Patent Publication Number: US-2009233138-A1

Title: Membrane Electrode and Current Collecting Board Assembly of Electrochemical Cell, and Electrochemical Cell Module

Description:
TECHNICAL FIELD 
     The invention relates to an electrochemical cell, and in particular, relates to a membrane electrode and current collecting board assembly of an electrochemical cell, as well as an electrochemical cell module. 
     TECHNICAL BACKGROUND 
     Chinese patent application 99808103.5 discloses a hermetic sealing assembly comprised of a bipolar plate and membrane electrode unit of a polymeric electrolyte membrane fuel. The bipolar plate and membrane electrode unit can be bonded by curable polymer. The hermetic sealing assembly is produced by coating adhesive beads on the gas conduits outside and inside the gas chamber. According to the present invention, these assemblies can be laminated and bonded together to form polymeric electrolyte fuel cell stack. 
     The above technical solution makes some improvement compared with the prior art. However, the bipolar plate not only acts to lead out voltage current, but also is used for constructing the sealed gas chamber, so the material of the bipolar plate should have both good conductivity and good resistance to air leakage. Meanwhile, an internal gas conduit is necessary in the bipolar plate&#39;s structure, which will result in some complexity as well as a decrease in the effective area available for the membrane electrode. In addition, in order to improve the cell&#39;s performance, it is always necessary to dispose the flow field on the bipolar plate, which requires the bipolar plate to be highly processable, thereby raising the requirements to the bipolar plate are further enhanced. 
     Chinese patent application 200610029938.1 discloses a sealing structure of an embedded compact power-generating cell. The compact power-generating cell includes a hydrogen side end plate, two pieces of metal conductive titanium webs, two diffusion layers, a proton exchange membrane electrode, an oxygen side end plate, a red and black socket, and four stainless steel screws with four nuts. One of the end plates of the compact power-generating cell is groove-like, and the other is boss-like. The titanium metal web is twisted on the end plates beforehand by means of a conductive socket which includes a red and a black socket disposed on the front side and back side of the end plate, respectively. 
     When compared with the prior art, the technical solution described above makes some progress. However, the structure and assembly process thereof are relatively complicated, and suffer from a high manufacturing cost. 
     SUMMARY OF THE INVENTION 
     For the purpose of overcoming the drawbacks described in the Chinese patent application 99808103.5 including high requirements for the bipolar plate and low effective area availability for the membrane electrode, as well as the drawbacks described in Chinese patent application 200610029938.1 relatively complicated structure and assembly process and high manufacturing cost, the present invention provides a membrane electrode and current collecting board assembly for an electrochemical cell and an electrochemical cell module. 
     The invention solves the afore-mentioned technical problems as follows: 
     An assembly for a membrane electrode and current collecting board is provided, which comprises a membrane layer, at least one gas diffusion layer on the one side and a layer of porous current collecting board on the one side, which are stacked in sequence, wherein the membrane includes a reactive area and a non-reactive area. The porous current collecting board on the one side comprises a reactive area, a non-reactive area and an electric leading-out area. The at least one gas diffusion layer on the one side is located between the porous current collecting board on one the side and the membrane. Its area corresponds to the reactive areas of the porous current collecting board and the membrane. The area surrounding the periphery of the at least one gas diffusion layer on the one side which corresponds to the non-reactive areas of the porous current collecting board and the membrane is filled with sealing material which is cured subsequently. 
     An alternative solution is to provide at least one gas diffusion layer on the other side which is attached to the side face of the membrane opposite to where the gas diffusion layer on the one side is disposed. In addition, a layer of porous current collecting board is provided on the other side which is attached to the gas diffusion layer on the other side. The porous current collecting board on the other side comprises a reactive area, a non-reactive area and an electric leading-out area. The area of the at least one gas diffusion layer on the other side corresponds to the reactive areas of the porous current collecting board on the other side and the membrane. The area surrounding the periphery of the at least one gas diffusion layer on the other side which corresponds to the non-reactive areas of the porous current collecting board on the other side and the membrane is filled with sealing material which is subsequently cured. 
     Another alternative solution is to provide a layer of porous current collecting board on the other side which is attached to the side face of the membrane opposite where the gas diffusion layer on the one side is disposed. The attached part of the non-reactive areas of the porous current collecting board on the other side and the membrane is filled with and adhered by sealing material which is cured subsequently. 
     Yet a further alternative solution is to provide at least one gas diffusion layer on the other side which is attached to the side face of the membrane opposite where the gas diffusion layer on the one side is disposed while a layer of porous current collecting board is disposed on the other side which is attached to the gas diffusion layer on the other side. The area of the at least one gas diffusion layer on the other side corresponds to the area of the membrane. 
     The cured seal material has a width of 0.05-2 mm. The sealing material may be thermoplastic plastic, thermoset plastic, or elastic polymer, although silicon rubber is preferred. 
     The membrane layer can be a proton exchange membrane, and there can be catalyst layers disposed at least in the reactive area on both sides of the membrane layer. 
     Each gas diffusion layer can be made of at least one conductive gas-permeable material selected from the group consisting of carbon fiber paper, carbon fiber cloth, gas-permeable graphite plate and metal web. The side adjacent to the membrane of each gas diffusion layer can be coated with a catalyst layer. 
     Each porous current collecting board is porous and gas-permeable in the reactive area, but is substantially gas-tight in the non-reactive area. Furthermore, each porous current collecting board is made of corrosion resistant and conductive metal material. 
     An electrochemical cell module is provided which includes at least one electrochemical single cell. The electrochemical single cell includes an end plate with gas channels on one side, an assembly having a membrane electrode and a current collecting plate, and an end plate with gas channels on the other side. The three components described above are stacked in sequence. 
     The end plate with gas channels can be made of at least one material selected from thermoplastic polymer, thermoset polymer and elastic polymer. The polymer material is preferably inject-moldable plastic material. 
     The electrochemical cell can be a fuel cell, an electrolytic cell, a regenerative fuel cell, or an electrochemical oxygen generator. 
     The electrochemical cell module further comprises a printed circuit board (PCB), which is directly welded onto the electric leading-out area of each porous current collecting board. 
     The PCB may include a circuit used for controlling the electrochemical cell, or light-emitting element. 
     The positive advancement of the present invention is that, when compared with the prior art, it distributes the requirements for conductivity, impermeability and processability to different materials so that the traditional costly carbon or metal material can be replaced by plastic material, and the structure and assembly process are also simplified. As a result, commercial production costs can be decreased. At the same time, the effective area availability of the membrane electrode is enhanced. The present solution is suitable for the production of a fuel cell, an electrolytic cell, a regenerative fuel cell, and an electrochemical oxygen generator. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  to  FIG. 4  are schematic views showing the first example of an assembly according to the invention. 
         FIG. 5  is a schematic view showing the second example of an assembly according to the invention. 
         FIG. 6  is a schematic view showing the third example of an assembly according to the invention. 
         FIG. 7  is a schematic view showing the fourth example of an assembly according to the invention. 
         FIG. 8  is a schematic view showing the first example of a cell module according to the invention. 
         FIG. 9  is a schematic view showing the second example of a cell module according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     1. Examples of the Assembly 
     EXAMPLE 1 
     A metal plate  1  used for the porous current collecting plate on the one side is shown in  FIG. 1 . The middle area of the metal plate, which is reactive area  101 , is full of fine through-holes, and the periphery without holes is non-reactive area  102 . The stem-like protrusion on the right side is electric leading-out area  103 . The end of the electric leading-out area has a through-hole used for electrical connection. 
       FIG. 2  shows an intermediate product provided with carbon paper  2  used as a gas diffusion layer on the one side and glue  3  used as sealing material. The area of carbon paper  2  substantially corresponds to the reactive area  101  of metal plate  1 . The location of glue  3  substantially corresponds to non-reactive area  102  of metal plate  1 . 
       FIG. 3  shows the assembly provided with membrane  4 . The center section of membrane  4  is reactive area  401 , and the periphery is non-reactive area  402 . 
     The area shown in the figure is filled with glue  3 , which produces good sealing after being cured. The glue  3  has a width of 1.5 mm after being cured. After pressing and assembling, the excess glue  3  will expanded outward, and the excess sections can be cut off. The glue  3  is silicon rubber. 
     Membrane  4  is proton exchange membrane with both sides coated with catalyst. The full name of carbon paper  2  is carbon fiber paper. 
     The surface of metal plate  1  is plated with gold, thus possessing good corrosion resistance. 
     EXAMPLE 2 
       FIG. 5  is a modification of the assembly shown in Example 1 which is further provided with carbon paper  5  used as a gas diffusion layer on the other side. Metal plate  6  is used as a porous current collecting plate on the other side, and glue  7  is used as sealing material. 
     The locational relationship of carbon paper  5 , metal plate  6  and glue  7 , as well as the distribution of the reactive area, the non-reactive area and the electric leading-out area is similar to that of metal plate  1 , membrane  4  and carbon paper  2  in example 1. The figures are already enough for clear comprehension, so it&#39;s not necessary to mark each part with indicative numbers. 
     EXAMPLE 3 
       FIG. 6  is a modification of the assembly shown in Example 1, which is further provided with metal plate  6  used as porous current collecting board on the other side and glue  7  used as seal material. Since the assembly is used to prepare an electrolytic cell module, the electrolytic cell has an extremely high polarized overvoltage during operation. No carbon paper  5  is used in order to avoid electric erosion, so the glue  7  is nearly too thin to be visible in the figures. The locational relationship of the other elements is similar to that of example  2 . 
     2. Examples of Module 
     EXAMPLE 1 
       FIG. 8  shows a fuel cell module which is constructed by providing the assembly of the above examples with an end plate  8  on one side, an end plate  9  on the other side to form a single cell. A plurality of single cells are stacked together. Both the end plate  8  on the one side and the end plate  9  on the other side comprise PC material, i.e., polycarbonate. 
     EXAMPLE 2 
       FIG. 9  shows a fuel cell module including PCB  10 , which is directly welded to the electric leading-out area  103  of metal plate of each single cell. An element  11  is used for the fuel cell control circuit, while light-emitting diode  12  is mounted on the PCB  10 .