Classifications

• • 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
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/097—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds comprising two or more noble metals or noble metal alloys
• • 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
  • H01M4/9008—Organic or organo-metallic compounds
• • 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
  • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
• • 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
• • 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
  • H01M8/08—Fuel cells with aqueous electrolytes
  • H01M8/083—Alkaline 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
  • 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
• • 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

• Catalysts for the production of hydrogen by the electrolysis of water electrolysers in which they are used, and processes for the production of hydrogen by the electrolysis of water.
• This invention relates to the production of hydrogen by electrolysis of water.
• the electrolysis of water is a well defined process: in an electrolyser, a potential difference between the electrodes splits water into hydrogen (at the cathode) and into oxygen (at the anode) (eq. 1):
• the electrolyser is an apparatus consisting of a cell containing: the solution to be electrolysed, two electrodes on which the surface due to the passage of current occur the oxidation/reduction reactions and an ion-exchange membrane between the two electrodes (as explained in more detail as follows).
• the electrodes normally consist of a metal element or some highly conducting surface onto which is applied a catalyst also usually a metal.
• the efficiency of an electrolyser depends directly upon the materials in which the electrodes are constructed. In particular the catalysts whose role is that of diminishing the activation energy of both the anodic and cathodic reactions.
• the electrode materials play an important role in improving the energetic efficiency of an electrolyser in terms of both the energy consumption ( for a particular reaction rate) and the maximum reaction rate of a cell.
• alkaline electrolysers AE
• solid polymer membrane electrolysers MPE
• solid oxides electrolysers which are still being developed.
• AE and MPE The main difference between AE and MPE is that the electrolyte in the AE case consists of an alkaline solution, generally KOH (25-30%), while in a MPE the electrolyte consists of a polymeric membrane through which pass ions, generally H + to the cathode where they are reduced to make H 2 .
• the other function of the membrane is to separate the gases that are produced at the two electrodes.
• the advantages of the MPE type are multiple: no moving parts, very low volume of corrosive liquids, high current density obtained, production of pressurised gas, quick response to applied load.
• the disadvantages include the high cost of the membrane (generally Nafion form DuPont) and the noble metals used in the catalyst (usually platinum and its alloys).
• the catalysts used are a high percentage of the active phase ((>(10 mg/cm 2 ) to obtain the required output.
• the high catalyst load is extremely costly especially if noble metals are used and hence limits the potential applications for MPE type electrolysers.
• the accepted definition for the efficiency of an electrolyser capable of generating hydrogen is expressed in kWh/Nm 3 of H 2 .
• a normal m 3 di H 2 has a "higher heating value" of 3.54 kWh.
• An electrolyser operates at 100% efficiency in the conversion of electrical energy into hydrogen when 3.54 kWh is used to produce 1 Nm 3 of H 2 .
• Other parameters characteristic for an electrolyser are the voltage applied to the electrolytic cell and the current density (A/cm 2 ).
• PME type electrolysers using catalysts based upon non-noble metals with anionic exchange solid polymeric membranes are virtually unknown in the sector or in the scientific literature.
• cathode catalysts containing one or more non-noble metals also alloys in AE type electrolysers with liquid electrolytes are well known in the literature. (F. C. Crnkovic, S.A.S. Machado, L.A. Avaca, Int. J. Hydrogen Energy 2004, 29, 249).
• metal catalysts for the production of hydrogen by the electrolysis of water in electrolysers containing anionic exchange solid polymeric membranes.
• These catalysts are formed from metal complexes obtained from transition metal salts, usually manganese, iron, cobalt, nickel, palladium, iridium or their alloys and polymers (already described in WO2004/036674) obtained by the condensation of a 4- ⁇ 1-[(fenil-2,4-disubstituted)- hydrazine]-alkyl ⁇ -benzene-1 ,3-diol with a 3,5-disubstituted phenol and formaldehyde or para-formaldehyde in the presence of an acid or basic catalysts in water/alcohol mixtures and at a temperature comprised between 20 - 15O 0 C and having a molecular weight comprised between 1000 and 50000.
• Figure 3 Change in potential of a cell at various current densities under the conditions of the experiment described in example 5.
• Figure 4. Change in potential of a cell with time during the experiment described in example 6.
• FIG. 1 A functional diagram of the electrolyser described in this invention is described in Figure 1.
• An electrolyser like that shown in Figure can contain anodic catalysts of the state of the art (C-C. Hu, Y.-S. Lee, T.-C. Wen, Materials Chemistry and Physics 1997, 48, 246; C. Bocca, A. Barbucci, M. Delucchi, G. Cerisola, Int. J. Hydrogen Energy, 1998, 23, 1) for AE type electrolysers and for electrolysers with commercial anionic exchange solid polymer membranes.
• cathode catalysts described in this invention are also described for use in fuel cells in WO 2004/036674 (also by the current inventors) in which is reported templating polymers formed form the condensation of an 1 ,3-diol, containing coordinating nitrogen atoms, with phenol or 3,5 disubstituted phenols and formaldehyde or paraformaldehyde which are capable of coordinating metal salts, none of which containing platinum and are preferentially salts or compounds of iron, cobalt and or nickel to give adducts that once reduced using gaseous hydrogen or other reducing agents or pyrolised under inert atmosphere at temperatures above 500 0 C, produce catalytic materials for anodes and cathodes in fuel cells fuelled by hydrogen or other compounds containing hydrogen in particular alcohols (methanol, ethanol, ethylene glycol), aldehydes, hydrazine and various hydrocarbons.
• alcohols methanol, ethanol, ethylene glycol
• aldehydes hydrazin
• the metal particles, containing one or metal metals are extremely small, between 3 and 50 A (10 "1 ° m).
• other catalysts made according to this invention are described in the Italian patent application FI20040000154 (also by the current inventors) that, using a completely analogous method to that used in the previously mentioned WO 2004/036674, describes the preparation of catalysts based upon platinum or platinum in combination with other transition metals for the production of catalytic materials for anodes and cathodes in fuel cells fuelled by hydrogen or other compounds containing hydrogen.
• the catalysts are formed from highly dispersed particles of sub-nanometric and nanometric dimentions(10 "9 m).
• the catalysts described in this invention are prepared starting from metal complexes formed from metal salts preferably manganese, molybdenum, iron, cobalt, nickel, palladium, iridium and their mixtures, binary, tertiary or quaternary and templating polymers (already described in WO2004/036674) obtained by: The condensation of a 4- ⁇ 1-[(fenil-2,4-disubstituted)-hydrazine]-alkyl ⁇ -benzene- 1 ,3-diol with a 3,5-disubstituted phenol and formaldehyde or para-formaldehyde in the presence of an acid or basic catalyst in water/alcohol mixtures and at a temperature comprised between 20 - 150 0 C and having a molecular weight comprised between 1000 and 50000.
• metal complexes formed from metal salts preferably manganese, molybdenum, iron, cobalt, nickel, palladium, iridium
• Ri is chosen in the group consisting og: H, a C-M O hydrocarbon radical, possibly halogenated, R 2 and R 3 independently from each other represent an electron-attractive group chosen in the group consisting of: H, halogen, acyl, ester, carboxylic acid, formyl, nitrile, sulphonic acid, aryl groups or linear or branched alkyl having 1 - 15 carbon atoms, possibly functionalised with halogens or joined to each other in order to form one or more cycles condensed with the phenyl ring, and nitro groups; and the 3,5 disubstituted phenol is a compound of formula (B)
• R 4 and R 5 independently from each other represent and electro-donating group chosen among H, OH, ether, amine, aryl and linear or branched alkyl groups having 1 - 15 carbon atoms.
• y is comprised between 2 and 120
• x is comprised between 1 and 2
• n is comprised between 1 and 3 and R-i
• R 2 , Rz, R 4 and R 5 are as above defined.
• the metal salts according to the invention are chosen from the group comprising carboxylates, halogens and pseudohalogens, alcolates, acetylacetonates, formates, oxalates, malonates and analogous organic salts and their mixtures or carbonates and bicarbonates or their mixtures.
• the metals used are preferably chosen from the group containing: Fe, Ru, Co, Ir, Ni, Pd, Mo, Mn.
• the catalysts used in this invention are prepared from either of the following methods 1 , 2 and 3.
• Method 1 Method 1 :
• a salt or metal compound from the Periodic Table preferably among those described above is dissolved in water and then added to an aqueous suspension containing a templating polymer as described above and in detail in WO 2004/036674, from now on known as the POLYMER.
• the mixture is adjusted to pH 8-9 by the addition of a solution of 1 M NaOH and then mixed vigorously for 10-15 h at room temperature.
• the solid product formed known as the MONO- METALLIZED POLYMER is filtered, washed with water and air dried.
• the dried solid is added to a suspension in acetone or some other organic solvent of nickel powder (3 micron), or porous conducting carbonaceous material for example Vulcan XC-72R.
• a reducing agent of the state of the art e.g. NaBH 4 or NH 2 NH 2
• the solid product obtained by the impregnation of the MONO-METALLIZED POLYMER on the nickel powder support (3 micron) or Vulcan XC-72R is isolated by evaporation of the solvent under reduced pressure and then is treated with a current of hydrogen at a temperature between 300 e 800 0 C.
• Method 2 Two salts or metal compounds of the Periodic Table preferably Mn, Fe, Ru, Co, Ir, Ni, Pt, Pd, Mo, Sn, are dissolved in water and the solution is added to an aqueous suspension of the POLYMER. The mixture is adjusted to pH 8-9 using a solution of 1 M of NaOH and then mixed vigorously for 10-15 h at room temperature. The solid product formed known as the BI-METALLIZED POLYMER, is filtered, washed with water and air dried. The dried solid is added to a suspension in acetone or some other organic solvent of nickel powder (3 micron), or a porous conducting carbonaceous material for example Vulcan XC-72R.
• the resulting product is treated with a reducing agent of the state of the art (e.g. NaBH 4 or NH 2 NH 2 ), filtered, washed with water and dried.
• a reducing agent of the state of the art e.g. NaBH 4 or NH 2 NH 2
• the solid product obtained by the impregnation of the BI-METALLIZED POLYMER on the nickel powder support (3 micron) or Vulcan XC-72R is isolated by evaporation of the solvent under reduced pressure and then is treated with a current of hydrogen at a temperature between 300 e 800 0 C.
• Three salts or metal compounds of the Periodic Table preferably Mn, Fe, Ru, Co, Ir, Ni, Pt, Pd, Mo, Sn, are dissolved in water and the solution is added to an aqueous suspension of the POLYMER.
• the mixture is adjusted to pH 8-9 using a solution of 1 M of NaOH and then mixed vigorously for 10-15 h at room temperature.
• the solid product formed known as the TRI-METALLIZED POLYMER is filtered, washed with water and air dried. The dried solid is added to a suspension in acetone or some other organic solvent of nickel powder (3 micron), or a porous conducting carbonaceous material for example Vulcan XC- 72R.
• the resulting product is treated with a reducing agent of the state of the art (e.g. NaBH 4 or NH 2 NH 2 ), filtered, washed with water and dried.
• a reducing agent of the state of the art e.g. NaBH 4 or NH 2 NH 2
• the solid product obtained by the impregnation of the TRI- METALLIZED POLYMER on the nickel powder support (3 micron) or Vulcan XC- 72R is isolated by evaporation of the solvent under reduced pressure and then is treated with a current of hydrogen at a temperature between 300 e 800 0 C.
• Analogous procedures can be used for the preparation of catalysts with more than three different metals from the Periodic Table deposited on the same support material.
• the catalysts prepared according to the methods described above preferably contain the three metals Mn, Co and Ni in various stoichiometric ratios, preferably equimolar, or only Co and Ni, supported on conducting supports such as nickel (3 micron) or porous conducting carbonaceous material for example Vulcan XC-72R and are able to promote the electrolysis of water in alkaline environments.
• conducting supports such as nickel (3 micron) or porous conducting carbonaceous material for example Vulcan XC-72R
• the advantages are as follows: - the use of non noble metals at low cost - the possibility of synthesising multi-metal catalysts with precise stoichiometric ratio between the metals present.
• this invention allows the production of hydrogen with an efficiency greater than 90% and a cost substantially lower with respect to currently used electrolysers, in addition with all the advantages of PME type electrolysers with proton exchange solid polymer membranes.
• the following examples describe in detail the preparation of several catalysts used for the realisation of cathodes in the electrolyser of this invention.
• the reduction can be effected in a current of hydrogen.
• 1 g of the solid product POLYMER-Co-Ni/Ni pO wcier isolated by evaporation of the solvent under reduced pressure is introduced into a quartz furnace heated to 360 °C per 1 h under a flow of hydrogen. The product is then kept under an inert atmosphere of N 2 or Ar.
• the reduction can be effected in a current of hydrogen.
• 1 g of the solid product POLYMER-Ni/Ni poW der isolated by evaporation of the solvent under reduced pressure is introduced into a quartz furnace heated to 360 0 C per 1 h under a flow of hydrogen.
• the product is then kept under an inert atmosphere of N 2 Or Ar.
• the activity of the catalysts is measured in electrolysers of the type EPP illustrated in Figure 1 , by assembling the cathodes of this invention with anodes of the state of the art and commercial anionic exchange membranes.
• a method for the fabrication of a cathode electrode is described below along with some examples of electrolytic experiments used to evaluate them.
• EXAMPLE 5 The anode catalyst and the corresponding positive electrode, upon whose surface occurs the oxygen gas evolution reaction, is prepared directly by the cathodic electrodeposition of Co and Ni from a solution of Ni(NOs)2 and Co(NO 3 ) 2 on a nickel foam electrode of the state of the art (E. B. Castro, S. G. Real, L. F. Pinheiro, Int. J. Hydrogen Energy 2004, 29, 255].
• the cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas is prepared according to the method described in 3 using an alloy of the metals Ni3 4 Co3 4 Mn32/Ni poW der- As ionic conductor in the cell is used an alkaline anionic exchange membrane Tokuyama Neosepta ® A-010 produced by ASTOM Corp.
• the resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentrations of 1 moi/dm 3 , 2 mol/dm 3 and 6 mol/dm 3 at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm 2 of current at 1.820 V where the electrolyte concentration was 1 mol/dm 3 , 1.780 V where the electrolyte concentration was 2 mol/dm 3 and 1.650 V where the electrolyte concentration was 6 mol/dm 3 . At the highest electrolyte concentration (6 mol/dm 3 ) an internal resistance of the cell of 30 mOhm was obtained.
• the faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to its standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 93% at 250 mA/cm 2 of constant current and at 75% at 750 mA/cm 2 of constant current.
• HHV Higher Heating Value
• the cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas is prepared according to the method described in 3 using an alloy of the metals Ni3 4 Co 34 Mn32/Nipowder- As ionic conductor in the cell is used an alkaline anionic exchange membrane Solvay ADP 08.
• the resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentration of 6 mol/dm 3 at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm 2 of current at 1.930 V and 2.180 V at 750 mA/cm 2 constant current.
• the anode catalyst and the corresponding positive electrode, upon whose surface occurs the oxygen gas evolution reaction is prepared directly by the cathodic electrodeposition of Co and Ni from a solution of Ni(NO 3 ) 2 and Co(NO 3 ) 2 on a nickel foam electrode of the state of the art (E. B. Castro, S. G. Real, L. F. Pinheiro, Int. J. Hydrogen Energy 2004, 29, 255].
• the cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas is prepared according to the method described in 3 using an alloy of the metals Ni3 4 C ⁇ 3 4 Mn 3 2/Nip OW der- As ionic conductor in the cell is used an alkaline anionic exchange membrane Tokuyama Neosepta ® A-010 produced by ASTOM Corp.
• the resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentration of 6 mol/dm 3 at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm 2 of current at 2.01 V and 2.20 V at 750 mA/cm 2 constant current. An internal resistance of the cell of 45 mOhm was obtained.
• the faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to its standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 80% at 250 mA/cm 2 of constant current and at 69% at 750 mA/cm 2 of constant current.
• HHV Higher Heating Value
• the cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas is prepared according to the method described in method 1 using the catalyst Ni/Ni po wder- As ionic conductor in the cell is used an alkaline anionic exchange membrane Tokuyama Neosepta ® A-010 produced by ASTOM Corp.
• the resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentration of 6 mol/dm 3 at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm 2 of current at 2.1 V and 2.52 V at 750 mA/cm 2 constant current. An internal resistance of the cell of 45 mOhm was obtained.
• the faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to it's standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 80% at 250 mA/cm 2 of constant current and at 67% at 750 mA/cm 2 of constant current.
• HHV Higher Heating Value

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