WO2017091955A1 - Bifunctional electrocatalyst for water splitting and preparation method thereof - Google Patents
Bifunctional electrocatalyst for water splitting and preparation method thereof Download PDFInfo
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- WO2017091955A1 WO2017091955A1 PCT/CN2015/096020 CN2015096020W WO2017091955A1 WO 2017091955 A1 WO2017091955 A1 WO 2017091955A1 CN 2015096020 W CN2015096020 W CN 2015096020W WO 2017091955 A1 WO2017091955 A1 WO 2017091955A1
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- Prior art keywords
- nickel
- mixture
- source compound
- urea
- dried
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- 239000010411 electrocatalyst Substances 0.000 title claims abstract description 27
- 230000001588 bifunctional effect Effects 0.000 title claims abstract description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims description 25
- 238000002360 preparation method Methods 0.000 title description 11
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 91
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 24
- 238000000034 method Methods 0.000 claims abstract description 20
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims abstract description 19
- 239000004202 carbamide Substances 0.000 claims abstract description 19
- 239000000203 mixture Substances 0.000 claims abstract description 18
- 150000001875 compounds Chemical class 0.000 claims abstract description 15
- 239000000843 powder Substances 0.000 claims abstract description 11
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 239000012298 atmosphere Substances 0.000 claims abstract description 9
- 239000002904 solvent Substances 0.000 claims abstract description 9
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 claims abstract description 8
- 239000011363 dried mixture Substances 0.000 claims abstract description 8
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims abstract description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 47
- 229910052742 iron Inorganic materials 0.000 claims description 21
- -1 iron ion Chemical class 0.000 claims description 9
- 229910001453 nickel ion Inorganic materials 0.000 claims description 9
- 229910021645 metal ion Inorganic materials 0.000 claims description 7
- 238000003756 stirring Methods 0.000 claims description 7
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 claims description 6
- 229920000049 Carbon (fiber) Polymers 0.000 claims description 5
- 239000004917 carbon fiber Substances 0.000 claims description 5
- 239000006260 foam Substances 0.000 claims description 5
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 5
- QMMRZOWCJAIUJA-UHFFFAOYSA-L nickel dichloride Chemical compound Cl[Ni]Cl QMMRZOWCJAIUJA-UHFFFAOYSA-L 0.000 claims description 3
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims description 2
- 229910021586 Nickel(II) chloride Inorganic materials 0.000 claims description 2
- MQRWBMAEBQOWAF-UHFFFAOYSA-N acetic acid;nickel Chemical compound [Ni].CC(O)=O.CC(O)=O MQRWBMAEBQOWAF-UHFFFAOYSA-N 0.000 claims description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims description 2
- RUTXIHLAWFEWGM-UHFFFAOYSA-H iron(3+) sulfate Chemical compound [Fe+3].[Fe+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O RUTXIHLAWFEWGM-UHFFFAOYSA-H 0.000 claims description 2
- 229910000360 iron(III) sulfate Inorganic materials 0.000 claims description 2
- 229940078494 nickel acetate Drugs 0.000 claims description 2
- LGQLOGILCSXPEA-UHFFFAOYSA-L nickel sulfate Chemical compound [Ni+2].[O-]S([O-])(=O)=O LGQLOGILCSXPEA-UHFFFAOYSA-L 0.000 claims description 2
- 229910000363 nickel(II) sulfate Inorganic materials 0.000 claims description 2
- KBJMLQFLOWQJNF-UHFFFAOYSA-N nickel(ii) nitrate Chemical compound [Ni+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O KBJMLQFLOWQJNF-UHFFFAOYSA-N 0.000 claims description 2
- 238000009210 therapy by ultrasound Methods 0.000 claims 1
- 239000000243 solution Substances 0.000 abstract description 17
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 abstract description 16
- 239000012670 alkaline solution Substances 0.000 abstract description 3
- 238000001035 drying Methods 0.000 abstract 1
- 239000003054 catalyst Substances 0.000 description 17
- 229910052799 carbon Inorganic materials 0.000 description 12
- 239000002105 nanoparticle Substances 0.000 description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 11
- 229910003271 Ni-Fe Inorganic materials 0.000 description 11
- 230000000694 effects Effects 0.000 description 10
- 229910045601 alloy Inorganic materials 0.000 description 9
- 239000000956 alloy Substances 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 238000013507 mapping Methods 0.000 description 6
- 238000002441 X-ray diffraction Methods 0.000 description 5
- 239000000919 ceramic Substances 0.000 description 5
- 229910021392 nanocarbon Inorganic materials 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 238000000527 sonication Methods 0.000 description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- 238000003917 TEM image Methods 0.000 description 4
- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 4
- 239000002041 carbon nanotube Substances 0.000 description 4
- 229910021393 carbon nanotube Inorganic materials 0.000 description 4
- 239000003792 electrolyte Substances 0.000 description 4
- 239000002071 nanotube Substances 0.000 description 4
- 238000011282 treatment Methods 0.000 description 4
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000005868 electrolysis reaction Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000002173 high-resolution transmission electron microscopy Methods 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 238000010348 incorporation Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 3
- 239000002243 precursor Substances 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- 238000004627 transmission electron microscopy Methods 0.000 description 3
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 2
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000012299 nitrogen atmosphere Substances 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 229910052723 transition metal Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- IUYOGGFTLHZHEG-UHFFFAOYSA-N copper titanium Chemical compound [Ti].[Cu] IUYOGGFTLHZHEG-UHFFFAOYSA-N 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000002484 cyclic voltammetry Methods 0.000 description 1
- 238000003411 electrode reaction Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910021389 graphene Inorganic materials 0.000 description 1
- 238000001198 high resolution scanning electron microscopy Methods 0.000 description 1
- 238000000024 high-resolution transmission electron micrograph Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- UGKDIUIOSMUOAW-UHFFFAOYSA-N iron nickel Chemical compound [Fe].[Ni] UGKDIUIOSMUOAW-UHFFFAOYSA-N 0.000 description 1
- 159000000014 iron salts Chemical class 0.000 description 1
- NQXWGWZJXJUMQB-UHFFFAOYSA-K iron trichloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].Cl[Fe+]Cl NQXWGWZJXJUMQB-UHFFFAOYSA-K 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000002055 nanoplate Substances 0.000 description 1
- 229940078487 nickel acetate tetrahydrate Drugs 0.000 description 1
- OINIXPNQKAZCRL-UHFFFAOYSA-L nickel(2+);diacetate;tetrahydrate Chemical compound O.O.O.O.[Ni+2].CC([O-])=O.CC([O-])=O OINIXPNQKAZCRL-UHFFFAOYSA-L 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 239000002109 single walled nanotube Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000010189 synthetic method Methods 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 238000002604 ultrasonography Methods 0.000 description 1
- 239000013598 vector Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/74—Iron group metals
- B01J23/755—Nickel
-
- B01J35/33—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/16—Reducing
-
- 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
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/03—Precipitation; Co-precipitation
- B01J37/031—Precipitation
- B01J37/033—Using Hydrolysis
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
- B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
- B01J37/343—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of ultrasonic wave energy
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Definitions
- the present application relates to the field of water splitting by electrolysis, in
- H 2 Molecular hydrogen
- HER hydrogen evolution reaction
- OER oxygen evolution reaction
- transition metal Mo, W, Ni, Co, Fe, Mn, Cu etc.
- their derivatives carbbide, oxide, sulfide, phosphide, hydroxide and mixed-metal alloy etc.
- HER or OER transition metal
- some of them exhibited comparable or even better electrocatalytic performances than the existing Pt/C for HER or Ir/C for OER in some specific cases.
- Chen et al. recently reported that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst was able to produce hydrogen from water at more than twice the rate of the state-of-the-art Pt/C catalyst.
- the present application provides a method for preparing a bifunctional electrocatalyst which could simultaneously promote HER and OER processes in alkaline solution.
- the preparation method comprises the following steps: (a) a nickel source compound and a ferric iron source compound being added into a solvent, wherein the molar ratio of the iron ion to the nickel ion in the obtained solution is in the range of from 0 to 2/3, and the total metal ion (the nickel ion plus the iron ion) content in the obtained solution is in the range of from 0.3 to 0.5 mmol; (b) a urea being added into the obtained solution to give a mixture; (c) the mixture obtained in step (b) being dried; (d) the dried mixture being ground into homogeneous powders and then subjected to a heating process under inert atmosphere.
- a bifunctional electrocatalyst is provided, which is made by the preparation method of the present application.
- a symmetric two- electrode water splitting cell comprising the bifunctional electrocatalyst of the present application is provided.
- the present application provides a method to prepare n Ni-based bifunctional electrocatalyst used in alkaline electrolyzers by simultaneously implementing nanos- grapplturing, hybridizing with nanocarbon and doping with heterogeneous elements by a facile synthetic approach.
- the iron content of the obtained bifunctional electrocatalyst has significant influences on both the HER and OER activities of the catalyst.
- the preparation method according to the present application is simple and scalable, which is easy to carry out and can be performed by pyrolyzing a precursor composed of nickel and iron salts mixed with urea under inert atmosphere without any post- treatments.
- FIG. 1 shows the overpotentials for HER and OER with different Fe contents in Ni i x Fe X /NC made by the method according to an embodiment of the present application.
- FIG. 2 shows low-magnification (a) and high-resolution (b) SEM images of the bifunctional electrocatalyst according to an embodiment of the present application.
- FIG. 3 shows TEM (a, b) and HRTEM (c) images of the Ni 09 Fe 0 JNC according an embodiment, and HAADF-TEM (d-g) image and the corresponding EDS mappings of C, Ni, Fe in the area marked in dotted rectangular frame; XRD (h) patterns of Ni/NC, Ni o . gFe o.i/NC and standard XRD pattern of face-centered cubic metallic Ni.
- FIG. 4 shows Full XPS spectrum (a) of the representative Ni o . gFe o.i/NC sample; and high-resolution XPS spectra (b-e) of C Is, N Is, Ni 2p and Fe 2p, respectively.
- FIG. 5 shows the performance of a cell containing the bifunctional catalyst according to the present application on overall electrochemical water splitting.
- the loading of the catalysts on carbon fiber paper was 2 mg cm 2 .
- FIG. 6 shows the cyclic voltammogram of a water splitting cell composed of two symmetric Ni o . gFe 0 .i/NC-NF electrodes.
- the loading of the catalysts on Ni foam was 2 mg cm 2 .
- a method for preparing a bifunctional electrocatalyst comprising the following steps: (a) a certain amount of nickel source compound and a certain amount of ferric iron source compound being added and dissolved into a solvent, wherein the molar ratio of the nickel ion to the iron ion in the obtained solution is in the range of from 100: 0 to 60: 40, and the total metal ion (the nickel ion plus the iron ion) content in the obtained solution is in the range of from 0.3 to 0.5 mmol; preferably, the molar ratio of the nickel ion to the iron ion in the obtained solution is in the range of from 99: 1 to 70: 30; (b) a certain amount of urea being added and dissolved into the obtained solution to give a mixture; (c) the mixture obtained in step (b) being dried in an oil
- the nickel source According to a specific example of the present application, the nickel source
- step (a) may be selected from the group consisting of nickel acetate, nickel chloride, nickel nitrate, nickel sulfate or the like and the combination thereof.
- the function of nickel source compound is to provide nickel ion in the solution.
- the ferric iron source compound in step (a) can be selected from the group consisting of ferric chloride, ferric nitrate, ferric sulfate and the combination thereof.
- the solvent in step (a) can be water, methanol, ethanol or propanol or the combination thereof, and the ethanol is preferred.
- the urea in step (b) of the preparation method, can be added in such an amount that the concentration of the urea in the solution is in the range of from 1 to 3 g/mL. More preferably, the concentration of urea in the solvent of ethanol is 1 g/mL.
- step (b) of the preparation method after adding urea, the solution can be treated with ultrasound for 4 to 8 minutes so as to dissolve the urea into the solvent (water or ethanol) quickly.
- this solution can also be treated with stirring. More preferably, the period of the sonication treatment is 5 minutes.
- the mixture in step (c) of the preparation method, can be dried at 60 °C to 90 °C in an oil bath upon stirring for 5 to 10 hours to remove the solvent. More preferably, the mixture is dried at 70 °C in an oil bath with stirring for 6 hours.
- step (d) of the preparation method the dried mixture is thoroughly ground into homogeneous fine powders and then transferred into a ceramic crucible with an equipped cover.
- the heating process is preferably carried out with three stages: in the first stage, the temperature is raised from room temperature (about 25 °C) to a temperature of 520 °C to 580 °C at a programming rate of from 0.4 to 0.6 °C/min and then maintained at that temperature for 3 hours; in the second stage, the temperature is further raised to 650 °C to 750 °C within about 1 hour and maintained at that temperature for about 2 hours; in the third stage, the product is cooled naturally.
- the whole heating process is preferably proceeded under inert atmosphere with a gas flow rate of 40 to 60 seem, wherein the inert atmosphere can be selected from the group consisting of Ar, N 2 and combination thereof.
- the metal ions Ni 2+ and Fe 3+
- the metallic nanoparticles serve as catalysts to induce the growth of nitrogen- doped bamboo-like single-wall carbon nanotubes (CNTs), affording Ni-Fe/nitrogen doped nanocarbon hybrids (NiFe/NC). All these in-situ formed hybrids exhibit good electrocatalytic performances toward both OER and HER.
- Ni-Fe/nitrogen doped nanocarbon hybrids NiFe/NC
- GC glass carbon
- aq KOH
- Figure 1 shows the result, i.e.
- the mass loading of the catalyst is 0.2 mg/cm 2 in this experiment. It can be seen from Figure 1 that the most effective content of Fe for both HER and OER is about 10 at%. Accordingly, the molar ratio of the nickel ion to the iron ion in the obtained nanocarbon hybrid is preferably about 90: 10, i.e., the atomic percent of Fe in the final alloy of Ni and Fe obtained in the above step (d) is about 10 at%.
- a black powder product is obtained after pyrolyzing the inexpensive starting materials, for example, (Ni(CH 3 COO) 2*4H 2 0, FeCl 3 ⁇ 6 ⁇ 2 0 and urea) at a temperature in the range of 650 °C to 750 °C in inert atmosphere.
- Scanning electron microscopy (SEM) images (Figure 2a is a low-magnification SEM image, and Figure 2b is a high-resolution SEM image) show that nanoparticles with sizes ranging from 10 to 50 nm were well dispersed on or encapsulated in the bamboo-like nanotubes. No obvious morphology and size differences were observed among these samples with different Fe content in the hybrid.
- Ni i_ x Fe X /NC samples were similar to each other, with three distinct diffraction peaks located around 44.3°, 51.7°, and 76.2° which can be assigned to the (111), (200), and (222) crystal-plane reflections of a face-centered cubic nickel phase (JCPDS card No. 89-7128).
- JCPDS card No. 89-7128 The incorporation of Fe into the Ni/NC didn't result in any additional crystal diffraction peaks.
- the TEM images also showed that some Ni-Fe alloy nanoparticles were completely encapsulated by a few carbon layers around them.
- Ni i_ x Fe X /NC samples are similar to each other, with three distinct diffraction peaks located around 44.3°, 51.7°, and 76.2° which can be assigned to the (111), (200), and (222) crystal-plane reflections of a face-centered cubic nickel phase.
- the incorporation of Fe into the Ni/NC doesn't result in any additional crystal diffraction peaks. However, a negative shift of 2 ⁇ angles with increasing iron concentrations could be observed, implying the substitutional incorporation of Fe atom into the nickel cubic structure. Scherrer analysis of the broadening of (111) diffraction peak of Ni o .
- gFe o.i/NC indicates an average grain size of 28 nm of Ni-Fe alloy nanoparticles along the (111) crystallographic axis direction, consistent with the results observed by SEM.
- Transmission electron microscopy (TEM) images (as shown in Fig. 3a and 3b) shows that the tube walls of bamboo-like nanotubes are composed of several dis- orderedly stacked graphene layers. This can explain why only a very weak diffraction peak could be observed at around 26.1°, corresponding to the graphitic (002) crystal- plane (see Fig. 3d).
- HRTEM high resolution TEM
- 3c presents 0.21 nm lattice fringes, which can be attributed to the (111) lattice plane of the Ni-Fe alloy, in line with the XRD results.
- the TEM images also show that some Ni-Fe alloy nanoparticles are completely encapsulated by a few carbon layers around them.
- the high-angle angular dark field TEM (HAADF-TEM) image and the corresponding EDS mapping demonstrate that the bamboo-like nanotubes are mainly composed of carbon and the nanoparticles were composed of Ni and Fe (as shown in Fig. 3 (d-g)).
- the perfect superposition of the element distribution of Ni and Fe in their EDS mapping images further confirms the alloy nature of the Ni-Fe nanoparticles in Ni o .
- X-ray photoelectron spectroscopy (XPS) measurement has also been performed to investigate the specific surface composition and chemical environment of the representative Ni o . gFe o.i/NC, the result is shown in Figure 4 (a) shows Full XPS spectrum of the representative Ni o . gFe o.i/NC sample; and Figure 4 (b-e) are high-resolution XPS spectra of C Is, N Is, Ni 2p and Fe 2p, respectively.
- XPS X-ray photoelectron spectroscopy
- mapping images further confirm the alloy nature of the Ni-Fe nanoparticles in Ni o . ⁇ Fe o.i/NC. All the characterization results above suggest that the pyrolyzed product is composed of metallic Ni-Fe alloy nanoparticles either encapsulated in or dispersed on bamboo-like CNTs.
- the present bifunctional electrocatalyst (Ni i_ x Fe X /NC) can be loaded onto carbon fiber papers (CFPs) or on nickel foams.
- CFPs carbon fiber papers
- Ni o . gFe 0 .i/NC exhibited overpotentials of 270 mV and 85 mV for OER and HER to reach a current density of 10 mA cm 2 , respectively.
- Ni o . gFe o . JNC-NF electrodes The voltage needed to support a current density of 10 mA cm 2 was about 1.58 V determined from the reverse scan of the CV curve.
- CPPs inert carbon fiber papers
- Ni o . gFe o . JNC exhibits overpotentials of 191 mV and 270 mV for HER and OER to reach a current density of 30 mA cm 2 , respectively.
- the present application provides a Ni i_ x Fe X /NC hybrid electrocatalyst which exhibits excellent performances to catalyze both HER and OER in alkaline electrolyte.
- an efficient electrolyzer (cell) composed of two symmetric Ni o.gFe o . JNC loaded carbon fiber paper electrodes can achieve a current density of 10 mA cm 2 for overall water splitting at a voltage of 1.65 V, which is among the best performances for symmetric two-electrode water electrolyzer reported so far.
- the metal salt precursors (nickel acetate tetrahydrate, Ni(CH 3 COO) 2 *4H 2 0 and Iron(III) chloride hexahydrate, FeCl 3 ⁇ 6 ⁇ 2 0) were completely dissolved into 2 ml ethanol with a molar ratio of 9: 1 while maintaining a total metal ion content of 0.5 mmol. Then, 2 g urea was added into the solution followed by a sonication treatment for 5 minutes. The obtained mixture was subsequently dried at 70 °C in an oil bath upon stirring for 6 hours to remove the ethanol. The dried mixture was thoroughly ground into homogeneous fine powders and then transferred into a ceramic crucible with an equipped cover.
- the covered ceramic crucible was placed at the central of a tubular furnace and the temperature was raised from 25 °C to 550 °C at a programming rate of 0.5 °C/min and then maintained at 550 °C for 3 hours. After that, the temperature was further raised to 700 °C in 1 hour and maintained at that temperature for 2 hours and then cooled naturally. The whole heating process was proceeded under inert Ar/N 2 atmosphere with a gas flow rate of 50 seem.
- the metal salt precursors (nickel chloride(NiCl 2 ) and Iron(III) ferric nitrate, Fe(NO 3 ) 3 ) were completely dissolved into 4 ml of water with a molar ratio of 90: 10 while maintaining a total metal ion content of 0.3 mmol. Then, 4 g urea was added into the solution followed by a sonication treatment for 8 minutes. The obtained mixture was subsequently dried at 90 °C in an oil bath upon stirring for 9 hours to remove the water. The dried mixture was thoroughly ground into homogeneous fine powders and then transferred into a ceramic crucible with an equipped cover.
- the covered ceramic crucible was placed at the central of a tubular furnace and the temperature was raised from 25 °C to 580 °C at a programming rate of 0.4 °C/min and then maintained at 580 °C for 3 hours. After that, the temperature was further raised to 750 °C in 1 hour and maintained at that temperature for 2 hours and then cooled naturally. The whole heating process was proceeded under inert N 2 atmosphere with a gas flow rate of 50 seem.
- a symmetric two-electrode water splitting cell containing two identical electrodes was made in this example, wherein these two electrodes were fabricated by the same method with the same catalyst.
- 20 mg of catalyst obtained in Example 1 was dispersed in a mixture of 0.75 ml of water, 0.25 ml of ethanol and 100 ⁇ of 5 wt% Nafion solution by at least 60 min sonication to form a homogeneous ink. After the sonication, 100 ⁇ of the homogeneous ink was drop-dried onto carbon a fiber paper with a catalyst-covered-area of 1 cm 2 to achieve a catalyst-loading of 2 mg cm 2 .
- one electrode was connected to the working electrode of the electrochemical workstation and another electrode was connected to the counter electrode and reference electrode of the electrochemical workstation. Finally, the two electrodes were inserted into 1 M KOH (aq) electrolyte with all the active areas being immersed.
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Abstract
A method for preparing a bifunctional electrocatalyst is provided, which comprises: adding a nickel source compound and a ferric iron source compound into a solvent of ethanol; adding a urea into the obtained solution to give a mixture; drying the mixture; grinding the dried mixture into homogeneous powders and then subjecting the homogeneous powders to a heating process under inert atmosphere. The bifunctional electrocatalyst could simultaneously promote HER and OER processes in alkaline solution.
Description
BIFUNCTIONAL ELECTROCATALYST FOR WATER SPLITTING AND PREPARATION METHOD
THEREOF
Technical Field
[0001] The present application relates to the field of water splitting by electrolysis, in
particular, it relates to a preparation method of bifunctional electrocatalyst and a cell containing the bifunctional electrocatalyst.
Background Art
[0002] Molecular hydrogen (H 2) is extensively regarded as one of the most ideal energy vectors due to its zero-carbon emission, recyclability, and high energy conversion efficiency. Water splitting by electrolysis is an environmental-friendly way to generate H 2. Especially, when coupling to photovoltaic modules, it will be a sustainable and promising energy system for future society. Currently, the state-of-the-art electro- catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are often Pt-based and Ir-based or Ru-based materials, respectively. However, the scarcity and high-cost of these noble metal-based electrocatalysts limit their large-scale application. Therefore, developing active, stable and low-cost electrocatalysts in place of precious metal-based materials is a vital step towards future hydrogen economy.
[0003] Recently, transition metal (Mo, W, Ni, Co, Fe, Mn, Cu etc.) and their derivatives (carbide, oxide, sulfide, phosphide, hydroxide and mixed-metal alloy etc.) have been extensively invested as either HER or OER and even bifunctional electrocatalysts. Excitingly, some of them exhibited comparable or even better electrocatalytic performances than the existing Pt/C for HER or Ir/C for OER in some specific cases. For example, Chen et al. recently reported that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst was able to produce hydrogen from water at more than twice the rate of the state-of-the-art Pt/C catalyst. As for the kinetically sluggish OER process, Dai et al. reported an electrocatalyst which could promote the OER process better than a commercial Ir/C catalyst through hybridizing ultrathin nickel-iron layered double hydroxide nanoplates with mildly oxidized multiwall CNTs. Notwithstanding these progresses, there are still very few success to develop bifunctional catalysts which could pair the two electrode reactions together in an integrated elec- trolyser for practical use. Although several feasible strategies to optimize the catalytic performance of transition metal based materials have been proposed, it remains highly challenging to develop facile synthetic methods to combine all these strategies for advanced catalysts.
Technical Problem
[0004] In order to improve the efficiency of water splitting by electrolysis, the present application provides a method for preparing a bifunctional electrocatalyst which could simultaneously promote HER and OER processes in alkaline solution. The preparation method comprises the following steps: (a) a nickel source compound and a ferric iron source compound being added into a solvent, wherein the molar ratio of the iron ion to the nickel ion in the obtained solution is in the range of from 0 to 2/3, and the total metal ion (the nickel ion plus the iron ion) content in the obtained solution is in the range of from 0.3 to 0.5 mmol; (b) a urea being added into the obtained solution to give a mixture; (c) the mixture obtained in step (b) being dried; (d) the dried mixture being ground into homogeneous powders and then subjected to a heating process under inert atmosphere.
Solution to Problem
Technical Solution
[0005] According to another embodiment of the present application, a bifunctional electrocatalyst is provided, which is made by the preparation method of the present application.
[0006] According to another embodiment of the present application, a symmetric two- electrode water splitting cell comprising the bifunctional electrocatalyst of the present application is provided.
Advantageous Effects of Invention
Advantageous Effects
[0007] The present application provides a method to prepare n Ni-based bifunctional electrocatalyst used in alkaline electrolyzers by simultaneously implementing nanos- tructuring, hybridizing with nanocarbon and doping with heterogeneous elements by a facile synthetic approach. The iron content of the obtained bifunctional electrocatalyst has significant influences on both the HER and OER activities of the catalyst. The preparation method according to the present application is simple and scalable, which is easy to carry out and can be performed by pyrolyzing a precursor composed of nickel and iron salts mixed with urea under inert atmosphere without any post- treatments.
Brief Description of Drawings
Description of Drawings
[0008] FIG. 1 shows the overpotentials for HER and OER with different Fe contents in Ni i x Fe X/NC made by the method according to an embodiment of the present application.
[0009] FIG. 2 shows low-magnification (a) and high-resolution (b) SEM images of the bifunctional electrocatalyst according to an embodiment of the present application.
[0010] FIG. 3 shows TEM (a, b) and HRTEM (c) images of the Ni 09Fe 0 JNC according an embodiment, and HAADF-TEM (d-g) image and the corresponding EDS mappings of C, Ni, Fe in the area marked in dotted rectangular frame; XRD (h) patterns of Ni/NC, Ni o.gFe o.i/NC and standard XRD pattern of face-centered cubic metallic Ni.
[0011] FIG. 4 shows Full XPS spectrum (a) of the representative Ni o.gFe o.i/NC sample; and high-resolution XPS spectra (b-e) of C Is, N Is, Ni 2p and Fe 2p, respectively.
[0012] FIG. 5 shows the performance of a cell containing the bifunctional catalyst according to the present application on overall electrochemical water splitting. The loading of the catalysts on carbon fiber paper was 2 mg cm 2.
[0013] FIG. 6 shows the cyclic voltammogram of a water splitting cell composed of two symmetric Ni o.gFe 0.i/NC-NF electrodes. The loading of the catalysts on Ni foam was 2 mg cm 2.
Mode for the Invention
Mode for Invention
[0014] Objects, advantages and embodiments of the present application will be explained below in detail with reference to the accompanying drawings. However, it should be appreciated that the following description of the embodiments is merely exemplary in nature and is not intended to limit the application, its application, or uses.
[0015] According to an embodiment of the present application, a method for preparing a bifunctional electrocatalyst is provided, wherein the bifunctional electrocatalyst could simultaneously promote HER and OER processes in alkaline solution. The method comprises the following steps: (a) a certain amount of nickel source compound and a certain amount of ferric iron source compound being added and dissolved into a solvent, wherein the molar ratio of the nickel ion to the iron ion in the obtained solution is in the range of from 100: 0 to 60: 40, and the total metal ion (the nickel ion plus the iron ion) content in the obtained solution is in the range of from 0.3 to 0.5 mmol; preferably, the molar ratio of the nickel ion to the iron ion in the obtained solution is in the range of from 99: 1 to 70: 30; (b) a certain amount of urea being added and dissolved into the obtained solution to give a mixture; (c) the mixture obtained in step (b) being dried in an oil bath with stirring; (d) the dried mixture being ground into homogeneous powders and then heated under inert atmosphere to give a black powder product.
[0016] According to a specific example of the present application, the nickel source
compound in step (a) may be selected from the group consisting of nickel acetate, nickel chloride, nickel nitrate, nickel sulfate or the like and the combination thereof. The function of nickel source compound is to provide nickel ion in the solution.
[0017] According to a specific example of the present application, the ferric iron source
compound in step (a) can be selected from the group consisting of ferric chloride, ferric nitrate, ferric sulfate and the combination thereof.
[0018] In particular, the solvent in step (a) can be water, methanol, ethanol or propanol or the combination thereof, and the ethanol is preferred.
[0019] According to a preferable embodiment of the present application, in step (b) of the preparation method, the urea can be added in such an amount that the concentration of the urea in the solution is in the range of from 1 to 3 g/mL. More preferably, the concentration of urea in the solvent of ethanol is 1 g/mL.
[0020] In step (b) of the preparation method, after adding urea, the solution can be treated with ultrasound for 4 to 8 minutes so as to dissolve the urea into the solvent (water or ethanol) quickly. Alternatively, this solution can also be treated with stirring. More preferably, the period of the sonication treatment is 5 minutes.
[0021] According to a preferable embodiment of the present application, in step (c) of the preparation method, the mixture can be dried at 60 °C to 90 °C in an oil bath upon stirring for 5 to 10 hours to remove the solvent. More preferably, the mixture is dried at 70 °C in an oil bath with stirring for 6 hours.
[0022] According to a preferable embodiment of the present application, in step (d) of the preparation method, the dried mixture is thoroughly ground into homogeneous fine powders and then transferred into a ceramic crucible with an equipped cover. The heating process is preferably carried out with three stages: in the first stage, the temperature is raised from room temperature (about 25 °C) to a temperature of 520 °C to 580 °C at a programming rate of from 0.4 to 0.6 °C/min and then maintained at that temperature for 3 hours; in the second stage, the temperature is further raised to 650 °C to 750 °C within about 1 hour and maintained at that temperature for about 2 hours; in the third stage, the product is cooled naturally. The whole heating process is preferably proceeded under inert atmosphere with a gas flow rate of 40 to 60 seem, wherein the inert atmosphere can be selected from the group consisting of Ar, N 2 and combination thereof.
[0023] During the heating process of the above step (b), the metal ions (Ni 2+ and Fe 3+) are reduced to metallic state by the reduced species released from the pyrolysis of urea and then the metallic nanoparticles serve as catalysts to induce the growth of nitrogen- doped bamboo-like single-wall carbon nanotubes (CNTs), affording Ni-Fe/nitrogen doped nanocarbon hybrids (NiFe/NC). All these in-situ formed hybrids exhibit good electrocatalytic performances toward both OER and HER.
[0024] The doping amount of Fe into the NiFe/NC is found to have significant influences on both the HER and OER activities of the catalyst. The electrochemical water splitting activities of Ni-Fe/nitrogen doped nanocarbon hybrids (NiFe/NC) with different Fe contents on glass carbon (GC) electrodes in 1 M KOH (aq) electrolyte have been de-
termined. In this experiment, the Ni-Fe/nitrogen doped nanocarbon hybrid is denoted as Ni i_xFe X/NC (with x = 0, 0.1, 0.2, 0.3 and 0.4, where x standing for the molar ratio of Fe to Fe+Ni). Figure 1 shows the result, i.e. the summaries of the overpotentials for HER and OER to achieve a current density of 10 mA cm 2 with different Fe contents in Ni i_xFe X/NC. The mass loading of the catalyst is 0.2 mg/cm 2 in this experiment. It can be seen from Figure 1 that the most effective content of Fe for both HER and OER is about 10 at%. Accordingly, the molar ratio of the nickel ion to the iron ion in the obtained nanocarbon hybrid is preferably about 90: 10, i.e., the atomic percent of Fe in the final alloy of Ni and Fe obtained in the above step (d) is about 10 at%.
[0025] According the preparation method of the present application, a black powder product is obtained after pyrolyzing the inexpensive starting materials, for example, (Ni(CH 3 COO) 2*4H 20, FeCl 3·6Η 20 and urea) at a temperature in the range of 650 °C to 750 °C in inert atmosphere. Scanning electron microscopy (SEM) images (Figure 2a is a low-magnification SEM image, and Figure 2b is a high-resolution SEM image) show that nanoparticles with sizes ranging from 10 to 50 nm were well dispersed on or encapsulated in the bamboo-like nanotubes. No obvious morphology and size differences were observed among these samples with different Fe content in the hybrid. The XRD patterns (not shown) of these Ni i_xFe X/NC samples were similar to each other, with three distinct diffraction peaks located around 44.3°, 51.7°, and 76.2° which can be assigned to the (111), (200), and (222) crystal-plane reflections of a face-centered cubic nickel phase (JCPDS card No. 89-7128). The incorporation of Fe into the Ni/NC didn't result in any additional crystal diffraction peaks. The TEM images also showed that some Ni-Fe alloy nanoparticles were completely encapsulated by a few carbon layers around them. The high-angle angular dark field TEM (HAADF-TEM) image and the corresponding EDS mapping demonstrated that the bamboo-like nanotubes were mainly composed of carbon and the nanoparticles were composed of Ni and Fe , the result is shown in Figure 3 (a-h), wherein Figures 3 (a) and 3 (b) are TEM images and Figure 3 (c) is HRTEM image of the Ni o.gFe 0.i/NC according an embodiment of the present disclosure, and Figures 3 (d-g) are HAADF-TEM images and the corresponding EDS mappings of C, Ni, Fe in the area marked in dotted rectangular frame in 3 (d); Figure 3 (h) shows XRD patterns of Ni/NC, Ni 0 9Fe 0 1/NC and standard XRD pattern of face-centered cubic metallic Ni .
[0026] The XRD patterns of these Ni i_xFe X/NC samples are similar to each other, with three distinct diffraction peaks located around 44.3°, 51.7°, and 76.2° which can be assigned to the (111), (200), and (222) crystal-plane reflections of a face-centered cubic nickel phase. The incorporation of Fe into the Ni/NC doesn't result in any additional crystal diffraction peaks. However, a negative shift of 2Θ angles with increasing iron concentrations could be observed, implying the substitutional incorporation of Fe atom into
the nickel cubic structure. Scherrer analysis of the broadening of (111) diffraction peak of Ni o.gFe o.i/NC indicates an average grain size of 28 nm of Ni-Fe alloy nanoparticles along the (111) crystallographic axis direction, consistent with the results observed by SEM. Transmission electron microscopy (TEM) images (as shown in Fig. 3a and 3b) shows that the tube walls of bamboo-like nanotubes are composed of several dis- orderedly stacked graphene layers. This can explain why only a very weak diffraction peak could be observed at around 26.1°, corresponding to the graphitic (002) crystal- plane (see Fig. 3d). The high resolution TEM (HRTEM) image of the nanoparticles in Fig. 3c presents 0.21 nm lattice fringes, which can be attributed to the (111) lattice plane of the Ni-Fe alloy, in line with the XRD results. The TEM images also show that some Ni-Fe alloy nanoparticles are completely encapsulated by a few carbon layers around them. The high-angle angular dark field TEM (HAADF-TEM) image and the corresponding EDS mapping demonstrate that the bamboo-like nanotubes are mainly composed of carbon and the nanoparticles were composed of Ni and Fe (as shown in Fig. 3 (d-g)). The perfect superposition of the element distribution of Ni and Fe in their EDS mapping images further confirms the alloy nature of the Ni-Fe nanoparticles in Ni o.^Fe o.i/NC. All the characterization results above suggest that the pyrolyzed product is composed of metallic Ni-Fe alloy nanoparticles either encapsulated in or dispersed on bamboo-like CNTs. The specific surface area of a representative Ni o.^Fe o.i/NC catalyst is measured to be 153.7 m 2 g 1 based on the Brunauer-Emmett-Teller (BET) surface area analysis, suggesting the hybrid owned a loose interior structure which could benefit the infiltration and flowage of electrolyte.
[0027] X-ray photoelectron spectroscopy (XPS) measurement has also been performed to investigate the specific surface composition and chemical environment of the representative Ni o.gFe o.i/NC, the result is shown in Figure 4 (a) shows Full XPS spectrum of the representative Ni o.gFe o.i/NC sample; and Figure 4 (b-e) are high-resolution XPS spectra of C Is, N Is, Ni 2p and Fe 2p, respectively.
[0028] The full spectra of the Ni o.gFe o.JNC reveals the presence of C, Ni, Fe and slight N and O. The high-resolution C Is core-level spectrum (as shown in Fig. 4b) could be deconvolved into three peaks centered at -284.5 eV, -285.3 eV and -286.4 eV, which is indexed to C=C/C-C, C=N and C-O/C-N, respectively. The sharpest peak corresponding to C=C/C-C indicates that most of the carbon atoms
[0029] The perfect superposition of the element distribution of Ni and Fe in their EDS
mapping images further confirm the alloy nature of the Ni-Fe nanoparticles in Ni o.^Fe o.i/NC. All the characterization results above suggest that the pyrolyzed product is composed of metallic Ni-Fe alloy nanoparticles either encapsulated in or dispersed on bamboo-like CNTs.
[0030] According to another embodiment of the present application, the present bifunctional
electrocatalyst (Ni i_xFe X/NC) can be loaded onto carbon fiber papers (CFPs) or on nickel foams. With a larger loading of 2 mg cm 2 on nickel foam, Ni o.gFe 0.i/NC exhibited overpotentials of 270 mV and 85 mV for OER and HER to reach a current density of 10 mA cm 2, respectively. We integrated two Ni o.gFe 0.i/NC-NF electrodes into a symmetric two-electrode cell and studied the performance of this bifunctional catalyst for overall electrochemical water splitting. It can be seen from Figure 6 that a remarkable electrocatalytic activity was achieved with Ni o.gFe o.JNC-NF electrodes. The voltage needed to support a current density of 10 mA cm 2 was about 1.58 V determined from the reverse scan of the CV curve. Using more inert carbon fiber papers (CFPs) as substrate can get rid of the contribution of the intrinsic HER activity and derived OER activity of the commercial Ni foam. According to a preferred embodiment, with a larger loading of 2 mg cm 2, Ni o.gFe o.JNC exhibits overpotentials of 191 mV and 270 mV for HER and OER to reach a current density of 30 mA cm 2, respectively.
[0031] Furthermore, the performance of a cell containing integrated two identical Ni o.^Fe 0.i / NC-CFP electrodes for overall electrochemical water splitting has been studied. It can be seen from Figure 5 that the CFPs exhibit little activity for electrocatalytic water splitting while a remarkable electrocatalytic activity was achieved with Ni o.^Fe o.i/NC catalyst. For the symmetric two-electrode cell according to the present application, an overall voltage of 1.65 V is needed for maintaining a water splitting current density of 10 mA cm A
[0032] The achieved electrocatalytic performance of the present Ni i_xFe ^C catalyst has been proved to be comparable or even superior to some existing advanced asymmetric and symmetric bifunctional water splitting electrocatalysts.
[0033] By pyrolyzing a mixture of metal salts and urea, the present application provides a Ni i_xFe X/NC hybrid electrocatalyst which exhibits excellent performances to catalyze both HER and OER in alkaline electrolyte. And an efficient electrolyzer (cell) composed of two symmetric Ni o.gFe o.JNC loaded carbon fiber paper electrodes can achieve a current density of 10 mA cm 2 for overall water splitting at a voltage of 1.65 V, which is among the best performances for symmetric two-electrode water electrolyzer reported so far.
[0034] The present application will be described with following specific example, it should be acknowledged that other parameters within the scope of the present description can also be applied to this example.
[0035] Example 1
[0036] The metal salt precursors (nickel acetate tetrahydrate, Ni(CH 3COO) 2*4H 20 and Iron(III) chloride hexahydrate, FeCl 3·6Η 20) were completely dissolved into 2 ml ethanol with a molar ratio of 9: 1 while maintaining a total metal ion content of 0.5
mmol. Then, 2 g urea was added into the solution followed by a sonication treatment for 5 minutes. The obtained mixture was subsequently dried at 70 °C in an oil bath upon stirring for 6 hours to remove the ethanol. The dried mixture was thoroughly ground into homogeneous fine powders and then transferred into a ceramic crucible with an equipped cover. Next, the covered ceramic crucible was placed at the central of a tubular furnace and the temperature was raised from 25 °C to 550 °C at a programming rate of 0.5 °C/min and then maintained at 550 °C for 3 hours. After that, the temperature was further raised to 700 °C in 1 hour and maintained at that temperature for 2 hours and then cooled naturally. The whole heating process was proceeded under inert Ar/N 2 atmosphere with a gas flow rate of 50 seem.
[0037] Example 2
[0038] The metal salt precursors (nickel chloride(NiCl 2) and Iron(III) ferric nitrate, Fe(NO 3 ) 3) were completely dissolved into 4 ml of water with a molar ratio of 90: 10 while maintaining a total metal ion content of 0.3 mmol. Then, 4 g urea was added into the solution followed by a sonication treatment for 8 minutes. The obtained mixture was subsequently dried at 90 °C in an oil bath upon stirring for 9 hours to remove the water. The dried mixture was thoroughly ground into homogeneous fine powders and then transferred into a ceramic crucible with an equipped cover. Next, the covered ceramic crucible was placed at the central of a tubular furnace and the temperature was raised from 25 °C to 580 °C at a programming rate of 0.4 °C/min and then maintained at 580 °C for 3 hours. After that, the temperature was further raised to 750 °C in 1 hour and maintained at that temperature for 2 hours and then cooled naturally. The whole heating process was proceeded under inert N 2 atmosphere with a gas flow rate of 50 seem.
[0039] Example 3 Manufacture Of A Symmetric Two-Electrode Cell
[0040] A symmetric two-electrode water splitting cell containing two identical electrodes was made in this example, wherein these two electrodes were fabricated by the same method with the same catalyst. Firstly, 20 mg of catalyst obtained in Example 1 was dispersed in a mixture of 0.75 ml of water, 0.25 ml of ethanol and 100 μΐ of 5 wt% Nafion solution by at least 60 min sonication to form a homogeneous ink. After the sonication, 100 μΐ of the homogeneous ink was drop-dried onto carbon a fiber paper with a catalyst-covered-area of 1 cm 2 to achieve a catalyst-loading of 2 mg cm 2. Secondly, one electrode was connected to the working electrode of the electrochemical workstation and another electrode was connected to the counter electrode and reference electrode of the electrochemical workstation. Finally, the two electrodes were inserted into 1 M KOH (aq) electrolyte with all the active areas being immersed.
[0041] The present application may be embodied in other forms without departing from the spirit or novel characteristics thereof. The embodiments disclosed in this application
are to be considered in all respects as illustrative and not limitative.
Claims
Claims
A method for preparing a bifunctional electrocatalyst comprising:
(a) a nickel source compound and a ferric iron source compound being added into a solvent, wherein the molar ratio of the nickel ion to the iron ion in the obtained solution is in the range of from 93:7 to 85: 15, and the total metal ion content in the obtained solution is in the range of from 0.3 to 0.5 mmol;
(b) a urea being added into the obtained solution to give a mixture;
(c) the mixture obtained in step (b) being dried;
(d) the dried mixture being ground into homogeneous powders and then subjected to a heating process under inert atmosphere.
The method of claim 1, wherein in step (b), the urea is added in such an amount that the concentration of the urea in the solution is in the range of from 1 to 3 g/mL.
The method of claim 1, wherein in step (c), the mixture is dried at 60
°C to 90 °C in an oil bath upon stirring for 5 to 10 hours.
The method of claim 1, wherein in step (d), the heating process comprises:
the temperature is raised to a temperature of 520 °C to 580 °C at a programming rate of from 0.4 to 0.6 °C/min and maintained at that temperature;
the temperature is further raised to 650 °C to 750 °C and maintained at that temperature.
The method of claim 1, wherein in step (b), after adding urea, the solution is subjected to ultrasonic treatment for 4 to 8 minutes.
The method of claim 1, wherein the nickel source compound in step (a) is selected from the group consisting of nickel acetate, nickel chloride, nickel nitrate, nickel sulfate and the combination thereof.
The method of claim 1, wherein the ferric iron source compound in step
(a) is selected from the group consisting of ferric chloride, ferric nitrate, ferric sulfate and the combination thereof.
A bifunctional electrocatalyst made by a method comprising:
(a) a nickel source compound and a ferric iron source compound being added into a solvent, wherein the molar ratio of the nickel ion to the iron ion in the obtained solution is in the range of from 93:7 to 85: 15, and the total metal ion content in the obtained solution is in the range of from 0.3 to 0.5 mmol;
(b) a urea being added into the obtained solution to give a mixture;
(c) the mixture obtained in step (b) being dried;
(d) the dried mixture being ground into homogeneous powders and then subjected to a heating process under inert atmosphere to give a product.
[Claim 9] A water splitting cell comprising two electrodes, each of the electrodes comprising the bifunctional electrocatalyst of claim 8.
[Claim 10] water splitting cell of claim 9, wherein the bifunctional electrocatalyst is loaded onto a carbon fiber paper or nickel foam.
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