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
  • C25B1/13—Ozone
• • 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
• • 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
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

• the present invention relates to an ozone generating electrolysis cell comprising a negative electrode, an ozone generating positive electrode comprising a mixture of lead(IV) oxide (referred to as lead dioxide) and polytetrafluoroethylene (PTFE), a mem- brane arranged between the negative electrode and the positive electrode, and an electrically conductive, liquid and gas permeable first electrode support in contact with a side of the positive electrode located opposite to the membrane, said side of the electrode support having a surface covered with a platinum-containing layer.
• lead dioxide lead(IV) oxide
• PTFE polytetrafluoroethylene
• electrolysis cells having a central part for effecting the electrolysis and thus for generating ozone are used, said central part being composed of an anode (positive electrode) usually in the form of a planar plate, a cathode (negative electrode) having the same construction, and a proton exchange membrane (e.g. NafionTM) constituting a solid electrolyte in the form of a planar plate arranged be- tween the anode and the cathode, as it is described in e.g. U.S. Patent No. 6,328,862.
• anode positive electrode
• a cathode negative electrode
• a proton exchange membrane e.g. NafionTM
• the anode itself is a porous member generally made of titanium and having liquid and gas permeable capabilities.
• a thin layer of platinum is applied, typically by an electroplating process.
• an electrode layer is arranged, said electrode layer comprising metallic or semimetallic conductors and/or oxides thereof (e.g. lead dioxide) characterized by high overvoltage with respect to the evolution potential of the oxygen. Adjacent to the outer surface of the anode, ie.
• an anode side collector plate (also referred to as an electrode support) is arranged in con- tact with the anode providing on the one hand an electrical connection between the anode and a power supply, and on the other hand, an outlet for the gas of oxygen/ozone produced.
• the anode side collector plate can also enable directing water required for the electrolysis to the anode itself.
• the cathode also comprises of a member made of a porous material or a material having suitable channels in it, generally stainless steel or titanium, and having liquid and gas permeable capabilities as well.
• a member made of a porous material or a material having suitable channels in it generally stainless steel or titanium, and having liquid and gas permeable capabilities as well.
• an electrode layer containing metal is applied for generating hydrogen.
• This metal containing electrode layer is generally a thin layer of platinum.
• a cathode side collector plate Adjacent to the outer surface of the cathode, a cathode side collector plate (also referred to as an electrode support) is arranged in contact with the cathode, said cathode side collector plate providing an electrical connection between the cathode and the power supply, on the one hand, and directing the water required for the electrolysis to the proton exchange membrane and to the anode therethrough and, if necessary, providing an outlet for the produced gas of hydrogen, on the other hand.
• the above described multilayer electrode structure is housed in a suitably formed cell housing.
• the cell housing is usually formed of two halves, which are aligned and then fixed together in a sealed manner by means of e.g. through-bolts.
• the compressive force required for the perfect contact between the adjacent layers of the electrode structure is also provided by the mutual screwed fixation of the two halves of the housing.
• the electrolysis of the water is caused to start and hydrogen ions with positive charge move from the anode to the cathode through the proton exchange membrane.
• oxygen and ozone are generated at the anode due to the electrolysis.
• the coefficient of efficiency of the ozone conversion ie. the amount of ozone in the produced gas of oxygen, is determined by the quality of the anodic electrode layer and the operational parameters, therefore the ozone production ca- pacity of the cell can be significantly affected through an appropriate manufacturing technology of the anodic electrode layer.
• the lead dioxide film is formed on the anode by electroplating.
• the electrode layer thus obtained is rather uneven, which implies a change of the superficial elec- trical conductivity (resistance) of the electrode layer.
• the electrode layer produced by electroplating can be formed difficultly, it is rather rigid and it can easily break, therefore it is not suitable for mass production of ozone generating electrolysis cells containing solid electrolyte.
• the pores of a thin porous PTFE sheet are filled with a mixture of lead dioxide and the material of the proton exchange membrane, as described in Japanese Patent No. 3,504,021 and U.S. Patent No. 6,054,230.
• the proton exchange membrane is placed on the member thus obtained, and then its surface is covered with a platinum containing material.
• this multilayer structure is subject to a hot pressing at a temperature between 120 0 C and 140 0 C.
• the pressed laminated mem- ber is inserted between the anode and the cathode, and then housed in a cell casing to obtain the electrolysis cell.
• U.S. Patent No. 6,328,862 discloses a method for producing an anodic electrode layer containing lead dioxide, wherein a dispersion of PTFE, pulverised lead dioxide and volatile dispersing agent (preferably ethanol or isopropyl alcohol) are mixed and the mix- ture thus obtained is shaped to a very thin sheet, preferably by calendering, and the dispersing agent is vaporised, for example, by heating.
• Each step of the production of the electrode layer is performed at a temperature of up to 100 0 C in order to avoid possible thermal decomposition of the lead dioxide.
• the PTFE content of the mixture obtained by this method is about 5% by weight, the film itself is rigid, easily breaking and less duc- tile.
• An object of the present inventions is therefore to provide an ozone generating electrolysis cell which allows to produce the ozone generating electrode from solid-phase raw materials at ambient temperature and without the use of dispersing agent.
• Another object of the invention is to provide a mixed material of lead dioxide and PTFE, for example for the anode of an ozone generating electrolysis cell, that is resilient and ductile due to its relatively high content of PTFE, that can be prepared at ambient temperature and that can be produced in less technological steps and with lower costs than the lead dioxide/PTFE films commonly used today.
• a further object of the present invention is to provide a negative electrode side (cathode side) electrode structure that in addition to its electrical conductivity and mechanical strength, due to its structure, inherently has liquid and gas permeable capabilities, too.
• an ozone generating electrolysis cell in which the positive electrode (ie. the anode) is made of a mixture prepared by high-pressure moulding of lead dioxide grains of colloid size and PTFE filaments having a dimension of at most 1 mm, and wherein the negative electrode (ie. the cathode) is adjoined to a side of the membrane located opposite to the positive electrode by a given compressing force and is formed on a surface of a porous sec- ond electrode support.
• the positive electrode ie. the anode
• the negative electrode ie. the cathode
• FIG. 1A is the cross-sectional view of a preferred embodiment of the electrode structure used for an ozone generating electrolysis cell according to the invention
• - Figure IB is a schematic enlarged view of the material structure of a preferred embodiment of the second electrode support for supporting the negative electrode forming a part of the electrode structure shown in Figure IA
• - Figure 2 is a longitudinal cross-sectional view of an assembled ozone generating electrolysis cell comprising the electrode structure schematically illustrated in Figure IA.
• the electrode structure 10 of Figure IA used in the ozone generating electrolysis cell according to the invention primarily comprises a negative electrode (or cathode) 13, an ozone generating positive electrode (or anode) 16, a proton exchange membrane 15 arranged between the electrodes 15, 16, and a first (positive electrode or anode side) electrode support 17 arranged on a side of the positive electrode 16 located opposite to the membrane 15.
• the electrode support 17 is arranged on an (anode side) bearing member 18 provided with a through-hole 19 for an electrical contact.
• the electrode 13 is formed on a second (cathode side) electrode support 12 arranged in a (cathode side) bearing member 11.
• the electrode support 12 serves for providing electrical contact between an ex- ternal DC power supply (not shown) and the negative electrode 13, on the one hand, and for directing the water required for the electrolysis to the electrode 13 during the operation of the cell, and diverting the produced gas of hydrogen from the electrode 13, on the other hand.
• the electrode support 12 is in the form of a member with high electrical conductivity and porous structure, as well as with high mechanical strength in order to tolerate the high pressures of up to 20 bars that may develop inside the cell.
• the electrode support 12 is a thin and porous titanium frit arranged in the bearing member 11 and produced by high-pressure cold moulding of a titan granulate.
• the term "frit” is referred to as a material produced from pulverised grains by cold moulding.
• the technological parameters of the moulding process are adjusted in such a manner that the obtained titanium frit have the desired mechanical strength, while reaching substantial porosity.
• the titanium granulate preferably comprises three different sizes of titanium grains in a layered structure, in which the layers are arranged in the order of the grain size in such a way that before moulding, a relatively coarse-grained titanium powder 12a (preferably comprising grains having a dimension of 600-1200 ⁇ m) is put into the bearing member 11, then a titanium powder 12b of medium sized grains (preferably comprising grains having a dimension of 350-600 ⁇ m) is applied thereon, and finally, a fine-grained titanium powder 12c (preferably comprising grains having a dimension of 150-350 ⁇ m) is applied thereon.
• a relatively coarse-grained titanium powder 12a preferably comprising grains having a dimension of 600-1200 ⁇ m
• a titanium powder 12b of medium sized grains preferably comprising grains having a dimension of 350-600 ⁇ m
• a fine-grained titanium powder 12c preferably comprising grains having a dimension of 150-350 ⁇ m
• the cathode side bearing member 11 is made of a special, chemically resistant plastic shaped to e.g. an annular member. It is obvious, however, that the bearing member 11 may be made of any other material and may have any other shape as well.
• An essential condition for the efficient cell operation is the good electrical contact between the electrodes 13, 16 and the membrane 15. Therefore, formation of the electrode 13 on the electrode support 12 made from the titanium frit has key importance.
• the negative electrode 13 it is preferred that for the negative electrode 13, extra fine-grained platinum powder (so called platinum black) is used.
• the platinum black is applied to the electrode support 12 at ambient temperature and pressure, without the use of a protective gas (ie. at ambient air) and in the form of a suspension.
• the suspension is made from the aqueous solution of 40 mg platinum black and sodium dodecyl sulphate (SDS) of 1 ml with a concentration of 0.001 mol/1.
• SDS sodium dodecyl sulphate
• an ultrasonic bath is used for a period of 5 minutes.
• the suspension remains stable till its application, that is, no deposition can be detected.
• the electrode support 12 is placed onto an absorbent paper, and then the suspension is applied onto the surface of the electrode support 12 comprising, the finest grains, in small quantities by means of an automated pipette.
• the electrode 13 in the form of a continuous platinum layer is caused to develop on the surface of the electrode support 12. Smoothness of the surface thus obtained may be improved, if necessary, for example by pressing.
• water may be used instead of the SDS solution to produce the suspension, which reduces the production costs.
• the proton exchange (or proton conducting) membrane 15 is preferably in the form of a sulphonylated, perfluorinated polymeric resin membrane, most preferably the polymeric membrane Nafion® of DuPont de Nemours, Co.
• the membrane 15 constitutes the solid electrolyte of the ozone generating electrolysis cell according to the invention.
• the membrane 15 also provides the separation of the gases produced on the cathode side and the anode side.
• the water required for the electrolysis is introduced at one side of the membrane 15, through the second electrode support 12 provided with the electrode 13, whereas the gaseous mixture of oxygen and ozone to be processed is pro- Jerusalem on the other side of the membrane 15, that is, at the ozone generating electrode 16.
• the positive electrode 16 serves for supporting the anode side electrochemical reaction.
• electrically conducting metals, semimetals and/or oxides thereof are used in general.
• the use of the oxides of transition metals is advantageous because those are commonly available and inexpensive.
• the mechanical strength of these oxides is low, thus they have to be placed on a substrate with high mechanical strength and chemical resistance against the highly corrosive gaseous mixture of oxygen and ozone so that said oxides could tolerate the high pressures arising in the cell during operation without being mechanically damaged.
• electrode support 17 used to support the positive electrode 16 noble metals (e.g. platinum) with good electrical conductivity or the alloys and/or mixture thereof can be used.
• a suitably perforated platinum sheet provided with through-holes preferably having a diameter of at least 0.8 mm is used as the electrode support 17.
• the anode side bearing member 18 serves for removing the gaseous mixture of oxygen and ozone produced at the electrode 16 during operation of the cell away from the electrode 16.
• the bearing member 18 is additionally used to fasten the electrode sup- port 17 to the electrode 16 and the latter to the membrane 15 in order to provide a perfect electrical contact, as well as to provide a homogenous transition surface therebetween.
• the bearing member 18 is made of a resilient, porous, chemically resistive material, preferably PTFE frit produced from grained PTFE by high-pressure moulding.
• the bearing member 18 is provided with a through-hole 19. In the assembled ozone generating electrolysis cell according to the invention, the through-hole 19 is adapted to receive an anode side conducting member used for electrically connecting the anode side electrode support 17 to an external DC power supply (see Figure 2).
• the ozone generating electrode 16 is made of a material with good electrical conductivity, plasticity, high overvoltage with respect to the evolution potential and chemical resistance against the highly corrosive gaseous mixture of oxygen and ozone, preferably a mixture of lead dioxide and PTFE comprising PTFE in an amount of at least 10% by weight.
• the mixture of lead dioxide and PTFE is produced from solid-phase raw materials at ambient temperature by a process described below, with no use of further additives.
• the evolution potential of the oxygen is very high and thus, the desired ozone can be produced thereon with a high conversional efficiency.
• Said component is advantageous because it is inexpensive, commonly available, chemically inert (due to not having a higher oxidation state) and insoluble in the majority of solvents and it has better electrical conductivity than certain metals. It is well known that during the ozone genera- tion, the crystal modification ⁇ of the two possible crystal modifications ⁇ and ⁇ of lead dioxide can be used to perform the desired oxygen-to-ozone conversion, wherein during the conversion, as proved by X-ray diffraction measurements, a ⁇ -type interfacial recrys- tallization takes place.
• the lead dioxide Before producing the positive electrode 16, the lead dioxide is subject to continuous grinding, which results in the production of lead dioxide grains of colloid size, ie. with an average grain size of 0.5-100 ⁇ m, from the initial macroscopic sized lead dioxide pieces.
• PTFE elementary filaments having a fibrous (cotton wool-type) structure having a thickness of 50-100 ⁇ m and a length of up to 1 mm are used.
• PTFE filaments with such dimensions can be produced by abrasive machining or abrasion of a PTFE block.
• the dimension of the initial PTFE elementary filaments has a definite effect on the plasticity and resiliency of the final mixture of lead dioxide and PTFE.
• lead dioxide ground into grains of colloid size in an amount of, for example, about 1600 mg and PTFE in the form of fine elementary filaments in an amount of, for example, about 300 mg are put into a mixing jar.
• the apolar materials can easily mix with one another. After some agitation, preferably for a period of 10 minutes, the mixture thus obtained is poured into a frit moulding tool especially formed for this purpose and then pressed therein by applying a pressure of at least 50 MPa, preferably 250 MPa, to shape a sheet with a thickness of 0.25 mm. During the moulding process, the PTFE filaments get tangled and fused, causing the lead dioxide grains to be joined at the same time. According to a microscopic examination of the resulted lead dioxide/PTFE sheet, it has been established that the mate- rial thus obtained has compact dimensions and a continuous surface, it can be easily formed mechanically, and in addition, it is resilient and ductile. Finally, the electrode 16 is produced by cutting to the desired size and shaping the resulted lead dioxide/PTFE sheet.
• an amount of about 16% by weight of PTFE in the above mentioned mixture of lead dioxide and PTFE is advantageous in respect of both plasticity/resiliency and electrical conductivity.
• the mixture will be more plastic but electrically less conductive.
• the mixture will be less plastic but electrically more conductive.
• the PTFE is subject to a structural conversion that, according to our experiences, results in a stabilizing effect on the ⁇ -type crystal modification of lead dioxide.
• the method according to the invention unlike prior art methods, does not include a step of heat treatment, no harmful crystal modification changes occur due to that. It has been experienced that the conductivity of the fibrous electrode is significantly higher than that of a material having a grained structure.
• the positive electrode 16 and the anode side electrode support 17 are formed as separate members. It should be noted, however, that the ozone generating electrode 16 and the first electrode support 17 may be formed as a combined electrode in such a manner that a thin platinum layer is applied on a (external) surface of the electrode 16 made from the mixture of lead dioxide and PTFE.
• the cell 100 in its assembled state is composed of a cathode side half cell 110 and an anode side half cell 115 that are fixed together in a form- fitting and thereby sealed manner.
• the electrode structure 10 is arranged in a seat 140 formed in the half cell 110 and defined by a bottom wall and a side wall, wherein the bearing member 11 of said electrode structure 10 abuts on the bottom wall of the seat 140 (see Figure IA).
• the form-fitting abutment is established between the outer surface of a compressive flange 145 of the half cell 115 and the side wall of the seat 140.
• the half cell 115 is provided with a depression 148 for receiving the anode side of the electrode structure 10, wherein said depression 148 is laterally defined by the compressive flange 145.
• the bearing member 18 of the electrode structure 10 shown in Figure IA
• compressive flange 145 pushes the electrode structure 10 to the bottom wall of the seat 140 with firmly fixing it thereby.
• the cathode side half cell 110 is provided with through-holes (without reference numbers in the drawing) for sealingly receiving a water feeding connector 160, a hydrogen and water discharging connector 162 and a cathode side electrical connector casing 130.
• the anode side half cell 115 is provided with through-holes (not marked in the drawings) for sealingly receiving an ozone/oxygen gas discharging connector 165 and an anode side electrical connector casing 135.
• the half cells 110, 115 are made of a chemically resistant, gas-proof material, preferably some kind of plastic, and formed preferably by injection moulding, machining or another shaping process.
• the electric connector casing 130 there is at least one current conducting member 150 (see Figure IA) arranged for providing electrical connection between the external power supply and the negative electrode 13.
• the current conductive member 150 is in the form of a member with the capability of reversible deformation along its longitudinal axis and thereby the exertion of a compressing force, said member 150 preferably being in the form of a cylindrical spring. It is also preferred that the electrical conductive member 150 is made of titanium.
• the electrical connector casing 135 there is at least one current conducting member 155 (see Figure IA) arranged for providing electrical connection between the external power supply and the electrode support 17.
• the current conductive member 155 is in the form of a member with the capability of reversible deformation along its longitudinal axis and thereby the exertion of a compressing force, said member 150 preferably being in the form of a cylindrical spring. It is also preferred that the electrical conductive member 155 is made of platinum.
• electrical conductive members 150, 155 in the form of resilient parts allows to eliminate the changes in dimension due to size devia- tions and temperature fluctuations.
• the external walls of the half cells 110, 115 ie. the walls not contacting with the electrode structure 10, are provided with a cathode side confining plate 120 and an anode side confining plate 125, respectively.
• the confining plates 120, 125 serve for protecting the half cells 110, 115 against the external mechanical influences. Accordingly, the confining plates 120, 125 are made of a material with high mechanical strength, preferably stainless steel.
• the water feeding connector 160, the hydrogen and water discharging connector 162 and the cathode side electrical connector casing 130 are firmly (but releas- ably) fixed into through-holes (not marked in the drawings) formed in the confining plate 120.
• the ozone/oxygen gas discharging connector 165 and the anode side electrical connector casing 135 are firmly (but releasably) fixed into through-holes (without reference numbers in the drawing) formed in the confining plate 125.
• through-bolts 185 are arranged in through-holes formed in the half cells 110, 115 and in the confining plates 120, 125, said through-bolts 185 being fastened by screw nuts 190.
• the cell 100 according to the invention is assembled in the steps described below.
• the through-bolts 185 are inserted into the through-holes formed in the cathode side confining plate 120, then the cathode side half cell 110 is arranged on the confining plate 120 with its seat 140 facing upwards.
• the cathode side electrode support 12 and the negative electrode 13 accommodated in the bearing member 11 are arranged in the seat 140 in a position of contacting with the half cell 110.
• the electrode support is then wetted and the proton conductive membrane 15, which has been cut to size and shaped, is placed thereon, followed by wetting said membrane 15 as well.
• the electrode 16 already cut to size and shaped and the anode side electrode support 17 are arranged on the membrane 15.
• the anode side bearing member 18 is placed onto the electrode support 17 and the anode side half cell 115 is pushed onto the assembly thus obtained, causing thereby the various parts of the electrode structure 10 to be securely fixed.
• the bearing member 18 is wetted, the confining plate 125 is placed onto the half cell 115 and the structural elements of the cell 100 are forced to each other by screwing the screw nuts 190 to the through-bolts 185, thereby providing the electrical and mechanical contacts between the structural elements, as well as the sealed joints.
• the connectors 160, 162, 165 and the connector casings 130, 135 with the current conducting members 150, 155 are mounted into the cell 100.
• water is fed into the side of the cell 100 adjacent to the negative electrode 13, and through the porous cathode side electrode support 12 and the porous cathode, the water flows to the proton conductive membrane 15 and further to the positive electrode 16 through the membrane 15.
• the electrolysis of the water is caused to start at the electrodes 13, 16, and hydrogen ions with positive charge move from the positive electrode 16 to the negative electrode 13 through the proton conductive membrane 15.
• the hydrogen ions transform into hydrogen of neutral charge by accepting an electron from the negative electrode 13.
• oxygen and ozone is generated at the positive electrode 16 as a result of the electrolysis.
• the efficiency of the ozone conversion ie. the amount of ozone in the produced gaseous mixture of oxygen and ozone, is determined by the quality of the electrode 16 and the operational parameters.
• the amount of the generated gaseous mixture of oxygen and ozone and thereby its pressure under particular conditions may be adjusted by changing the electrolysing current.
• the amount of ozone in the gaseous mixture of oxygen and ozone generated by the cell 100 according to the invention is preferably at most 12% by volume. Cooling the cell is provided by means of a water flow introduced through the connector 160 and diverted partly through the connector 162.

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• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)

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• 2005
  • 2005-12-23 HU HU0501204A patent/HUP0501204A2/hu unknown
• 2006
  • 2006-12-22 AU AU2006327902A patent/AU2006327902A1/en not_active Abandoned
  • 2006-12-22 WO PCT/HU2006/000126 patent/WO2007072098A2/en active Application Filing
  • 2006-12-22 US US12/158,909 patent/US20080314740A1/en not_active Abandoned
  • 2006-12-22 JP JP2008546654A patent/JP2009520881A/ja active Pending
  • 2006-12-22 EP EP06831525A patent/EP1979509A2/en not_active Withdrawn
  • 2006-12-22 RU RU2008129184/15A patent/RU2008129184A/ru not_active Application Discontinuation
  • 2006-12-22 CN CNA2006800516790A patent/CN101360848A/zh active Pending
• 2008
  • 2008-06-23 IL IL192391A patent/IL192391A0/en unknown
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