Patent Publication Number: US-2006011489-A1

Title: Electrolysis process and apparatus

Description:
FIELD OF THE INVENTION  
      The invention relates to electrolysis of a fluid. In particular the invention relates to an electrolysis process and an apparatus for carrying out the process.  
     BACKGROUND OF THE INVENTION  
      Due to concerns about the environment, pollution and depletion of limited fossil energy sources attention is given worldwide to renewable clean energy sources.  
      Due to the intermittent nature of these sources (solar, wind, etc.) some means of energy storage is required.  
      Hydrogen gas produced by electrolysis during the availability of the primary energy has been identified as a viable way to store energy. It can also serve as an energy carrier where hydrogen is produced at the site of the source (nuclear, fossil or renewables) and converted to hydrogen through electrolysis which is then transported to where the energy is required. Hydrogen is further a candidate for fuel for vehicles utilizing high efficient fuel cells.  
      The basic science involved in electrolysis is well known. Commercial plants have been in operation for decades, but due to the projected large future demand for hydrogen the following problems were identified with present technologies as set out in a United Nations report—Renewable Energy—United Nations Project, Johansen et al, p 929: 
          “Changing the cell configuration and geometry with the goal of reducing the cell resistance by a factor of 3 to 10 thereby reducing the ohmic voltage losses     Developing new and inexpensive electrocatalyst materials able to reduce the sum of anodic and cathodic overvoltage to about 0.3 volt or less     Developing new diaphragm materials that are superior to conventional asbestos cloth.”       

      The applicant has identified a need for an improved electrolysis cell, and a method of producing gasses by electrolysis, with high current density and efficiency, cheap and simple construction and with high gas purities without the need for subsequent purification.  
     SUMMARY OF THE INVENTION  
      According to a first aspect of the invention, there is provided an electrolysis apparatus for the production of hydrogen and oxygen, which apparatus includes at least: 
          two or more tubular electrodes, at least one of which is an inner electrode located in at least one outer electrode; and     a separator interposed between the inner and outer electrodes and substantially coextensive therewith.        

      One or more of the electrodes may, in use, be an anode.  
      One or more of the electrodes may, in use, be a cathode.  
      The separator may be positioned between the anode and the cathode so that there is substantially no gap between the separator and the anode, and the separator and the cathode.  
      A portion of the separator may be bonded to a support structure associated with the anode and/or the cathode using, for example, an epoxy sealant.  
      The electrodes may be made of an apertured conductive material.  
      The electrodes may be plated.  
      The apertured conductive material may be a sintered body having flow channels extending between the inside and the outside thereof.  
      The apertured conductive material may be a single layer mesh.  
      The apertured conductive material may be made of two or more layers of mesh.  
      The apertured conductive material may be a three dimensional mesh.  
      The apertured conductive material may comprise a conductive polymer. The polymer may be coated with a conductive material, for example, a metal.  
      The apertured conductive material may comprise of silver, nickel, stainless steel or copper.  
      The anode and cathode may be substantially concentric.  
      A plurality of anodes and cathodes of various diameters may be nested to provide a high electrolysis surface area to electrolysis apparatus volume ratio.  
      The cathode and/or anode may be made of one or more first material i.e. the substrate, and plated with a second material or composition of matter which is electrically conductive.  
      The anode may be made of a conductive metal, for example, stainless steel mesh.  
      The anode may comprise two or more layers of stainless steel mesh.  
      The anode may be nickel plated.  
      The cathode may be made of a conductive metal, for example, stainless steel mesh.  
      The cathode may comprise two or more layers of stainless steel mesh.  
      The cathode may be nickel plated.  
      The mesh may be nickel plated before or after the layers of stainless steel are placed together.  
      One or more of the tubular anode and the cathode may be closed off at one end such that, in use, an overpressure is established within the closed off tubular anode or cathode.  
      One or more conductors may be provided in association with the anode and/or the cathode.  
      In one embodiment a tubular mesh conductor is provided on the outside of the anode and another on the inside of the cathode.  
      In another embodiment, the conductors are in the form of one or more conductive strips attached to a portion or portions of the anode and/or the cathode.  
      The separator may comprise one or more layers of a fibrous material.  
      The separator may comprise one or more layers of a wettable material.  
      The separator may comprise one or more layers of a wettable fibrous material.  
      The separator may comprise one or more layers of cellulose containing composition.  
      The cellulose containing composition may be paper.  
      The paper may be a filter paper.  
      The filter paper may be chemical resistant filter paper.  
      The filter paper may be medium to fast grade filter paper.  
      In an embodiment, the apparatus may consist of: 
          a tubular apertured stainless steel mesh anode electrode; and     a tubular apertured nickel-plated stainless steel cathode electrode, wherein the cathode and anode are substantially concentric and the cathode lies within the anode; and     a separator means between the anode and cathode comprising one or more layers of a fibrous material.        

      The apparatus may, in use, include an alkaline electrolyte solution.  
      The apparatus may, in use, include an acidic electrolyte solution.  
      The apparatus may include means for supplying and conducting electrical current to the electrodes.  
      The apparatus may include means for drawing off the gasses.  
      The apparatus may include means for removing vapour from the generated gasses.  
      A plurality of anode and cathode sets may be used in parallel.  
      A plurality of anode and cathode sets may be used in series.  
      The anode and cathode sets and the conductors may be configured in such a way that a plurality of such sets is arranged around a tubular conductor for the anodes, all in a common electrolyte. Each cathode may be connected to its own conductor.  
      The invention extends to a separator for an electrolysis apparatus, which separator is interposed between the anode and the cathode of the apparatus, said separator comprising one or more layers of fibrous material.  
      The fibrous material may be wettable.  
      The wettable material may be a cellulose containing composition.  
      The cellulose containing composition may be paper.  
      The paper may be a filter paper.  
      The filter paper may be chemical resistant filter paper.  
      The filter paper may be medium to fast grade filter paper.  
      The invention extends to an electrolysis process carried out in an apparatus substantially as described above.  
      The process may include: 
          establishing a potential difference between the anode and the cathode; and     contacting the anode and cathode with an electrolyte from which gasses are liberated by electrolysis.        

      The process may include contacting the apparatus with an electrolyte solution of between 10% and 50% by mass of electrolytic salts, typically from 20% to 35% by mass.  
      The electrolyte solution may be a KOH, NaOH, or other alkaline solution.  
      The electrolyte solution may be acidic.  
      The process may be carried out at from 40° C. to 100° C., typically from 60° C. to 90° C.  
      The electrodes may be submerged in the electrolyte.  
      The electrolyte may be pumped through the separator of the apparatus.  
      The electrolyte may be drip fed through the separator, thereby maintaining the separator saturated with electrolyte while minimizing the volume of fluid being circulated.  
    
    
     DESCRIPTION OF AN EXAMPLE OF THE INVENTION  
      The invention will now be described, by way of a non-limiting example only, with reference to the accompanying diagrammatic drawings and graph.  
     EXAMPLE  
      A cross section of an electrode pair  10  is shown in  FIG. 1 ( a ).  
      The electrodes  12 ,  14  of the electrode pair  10  are made of a stainless steel mesh.  
      The nickel plated copper pipe  22  is used as support and electrical connector to the cathode. It serves also to extract the hydrogen gas.  
      The top part of the pipe is covered with insulating material  13  to prevent contact with the electrolyte.  
      A cylindrical plastic plug  18  serve as support and seal of the inner cathode.  
      The cathode, anode and separator are sealed  16  at the bottom and top ends to prevent any mixing of the gasses.  
      Electrical connection to the outer anode is achieved by connecting it with nickel plated copper strips to a nickel plated copper conductor immersed in the electrolyte.  
      The inner electrode  12  i.e. the H 2  cathode consists of two layers of fine mesh stainless steel. A copper pipe  22  forms the electrical contact. The total length is 130 mm with 100 mm exposed to the electrolyte. The inner electrode  12  is nickel plated to a thickness of about 200 μm on the mesh. Two layers of medium filter paper  20  are wrapped around this mesh and the end points sealed with epoxy  16   
      The outer electrode  14 , i.e. the O 2  anode consists of two layers of fine mesh stainless steel. The anode  14  is not plated with nickel. The bottom of the electrode  14  is sealed with a plastic stopper  18 . An electrical contact is attached to the anode (not shown).  
      The electrode pair is immersed in the electrolyte. The electrolyte enters the inner pipe by liquid diffusion through the porous separator. The generated gasses are prevented from passing through the separator.  
      A plastic pipe  22  provides support.  
      The structure of a demister  40  is shown in  FIG. 1 ( b ).  
      The demister  40  consists of a 30 cm 22 mm diameter nickel plated copper pipe. The lower half  42  of the pipe contains rolled layers of course mesh stainless steel  44  around a plastic bar  46  with 10 mm diameter. The roll fits snugly in the pipe and traps all KOH spray and condenses most of the water vapour. The top half  48  is filled with brass curling to trap the remaining water vapour and cool the gasses down to room temperature. The heat is liberated to the atmosphere by normal convection and radiative cooling.  
      The above electrodes were tested using apparatus as described below.  
      A reactor which consists of a transparent plastic jar of 10 cm diameter and height 40 cm was used.  
      A KOH solution (25% m/m) was placed in the jar. The electrolyte was kept at a constant temperature for each experiment by supplying external heating. The electrode pair (as described above) was submerged in the electrolyte.  
      The generated gasses pass through demisters  40  on top of the reactor. These demisters  40  trap the KOH spray and water vapour at the high temperatures and deliver cooled dry gasses at room temperature.  
      A series of experiments were performed, measurement taken and current density (J-V) curves drawn as shown in  FIG. 2 .  
      The purity of the gasses produced with a 79° C. electrolyte was above 99.9%, without the need for further (separate) purification.