Sealing structure of flow guide bipolar plate or membrane electrode for fuel cell
Technical Field
The invention relates to a fuel cell, in particular to a sealing structure of a flow guide bipolar plate or a membrane electrode of the fuel cell.
Background
An electrochemical fuel cell is a device capable of converting hydrogen and an oxidant into electrical energy and reaction products. The inner core component of the device is a Membrane Electrode (MEA), which is composed of a proton exchange Membrane and two porous conductive materials sandwiched between two surfaces of the Membrane, such as carbon paper. The membrane contains a uniform and finely dispersed catalyst, such as a platinum metal catalyst, for initiating an electrochemical reaction at the interface between the membrane and the carbon paper. The electrons generated in the electrochemical reaction process can be led out by conductive objects at two sides of the membrane electrode through an external circuit to form a current loop.
At the anode end of the membrane electrode, fuel can permeate through a porous diffusion material (carbon paper) and undergo electrochemical reaction on the surface of a catalyst to lose electrons to form positive ions, and the positive ions can pass through a proton exchange membrane through migration to reach the cathode end at the other end of the membrane electrode. At the cathode end of the membrane electrode, a gas containing an oxidant (e.g., oxygen), such as air, forms negative ions by permeating through a porous diffusion material (carbon paper) and electrochemically reacting on the surface of the catalyst to give electrons. The anions formed at the cathode end react with the positive ions transferred from the anode end to form reaction products.
In a pem fuel cell using hydrogen as the fuel and oxygen-containing air as the oxidant (or pure oxygen as the oxidant), the catalytic electrochemical reaction of the fuel hydrogen in the anode region produces hydrogen cations (or protons). The proton exchange membrane assists the migration of positive hydrogen ions from the anode region to the cathode region. In addition, the proton exchange membrane separates the hydrogen-containing fuel gas stream from the oxygen-containing gas stream so that they do not mix with each other to cause explosive reactions.
In the cathode region, oxygen gains electrons on the catalyst surface, forming negative ions, which react with the hydrogen positive ions transported from the anode region to produce water as a reaction product. In a proton exchange membrane fuel cell using hydrogen, air (oxygen), the anode reaction and the cathode reaction can be expressed by the following equations:
and (3) cathode reaction:
in a typical pem fuel cell, a Membrane Electrode (MEA) is generally placed between two conductive plates, and the surface of each guide plate in contact with the MEA is die-cast, stamped, or mechanically milled to form at least one or more channels. The flow guide polar plates can be polar plates made of metal materials or polar plates made of graphite materials. The fluid pore channels and the diversion trenches on the diversion polar plates respectively guide the fuel and the oxidant into the anode area and the cathode area on two sides of the membrane electrode. In the structure of a single proton exchange membrane fuel cell, only one membrane electrode is present, and a guide plate of anode fuel and a guide plate of cathode oxidant are respectively arranged on two sides of the membrane electrode. The guide plates are used as current collector plates and mechanical supports at two sides of the membrane electrode, and the guide grooves on the guide plates are also used as channels for fuel and oxidant to enter the surfaces of the anode and the cathode and as channels for taking away water generated in the operation process of the fuel cell.
In order to increase the total power of the whole proton exchange membrane fuel cell, two or more single cells can be connected in series to form a battery pack in a straight-stacked manner or connected in a flat-laid manner to form a battery pack. In the direct-stacking and serial-type battery pack, two surfaces of one polar plate can be provided with flow guide grooves, wherein one surface can be used as an anode flow guide surface of one membrane electrode, and the other surface can be used as a cathode flow guide surface of another adjacent membrane electrode, and the polar plate is called a bipolar plate. A series of cells are connected together in a manner to form a battery pack. The battery pack is generally fastened together into one body by a front end plate, a rear end plate and a tie rod.
A typical battery pack generally includes: (1) the fuel (such as hydrogen, methanol or hydrogen-rich gas obtained by reforming methanol, natural gas and gasoline) and the oxidant (mainly oxygen or air) are uniformly distributed in the diversion trenches of the anode surface and the cathode surface; (2) the inlet and outlet of cooling fluid (such as water) and the flow guide channel uniformly distribute the cooling fluid into the cooling channels in each battery pack, and the heat generated by the electrochemical exothermic reaction of hydrogen and oxygen in the fuel cell is absorbed and taken out of the battery pack for heat dissipation; (3) the outlets of the fuel gas and the oxidant gas and the corresponding flow guide channels can carry out liquid and vapor water generated in the fuel cell when the fuel gas and the oxidant gas are discharged. Typically, all fuel, oxidant, and cooling fluid inlets and outlets are provided in one or both end plates of the fuel cell stack.
The proton exchange membrane fuel cell can be used as a power system of all vehicles, ships and other vehicles, and can also be used as a portable, movable and fixed power generation device. Sealing is critical to ensure that the fuel and oxidant in a pem fuel cell are distributed over the entire membrane electrode surfaces without mixing. If the seal is not good, two situations may arise: one case is where the fuel gas and the oxidant gas are mixed inside the fuel cell. In fuel cells operating with hydrogen and oxygen, this mixing is extremely fatal, and once an explosion is initiated, the destructive power is very large; another situation is that the fuel gas or the oxidant gas leaks to the outside of the fuel cell, which not only reduces the efficiency of the fuel cell, but also causes explosion once the fuel hydrogen gas accumulates to some extent in the outside concentration. Therefore, great attention is paid to the sealing technique of the fuel cell. The sealing technology of the current fuel cell mainly comprises the following 4 methods:
method 1: the area of the proton exchange membrane adopted by the membrane electrode is far larger than that of a porous supporting material in the membrane electrode, such as carbon paper, the membrane exceeding the area of the carbon paper is not an active area of electrochemical reaction, and two pieces of carbon paper (the catalyst layer is pressed in the middle) are respectively pressed on two sides of the membrane in the active area of the electrochemical reaction. After the membrane electrode is placed between two flow guide plates, the membrane with the electrochemical activity higher than that of the membraneis directly used as a base material of a sealing material and plays a role in preventing two adjacent flow guide plates from being in direct contact with each other to cause short circuit, as shown in figure 1, the membrane electrode is a structural schematic diagram of the existing membrane electrode. The figure includes an air inlet 1, a cooling water inlet 2, a hydrogen inlet 3, a proton exchange membrane 4, and an active portion 5 coated with a catalyst. Fig. 2 is a schematic structural diagram of a baffle and a sealing element, and the diagram includes an air inlet 1, a cooling water inlet 2, a hydrogen inlet 3, a baffle 6, a baffle groove 7, and a sealing element 8. The sealing elements 8 are arranged in the sealing grooves or on the planes of the front and back surfaces of the guide plate 6, and a part of the sealing elements is higher than the surface of the guide plate 6 respectively, so that the sealing elements and the base material film 4 in the film electrode achieve the sealing effect in a pressing mode (figure 3).
The 2 nd method: the sealing device adopted in european patent EP0604683a1 is shown in fig. 4, and comprises an air inlet 1, a sealing element 8 and a membrane electrode 10, fig. 5 is a cross-sectional view of fig. 4, and the cross-sectional view comprises the air inlet 1, a proton exchange membrane 4, the sealing element 8 and a carbon paper 9, and is characterized in that two porous supporting materials on the membrane electrode, such as two carbon papers 9, greatly extend out of the active area of the membrane electrode, and the sealing material 8 is placed on the proton exchange membrane 4 of the membrane electrode, so that two diversion plates sandwiching the membrane electrode do not need to be placed with sealing material.
The 3 rd method: the sealing device adopted in shanghai Shenli company patent (patent No. 01238847.5) is characterized in that a membrane electrode is divided into two partsas shown in fig. 6, wherein part 10 in fig. 6 is an active part of the membrane electrode for reaction, and part 11 in fig. 6 is a frame (only the part outside the dotted line) of the membrane electrode. The parts 10 and 11 are two distinct materials, and the two parts 10 and 11 are well defined, the part 11 is generally made of plastic or elastic rubber, resin, and is connected with the part 10 into a body by adhesion method. The sealing between the electrode assembly and the baffle can also be performed by placing the sealing member on the frame or on the baffle (see fig. 7 and 8).
The 4 th method comprises the following steps: the membrane electrode is cut orderly, the periphery of the membrane electrode is wrapped and sealed by an elastomer such as a rubber material (as shown in figures 9 and 10), and the membrane electrode is tightly pressed with a corresponding guide plate (provided with a sealing groove) (as shown in figures 11 and 12) to achieve the sealing purpose.
The four sealing methods described above all have a very serious common technical drawback: because the fuel cell stack is assembled by combining a plurality of membrane electrodes and bipolar plates, and the front end plate and the rear end plate of the fuel cell stack must bear larger uniform fastening force, the sealing element has certain elastic deformation and is tightly attached to the membrane electrodes and the bipolar plates, and the sealing effect can be achieved. Therefore, the surfaces of the sealing member can generate adhesion force on the surfaces of the membrane electrode and the bipolar plate which are contacted with the sealing member under the action of long-time fastening force. Whether the sealing elements are arranged on the front surface and the reverse surface of the bipolar plate or the sealing elements are arranged on the membrane electrodes, when the fuel cell stack is disassembled, because the surface membrane electrode and the bipolar plate whichare contacted with the sealing elements generate great adhesion, two possibilities are generated:
1. the original sealing element is arranged on the bipolar plate, although the surface of the sealing element and the sealing groove on the bipolar plate is provided with adhesive, the sealing element is fastened with the end faces of certain sealing areas of the membrane electrode for a long time and generates larger adhesive force, when the galvanic pile is disassembled to separate the bipolar plate from the membrane electrode, the sealing element is often torn off and deformed, so that the sealing element cannot be reassembled, and the sealing element cannot be reused after being deformed;
2. the original sealing element is arranged on the membrane electrode under the similar condition, when the galvanic pile is disassembled to separate the bipolar plate from the membrane electrode, the sealing element is usually elongated and deformed, falls off from the original membrane electrode, cannot be reassembled, and cannot be reused after the sealing element is deformed.
Disclosure of Invention
The present invention is directed to overcome the above-mentioned drawbacks of the prior art, and provides a sealing structure for a flow guiding bipolar plate or a membrane electrode of a fuel cell, wherein when the flow guiding bipolar plate is separated from the membrane electrode, the sealing member is not easy to deform or fall off, and can be reused.
The purpose of the invention can be realized by the following technical scheme: the sealing structure for the flow guide bipolar plate or the membrane electrode of the fuel cell comprises a flow guide bipolar plate or a membrane electrode and a sealing element, and is characterized in that the sealing element is arrangedat the symmetrical positions of the front side and the back side of the flow guide bipolar plate or the membrane electrode, a plurality of connecting through holes are formed at the positions where the sealing element is arranged on the flow guide bipolar plate or the membrane electrode, and the two sealing elements arranged at the front side and the back side of the flow guide bipolar plate or the membrane electrode are connected together by the same material as the two sealing elements through the connecting through holes.
The sealing element completely seals the connecting through hole on the flow guide bipolar plate or the membrane electrode, so that two fluids on two sides of the flow guide bipolar plate or the membrane electrode cannot be communicated with each other.
The sealing element is arranged in the sealing groove or on the plane of the guide bipolar plate with the symmetrical front and back surfaces and is connected with the sealing groove or the plane by a plurality of connecting through holes which are arranged in the sealing groove or on the plane and are made of the same material as the sealing element.
The sealing elements are arranged on the gasket frames at the periphery of the front side and the back side of the membrane electrode and are connected by the same material as the sealing elements through a plurality of connecting through holes arranged on the gasket frames.
The flow guide bipolar plate or the membrane electrode is arranged in a mould after being punched, and a sealing structure is formed by injecting sealing materials into the mould and heating and curing the sealing materials.
The sealing material comprises silicon rubber.
Compared with the prior art, the sealing elements are arranged at the symmetrical positions of the front surface and the back surface of the flow guide bipolar plate or the membrane electrode, and the two sealing elements are connected together through the same material as the sealing elements at a plurality of points of the two sealing elements. Because the sealing element of the invention is positioned at the symmetrical positions of the front and back surfaces of the flow guide bipolar plate or the membrane electrode, and the two sealing elements are connected together through the through hole, namely the two sealing elements form a whole, when the flow guide bipolar plate is separated from the membrane electrode, the sealing element is not easy to deform and fall off, and the sealing element can be reused when being repeatedly assembled.
Drawings
FIG. 1 is a schematic structural diagram of a first conventional membrane electrode;
FIG. 2 is a schematic structural view of a first prior art bipolar plate with a seal installed;
FIG. 3 is a cross-sectional view A-A of FIG. 2;
FIG. 4 is a schematic structural view of a second membrane electrode of the prior art after a sealing member is installed;
FIG. 5 is a cross-sectional view A-A of FIG. 4;
FIG. 6 is a schematic structural view of a third conventional membrane electrode assembly;
FIG. 7 is a schematic structural view of a third conventional membrane electrode assembly with a seal member mounted thereon;
FIG. 8 is a schematic view of a second prior art bipolar plate with a seal installed;
FIG. 9 is a schematic view of a fourth conventional membrane electrode assembly with a seal installed thereon;
FIG. 10 is a cross-sectional view A-A of FIG. 9;
FIG. 11 is a schematic structural view of a third prior art flow guiding bipolar plate;
FIG. 12 is a cross-sectional view A-A of FIG. 11;
FIG. 13 is a schematic view of a flow-guiding bipolar plate according to the present invention after a through hole is formed in a sealing groove thereof;
FIG. 14 is a schematic structural view of a sealing member of the present invention disposed in a through hole of a sealing groove on both sides of a flow guiding bipolar plate;
FIG. 15 is a schematic view of the sealing member of the present invention disposed in planar through holes on the front and back sides of a flow directing bipolar plate;
FIG. 16 is a schematic view of the sealing member of the present invention disposed in the through-hole of the gasket frame around the membrane electrode;
FIG. 17 is a schematic view of the sealing member of the present invention disposed in the through-hole of the gas diffusion layer material around the membrane electrode;
FIG. 18 is a schematic view of a seal according to the present invention wrapping the membrane electrode;
FIG. 19 is a schematic structural view of a flow-guiding bipolar plate according to the present invention showing the positional relationship between a sealing member and a through hole;
fig. 20 is a schematic view of a flow directing bipolar plate or membrane electrode of the present invention being processed in a mold.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments.
Example 1
As shown in fig. 13, 14 and 15, a sealing structure of a flow guiding bipolar plate for a fuel cell comprises a flow guiding bipolar plate 6 and a sealing member 8, wherein the sealing member 8 is arranged at symmetrical positions on the front and back surfaces of the flow guiding bipolar plate 6, a plurality of connecting through holes 14 are formed at the position of the flow guiding bipolar plate 6 where the sealing member 8 is arranged, and the two sealing members 8 arranged on the front and back surfaces of the flow guiding bipolar plate 6 are connected together by the same material as the connecting through holes 14.
The two seals 8 of this embodiment are located in the seal grooves 13 on the front and back sides of the flow directing bipolar plate 6 (fig. 14) or on the flat surface (fig. 15) and are joined together at a plurality of points, and the joint material completely seals the joint channels connecting the seals 8 on the front and back sides, and no gas can cross each other. Thus, when the galvanic pile is disassembled and the flow-guiding bipolar plate is separated from the membrane electrode, the sealing elements 8 on the front and back surfaces are mutually pulled to each other and can not fall off, and the connecting channels 14 of the two sealing elements are completely sealed by the same sealing element material, so that two fluids on the two surfaces of the flow-guiding bipolar plate can not be communicated with each other.
Example 2
As shown in fig. 16 and 17, a sealing structure for a membrane electrode of a fuel cell comprises a membrane electrode 10 and a sealing member 8, wherein the sealing member 8 is arranged at symmetrical positions on the front and back sides of the membrane electrode 10, a plurality of connecting through holes 14 are formed at the position where the sealing member 8 is arranged on the membrane electrode 10, and the two sealing members 8 arranged on the front and back sides of the membrane electrode are connected together by the same material as the sealing members through the plurality of connecting through holes 14.
The seal 8 of the present embodiment is disposed on the membrane electrode 10, including on the gasket border 11 around the membrane electrode (fig. 16), or on the gdl material 15 of the membrane electrode (fig. 17). The two sealing members 8 are located on the front and back sides of the membrane electrode and are connected together at a plurality of points, and the connecting material completely seals the connecting channels 14 connecting the sealing members on the front and back sides, so that no gas or fluid can pass through or communicate with each other. When the stack is disassembled and the bipolar plate is separated from the membrane electrode, the sealing rings on the front and back surfaces are mutually pulled to each other and cannot fall off, and the connecting channels of the two sealing rings are completely sealed by the same sealing element material, so that two different fluids flowing through the front and back surfaces of the membrane electrode cannot be communicated with each other.
Example 3
As shown in fig. 18, and fig. 9 and 10, a sealing structure for a membrane electrode of a fuel cell includes a membrane electrode 10 and a sealing member 8, wherein the sealing member 8 seals the periphery of the membrane electrode 10 in an enveloping manner, a plurality of connecting through holes 14 are formed at the position where the sealing member 8 is disposed on the membrane electrode 10, and the two sealing members 8 disposed on the front and back surfaces of the membrane electrode are connected together by the same material as the sealing members themselves through the plurality of connecting through holes 14.
The sealing member 8 of the present embodiment wraps the periphery of the three-in-one membrane electrode, the sealing regions at the periphery of the front and back faces of the membrane electrode are provided with the sealing members 8 and are connected together at a plurality of points, and the connecting material completely seals the connecting channels connecting the sealing members at the front and back faces, and no gas or fluid can pass through or communicate with each other. Thus, when the galvanic pile is disassembled and the diversion bipolar plate is separated from the membrane electrode, the sealing elements of the sealing areas around the front and the back surfaces are mutually pulled and do not fall off, and the connecting channels between the two sealing rings 8 are completely sealed by the same sealing element material, so that two different fluids flowing through the front and the back surfaces of the membrane electrode can not be mutually communicated.
The implementation process of the sealing structure comprises the following technical scheme:
as shown in fig. 19 and 20, when the sealing member 8 is disposed on the bipolar plate 6, a plurality of front and back sealing member connection points are selected on the bipolar plate 6, holes 14 are formed, the bipolar plate 6 is pressed by upper and lower molds 16, 17, a sealing material such as silicon rubber is injected into a mold casting groove 18, and the sealing material is heated to 70 ℃ for curing.
Referring to fig. 20 and fig. 17, when the sealing member 8 is disposed on the three-in-one membrane electrode 10, a plurality of front and back sealing member connection points are selected in the sealing area 15 of the membrane electrode 10, and holes 14 are formed, the three-in-one membrane electrode 10 is pressed by the upper and lower molds 16, 17, and a sealing material, such as silicone rubber, is injected into the mold casting groove 18, and heated to 70 ℃ for curing.