RUTHENIUM-MOLYBDENUM ALLOY NANOFLOWER PARTICLE FOR AMMONIA ELECTROSYNTHESIS
20250345848 ยท 2025-11-13
Inventors
Cpc classification
B22F9/24
PERFORMING OPERATIONS; TRANSPORTING
B82Y30/00
PERFORMING OPERATIONS; TRANSPORTING
B22F2304/054
PERFORMING OPERATIONS; TRANSPORTING
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
B22F2301/25
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
Ruthenium-molybdenum alloy nanoflower particles having a plurality of ruthenium-molybdenum nanosheets, wherein the plurality of ruthenium-molybdenum nanosheets are in a form of a nanoflower useful for the electrochemical synthesis of ammonia; an electrode including the ruthenium-molybdenum alloy nanoflower particles; and methods of preparation and use thereof.
Claims
1. A ruthenium-molybdenum (RuMo) alloy nanoflower particle comprising: a plurality of RuMo nanosheets, wherein the plurality of RuMo nanosheets are in a form of a nanoflower.
2. The RuMo alloy nanoflower particle of claim 1, wherein the plurality of RuMo nanosheets comprise RuMo in a face-centered cubic (fcc) phase or a heterophase comprising a hexagonal close-packed (hcp) phase and a face-centered cubic (fcc) phase.
3. The RuMo alloy nanoflower particle of claim 1, wherein the RuMo alloy nanoflower particle has a diameter of 20-100 nm.
4. The RuMo alloy nanoflower particle of claim 1, wherein the plurality of RuMo nanosheets have an average thickness of 2.3-3.3 nm or 2.6-3.6 nm.
5. The RuMo alloy nanoflower particle of claim 1, wherein the plurality of RuMo nanosheets have an average thickness of 2.6-3.0 nm or 2.9-3.3 nm.
6. The RuMo alloy nanoflower particle of claim 1, wherein the RuMo alloy nanoflower particle comprises Ru and Mo in an atomic ratio of 85:15 to 95:5, respectively.
7. The RuMo alloy nanoflower particle of claim 1, wherein the RuMo alloy nanoflower particle comprises Ru and Mo in an atomic ratio of 89.9:10.1 to 91.4:9.6, respectively.
8. The RuMo alloy nanoflower particle of claim 1, wherein the plurality of RuMo nanosheets comprise RuMo in a face-centered cubic (fcc) phase; the plurality of RuMo nanosheets have an average thickness of 2.6-3.0 nm; and the RuMo alloy nanoflower particle comprises Ru and Mo in an atomic ratio of 89.9:10.1 to 91.4:9, respectively; or the plurality of RuMo nanosheets comprise RuMo in a heterophase comprising a hexagonal close-packed (hcp) phase and a face-centered cubic (fcc) phase; the plurality of RuMo nanosheets have an average thickness of 2.9-3.3 nm; and the RuMo alloy nanoflower particle comprises Ru and Mo in an atomic ratio of 89.9:10.1 to 91.4:9, respectively.
9. The RuMo alloy nanoflower particle of claim 1, wherein the plurality of RuMo nanosheets comprise RuMo in a face-centered cubic (fcc) phase; the plurality of RuMo nanosheets have an average thickness of 2.6-3.0 nm; and the RuMo alloy nanoflower particle comprises Ru and Mo in an atomic ratio of 89.9:10.1 to 91.4:9, respectively.
10. The RuMo alloy nanoflower particle of claim 1, wherein the RuMo alloy nanoflower particle is prepared by a method comprising: combining Ru.sub.3(CO).sub.12, Mo(CO).sub.6, glucose, and citric acid or salicylic acid in a solvent comprising oleylamine thereby forming a reaction solution and heating the reaction solution thereby forming the RuMo alloy nanoflower particle.
11. An electrode comprising the RuMo alloy nanoflower particle of claim 1 and a base electrode.
12. An electrochemical cell comprising: the electrode of claim 11; a counter electrode; optionally a reference electrode; and an electrolyte solution between and in contact with the electrode, the counter electrode, and optionally the reference electrode.
13. A method of producing ammonia, the method comprising: providing the electrochemical cell of claim 12, wherein the electrolyte solution comprises a substrate selected from the group consisting of a nitrate salt, a nitrite salt, nitric oxide, nitrogen (N.sub.2), and a mixture thereof; and applying a potential between the electrode and the counter electrode resulting in the electrolytic reduction of the substrate thereby forming ammonia.
14. The method of claim 13, wherein the potential is-0.1 to 0.05 volts vs reversible hydrogen electrode.
15. The method of claim 13, wherein the nitrate salt is present in the electrolyte solution at a concentration of 0.01 to 0.1 M.
16. The method of claim 13, wherein the method has a NH.sub.3 Faradaic efficiency (FE) of 91.7%-95.2% at 0.1 to 0 V vs reversible hydrogen evolution.
17. A method of preparing the RuMo alloy nanoflower particle of claim 1, the method comprising: combining Ru.sub.3(CO).sub.12, Mo(CO).sub.6, glucose, and citric acid or salicylic acid in a solvent comprising oleylamine thereby forming a reaction solution and heating the reaction solution thereby forming the RuMo alloy nanoflower particle.
18. The RuMo alloy nanoflower particle of claim 16, wherein the reaction solution is heated at a temperature of 150-250 C.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated and understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings.
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DETAILED DESCRIPTION
Definitions
[0071] Throughout the present disclosure, unless the context requires otherwise, the word comprise or variations such as comprises or comprising, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as comprises, comprised, comprising and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean includes, included, including, and the like; and that terms such as consisting essentially of and consists essentially of have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the present invention.
[0072] Furthermore, throughout the present disclosure and claims, unless the context requires otherwise, the word include or variations such as includes or including, will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.
[0073] The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise. In addition, where the use of the term about is before a quantitative value, the present teachings also include the specific quantitative value itself, unless specifically stated otherwise. As used herein, the term about refers to a +10%, +7%, +5%, +3%, +1%, or +0% variation from the nominal value unless otherwise indicated or inferred.
[0074] The term substantially crystalline refers to compositions or compounds with at least 70% by weight, at least 75% by weight, at least 80% by weight, at least 85% by weight, at least 90 by weight, at least 95% by weight, at least 96% by weight, at least 97% by weight, at least 98% by weight, at least 99% by weight, at least 99.5% by weight, or more of the composition or compound is present in crystalline form. The compositions or compounds can exist in a single crystalline form or more than one crystalline form. In certain embodiments, the composition or compound has at least 70% by weight, at least 75% by weight, at least 80% by weight, at least 85% by weight, at least 90 by weight, at least 95% by weight, at least 96% by weight, at least 97% by weight, at least 98% by weight, at least 99% by weight, at least 99.5% by weight, or more of the composition or compound present in a single crystalline form. The degree (%) of crystallinity may be determined by the skilled person using X-ray powder diffraction (XRPD). Other techniques, such as solid-state NMR, FT-IR, Raman spectroscopy, differential scanning calorimetry (DSC) and microcalorimetry, may also be used.
[0075] As used herein, the tern nanoflowers refers to particles exhibiting a characteristic three-dimensional flowerlike morphology.
[0076] Provided herein is a RuMo alloy nanoflower particle comprising a plurality of RuMo nanosheets, wherein the plurality of RuMo nanosheets are in a form of a nanoflower. In certain embodiments, each of the plurality of RuMo nanosheets are substantially crystalline.
[0077] In certain embodiments, the plurality of RuMo nanosheets comprise RuMo in a face-centered cubic (fcc) phase or a heterophase comprising a hexagonal close-packed (hcp) phase and a face-centered cubic (fcc) phase.
[0078] The RuMo alloy nanoflower particle can range in size between 20-100 nm, 20-90 nm, 20-80 nm, 20-70 nm, 20-60 nm, 20-40 nm, 20-30 nm, 30-100 nm, 40-100 nm, 50-100 nm, 60-100 nm, 70-100 nm, 80-100 nm, 90-100 nm, 30-90 nm, 40-80 nm, 50-70 nm, 60-70 nm, 50-60 nm, 30-70 nm, or 40-60 nm. A plurality of the RuMo alloy nanoflower particles can have an average size between 20-100 nm, 20-90 nm, 20-80 nm, 20-70 nm, 20-60 nm, 20-40 nm, 20-30 nm, 30-100 nm, 40-100 nm, 50-100 nm, 60-100 nm, 70-100 nm, 80-100 nm, 90-100 nm, 30-90 nm, 40-80 nm, 50-70 nm, 60-70 nm, 50-60 nm, 30-70 nm, or 40-60 nm.
[0079] Each of the plurality of RuMo nanosheets can have an average thickness of 2.3-3.3 nm, 2.4-3.2 nm, 2.5-3.1 nm, 2.6-3.0 nm, 2.7-2.9 nm, 2.6-3.6 nm, 2.7-3.5 nm, 2.8-3.4 nm, 2.9-3.3 nm, or 3.0-3.2 nm. In instances in which the plurality of RuMo nanosheets comprise RuMo in a face-centered cubic (fcc) phase, each of the plurality of RuMo nanosheets can have an average thickness of 2.3-3.3 nm, 2.4-3.2 nm, 2.5-3.1 nm, 2.6-3.0 nm, 2.7-2.9 nm. In instances in which the plurality of RuMo nanosheets comprise RuMo in a heterophase comprising a hexagonal close-packed (hcp) phase and a face-centered cubic (fcc) phase, each of the plurality of RuMo nanosheets can have an average thickness of 2.6-3.6 nm, 2.7-3.5 nm, 2.8-3.4 nm, 2.9-3.3 nm, or 3.0-3.2 nm.
[0080] The atomic ratio of ruthenium to molybdenum in the RuMo alloy nanoflower particle can range from 85:15 to 95:5, 86:14 to 95:5, 87:13 to 95:5, 88:12 to 95:5, 89:11 to 95:5, 90:10 to 95:5, 90:10 to 94:6, 90:10 to 93:7, or 90:10 to 92:8, respectively. In certain embodiments, the atomic ratio of ruthenium to molybdenum in the RuMo alloy nanoflower particle is about 90.9:9.1, respectively. A plurality of the RuMo alloy nanoflower particles can have an average atomic ratio of ruthenium to molybdenum in the plurality of RuMo alloy nanoflower particles from 85:15 to 95:5, 86:14 to 95:5, 87:13 to 95:5, 88:12 to 95:5, 89:11 to 95:5, 90:10 to 95:5, 90:10 to 94:6, 90:10 to 93:7, or 90:10 to 92:8, respectively. In certain embodiments, a plurality of the RuMo alloy nanoflower particles can have an average atomic ratio of ruthenium to molybdenum in the plurality of RuMo alloy nanoflower particles about 90.9:9.1, respectively.
[0081] The present disclosure also provides an electrode comprising a base electrode and the RuFe nanoflower particle or a plurality of the RuFe nanoflower particles described herein. In certain embodiments, the RuMo alloy nanoflower particle or the plurality of RuMo alloy nanoflower particles are coated on a surface of the base electrode. The base electrode can be an inert electrode such as a GCE, a graphite electrode, an indium tin oxide (ITO) electrode, a fluorine doped tin oxide (FTO) electrode, carbon paper electrode, carbon fiber electrode, polycarbonate track etch (PCTE)-based electrode, or a titanium-based electrode. In certain embodiments, the electrode is a cathode.
[0082] The electrode can optionally comprise a binder. The binder may optionally be cured to further bind the RuFe nanoflower particle or a plurality of the RuFe nanoflower particles with the base electrode and can increase the conductivity of electrode. Typical binders include, for example polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), starch, sodium alginate, hydroxypropyl cellulose, carboxymethyl cellulose (CMC), regenerated cellulose, polyvinylpyrrolidone, polyimide, polyamideimide, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber, polytetrafluoroethylene (PTFE), a polyacrylic polymer, and combinations thereof. In certain embodiments, the binder is PVA.
[0083] The present disclosure also provides an electrochemical cell comprising: the electrode described herein; a counter electrode (or counter/reference electrode); optionally a reference electrode (e.g., in a three-electrode system); and an electrolyte solution between and in contact with the electrode, the counter electrode, and optionally the reference electrode. In certain embodiments, the electrolyte solution comprises an aqueous solution.
[0084] A counter electrode refers to an electrode paired with the working electrode, through which passes a current equal in magnitude and opposite in sign to the current passing through the working electrode. The counter electrode can include counter electrodes which also function as reference electrodes (i.e., a counter/reference electrode). Any suitable counter electrode known in the art can be used in connection with the methods described herein. For example, the counter electrode can comprise carbon (e.g., highly oriented pyrolytic graphite), a metal (e.g., platinum), an alloy (e.g., stainless steel), glassy carbon, a conductive polymer, or the like.
[0085] The reference electrode can be selected from a standard hydrogen electrode, calomel electrode, copper-copper (II) sulfate electrode, silver chloride electrode, palladium-hydrogen electrode, mercury-mercurous sulfate electrode, and the like.
[0086] In certain embodiments, the electrolyte comprises a nitrate salt. The type of nitrate salt is not particularly limited and can be any nitrate salt that is at least partially soluble in the electrolyte solution. The nitrate salt can include one or more cations selected from alkali metals, such as lithium, sodium, potassium, rubidium, and cesium; alkaline earth metals, such as beryllium, magnesium, calcium, strontium, and barium; Group 3-12 transition metals; and NR.sub.4.sup.+, wherein R is independently for each instance selected from hydrogen and C.sub.1-C.sub.6 alkyl. In certain embodiments, the nitrate salt is selected from the group consisting of LiNO.sub.3, NaNO.sub.3, KNO.sub.3, Ca(NO.sub.3).sub.2, Mg(NO.sub.3).sub.2, NH.sub.4NO.sub.3, CsNO.sub.3, and mixtures thereof.
[0087] The concentration of the nitrate salt in the electrolyte solution can range from 0.01 to 1 M, 0.01 to 0.9 M, 0.01 to 0.8 M, 0.01 to 0.7 M, 0.01 to 0.6 M, 0.01 to 0.5 M, 0.01 to 0.4 M, 0.01 to 0.3 M, 0.01 to 0.2 M, 0.01 to 0.1 M, 0.04 to 0.1 M, 0.07 to 0.1 M, 0.01 to 0.07 M, 0.01 to 0.04 M, 0.05 to 0.1 M, 0.075 to 0.1 M, 0.01 to 0.075 M, 0.01 to 0.05 M, or 0.05 to 0.75 M.
[0088] In certain embodiments, the electrolyte solution further comprises one or more supporting electrolytes. In certain embodiments, the supporting electrolyte is an alkali metal (e.g., lithium, sodium, potassium, rubidium, and cesium), alkaline earth metal (e.g., beryllium, magnesium, calcium, strontium, and barium), or ammonium salt of a halide, acetate, carbonate, perchlorate, phosphate, monohydrogen phosphate, dihydrogen phosphate, or sulfate. Exemplary supporting electrolytes include, but are not limited to, LiClO.sub.4, NaClO.sub.4, KClO.sub.4, Na.sub.2SO.sub.4, K.sub.2SO.sub.4, NaCl, KCl, MgCl.sub.2, NH.sub.4Cl, (NH.sub.4).sub.2SO.sub.4, Na.sub.3PO.sub.4, K.sub.3PO.sub.4, MgSO.sub.4, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, MgCO.sub.3, NaOH, and KOH.
[0089] Also provided herein is a method of producing ammonia gas, the method comprising providing the electrochemical cell described herein, wherein the electrolyte solution comprises a substrate selected from the group consisting of a nitrate salt, a nitrite salt, nitric oxide, nitrogen (N.sub.2), and mixtures thereof; and applying a potential between the electrode and the counter electrode resulting in the electrolytic reduction of the substrate thereby forming ammonia.
[0090] The potential applied to the electrode and the counter electrode can range from-0.2 to 1 volts. In certain embodiments, the potential applied to the electrode and the counter electrode can range from 0.2 to 0.9 volts, 0.2 to 0.8 volts, 0.2 to 0.7 volts, 0.2 to 0.6 volts, 0.2 to 0.5 volts, 0.2 to 0.4 volts, 0.2 to 0.3 volts, 0.2 to 0.2 volts, 0.2 to 0.15 volts, 0.2 to 0.1 volts, 0.2 to 0.05 volts, 0.2 to 0.0 volts, 0.2 to 0.05 volts, 0.2 to 0.1 volts, 0.2 to 0.15 volts, 0.2 to 0.2 volts, 0.15 to 0.2 volts, 0.1 to 0.2 volts, 0.05 to 0.2 volts, 0 to 0.2 volts, 0.05 to 0.2 volts, 0.1 to 0.2 volts, 0.15 to 0.2 volts, 0.5 to 0.2 volts, 0.15 to 0.0 volts, 0.1 to 0.0 volts, or 0.05 to 0.0 volts.
[0091] The method can have a NH.sub.3 Faradaic efficiency (FE) of 91.7% and 95.2% at 0.1 to 0.0 volts vs reversible hydrogen evolution, respectively.
[0092] The RuMo alloy nanoflower particle described herein can be prepared by a solvothermal method comprising: combining Ru.sub.3(CO).sub.12, Mo(CO).sub.6, glucose, and citric acid or salicylic acid in a solvent comprising oleylamine thereby forming a reaction solution and heating the reaction solution thereby forming the RuMo alloy nanoflower particle.
[0093] In certain embodiments, the solvent further comprises a C.sub.6-C.sub.12 alkyl alcohol. Exemplary alcohols include n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-dodecanol, or the like.
[0094] The reaction solution can be heated at a temperature of 150-400 C., 150-350 C., 150-300 C., 150-250 C., or 175-225 C. In certain embodiments, the reaction solution is heated at about 200 C. The reaction solution can be heated for a period of 2 hours to 144 hours, 12 hours to 144 hours, 12 hours to 120 hours, 12 hours to 96 hours, 12 hours to 72 hours, 24 hours to 72 hours, or 30 hours to 54 hours. In certain embodiments, the reaction solution is heated for a period of about 48 hours.
[0095] In certain embodiments, the step of heating the reaction solution is conducted under autogenic pressure, i.e., pressure generated as a result of heating in a closed system. Alternatively or additionally, the pressure can be applied externally, e.g., by mechanical means. In certain embodiments, the step of heating the reaction solution is conducted at a pressure of 0.1 to 10 MPa or 0.1 to 1 MPa.
Synthesis and Structural Characterization
[0096] The unconventional fcc phase and hcp/fcc heterophase RuMo alloy NFs were synthesized via a one-pot solvothermal method, as schematically illustrated in
[0097] It is worth mentioning that the reaction temperature, dosages of glucose and salicylic acid play a crucial role in the controlled synthesis of fcc RuMo NFs. With increasing the temperature, the morphology of nanoflowers changed a little, while the diffraction peaks ascribed to hcp phase gradually appeared (
[0098] By rationally regulating the reaction conditions, RuMo alloy NFs with unconventional hcp/fcc heterophase were also obtained. TEM and HAADF-STEM images show that the obtained hcp/fcc RuMo NFs are a 3D flower-like structure assembled by nanosheets with a thickness of around 3.1 nm, which is similar to the fcc RuMo NFs (
X-Ray Spectral Analysis
[0099] X-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures of hcp/fcc Ru NSs, fcc and hcp/fcc RuMo alloy NFs. As shown in
Electrochemical NO.SUB.3.RR Performance
[0100] The electrochemical NO.sub.3RR performance of the obtained samples was tested in a standard three-electrode H-type cell under ambient conditions with Ar-saturated electrolyte composed of 0.1 M KOH and 100 mM KNO.sub.3. In the presence of KNO.sub.3, there is a downward hump for fcc and hcp/fcc RuMo alloy NFs at about 0.05 to 0.05 and 0 to 0.1 V (vs RHE), respectively (
[0101] Chronoamperometry measurements were further performed at various potentials to evaluate the NO.sub.3RR performance (
[0102] To confirm the origin of the nitrogen source and the accuracy of NO.sub.3RR performance test, control experiments were conducted. The current density and NH.sub.3 yield rate of bare carbon paper (CP) show a negligible change after adding KNO.sub.3, suggesting the inertness of CP toward electrocatalytic NO.sub.3RR. In contrast, compared with the pure KOH, the current density and NH.sub.3 yield rate of fcc RuMo alloy NFs increase a lot in the presence of KNO.sub.3 (
[0103] The influence of NO.sub.3.sup. concentration on the NO.sub.3RR performance was also investigated using fcc RuMo alloy NFs (
[0104] The catalytic stability of fcc RuMo alloy NFs was evaluated by the consecutive electrolysis cycles and long-term chronoamperometry test. During the 20 consecutive electrolysis cycles at 0 V (vs RHE), no obvious changes of the current density were observed from the chronoamperometry curves (
Mechanism Investigation
[0105] The electrochemically active surface areas (ECSAs) of hcp/fcc Ru NSs, fcc and hcp/fcc RuMo alloy NFs were determined by the electrochemical double-layer capacitance (C.sub.dl) method (
Theoretical Calculations
[0106] To investigate the origins of superior NO.sub.3RR performance of unconventional fcc phase RuMo alloy NFs, DFT calculations were carried out to demonstrate the intrinsic electroactivity and reaction trends of fcc RuMo NFs and other control samples including hcp/fcc RuMo alloy NFs and hcp/fcc Ru NSs. The influences of crystal phases and compositions have been revealed in the electronic distributions near the Fermi level (E.sub.F) in different electrocatalysts (
[0107] The reaction trends were also investigated from the energetic aspects regarding the adsorption of key intermediates (
Demonstration of ZnNO.sub.3.sup. Batteries
[0108] Ammonia has been regarded as a kind of potential energy carrier due to its high energy density (4.32 kW h L.sup.1). Given the excellent catalytic activity of unconventional fcc phase RuMo alloy NFs in NO.sub.3RR for NH.sub.3 production, ZnNO.sub.3.sup. electrochemical batteries were assembled in which both the electricity generation and NH.sub.3 production can be simultaneously realized. Typically, during the discharge process, the NO.sub.3RR proceeds at the cathode, while the dissociation of Zn occurs at the anode (4Zn+8OH.sup..fwdarw.4ZnO+4H.sub.2O+8e.sup.).
[0109] In summary, unconventional fcc phase RuMo alloy NFs and heterophase hcp/fcc RuMo alloy NFs were successfully synthesized via a facile one-pot solvothermal method. It was observed that fcc RuMo NFs demonstrate superior NO.sub.3RR performance over both hcp/fcc Ru NSs and hcp/fcc RuMo NFs. Remarkably, fcc RuMo NFs deliver an excellent NH.sub.3 FE of 95.2% and high half-cell EE of 41.9% at 0 V (vs RHE), as well as a maximum NH.sub.3 yield rate of 32.7 mg h.sup.1 mg.sub.cat.sup.1 at 0.1 V (vs RHE). Moreover, fcc RuMo NFs also show outstanding catalytic durability during the 20 consecutive electrolysis cycles and the long-term chronoamperometry test. In addition, when the nitrate concentration is as low as 10 mM, the NH.sub.3 FE of 69.7% can still be achieved with fcc RuMo NFs at 0 V (vs RHE). In-situ DEMS results uncovered that fcc RuMo NFs exhibit much lower overpotential for NH.sub.3 electrosynthesis than those of hcp/fcc RuMo NFs and hcp/fcc Ru NSs in NO.sub.3RR. DFT calculations have indicated the optimizations of electronic structure induced by both the fcc phase and the introduction of Mo sites, which improve the surface electroactivity to enhance adsorptions of key intermediates and accelerate electron transfer for efficient reduction processes. Owing to the electronic modulations, fcc RuMo NFs display the strongest adsorption preferences of key intermediates due to the highest d-band center, which not only reduces the RDS barrier but also largely suppresses the competitive hydrogen evolution process. Besides, the successful demonstration of high-performance ZnNO.sub.3.sup. batteries with fcc RuMo alloy NFs as the cathode catalyst suggest their great application potential in the energy supply systems. This work not only provides a feasible method to synthesize unconventional phase metal/alloy nanomaterials, but also offers an effective strategy in promoting the NO.sub.3RR performance towards a sustainable nitrogen cycle.
Experimental Section
Chemicals and Reagents
[0110] Triruthenium dodecacarbonyl (Ru.sub.3(CO).sub.12, 98%) was bought from Energy Chemical. Sodium nitroprusside and molybdenum hexacarbonyl (Mo(CO).sub.6, 98%) were purchased from Alfa Aesar. Oleylamine (OAm, 80%-90%), glucose (99%), n-heptanol (99%), salicylic acid (AR, 99.5%), p-aminobenzenesulfonamide (ACS, 99%), sodium hydroxide (NaOH, AR, 96%), potassium hydroxide (KOH, AR, 99%), trisodium citrate dihydrate (98%), potassium nitrate (KNO.sub.3, 99%), potassium nitrite (KNO.sub.2, 99.99% metals basis), ammonium chloride (ACS, 99.5%), zinc acetate (Zn(Ac).sub.2, AR, 99.0%), N-(1-naphthyl)ethylenediamine dihydrochloride (AR, 98%), 4-(dimethylamino)benzaldehyde (ACS, 99%), phosphoric acid (H.sub.3PO.sub.4, ACS, 85 wt. % in H.sub.2O, p=1.70 g/mL), potassium nitrate-.sup.15N (99 atom %, 98.5%), ammonium chloride-.sup.15N (98 atom %, 98%) and maleic acid (AR, 99.0% (HPLC)) were supplied by Shanghai Aladdin Biochemical Technology Co., Ltd. Citric acid (AR, >99%), and solution of sodium hypochlorite (NaClO, 0.1 M) were bought from Macklin. Ethanol (Absolute, 99.9%), sulfuric acid (ACS, 98%), hydrochloric acid (ACS, wt. 37%) and hexane (Absolute, 99%) were purchased from Anaqua Global International Inc. Limited. All the chemicals and reagents were used as received without further purification. Deionized (DI) water used in the experiments was obtained from the Milli-Q Plus System with a resistance of 18.2 M.Math.cm.
Synthesis of Face-Centered Cubic (Fcc) RuMo Alloy Nanoflowers (NFs)
[0111] In a typical synthesis, 4 mg of Ru.sub.3(CO).sub.12, 5 mg of Mo(CO).sub.6 and 5 mg of glucose were added into 2 mL of OAm. Then 1 mL of salicylic acid solution (10 mg/mL in n-heptanol) was added into the above solution. Subsequently, the growth solution was transferred to a Teflon-lined autoclave, and heated from room temperature to 200 C. and maintained at this temperature for 48 h. After cooling the reactor to room temperature naturally, the final products were collected by centrifugation and washed with 3 mL of the mixture of ethanol and hexane (v/v=1/2) three times. The obtained fcc RuMo alloy NFs were re-dispersed into hexane for further use.
Synthesis of Heterophase Hexagonal Close-Packed (Hcp)/Fcc RuMo Alloy NFs
[0112] In a typical synthesis, 4 mg of Ru.sub.3(CO).sub.12, 5 mg of Mo(CO).sub.6 and 5 mg of glucose were added into 2 mL of OAm. Then 1 mL of citric acid solution (50 mg/mL in n-heptanol) was added into the above solution. After that, the growth solution was transferred to a Teflon-lined autoclave, and heated from room temperature to 200 C. and maintained at this temperature for 48 h. After cooling the reactor to room temperature naturally, the final products were acquired by centrifugation and washed with 3 mL of the mixture of ethanol and hexane (v/v=1/2) for three times. The as-synthesized hcp/fcc RuMo alloy NFs were re-dispersed into hexane for further use.
Synthesis of Heterophase Hcp/Fcc Ru Nanosheets (NSs)
[0113] In a typical synthesis, 4 mg of Ru.sub.3(CO).sub.12 and 5 mg of glucose were added into 2 mL of OAm. Then 1 mL of salicylic acid solution (10 mg/mL in n-heptanol) was added into the above solution. After that, the growth solution was transferred to a Teflon-lined autoclave, and heated from room temperature to 200 C. and maintained at this temperature for 12 h. After the reaction, the final products were collected by centrifugation and washed with 3 mL of the mixture of ethanol and hexane (v/v=1/1) three times. The obtained hcp/fcc Ru NSs were re-dispersed into hexane for further use.
Characterization
[0114] Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku SmartLab X-ray diffractometer with Cu K X-ray source (=1.5406 ). The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images were taken on a JEOL-2100F transmission electron microscope operated at 200 kV. The spherical aberration-corrected high-angle annular dark-field scanning TEM (HAADF-STEM) images were obtained on a high-resolution aberration-corrected TEM (JEOL JEM-ARM200F). Scanning transmission microscopy (SEM) measurements were conducted on QUANTA 250. X-ray photoelectron spectroscopy (XPS) tests were performed on Thermo Scientific Nexsa spectrophotometer with Al-K radiation system. The calibration of XPS spectra was performed by using the C Is peak at 284.8 eV. X-ray absorption measurements, including XANES and EXAFS were obtained in ambient condition at TLS 01C (National Synchrotron Radiation Research Center, Taiwan). XAS data normalization and background subtraction were performed using Demeter 0.9.25 software package. The edge energy of X-ray absorption near edge structure (XANES) spectra was determined from the inflection point in the leading edge, i.e., the maximum in the first derivative of the leading edge of XANES spectra. The coordination parameters were obtained by a least square fit in the R-space Fourier transformed data using Artemis. The amplitude reduction factor (S.sub.0.sup.2) was determined as 0.7 for Ru K-edge by fitting a reference spectrum of Ru foil, and then it was used for fitting all the other Ru K-edge EXAFS spectra. In-situ differential electrochemical mass spectrometry (DEMS) studies were performed on a Linglu DEMS analysis system from Shanghai Linglu Instrument Co., Ltd.
Electrochemical NO.SUB.3.RR Measurement
[0115] Preparation of the working electrode. The as-prepared catalysts were further centrifuged and washed by the mixture of ethanol and hexane (v/v=1/1) for two times to remove the surfactants on the catalyst surface. Typically, to prepare the working electrode, 1.6 mg of the catalyst were added into the mixture of 368 L of isopropanol and 32 L of Nafion solution. Subsequently, it was ultrasonicated in an ice-water bath for about 0.5 h to enable the well dispersion of the catalyst ink. After that, 50 L of the catalyst ink were dropped onto the carbon paper (1 cm1 cm). Finally, the working electrodes were dried in vacuum oven at room temperature for around 2 h.
[0116] NO.sub.3RR performance test. The electrochemical NO.sub.3RR performance test was conducted on an Ivium-n-Stat electrochemical workstation using a standard H-type cell separated by Nafion 117 membrane. In the typical three-electrode system, Pt plate, Ag/AgCl (filled with saturated KCl solution) and catalyst supported on carbon paper were used as the counter, reference and working electrodes, respectively. All the potentials were converted to the reversible hydrogen electrode (RHE) scale by the equation: E (vs RHE)=E (vs Ag/AgCl)+0.197 V+0.059pH. All the measured potentials were manually 85% compensated. The solution containing 0.1 M KOH and 100 mM KNO.sub.3 was used as the electrolyte, which was purged with high purity argon (Ar) for at least 30 mins before the test. Then, 30 mL of electrolyte were added into both the anode and cathode compartments of the H-type cell. The linear sweep voltammetry (LSV) curve was acquired at a scan rate of 5 mV s.sup.1 with the potential range from 0.3 to-0.4 V (vs RHE). The chronoamperometry test was conducted for 1 h at each potential under a stirring rate of 600 rpm. The consecutive recycling stability test was performed at 0 V (vs RHE) with the stirring rate of 600 rpm for 1 h of each cycle. After finishing the electrolysis of each cycle, the electrolyte was taken out for UV-vis analysis and new electrolyte was immediately added into the cell. The next cycle electrolysis was performed under the same conditions. For the long-term chronoamperometry test, the electrochemical measurement was conducted at 0 V (vs RHE). Typically, 200 L of electrolyte were taken out for UV-vis analysis at each time. Cyclic voltammetry (CV) curves were collected at the non-Faradaic region with different scan rates of 60, 80, 100, 120, 140, 160, 180 and 200 mV s.sup.1 to determine the electrochemical double-layer capacitance (C.sub.dl). The electrochemical active surface area (ECSA) can be calculated according to the following equation: ECSA=C.sub.dl/C.sub.s, where C.sub.s is the specific capacitance (40 F cm.sup.2).
Electrochemical In-Situ DEMS Test
[0117] The in-situ DEMS test was performed with a homemade electrochemical cell. Pt wire, Ag/AgCl and catalyst supported on carbon paper were used as the counter, reference and working electrodes, respectively. The electrolyte composed of 0.1 M KOH and 100 mM KNO.sub.3 was purged with high purity Ar for at least 30 mins before the measurement. The LSV curves were acquired from 0.2 to-0.2 V (vs RHE) after the baseline of mass signals became smooth and steady. Meanwhile, the mass signals were recorded during the LSV scanning. After the LSV test was finished, the next cycle of LSV test and mass signal collection started again when the mass signal intensity returned to the baseline.
Isotope Labeling Experiments
[0118] The isotope labeling experiments were performed by using K.sup.15NO.sub.3 as the feeding nitrogen source instead of K.sup.14NO.sub.3. According to the aforementioned electrocatalytic method, 30 mL of electrolyte containing 0.1 M KOH and 0.1 M K.sup.15NO.sub.3 were added into the cathode compartment of the H-type cell. After electrolysis for 1 h, the electrolyte was collected and a certain amount of maleic acid was added into it, resulting in the concentration of 0.4 mg mL.sup.1 for maleic acid. After that, 0.45 mL of the above solution was mixed with 50 L of deuterium oxide (D.sub.2O) for the .sup.1H-NMR (300 MHz) test. A series of .sup.15N-.sup.15NH.sub.4.sup.+ (or .sup.14N-.sup.14NH.sub.4.sup.+) solutions with different .sup.15NH.sub.4.sup.+ (or .sup.14NH.sub.4.sup.+) concentrations were prepared using .sup.15NH.sub.4Cl (or .sup.14NH.sub.4Cl) (98 atom %, 98%). The calibration curves were obtained by correlating the relationship between .sup.15NH.sub.4.sup.+ (or .sup.14NH.sub.4.sup.+) concentration and the peak area ratio of H-.sup.15NH.sub.4.sup.+ (or H-.sup.14NH.sub.4.sup.+) and H-maleic acid.
Product Detection of NO.SUB.3.RR
[0119] Determination of ammonia. The concentration of NH.sub.3 was spectrophotometrically determined by using the indophenol blue method. Typically, 2 mL of pre-diluted electrolyte were taken out and mixed with 2 mL of 1 M NaOH solution containing 5 wt. % salicylic acid and 5 wt. % trisodium citrate dihydrate. Then, the above solution was mixed with 1 mL of 0.05 M NaClO solution and 0.2 mL of an aqueous solution of 1 wt. % sodium nitroprusside. After the above mixture was kept in the dark for 2 h, the absorption spectrum was acquired using an UV-vis spectrophotometer (Shimadzu-UV1700) at the wavelength of 654 nm. The calibration curve of ammonia concentration and absorbance was prepared by using a series of standard NH.sub.4Cl solutions.
[0120] Determination of nitrite. Firstly, 4 g of p-aminobenzenesulfonamide, 0.2 g of N-(1-Naphthyl)ethylenediamine dihydrochloride, and 10 mL of phosphoric acid (=1.70 g/mL) were added into 50 mL of ultrapure water. After ultrasonication for about 2 mins, the obtained transparent solution was used as the color reagent. Then, 5 mL of dilution electrolyte were mixed with 0.1 mL of color regent. After 20 mins, the absorption spectrum was taken by using an UV-vis spectrophotometer (Shimadzu-UV1700) at the wavelength of 540 nm. A series of standard potassium nitrite solutions were prepared to obtain the calibration curve.
[0121] Determination of hydrazine. Hydrazine (N.sub.2H.sub.4) in the electrolyte was determined by the Watt and Chrisp method. Typically, 5.99 g of 4-(dimethylamino)benzaldehyde, 30 mL of hydrochloric acid and 300 mL of ethanol were thoroughly mixed and used as a color reagent. Then, 2.5 mL of electrolyte were collected from the cathode compartment and mixed with 2.5 mL of the above color reagent. After standing in the dark for about 20 mins at room temperature, the absorbance of the obtained solution was measured at a wavelength of 457 nm by using the UV-vis spectrophotometer (Shimadzu-UV1700). The concentration-absorbance curve was made by standard hydrazine monohydrate solutions with a series of known concentrations.
Calculation of the Faradaic Efficiency (FE) and Yield Rate (R)
[0122] In this work, the FE of NH.sub.3, NO.sub.2.sup. or N.sub.2H.sub.4 was calculated as follows:
[0123] The yield rate of NH.sub.3 was calculated according to the following equation:
Calculation of the Half-Cell Energy Efficiency for NH.SUB.3 .Synthesis
[0125] The energy efficiency is defined as the ratio of chemical energy to applied electrical power, which was calculated by the following equation:
Assembly of Zinc-Nitrate (ZnNO.sub.3.sup.) Battery
[0127] A typical H-type cell separated by a bipolar membrane was used to assemble the ZnNO.sub.3.sup. battery. The catalyst supported on carbon paper and a polished Zn foil were applied as the working and counter electrodes, respectively. 25 mL of electrolyte containing 1 M KOH and 0.02 M Zn(Ac).sub.2 were added into the anode compartment, while 25 mL of electrolyte composed of 0.1 M KOH and 100 mM KNO.sub.3 were added into the cathode compartment. The discharging curves were acquired by an Ivium-n-Stat electrochemical workstation with the sweep rate of 5 mV s.sup.1. The galvanostatic discharge measurements of the assembled batteries were carried out using LAND battery test systems (CT2001A, Wuhan LAND Electronic Co. Ltd).
Theoretical Calculations Setup
[0128] In this work, density functional theory (DFT) calculations embedded in CASTEP packages have been applied to investigate both electronic structures and reaction trends of unconventional fcc and hcp/fcc RuMo alloy NFs. To accurately describe the exchange-correlation interactions in the materials, we have selected the generalized gradient approximation (GGA) and Perdew-Burke-Ernzerhof (PBE) functionals. By choosing the ultrafine quality with the ultrasoft pseudopotentials, the plane-wave cutoff energy has been set to 380 eV by default. The Broyden-Fletcher-Goldfarb-Shannon (BFGS) algorithm has been introduced for all the energy minimizations and the k-point has been set to coarse quality based on the balance between calculation efficiency and accuracy. We have considered three different electrocatalysts in this work. The fcc RuMo NFs have been constructed by cleaving the (111) surfaces of fcc Ru with 5-layer thickness in a 441 supercell. The hcp/fcc RuMo NFs and hcp/fcc Ru NSs are built by a combination of the hep and fcc phases of Ru, which include 84 atoms with 5-layer thickness. Based on the experimental characterizations, fcc RuMo NFs and hcp/fcc RuMo NFs have a close composition of Ru.sub.72Mo.sub.8 and Ru.sub.76Mo.sub.8, respectively. To guarantee sufficient geometry optimizations, 20 vacuum space has been introduced in the c-axis for all the electrocatalyst surfaces. To achieve sufficient geometry optimizations, we have applied stringent convergence criteria including the Hellmann-Feynman forces and the total energy difference should not exceed 0.001 eV/ and 510.sup.5 eV/atom, respectively.