JP2006318717A - Polyelectrolyte fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyelectrolyte fuel cell with high energy efficiency without giving birth to choking of fluid flow channels with vapor contained in fuel gas or oxidant gas, or excess product water generated by power generation. <P>SOLUTION: The polyelectrolyte fuel cell includes fluid flow channels where fuel gas G1 or oxidant gas G2 is circulated. The surface of an anode-side fluid flow channel 13 has a receding contact angle θb of water of less than 50°, and that of a cathode-side fluid flow channel 14 has a receding contact angle θb of water of not less than 50°. The receding contact angle θb may be obtained by roughening the surface of the anode-side fluid flow channel 13, or may be obtained by smoothening the surface of the cathode-side fluid flow channel 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell using a polymer electrolyte used for a portable power source, a power source for an electric vehicle, a domestic cogeneration system, and the like.

  A fuel cell using a polymer electrolyte generates electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air. .

  The polymer electrolyte fuel cell is manufactured as follows. First, a catalytic reaction layer composed mainly of carbon powder carrying a platinum-based metal catalyst is formed on both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions. Next, a diffusion layer is formed on the outer surface of the catalytic reaction layer using, for example, carbon paper or carbon cloth having both air permeability of fuel gas and electronic conductivity. The diffusion layer and the catalytic reaction layer are collectively referred to as a reaction electrode. A reaction electrode containing hydrogen is used as an anode (hydrogen electrode, fuel electrode), and a reaction electrode containing oxygen as a cathode (oxygen electrode, Called the air electrode).

  Next, a gas seal material is placed around the reaction electrode with a polymer electrolyte membrane so that the supplied fuel gas or oxidant gas does not leak outside or the fuel gas and oxidant gas are mixed with each other. And a gasket is placed. The sealing material and gasket are integrated in advance with the reaction electrode and the polymer electrolyte membrane, and this may be referred to as MEA (membrane electrode assembly), which is hereinafter referred to as MEA. On the outside of the MEA, a conductive separator for mechanically fixing the MEA and electrically connecting adjacent MEAs to each other in series is disposed. In the portion of the separator that comes into contact with the MEA, a gas flow path is formed for supplying the reaction gas to the reaction electrode surface and carrying away the generated gas and surplus gas. This gas flow path can be provided separately from the separator, but a system in which a groove is provided on the surface of the separator to form a gas flow path is common.

  In order to supply the fuel gas to the groove as the gas flow path, a piping jig for branching the fuel gas supply pipe into the number of separators to be used and connecting the branch destination directly to the separator-like groove is required. It becomes. This jig is called a manifold, and the type that connects directly from the fuel gas supply pipe as described above is called an external manifold. There is a type of this manifold called an internal manifold with a simplified structure. The internal manifold is a separator in which a gas flow path is formed, and a through hole is provided, and the gas flow path is passed through to the hole and fuel gas is directly supplied from the hole.

  Since the fuel cell generates heat during operation, it is necessary to cool it with cooling water or the like in order to maintain the battery at a good temperature. Usually, a cooling part that allows cooling water to flow every 1 to 3 cells is inserted between the separators, but in many cases, a cooling water channel is provided on the back surface of the separator to form a cooling part. These MEAs, separators, and cooling units are alternately stacked, and after stacking 10 to 400 cells, they are sandwiched between end plates via current collector plates and insulating plates, and both ends are fixed with fastening bolts. A general polymer electrolyte fuel cell is manufactured.

  The separator used in such a polymer electrolyte fuel cell has high conductivity and high gas tightness with respect to the fuel gas, and also has high corrosion resistance against the reaction when oxidizing / reducing hydrogen / oxygen. That is, it must have acid resistance. For this reason, conventional separators have a gas flow path formed by cutting on the surface of a glassy carbon plate or a resin-impregnated graphite plate, or expanded graphite powder together with a binder in a press mold in which a gas flow channel groove is formed. , And after pressing this, it was manufactured by heat treatment.

  In recent years, attempts have been made to use a metal plate such as stainless steel instead of a carbon material as the material of the separator. In the separator using the metal plate, the metal plate is exposed to an oxidizing atmosphere at a high temperature. Therefore, when used for a long time, the metal plate may be corroded or dissolved. When the metal plate is corroded, the electric resistance of the corroded portion increases and the output of the battery decreases. Further, when the metal plate is dissolved, the dissolved metal ions are diffused into the polymer electrolyte and trapped at the ion exchange site of the polymer electrolyte, resulting in a decrease in the ionic conductivity of the polymer electrolyte itself. In order to avoid such deterioration, it is usual to apply gold plating having a certain thickness on the surface of the metal plate.

Next, the state of the polymer electrolyte fuel cell during power generation will be described.
In polymer electrolyte fuel cells, in order to facilitate the movement of ionized hydrogen in the polymer electrolyte membrane, water vapor is mixed with gas containing hydrogen as the fuel gas or oxygen gas as the oxidant. It is common to do. On the other hand, since water (water vapor) is generated by a combustion reaction during power generation, water vapor mixed with fuel and oxidant and water (water vapor) generated by power generation are formed in a groove as a gas flow path formed in the separator. pass. The separator surface is generally controlled at a constant temperature so that the generated water does not condense more than necessary, but the amount of heat generated within the fuel cell changes due to changes in the amount of power generated and the fuel supply. However, the amount of produced water may fluctuate due to fluctuations in the internal temperature. For example, when the temperature is lowered, the separator surface is likely to condense, and it is impossible to completely eliminate such a phenomenon.

  When condensation occurs, water droplets block the groove as a gas flow path, and fuel shortage occurs to the reaction electrode after the plugged place, so the voltage gradually decreases, and when the water droplets are discharged, There is a problem that a voltage instability phenomenon (flooding) occurs in which the fuel supply is restored and the voltage rises because the blockage of the flow path is released.

  In order to solve such problems, a method has been proposed in which the hydrophilicity of the separator surface is increased and the water drainage is improved by spreading condensed water into a thin film.

  As a material for a conventional fuel cell separator, an impermeate obtained by processing a graphite block, a corrosion-resistant metal, and a liquid resin-containing material obtained by impregnating and hardening a liquid resin in an expanded graphite sheet laminated molded body are used. The separator made of was inferior in hydrophilicity. For this reason, various methods have been developed as means for improving the hydrophilicity of the separator.

Examples of conventional methods include (1) a method in which a base material contains a hydrophilic substance such as a metal oxide such as alumina, silica, or zeolite, or a hydrophilic resin such as PVA, PEG, or acrylic acid (see Patent Document 1). (2) A method in which a hydrophilic resin containing a metal oxide is applied to and impregnated into a molded body obtained by molding a composition mainly composed of conductive powder and a binder, and then the hydrophilic resin is made effective. (See Patent Document 2), (3) A method of subjecting a molded substrate to surface treatment such as oxidation treatment, acid treatment, plasma treatment, ultraviolet treatment, treatment with a surfactant, treatment with a silane coupling material (Patent Literature 3) ) Etc. have been developed. As a method for imparting permanent hydrophilicity, (4) the carbon molded body is treated with a gas mixture containing fluorine and oxygen, and then treated again with a gas having a smaller molar ratio of oxygen to fluorine than the mixed gas. Method (see Patent Document 4).
Japanese Patent Laid-Open No. 10-3931 JP 2003-217608 A Republished WO99-40642 JP 2003-112910 A

  However, the separator obtained by the method (1) has a problem that metal ions and organic substances that inhibit power generation are eluted from the metal oxide and hydrophilic resin contained in the substrate, respectively, and exists in the surface layer portion. In order to increase the amount of hydrophilic substance to be used, it is necessary to increase the content thereof, which causes a decrease in physical properties of the separator itself.

  The separator obtained by the method (2) has good initial physical properties, but elution of metal ions and organic substances occurs during long-term operation of the fuel cell, which adversely affects the electrolyte membrane and the catalyst. There is. In addition, due to concerns about the increase in contact resistance, it is necessary to process only the gas flow path, resulting in a complicated manufacturing process, resulting in an increase in cost.

The separator obtained by the method (3) has a problem that the hydrophilicity does not last.
In the method (4) of imparting permanent hydrophilicity, there is a problem that sufficient hydrophilicity to ensure water discharge cannot be obtained and the cost is high. In many cases, a polymer electrolyte fuel cell supplies hydrogen as fuel gas to the anode side and air as oxidant gas to the cathode side. Therefore, the cathode side uses oxygen contained in the air as the oxidant, and the oxygen utilization rate is lower than the anode side because oxygen is less diffusible than hydrogen. . In the separator on the cathode side, generated water is generated on the flow path by an electrochemical reaction, so that a groove shape and a flow path configuration that generally increase the pressure loss of the supply gas are formed. Therefore, when the same treatment as that on the anode side is performed, the flow rate on the cathode side is large, so that the pressure loss is often very high, and the energy efficiency is deteriorated.

  From the above, the methods (1) to (4) have a problem that they cannot cope with the problem of eliminating the voltage instability phenomenon (flooding).

  The present invention has been made in view of the above problems, and a polymer electrolyte fuel cell that can permanently eliminate the voltage instability phenomenon (flooding) of the polymer electrolyte fuel cell and prevent a decrease in energy efficiency. The purpose is to provide.

  In order to solve the above problems and achieve the object, a polymer electrolyte fuel cell according to the present invention includes a fuel cell including an anode-side fluid channel through which a fuel gas flows and a cathode-side fluid channel through which an oxidant gas flows. The surface of the anode fluid passage may have a receding contact angle of water of less than 50 degrees, and the surface of the cathode fluid passage may have a receding contact angle of water of 50 degrees or more.

  As a result, on the anode side, the generated water condensed in the fluid flow path is greatly bulged out in a ball shape on the surface of the fluid flow path, and the phenomenon that the fluid flow path is completely blocked is less likely to occur. It is possible to ensure almost always. This is optimal for the anode side where the flow rate of the fluid flowing through the fluid flow path is relatively small and the flow rate is relatively slow.

  On the other hand, on the cathode side, the difference between the advancing contact angle and the receding contact angle is reduced, and the generated water can easily move inside the fluid flow path, and can be discharged before the generated water droplet grows and becomes blocked. This is optimal for the cathode side where the flow rate of the fluid flowing through the fluid flow path is relatively large and the flow velocity is relatively fast.

  The receding contact angle preferably satisfies the above value by roughening the surface of the constituent material forming the anode-side fluid flow path.

  Further, the surface of the anode side fluid flow path is formed to have an average roughness (Ra) of 1.5 μm or more and 4.0 μm or less, or the surface of the anode side fluid flow path is generated by the roughening. If the average interval (Sm) of the unevenness is 10 μm or more and 200 μm or less, the generated water that has permanently dewed in the anode-side fluid flow channel is greatly swelled in a ball shape on the surface of the fluid flow channel, and the fluid flow channel is Complete occlusion can be avoided.

  Further, the surface of the anode-side fluid flow path is roughened by at least one of blasting, laser processing, or cutting, or the anode is formed by roughening the surface of the fluid flow path by molding. If it shape | molds by, the anode which roughened the surface of the fluid flow path can be obtained easily.

  In addition, if the hydrophilic functional group is provided on at least a part of the surface of the anode-side fluid flow path, blockage of the anode-side fluid flow path due to generated water can be further avoided.

  In addition, carbon is exposed on the surface of the anode-side fluid flow path, and the surface of the anode-side fluid flow path is subjected to the hydrophilicity by at least one of plasma treatment with a gas containing oxygen or UV ozone treatment. By providing the functional group, it is possible to easily obtain an anode that avoids clogging with generated water.

  On the other hand, the cathode-side fluid flow channel has a basal surface (crystal base surface) of carbon particles exposed on the surface, and the total area of the exposed basal surface with respect to the surface area of the cathode-side fluid flow channel It may be 70% or more.

Thereby, it becomes possible to make it easy to flow a water drop permanently.
The object can also be achieved by satisfying the receding contact angle of water by smoothing the surface of the constituent material forming the fluid flow path on the surface of the cathode side fluid flow path.

  If the average roughness (Ra) of the surface of the cathode-side fluid flow path is 1.0 μm or less, the above-described effects can be obtained.

  In addition, if the surface of the cathode-side fluid flow path is smoothed by at least one of grinding or polishing, a cathode in which the surface of the fluid flow path is easily smoothed can be obtained.

  Moreover, it is preferable that the manufacturing method of a fuel cell provided with the fluid flow path through which fuel gas and oxidant gas individually circulate includes a roughening step of roughening the surface of the anode-side fluid flow path.

  The roughening step is preferably at least one of blast processing, laser processing, and cutting processing.

  The manufacturing method further includes a hydrophilic functional group forming step of forming a hydrophilic functional group on the surface of the anode-side fluid flow path by at least one of a plasma treatment with a gas containing oxygen or a UV ozone treatment. preferable.

  Moreover, it is a manufacturing method of a fuel cell provided with the fluid flow path through which fuel gas and oxidant gas each distribute | circulate, Comprising: It is preferable to include the smoothing process of smoothing the surface of a cathode side fluid flow path.

  The smoothing step is preferably at least one of grinding or polishing.

  In the polymer electrolyte fuel cell, blockage of the flow path by generated water can be avoided, and stable operability can be provided. In addition, since the pressure loss due to the supply gas can be kept low, energy efficiency can be increased. They also have a lasting effect. As described above, in the polymer electrolyte fuel cell, it is possible to improve performance such as stability and efficiency.

  Next, an embodiment of a polymer electrolyte fuel cell according to the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view schematically showing a part of a unit cell 21 which is a unit of a polymer electrolyte fuel cell. FIG. 2 is a cross-sectional view taken virtually along the line II shown in FIG.

  As shown in the figure, the unit cell 21 includes an MEA (membrane electrode assembly) sheet 12, an anode side separator 10, and a cathode side separator 11.

  The MEA (membrane electrode assembly) sheet 12 is a sheet in which reaction electrodes 23 and 23 which are electrodes each provided with a catalyst are provided on the front and back surfaces of the proton conductive polymer electrolyte membrane 22.

  The type and shape of the proton conductive polymer electrolyte membrane 22 are not particularly limited as long as they are generally used for fuel cells.

  Similarly, the reaction electrode 23 is not limited, and may be a general reaction electrode in which platinum as a catalyst is supported on a carbon mesh.

  The separators 10 and 11 are plate-like bodies that electrically connect an MEA (membrane electrode assembly) sheet 12 and an adjacent MEA sheet of a unit cell (not shown) in series, and a fuel gas and an oxidant gas circulate therethrough. A large number of fluid flow paths 13 and 14 are arranged in parallel over the entire plate state. In addition, on the surface opposite to the surface on which the plate-like fluid flow paths 13 and 14 are provided, a flow path for circulating a cooling fluid is provided.

  The fluid flow path provided in the anode separator 10 is a fuel flow path 13 through which fuel gas flows. The surface of the fuel flow path 13, that is, the bottom surface and both side surfaces of the groove are roughened so that the receding contact angle of water is less than 50 degrees.

  Here, the receding contact angle of water is an angle measured by a so-called dynamic wetting test. In this dynamic wetting test, a contact angle (advanced contact angle) obtained in the process of submerging a predetermined material in distilled water and a contact angle (recessed contact angle) obtained in the process of pulling up are measured. For the wettability of the material, the advancing contact angle represents the hydrophilicity when the material is dry, and the receding contact angle represents the hydrophilicity after the material is once wetted.

  FIG. 3 is a cross-sectional view schematically showing the state of water adhering to the fuel flow path 13 whose surface is roughened and whose water receding contact angle θb is less than 50 degrees. On the other hand, FIG. 4 is a cross-sectional view schematically showing the state of water adhering to the fuel flow path 13 in which the receding contact angle of water is 50 degrees or more.

  As shown in FIG. 3, when the surface of the separator 10 is roughened and the receding contact angle θb of water becomes less than 50 degrees, the water is relatively likely to spread on the surface of the separator 10, and as shown in FIG. It can be avoided that water is repelled on the surface 10 to become particles and block the fuel flow path 13. In addition, it is thought that it is an anchor effect that a receding contact angle becomes small by roughening.

  Further, although the fuel gas G1 flowing through the fuel flow path 13 has a smaller flow rate and a relatively low flow rate as compared with the oxidant gas on the cathode side, water particles do not block the fuel flow path 13 and the fuel gas G1 It will move slowly according to the flow and be discharged. If the receding contact angle θb of water is less than 50 degrees, water adheres to the surface of the separator 10 and narrows the fuel flow path 13, but the fuel gas G1 has a relatively small flow rate and low flow rate, so that the pressure loss The increase is not significant and has little effect on fuel cell performance.

  The surface roughening method of the fuel flow path 13 is not particularly limited. For example, the surface of the fuel flow path 13 of the formed separator 10 is roughened by blasting, laser processing, or cutting. can do. In particular, blasting is optimal because the surface can be randomly roughened regardless of whether it is dry or wet. Further, a roughened fuel flow path 13 may be provided when the separator 10 is molded. For example, when the separator 10 is formed by hot pressing or the like, a roughened fuel flow path 13 is obtained by transferring a rough surface using a mold whose surface corresponding to the fluid flow path is previously roughened. May be.

  On the other hand, the fluid channel of the cathode separator 11 is an oxidant channel 14 through which an oxidant gas flows. The surface of the oxidant channel 14, that is, the bottom surface and both side surfaces of the groove, is smoothed so that the receding contact angle of water is 50 degrees or more.

  FIG. 5 is a cross-sectional view schematically showing the state of water adhering to the oxidant channel 14 whose surface is smoothed and whose water receding contact angle θb is 50 degrees or more.

  As shown in the figure, when the surface of the separator 11 is smoothed and the water receding contact angle θB is 50 degrees or more, the water is easily repelled on the surface of the separator 11. Further, since the difference from the forward contact angle θa of water becomes small, the repelled water is easy to roll. Accordingly, the oxidant gas G2 flowing through the oxidant flow path 14 has a relatively high flow rate and a high flow rate, so that water can be easily discharged before the water particles grow and close the oxidant flow path 14. Since water easily rolls, an increase in pressure loss can be suppressed and adverse effects on fuel cell performance can be suppressed.

  The method for smoothing the oxidant flow path 14 is not particularly limited. For example, the surface of the oxidant flow path 14 of the molded separator 11 may be smoothed by grinding or polishing. it can. Moreover, you may provide the oxidizing agent flow path 14 smooth | blunted when the separator 11 is shape | molded. In particular, if the material constituting the separator 11 is selected and a molding method is selected, the receding contact angle θb of water can be 50 degrees or more as it is after molding. The material and the molding method will be described later.

  In the polymer electrolyte fuel cell according to the present embodiment, a large number (for example, 100 layers) of the unit cells 21 are stacked while securing a cooling water channel to form a battery stack, and then current collector plates are provided at both ends of the battery stack. And an insulating plate made of an electrically insulating material, and further fixed by an end plate and a fastening rod.

  As described above, since the MEA (membrane electrode assembly) sheet 12 requires moisture in the polymer electrolyte fuel cell including the unit cell 21, the anode-side fuel flow path 13 and the cathode-side oxidation are used. The gas supplied together with the agent flow path 14 is generally humidified, and the fuel gas and the oxidant gas react to generate moisture. In other words, it is considered that the surface of the fluid flow path of the separator during power generation has more parts wet due to moisture condensation of the supply gas than the dry parts.

  Therefore, the separator 10 having a receding contact angle of less than 50 degrees by selecting a constituent material and a molding method of the anode-side separator 10 or having a receding contact angle of less than 50 degrees due to the anchor effect of the roughened surface is provided. If it is used, water will spread to the surface of the fuel flow path 13 once wet, and it is considered difficult to block the fuel flow path 13, and even the anode-side separator 10 with a relatively small flow rate of fuel gas is affected by moisture. It becomes possible to avoid the performance degradation of the fuel cell. The receding contact angle of the anode side fuel flow path 13 is preferably less than 40 degrees. This is because water sufficiently spreads on the surface of the fuel flow path 13.

  On the other hand, if the constituent material and the molding method of the cathode-side separator 11 are selected to set the receding contact angle to 50 degrees or more, or the separator 11 having the receding contact angle of 50 degrees or more depending on the surface state is used, the oxidant Since water is repelled on the surface of the flow path 14 and becomes granular, and the difference between the advancing contact angle and the receding contact angle becomes small and the water particles easily roll, the pressure caused by the oxidant gas having a relatively high flow rate. Excess generated water can be easily discharged without increasing the loss, and it is possible to avoid degradation of the performance of the fuel cell due to moisture. The receding contact angle of the oxidant channel 14 on the cathode side is desirably 60 degrees or more. This is because the water grains can sufficiently roll.

  In addition, the material of the separators 10 and 11 is not particularly limited, and a material corresponding to each characteristic may be selected. However, in consideration of corrosiveness (oxidation resistance) and electrical conductivity at present. A material obtained by solidifying carbon particles with a resin binder is considered suitable.

  And when the material which solidified the carbon particle with the binder is employ | adopted as a material of the separators 10 and 11, the hot pressing process using the metal mold | die which can obtain the shape of the said separators 10 and 11 is suitable for the shaping | molding processing method. It is.

  This is because the receding contact angle of water can be ensured to be 50 degrees or more in the surface state as molded, and the receding contact angle of water can be arbitrarily set by surface processing.

  FIG. 6 is a cross-sectional view conceptually showing the surface state of the separators 10 and 11 obtained by molding the separators 10 and 11 made of carbon particles and a resin binder by hot pressing.

  As shown in the figure, in the layer A of the surface layer portion of the separators 10 and 11 formed by hot pressing, the basal surface of the carbon particles 1 is parallel to the surfaces of the separators 10 and 11, and the carbon particles 1 of the outermost layer are The basal surface is exposed to form the surfaces of the separators 10 and 11. The total sum of the exposed basal surfaces occupies 70% or more of the surface areas of the separators 10 and 11.

  Thus, since the basal surfaces of the individual carbon particles are arranged on one side only by hot pressing, and constitute the surfaces of the separators 10, 11, the arithmetic average roughness Ra of the surfaces of the separators 10, 11 is 1.0 μm or less. Separators 10 and 11 having a relatively smooth surface with a receding contact angle of water of 50 degrees or more can be obtained.

  And the obtained separator 10 can be roughened so that the receding contact angle of water is less than 50 easily. For example, if the surface of the separator 10 is blasted and the layer A in which the basal planes are arranged in parallel is removed, the layer B in which the carbon particles are randomly arranged appears and a rough surface can be easily obtained. In addition, the secondary effect that the surface of the carbon particles becomes chemically unstable due to the blasting process so that water is easily adsorbed and the receding contact angle can be reduced can be expected.

  FIG. 7 is a cross-sectional view conceptually showing a surface state in which the surface of the separator 10 is roughened by blasting.

  As shown in the figure, the layer containing the carbon particles 1 whose basal plane direction is aligned parallel to the surface of the separator 10 is removed, and the protruding carbon particles 3 protruding from the surface and the concave carbon in which a part of the crystal is lost are removed. Many particles 4 are exposed. This is because the layer A is removed by blasting, the binder 2 is selectively dug, and a part of the carbon particles 1 is removed.

FIG. 8 is an enlarged view showing the concave carbon particles 4.
The carbon particles are aggregates of smaller fine particles 6, and some of the fine particles 6 of the carbon particles 1 are also removed by the blasting or the like. In the remaining part removed, a large number of fine particles on which prism surfaces (crystal side surfaces) 5a to 5c are exposed, such as fine particles 6a to 6c, are present. When the prism surfaces (crystal side surfaces) 5a to 5c are further enlarged, a part of covalent bonds such as the graphite crystal 8 shown in FIG.

  Similarly, a part having many unbonded portions of covalent bonds as shown in FIG. 10 is generated on the surface of the protruding carbon particles 3 by blasting. In addition, the thick line part in FIG. 10 has shown supply coupling | bonding.

  In other words, the surface or part of the chemically stable carbon particles is destroyed, and many chemically unstable surfaces such as many unbonded parts are exposed on the surface. Become. In this way, the hydrophilicity of the surface is increased because water molecules and the like are easily adsorbed to the chemically unstable surface. Further, since the uneven shape is formed when the surface layer is removed, the surface area is increased and the receding contact angle of water is further reduced by the anchor effect.

  Further, if the separators 10 and 11 are made of the above materials, the blockage of the flow path can be improved by different actions without causing any decrease in physical properties of the separator itself, elution of metal ions or organic substances, or increase in contact resistance. it can.

Next, embodiments of the present invention will be described with reference to the drawings.
First, the unit cell 21 is prepared.

First, a method for producing the reaction electrode 23 including the catalyst layer will be described.
A acetylene black powder carrying 25% by weight of platinum particles having an average particle diameter of about 30% is prepared. A dispersion solution in which perfluorocarbonsulfonic acid powder was dispersed in ethyl alcohol was mixed with a solution in which the catalyst powder was dispersed in isopropanol to form a catalyst paste.

  On the other hand, the water-repellent treatment is performed on the carbon paper that becomes the support for the reaction electrode. After impregnating a carbon nonwoven fabric (made by Toray, TGP-H-120) having an outer size of 14 cm × 14 cm and a thickness of 360 μm into a fluororesin-containing aqueous dispersion (manufactured by Daikin Industries, Neoflon ND1), this is dried. Heating at 400 ° C. for 30 minutes gives water repellency.

  A reaction electrode 23 having a catalyst layer on one surface of the carbon nonwoven fabric is formed by applying the paste-like catalyst on one surface of the water-repellent carbon nonwoven fabric using a screen printing method. At this time, a part of the catalyst layer is embedded in the carbon nonwoven fabric.

The coating amount of the paste-like catalyst by the screen printing, the amount of platinum contained in the reaction electrode after formation 0.6 mg / cm ^2, the amount of perfluorocarbon sulfonic acid so that 1.2 mg / cm ² It is adjusted.

  Next, a pair of the reaction electrodes 23 are bonded to the back and front surfaces of the proton conductive polymer electrolyte membrane 22 having an outer dimension of 15 cm × 15 cm by hot press so that the catalyst layer is in contact with the electrolyte membrane side. Create In the case of this example, a proton conductive polymer electrolyte obtained by thinning perfluorocarbon sulfonic acid to a thickness of 30 μm was used.

  Next, the manufacturing method of the conductive separators 10 and 11 which are the points of this invention is described.

First, artificial graphite powder having an average particle size of about 50 μm to 100 μm is prepared, and 80% by weight of the artificial graphite powder is extruded and kneaded by 20% by weight of a thermosetting phenol resin, and this kneaded powder is used for a gas channel. It puts into the metal mold | die which gave the process for shape | molding a groove | channel, the groove | channel for cooling water flow paths, and a manifold, and it hot-presses and obtains the separators 10 and 11. FIG. The hot pressing is performed at a mold temperature of 150 ° C. and a pressure of 100 kg / cm ² for 10 minutes.

  The obtained separator has an outer size of 20 cm × 20 cm, a thickness of 3.0 mm, and the cross-sectional shapes of the groove-like fluid flow paths 13 and 14 and the cooling water flow path are both square and 1.0 mm × 1.0 mm. Has been adjusted. Therefore, the thickness of the thinnest part of the separator is 1.0 mm.

  In this embodiment, artificial graphite is used for the conductive carbon material. However, for example, natural graphite, carbon black, ketjen black, and the like can be applied.

  As shown in FIG. 6, flat carbon particles 1 having a thickness of about 1 μm to 5 μm and a diameter of 50 to 100 μm are parallel to the separator surface on the surfaces of the separators 10 and 11 prepared under the above conditions. Arranged layer A is formed. The basal surface of the carbon particles 1 is exposed on the surfaces of the separators 10 and 11, and the total sum of the basal surfaces occupies 70% or more of the surface area of the separators 10 and 11. And by the said layer A, the arithmetic mean roughness (Ra) of the separator 10 and 11 surface becomes 1.0 micrometer or less, and the separator 10 and 11 of a comparatively smooth surface state is obtained.

  FIG. 11 shows an image taken by a laser confocal microscope on the separator surface immediately after molding according to this example. By analyzing the image, it was confirmed that the arithmetic average roughness of the surface was Ra = 1.0.

  Next, the surface of the fuel flow path 13 of the anode-side separator 10 is roughened. Specifically, the anode side removes the layer A having the above-described basal surface from the surface of the fluid flow path, exposes the carbon particles 1 in a random direction, and further removes a part of the exposed carbon particles 1. Deficient.

  As a method for removing the layer A and causing the carbon particles 1 to be lost, so-called sand blasting is employed. The conditions for this sandblasting are a plane moving speed of 0.5 m / min with a discharge rate of 1 kg / min from a nozzle having a diameter of 5 mm of alumina oxide powder having an average particle diameter of 20 μm. If a 10 μm thickness (approximately the thickness of the layer A) is removed from the surface of the separator 10 by the sandblasting process, a roughened surface capable of realizing a receding contact angle of water of less than 50 degrees can be obtained. This processing can be replaced by other methods such as wet blasting.

  FIG. 12 is a photographed image taken by a laser confocal microscope on the surface of the separator 10 after blasting. Based on the figure, it was confirmed that the arithmetic average roughness (Ra) of the surface was 1.5.

  Further, in order to further improve the blocking property on the anode side, the surface of the anode-side separator 10 was subjected to oxygen plasma treatment.

  The plasma processing apparatus used in this example is a general decompression type parallel RF plasma apparatus. The RF power source has a frequency of 13.56 MHz, an output of 500 W, an oxygen supply amount of 500 sccm, a processing time of 5 minutes, and a chamber. The internal pressure was 0.5 Torr.

  When such plasma treatment is performed after blasting, oxygen radical species in which a part of four covalent bonds around one carbon atom generated by blasting is chemically unstable and an unbonded part is active. This is preferable because a hydrophilic functional group containing oxygen is formed, and the receding contact angle of water is further reduced.

  When the surface analysis of the separator 10 after this plasma treatment was performed by X-ray photoelectron spectroscopy (XPS), the carbon surface had oxide functional groups represented by chemical formulas 1 and 2, that is, hydrophilic. It was confirmed that a functional functional group was added.

(Chemical formula 1)
-C = O
(Chemical formula 2)
-C-OH

  When plasma treatment is performed for the purpose of attaching a hydrophilic functional group to a portion where many chemically unstable surfaces are exposed on the surface where many covalent bonds are not bonded, the C and O bonding sites Is formed, and the bond strength between C and O is increased, so that it exhibits extremely strong hydrophilicity and the durability of the effect is also increased. However, the effect is not permanent, but it goes without saying that the hydrophilicity (the receding contact angle of water is less than 50 degrees) due to the roughened surface can be maintained.

  In this embodiment, a parallel plate type in which electrodes are opposed in parallel is used as the plasma processing apparatus. However, a barrel type in which electrodes are arranged on the side surface of a cylindrical chamber may be used. Further, UV ozone treatment in which ultraviolet light is irradiated in an ozone atmosphere may be used.

On the other hand, the cathode-side separator 11 was smoothed.
As described above, the surface of the separator 11 immediately after forming by hot pressing has a carbon particle layer A in which basal surfaces are arranged in parallel, and is relatively smooth. And the evaluation result by the dynamic wetting test (after-mentioned) of the separator 11 immediately after shaping | molding is a forward contact angle of 85 degree | times, and a backward contact angle is 55 degree | times, and the required specification of the cathode side separator 11 is satisfied.

  However, in order to increase energy efficiency, it is preferable to further reduce the pressure loss, and it is desirable to further increase the receding contact angle of the separator 11 immediately after molding and to reduce the difference between the advancing contact angle and the receding contact angle.

  Therefore, in this embodiment, the difference between the advancing contact angle and the receding contact angle is sufficiently reduced by smoothing the surface with a precision grinding apparatus.

  Specifically, diamond, cubic boron nitride (CBN), alumina, or the like was used for the grinding process, and the processing was performed with sufficient time. Moreover, this process is also possible by polishing with loose abrasive grains such as lapping.

  FIG. 13 shows a photographed image taken by a laser confocal microscope on the surface of the cathode separator 11 after grinding. From the image, it was confirmed that the arithmetic average roughness of the surface was Ra = 0.2 μm.

  Next, the wettability, that is, the advancing contact angle and the receding contact angle of the separators 10 and 11 prepared above and the separator surface immediately after the molding process were measured. This measurement was performed using a dynamic wetting tester (Resca WET-6000) by cutting the plane portions of the separators 10 and 11 into a length of 30 mm and a width of 30 mm to prepare a sample plate.

  In this dynamic wetting test, a contact angle (advanced contact angle) obtained in the process of submerging the sample plate in distilled water and a contact angle (retreated contact angle) obtained in the process of pulling up are measured. For the wettability of the material, the advancing contact angle represents the hydrophilicity when the material is dry, and the receding contact angle represents the hydrophilicity after the material is once wetted.

  As a result of the test, the anode-side separator 10 after blasting and plasma treatment had an advancing contact angle of 5 degrees and a receding contact angle of 5 degrees.

  FIG. 14 is a cross-sectional view showing the state of water adhering to the surface where the water receding contact angle θa is 5 degrees and the water receding contact angle θb is less than 5 degrees.

  As shown in the figure, when not only the receding contact angle but also the advancing contact angle becomes small, the water sticks to the surface without bulging, ensuring a large fuel flow path 13 and avoiding pressure loss as much as possible. It becomes possible to do. Further, since there is almost no difference between the receding contact angle and the advancing contact angle, it is considered that water can be easily moved and excess water can be easily discharged.

  On the other hand, the cathode-side separator 11 after grinding had an advancing contact angle of 80 degrees and a receding contact angle of 70 degrees.

  As described above, the separator immediately after molding had an advancing contact angle of 85 degrees and a receding contact angle of 55 degrees.

  Further, as comparative examples, separators having various surface states were produced by changing the surface treatment method. FIG. 15 is a table showing the surface treatment methods and contact angles as hairs of the examples and comparative examples 1 to 3.

  Next, using the above-described anode-side separator 10, cathode-side separator 11, and various separators as comparative examples, an anode-side separator is provided on one side of a MEA (membrane electrode assembly) sheet 12, and a cathode is provided on the back side. A unit cell 21 as shown in FIGS. 1 and 2 was produced by stacking the separators on the side.

  Then, after stacking two cells of this single battery 21, the two-cell stacked battery was sandwiched by a separator having a cooling water channel groove, and this pattern was repeated to produce a battery stack having a stack of 100 cells.

At this time, the both ends of the battery stack were fixed with a current collector plate made of stainless steel, an insulating plate made of an electrically insulating material, and an end plate and a fastening rod. The fastening pressure at this time was 15 kgf / cm ² per separator area.

  Various polymer electrolyte fuel cells produced in this way were maintained at 80 ° C., and humidified and heated to a dew point of 75 ° C. on the anode side separator, and 65 ° C. on the other cathode side separator. Humid and warmed air was supplied so that the dew point would be. As a result, a battery open voltage of 96 V was obtained at no load when no current was output to the outside. Further, when the internal resistance of the whole laminated battery at this time was measured, it was about 45 mΩ.

  Next, in order to obtain the limit fuel utilization rate (limit Uf), each polymer electrolyte fuel cell was subjected to the following operation.

That is, the fuel utilization rate of the fuel cell was increased from 50% to 5% at a rate of 40% oxygen utilization and 0.15 A / cm ² current density. At this time, the fuel utilization rate is increased by 5% when all the cell voltages can be stably operated during the 5-hour operation. Then, when the cell voltage reached 600 mV during the operation for 5 hours, the test was stopped, and the highest fuel utilization rate at which all the cell voltages can be stably operated was defined as the limit fuel utilization rate (limit Uf).

  Next, in order to obtain the limiting oxygen utilization rate (limit Uo), the following operation was performed on each polymer electrolyte fuel cell.

  That is, the oxygen utilization rate of the fuel cell was increased from 30% to 5% at a fuel utilization rate of 60% and a current density of 0.3 A / cm 2. At this time, the oxygen utilization rate is increased by 5% when all the cell voltages can be stably operated during the 5-hour operation. Then, when the cell voltage reached 600 mV during the operation for 5 hours, the test was stopped, and the highest oxygen utilization rate at which all the cell voltages can be stably operated was defined as the limiting oxygen utilization rate (limit Uo).

  It can be said that a polymer electrolyte fuel cell having a larger limit fuel utilization rate (limit Uf) and oxygen utilization rate (limit Uo) has higher stability and better flooding resistance. This value was used as an index for evaluating battery characteristics of the polymer electrolyte fuel cell. Further, pressure loss values on the anode side and the cathode side were measured and compared under the conditions of a fuel utilization rate of 60%, an oxygen utilization rate of 40%, and a current density of 0.2 A.

  FIG. 16 is a table showing battery characteristic tests and pressure loss values at ratings of Comparative Examples 1 to 3 and this example. The separators immediately after molding in Comparative Examples 1 to 3 and the examples in the present invention are exactly the same.

From the results shown in FIG. 15 and FIG.
First, the value of the limit Uf is particularly low in Comparative Example 1, and it is considered that the anode side has a problem with the blockage due to excess generated water.

  Next, in Comparative Example 2, both the limit Uf and the limit Uo are improved by blasting as compared with Comparative Example 1. However, a rapid increase in pressure loss is observed particularly on the cathode side, which is considered to be a problem in energy efficiency.

  Next, in Comparative Example 3, the limit Uo is improved and the pressure loss is reduced by grinding processing on the cathode side. However, the limit Uf is not improved on the anode side, and the pressure loss is not reduced. This is because the difference between the advancing contact angle and the receding contact angle was reduced by grinding, so the excess water was easily discharged, but the anode side was clogged before being discharged because the flow rate was slow. It is considered that the limit Uf does not improve, and conversely, the pressure loss is increased by the clogging of the surplus generated water.

  Finally, examples of the present invention will be described. In the embodiment of the present invention, it can be seen that both the limit Uf and the limit Uo show high values. It was also confirmed that the pressure loss on the anode side and the cathode side was also reduced.

  As described above, according to the present invention, in a polymer electrolyte fuel cell, it is possible to operate at a high limit utilization rate only when the surface state is suitable for each of the anode side and the cathode side, and the pressure loss is reduced. It can be kept low. That is, it is possible to construct a polymer electrolyte fuel cell having high stability and high energy efficiency.

  The present invention can be applied to a polymer electrolyte fuel cell, and in particular, a polymer electrolyte such as an electric vehicle, a household power source, a portable power source, and a building cogeneration can be applied to other fuel cells.

It is a perspective view which shows typically a part of unit cell which is one unit of the polymer electrolyte fuel cell concerning this invention. It is sectional drawing which shows the cross section cut | disconnected virtually by the II line | wire shown in FIG. It is sectional drawing which shows typically the mode of the water when the surface is roughened and the receding contact angle of water is set to less than 50 degree | times. It is sectional drawing which shows typically the mode of water when the receding contact angle of water shall be 50 degree | times or more. It is sectional drawing which shows typically the mode of the water when the surface is smooth | blunted and the receding contact angle of water shall be 50 degree | times or more. It is sectional drawing which shows typically the cross section of the separator surface vicinity after shaping | molding. It is sectional drawing which shows typically the cross section of the separator surface vicinity after carrying out the blast process to the separator surface after the said shaping | molding. It is sectional drawing which expands and shows typically a part of concave-shaped carbon particle which one part lost | missed by the blasting process. It is a schematic diagram which expanded the prism surface of the graphite crystal. It is a perspective view which shows typically the surface of the graphite crystal | crystallization which has many unbonded parts of a covalent bond. It is a figure which shows the picked-up image by the laser confocal microscope of the separator surface immediately after shaping | molding. It is a figure which shows the picked-up image by the laser confocal microscope of the separator surface after a blast process. It is a figure which shows the picked-up image by the laser confocal microscope of the separator surface after a grinding process. It is sectional drawing which shows typically the mode of water when hydrophilicity is provided to the roughened surface by plasma processing, the receding contact angle of water is 5 degrees, and the forward contact angle of water is 5 degrees. . It is a table | surface which shows the result of each surface treatment condition in a comparative example and an Example, and the wettability evaluation test of a surface. It is a table | surface which shows the measurement result of each battery characteristic and pressure loss value in a comparative example and an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carbon particle 2 Binder resin 3 Protruding carbon particle 4 Concave carbon particle 5a Prism surface a of graphite crystal
5b Prism surface b of graphite crystal
5c Prism surface c of graphite crystal
6a Fine particles a
6b Fine particles b
6c Fine particle c
7 A portion of the covalent bond in the graphite crystal where some of the covalent bonds are not bonded 8 Graphite crystal whose prism surface is enlarged 9 Graphite crystal on the surface of the protruding carbon particle 3 10 Anode-side separator 11 Cathode-side separator 12 MEA (membrane electrode assembly) sheet 13 Fuel Channel 14 Oxidant Channel 21 Single Cell 22 Proton Conducting Polymer Electrolyte Membrane 23 Reaction Electrode

Claims (18)

A fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
The polymer electrolyte fuel cell characterized in that the surface of the anode-side fluid flow channel has an average interval (Sm) of irregularities of 10 μm or more and 200 μm or less. A fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
The surface of the anode-side fluid flow channel has an average roughness (Ra) of 1.5 μm or more and 4.0 μm or less. A fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
The polymer electrolyte fuel cell according to claim 1, wherein the surface of the anode fluid passage has a receding contact angle of water of less than 50 degrees.   The surface of the anode side fluid flow path is provided with the surface property by roughening the surface of the constituent material forming the fluid flow path. The polymer electrolyte fuel cell according to 1.   5. The polymer electrolyte fuel cell according to claim 4, wherein the surface of the anode-side fluid flow path is roughened by at least one of blast processing, laser processing, and cutting processing.   5. The polymer electrolyte fuel cell according to claim 4, wherein the anode is molded in a state where the surface of the fluid flow path is roughened by molding.   The polymer electrolyte fuel cell according to claim 4, wherein the surface of the anode-side fluid flow path further comprises a hydrophilic functional group at least in part. The anode side fluid flow path has carbon exposed on the surface,
8. The polymer electrolyte according to claim 7, wherein the surface of the anode-side fluid flow path is provided with the hydrophilic functional group by at least one of a plasma treatment with a gas containing oxygen or a UV ozone treatment. 9. Type fuel cell. A fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
The polymer electrolyte fuel cell according to claim 1, wherein the surface of the cathode fluid passage has an average roughness (Ra) of 1.0 μm or less. A fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
The polymer electrolyte fuel cell according to claim 1, wherein the surface of the cathode fluid passage has a receding contact angle of water of 50 degrees or more. A fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
The cathode-side fluid flow channel has a basal surface (crystal base surface) of carbon particles exposed on the surface,
The polymer electrolyte fuel cell, wherein a total area of the exposed basal surface is 70% or more with respect to a surface area of the cathode-side fluid flow path.   The surface of the cathode side fluid flow path satisfies the receding contact angle of the water by smoothing the surface of the constituent material forming the fluid flow path. Polymer electrolyte fuel cell.   13. The polymer electrolyte fuel cell according to claim 12, wherein the surface of the cathode side fluid flow path is smoothed by at least one of grinding or polishing. A method for manufacturing a fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
A method for producing a polymer electrolyte fuel cell, comprising a roughening step of roughening a surface of an anode fluid passage.   The method of manufacturing a polymer electrolyte fuel cell according to claim 14, wherein the roughening step is at least one of blasting, laser processing, and cutting. The manufacturing method further includes:
15. A hydrophilic functional group forming step of forming a hydrophilic functional group on the surface of the anode-side fluid flow path by at least one of a plasma treatment with a gas containing oxygen or a UV ozone treatment. A method for producing a polymer electrolyte fuel cell as described in 1). A method for manufacturing a fuel cell comprising an anode-side fluid flow path through which fuel gas flows and a cathode-side fluid flow path through which oxidant gas flows,
A method for producing a polymer electrolyte fuel cell, comprising a smoothing step of smoothing a surface of a cathode-side fluid flow path.   The method of manufacturing a polymer electrolyte fuel cell according to claim 17, wherein the smoothing step is at least one of grinding and polishing.