EP2616173A1 - Process for producing carbon-comprising support - Google Patents
Process for producing carbon-comprising supportInfo
- Publication number
- EP2616173A1 EP2616173A1 EP11824677.6A EP11824677A EP2616173A1 EP 2616173 A1 EP2616173 A1 EP 2616173A1 EP 11824677 A EP11824677 A EP 11824677A EP 2616173 A1 EP2616173 A1 EP 2616173A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- carbon
- metal
- support
- process according
- nitrogen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
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- 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
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
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- 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
- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/18—Carbon
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- 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
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
- H01M4/921—Alloys or mixtures with metallic elements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
- H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M8/1007—Fuel cells with solid electrolytes with both reactants being gaseous or vaporised
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- 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
- Y02E60/50—Fuel cells
Definitions
- the invention relates to a process for producing a material comprising carbide-, nitride-, carbonitride-, carboxide-, oxynitride- or carboxynitride-functionalized carbon, as is used, for example, as support for catalytically active material in catalysts.
- the invention further relates to a use of the material comprising carbide-, nitride-, carbonitride-, carboxide-, oxynitride- or carboxynitride-functionalized carbon.
- Carbon-comprising supports are used, for example, as supports for catalytically active material for heterogeneous catalysts. In a specific example, these supports are used for electrochemical reactions. Carbon supports (conductive carbon blacks) are usually used for electrochemical applications since they have a sufficiently good electrical conductivity. Conductive carbon blacks usually have a BET surface area in the range from 100 to 1500 m 2 /g and therefore make it possible to apply catalytically active material in finely divided form and also to produce porous electrode layers. The latter is important to ensure wetting with the electrolyte and also to be able to transport starting materials and products.
- conductive carbon blacks as supports is that the carbon can be oxidized to C0 2 at high potentials and/or temperatures and the electrode structure or support structure is therefore destroyed. This irreversibly impairs the performance and the catalytically active material can become detached from the support, as a result of which it is no longer available for the electrochemical reaction. This is described, for example, in Mayrhofer et al., J. Power Sources, 185 (2008), 734-739.
- Transition metal carbides or nitrides are known for their thermal and chemical resistance as bulk materials and are usually also electrically conductive. Some carbides and nitrides also have catalytic properties. For example, tungsten carbide has been tested as platinum-free anode catalyst in fuel cells, but the performance is far below that of comparable platinum catalysts. Thus, for example, Yang and Wang, Applied Physics Letter, 86 (2005), Art. 224104, describe the production and measurement of a cell having an electrode having 0.48 mg of WC/cm 2 on the anode side and an electrode having 0.3 mg of Pt/cm 2 on the cathode side at a temperature of 80°C. Hydrogen was supplied to the anode side and air was supplied to the cathode side.
- the power at 0.2 A/cm 2 was about 1 10 mW/cm 2 .
- the power of an electrode having 0.05 mg of Pt/cm 2 (i.e. 1/10 loading) on the anode is about 160 mW/cm 2 under otherwise identical conditions.
- the differences become particularly clear at high power densities of more than 1 A/cm 2 .
- the WC anode barely achieves 1 A/cm 2 , while the Pt anode still displays a power of more than 750 mW/cm 2 at 1 .5 A/cm 2 .
- the carbides or nitrides have to be very finely divided, i.e. have an average diameter of less than 10 nm. This can result in oxidation reactions on the particle surface, which significantly reduces the chemical and/or electrochemical stability. Transition metal carbides and nitrides usually have a very low BET surface area of less than 5 m 2 /g, which restricts their use as supports for catalytically active metals since the latter cannot be applied in sufficiently finely divided form.
- WO 2006/002228 describes a process in which tungsten carbide or molybdenum carbide is used for modifying the surface of carbon supports. This is said to increase the stability of the overall system of carbide and carbon.
- the method comprises reduction of the metal on the support, e.g. ammonium tungstate, by means of NaBH 4 and subsequent heat treatment at from 900 to 1000°C to form the carbide.
- decomposition of an organometallic precursor under nitrogen up to 1 100°C is also described in the case of Ti.
- Disadvantages of the method are the limitation to a few transition metal carbides, in particular tungsten and molybdenum, the multistage nature of the synthesis, the necessity of high temperatures of over 1000°C for preparing the carbides since at low temperatures a large proportion of oxides remains and/or the deposition does not occur quantitatively. At the relatively high temperatures required, relatively large nanoparticles having an average diameter of more than 50 nm are also obtained.
- the modification can be in the form of a closed or porous layer or as a partly covered surface of the carbon-comprising support or in the form of individual particles.
- the carbide, nitride, carbonitride, oxynitride, carboxide or carboxynitride particles produced by the process of the invention can also be present in a plurality of layers which partly or completely cover the surface of the carbon-comprising support. In the following, reference will be made to a layer in the interests of simplicity, with all abovementioned cases being encompassed.
- the modification by means of the process of the invention leads to an increase in the corrosion stability of the support.
- the carbon is bound to the surface of the support by the metal carbides, metal nitrides, metal oxycarbides, metal oxynitrides, metal carboxynitrides and/or metal carbonitrides produced in step (c) and no longer undergoes any reaction with the oxygen surrounding the support. In this way, the corrosion of the carbon-comprising support can be reduced or even avoided completely.
- step (a) the reaction proceeds quantitatively even at temperatures lower than in the prior art and can be applied to various transition metals. Due to the lower temperature, the carbides, nitrides, carbonitrides, carboxides, oxynitrides and/or carboxynitrides are more finely divided, have a higher BET surface area and are more catalytically active.
- the carbon-supported carbides, nitrides, carbonitrides, carboxides, oxynitrides and/or carboxynitrides produced according to the invention are more sintering and oxidation stable than unsupported compounds of this type.
- metal compounds preferably metal salts, and mixtures thereof with the carbon- and/or nitrogen-comprising organic substance, optionally with use of a dispersion medium, results in formation of reactive precursor substances, which makes a more rapid reaction possible.
- a further advantage of the use of the carbon-comprising support for producing catalysts is that discharge of catalytically active material can be prevented by the layer comprising metal carbide, metal nitride, metal oxycarbide, metal oxynitride, metal carboxynitride and/or metal carbonitride, so that the catalytic activity of the catalyst produced is not reduced during operation by discharge of catalytically active material.
- the fact that the catalytically active material does not become detached from the support is also related to the fact that the particles of the catalytically active material adhere better to the support as a result of the layer comprising metal carbide, metal nitride, metal oxycarbide, metal oxynitride, metal carboxynitride and/or metal carbonitride. Due to the catalyst particles barely sintering and not becoming detached from the support, the catalytic surface of catalyst particles which have been produced using the carbon-comprising support according to the invention remains stable over a long period of time and the performance, for example of an electrode, for which the catalyst is used, remains high. For electrochemical applications, catalytically active materials are applied to an electrically conductive support or mixed with an electrically conductive support.
- Carbon supports used normally have a high specific surface area (e.g. BET surface area) which makes fine dispersion of the particles of catalytically active material, which are usually present as nanoparticles, possible.
- BET surface area is generally above 100 m 2 /g and can be up to 1500 m 2 /g.
- these carbon supports for example Vulcan XC72® having a BET surface area of about 250 m 2 /g or Ketjen Black EC 300J® having a BET surface area of about 850 m 2 /g, have the disadvantage that they corrode very quickly when, for example, high overpotentials occur. In the case of carbons having a relatively high content of graphitic material, corrosion is delayed.
- the corrosion of carbon-comprising supports can, for example, be compared by subjecting them to potentials above 1 V in the presence of water, for example in a humid stream of nitrogen or in an aqueous electrolyte solution, optionally at elevated temperature.
- the carbon is converted into carbon dioxide, and the carbon dioxide formed can be measured.
- the higher the temperature and the higher the potential the more rapidly does the carbon- comprising support corrode.
- about 60% of the carbon is corroded away by oxidation to carbon dioxide after 15 hours at a temperature of 180°C in the case of Vulcan XC72® at potentials of 1.1 V.
- the surface treatment provides the carbon with a metal carbide layer.
- metal for producing the metal carbide layer use is made of, for example, titanium, tungsten or molybdenum.
- a metal salt solution is firstly applied to the surface of the carbon-comprising support, and this metal salt is then reduced to the metal.
- the support is subsequently heated in order to convert the metal into metal carbide. Heating to form the metal carbide layer is carried out at a temperature in the range from 850 to 1 100°C.
- the carbide layer produced as described in WO-A 2006/002228 is incomplete, i.e. it comprises largely oxidic material which is reacted only at higher temperatures, for example at 1500°C.
- the process of the invention modifies the surface of the carbon-comprising support. This modification leads to an increase in the corrosion stability of the support.
- the metal carbides, metal nitrides, metal oxynitrides, metal carboxides, metal carboxynitrides and/or metal carbonitrides produced in step (c) the carbon is bound to the surface of the support and no longer undergoes any reaction with the oxygen surrounding the support. In this way, corrosion of the carbon-comprising support can be reduced and even avoided completely.
- the process of the invention makes it possible to produce a larger number of compounds, for example various metal carbides or metal nitrides and also mixed phases derived therefrom.
- M represents one or more transition metals, preferably one or two transition metals, in particular of the IVth period and groups 4, 5 and 6 of the Periodic Table of the Elements.
- M is preferably selected from among titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, hafnium, tantalum and tungsten.
- the carbide, nitride, carbonitride, carboxide, oxynitride or carboxynitride comprising one or more metals produced on the surface of the carbon- comprising support as a result of the use of the carbon- and nitrogen-comprising organic substance and the at least one metal compound is additionally doped with a further metal and can be described by the general formula
- a 0.05 to 20, preferably from 0.3 to 10,
- M one or more transition metals, preferably one or two transition metals, in particular of the IVth period and groups 4, 5 and 6 of the Periodic Table, preferably selected from among Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W and
- metal D one or more metals, preferably one or two metals, particularly preferably one metal, in particular of groups 1 and 2 of the Periodic Table, preferably selected from among Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba; particularly preferably Li, Na, K and Ca.
- the metal compound used for producing the catalyst according to the invention is preferably selected from among metal complexes or metal salts, for example halides, oxides, hydroxides and alkoxides of the transition metals. When halides are used, preference is given to chlorides.
- metal compounds preferably metal salts.
- metal compounds Preference is given to the metal compounds in each case comprising different metals but with the anion of the metal compounds being the same.
- metal salts which comprise not only different metals but also different anions.
- Particularly preferred metal salts used for producing the catalyst according to the invention are chlorides, for example tungsten chloride, molybdenum chloride, vanadium chloride, iron chloride, manganese chloride, chromium chloride, and also oxidic compounds, in particular ammonium heptatungstate, ammonium hexamolybdate, vanadium oxide, iron oxide.
- Alkoxides for example titanium isopropoxide or zirconium butoxide, are also suitable.
- Suitable carbon-comprising supports which can be used for producing the surface-modified carbon-comprising support are, for example, conductive carbon blacks, graphites, expanded graphites, graphenes or carbon nanotubes.
- Conductive carbon blacks are particularly preferably used as carbon-comprising supports, with preference being given to conductive carbon blacks having a BET surface area in the range from 30 to 1000 m 2 /g. Particular preference is given to conductive carbon blacks having a BET surface area in the range from 30 to 250 m 2 /g.
- As conductive carbon black it is possible to use any carbon black which is known to those skilled in the art and has an appropriate BET surface area.
- Carbon blacks which are normally used are, for example, furnace black, flame black or acetylene black.
- Preferred carbon blacks which can be used as carbon-comprising supports are, for example, SKW Carbon having a BET surface area of 72 m 2 /g, DenkaBlack® having a BET surface area of 53 m 2 /g or XMB206® or AT325® from Evonik Degussa GmbH having a BET surface area of about 30 m 2 /g.
- Carbon blacks having a higher BET surface area for example Ketjen Black® having a BET surface area of 850 m 2 /g or Vulcan XC72® having a BET surface area of 253 m 2 /g, are likewise possible.
- the abovementioned low surface area carbon blacks are particularly preferred.
- the carbon-comprising support is mixed with at least one metal compound, a carbon- and/or nitrogen-comprising organic substance and optionally a solvent in a first step a).
- the amount of carbon- and nitrogen-comprising organic substance is preferably selected so that the molar ratio of metal compound or the sum of all metal compounds to the carbon- and nitrogen-comprising organic substance is in the range from 1 : 1 to 1 :20, in particular in the range from 1 :5 to 1 : 10.
- a solvent is preferably also added in order to obtain a paste-like composition.
- Suitable solvents are, for example, water, in particular when using chlorides which are not sensitive to hydrolysis, for example iron chloride, or when using oxides, for example tungstate or molybdate, or organic solvents, in particular alcohols, diols, for example glycols, or polyols, ketones, ethers when using hydrolysis-sensitive chlorides such as titanium tetrachloride, molybdenum chloride, tungsten chloride and mixtures thereof. Mixtures of two or more different solvents can also be used. When an alcohol is used, ethanol is particularly preferred.
- the mixture produced in step a), which has optionally been dried in a second step b), is heated in the third step c). Heating is carried out at a temperature in the range from 500 to 1200°C, preferably in the range from 700 to 900°C.
- the temperature to which the mixture is heated is, in particular, dependent on the metal compound and the carbon- and nitrogen-comprising organic substance used.
- Heating of the mixture can, for example, be carried out in a furnace.
- a suitable furnace is, for example, a rotary bulb furnace.
- a rotary tube furnace can also be used, either in batch operation or in continuous operation .
- the use of a plasma or the use of microwave radiation is also possible for heating.
- the mixture produced in step a) can be sprayed and dried in a spray dryer and, in a step following the spray dryer, to heat the spray-dried powder to a temperature in the range from 500 to 1200°C.
- the suspension to be sprayed usually has a solids content in the range from 1 to 30% by weight, preferably from 5 to 15% by weight.
- This suspension is generally sprayed at an inlet temperature in the range from 150°C to 350°C; the suspension cools very quickly and the actual drying step occurs at a starting temperature in the range of usually from 80 to 150°C.
- the use of a spray dryer for removing the solvent is preferred.
- all steps are carried out in a paddle dryer.
- step b) In order to prevent oxidation of the carbon-comprising support, preference is given to carrying out the heating in step b) in an inert atmosphere.
- a suitable inert atmosphere is, for example, a nitrogen atmosphere.
- a noble gas atmosphere for example an argon atmosphere, is also conceivable.
- the heating for producing carbides or nitrides can also be carried out in a reactive atmosphere.
- the atmosphere can comprise hydrocarbons, for example methane or ethane, NH 3 , ethylamine, H 2 or mixtures thereof.
- a mixture with nitrogen or other inert gases is also possible here.
- preference is given to a nitrogen atmosphere.
- the process of the invention makes it possible to produce a surface-modified carbon- comprising support which, based on the total mass of the carbon-comprising support, comprises from 1 to 80% by weight of metal.
- the proportion of metal based on the total mass of the carbon-comprising support is at least 10% by weight, preferably about 20% by weight.
- the proportion of metal based on the amount of carbon is preferably not more than 50% by weight.
- higher loadings are also possible, but usually not more than 80% by weight.
- the use of the carbon- and nitrogen-comprising organic substance makes it possible for the modification of the surface to be carried out by carbidization or nitridization at relatively low temperatures.
- a temperature of 800°C is sufficient for producing a tungsten carbide surface when using urea as carbon- and nitrogen-comprising organic substance, while a temperature of 1500°C is required when the tungsten carbide is to be produced using the carbon of the carbon-comprising support.
- carbon- and nitrogen-comprising organic substance also leads to a more rapid reaction, so that compounds which can otherwise not be used are also possible.
- surface modification by means of nitrides, carbides and/or carbonitrides and also oxynitrides of titanium, hafnium or zirconium is also possible.
- carbides, nitrides or mixed phases can be adjusted by adjusting the ratio of metal compound to the carbon- and nitrogen-comprising organic substance.
- the heating rate and final temperature, the temperature ramp, and also the atmosphere used are critical in determining whether carbides, nitrides or mixed phases (carbonitrides, oxynitrides, carboxynitrides, oxycarbides) are obtained.
- carbides, nitrides or mixed phases carbonitrides, oxynitrides, carboxynitrides, oxycarbides
- molybdenum starting from molybdenum(V) chloride and 5 molar equivalents of urea
- crystalline MoC is formed at 600°C
- Mo 2 C is formed at higher temperatures (800°C).
- the phase composition can be shifted from Mo 2 C to MoC by increasing the proportion of urea (or in general terms the molar excess of the carbon- and nitrogen-comprising substance).
- urea or in general terms the molar excess of the carbon- and nitrogen-comprising substance.
- pure supported vanadium carbide (VC) is obtained, while in the production of unsupported nanoparticles vanadium carbonitride is formed, with the proportion of carbide being higher when an additional carbon source is used than when only the chloride and urea are used (cf. examples 4 and 5 below).
- the modification according to the invention of the surface of the carbon support by means of transition metal carbides or nitrides (or carbonitrides) increases the corrosion resistance of the support. As described above, this can be tested in an accelerated manner by application of an electric potential at elevated temperatures. Here, the amount of carbon removed is calculated from the amount of C0 2 formed.
- noble metals in particular metals of the platinum group, for example platinum, palladium, ruthenium, rhodium or iridium or alloys of the metals of the platinum group, and also of the copper group, for example copper, silver or gold or alloys thereof.
- metals of the platinum or copper group and also transition metals such as nickel, cobalt, vanadium, iron, titanium, chromium, etc., in each case individually or in combination with one or more further metals, can be used as alloy component.
- Catalysts produced using the support according to the invention can be used, for example, in fuel cells.
- the catalysts can be used both on the anode side and on the cathode side. Particularly on the cathode side, it is necessary to use active cathode catalysts which are also corrosion-stable, with the stability being determined both by the stability of the support itself and by the interaction of catalyst particles with the support surface.
- active cathode catalysts use is generally made of alloy catalysts.
- the carbon-comprising support is, for example, also suitable, owing to its improved corrosion stability, as corrosion-resistant filler, in particular as filler in electrode layers, as support for catalytically active material, for example noble metals such as platinum, palladium or silver, transition metals such as nickel, cobalt, vanadium, iron or titanium, alloys of these metals or oxides of one or more of these metals, for use in metal-air batteries or electrolysis cells, for example for the electrolysis of water.
- noble metals such as platinum, palladium or silver
- transition metals such as nickel, cobalt, vanadium, iron or titanium
- alloys of these metals or oxides of one or more of these metals for use in metal-air batteries or electrolysis cells, for example for the electrolysis of water.
- the carbon-comprising support produced according to the invention is particularly preferably used for electrocatalysts in which a noble metal-comprising catalytically active material is applied to the carbon-comprising support produced according to the invention.
- the carbon-comprising support is used for producing a catalyst, in particular an electrocatalyst as is used, for example in fuel cells
- the surface-modified carbon-comprising support is cooled after formation of the surface modification and the catalytically active material is applied.
- Application of the catalytically active material can be effected by any method known to those skilled in the art.
- the catalytically active material can be applied by deposition from solution.
- metal compounds comprising the catalytically active material in a solvent.
- the metal can be bound covalently, ionically or by complexation.
- the metal it is also possible for the metal to be deposited reductively, as precursor or under alkaline conditions by precipitation of the corresponding hydroxide.
- Further possibilities for depositing the catalytically active material are impregnation using a solution comprising the catalytically active material (incipient wetness), chemical vapor deposition (CVD) or physical vapor deposition (PVD) and all further processes known to those skilled in the art by means of which the catalytically active material can be deposited.
- CVD chemical vapor deposition
- PVD physical vapor deposition
- Suitable catalytically active materials are, for example, metals of the platinum group (Pt, Pd, Ru, Rh, Ir) or the copper group (Cu, Ag, Au), transition metals (Ni, Co, V, Fe, Ti, Cr), alloys of these metals or an alloy comprising at least one metal of the platinum group.
- the catalytically active material is preferably selected from among platinum and palladium and alloys of these metals and alloys comprising at least one of these metals.
- the catalytically active material is very particularly preferably platinum or a platinum-comprising alloy.
- Suitable alloying metals are, for example, nickel, cobalt, iron, vanadium, titanium, ruthenium and copper, in particular nickel and cobalt.
- Suitable alloys comprising at least one metal of the platinum group are, for example, selected from the group consisting of PtNi, PtFe, PtV, PtCr, PtTi, PtCu, PtPd, PtRu, PdNi, PdFe, PdCr, PdTi, PdCu and PdRu.
- Particular preference is given to a platinum-nickel alloy, a platinum-iron alloy or a platinum-cobalt alloy, or a ternary alloy comprising PtNi, PtCo or PtFe.
- the proportion of the metal of the platinum group in the alloy is preferably in the range from 25 to 85 atom% and preferably in the range from 40 to 80 atom%, more preferably in the range from 50 to 80 atom% and in particular in the range from 60 to 80 atom%.
- alloys which comprise more than two different metals for example ternary alloy systems.
- the catalytically active material is applied by precipitation
- a reductive precipitation for example of platinum from platinum nitrate in ethanol
- decomposition and reduction in H 2 /N 2 for example of platinum acetylacetonate mixed with the surface-modified carbon- comprising support
- reductive precipitation is effected by means of formate, in particular ammonium formate.
- the catalytically active material can be applied directly during carbidization/nitridization, for example in the case of transition metals such as cobalt or nickel where metallic cobalt or nickel rather than cobalt carbide or nitride or nickel carbide or nitride is formed in a pure inert atmosphere (e.g. N 2 at 800°C).
- transition metals such as cobalt or nickel where metallic cobalt or nickel rather than cobalt carbide or nitride or nickel carbide or nitride is formed in a pure inert atmosphere (e.g. N 2 at 800°C).
- Corrosion of the carbon-comprising support can lead to detachment of the particles from the catalytically active material and thus to a decrease in performance of the system.
- the catalyst particles can also sinter, which leads to the catalytically active surface area decreasing significantly, likewise resulting in a decrease in performance.
- a further advantage of the use of the carbon-comprising support for producing catalysts is that discharge of catalytically active material can be prevented by the layer comprising metal carbide, metal nitride and/or metal carbonitride, so that the catalytic activity of the catalyst produced is not reduced by catalytically active material which is discharged.
- the fact that the catalytically active material does not become detached from the support is related to the fact that the particles of the catalytically active material adhere better to the support due to the layer comprising metal carbide, metal nitride and/or metal carbonitride.
- the catalytic surface area of the catalyst particles produced using the carbon- comprising support according to the invention remains stable over a long period of time and the performance, for example of an electrode for which the catalyst is used, remains high.
- these catalysts can be used, for example, to produce electrodes which are used in electrochemical cells, for example batteries, fuel cells or electrolysis cells.
- electrochemical cells for example batteries, fuel cells or electrolysis cells.
- a specific example is the use of the electrodes in fuel cells, for example proton-exchange membrane fuel cells (PEMFCs), direct methanol fuel cells (DMFCs), direct ethanol fuel cells (DEFCs), etc.
- PEMFCs proton-exchange membrane fuel cells
- DMFCs direct methanol fuel cells
- DEFCs direct ethanol fuel cells
- Fields of application of such fuel cells are local energy generation, for example for household fuel cell systems, and also mobile applications, for example in motor vehicles. Particular preference is given to use in PEMFCs.
- the carbide-, nitride-, carbonitride-, carboxide-, oxynitride- or carboxynitride-modified carbon-comprising material can be used in electrodes, in particular as corrosion-resistant filler in electrodes.
- Such electrodes which usually but not necessarily comprise a further catalytically or electrochemically active material, for example metal oxides, transition metals, etc., optionally supported on another material, can again be used in various electrochemical cells, for example batteries, electrolysis cells, fuel cells. Particular preference is given to use in batteries and among these especially in metal-air batteries.
- carbide-, nitride-, carbonitride-, carboxide-, oxynitride- or carboxynitride- modified carbon-comprising materials can themselves be used as catalysts.
- Transition metal carbides in particular tungsten carbide, preferably supported, optionally comprising further elements, can be used as anode catalyst in fuel cells (PEMFC, DMFC, DEFC, etc.).
- Further catalytic applications are use as catalysts for the preparation of olefins by the Fischer-Tropsch process or as cathode catalyst (both for the oxygen evolution reaction (OER) and, particularly preferably, for the oxygen reduction reaction (ORR)) in metal-air batteries, etc. Examples
- Example 1 Surface modification of carbon black by means of tungsten carbide from tungsten chloride using urea
- Example 2 Surface modification of carbon black by means of tungsten carbide from ammonium heptatungstate using urea
- the BET surface area was 26 m 2 /g.
- the carbon loss (calculated on the basis of the carbon present) is 2% after one hour, 8% after 5 hours and 21 % after 15 hours at a potential of 1 .2 V and a temperature of 180°C. Based on the total support, the values are even lower by a factor of 2.
- the carbon loss of DenkaBlack® was 7% after only one hour, 33% after 5 hours and 73% after 15 hours, likewise at a potential of 1 .2 V and a temperature of 180°C.
- Example 3 Surface modification of carbon black by means of vanadium carbide from vanadium chloride using urea 3.9 g of VCI 3 were dissolved in 50 ml of ethanol. A solution of 5.4 g of urea in 50 ml of ethanol was added thereto and the mixture was stirred for 30 minutes. 3.5 g of carbon black (AT325 from Evonik Degussa GmbH) and also a further 50 ml of ethanol were subsequently added and the mixture was stirred for a further 30 minutes.
- the mixture was concentrated on a rotary evaporator until a viscous mass had been obtained, and this mass was then heated in a tube furnace firstly at 100°C for 2 hours under a nitrogen atmosphere and subsequently at a temperature of 850°C for 6 hours, likewise under a nitrogen atmosphere.
- the vanadium loading of the carbon-comprising support produced in this way was 21 %, and the crystallite size of the carbide phase (VC) was 53 nm.
- Example 4 Surface-modification of carbon black by means of vanadium carbide from vanadium oxide using urea
- Example 5 Preparation of vanadium carbide (unsupported) from vanadium chloride using urea
- VCI 3 12.5 g of VCI 3 , 23.8 g of urea and 0.9 g of Vulcan XC72 carbon black (Cabot Technologies) as additional carbon source were added to 100 ml of ethanol.
- the paste-like mixture was mixed and made inert while flushing with nitrogen (10 standard l/h) in a rotary bulb furnace for 30 minutes.
- the mixture was then, still under a stream of nitrogen, heated to 80°C at a heating rate of 2 K/min, then to 300°C at a heating rate of 1 K/min and finally to 800°C at a heating rate of 3 K/min.
- the temperature was maintained at 800°C under a nitrogen atmosphere for 6 hours before the product was slowly cooled to room temperature.
- a vanadium carbonitride having a vanadium loading of 45% by weight; the crystallite size was 49 nm.
- the ratio of carbide to nitride was 1 .6:1.
- a vanadium carbonitride is likewise formed but has a higher proportion of nitride.
- Example 6 Mixed carbide - Fe2.1 Mno.9C1
- Example 7 Mixed carbide with metal doping - K 0 .o23(Fe 2.4 Mn 0 .6)Ci
- Example 8 Carbonitride - TaCN 9.3 g of TaCI 5 , 15.6 g of urea and 0.6 g of Vulcan XC72 carbon black (Cabot Technologies) as additional carbon source were introduced into 100 ml of ethanol.
- the paste-like mixture was mixed and made inert while flushing with nitrogen (10 standard l/h) in a rotary bulb furnace for 30 minutes.
- the mixture was then, still under a stream of nitrogen, heated to 80°C at a heating rate of 2 K/min, subsequently to 300°C at a heating rate of 2 K/min and finally heated to 800°C at a heating rate of 3 K/min.
- the temperature was maintained at 800°C, still under a nitrogen atmosphere, for 6 hours, before the mixture was slowly cooled to room temperature.
- the synthesis gave a tantalum carbonitride having a tantalum loading of 75% by weight.
- the ratio of carbide to nitride was 1.8:1.
- Example 10 Surface modification of carbon black by means of molybdenum-tungsten carbide from the corresponding chlorides and urea
- tungsten(VI) hexachloride, 2.3 g molybdenum(V) pentachloride and 4.9 g of urea are slowly dissolved in 50 ml of ethanol, and 2.5 g of Vulcan XC72 (Cabot Technologies) are subsequently added.
- the mixture is mixed and made inert under nitrogen (10 standard l/h) in a rotary bulb furnace for 30 minutes.
- the calcination under a nitrogen atmosphere (10 standard l/h of nitrogen) is carried out by heating to 300°C at 2 K/min, then to 800°C at 3 K/min and holding 800°C for 6 hours.
- the product is subsequently cooled under nitrogen.
- Example 1 1 Surface modification of carbon black by means of molybdenum-tungsten carbide from the corresponding oxides (tungstate and molybdate) and urea 2.1 g of ammonium tungstate, 1.5 g of ammonium molybdate and 4.9 g of urea are dissolved in 100 ml of water, and 2.5 g of Vulcan XC72 (Cabot Technologies) are subsequently added and the suspension is homogenized by means of an Ultra-Turrax® for 15 minutes. The mixture is subsequently concentrated at 40-50°C and 40 mbar on a rotary evaporator and calcined under nitrogen (40 standard l/h) in a tube furnace.
- the furnace is firstly made inert at room temperature for 30 minutes, then heated to 100°C at a heating rate of 1 K/min, then to 850°C at a heating rate of 3 K/min and the temperature is maintained at 850°C for 6 hours.
- the product is subsequently cooled under nitrogen.
- Example 12 Production of a tungsten carbide-modified carbon support by means of spray drying and calcination
- a suspension having a solids content of about 13% by weight of ammonium tungstate (32.5 g), melamine (80.5 g) and DenkaBlack® (25 g) in 1 I of water was produced and homogenized by means of an Ultra-Turrax® for 30 minutes.
- the mixture was processed in a spray dryer at an inlet temperature of 250°C and an outlet temperature of 150°C to give a powder.
- the spray-dried powder obtained in this way was calcined under nitrogen (40 standard l/h) in a tube furnace.
- the furnace was firstly made inert at room temperature for 30 minutes, then heated to 100°C at a heating rate of 1 K/min, then heated to 850°C at a heating rate of 3 K min and the temperature was maintained at 850°C for 6 hours.
- the product was subsequently cooled under nitrogen.
- Example 13 Surface modification of a carbon black support and simultaneous application of the catalytic active material from cobalt chloride and urea
- This method can also be carried out analogously using ethylenediamine (EDA, example 12-EDA) or melamine. It is also possible to use cobalt acetate, cobalt hydroxide, cobalt nitrate or cobalt sulfate in place of cobalt chloride. In all cases, a nitrogen-modified carbon support with metallic cobalt (crystallite sizes in the range from 10 to 60 nm, depending on the maximum temperature - at 700°C in the range from 10 to 25 nm) is formed. In these process alternatives, the use of EDA or melamine in a molar excess of from 5 to 10 and the use of cobalt chloride or cobalt hydroxide is particularly preferred.
- Example 14 Production of an electrocatalyst on a surface-modified carbon-comprising support as per example 1 4.4 g of the surface-modified carbon-comprising support produced in example 1 were dispersed in 500 ml of water and homogenized by means of an Ultra Turrax® at 8000 rpm for 15 minutes. 3.28 g of platinum nitrate were dissolved in 100 ml of water and slowly added to the homogenized dispersion comprising the carbon-comprising support. 355 ml of water and 285 ml of ethanol were subsequently added to the mixture and the mixture was heated under reflux for 6 hours.
- Example 15 Production of an electrocatalyst on a surface-modified carbon-comprising support as per example 3
- Comparative production examples Comparative example 1 Surface modification of carbon black by means of tungsten carbide without C/N-comprising organic substance at 850°C
- tungsten carbide was formed even without use of urea or another C/N source, but this has larger crystallites than that in example 1 .
- Comparative example 2 Reworking of the preparation from WO 2006/002228 - surface modification of carbon black by means of tungsten carbide
- the preparation was carried out by a method analogous to that described in WO 2006/002228.
- 8 g of Vulcan XC72 were suspended in 1000 g of H 2 0 and homogenized by means of an Ultra-Turrax at 8000 rpm for 30 minutes.
- 3.2 g of ammonium tungstate were dissolved in 200 ml of H 2 0 and slowly added to the suspension.
- a further 750 ml of H 2 0 were added to the mixture and the mixture was heated under reflux for 4 hours.
- 30.4 g of NaBH 4 were subsequently dissolved in 100 ml of water and added dropwise over a period of one hour with vigorous gas evolution and the mixture was heated under reflux for a further 20 minutes.
- Comparative example 4 Production of an electrocatalyst on unmodified carbon black
- Comparative example 5 Production of an electrocatalyst on tungsten carbide nanoparticles 4 g of nanoparticulate tungsten carbide from SDC Materials, particle size 6 nm, were dispersed in 50 ml of water and homogenized by means of an Ultra Turrax ® at 8000 rpm for 15 minutes. 5.13 g of platinum nitrate were dissolved in 100 ml of water and slowly added to the carbon black dispersion. 200 ml of water and 900 ml of ethanol were subsequently added to the mixture and the mixture was heated under reflux for 6 hours. After cooling overnight, the suspension was filtered and the solid was washed free of nitrate with 2 I of hot water and dried under reduced pressure. The platinum loading was 42% and the average platinum crystallite size in the XRD pattern was 3.0 nm.
- Comparative example 6 Production of an Ag-based electrocatalyst on unmodified carbon black 24 g of carbon black support (SKW Acetylene Black) were dispersed in 2 I of water and homogenized by means of an Ultra-Turrax (8000 rpm) for 15 minutes. 9.65 g of silver nitrate were dissolved in 300 ml of water and added to the carbon suspension. The mixture was introduced into a nitrogen-flushed stirred apparatus and flushed with nitrogen for a further 15 minutes before a sodium borohydride solution (10.5 g of NaBH 4 in 200 ml of water) was added dropwise over a period of about 5 minutes. The mixture was stirred at room temperature for another 2 hours.
- SKW Acetylene Black carbon black support
- the catalyst was filtered off, washed free of nitrate with 1 .5 I of hot water and dried.
- the silver loading was 20.1 % by weight and the average crystallite size in the XRD pattern was 40 nm.
- the decrease in performance of electrocatalysts can be estimated by means of accelerated aging tests. For example, measurements by means of a rotating disk electrode (RDE) can be carried out for this purpose.
- RDE rotating disk electrode
- a possible test procedure can be, for example, firstly to determine the catalytic activity in respect of the reduction of oxygen (cathode reaction) of the catalyst, then to carry out potential cycles and finally measure the final activity.
- the RDE measurements to determine the activity are carried out in oxygen-saturated 1 M HCIO4.
- the catalyst to be examined is applied to a glassy carbon electrode having an area of 1 cm 2 .
- the loading is about 15-20 ⁇ g of active composition (e.g. platinum).
- a platinum sheet serves as counter electrode.
- the reference electrode is a mercury-mercury sulfate electrode. All potentials are reported relative to the reversible hydrogen electrode (RHE). Five cycles between 50 and 950 mV (RHE) are carried out at a speed of 5 mV/s and a speed of rotation of the disk of 1600 rpm. The evaluation to determine the activity in respect of the reduction of oxygen is carried out at 900 mV: the ratio of the product and the difference between limiting diffusion current and kinetic current at 900 mV is formed and normalized to the amount of platinum. This gives a mass-specific activity. Pure supported platinum catalysts typically have activities for the reduction of oxygen in the range from 100 to 120 mA/mg of Pt.
- Example 17 Comparison of the activity and stability of electrocatalysts in an alkaline medium Apart from applications of electrocatalysts in polymer electrolyte fuel cells, which require a high activity and selectivity in an acidic medium, there are also applications in an alkaline medium. These include, for example, metal-air batteries.
- the cathode reaction is the oxygen reduction reaction and the stability of the catalyst at high potentials has to meet demanding requirements.
- RDE measurements to determine the activity or accelerated aging tests are carried out in oxygen-saturated 1 M KOH.
- the catalyst to be examined is applied to a glassy carbon electrode having an area of 1 cm 2 .
- the loading is about 100 ⁇ g of catalyst, i.e. a 20% loading with active composition corresponds to about 20 ⁇ g of active component.
- a platinum sheet serves as counter electrode.
- the reference electrode is a mercury-mercury oxide electrode. All potentials are reported relative to the reversible hydrogen electrode (RHE).
- Ten cycles between 50 and 1320 mV (RHE) are carried out at a speed of 5 mV/s and a speed of rotation of the disk of 1600 rpm.
- An electrocatalyst frequently used in an alkaline medium viz. silver on carbon (comparative example 6)
- a current density of -1 mA/cm 2 is obtained only at a potential of 759 mV.
- the activity decreases relatively quickly: after ten potential cycles between 50 and 1320 mV, the curve has been shifted by a further 33 mV to lower potentials. This shows the necessity of more stable and more active catalysts.
- the catalyst according to the invention displays such an improvement while additionally avoiding the use of expensive noble metals since cobalt is used in place of silver.
- the onset potential can be shifted to about 885 mV.
- the reduction of oxygen occurs with lower kinetic hindrance since the curve is very steep.
- a current density of -1 mA cm 2 is achieved at potentials of 831 mV, i.e. an improvement of more than 70 mV compared to the silver catalyst.
- the catalyst is significantly more stable. After 10 cycles, the curve has been shifted by only 3 mV toward lower potentials.
- example 12 is produced using ethylenediamine (example 12 EDA) instead of urea, a further improvement in the activity can be achieved (onset at -920 mV; -1 mA/cm 2 achieved at 862 mV), without the stability becoming significantly worse (shift by 4 mV after 10 cycles).
- Table 2 Decrease in activity in an alkaline medium
- Example 18 Comparison of the catalytic activity of carbides prepared by various methods for the example of the hydrogen oxidation reaction (anode reaction in fuel cells, PEMFC)
- the hydrogen oxidation reaction is catalyzed in an excellent way with virtually no overvoltage by platinum catalysts; even very low loadings, e.g. 0.05 mg of Pt cm 2 , are sufficient for this. Nevertheless, non-noble metal alternatives are sought for the anode catalyst because of the high price of platinum.
- Tungsten carbide has a density of electronic states which is very similar to that of platinum, as a result of which it is considered to be an ideal candidate for replacing platinum as catalyst, including for the oxidation of hydrogen. However, this reaction proceeds much less well and with a higher overvoltage over tungsten carbide, which can be attributed at least partly to the excessively large particles.
- the hydrogen oxidation reaction can, like the oxygen reduction reaction, be characterized ex-situ by means of an RDE.
- 60 ⁇ g of the tungsten carbide-based catalyst to be examined are applied to the glassy carbon electrode.
- 0.5 M H 2 S0 4 is used as electrolyte. All other parameters are unchanged, compared to example 16.
- Two cycles between -50 and 1000 mV (RHE) are carried out in each case at a speed of 20 mV/s in the hydrogen- saturated electrolyte.
- the Pd catalyst similarly to Pt, oxidizes the hydrogen virtually immediately and even after only 50 mV achieves a current density of 1 mA cm 2 , above about 100 mV a plateau (limiting diffusion current) of about 1.8 mA/cm 2 is achieved, corresponding to a value of about 800 mA/mg of Pd.
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WO2013182535A1 (en) * | 2012-06-06 | 2013-12-12 | Basf Se | Method for producing nitrogen-doped transition metal catalysts and use thereof for the electrochemical oxidation of s(iv) compounds |
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WO2015005309A1 (en) * | 2013-07-12 | 2015-01-15 | 昭和電工株式会社 | Oxygen reduction catalyst and use therefor |
US10230114B2 (en) | 2013-07-12 | 2019-03-12 | Showa Denko K.K. | Oxygen reduction catalyst, uses thereof and production process therefor |
KR101437390B1 (en) | 2013-12-05 | 2014-09-04 | 대한민국 | Magnetized activated carbon by microwave irradiation and the manufacturing method |
JP2015150480A (en) * | 2014-02-13 | 2015-08-24 | 国立研究開発法人産業技術総合研究所 | catalyst for fuel cell |
JP6517316B2 (en) * | 2014-03-18 | 2019-05-22 | ビーエーエスエフ ソシエタス・ヨーロピアBasf Se | Method for producing a carbon supported catalyst |
CN103920519B (en) * | 2014-04-23 | 2016-03-30 | 西南大学 | The preparation method of the oxygen reduction electro-catalyst of nitrogen-doped graphene is strengthened based on ferrotungsten bimetallic oxide |
JP6430168B2 (en) * | 2014-08-05 | 2018-11-28 | 旭化成株式会社 | Carbon material composite, nitrogen-containing carbon material, and production method thereof |
US9780386B2 (en) | 2014-08-08 | 2017-10-03 | Samsung Electronics Co., Ltd. | Composite for lithium air battery, method of preparing the composite, and lithium air battery employing positive electrode including the composite |
EP3106543A1 (en) * | 2015-06-17 | 2016-12-21 | Basf Se | Modified carbon material for use in water electrolysis |
CN105032460B (en) | 2015-06-23 | 2018-02-02 | 华南理工大学 | Low-platinum catalyst based on nitride nano particle and preparation method thereof |
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CN105200450B (en) * | 2015-09-10 | 2017-08-25 | 北京航空航天大学 | A kind of molybdenum disulfide/carbon black is combined Electrocatalytic Activity for Hydrogen Evolution Reaction material and preparation method thereof |
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CN107768687B (en) * | 2017-10-22 | 2020-05-15 | 苏州朗泰新能源科技有限公司 | Fuel cell catalyst and preparation method thereof |
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CN109686982A (en) * | 2019-01-29 | 2019-04-26 | 冯良荣 | A method of preparing load type carbon nitride |
US11600812B2 (en) * | 2019-07-17 | 2023-03-07 | Phillips 66 Company | Electrode particles suitable for batteries |
CN112705235B (en) * | 2019-10-24 | 2023-08-08 | 中国石油化工股份有限公司 | Carbon-coated nickel carbide nanocomposite and preparation method and application thereof |
KR102467797B1 (en) * | 2020-10-22 | 2022-11-16 | 에쓰대시오일 주식회사 | A metal hydroxide layer/tungsten carbide nanowire composite, a method for manufacturing the same, and a catalyst for hydrogen generation reaction comprising the metal hydroxide layer/tungsten carbide nanowire composite |
CN115505954A (en) | 2021-06-04 | 2022-12-23 | 丰田自动车株式会社 | Platinum-based nano heterogeneous material and preparation method thereof |
CN113506885B (en) * | 2021-06-25 | 2022-11-15 | 中自环保科技股份有限公司 | Graphitized carbon carrier for hydrogen fuel cell, preparation method and cell catalyst thereof |
CN114538517B (en) * | 2022-03-31 | 2023-12-22 | 洛阳师范学院 | Mo (molybdenum) 2 C and carbon-coated molybdenum-based heterostructure material and preparation method and application thereof |
CN114990628B (en) * | 2022-07-13 | 2023-10-20 | 山东大学 | Double-function electrocatalyst for quick synthesis of Joule heat and its application in high-efficiency water decomposition |
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