JP2005044527A - Solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deterioration of battery performance due to an eluted ion from a battery member of a solid polymer fuel cell. <P>SOLUTION: In the fuel cell, by improving the arrangement of a manifold of gas and a current collector, the eluted ion from the battery member is reduced and the deterioration of the battery performance is prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell.
[0002]
[Prior art]
The polymer electrolyte fuel cell has advantages such as high output, long life, little deterioration due to start / stop, and low operating temperature (about 70-80 ° C), which makes it easy to start / stop. Therefore, a wide range of uses such as power sources for electric vehicles, distributed power sources for business use and home use are expected.
[0003]
Among these applications, a distributed power source (for example, a cogeneration power generation system) equipped with a polymer electrolyte fuel cell takes out electricity from the polymer electrolyte fuel cell, and at the same time, generates heat from the battery during power generation with hot water. It is a system that tries to make effective use of energy by collecting as Such a distributed power source is required to have a long life of 50,000 hours or more as a period of use, and improvements in membrane-electrode assemblies, cell configurations, power generation conditions, and the like are being promoted.
[0004]
However, further technological development is required to extend the life of solid polymer fuel cells at a practical level. In particular, according to research on membrane-conjugates, elution ions of metal members used in fuel cells, impurity ions contained in water that humidifies gas, etc. reach the membrane-electrode assembly, and these ions are found in the membrane. It has been pointed out that as a result of replacement with hydrogen ions, the output characteristics and lifetime of the fuel cell are reduced due to an increase in hydrogen ion resistance (Non-Patent Document 1).
[0005]
[Non-Patent Document 1]
Proceedings of the 4th Fuel Cell Symposium, p. 134-139
[0006]
[Problems to be solved by the invention]
In order to prevent deterioration of battery performance due to an increase in resistance of the membrane-electrode assembly, it is desirable to prevent the generation of eluted ions from the battery member. However, in order to simplify the battery structure, a through hole (manifold) through which gas and cooling water are circulated is often provided inside the battery, which may cause the following deterioration in battery performance.
[0007]
That is, such a manifold is also provided on a current collector plate for extracting electric power from the fuel cell, and the manifold distributes a gas containing humidified oxygen or hydrogen so that a local battery made of oxygen and hydrogen is supplied to the collector plate manifold. As a result, ions eluted from the current collector plate are likely to be generated. The elution ions generated in this way reach the electrode surface of the membrane-electrode assembly together with the gas containing oxygen or hydrogen, where there is an increase in membrane resistance due to ion exchange with hydrogen ions in the membrane, and the electrode of the elution ions The activity of the catalyst is reduced by electrodeposition on the surface.
[0008]
In a polymer electrolyte fuel cell, in order to suppress an increase in membrane resistance due to drying of the membrane-electrode assembly, water added to a gas containing oxygen or hydrogen and water generated by combustion of hydrogen during power generation are generated. Included inside the battery. These waters may aggregate and stay in the manifold inside the battery stack due to changes in battery temperature. When this agglomerated water exists between the positive electrode current collector plate and the negative electrode current collector plate, a dissolution reaction of a metal or the like from the positive electrode current collector plate easily occurs due to an electrochemical reaction between both electrodes. Eluted ions generated by such a mechanism cause an increase in the membrane resistance of the membrane-electrode assembly.
[0009]
In order to achieve both simplification of the battery structure and suppression of deterioration in battery performance, the eluting ions from the battery member such as the current collector are hardly generated, and even if the eluting ions are generated, the membrane electrode A battery structure that does not easily reach the joined body is required. An object of the present invention is to provide a battery member, in particular, a battery that can prevent deterioration of the output and life of a fuel cell due to ions eluted from a current collector plate.
[0010]
[Means for Solving the Problems]
The present invention provides two separators for a single cell having gas flow grooves and both ends of a laminate in which a plurality of unit cells each having a catalyst layer and a membrane-electrode assembly composed of a hydrogen ion conductive polymer membrane are sandwiched. Conductive positive and negative current collector plates are arranged on the surface, and the laminate and the current collector plate are sandwiched between end plates, and the end plates contain oxygen-containing gas, hydrogen-containing gas, and cooling water. A polymer electrolyte fuel cell having a manifold for supplying and discharging, wherein the supply side manifold passing through the negative electrode current collector plate provided in the separator and the positive electrode current collector plate are electrochemically separated by an electrolysis suppression unit. The discharge side manifold and the negative electrode current collector plate provided in the separator are electrochemically cut off by the electrolysis suppressing part, and the polymer electrolyte fuel cell is provided. . The present invention also provides a polymer electrolyte fuel cell in which the manifold is connected to a connector formed on the single plate.
[0011]
A solid polymer fuel cell has a basic configuration consisting of a solid polymer electrolyte membrane having a function of permeating hydrogen ions, electrode layers formed on both sides of the membrane, and a separator disposed so as to sandwich the electrode layer. The cell usually has a configuration in which a plurality of the single cells are connected in series in order to obtain sufficient power.
[0012]
A solid polymer electrolyte membrane having a function of permeating hydrogen ions is generally a polymer membrane in which a part of fluorine of a fluorine-based polymer is replaced with sulfonic acid, and is a polymer membrane having a function of moving hydrogen ions. If present, the present invention is applicable. For example, the fluorine atom contained in the polymer chain having tetrafluoroethylene as a basic unit is passed through about 2 to 5 alkyl chains (—CF ₂ CF ₂ —, —CF ₂ CF (CF ₃ ) —, etc.). There is a polymer membrane having a sulfonic acid group (—SO ₃ H) at the end of the alkyl chain.
[0013]
The electrode layer is a layer made of platinum or an alloy of a different element such as platinum and ruthenium as an electrode catalyst and comprising the catalyst, carbon powder, and a binder. The fuel gas supplied to the polymer electrolyte fuel cell is pure hydrogen or a mixed gas containing hydrogen, and this hydrogen is oxidized by the oxidation reaction shown in (Equation 1) on the above electrode catalyst. At the same time, the oxygen reduction reaction (formula 2) proceeds on the opposite electrode catalyst. Hydrogen ions generated by the oxidation reaction of hydrogen are transferred to the solid polymer electrolyte membrane, and the ions are combined with oxygen in the opposite electrode layer to generate water.
[0014]
H ₂ → 2H ⁺ + 2e ⁻ (Formula 1)
2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (Formula 2)
Due to this battery reaction, the electromotive force of a single cell is about 1.2V, and when a load is connected to generate power, a voltage of about 0.5 to 0.7V can be obtained, so a plurality of single cells that contribute to this power generation are stacked. By doing so, a voltage of tens to hundreds of volts can be taken.
[0015]
A basic configuration of a fuel cell used in the present invention is shown in FIG. The power generation unit is a single cell, and DC power is taken out from the fuel cell by a multi-layered cell of usually several tens of cells or more. This single cell includes a membrane-electrode assembly (a membrane composed of 102 and 103 in FIG. 1 (b) which is an enlarged view), a gas diffusion layer 106, and an electrode layer provided on both sides of a solid polymer electrolyte membrane. It consists of two separators 104 to be sandwiched, and a gasket 105 is inserted between the separators 104.
[0016]
An enlarged view of the periphery of this membrane-electrode assembly is shown in FIG. On one side of the separator 104, a groove through which the fuel gas flows is processed. The other separator 104 has a groove through which an oxidant gas, usually air, flows. These are laminated, and the positive electrode current collector plate 113 and the negative electrode current collector plate 114 are disposed at the ends. Pressure is applied from the outside of the current collecting plates 113 and 114 by the end plate 109 through the insulating plate 107.
[0017]
Components for fixing the end plate 109 are a bolt 116, a disc spring 117, and a nut 118. Fuel gas, oxidant gas, and cooling water are supplied from connectors 110, 111, and 112 provided on the end plate, and discharged from the connector provided on the other end plate. DC power (output) can be obtained from the positive current collector 113 and the negative current collector 114.
[0018]
According to a first means for achieving the object of the present invention, at least oxygen-containing gas is supplied from a manifold connected to an end plate installed on the negative electrode current collector plate side having a low potential, particularly from a manifold connected to a connector. Is. When such a method is adopted, the ion eluted from the current collector plate generated by the oxidation reaction with oxygen is not carried into the membrane-electrode assembly together with the gas containing oxygen, and the battery performance is increased due to an increase in membrane resistance. The decrease is less likely to occur. Note that the manifolds or connectors of oxygen-containing gas, hydrogen-containing gas, and cooling water are arranged side by side in the depth of the paper surface of FIG. 1 or FIG.
[0019]
The second means for achieving the object of the present invention is to provide a portion for suppressing or blocking electrolysis (electrolysis suppressing portions 212 and 213 in FIG. 2) in the middle of the manifold connecting the positive and negative current collecting plates. Thus, the positive electrode current collector plate 203 and the negative electrode current collector plate 209 are prevented from being directly communicated with each other through moisture accumulated in the manifold. By adopting such a configuration, electrolysis through the water (aggregated water) accumulated in the manifold is less likely to occur between the positive electrode current collector plate and the negative electrode current collector plate, and the generation of eluted ions from the current collector plate is prevented. It is suppressed.
[0020]
The electrolysis suppressing part used in the fuel cell of the present invention may use the part facing the manifold as it is in the graphite separator in contact with the current collector plate. That is, in the case of the gas discharge manifold 208, the graphite separator 207 in contact with the negative electrode current collector plate is not provided with a through hole at the position of the gas discharge manifold, and the manifold is sealed with the graphite separator itself, The plate 203 and the negative electrode current collector plate 209 are not opposed to each other. On the contrary, in the case of the gas supply manifold 204, the through hole is not provided at the position of the gas supply manifold of the graphite separator 205 in contact with the positive electrode current collector plate 203.
[0021]
It is more preferable to use a member having a small action of electrochemically oxidizing and reducing water in the electrolytic suppression unit, that is, an electrically insulating member, for the electrolytic suppression unit. One method is to seal one end of the manifold with an insulating component to prevent electrolysis between the positive and negative current collector plates. For example, in the case of a gas supply manifold, a graphite separator in contact with the negative electrode current collector plate, a resin plate such as tetrafluoropolyethylene or polypropylene, or silicon rubber, ethylene / propylene rubber, fluorine rubber at the position of the gas supply manifold It is possible to have a structure in which a rubber plate such as a rubber plate is fitted, and one end of the manifold can be sealed with a resin plate. Conversely, in the case of a gas discharge manifold, the effect of the present invention can be obtained by fitting a resin plate such as tetrafluoropolyethylene at the position of the gas discharge manifold of the graphite separator in contact with the positive electrode current collector plate. The electrolysis suppression part is not limited to the above-mentioned material, and the effect of the present invention can be obtained regardless of the shape of the plate, columnar, or thin film.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The contents of the present invention will be described below with reference to examples. In addition, this invention is not limited to the Example described below.
[0023]
(Example 1)
FIG. 2 is a configuration diagram of the polymer electrolyte fuel cell of the present invention. As shown in FIG. 1, the structure of the single cell is a membrane-electrode assembly (a membrane composed of 102 and 103 in FIG. 1B) in which a platinum-based catalyst layer 103 is bonded to both surfaces of a fluorine-based electrolyte membrane 102. The separator 104 is configured to sandwich this. For the gas diffusion layer (106 in FIG. 1B), carbon paper having a thickness of 200 μm was used.
[0024]
An anode gas channel having a width of 1 mm and a depth of 0.5 mm was provided on the anode side separator surface, and a cathode gas channel having a width of 1 mm and a depth of 0.8 mm was provided on the cathode side separator surface.
[0025]
The polymer electrolyte fuel cell of this example has a configuration in which a plurality of 50 single cells are connected in series, and a cooling water separator 108 in which a cooling water flow path is formed every two cells is inserted. This is because the cooling water is supplied to the cooling water separator 108 by a pump installed outside the battery, and the heat generated inside the battery is generated by a heat exchanger provided in the middle of the cooling water pipe connecting the pump and the battery. This is for recovery.
[0026]
In the fuel cell of the present invention, air is used as a gas containing oxygen. Air was supplied from a pipe connector provided in the end plate surface on which the positive electrode current collector plate was installed. Further, pure hydrogen was used as the gas containing hydrogen, and the gas was supplied from a pipe connector provided in the end plate surface on which the positive electrode current collector plate was similarly installed. In order to obtain the effect of the present invention, a gas containing at least oxygen may be supplied from the end plate side on which the positive electrode current collector plate is provided. Further, as the gas containing hydrogen, a reformed gas in which hydrogen is generated by a catalytic action of an organic substance such as natural gas or kerosene can also be used.
[0027]
The current collector plates 113 and 114 with output terminals protruded from the side surface of the battery stack. By connecting this terminal to an external load, electric power can be taken out. These current collector plates were made of nickel. As the material of the current collector plate, stainless steel, carbon, conductive resin, or the like can be used. An insulating sheet 107 was inserted between the current collector plates 113 and 114 and the end plate 109 to achieve electrical insulation.
[0028]
The laminate composed of the unit cell 101, the cooling water separator 108, the current collector plates 113 and 114, and the like was fixed by fastening parts including a bolt 116, a disc spring 117, and a nut 118. The fixing condition was to compress the laminate sandwiched between the two end plates with a hydraulic press and leave it for 1.5 hours, and then tighten the nut 118.
[0029]
A manifold that circulates a gas containing oxygen or hydrogen is formed inside the laminate constituting the single cell. The concept of the manifold of the present invention is shown in FIG. The manifold is divided into a supply-side manifold 204 until gas is supplied to each single cell, and a discharge-side manifold 208 for discharging exhaust gas generated after power generation in the single cell to the outside of the battery.
[0030]
In the present invention, the supply-side manifold 204 passes through the negative electrode current collector plate 206, but the positive electrode current collector plate 203 is separated from the positive electrode current collector plate 203 by the electrolytic suppression unit 213 of the separator 205 (in this embodiment, the separator 205 itself in FIG. 2). The structure is such that the supply side manifold 204 is not connected to the positive electrode current collector plate 203 while being electrochemically cut off. On the other hand, the discharge-side manifold 208 was electrochemically cut off by the electrolysis suppressing part 212 (in this embodiment, the separator 207 itself in FIG. 2) and was in communication only with the manifold of the positive electrode current collector plate 203. By adopting such a structure, the positive electrode current collector plate 203 and the negative electrode current collector plate 206 do not communicate with any one of the manifolds by the electrolysis suppressing portions (212, 213), and thus stay in the manifold. An electrochemical reaction (corrosion reaction of the current collector plate) is less likely to occur through the condensed water. According to the configuration of the present invention, since the oxygen-containing gas is supplied to each single cell from the manifold 204 of the negative electrode current collector plate 206 that is at a low potential and hardly generates eluted ions, the eluted ions from the current collector plate It is difficult to reach the membrane-electrode assembly, and deterioration of battery performance due to increase in membrane resistance, deactivation of the electrode catalyst, etc. can be suppressed.
[0031]
In this example, the electrode effective area capable of power generation was set to 100 cm ² and the output was measured at a current of 50 A. The gas supplied to the anode was hydrogen, the gas supplied to the cathode was air, and the pressure was normal pressure (one atmospheric pressure). The utilization rates of hydrogen and oxygen were 70% and 40%, respectively. The temperature of the cooling water supplied to the cell was set to 70 ± 2 ° C. The battery of this example is designated as S1.
[0032]
(Example 2)
A battery having the same single cell configuration as that of Example 1 and having the electrolytic suppression portions (212, 213) changed to insulating parts was manufactured. In the electrolysis suppression part, a recess was processed in the manifold facing part of the separators 205 and 207, and an ethylene / propylene rubber sheet (thickness 0.3 mm) was inserted into the recessed part. Other battery configurations and power generation conditions were the same as those of the battery S1 of Example 1. The battery of this example is designated S2.
[0033]
(Comparative example)
The separator 205 used in the polymer electrolyte fuel cell of Example 1 was provided with a through hole, and the negative electrode current collector plate 206 and the positive electrode current collector plate 203 were opposed to each other through the manifold 204. Let R be the battery of this comparative example.
[0034]
(Example 3)
A device in which the batteries S1 and S2 of Examples 1 and 2 and the battery R of Comparative Example 1 were incorporated in the power generation system shown in FIG. 3 was manufactured.
[0035]
In FIG. 3, natural gas 1001 is stored in a desulfurizer 1016 and supplied to a reformer 1003 by a blower 1008 to produce a hydrogen rich gas, which is supplied to a fuel cell stack 1012. Further, air 1002 is supplied to the anode of the fuel cell stack 1012 by a blower 1009. Also, distilled water 1006 is supplied to the fuel cell by the cooling water pump 1010. The cathode gas that has consumed hydrogen in the fuel cell is discharged from the cathode gas discharge pipe 1013. The cooling water circulates through the fuel cell and is discharged from the fuel cell. The warmed water is heat-exchanged by the heat exchanger 1011 to lower the temperature and return to the supply side again. The water heated by heat exchange is sent to the hot water tank 1007 by the circulating water pump 1015.
[0036]
The device (fuel cell system) on which the battery S1 is mounted is A1, the device (fuel cell system) on which the battery S2 is mounted is A2, and the device (fuel cell system) on which the battery R is mounted is A3. These devices differ only in the type of battery, but the other components and configurations are the same.
[0037]
In each apparatus, a fuel gas having a hydrogen concentration of 70% was introduced into the anode by reforming the city gas, and air was supplied to the cathode. The temperature of the hot water storage tank at the start of power generation was 40 ° C., and the temperature of the circulating water supplied to the fuel cell was also 40 ° C. The test was carried out in a constant temperature laboratory having an air conditioner so that the outside air temperature was constant at 10 ° C.
[0038]
The utilization rates of hydrogen and oxygen were 70% and 40%, respectively, and were constant for each current. The gas pressure was normal pressure.
[0039]
The current density was set to 0.5 mA / cm ² and a continuous power generation test was performed. The device (fuel cell system) A1 of the present invention obtained a voltage drop rate of 100 mV / 1000 h per unit cell by continuous power generation. The device A2 of the present invention obtained an excellent characteristic value with a voltage drop rate per unit cell of 15 mV / 1000 h under the same power generation conditions. On the other hand, the voltage drop rate per unit cell when using the device A3 equipped with the battery R of the comparative example was as large as 250 mV / 1000 h, and a performance drop was recognized.
[0040]
【The invention's effect】
With the battery configuration of the present invention, it is possible to reduce the performance degradation of the polymer electrolyte fuel cell.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part showing a basic configuration of a solid polymer fuel cell.
FIG. 2 is a schematic cross-sectional view showing a configuration of a manifold according to the present invention.
FIG. 3 is a diagram of an embodiment of a power generation system equipped with the polymer electrolyte fuel cell of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Single cell, 102 ... Solid polymer electrolyte membrane, 103 ... Catalyst layer, 104 ... Single cell separator, 105 ... Gasket, 106 ... Gas diffusion layer, 107 ... Insulating plate, 108 ... Cooling water separator, 109 ... End Plate 110, connector for anode gas piping, 111 ... connector for cooling water piping, 112 ... connector for cathode gas piping, 113 ... current collector plate, 114 ... current collector plate, 116 ... bolt, 117 ... disc spring, 118 ... nut 201 ... Gas supply connector, 202 ... Positive electrode end plate, 203 ... Positive current collector plate, 204 ... Gas supply manifold, 205 ... Separator in contact with the positive current collector plate, 206 ... Negative current collector plate, 207 ... Separator in contact with the negative electrode current collector plate, 208 ... Gas discharge manifold, 209 ... Insulating sheet, 210 ... End plate on the negative electrode side, 211 ... Gas Connector for discharge, 212 ... Electrolysis suppression unit, 213 ... Electrolysis suppression unit, 1001 ... Natural gas, 1002 ... Air, 1003 ... Reformer, 1006 ... Distilled water, 1007 ... Hot water storage tank, 1008 ... Pump for anode gas, 1009 ... Cathode gas pump, 1010 ... Cooling water pump, 1015 ... Circulating water pump, 1011 ... Heat exchanger, 1012 ... Fuel cell, 1013 ... Cathode gas exhaust pipe, 1014 ... Anode gas exhaust pipe, 1016 ... Desulfurizer .

Claims (4)

Conductivity is provided on both end faces of a laminate in which a plurality of single cells having a gas-flow groove and a single cell sandwiching a membrane-electrode assembly composed of a catalyst layer and a hydrogen ion conductive polymer membrane are stacked. The positive electrode current collector plate and the negative electrode current collector plate are disposed, and the laminate and the current collector plate are sandwiched by end plates, and the end plates supply and discharge oxygen-containing gas, hydrogen-containing gas, and cooling water. In the polymer electrolyte fuel cell having a manifold for performing the operation, the supply-side manifold penetrating the negative electrode current collector plate provided in the separator and the positive electrode current collector plate are electrochemically cut off by the electrolysis suppression unit. A solid polymer fuel cell, wherein the discharge side manifold and the negative electrode current collector plate provided in the separator are electrochemically cut off by an electrolysis suppressing part. Conductivity is provided on both end faces of a laminate in which a plurality of single cells having a gas-flow groove and a single cell sandwiching a membrane-electrode assembly composed of a catalyst layer and a hydrogen ion conductive polymer membrane are stacked. The positive electrode current collector plate and the negative electrode current collector plate are disposed, and the laminate and the current collector plate are sandwiched by end plates, and the end plates supply and discharge oxygen-containing gas, hydrogen-containing gas, and cooling water. In the polymer electrolyte fuel cell having a connector, the supply-side manifold penetrating the negative electrode current collector plate provided in the separator and the positive electrode current collector plate are electrochemically cut off by an electrolysis suppression unit. A solid polymer fuel cell, wherein the discharge side manifold and the negative electrode current collector plate provided in the separator are electrochemically cut off by an electrolysis suppressing part. The oxygen-containing gas supplied from the supply-side manifold does not pass through the separator flow path and does not contact the positive electrode current collector plate and the negative electrode current collector plate. 3. The polymer electrolyte fuel cell according to 2. 3. A power generation system comprising: a device for producing a gas containing hydrogen or a device for storing hydrogen; and the polymer electrolyte fuel cell according to claim 1 or 2 connected via a pipe for circulating the gas containing hydrogen. .

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