiment, whereby the volume ratios of the precursor solution is: Viron(iii) saits/Vborate = 0.8 ~ 1 .2.
A material synthesized according to the first particular embodiment, whereby the material is an amorphous phase.
A material synthesized according to the first particular embodiment, whereby the size of the material ranges from 2~5 nm.
A material synthesized according to the first particular embodiment, whereby the material shows superparamagnetic properties.
A material synthesized according to the first particular embodiment can be used as an electrocatalyst for NRR application.
A material synthesized according to the first particular embodiment for NRR application, whereby the electrolyte is the mixture of alkali (NaOH or KOH) and lithum salt (LhSCri,
Li OH or LiC104).
A material synthesized according to the first particular embodiment for NRR application, whereby the concentration ratios of alkli and lithum salt in electrolyte ranges from 0.5 to 2.
A material synthesized according to the first particular embodiment for NRR application, whereby the electrolyte concentrations range from 0.05 to 0.5 M for the both alkali and lithum salts each.
A material synthesized according to the first particular embodiment for NRR application, whereby the applied potentials range from -0.4 to 0.2 V vs RHE. A material synthesized according to the first particular embodiment for NRR application, the current collector is glassy carbon, carbon paper or carbon cloth.
According to an particular second embodiment of the present invention there is provided material that is synthesized using borates and iron(III) salts as precursors, 'cc whereby borates are NaiE^Cb or K2B4O7, iron(III) salts are FeCh, Fe2(SC>4)3 or Fe(N03)3.
A material synthesized according to the second particular embodiment, whereby the stirring rates range from 800-12000 rpm.
A material synthesized according to the second particular embodiment, whereby the material comprises Fe, B, O, and Na.
A material synthesized according to the second particular embodiment, whereby the Fe/B ratios in precursors range from 0.04 to 0.07.
A material synthesized according to the second particular embodiment, whereby the concentrations of the iron(III) salt precursor solution in the range from 15 to 30 mM.
A material synthesized according to the second particular embodiment, whereby the materials formed at temperatures ranging from 293 to 323 K.
A material synthesized according to the second particular embodiment, whereby the volume ratios of the precursor solution is: Viron(iii) saits/Vborate = 0.8 - 1 .2.
A material synthesized according to the second particular embodiment, whereby the material is an amorphous phase.
A material synthesized according to the second particular embodiments, whereby the size of the material ranges from 2-5 nm.
A material synthesized according to the second particular embodiments, whereby the material shows superparamagnetic properties.
A material synthesized according to the second particular embodiments can be used as an electrocatalyst for NRR application. A material synthesized according to the second particular embodiments for NRR application, whereby the electrolyte is the mixture of alkali (NaOH or KOH) and lithum salt (L12SO4,
Li OH or L1CIO4).
A material synthesized to the second particular embodiments for NRR application, whereby the concentration ratios of alkli and lithum salt in electrolyte ranges from 0.5 to 2.
A material synthesized according to the second particular embodiments for NRR application, whereby the electrolyte concentrations range from 0.05 to 0.5 M for the both alkali and lithum salts each.
A material synthesized to the second particular embodiments for NRR application, whereby the applied potentials range from -0.4 to 0.2 V vs RHE.
A material synthesized to the second particular embodiments for NRR application, the current collector is glassy carbon, carbon paper or carbon cloth.
According to the present invention there is provided a N2 reduction electrocatalyst comprising iron-boron-oxygen (Fe-B-O) or a N2 reduction electrocatalyst essentially consisting of iron-boron-oxygen (Fe-B-O). Hereby the electrocatalyst can be any of the following an iron-boron-oxygen (Fe-B-O) is amorphous, an iron-boron-oxygen (Fe-B-O) is doped with an alkali metal, an iron-boron-oxygen (Fe-B-O) is doped with an alkali metal of the group consisting of lithium (Li), sodium (Na) and potassium (K), an iron-boron-oxygen (Fe-B-O) is amorphous and the amorphous iron-boron-oxygen (Fe-B-O) comprising crystallites, an iron-boron-oxygen (Fe-B-O) is amorphous and the amorphous iron-boron- oxygen (Fe-B-O) comprising crystallites at an amount less than 1 % of the iron-boron-oxygen (Fe-B-O) material, that iron-boron-oxygen (Fe-B-O) is comprised in a composite material, an iron-boron-oxygen (Fe-B-O) is comprised in a matrix material, an iron-boron-oxygen (Fe-B- O) is comprised in a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, an iron- boron-oxygen (Fe-B-O) is comprised in an electrode, an iron-boron-oxygen (Fe-B-O) is coated on an electrode, an iron-boron-oxygen (Fe-B-O) is in the form of particles, an iron- boron-oxygen (Fe-B-O) is in the form of particles and the size of the material ranges from 2~5 nm, an iron-boron-oxygen (Fe-B-O) is comprised in aggregations of particles, an iron- boron-oxygen (Fe-B-O) is nanostructured, an iron-boron-oxygen (Fe-B-O) is essentially free of noble metal, for instance such noble metal contamination being less than 0,001% of the iron-boron-oxygen (Fe-B-O).
This embodiment of the invention advantageously comprises that the electrocatalyst is a selective N2 reduction electrocatalyst. A further disadvantageous aspect is also that the electrocatalyst is a selective N2 reduction into N¾ electrocatalyst at a low overpotential.
According to one embodiment of the invention the iron-boron-oxygen (Fe-B-O) is produced from an iron(III) salt precursor solution in the range from 15 to 30 mM. For instance the iron- boron-oxygen (Fe-B-O) can be produced from a precursor whereby the Fe/B ratios in precursors range from 0.04 to 0.07, for instance the iron-boron-oxygen (Fe-B-O) is formed directly by adding iron(III) salts solution into the borates solution with stirring, the iron- boron-oxygen (Fe-B-O) can be synthesized using borates and iron(III) salts as precursors, whereby borates are the group consisting of Na2B407 and K2B4O7 and whereby the iron(III) salts are FeCh, Fe2(S04)3 or Fe(N03)3, the iron-boron-oxygen (Fe-B-O) can be synthesized or formed according to the claims 20 - 23 and whereby the stirring rates range from 800-12000 rpm, the iron-boron-oxygen (Fe-B-O) is synthesized or formed according to the claims 20 - 23 and at temperatures ranging from 293 to 323 K or the iron-boron-oxygen (Fe- B-O) is synthesized or formed according to the claims 20 - 23 and whereby the volume ratios of the precursor solution is: Viron(III) salts/Vborate = 0.8 - 1.2.
In a particular embodiment of present invention the use of the electrocatalyst described in greater detail above for the conversion of N2 into ammonia (NFF) under ambient conditions, for NH3 electrosynthesis from N2 and H2O at ambient conditions.
According to the present invention there is provided a method for the electrochemical reduction of dinitrogen to ammonia, the method comprising the steps of: (1) contacting a cathodic working electrode comprising an electrocatalyst of present with an electrolyte and (2) introducing dinitrogen to the electrolyte, wherein the dinitrogen is reduced to ammonia at the cathodic working electrode and for instance whereby the electrolyte further comprises comprising (a) one or more liquid salts optionally in combination and supporting high ionic conductivity, whereby the electrolyte comprises a product of the group consisting of alkali (NaOH or KOH) and lithum salts (L12SO4, LiOH and LiCICri) a combination thereof or whereby the electrolyte is a product of the group consisting of alkali (NaOH or KOH) and lithum salts (LESCE, LiOH and LiClCE) a combination thereof.
Preferred embodiments of said method for the electrochemical reduction of dinitrogen to ammonia concerns the use of the electrolyte concentrations range from 0.05 to 0.5 M.
Preferred embodiments of said method for the electrochemical reduction of dinitrogen to ammonia concerns applying potentials range from -0.1 to 0.4 V vs RHE.
In another aspect of the electrochemical reduction of dinitrogen to ammonia method of present invention is provided that the current collector is glassy carbon, carbon paper or carbon cloth.
Yet another aspect of present invention is a cell for electrochemical reduction of dinitrogen to ammonia, the cell comprising: a cathodic working electrode comprising a the electrocatalyst of present invention here above described in detail and an electrolyte according of present invention here above described in detail for reduction of dinitrogen and a counter electrode, wherein dinitrogen introduced to the cell is reduced to ammonia at the cathodic working electrode in the presence of a source of hydrogen, for instance H2O.
Detailed Description
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents thereof.
Several documents are cited throughout the text of this specification. Each of the documents herein (including any manufacturer’s specifications, instructions etc.) are hereby incorporated by reference; however, there is no admission that any document cited is indeed prior art of the present invention. The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term“comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to the devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Reference throughout this specification to“one embodiment” or“an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.
It is intended that the specification and examples be considered as exemplary only.
Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are part of the description and are a further description and are in addition to the preferred embodiments of the present invention.
Each of the claims set out a particular embodiment of the invention. The following terms are provided solely to aid in the understanding of the invention.
Definitions
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
Naflion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, in particular CVHFI 05S . C2F4
EXAMPLE
The Fe-B-0 sample is synthesized via a wet-chemical method at ambient conditions. 2.0 g sodium borate is dispersed into 50 mL water with the assistance of a sonic bath for 5 min. Subsequently, 50 mL water with 1 mmol FeCF is poured into the sodium borate solution under stirring (1000 rpm). After 2 minutes, the big particles are removed by centrifugation (8000 rpm, 1 min). Then, equal volume of acetone is added into the supernatant to form the precipitation. Subsequently, the precipitation is repeatedly washed with 500 mL the mixture of water and acetone for 5 times. Then the solid obtained is sonically dispersed into 1 mL water or ethanol (10 mg/mL).
To prepare the catalyst ink, 0.5 mL ethanol and 10 pL Nafion solution (5%) were added into 0.5 ml of the sample dispersion. After that, the mixture was ultrasonically treated for 30 min. Subsequently, 5 pL of the as-prepared ink was drop coated on the glassy carbon electrode with a surface area of 0.079 cm2. The electrode was then dried slowly for the subsequent electrochemical testing experiments.
The sample synthesized from the previous procedure is in the amorphous phase, which is demonstrated by the X-ray powder diffraction results (Figure 1). Taking the XRD spectrum of Fe203 as a reference, it’s found that the as-synthesized sample is not in the Fe oxide phase. To further confirm the phase information, the Raman spectrum was collected (Figure 2). The peak attributed to OH group around 3000 cm 1 is not shown, suggesting the sample is not Fe hydroxide. To check the composition information, EDX was carried out (Figure 3). The sample is composed of Fe, O, B and a little amount of Na. The TG-DSC analysis further reveal the glass-like properties of the as-synthesized Fe-B-0 sample (Figure 4). Therefore, the sample is an amorphous Fe-B-0 compound.
TEM was conducted to investigate the morphology of the as-synthesized sample. As shown in Figure 5, the sample has a dendritic morphology, possible due to the aggregation of the nanoparticles during the sample washing process. No obvious lattice was observed in the HRTEM image, in accordance with the XRD results. Further analyses the particle size of the individual particles shows the diameters range from 2 to 5 nm. It can be concluded that the as- synthesized sample shows a dendritic morphology with nanostructured features on the scale of 2-5 nm.
The magnetic properties of the as-synthesized sample were studied using EPR. The commercial FeiCb shows EPR signals at g = 2.0 and g = 4.3, which could be attributed to Fe3+ ions coupled by exchange interactions and Fe3+ ions in rhombic and axial symmetry sites, respectively (Figure 6). There is only a single broad resonance line centered at about g = 2.0 is found in the spectrum of Fe-B-0 sample. The EPR spectra of Fe-B-0 sample at different temperatures ranging from 142 to 363 K were collected. An increase in its linewidth (DHRR) with a decrease in temperature is shown. The shifting and broadening observed for the two main features can be correlated to the superparamagnetic behavior of the sample, which is possible due to its nanostructured nature.
The NRR performance of the Fe-B-0 sample was investigated. The Fe-B-0 sample showed a superior high Faradaic efficiency in the range of 61-65% at 0.2 V vs RHE (Figure 7 shows an example of 63%), which is even much higher than the highest value over the noble metal- based NRR electrocatalyst (35.9% over Au). High Faradaic efficiency of 53% can also be achieved after six cycles, suggesting the great advantages as NRR catalyst of these noble- metal free Fe-B-0 material.
Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Drawing Description
BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
FIG. 1 XRD patterns of the as-synthesized Fe-B-0 and FeiCb. FIG. 2 Raman spectrum of the as-synthesized Fe-B-O.
FIG. 3 EDS spectrum of the as-synthesized Fe-B-0
FIG. 4 TG-DSC curves of the as-synthesized Fe-B-0
FIG. 5 TEM images of the as-synthesized Fe-B-0
FIG. 6 EPR spectra of (a) Fe203 and Fe-B-0 sample, and (b) Fe-B-0 sample at different temperatures.
FIG. 7 NRR performance of Fe-B-0 sample (a) Faradaic efficiency at different applied potentials (b) Cycle performance at 0.2 V vs RHE.

Claims

ELECTROCATALYTIC REDUCTION OF NITROGEN TO AMMONIA Claims What is claimed is:
1. A N2 reduction electrocatalyst comprising iron-boron-oxygen (Fe-B-O).
2. A N2 reduction electrocatalyst essentially consisting of iron-boron-oxygen (Fe-B-O).
3. The electrocatalyst of any of the previous claims 1 to 2, characterised in that iron- boron-oxygen (Fe-B-O) is amorphous.
4. The electrocatalyst of any of the previous claims 1 to 2, characterised in that the iron- boron-oxygen (Fe-B-O) is doped with an alkali metal.
5. The electrocatalyst of any of the previous claims 1 to 2, characterised in that the iron- boron-oxygen (Fe-B-O) is doped with an alkali metal of the group consisting of lithium (Li), sodium (Na) and potassium (K).
6. The electrocatalyst of any of the previous claims 1 to 5, characterised in that iron- boron-oxygen (Fe-B-O) is amorphous and the amorphous iron-boron-oxygen (Fe-B- O) comprising crystallites.
7. The electrocatalyst of any of the previous claims 1 to 5, characterised in that iron- boron-oxygen (Fe-B-O) is amorphous and the amorphous iron-boron-oxygen (Fe-B- O) comprising crystallites at an amount less than 1 % of the iron-boron-oxygen (Fe-B- O) material.
8. The electrocatalyst of any of the previous claims 1 to 7, characterised in that iron- boron-oxygen (Fe-B-O) is comprised in a composite material.
9. The electrocatalyst of any of the previous claims 1 to 7, characterised in that iron- boron-oxygen (Fe-B-O) is comprised in a matrix material.
10. The electrocatalyst of any of the previous claims 1 to 7, characterised in that iron- boron-oxygen (Fe-B-O) is comprised in a sulfonated tetrafluoroethylene based fluoropolymer-copolymer.
11. The electrocatalyst of any of the previous claims 1 to 10, characterised in that iron- boron-oxygen (Fe-B-O) is comprised in an electrode.
12. The electrocatalyst of any of the previous claims 1 to 10, characterised in that iron- boron-oxygen (Fe-B-O) is coated on an electrode.
13. The electrocatalyst of any of the previous claims 1 to 12, characterised in that iron- boron-oxygen (Fe-B-O) is in the form of particles.
14. The electrocatalyst of any of the previous claims 1 to 12, characterised in that iron- boron-oxygen (Fe-B-O) is in the form of particles and the size of the material ranges from 2~5 nm.
15. The electrocatalyst of any of the previous claims 1 to 12, characterised in that iron- boron-oxygen (Fe-B-O) is comprised in aggregations of particles.
16. The electrocatalyst of any of the previous claims 1 to 12, characterised in that iron- boron-oxygen (Fe-B-O) is nanostructured.
17. The electrocatalyst of any of the previous claims 1 to 16, characterised in that iron- boron-oxygen (Fe-B-O) is essentially free of noble metal, for instance such noble metal contamination being less than 0,001% of the iron-boron-oxygen (Fe-B-O).
18. The electrocatalyst of any of the previous claims 1 - 17, characterised in that it is a selective N2 reduction electrocatalyst.
19. The electrocatalyst of any of the previous claims 1 - 17, characterised in that it is a selective N2 reduction into NFF electrocatalyst at a low overpotential.
20. The electrocatalyst of any of the previous claims 1 - 19, characterised in that the iron- boron-oxygen (Fe-B-O) is produced from an iron(III) salt precursor solution in the range from 15 to 30 mM.
21. The electrocatalyst of any of the previous claims 1 - 20, characterised in that the iron- boron-oxygen (Fe-B-O) is produced from a precursor whereby the Fe/B ratios in precursors range from 0.04 to 0.07.
22. The electrocatalyst of any of the previous claims 1 - 20, characterised in that the iron- boron-oxygen (Fe-B-O) is formed directly by adding iron(III) salts solution into the borates solution with stirring.
23. The electrocatalyst of any of the previous claims 1 - 21, characterised in that the iron- boron-oxygen (Fe-B-O) is synthesized using borates and iron(III) salts as precursors, whereby borates are the group consisting of Na2B407 and K2B4O7 and whereby the iron(III) salts are FeCh, Fe2(S04)3 or Fe(N03)3.
24. The electrocatalyst of any of the previous claims, characterised in that the iron-boron- oxygen (Fe-B-O) is synthesized or formed according to the claims 20 - 23 and whereby the stirring rates range from 800-12000 rpm.
25. The electrocatalyst of any of the previous claims, characterised in that the iron-boron- oxygen (Fe-B-O) is synthesized or formed according to the claims 20 - 23 and at temperatures ranging from 293 to 323 K.
26. The electrocatalyst of any of the previous claims, characterised in that the iron-boron- oxygen (Fe-B-O) is synthesized or formed according to the claims 20 - 23 and whereby the volume ratios of the precursor solution is: Viron(III) salts/Vborate = 0.8 ~ 1 2
27. The use of the electrocatalyst of any of the previous claims 1 to 26, for the conversion of N2 into ammonia (ML) under ambient conditions.
28. The use of the electrocatalyst of any of the previous claims 1 to 26, for ML
electrosynthesis from N2 and H2O at ambient conditions.
29. A method for the electrochemical reduction of dinitrogen to ammonia, the method comprising the steps of: (1) contacting a cathodic working electrode comprising he electrocatalyst of any of the previous claims 1 to 28 with an electrolyte and (2) introducing dinitrogen to the electrolyte, wherein the dinitrogen is reduced to ammonia at the cathodic working electrode.
30. The method according to claim 29, whereby the electrolyte further comprises
comprising (a) one or more liquid salts optionally in combination and supporting high ionic conductivity.
31. The method according to claim 29, whereby the electrolyte comprises a product of the group consisting of alkali (NaOH or KOH) and lithum salts (L12SO4, LiOH and L1CIO4) a combination thereof.
32. The method according to claim 29, whereby the electrolyte is a product of the group consisting of alkali (NaOH or KOH) and lithum salts (L12SO4, LiOH and LiClCL) a combination thereof.
33. The method according to any one of the claims 29 to 32, whereby the electrolyte
concentrations range from 0.05 to 0.5 M.
34. The method according to any one of the claims 29 to 33, whereby the applied
potentials range from -0.1 to 0.4 V vs RHE.
35. The method according to any one of the claims 29 to 34, whereby the current collector is glassy carbon, carbon paper or carbon cloth.
36. A cell for electrochemical reduction of dinitrogen to ammonia, the cell comprising: a cathodic working electrode comprising a the electrocatalyst of any of the previous claims 30 to 34 and an electrolyte according to one any of the claims 29 to 33 for reduction of dinitrogen and a counter electrode, wherein dinitrogen introduced to the cell is reduced to ammonia at the cathodic working electrode in the presence of a source of hydrogen, for instance H2O.
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