Fuel cell assembly and method for making the same

[0001] (Related application) This application benefits from being based on US Provisional Application No. 60 / 202,827 filed May 8, 2000 and US Provisional Application No. 60 / 242,136 filed October 23, 2000. As such, those statements shall form part of this application. [0002] (Technical field) The present invention has an electrolyte layer, a pair of gas diffusion electrode layers sandwiching the electrolyte layer, and a pair of distribution plates for defining passages of fuel gas and oxidant gas in contact with each gas diffusion electrode layer. It relates to a fuel cell composed of at least one cell. [0003] (Background of invention) A fuel cell has a pair of electrodes attached to both sides of the electrolyte layer, and supplies fuel gas such as hydrogen and alcohol to one electrode and oxidant gas such as oxygen and air to the other electrode to cause an electrochemical reaction by a catalyst. It is used to generate electricity, and there are phosphoric acid type, solid polymer type, molten carbonate type and the like depending on the electrolyte used for the electrolyte layer. [0004] Of these, the polymer electrolyte electrolyte fuel cell (SPFC), which uses an ion exchange membrane as the electrolyte, can be made smaller and has a lower operating temperature than the solid oxide fuel cell (SOFC) (SOFC). It is attracting attention because of its high power generation efficiency (100 ° C or less). [0005] In the above solid polymer electrolyte fuel cell, examples of the solid polymer electrolyte (SPE) include perfloolocarbon sulphonic acid (Nafion: trade name), phenol sulphonic acid, polystyrene sulphonic acid, and polytrifluorostyrene sulphonic acid. A thin film of an ion exchange resin such as the above is used, and carbon paper containing a catalyst powder made of platinum or the like is provided on both sides of the thin film of the ion exchange resin as a gas diffusion electrode to form a membrane / electrode assembly (MEA). A fuel cell is formed by defining a fuel gas passage on one surface side and an oxidizing agent gas passage such as air on the other surface side by a flow distribution plate (separator). [0006] Normally, a large number of these fuel cell cells are connected in series and used, but a stack is formed by stacking fuel cell cells and sharing a distribution plate between cells adjacent to each other in the stacking direction. [0007] On the other hand, in order to operate the fuel cell stably, it is important to control the temperature of each gas, distribution plate, electrolyte, flow rate of each gas, etc. as necessary. For example, Japanese Patent Application Laid-Open No. 8-185878 Japanese Patent Application Laid-Open No. 11-162490 discloses that the fuel cell is provided with a sensor for detecting the temperature, flow rate, etc. of the reaction gas. [0008] However, according to the above publication, since each sensor is provided outside the fuel cell, information for each fuel cell cannot be obtained, and highly accurate detection and control cannot always be performed. Further, Japanese Patent Application Laid-Open No. 11-162490 discloses that a voltage sensor and a resistance value sensor are incorporated in the fuel cell stack, but when these sensors are separately attached to the stack, the structure of the gas seal becomes complicated. There is a problem that the assembly of the stack becomes complicated, and in some cases, the durability of the seal portion is also lowered. This problem is exacerbated when a sensor is incorporated in each fuel cell. [0009] (Outline of the invention) In view of such problems of the prior art, a main object of the present invention is to provide a fuel cell in which a sensor and / or a heater can be easily incorporated into the fuel cell without complicating the seal structure. To do. [0010] A second object of the present invention is to provide a fuel cell in which a sensor and / or a heater can be easily incorporated into the fuel cell without complicating the manufacturing process. [0011] According to the present invention, such an object is to define a passage of a fuel gas and an oxidant gas in contact with an electrolyte layer, a pair of gas diffusion electrode layers sandwiching the electrolyte layer, and each gas diffusion electrode layer. A fuel cell composed of at least one cell having a distribution plate forming a pair of the above, and at least one of the temperature of the distribution plate, the temperature of each gas, and the flow velocity in at least one of the distribution plates. This is achieved by providing a fuel cell characterized in that a sensor for detecting the species and / or a heater for heating the distribution plate is integrally formed. In particular, the sensor and / or the heater is formed by forming a material constituting the sensor and / or the heater on each of the distribution plates in a desired shape, and each distribution plate etches the substrate. By performing the process of forming the sensor and / or the heater in a series of the process of forming each of the distribution plates, the sensor and the heater can be easily incorporated and the embedded structure is formed. There is no need for a separate seal structure for sensors and the like. [0012] (Form for carrying out the invention) FIG. 1 is an exploded perspective view showing a part of the structure of the fuel cell stack to which the present invention is applied. Actually, a fuel cell is obtained by connecting a plurality of these stacks in series or in parallel, reforming alcohol or the like, or directly supplying hydrogen gas or the like as fuel, and further supplying air or the like as oxidant gas. Is configured. [0013] This fuel cell stack is formed by stacking a plurality of fuel cell cells 1. As shown in FIGS. 2 (a) and 2 (b), each fuel cell 1 has an electrolyte layer 2 in the center of the stacking direction and a pair provided on the front and back surfaces thereof via gas diffusion electrode layers 3 and 4. It is composed of an eggplant distribution plate 5. Here, each distribution plate 5 is shared with the next-stage or previous-stage cell adjacent to the cell 1 in the stacking direction by processing both sides thereof. [0014] The electrolyte layer 2 is composed of a grid-like frame 21 and SPE22 filled between the grids 21a of the frame 21, that is, the through holes 21b as an electrolyte. As SPE22, for example, perfloolocarbon sulphonic acid (Nafion: trade name), phenol sulphonic acid, polystyrene sulphonic acid, polytrifluorostyrene sulphonic acid and the like are used. [0015] Here, the lattice-shaped frame 21 is formed by etching a silicon substrate and other processing, and has a quadrangular and annular peripheral portion and a quadrangular lattice portion provided inside the annular peripheral edge portion. As shown in FIGS. 2 (a) and 2 (b), each grid 21a of the grid portion of the grid frame 21 is provided with protrusions 21c so as to project toward the intermediate portion of the corresponding through holes 21b. There is. The protrusions 21c form ridges extending in the longitudinal direction of each grid 21a, defining a narrow intermediate portion within each through hole 21b. The protrusion 21c helps hold the SPE22 within each through hole 21b. [0016] Such protrusions can conveniently be formed at the same time as forming the grid-like frame 21. FIGS. 3 (a) to 3 (c) show the process of forming the electrolyte layer 2. First, as shown in FIG. 3A, resists 13 and 14 are formed in a predetermined pattern on both the front and back surfaces of a silicon substrate as a material for the grid-like frame 21. As shown in FIG. 3 (b), by anisotropic etching (wet etching) from both sides, a through hole 21b having a narrow middle portion in the thickness direction is formed by the protrusion 21c. .. Next, SPE22 is injected into each through hole 21b to make each surface of the electrolyte layer 2 a substantially flat surface. [0017] In this embodiment, quadrangular through holes 23a, 23b, 24a, and 24b are formed at diagonal positions of the grid-like frame 21. One diagonal through hole 23a, 23b of the lattice frame 21 constitutes a fuel gas supply path and a discharge path, and another diagonal through hole 24a, 24b constitutes an oxidant gas supply path and an discharge path. To do. If these through holes 23a, 23b and through holes 24a, 24b are formed by the same anisotropic etching (wet etching) as described above, they become holes having a rectangular opening having the same shape as the through holes 21b, and can be formed by, for example, dry etching. Once formed, the opening shape is arbitrary. [0018] On the other hand, the distribution plate 5 is also made by processing a silicon substrate and has almost the same shape as a quadrangle. Square recesses 51 and 52 having a flat bottom are formed on both the front and back surfaces of the central portion, and a large number of quadrangular pyramid-shaped protrusions 53 and 54 are provided on the flat bottom of the central recesses 51 and 52. ing. Further, on the surfaces of the recesses 51 and 52 and the protrusions 53 and 54, electrode terminal films 55 and 56 made of a gold (Au) plating layer for connecting the external circuit and the gas diffusion electrode layers 3 and 4 are known. The film is formed by the film method. [0019] FIGS. 4 (a) to 4 (c) show a method of forming each distribution plate 5. As shown in FIG. 4 (a), resists 15 and 16 are formed on each surface of the silicon substrate in a predetermined pattern, and as shown in FIG. 4 (b), the silicon substrate is anisotropically etched from both sides thereof. The recesses 51 and 52 and the protrusions 53 and 54 are formed at the same time. The distribution plates 5 at both ends of the fuel cell 1 in the stacking direction may be provided with a central recess and a quadrangular pyramid-shaped protrusion only on the inner surface. Next, the resists 15 and 16 are removed, and as shown in FIG. 4C, electrode terminal films 55 and 56 are formed on the surfaces of the recesses 51 and 52 and the protrusions 53 and 54. [0020] The distribution plate 5 is isomorphic to the grid frame 21 and thus forms a quadrangle. Square through holes 57a, 57b, 58a, 58b are provided at each corner of the edge. The through holes 57a and 57b provided at one diagonal position constitute the fuel gas supply path and the discharge path, and the through holes 58a and 58b provided at the other diagonal positions form the oxidant gas supply path and the discharge path. Make up the road. Here, as shown in FIG. 1, the recess 51 and the through holes 58a and 58b are communicated with each other by the oxidant gas grooves 59a and 59b provided at the edge, and the recess 52 and the through holes 57a and 57b are communicated with each other. It is communicated by similar fuel gas grooves 60a and 60b. These grooves 59a and 59b and the grooves 60a and 60b are formed by anisotropic etching (wet etching) to form a groove having a V-shaped cross section. Further, the through holes 57a and 57b and the through holes 58a and 58b are also formed by the same anisotropic etching as described above, so that the holes have a square opening having the same shape as the through holes 21b of the lattice frame 21. .. [0021] [0021] As is well shown in FIG. 5, a gas temperature sensor 61a, a flow rate sensor 61b, and a distribution plate temperature sensor 61c are integrally formed with the distribution plate 5 at appropriate positions of the distribution plate 5. The gas temperature sensor 61a and the distribution plate temperature sensor 61c are, for example, composed of a thermocouple in which a platinum film and a platinum rhodium film are in contact with each other, and these materials are formed on the distribution plate 5 and processed. Actually, for example, a sensor may be obtained by doping a part of a silicon substrate and utilizing a current change due to heat of a semiconductor film. Further, the gas temperature sensor 61a is located in an independent recess 64 of the distribution plate 5 for measuring the temperature of the non-flowing gas. The flow rate sensor 61b is composed of a resistance sensor, and utilizes the fact that the resistance changes in temperature and the resistance value changes as the flow rate changes. Further, a heater 62 is formed around the entire circumference of the distribution plate 5 in order to obtain a desired output at an early stage such as at the start of operation and to generate stable power generation. Although FIG. 1 shows the gas temperature sensor 61a, the flow rate sensor 61b, the distribution plate temperature sensor 61c and the heater 62 only on the upper surface of the distribution plate 5 at the bottom of the figure, the distribution plate 5 in the middle is actually shown. Sensors 61a, 61b, 61c and heater 62 are formed on both sides of the distribution plate 5 at the uppermost stage, respectively, on the lower surface thereof. Further, the positions and numbers of the sensors and heaters are also arbitrary as long as they can be manufactured in the film forming and etching steps as described later. [0022] The manufacturing procedure of the flow rate sensor 61b and the heater 62 is shown in FIGS. 6 (a) to 6 (i). First, a SiN insulating film 65, a Pt resistance film 66, and a SiN insulating film 67 are deposited on the surface of a silicon substrate in this order by, for example, a physical vapor deposition method (FIG. 6 (a)), and the patterns of the flow sensor 61b and the heater 62 are formed. Resists 68 and 69 are formed (Fig. 6 (b)). Then, the Pt resistance film 66 and the SiN insulating film 67 where the resists 68 and 69 are not present are removed by etching (FIG. 6 (c)), and the SiN insulating film 70 is overcoated again (FIG. 6 (d)). Further, a resist 71 is formed in a portion other than the portion serving as the window 72 for the electrode of the heater 62 (FIG. 6 (e)), and the SiN insulating films 67 and 70 of the portion are etched to form the window 72 (FIG. 6). 6 (f)) After removing the resist 71, the SiN insulating films 65 and 70 of the portions where the recesses 51 and 52 and the grooves 59a and 59b should be formed are further removed by the same procedure as described above (Fig. 6 (g)). .. Then, a Cr or Au film is formed and patterned in the same manner as described above to obtain an electrode film 74 to form a heater 62 (FIG. 6 (h)). After that, by performing the etching process shown in FIGS. 4 (a) to 4 (d), the recesses 51 and 52 and the protrusions 53 and 54 are formed, and at the same time, the flow rate sensor 61b is formed (FIG. 6 (i)). ). Here, by arranging the flow rate sensor 61b obliquely with respect to the crystal direction of the silicon substrate and performing anisotropic etching, the lower part of the flow rate sensor 61b is also etched (undercut), and a gas passage can be secured. [0023] Although the gas temperature sensor 61a requires more steps to form a platinum rhodium film, the other steps of forming a film are performed at the same time as the flow sensor 61b and the heater 62.<u style="single">Do</u>In particular, etching of the lower part of the sensor can be performed in the same manner as the flow rate sensor 61b. Further, the distribution plate temperature sensor 61c can be formed at the same time and in the same procedure using the same film forming material as the gas temperature sensor 61a, although the lower part of the sensor is not etched.<u style="single">To.</u>Therefore, the gas temperature sensor 61a and the distribution plate temperature sensor 61c<u style="single">of</u>The description of the manufacturing procedure will be omitted. [0024] As the film forming step, in addition to various physical vapor deposition methods (PVD), various chemical vapor deposition methods (CVD), sputtering methods, various plating methods, coating methods including solgel method, and methods by drying / solidification may be used to remove the film. As the steps to be performed, wet etching, dry etching, plasma etching, electric discharge machining, laser machining, electron beam machining and the like can be used. [0025] The gas diffusion electrode layers 3 and 4 are formed by dispersing platinum (Pt) catalysts 3b and 4b together with SPE similar to SPE22 in the vicinity of the surface of the gas diffusion layers 3a and 4a made of carbon paper on the electrolyte layer 2 side. [0026] The electrolyte layer 2 is sandwiched between a pair of distribution plates 5 via gas diffusion electrode layers 3 and 4, and the inside is airtight by adhering the electrolyte layer 2 with an adhesive 8 over the entire circumference so as to surround the recesses 51 and 52. The air passage 10 as an oxidant gas is defined as a narrow passage on the central recess 51 side, and the fuel gas passage 11 is defined as a narrow passage on the central recess 52 side. Here, the protrusions 53 and 54 of each distribution plate 5 are substantially entirely covered with the gold-plated layers as the electrode terminals 55 and 56, and the gas diffusion electrode layers 3 and 4 are formed on the frame 21 of the electrolyte layer 2. Lightly press against. Therefore, the gas diffusion electrode layers 3 and 4 are electrically connected in parallel to the corresponding distribution plate 5 via a large number of protrusions 53 and 54, so that the electrolyte layer 2 and the external circuit are reliably conducted. It has become like. [0027] The connection between the frame 21 and the distribution plate 5 can be realized in various ways. Preferably, anodic bonding is used instead of bonding with an adhesive. In that case, it is preferable to connect the lead wires of the sensors 61a, 61b, 61c and the heater 62 to the external circuit by forming through holes in the distribution plate, for example, and putting them out on the back surface side of the distribution plate 5. [0028] By flowing fuel gas and oxidant gas (air) through the fuel cell 1 while being heated by the heater 62 according to the measurement results of the sensors 61a, 61b, and 61c, electricity by the catalyst (Pt) is generated. A chemical reaction occurs, a potential difference is generated between the electrode terminal films 55 and 56, and this can be supplied as a power source to an external circuit from a stack connected in series. [0029] As is clear from the above description, according to the fuel cell and its manufacturing method according to the present invention, the electrolyte layer, the pair of gas diffusion electrode layers sandwiching the electrolyte layer, the fuel gas in contact with each gas diffusion electrode layer, and the fuel gas in contact with each gas diffusion electrode layer. A fuel cell composed of one or more cells having a pair of distribution plates for defining an oxidant gas passage is placed on at least one distribution plate at the temperature of the distribution plates, the temperature of each gas, or the flow velocity. By integrally forming a sensor for detecting and / or a heater for heating the electrolyte, it is easy to incorporate the sensor and the heater, and by adopting an embedded structure, the sensor, etc. There is no need for a separate seal structure for this purpose. In particular, the sensor and / or the heater is formed by forming the material constituting the sensor and / or the heater on each distribution plate in a desired shape, and each distribution plate is further formed by etching the substrate. By performing these as part of a series of manufacturing processes, it becomes easier to incorporate sensors and heaters and to manufacture fuel cells. [0030] Although the present invention has been described above with respect to specific examples, those skilled in the art may make various modifications to the present invention without departing from the technical fields of the present invention described in the appended claims. Needless to say. For example, in the present application, it is stated in the detailed description or claims of the invention that the fuel and the oxidant for the fuel cell are gases, but the liquid does not deviate from the technical field of the present invention. Please understand that it may be. [Simple explanation of drawings] FIG. 1 is an exploded perspective view showing the structure of a fuel cell stack to which the present invention is applied. FIG. 2a is a partially enlarged cross-sectional view of the line IIa-IIa of FIG. FIG. 2b is a partially enlarged cross-sectional view of the line IIb-IIb of FIG. FIG. 3a is a cross-sectional view illustrating a procedure for manufacturing an electrolyte layer of a fuel cell to which the present invention has been applied. FIG. 3b is a cross-sectional view illustrating a procedure for manufacturing an electrolyte layer of a fuel cell to which the present invention is applied. FIG. 3c is a cross-sectional view illustrating a procedure for manufacturing an electrolyte layer of a fuel cell to which the present invention has been applied. FIG. 4a is a cross-sectional view illustrating a procedure for manufacturing a distribution plate of a fuel cell to which the present invention is applied. [Fig. 4b] The cross-sectional view explaining the manufacturing procedure of the distribution plate of the fuel cell to which this invention was applied. FIG. 4c is a cross-sectional view illustrating a procedure for manufacturing a distribution plate of a fuel cell to which the present invention is applied. FIG. 5 is an enlarged perspective view showing a main part of a sensor and a heater of a fuel cell to which the present invention is applied. FIG. 6a is a cross-sectional view illustrating a manufacturing procedure of a sensor and heater portion of a fuel cell to which the present invention is applied. FIG. 6b is a cross-sectional view illustrating a manufacturing procedure of a sensor and a heater portion of a fuel cell to which the present invention is applied. FIG. 6c is a cross-sectional view illustrating a manufacturing procedure of a sensor and a heater portion of a fuel cell to which the present invention is applied. FIG. 6d is a cross-sectional view illustrating a manufacturing procedure of a sensor and heater portion of a fuel cell to which the present invention is applied. FIG. 6e is a cross-sectional view illustrating a manufacturing procedure of a sensor and a heater portion of a fuel cell to which the present invention is applied. FIG. 6f is a cross-sectional view illustrating a manufacturing procedure of a sensor and a heater portion of a fuel cell to which the present invention is applied. FIG. 6g is a cross-sectional view illustrating a manufacturing procedure of a sensor and a heater portion of a fuel cell to which the present invention is applied. [Fig. 6h] The cross-sectional view explaining the manufacturing procedure of the sensor and the heater part of the fuel cell to which this invention was applied. FIG. 6i is a cross-sectional view illustrating a manufacturing procedure of a sensor and a heater portion of a fuel cell to which the present invention is applied.