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
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/60—Constructional parts of cells
  • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections
• • 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
• • 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
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes

Definitions

• the invention relates to an electrochemical half cell, in particular for the electrolysis of an aqueous alkali metal chloride solution.
• an electrochemical half cell for the electrolysis of an aqueous alkali chloride solution with several gas pockets lying one above the other is known, a gas diffusion electrode (GDE) being located between each gas pocket and the electrolyte space.
• the gas diffusion electrodes are attached and sealed to structural elements of the half cell with the aid of holding elements, which e.g. are designed as terminal strips.
• the main disadvantage of a clamp connection is that it cannot guarantee a sufficient seal from the gas space to the electrolyte space in the long run. For the technical implementation, downtimes of over three years are necessary, otherwise there is no economic use. Small pressure surges also occur in the electrolyzer, which can loosen the GDE clamp connection. This impairs the tightness of the connection, so that gas escapes from the gas pocket into the electrolyte space or electrolyte floods the gas pockets.
• EP-A-1 029 946 describes a gas diffusion electrode consisting of a reactive layer and a gas diffusion layer and a collector plate, e.g. a silver net.
• the coating does not completely cover the collector plate, but rather leaves a coating-free edge.
• a thin, frame-shaped metal plate, preferably made of silver, is applied to the gas diffusion electrode in such a way that the metallic frame covers the smallest possible area of the electrochemically active coating.
• the frame projecting beyond the gas diffusion electrode serves to connect the gas diffusion electrode to the housing of the half cell, for example by welding.
• This contacting is complicated and covers part of the GDE area, as a result of which the local current density of the free GDE area increases and the performance of the electrolyser decreases due to the higher electroysis voltage.
• the complicated installation means high manufacturing costs for the electrolyzer.
• EP-A-1 041 176 also describes a gas diffusion electrode with a coating-free edge, the gas diffusion electrode being connected in the coating-free edge region to the current collector frame of the cathode half-cell by means of welding.
• the cavities between two adjacent gas diffusion electrodes are sealed with an alkali-resistant material.
• a disadvantage of this installation method is the sealing material required for adequate sealing. The sealing effect diminishes during the operating time of the electrolyzer, so that the service life is not long enough from an economic point of view. Since the gas diffusion electrode must be connected to the electrolyzer, a low-resistance connection is particularly important in the technical design. The lowest contact resistance leads to significant economic disadvantages in technical electrolysis.
• Low-resistance connections can generally be established by short current paths, as mentioned in DE-A-44 44 114.
• a low-resistance connection is also provided by a metal-to-metal contact if the two metals are connected by soldering or welding.
• the carrier of the GDE is best connected to the holding structure of the electrolyzer with low resistance by welding or soldering.
• a sealing effect must also be achieved.
• the object of the present invention is to make the gas diffusion electrode low-resistance, i.e. with the lowest possible ohmic resistance, to be installed in the electrochemical half cell and at the same time to produce a sealing effect between the gas and electrolyte space.
• the structure of the gas diffusion electrode must be designed so that neither gas from the gas pocket into the electrolyte space nor electrolyte from the electrolyte space can enter the gas pocket. At the same time, as little as possible electrochemically active area of the gas diffusion electrode should be lost due to the installation. Furthermore, the installation should be technically as simple as possible.
• the invention relates to an electrochemical half cell, at least consisting of a gas space, an electrolyte space and a gas diffusion electrode separating the gas space from the electrolyte space as a cathode or anode, which comprises at least one electrically conductive support and an electrochemically active coating, the gas diffusion electrode having a coating-free edge region and is connected to a holding structure, characterized in that the gas diffusion electrode in the coating-free edge area is connected to the holding structure with the aid of an electrically conductive plate which covers at least the coating-free edge area and an edge area of the electrochemically active coating.
• the electrochemical half cell according to the invention consists of at least one gas space, which is divided into several gas pockets one above the other. Each gas pocket is separated from the electrolyte compartment by a gas diffusion electrode.
• the half cell is used in particular as a cathode half cell for the electrolysis of aqueous alkali chloride solutions.
• the electrolyte space is filled with the electrolyte, for example an aqueous alkali hydroxide solution.
• the gas diffusion electrodes are used as oxygen consumption cathodes. Gas, for example air or oxygen, flows through the gas pockets, the gas being introduced into the lowermost gas pocket and flowing from it cascading into the gas pockets above. From the top one Excess gas is removed from the gas pocket.
• the functioning of an electrolysis cell with a gas diffusion electrode based on the principle of pressure compensation is described for example in DE-A-44 44 114.
• the gas diffusion electrode consists at least of an electrically conductive carrier and an electrochemically active coating.
• the electrically conductive carrier is preferably a mesh, fabric, braid, knitted fabric, fleece or foam made of metal, in particular made of nickel, silver or silver-plated nickel.
• the electrochemically active coating preferably consists of at least one catalyst, e.g. Silver (I) oxide, and a binder, e.g. Polytetrafluoroethylene (PTFE).
• the electrochemically active coating can be constructed from one or more layers.
• a gas diffusion layer for example composed of a mixture of carbon and polytetrafluoroethylene, can be provided, which is applied to the carrier.
• a method for producing such a gas diffusion electrode is known for example from DE-A-37 10 168.
• the coating material penetrates into the cavities of the carrier and lies on the carrier.
• the gas diffusion electrode of the electrochemical half cell according to the invention has a coating-free edge area along the four edges.
• the coating-free edge area is preferably from 2 to 10 mm, particularly preferably from 4 to 8 mm.
• the electrochemically active coating and, if present, further coatings in the edge area are removed.
• the support structure preferably consists of the 'same material, are made of the the half-shells of the electrolysis half-elements, in particular of nickel in the case of chlor-alkali electrolysis.
• the holding structure is frame-shaped and, together with the gas diffusion electrode and the rear wall of the gas pocket, forms the spatial limitation of the gas pocket.
• the electrically conductive support of the gas diffusion electrode rests on the holding structure, to the extent that the support rests not only in the coating-free edge area but also in an edge area of the coating on the holding structure.
• the gas diffusion electrode preferably lies on the holding structure up to an edge region of the coating of 2 to 8 mm, particularly preferably 2 to 5 mm.
• the carrier of the gas diffusion electrode thus lies on the holding structure in total in a range from 4 to 18 mm, particularly preferably from 2 to 13 mm.
• an electrically conductive plate preferably made of metal, in particular nickel, is placed on the coating-free edge area, ie the uncoated electrically conductive support, and an edge area of the coating.
• the edge region of the coating covered by the electrically conductive plate is preferably 1 to 10 mm.
• the plate may protrude beyond the carrier of the gas diffusion electrode in a range of at most 5 mm, preferably at most 3 mm.
• the plate can contact the holding structure.
• the width of the electrically conductive plate is preferably from 3 to 21 mm. The plate is pressed firmly onto the gas diffusion electrode and the holding structure, since sufficient sealing between the gas diffusion electrode and the holding structure must be ensured because of the sealing and the power supply.
• the gas diffusion electrode is over the plate-.jtrat.-dsr-. Holding structure, preferably connected by welding.
• the welding takes place in the area of the coating-free edge of the gas diffusion electrode.
• Laser welding or ultrasonic welding is preferably used.
• the ratio of the thickness of the plate to the distance between the plate and the carrier must be taken into account. In the case of laser welding in particular, the ratio is preferably less than 0.5, particularly preferably less than 0.2. Is the distance between the plate and the support relatively large, e.g. with a relatively thick coating on the carrier, this can be compensated for by a thicker plate.
• the thickness of the coating that is applied to the electrically conductive carrier must be taken into account.
• the part of the coating which lies on the carrier is greater than 0.5 mm and the distance between the plate and the carrier cannot be reduced to preferably less than 1 mm, particularly preferably less than 0.5 mm, by pressing the plate , it is advantageous to insert a wedge-shaped spacer between the plate and the support.
• a thicker plate without a spacer can be used.
• the electrically conductive plate preferably has a thickness of 0.05 to 2 mm.
• the plate preferably runs frame-shaped around the gas diffusion electrode.
• a seal is provided in the area of the contact surface of the gas diffusion electrode or the electrically conductive carrier on the holding structure.
• the seal is located between the support structure and the carrier.
• the coating in the edge region which is covered by the plate is hydrophilized in order to produce a gas-tight connection.
• the hydrophilization is carried out, for example, by applying a surfactant-containing solution to the surface of the coating, as a result of which the electrolyte penetrates into the coating and causes sealing by capillary forces.
• the advantage of the half-cell according to the invention is that the gas diffusion electrode is electrically conductively connected to the holding structure by means of the electrically conductive plate and at the same time the gas space is sealed off from the electrolyte space, so that no electrolyte can enter the gas space and no gas can enter the electrolyte space.
• the smallest possible electrochemically active area of the gas diffusion electrode is lost as a result of the installation.
• FIG. 1 shows a schematic section from a first embodiment of the half cell according to the invention
• Figure 2 shows a schematic section of a second embodiment with seal
• Figure 3 shows a schematic section of a third embodiment with a wedge-shaped spacer
• FIG. 1 shows a gas space 2 of the electrochemical half cell with a holding structure 1 at the edge of the gas space 2.
• the holding structure 1, the gas diffusion electrode 6 and the rear wall 11 form the gas space 2 in the form of a gas pocket.
• the gas diffusion electrode 6 has a coating-free edge area 8, in which the coating has been removed and the carrier 5 is exposed.
• the coating 4 penetrates the support 5 and lies on it.
• the coating-free edge 8 of the gas diffusion electrode 6 and the edge region 7 of the coating 4 rest on the holding structure 1.
• An electrically conductive plate 3 rests on the gas diffusion electrode 6 in such a way that it covers the coating-free edge 8 and the edge area 7 of the coating 4. It also protrudes over the coating-free edge 8 out, where it comes to lie on Haltestniktur 1.
• the plate 3 is connected to the gas diffusion electrode 6 and the holding structure 1, preferably by means of welding.
• FIG. 2 shows a further embodiment, the same or similar components having the same reference numbers.
• the embodiment differs from that shown in FIG. 1 in that a seal 9 is provided between the holding structure 1 and the gas diffusion electrode 6.
• a gas diffusion electrode was used, which consisted of an electrically conductive support and an electrochemically active layer made of a mixture of silver (I) oxide and PTFE.
• the carrier of the gas diffusion electrode consisted of a network of nickel, in which the wire thickness was 0.14 mm and the mesh size was 0.5 mm.
• the gas diffusion electrode was freed of the silver (I) oxide / PTFE-containing layer in an edge region of 4 mm.
• a PTFE seal was inserted between the holding structure and the gas diffusion electrode.
• a metal strip of nickel having a thickness of 1 and a width of 8 mm was positioned such that the coating-free edge completely, and an edge region of the gas diffusion electrode of 4 mm covered ⁇ ar.- was subsequently pressed the nickel strips on the support structure and by means of Laser welding connected to the carrier and the holding structure.
• a gas diffusion electrode was used which had two layers: a gas diffusion layer consisting of PTFE and carbon, and an electrochemically active layer consisting of PTFE, carbon and silver.
• the electrically conductive carrier of the gas diffusion electrode consisted of a network of silver-plated nickel, in which the wire thickness was 0.16 mm and the mesh size was 0.46 mm.
• the gas diffusion electrode was freed of the coating consisting of gas diffusion layer and electrochemically active layer in an edge region of 4 mm.
• a PTFE seal was inserted between the holding structure and the gas diffusion electrode.
• the coating was hydrophilized in an edge region of the coating of the gas diffusion electrode. For this purpose, it was coated with a surfactant-containing solution (Triton®-X-100 solution, Merck).
• a metal tire made of nickel with a thickness of 1 mm and a width of 8 mm was positioned so that the coating-free edge was completely covered and an edge area of the gas diffusion electrode was covered by 4 mm.
• the nickel strip was then pressed onto the holding structure and connected to the carrier and the holding structure by means of laser welding.

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• 2003
  • 2003-07-04 DE DE10330232A patent/DE10330232A1/de not_active Withdrawn
• 2004
  • 2004-06-21 EP EP04740108A patent/EP1644556B1/fr not_active Not-in-force
  • 2004-06-21 JP JP2006518015A patent/JP4729485B2/ja not_active Expired - Fee Related
  • 2004-06-21 WO PCT/EP2004/006667 patent/WO2005003410A1/fr active Application Filing
  • 2004-06-21 AT AT04740108T patent/ATE541069T1/de active
  • 2004-06-21 CN CN2004800190392A patent/CN1816649B/zh not_active Expired - Fee Related
  • 2004-07-02 US US10/882,644 patent/US20050224341A1/en not_active Abandoned
  • 2004-07-02 TW TW093119956A patent/TW200519232A/zh unknown
• 2008
  • 2008-06-18 US US12/141,399 patent/US7691242B2/en not_active Expired - Fee Related

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