JP3780775B2 - Solid polymer electrolyte fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid polymer electrolyte fuel cell, and more particularly to a cooling water and a reaction gas flow structure.
[0002]
[Prior art]
FIG. 7 is an exploded perspective view showing a basic configuration of a general solid polymer electrolyte fuel cell. Centering on a membrane electrode assembly (MEA) 14 in which electrodes 13 are formed on both surfaces of an electrolyte membrane 12 having proton conductivity, a diffusion layer 15 is arranged outside both surfaces, and further outside the membrane. An anode side separator 16 having a fuel gas flow passage facing the diffusion layer 15 and a cathode side separator 17 having an oxidant gas flow passage facing the diffusion layer 15 are also disposed. The cell is configured. In addition, since the voltage obtained with only a single cell is low, a plurality of cells are usually stacked and used. The diffusion layer 15 serves to pass the fuel gas or oxidant gas flowing through the gas passage of each separator to the electrode 13 of the membrane electrode assembly 14 and to transmit the current obtained by the power generation reaction to the outside. . The anode-side separator 16 and the cathode-side separator 17 serve to collect current, and as described above, supply the fuel gas or the oxidant gas through the gas flow path provided facing the diffusion layer 15. Fulfill. In addition, a cooling water passage is provided on a surface opposite to the surface of the anode separator 16 and the cathode separator 17 on which the gas passage is provided, and heat is generated due to a power generation reaction. In order to remove water and maintain at a predetermined temperature, cooling water is passed.
[0003]
The four through holes provided in the end portions of the flat plate anode separator 16, cathode separator 17, and electrolyte plate 12 are manifolds for supplying and discharging fuel gas and oxidant gas. The oxidant gas (in this case, air is used) is introduced into the gas passage of the cathode separator 17 from the oxidant gas inlet manifold 4 arranged at one end as seen in the figure, and from above in the figure. It flows downward, reaches an oxidant gas outlet manifold 3 provided at one end opposite to the exhaust gas, and is discharged. On the other hand, fuel gas (generally, hydrogen is used) is introduced from the fuel gas inlet manifold 1 into a gas passage (not shown) of the anode-side separator 16 and flows upward from the lower side in the figure to one opposite end. Is discharged from the fuel gas outlet manifold 2. Accordingly, the oxidant gas and the fuel gas are configured to flow with each separator as a counter flow. Further, the through holes provided in the vicinity of the fuel gas outlet manifold 2 and the fuel gas inlet manifold 1 of the anode side separator 16, the cathode side separator 17, and the electrolyte plate 12 are manifolds for supplying and discharging cooling water, respectively. A cooling water inlet manifold 5 and a cooling water outlet manifold 6.
[0004]
[Problems to be solved by the invention]
In the solid polymer electrolyte fuel cell as described above, the following reaction occurs in the catalyst layer of the electrode 13, so that electricity can be taken out.
[0005]
[Chemical 1]
In the ^{anode: 2H → 2H + + 2e -} (1)
At the cathode: (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
As seen in equation (2), in the above reaction, water is generated at the cathode electrode, so that the generated water penetrates into the pores of the electrode and the diffusion layer, so-called “electrode wetting” occurs, and gas diffusion The cell performance may be reduced and the cell characteristics may be deteriorated.
[0006]
On the other hand, in solid polymer electrolyte fuel cells, the proton conductivity of the polymer electrolyte membrane remarkably depends on the humidity of the reaction gas. If the humidity of the reaction gas is too low, the polymer electrolyte membrane dries and the membrane resistance Will increase, leading to a decrease in cell characteristics. For this reason, in order to appropriately maintain the wet state of the electrode, a method of humidifying and supplying the reaction gas by humidifying means such as a humidifier has been studied. However, if humidifying means such as a humidifier is used in this way, the solid polymer electrolyte fuel cell becomes large and the power generation efficiency as a system decreases.
[0007]
For this reason, an unhumidified operation in which a solid polymer electrolyte fuel cell is operated without humidifying the reaction gas has been attempted. For example, a method of thinning a polymer electrolyte membrane or a reaction gas supplied to an anode and a cathode are mutually connected. Attempts have been made to use a so-called counterflow, for example, in which the flow is made in the opposite direction.
[0008]
The present invention has been made in consideration of the current state of the art as described above, and its purpose is to suppress electrode wetting by water generated by a battery reaction and to cause deterioration of cell characteristics even in a non-humidified operation. An object of the present invention is to provide a solid polymer electrolyte fuel cell that has high power generation efficiency and can be miniaturized.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention,
An electrode comprising a catalyst layer containing a polymer electrolyte and a porous diffusion layer is disposed on both surfaces of the electrolyte membrane to form a membrane electrode assembly, and the membrane is formed by an anode side separator and a cathode side separator each having a gas flow path. A cell is formed by sandwiching the electrode assembly, and fuel gas that is not humidified is passed through the gas passage of the anode separator, and oxidant gas that is not humidified is passed through the gas passage of the cathode separator so as to face each other. In a solid polymer electrolyte fuel cell to be operated,
(1) At least one of the cathode-side separator and the anode-side separator so that the temperature at the center is higher than the temperature at the inlet and outlet of the fuel gas or oxidant gas provided at the end. A cooling water passage is formed on the back of one separator.
(2) For example, after the cooling water flows in the vicinity of the inlet and outlet portions of the fuel gas or oxidant gas disposed at the end of the cooling water passage of (1), It shall be formed so as to be discharged through the central part. Alternatively, the cooling water is formed so as to be discharged only through the vicinity of the inlet and outlet portions of the fuel gas or the oxidant gas disposed at the end portion.
[0010]
(3) Alternatively, the flow rate of the fuel gas or oxidant gas in the central portion of each separator is higher than the flow velocity in the vicinity of the fuel gas or oxidant gas inlet and outlet portions provided at the end. A gas flow passage is formed in
(4) For example, the gas flow path of (3) is made up of a plurality of flow grooves in which the gas flow paths in the vicinity of the inlet and outlet of the fuel gas or oxidant gas of each separator are connected in parallel. It is assumed that the number of the flow channels is larger than the number of flow grooves of the gas flow path in the central portion of the separator including the flow grooves having the same flow path cross-sectional area. Alternatively, the fuel gas or oxidant gas flow passages of the respective separators are constituted by a plurality of flow passages connected in series, and the flow passages near the inlet and outlet portions of the fuel gas or oxidant gas The flow passage cross-sectional area of the flow groove in the central portion of the separator is made smaller than that of the flow passage cross-sectional area.
[0011]
In a non-humidified operation of a solid polymer electrolyte fuel cell, it is common that the characteristics are significantly reduced compared to when it is operated with humidification. The electrode dries out because of no humidification, and the resistance of the electrolyte membrane Has been thought to be the cause.
[0012]
The present inventor has shown in FIG. 8 in order to investigate the cause of the deterioration of the cell characteristics that occurs when the solid polymer electrolyte fuel cell of the type in which the fuel gas and the oxidant gas are supplied as opposite flows is operated without humidification. For example, in a battery in which 10 small cells with an electrode area of 10 cm ² are electrically connected in parallel and the flow of fuel gas and oxidant gas are connected in series, the gas flow between the cells is A dew point meter was installed inside and the humidity of the reaction gas was measured. According to the results, the humidity of the reaction gas is such that the gas inlet part <the gas outlet part <100% (saturated state) <the central part, and even in the non-humidified operation, the cell reaction proceeds in the central part. And it turns out that it is in the wet state with the produced water accompanying reaction. That is, in a solid polymer electrolyte fuel cell of a type in which fuel gas and oxidant gas are supplied as counterflows to each other, the cell in the central part becomes wet even in non-humidifying operation, and the characteristics are deteriorated. Therefore, in a cell having a practical size, if the fuel gas and the oxidant gas are supplied to the uniform flow path provided in the separator as a counter flow, the central portion becomes wet even in the non-humidified operation. Therefore, in the solid polymer electrolyte fuel cell, as described in (1) above, the temperature of the central portion of the separator is changed to the fuel gas or oxidant gas inlet portion provided at the end portion. In addition, a cooling water flow path is formed on the back surface of at least one of the separators so as to be higher than the temperature of the outlet portion. For example, as shown in (2), the temperature increases. Since the amount of saturated water vapor increases, the wet state at the center is relaxed. In addition, at the inlet and outlet, the saturated water vapor amount decreases due to a decrease in temperature, and the dryness decreases.
[0013]
In addition, as described in (3) above, the flow velocity at the center of each separator is faster than the flow velocity near the inlet and outlet portions of the fuel gas or oxidant gas provided at the end of each separator. For example, if the gas passage is formed as shown in (4), the flow velocity in the central portion is increased, so that water droplets generated by the progress of the wet state are removed together with the gas flow. Therefore, the risk of clogging with water droplets attached to the gas flow path is avoided, the reaction gas flows uniformly with a predetermined pressure loss, and the gas diffusibility is maintained. Therefore, the deterioration of characteristics is suppressed and stable operation is possible.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
<Example 1>
FIG. 1 is a plan view showing a configuration of a cooling water passage for a separator incorporated in a first embodiment of a solid polymer electrolyte fuel cell according to the present invention, and is a rear surface of a gas passage for an anode side separator 16A. The form of the cooling water flow path provided in is shown.
[0015]
In the figure, 1, 2, 3 and 4 are a fuel gas inlet manifold, a fuel gas outlet manifold, an oxidant gas outlet manifold and an oxidant gas inlet manifold, respectively, and 5 and 6 are a cooling water inlet manifold and a cooling water, respectively. Outlet manifold. The fuel gas is introduced from the fuel gas inlet manifold 1, flows from the upper part to the lower part through the fuel gas passage provided on the rear surface, and is discharged from the fuel gas outlet manifold. On the other hand, as shown in FIG. 5, the oxidant gas passes through the membrane electrode assembly 14 and the diffusion layer 15 to the gas flow path of the cathode side separator 17 disposed opposite to the anode side separator 16A. The gas is introduced from the gas inlet manifold 4, flows from the lower part to the upper part so as to face the flow of the fuel gas, and is discharged from the oxidant gas outlet manifold 3.
[0016]
The feature of this embodiment is the configuration of the cooling water passage, and the cooling water flows through the vicinity of the inlet and outlet portions of the fuel gas or oxidant gas at the end, and then flows through the central portion of the separator. It is in the point that it is formed to be discharged. That is, in the configuration of this cooling water passage, as shown in FIG. 1, the cooling water introduced from the lower cooling water inlet manifold 5 is first near the outlet of the lower fuel gas (at the same time, the oxidizing gas Flows in the gas flow groove 8 formed between the ribs 9 in the vicinity of the inlet), and then flows in the gas flow groove 8 in the vicinity of the upper fuel gas inlet (at the same time, in the vicinity of the oxidant gas outlet). Thereafter, it flows through the central portion and is discharged from the cooling water outlet manifold 6 to the outside.
[0017]
In this configuration, the cooling water whose temperature is still low flows through the vicinity of the inlet and outlet portions of the fuel gas or oxidant gas at the end, and the cooling water whose temperature has increased flows through the central portion of the separator. Therefore, the temperature at the center is higher than the temperatures at the gas inlet and outlet. Thus, when temperature rises, the amount of saturated water vapor increases and condensation is suppressed. Therefore, the dew condensation at the central part where the battery reaction is activated by the counter flow method is suppressed, the transition to the wet state is relaxed, and excellent battery characteristics are obtained.
<Example 2>
FIG. 2 is a plan view showing the configuration of the cooling water passage of the separator incorporated in the second embodiment of the solid polymer electrolyte fuel cell of the present invention, and the back surface of the gas passage of the anode separator 16B. The form of the cooling water flow path provided in is shown.
[0018]
The configuration of the present embodiment is based on the idea that the cooling water is allowed to flow only to the upper and lower portions of the anode-side separator 16B and the central portion is cooled by heat transfer. That is, the cooling water introduced from the lower cooling water inlet manifold 5 flows through the lower gas flow groove 8, and then is sent to the upper gas flow groove 8 through the left and right end flow passages. It is discharged from the outlet manifold 6 to the outside.
[0019]
Also in this configuration, as in the first embodiment, the temperature in the central portion is increased, the amount of saturated water vapor is increased, and dew condensation is suppressed. Therefore, the transition to the wet state is eased, and excellent battery characteristics can be obtained.
[0020]
In the first and second embodiments, the temperature of the central portion of the separator is configured to be higher than the temperatures of the inlet portion and the outlet portion of the fuel gas or oxidant gas provided at the end portion. Examples of realizing the policy 1 are illustrated, and the configuration of the present invention is not limited to these illustrated examples. The temperature of the central part of the separator is a fuel gas provided at the end. Or what is necessary is just to be comprised so that it may become high compared with the temperature of the inlet part of an oxidizing agent gas, and an outlet part.
<Example 3>
FIG. 3 is a plan view showing the configuration of the gas flow path of the separator incorporated in the third embodiment of the solid polymer electrolyte fuel cell of the present invention, and shows the oxidant gas flow path of the cathode side separator 17A. The form is illustrated. Also in this figure, the same reference numerals are given to components having the same function.
[0021]
The feature of this embodiment is that the flow velocity of the gas flowing through the gas passage of the separator is configured so that the central portion is faster than the end portion. That is, in this configuration, as shown in FIG. 3, the fuel gas introduced from the fuel gas inlet manifold 1 first flows through the four gas flow grooves 10 arranged in parallel on the inlet side, After flowing through a single gas flow groove 10 having the same flow path cross-sectional area disposed in the center, and then flowing through four gas flow grooves 10 disposed in parallel on the outlet side, a fuel gas outlet manifold 2 is configured to be discharged. Therefore, in this configuration, the fuel gas flowing through the gas flow groove 10 in the central portion has a flow rate four times faster than the fuel gas flowing through the gas flow grooves 10 arranged in parallel on the inlet side and the outlet side. It will be. If the gas flow rate is increased in this way, water droplets generated by the progress of the wet state can be removed together with the gas flow, so that blockage of the gas flow path due to the attached water droplets is avoided.
[0022]
Although it is possible to increase the flow velocity with the single gas flow groove 10 on the inlet side and the outlet side, the pressure loss as a whole increases and the capacity of the required equipment needs to be increased. Consideration is given to increase the flow velocity only in the part where there is a risk of occurrence of the condition, and to suppress the increase in the overall pressure loss.
<Example 4>
FIG. 4 is a plan view showing the configuration of the gas flow path of the separator incorporated in the fourth embodiment of the solid polymer electrolyte fuel cell of the present invention, and shows the oxidant gas flow path of the cathode side separator 17B. The form is illustrated.
[0023]
In this embodiment, as in the third embodiment, the configuration example of the gas flow path is configured such that the flow rate of the reaction gas flowing through the gas flow path of the separator is faster in the central portion than in the inlet side or the outlet side. In this example, the cross-sectional area of the gas flow groove 10 disposed in the central portion is made smaller than that of the end portion. Therefore, in the configuration of the present embodiment, the gas flow velocity in the central portion increases in inverse proportion to the cross-sectional area of the flow path, and water droplets generated by the progress of the wet state can be removed together with the gas flow. In order to avoid excessive pressure loss, the flow passage is configured to have a large cross-sectional area on the inlet side and the outlet side where there is no fear of progress of the wet state.
[0024]
In Examples 3 and 4, the flow rate of the reaction gas flowing through the gas flow path of the separator is configured such that the central portion is faster than the inlet side and the outlet side, and water droplets are removed. Examples of realizing the two measures are illustrated, and the configuration of the present invention is not limited to these illustrated examples, and the flow velocity of the gas flowing through the gas flow path of the separator is the inlet side or the outlet. What is necessary is just to be comprised so that a center part may become quick compared with the side.
[0025]
【The invention's effect】
In Example 1 above, a counter flow type cell is configured using a separator having the cooling water flow path of the form shown in FIG. 1 and the gas flow path of the form shown in Example 3. FIG. 6 shows the result of measuring the voltage-current characteristics by performing the humidifying operation. In the figure, the characteristics indicated by the white circle of A are the characteristics of the cell having the above-described configuration, and the characteristics indicated by the black circle of B are the cooling water passage and gas passage having a uniform structure as shown in FIG. It is the characteristic of the cell using the conventional separator provided with the flow path.
[0026]
As shown in the figure, in the case of a cell using a conventional separator, a rapid decrease in voltage was observed as the current density increased, but the cell according to the present invention has good characteristics up to a high current density. It was confirmed.
[Brief description of the drawings]
FIG. 1 is a plan view showing a configuration of a cooling water flow path of a separator incorporated in a first embodiment of a solid polymer electrolyte fuel cell of the present invention. FIG. 2 is a solid polymer electrolyte fuel of the present invention. FIG. 3 is a plan view showing a configuration of a cooling water flow path of a separator incorporated in the second embodiment of the battery. FIG. 3 is a diagram of the separator incorporated in the third embodiment of the solid polymer electrolyte fuel cell of the present invention. FIG. 4 is a plan view showing the configuration of the gas flow path of the separator incorporated in the fourth embodiment of the solid polymer electrolyte fuel cell of the present invention. FIG. 6 is an exploded vertical cross-sectional view schematically showing a counter-flow type cell. FIG. 6 shows characteristics of a cell incorporating a separator having the configuration shown in FIG. 1 and a separator having the configuration shown in FIG. Fig. 7 shows the basic configuration of a general solid polymer electrolyte fuel cell. System diagram of the humidity distribution measurement test in non-humidified operation of counter flow method was performed using to exploded perspective view 8 ten small cells [Description of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel gas inlet manifold 2 Fuel gas outlet manifold 3 Oxidant gas outlet manifold 4 Oxidant gas inlet manifold 5 Cooling water inlet manifold 6 Cooling water outlet manifold 8 Gas flow groove 9 Rib 10 Cooling water flow groove 11 Rib 12 Electrolyte membrane (Solid polymer electrolyte membrane)
13 Electrode 14 Membrane electrode assembly 15 Diffusion layer 16 Anode side separator 16A, 16B Anode side separator 17 Cathode side separator 17A, 17B Cathode side separator

Claims (6)

An electrode comprising a catalyst layer containing a polymer electrolyte and a porous diffusion layer is disposed on both surfaces of the electrolyte membrane to form a membrane electrode assembly, and the membrane is formed by an anode side separator and a cathode side separator each having a gas flow path. A cell is formed by sandwiching the electrode assembly, and fuel gas that is not humidified is passed through the gas passage of the anode separator, and oxidant gas that is not humidified is passed through the gas passage of the cathode separator so as to face each other. In a solid polymer electrolyte fuel cell to be operated,
At least one of the cathode side separator and the anode side separator is set so that the temperature at the center is higher than the temperature at the inlet and outlet of the fuel gas or oxidant gas provided at the end. A solid polymer electrolyte fuel cell, characterized in that a cooling water passage is formed on the back surface. The cooling water passes through the vicinity of the inlet and outlet portions of the fuel gas or oxidant gas disposed at the end, and then flows through the central portion of the separator to be discharged. The solid polymer electrolyte fuel cell according to claim 1, wherein a flow path is formed. That the cooling water flow path is formed so that the cooling water is discharged only through the vicinity of the inlet and outlet of the fuel gas or oxidant gas disposed at the end. The solid polymer electrolyte fuel cell according to claim 1, wherein the fuel cell is a solid polymer electrolyte fuel cell. An electrode comprising a catalyst layer containing a polymer electrolyte and a porous diffusion layer is disposed on both surfaces of the electrolyte membrane to form a membrane electrode assembly, and the membrane is formed by an anode side separator and a cathode side separator each having a gas flow path. A cell is formed by sandwiching the electrode assembly, and fuel gas that is not humidified is passed through the gas passage of the anode separator, and oxidant gas that is not humidified is passed through the gas passage of the cathode separator so as to face each other. In a solid polymer electrolyte fuel cell to be operated,
The flow rate of the central part of the fuel gas or oxidant gas of each separator is faster than the flow rate in the vicinity of the fuel gas or oxidant gas inlet and outlet portions provided at the end of each separator. A solid polymer electrolyte fuel cell, characterized in that a gas passage is formed. The gas flow passages in the vicinity of the fuel gas or oxidant gas inlet and outlet portions of each separator are composed of a plurality of flow grooves connected in parallel, and the number of the flow passages has the same flow passage cross-sectional area. 5. The solid polymer electrolyte fuel cell according to claim 4, wherein the number of flow grooves of the gas flow path at the center of the separator formed of flow grooves is larger than the number of flow grooves. Each separator gas flow path for the fuel gas or oxidant gas is composed of a plurality of flow grooves connected in series, and the flow in the flow groove near the inlet and outlet of the fuel gas or oxidant gas 5. The solid polymer electrolyte fuel cell according to claim 4, wherein the flow passage cross-sectional area of the flow groove in the central portion of the separator is smaller than the cross-sectional area of the passage.

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