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
  • 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
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/077—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the compound being a non-noble metal oxide
  • C25B11/0771—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the compound being a non-noble metal oxide of the spinel type

Definitions

• the subject of the present invention is a process for the electrolytic production of hydrogen in an alkaline medium in which the hydrogen is released on the active surface of a cathode.
• electrolysis processes it is generally sought to reduce the potentials of electrochemical reactions at the electrodes to as low a value as possible. This is particularly the case in the electrolysis processes in which hydrogen gas is produced on the active surface of a cathode, such as the processes for the electrolysis of water, aqueous solutions of hydrochloric acid and aqueous solutions of sodium chloride.
• the cathodes used until now in practice for the electrolysis of water or sodium chloride have generally consisted of plates or lattices of mild steel.
• the present invention aims to produce hydrogen in an alkaline medium by release on the surface of cathodes whose manufacture does not have the drawbacks of that of the cathodes described above and which have properties, and in particular an overvoltage on release of hydrogen, as favorable as those of the aforementioned cathodes.
• the cathodes used according to the invention have a particularly favorable service life.
• the invention therefore relates to a process for the electrolytic production of hydrogen in an alkaline medium in which the hydrogen is released in gaseous form at the active surface of a cathode and in which a cathode is used, a layer of the active surface consists of certain oxidized compounds of the spinel type and free of boron.
• the oxidized compounds of the spinel type used according to the invention, are mineral compounds of general formula M II M III 2 O 4 , where M "denotes a bivalent metallic element or several bivalent metallic elements and M"' denotes a trivalent metallic element or several trivalent metallic elements.
• the oxidized compounds used according to the invention are those of general formula M II M III 2 O 4 where M "denotes a bivalent metal or several bivalent metals chosen from iron, zinc, manganese, nickel, cobalt, magnesium , cadmium and copper, and where M III denotes a trivalent metal or several trivalent metals chosen from iron, chromium, manganese, nickel and cobalt.
• the magnetite of general formula Fe 3 0 4 (or Fe II Fe III 2 O 4 ) is the compound leading to the best results when the cathodes are used in the presence of aqueous solutions of alkali metal hydroxide such as caustic detergents and caustic brines obtained by electrolysis of sodium chloride brines respectively in electrolysis cells with membrane with selective permeability and in electrolysis cells with permeable diaphragm.
• alkali metal hydroxide such as caustic detergents and caustic brines obtained by electrolysis of sodium chloride brines respectively in electrolysis cells with membrane with selective permeability and in electrolysis cells with permeable diaphragm.
• membrane with selective permeability is understood to mean a thin, non-porous separator, separating the anodes from the cathodes and comprising an ion-exchange material.
• selectively permeable membranes suitable for brine electrolysis cells, include cationic membranes containing SO 3 groups and resulting from the copolymerization of tetrafluorethylene and sulfonated perfluorvinyl ether, such as the membranes known as NAFION and sold by EI du Pont de Nemours & Co.
• diaphragm is meant a partition permeable to the electrolyte, made of an inert material, separating the anodes from the cathodes.
• known diaphragms include asbestos diaphragms, such as those described in United States patents 1 855 497, of May 7, 1928, of Stuart and Belgian 773 918 of October 14, 1971, in the name of the Applicant, porous sheets formed of a mixture of asbestos and a polyelectrolyte such as those described and claimed in Luxembourg patent 74 835 of April 26, 1976, in the name of the Applicant and porous polytetrafluoroethylene sheets, such as those described in Belgian patents 794 889 of February 2, 1973, 817 675, 817 676 and 817 677 of July 15, 1974, on behalf of Imperial Chemical Industries Limited.
• the active surface of the cathodes used according to the invention may contain, in addition to oxidized compounds of the spinel type, foreign substances, except boron, for example in trace amounts, provided that these do not affect the properties of the oxidized compounds which are essential for the process according to the invention.
• cathodes used according to the invention can for example consist of solid blocks obtained by sintering a powder of the oxidized compound.
• a cathode consisting of a metal support, for example a metal plate, carrying the oxidized compound on at least part of its surface.
• the metal support can be of any metal or alloy resistant to the chemical and / or thermal conditions to which the cathode is subjected.
• the metal support advantageously consists of a steel plate, generally a plate openwork.
• the perforated plate can for example have a substantially planar profile in the case of a cathode intended to equip a cell of the type described, for example, in French patents 2,164,623 of December 12, 1972 and 2,230,411 of 27 March 1974, on behalf of the Applicant.
• the perforated plate may have a corrugated profile in the case where the cathode is intended for an electrolysis cell of the type described, for example, in French patents 2,223,083 of March 28, 1973 and 2 248,335 of October 14, 1974, in the name of the Claimant.
• any technique known per se can be used to form or apply the oxidized compound to the metal support.
• a compound of general formula M 3 0 4 such as magnetite
• a powder of the oxidized compound in a suitable liquid containing a binder and apply one or more layers of the liquid suspension thus obtained to the support, for example by brushing, soaking or spraying, then optionally heating, by thereafter, the coated support to melt the binder and coat the particles of the oxidized compound.
• the oxide compound in the finely divided state can be directly sprayed into the plasma jet, in an inert atmosphere such as an argon atmosphere.
• the metal or metals used in the composition of the oxidized compound are projected, in the finely divided state, into a plasma jet in an inert atmosphere (for example argon), then the support thus coated is heated in a controlled oxidizing atmosphere to form the oxidized compound.
• an inert atmosphere for example argon
• the layer of the oxidized compound on the metal support generally has a thickness sufficient to resist abrasion wear in contact with the hydrogen gas and the electrolytes which circulate in contact with it during the electrolysis.
• the thickness of the layer of the oxidized compound on the metal support is at least 0.5 microns, preferably at least 5 microns. In the case where the layer is obtained by metallic projection in a plasma jet, as described above, good results are obtained with a thickness of the order of about 100 microns.
• the invention finds a particularly interesting application in cells with a permeable diaphragm and a membrane with selective permeability for the electrolysis of sodium chloride brines, such as those described, by way of example, in French patents 2 164 623 of 12 December 1972, 2,223,083 of March 28, 1973, 2,230,411 of March 27, 1974, 2,248,335 of October 14, 1974 and in French patent application 77.11,370 of April 12, 1977, all in the name of the Applicant.
• an aqueous brine containing 255 g of sodium chloride per kg was electrolysed in a laboratory cell with vertical electrodes, separated by an asbestos diaphragm.
• the cylindrical cell included an anode formed of a circular titanium plate, pierced with vertical slits and coated with an active material of mixed crystals, consisting of 50% by weight of ruthenium dioxide and 50% by weight of titanium dioxide.
• the cathode consisted of a circular metallic lattice structure, the shape of which was identical in each example, but the constitution of which varied from one example to another.
• each electrode of the cell was 113 cm 2 , and the distance between the anode and the cathode was set at 5 mm.
• the diaphragm was applied to the face of the cathode, oriented towards the anode from a suspension of asbestos in a caustic brine, then heated for 16 hours at 90 ° C., applying the technique described in the application for Luxembourg patent 77.996 of August 19, 1977, in the name of the Applicant.
• the grammage of the resulting diaphragm was 1.3 kg / m 2 of cathode.
• the abovementioned brine was electrolysed in the cell, at 85 ° C., at a current density of 2 kA per square meter of anode, and the flow rate of brine introduced into the cell was adjusted.
• anode chamber so that the caustic brine leaving the cathode chamber contains approximately 100 g of sodium hydroxide and 140 g of sodium chloride per kg.
• the cathode potential was measured periodically using the Luggin capillary measurement method. connected to a saturated calomel reference electrode (ECS) (Modern Electrochemistry, Bockris and Reddy, Plenum Press, 1970, vol. 2, p. 890 and 891).
• ECS saturated calomel reference electrode
• the cathode consisted of a mild steel mesh which was successively pickled using hydrochloric acid passivated with formalin, then heated to 750 ° C, in contact with an oxidizing flame produced by a laboratory bunsen burner, supplied in gas from the city of Brussels. The treatment was continued for a sufficient time to form on the surface of the steel lattice, a layer of magnetite approximately 10 microns thick.
• the cathode used consisted of a mild steel lattice, identical to that of the test of Example 1, which was successively pickled with hydrochloric acid passivated with formalin, then coated with a layer of magnetite by spraying a magnetite powder into a plasma jet, in an inert atmosphere.
• the mean grain diameter of the magnetite powder was approximately 8 microns, and the quantity of magnetite used was adjusted to obtain a coating of magnetite of approximately 250 microns on the cathode.
• a mild steel mesh identical to that of the preceding examples, pickled with formaldehyde passivated hydrochloric acid, was used to manufacture the cathode.
• the pickled lattice was then coated with ten successive layers of mixed crystals of nickel oxide and cobalt oxide, having the structure of spinels, of general formula NiC 02 0 4 .
• the mesh previously heated to 250 ° C., was immersed in a solution 0.1 molar of nickel nitrate and 0.2 molar of cobalt nitrate in butanol, then heated in air for 10 minutes at 250 ° C. After the application of the tenth layer of the coating, the coated mesh was heated in air for 16 hours at 350 ° C, then cooled to room temperature.
• a cathode prior to the invention consisting of a mild steel lattice, identical to that of Examples 1 and 2, and which was only pickled by treatment with hydrochloric acid passivated with formalin, then mounted as is in the cell.
• Table IV shows the evolution of the potential of the cathode during electrolysis.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)

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• 1978
  • 1978-08-24 FR FR7824757A patent/FR2434213A1/fr active Granted
• 1979
  • 1979-08-13 EP EP79200445A patent/EP0008476B1/fr not_active Expired
  • 1979-08-13 FI FI792508A patent/FI65283C/fi not_active IP Right Cessation
  • 1979-08-13 DE DE7979200445T patent/DE2965571D1/de not_active Expired
  • 1979-08-13 AT AT79200445T patent/ATE3653T1/de not_active IP Right Cessation
  • 1979-08-14 ZA ZA00794241A patent/ZA794241B/xx unknown
  • 1979-08-16 AU AU50008/79A patent/AU522946B2/en not_active Ceased
  • 1979-08-17 BR BR7905329A patent/BR7905329A/pt not_active IP Right Cessation
  • 1979-08-22 US US06/068,521 patent/US4243497A/en not_active Expired - Lifetime
  • 1979-08-23 CA CA000334338A patent/CA1142129A/fr not_active Expired
  • 1979-08-23 NO NO792732A patent/NO153110C/no unknown
  • 1979-08-23 JP JP10764479A patent/JPS5531195A/ja active Pending
  • 1979-08-23 ES ES483595A patent/ES483595A1/es not_active Expired
  • 1979-08-23 PT PT70103A patent/PT70103A/pt unknown

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