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• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0031—Intermetallic compounds; Metal alloys; Treatment thereof
• • 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
  • B01J25/00—Catalysts of the Raney type
• • 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
  • B01J37/06—Washing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/054—Nanosized particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
  • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
  • C01B3/0031—Intermetallic compounds; Metal alloys; Treatment thereof
  • C01B3/0042—Intermetallic compounds; Metal alloys; Treatment thereof only containing magnesium and nickel; Treatment thereof
• • 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
• • 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
• • 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
  • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
  • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
  • H01M8/065—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants by dissolution of metals or alloys; by dehydriding metallic substances
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
  • B22F2009/041—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by mechanical alloying, e.g. blending, milling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • 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
  • Y02E60/32—Hydrogen storage
• • 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
• • 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
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
• • 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
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S420/00—Alloys or metallic compositions
  • Y10S420/90—Hydrogen storage
• • 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
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S502/00—Catalyst, solid sorbent, or support therefor: product or process of making
  • Y10S502/523—Miscellaneous specific techniques of general applicability
• • 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
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/778—Nanostructure within specified host or matrix material, e.g. nanocomposite films
  • Y10S977/779—Possessing nanosized particles, powders, flakes, or clusters other than simple atomic impurity doping

Definitions

• the present invention relates to new nanocrystalline materials having a large specific surface.
• the invention also relates to the use of said new nanocrystalline materials with a large specific surface in the energy sector, and more precisely for the storage of hydrogen and / or the manufacture of electrodes for catalysis or electrocatalysis, such than those used in fuel cells or for the production of hydrogen.
• the invention finally relates to certain composites or alloys of nanocrystalline structure which can be used as intermediate products for the implementation of said process.
• nanocrystalline is used to designate a material consisting of crystallites whose grain size is less than 100 nm.
• the first object of the invention is therefore a method of manufacturing nanocrystalline materials having a large specific surface, characterized in that: in a first step, a nanocrystalline material is prepared consisting of a composite or metastable alloy of at least two elements separate chemicals, this material having a crystal structure with crystals of size less than 100 nm; and - in a second step, the nanocrystalline material thus prepared is subjected to leaching so as to partially or totally eliminate at least one of the elements of the composite or of the alloy, this leaching giving the resulting material a porous structure and, hence, a large specific surface.
• a second object of the invention is the nanocrystalline materials obtained by this process. These materials have a crystal structure with crystals less than 100 nm in size. They also have a specific surface greater than or equal to 2 m 2 / g, and preferably greater than or equal to 10 m 2 / g.
• the third object of the invention is certain uses of the new nanocrystalline materials thus produced in the energy sector.
• the materials in question comprise at least one phase or a chemical element known to reversibly absorb hydrogen, they can be used for the storage of hydrogen. Their large specific surface significantly improves their absorption / desorption kinetics.
• the materials in question comprise at least one phase or a chemical element which can be used as catalysts or electrocatalysts, these materials can be used for the manufacture of electrodes. Their large specific surface area substantially improves their efficiency.
• the fourth and final object of the invention is finally certain nanocrystalline materials which can be used as intermediates for the manufacture of the materials according to the invention as defined above.
• the subject of the invention is such intermediates which can be used for the manufacture of materials which can themselves be used for the manufacture of electrodes, these intermediates having a crystal structure with crystals of size less than 100 nm and being in the form a composite or an alloy of the type:
• A-X-Y in which: - A is Pt, Ru or a compound of Pt or Ru;
• X is one or more elements chosen from the group consisting of Ru, Ge, Si, W, Sn, Ga, As, Sb, Mo, Ti, Ta, Cr, Mn, Fe, Co, Ni, Cu, Rh, V, Pd, Ag, In, Os, Ir, Au, Pb, C, Cd, N, P, Bi, Nb and Zr; and Y is one or more elements chosen from the group consisting of Al, Mg, Zn, Li, Na, K, Ca, Zr, Mo, Ti and their oxides (these elements can be leached with an acid or a base in the liquid phase); or
• Y is U (this element is leachable by anodic polarization);
• Y is one or more elements chosen from the group consisting of H, C, N, O, F, Cl, P and S (these elements are leachable in the gas phase), or
• Y is a combination of the elements Y listed above.
• the subject of the invention is other intermediates which can be used for the manufacture of materials for the storage of hydrogen, these other intermediates having a crystal structure with crystals of size less than 100 nm and in that they are present in the form of a composite or type alloy
• a ' is Mg, Be or a compound of Mg or Be
• X ' is one or more elements chosen from the group consisting of Li, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, In, Sn, O, Si , B and F
• - Y ' is one or more leachable elements in aqueous liquid phase, these elements being chosen from the group consisting of Al, Mg, Li, Zn, Na, K, Ca, Zr, Ti, Mo and their oxides; or
• Y ' is one or more elements chosen from the group consisting of H, C, N, O, F, Cl, P or S (these elements are leachable in the gas phase) or Y' is an organometallic compound in which the metallic element is one of the metals listed in the definition of X 'or a metal selected from the group consisting of Ru, Rh, Pd, Ir and Pt, and the organic part is leachable; or Y 'is a combination of the elements Y' listed above.
• the leaching takes place in the gas phase by heat treatment or pyrolysis in the presence or not of another capable gas. to react with Y 'and form another eliminable gas.
• the method according to the invention comprises two steps.
• the first consists in preparing a metastable composite or alloy of several distinct chemical elements, the structure of which is nanocrystalline and the crystals are less than 100 nm in size.
• This first step therefore consists in preparing, by an "out of equilibrium” technique, a nanocrystalline alloy or a nanocomposite having a micro structure on the nanometric scale.
• this alloy or composite can be carried out in various ways.
• the nanocrystalline material can be prepared by intense mechanical grinding. If the elements are highly soluble in each other, a solid solution or a nanocrystalline alloy will be obtained. If the elements have a positive heat of mixture and therefore a low solubility in each other, we will obtain a nanocomposite whose chemical elements will be finely nested one in the other.
• a nanocrystalline material is in the form of a powder.
• the preparation of this powder can be carried out in a single step or in two steps.
• the nanocrystalline material can be prepared by subjecting the first non-leachable element (s) chosen to a first intense mechanical grinding until a nanocrystalline powder is obtained. The leach element is then added to the powder thus obtained and the whole is subjected to a second intense mechanical grinding.
• the nanocrystalline material can also be prepared by rapid quenching (solidification from a liquid state), followed, if necessary, by a heat treatment of the precursor material obtained if it is not crystalline.
• the nanocrystalline material can also be prepared by vapor phase condensation. This condensation can be carried out following evaporation in an inert gas, in order to form agglomerates which deposit. It can also be carried out under vacuum by sputtering followed by condensation of the vapor produced on a substrate. In all cases, the only requirement is that the product thus obtained has a nanocrystalline structure.
• the second step of the process according to the invention consists in leaching at least one of the chemical elements of the nanocrystalline material previously produced, with a view to eliminating it and giving the resulting material a porous structure and, hence, a greater specific surface.
• the size of the pores or asperities thus obtained is of the order of a few nanometers, since the structure of the nanocrystalline material subject to leaching is itself nanocrystalline. From a practical point of view, this leaching can be carried out in various ways: in the liquid phase, in the gas phase or by anodic polarization. It can also be partial or whole, depending on needs.
• the element or elements to be leached can be chosen from the group consisting of Al, Mg, Zn, Li, Na, K, Ca, Zr, Ti, Mo or Zn.
• the leaching is carried out in the liquid phase using an acid or a base chosen so as to leach the element or elements in question without attacking the other elements of the composite or of the alloy.
• the leached element is Mg
• the leaching of this element is carried out in the liquid phase with an acid, such as hydrochloric acid 1 M.
• the leaching element is Al
• the leaching of this element can be carried out in the liquid phase with a base, such as NaOH 1 M.
• leaching can be carried out in the liquid phase with hydrofluoric acid.
• the leaching element can be U.
• the leaching is carried out by anodic polarization.
• the element to be leached can finally be chosen from the group consisting of H, C, N, O, F, Cl, P and S.
• the leaching of this element is carried out by heat treatment in the presence or not of a gas capable of reacting with said element to form another gas and eliminate it.
• a gas capable of reacting with said element to form another gas and eliminate it can be chosen from the group consisting of H, C, N, O, F, Cl, P and S.
• gas phase leaching can be carried out using, as an additional element, an organometallic compound. It is also possible to use a combination of the above-mentioned elements.
• the present invention allows nanocrystalline materials having a large specific surface area to be obtained in a simple and flexible manner, which makes them particularly useful for catalysis, electrocatalysis and the production and storage of energy (fuel cells). , hydrogen storage, etc.).
• the invention can be used for the manufacture of electrodes for catalysis and electrocatalysis, for example, the electrodes used in electrocatalysts for the production of hydrogen, the production of sodium chlorate or the electrodes used in fuel cells.
• the invention can also be used for the manufacture of absorbent and / or adsorbent materials, which require large specific surfaces, to be effective. It can be, for example, metal hydrides or hydrogen storage materials, porous, mesoporous materials, molecular sieves or membranes for filtration.
• the nanocrystalline material according to the invention is intended to be used for catalysis, it is preferably obtained by leaching of a nanocrystalline material which is in the form of a composite or of an alloy of the type
• A-X-Y in which: - A is Pt, Ru or a compound of Pt or Ru;
• X is at least one element chosen from the group consisting of Ru, Ge, Si, W, Sn, Ga, As, Sb, Mo, Ti, Ta, Cr, Mn, Fe, Co, Ni, Cu, Rh, V, Pd, Ag, In, Os, Ir, Au, Pb, C, Cd, N, P, Bi, Nb and Zr; and
• Y is at least one element chosen from the group consisting of Al, Mg, Zn, Li, Na, K, Ca, Ti, Zr, Mo, U and their oxides; or
• Y is at least one element chosen from the group consisting of H, C, N, O, F, Cl, P and S; or
• Y is a combination of the various elements Y listed above. It will be understood that, in the above formula, Y is the leachable element.
• nanocrystalline material according to the invention is intended to be used for the storage of hydrogen, it is preferably obtained by leaching of a nanocrystalline material of formula A'-X'-Y 'in which:
• - X ' is at least one element chosen from the group consisting of Li, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, In, Sn, O, Si, B and F; and
• - Y ' is at least one element chosen from the group consisting of Al, Mg, Zn, Li, Na, K, Ca, Ti, Zr, Mo and their oxides; or
• - Y ' is at least one element chosen from the group consisting of H, C, N, O, F, Cl, P and S, or is an organometallic compound in which the metallic element is one of the metals listed in the definition of X 'or a metal chosen from the group consisting of Ru, Rh , Pd, Ir and Pt, and the organic part is leachable (this organometallic compound can be, for example, a phthalocyanine); or
• Y ' is a combination of the elements Y' listed above.
• Y ' is the leachable material.
• the quantity of elements to be leached combined with the other elements of the composite or of the alloy thus prepared can be extremely variable. This quantity is preferably chosen so that the atomic percentage of the element or elements to be leached in the composite or the alloy is greater than 2% and less than 95%. We will however prefer to minimize the quantity of elements to leach. Examples of applications of the invention for the storage of hydrogen and the manufacture of electrodes for fuel cells will now be given with reference to the appended figures.
• FIG. 1 represents polarization curves giving the value of the voltage measured as a function of the current density in a fuel cell provided with anodes respectively covered with a leached nanocrystalline material of formula PtRu according to the invention , a nanocrystalline unleached of formula PtRu material and a brand of catalyst E-TEK ®;
• FIG. 2 represents polarization curves similar to those of FIG. 1 and obtained under the same conditions but in the presence of carbon monoxide;
• FIG. 3 represents polarization curves similar to those of FIG.
• FIG. 4 represents polarization curves similar to those of FIG. 1 and obtained under the same conditions, where the catalysts covering the anode are leached nanocrystalline materials of formulas PtRu, PtGe, PtSi, PtW and PtSn;
• FIG. 5 represents polarization curves similar to those of FIG. 4 and obtained under the same conditions, but in the presence of carbon monoxide;
• FIG. 6 represents polarization curves similar to those of FIG.
• FIG. 7 represents the hydrogen absorption curves as a function of time (expressed in seconds) for a nanocrystalline alloy of formula Mg 2 Ni and a nanocrystalline alloy of the same formula additionally containing a small amount of C, part of which has been leached;
• FIGS. 8a and 8b are photographs of nanocrystalline particles of formula MgLi 10% by weight, respectively before and after leaching of Li;
• FIG. 9 represents the hydrogen absorption curves as a function of time (expressed in seconds) for pure nanocrystalline Mg and for nanocrystalline Mg obtained by leaching of a nanocrystalline composite of formula MgLi 10%.
• the product collected was applied as a catalyst to the anode of a fuel cell at a rate of 4 mg / cm 2 .
• the cathode of this cell was made of ELAT ® (0.37 mg Pt / cm 2 and 0.6 mg NAFION ® / cm 2 ).
• T water / anode 1 10 ° CT water / cathode: 1 10 ° C pressure H 2 : 30 psi pressure O 2 : 60 psi
• Example 2 By proceeding in the same way and under the same conditions as above but using pure Pt powder rather than a mixture of Pt and Ru powders, activity tests were carried out in a fuel cell. The results obtained with the leached nanocrystalline Pt thus prepared and used as anode catalyst are reported in FIG. 3 (see curve •). By way of comparison, the results obtained with the leached PtRu and already reported in FIG. 1 are also indicated (see curve °).
• 7.5 g of a mixture of Pt and Al average composition PTAI 4 were milled under argon for 40 h using a brand mill SPEX 8000 ® in a WC crucible with 3 beads WC.
• the weight ratio of the beads to the weight of the powder was 4: 1.
• the powder was leached in 1 M NaOH and the product collected was applied as a catalyst to the anode of a fuel cell similar to that described in Example 1, at a rate of 4 mg / cm 2 .
• Example 5 By proceeding in the same way and under the same conditions as in Example 3 but using a mixture of Pt and Ru to obtain a final mixture of average composition Pt 0 5 Ru 0 5 AI 4 , activity tests were performed in a fuel cell. The results obtained are reported in Figure 3 (see curve ⁇ ).
• Example 5
• Example 6 A mixture of 2.21 g of a PtCI 2 powder and 4.79 g of an AI 4 C 3 powder corresponding to an average composition (PtCI 2 ) 0 2 (AI 4 C 3 ) 0 8 was milled under argon for 40 h in a WC crucible with 3 beads WC in a brand mill SPEX 8000 ®. The beads weighed approximately 30 g and the weight ratio of the beads to the total weight of the powders (7 g) was 4: 1.
• the nanocrystalline compound thus obtained was then deposited very slowly and gently in a beaker of water under an inert atmosphere. NaOH was then added by mechanically stirring the mixture to a concentration of 1 M (this slow addition is necessary because AI 4 C 3 reacts exothermically with water and forms with it hydrocarbons susceptible to ignition or explosion).
• the leached product thus obtained was then filtered, rinsed and dried.
• the product was then applied as a catalyst to the anode of a fuel cell similar to that described in Example 1, at a rate of 4 mg / cm 2 .
• the cathode was made with ELAT ® and the operating conditions were identical to those already described.
• Figure 7 shows the absorption curve at 300 ° C under a pressure of 200 psi, after an absorption / desorption cycle.
• a nanocrystalline alloy was prepared.
• the grinding was carried out hot (200 ° C) for 8 hours.
• Figure 7 shows the absorption rate of this powder at 300 ° C under a pressure of 200 psi after an absorption / desorption cycle. It can be seen that the absorption kinetics are much higher than that obtained in part (a), even though the grinding was shorter (but hot). This can be explained as follows: after grinding, the proportion of carbon measured was 5.2% by weight. After a few hydrogen absorption / desorption cycles, the proportion of carbon dropped to 3.7% by weight.
• a nanocrystalline material of composition MgLi 10% by weight was prepared. To do this, 3.3 g of Mg and 0.331 g of Li were used as starting material. The charge was ground for 50 hours. The powder obtained was leached in distilled water with magnetic stirring then ultrasonic.
• the specific surface area of the powder thus obtained before and after leaching was measured.
• the specific surfaces thus measured were as follows: before leaching: 1, 1 1 1 8 m 2 / g after leaching: 1 1, 4688 m 2 / g
• FIG. 9 shows the absorption speed of the nanocrystalline powder thus obtained after leaching (curve ⁇ ).
• curve T the results obtained with pure nanocrystalline Mg powder are also given (curve T). These tests were carried out at 400 ° C under a pressure of 36 bars. As can be seen, the absorption kinetics of the leached Mg powder is much higher than that of the non-leached Mg powder.

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• 1997
  • 1997-01-24 US US08/788,301 patent/US5872074A/en not_active Expired - Lifetime
• 1998
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