JPH1116591A - Solid polymer type fuel cell, solid polymer type fuel cell system, and electrical machinery and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell and a cell system capable of attaining highly efficient cell performance in supply of relatively low pressure and small volume of gas, and capable of keeping high efficiency for a cell system. SOLUTION: A gas supplying passage 12 engraved in a collector separator 5 is separated from a gas discharging passage 13, and all the gases of the gas supplying passage 12 are discharged to the gas discharging passage 13 after passed through an electrode layer and a catalyst layer. Since water drops in vicinity of the catalyst layer and unnecessary gas such as nitrogen are forcibly discharged, supplying of high pressure and high speed of gas is not required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a room-temperature fuel cell which can be used as a portable power supply, a power supply for an electric vehicle, or a home power supply system.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell which operates at room temperature is one in which a fuel gas such as hydrogen is electrochemically reacted with oxygen to supply electricity and heat at the same time. As shown in the figure, a catalyst layer 2 composed mainly of carbon powder carrying a platinum-based metal catalyst sandwiching a polymer electrolyte membrane 1 made of a fluororesin containing a sulfone group, and having gas permeability and conductivity. It is composed of an electrode layer 3 that also has a function. Further, outside the electrode layer 3, a gas flow path 4 for supplying gas to the catalyst layer 2, these electrodes / electrolyte are mechanically fixed, and at the same time, a supply gas is distributed to each battery through a manifold hole 6. The current collector separator 5 electrically connected in series with the battery to be used is a basic battery constituent unit.

[0003] The current collector separator 5 requires airtightness, conductivity, and corrosion resistance, and generally a carbon material is often used. There are various types of gas flow paths formed on the contact surface of the current collector separator 5 with the electrode 3. As shown in FIG. 12, the manifold hole 6 is made relatively large, and a large number of linear flow paths are formed from the gas supply side manifold to the gas discharge side manifold. One to several thin gas flow paths in FIG. 13 meander. Type, or an intermediate type thereof.

[0004] As a basic configuration of any of these conventional gas flow paths, a gas flow path is formed from the gas supply side manifold to the gas discharge side manifold. In some batteries, a current collector that forms a gas flow path and a separator that separates gas from an adjacent battery are separately configured as components.

[0005] Of the pair of electrode layers, one is supplied with a fuel gas such as hydrogen and the other is supplied with an oxidizing gas. The case where hydrogen is used as the fuel gas and oxygen is used as the oxidizing gas will be described. The hydrogen gas supplied by the gas flow path 4 is taken into the electrode layer 3 while passing through the electrode on the hydrogen gas supply side, that is, the anode surface. And reaches the catalyst layer 2 while diffusing inside the electrode layer 3. The hydrogen gas that has not been taken into the electrode layer 3 passes through the gas flow path 4 and is discharged as a drain gas. In the catalyst layer 2, an electrochemical reaction occurs in a region where the hydrogen gas and the polymer electrolyte 1 coexist, and hydrogen ions are taken into the polymer electrolyte membrane. On the other hand, also on the electrode layer 3 on the oxygen gas supply side, that is, on the cathode side, oxygen gas is similarly taken into the electrode layer 3 while passing through the cathode surface, and reaches the catalyst layer 2 on the cathode side while diffusing inside the electrode layer 3. . Similarly, oxygen gas not taken into the electrode layer 2 is discharged as it is as a drain gas through the gas flow path 4. In the catalyst layer 2 on the cathode side, hydrogen ions and oxygen supplied from the anode side through the electrolyte membrane 1 react to form water vapor. During that time, electrons move from the anode to the cathode through an external load, and can be output as electric power. Further, in such an electrochemical reaction, part of the chemical energy of hydrogen-oxygen becomes heat and generates heat in the battery, and can be used as heat energy such as changing cooling water to hot water.

This polymer electrolyte fuel cell is usually operated at a temperature from room temperature to about 90 ° C., so that most of the water vapor generated as a result of the electrochemical reaction in the catalyst layer 2 on the cathode side becomes water and becomes water. Condensation in the vicinity. When the dew water stagnates in the vicinity of the catalyst layer 2, oxygen does not reach the catalyst layer 2, which is a reaction site, and the battery performance is reduced. On the other hand, water generated as a result of the electrochemical reaction is not generated on the anode side, but water generated on the cathode side reversely penetrates the polymer electrolyte membrane and water vapor mixed in the anode gas to prevent the electrolyte membrane from drying. Is condensed and stays in the catalyst layer 2, so that hydrogen is no longer supplied to the reaction site, so that the battery performance is similarly reduced. The tendency of the battery performance to decrease due to the stagnation of dew water is even more remarkable when air having a low oxygen concentration is used as the oxidizing gas.

In addition to the deterioration of the cell performance due to the stagnation of the generated condensed water, when fuel such as methanol or methane is reformed and used as fuel gas or when air is used as oxidizing gas, Since carbon dioxide and nitrogen coexist in addition to hydrogen and oxygen involved in the reaction, the gas in which the concentration of hydrogen and oxygen has decreased due to the progress of the electrode reaction will deteriorate the battery performance unless the gas is quickly removed from the vicinity of the catalyst layer. I do.

Therefore, conventionally, a water repellent treatment of the catalyst layer and the electrode layer and an increase in the gas flow rate flowing through the gas flow path are performed to promptly remove excess condensed water, carbon dioxide, or nitrogen, thereby reducing the reaction site. Efforts have been made to maintain a good catalyst layer.

Further, when a reformed gas such as methane or methanol is used as a fuel gas, a region in which performance deteriorates due to carbon monoxide poisoning occurs in the same anode during a long-term operation of the battery, and the overall battery performance is reduced. Has recently been found to decrease. The concentration of trace carbon monoxide contained in the fuel gas, which is the reformed gas, increases toward the downstream of the anode-side gas flow channel due to the consumption of hydrogen in the catalyst layer. As a result, if the reactivity of the catalyst layer decreases due to poisoning of the catalyst surface in the downstream region with carbon monoxide, it is considered that the temperature of that portion becomes lower than that of the other portion. Since the poisoning of carbon monoxide is more likely to occur as the temperature is lower, the poisoning of carbon monoxide is accelerated downstream of the anode-side gas flow path, and the overall battery performance is reduced. In addition to the concentration of the carbon monoxide concentration in the fuel gas, there is a performance reduction factor due to the fact that the concentration of hydrogen or oxygen as a reaction gas becomes lower toward the downstream of the gas flow path due to gas consumption by the reaction. That is, when the concentration of the reaction gas decreases in the downstream portion of the gas flow path and the reactivity decreases, the temperature becomes lower than that in the upstream portion. In the case of a polymer electrolyte fuel cell, if a temperature difference occurs in the cell, the polymer electrolyte tends to dry out in the higher temperature area, causing the conductivity to decrease, and conversely, in the low temperature area, water vapor condenses and stays. Easier to do. Therefore, high performance cannot be expected as compared with a battery in which the entire battery is at a uniform temperature and the balance between condensation and elimination of water vapor is well maintained. Therefore, various measures have been taken to make the temperature in the anode surface as uniform as possible by improving the manifold system and the cooling water flow path.

[0010]

However, the above-described attempts to increase the removability of dew water by the water-repellent treatment have a limited effect, and the battery performance deteriorates due to a decrease in the water-repellency during long-time battery operation. Was. Also, in order to increase the gas flow rate flowing through the gas flow path cut into the current collector separator, reduce the cross-sectional area of the gas flow path to increase the pressure loss, or on the contrary, keep the pressure loss relatively low and Gas must be sent in, but doing so increases the load on the blowers, such as blowers and compressors, and the energy efficiency of the entire polymer electrolyte fuel cell system has been reduced. Further, when operating conditions of the battery, for example, when a large amount of water generated at a high current density is generated or when the gas flow rate is reduced, it is difficult to remove the dew condensation water, and the battery performance is further reduced.

[0011] Further, there is a limit to a method for suppressing poisoning of carbon monoxide and making the temperature in the battery uniform by improving the cooling water flow path, the manifold system, and the current collector separator gas flow path as in the prior art. The high performance could not be maintained for a long time.

The present invention has been made in consideration of the above-described conventional problems, and provides a polymer electrolyte fuel cell capable of obtaining high efficiency battery performance by supplying gas at a relatively low pressure and small volume and maintaining high efficiency as a battery system. , And a battery system.

[0013]

SUMMARY OF THE INVENTION The present invention is directed to a polymer electrolyte membrane having hydrogen ion conductivity, and conductive and air-permeable membranes disposed on both sides of the polymer electrolyte thin film with a catalytic reaction layer interposed therebetween. A pair of electrode layers having both properties, and a conductive current collector having a gas flow path for supplying gas to the electrode layer or discharging gas from the electrode layer; Wherein the gas flow path for gas supply and the gas flow path for gas discharge are separated and not connected on the current collector.

In the present invention, in order to efficiently remove water vapor and water droplets and carbon dioxide and nitrogen as contaminants in the supply gas in the vicinity of the catalyst layer, a gas for gas supply formed on the current collector is provided. Separate the flow path and the gas flow path for gas discharge,
All of the gas supplied to the electrode portion along the supply gas flow path is once sent to the gas-permeable electrode layer and contributes to the electrode reaction, and then is discharged into the discharge gas flow path. I have.

Further, in order to effectively guide the gas flow to the entire electrode portion with low pressure loss, the comb-shaped gas flow path for gas supply and the comb-shaped gas flow path for gas discharge are gathered so as to mesh with each other. It is configured on a conductor.

Further, one gas supply gas flow path and another gas discharge gas flow path opposed to each other are formed on a current collector by meandering or bending as a pair.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

In the polymer electrolyte fuel cell implemented in the present invention, the shapes of the components other than the current collector separator are almost the same as those of the conventional battery shown in FIG. 11, and therefore, here, FIG. It will be described using FIG.

A platinum catalyst was supported on a carbon powder having a particle size of several microns or less by reducing an aqueous chloroplatinic acid solution.
The supported amount of platinum was 1: 1 by weight with respect to carbon. This platinum-supported carbon powder and an alcohol solution of a solid polymer electrolyte were dispersed in an organic solvent to prepare a catalyst layer slurry. The 250-micron-thick carbon nonwoven fabric serving as an electrode layer is immersed in an emulsion liquid of a fluorine-based water repellent (ND1 manufactured by Daikin) in order to perform a water-repellent treatment, and dried at 400 ° C.
Was heat-treated.

Two water-repellent carbon nonwoven fabrics are prepared, a catalyst layer slurry containing platinum-carrying carbon powder is uniformly applied to one surface of each, and a 50 μm thick polymer electrolyte membrane 1 is sandwiched therebetween. And dried with the slurry surface inside. The size of this electrode was 5 cm square, and it was arranged at the center of a polymer electrolyte of 8 cm square, which is slightly larger. In this electrode-electrolyte assembly, it was confirmed that the catalyst layer 2 was formed on both surfaces of the polymer electrolyte membrane with a thickness of several tens to hundreds of microns, and was bonded to the electrode layer 3 thereon. Example 1 Gas channels as shown in FIG. 1 were formed on both sides of an airtight carbon plate having a thickness of 4 mm by cutting. The comb-shaped gas flow path 12 for gas supply and the comb-shaped gas flow path 13 for gas discharge were separated and arranged so as to engage with each other so that the distance between adjacent flow paths was 2 mm. The depth of the groove was 1.5 mm, and the groove width was 0.5 mm at the engagement portion and 2 mm at the trunk. The inside of the groove was coated with an emulsion liquid of a fluorine-based water repellent (ND1 manufactured by Daikin), dried, and heat-treated at 400 ° C. to impart water repellency. Using the carbon plate having the comb-shaped flow channels cut therein as a current collector separator, a battery was constructed by sandwiching the joined body of the electrode and the polymer electrolyte membrane. At this time, a fluororesin was used as the electrically insulating sealing material 7 between the current collector separator plate 5 and the polymer electrolyte membrane. For the evaluation of battery characteristics, three such single-cell batteries were stacked, and pressurized (10 kgf / cm ² ) with an end plate serving also as a cooling plate. Pure hydrogen was used as the fuel gas, and air was used as the oxidant gas. In addition, each gas supply unit is provided with a temperature controller and a humidifier, and the temperature of the supply gas is basically set to the same as the battery temperature (70 ° C.). The temperature was lowered by 15 ° C to 35 ° C.

In the battery characteristic test, first, the utilization rate of hydrogen gas was kept constant at 70%, and the oxygen utilization rate of air was reduced to 20%.
And the current-voltage characteristics were examined. Thereafter, the oxygen gas utilization rate was increased to 50% for measurement. Next, the oxygen gas utilization was fixed at 20%, and the battery utilization was measured while changing the hydrogen utilization from 70% to 95%. FIG. 2 shows current-voltage characteristics when the utilization rate of oxygen gas is changed, and FIG. 3 shows current-voltage characteristics when the utilization rate of hydrogen gas is changed.
Under all conditions, higher performance was obtained as compared with the conventional battery, but the tendency of the performance improvement was more remarkable as the gas utilization rate was higher, that is, when the passing gas was at a lower flow rate. In particular, the effect of the present invention is remarkable when the utilization rate of oxygen gas is increased by narrowing the flow rate of air, and a relatively high performance can be obtained even when the utilization rate of oxygen gas, which is hardly obtained by the conventional battery, is 50%. Was.

In the battery having the gas flow path of this embodiment,
The supplied gas is supplied to the trunk 8 of the gas flow path on the supply side 12 in FIG.
And is distributed to the engagement section 9. Since the electrode layer formed between the catalyst layer and the gas flow path has gas permeability, the gas that has reached the gas flow path on the gas supply side is forcibly fed into the electrode layer and undergoes an electrode reaction in the catalyst layer. As a result of the electrode reaction, water vapor or water droplets generated in the catalyst layer, or carbon dioxide or nitrogen that hinders the reaction is forcibly pushed out to the gas flow path 9 of the engagement portion on the gas discharge side 13. These exhaust gases are discharged as a so-called drain gas containing a large amount of water droplets, carbon dioxide, and nitrogen through the stem 8 of the exhaust gas flow path.

FIG. 4 shows such a gas flow and reaction mechanism taking the air side as an example. 12 and 13, the main flow 10 of the supply gas passes through the surface of the electrode layer 3 to supply the gas to the catalyst layer 2 and the unnecessary gas such as nitrogen as shown in FIG. It is considered that the exhaust from the catalyst layer 2 is performed by gas diffusion in the electrode layer 3 or a minute gas flow induced in the electrode layer 3.
Also, the force for discharging the excess water droplets 11 in the electrode layer 3 to the gas flow path is considered to be very small generated by the minute gas flow in the electrode layer 3.

On the other hand, in the battery of the present invention, as shown in FIG. 4, the main flow 10 of the supply gas flows in the vicinity of the catalyst layer 2 which is the reaction site, so that the supply of oxygen to the catalyst layer 2 and the discharge of nitrogen can be smoothly performed. Done. It is also considered that the force for discharging the generated water droplets is large. Furthermore, the dissolution rate of oxygen in the catalyst layer 2 is considered to increase as the flow rate of the gas in contact increases, leading to improvement in battery performance.

Also, the change over time in the initial performance of the battery was tracked in comparison with the conventional battery. As shown in FIG. 6, the performance of the battery having the conventional gas flow path configuration was considerably reduced with time, whereas the performance of the battery of the present invention could be suppressed. In the battery of the present invention, since the generated dew condensation water in the vicinity of the catalyst layer 2 is forcibly eliminated, the effect on the performance of the reduction in water repellency in the electrode layer 3 and the catalyst layer 2 is not so large. It is thought to be. Furthermore, in the fuel cell having the gas flow channel of the present invention, the change in the gas composition is small in the entire area of the electrode surface, the temperature distribution based on the change in the gas composition as in the related art, and the associated electrolyte membrane being too dry or too wet. It is important that it does not occur easily.

Next, in order to investigate the effect of carbon monoxide poisoning due to carbon monoxide enrichment when a hydrocarbon fuel such as methane is reformed into hydrogen and used as a fuel gas, a modified fuel containing 10 ppm of carbon monoxide was used. Simulated gas (H2: 80%, CO
(2: 20%). The utilization rate of hydrogen gas was 90%, and the utilization rate of oxygen in air was 20%. Other experimental conditions were the same as before. Fig. 7 is 300mA
Represents a change in battery voltage when current is continuously taken. In the conventional batteries having the gas flow paths as shown in FIGS. 12 and 13, the battery performance gradually deteriorated, and after 2000 hours, the output characteristics decreased by about 100 mV as compared with the initial performance. On the other hand, in the fuel cell having the gas flow path of the present invention, about 3 hours after 2000 hours.
It stopped at 0 mV. According to the temperature measurement by the thermocouple configured in the test battery, after 2100 hours in the conventional battery,
The temperature around the gas discharge section was lower by about 10 ° C. than that near the gas supply section.

Such a phenomenon was not observed in the battery of the present invention. Since the concentration of carbon monoxide contained in the fuel gas mainly occurs at 2 mm between the gas supply side flow path and the gas discharge side flow path adjacent to each other, even if carbon monoxide poisoning occurs at the downstream side of 2 mm, the temperature becomes high. It is considered that there is little difference, and that the poisoning is not accelerated due to the local low temperature.

Of these experiments, a current density of 300 mA /
For ² cm ² and an oxygen utilization of 20%, the required air supply is about 0.7 liter / min and the pressure loss at the battery is 0,1.
Although it was 086 kgf / cm ² , pressure loss is desired to be suppressed as much as possible in consideration of improvement in efficiency as a fuel cell system. Therefore, as shown in FIG. 8, a current collector separator was designed such that the distance between the supply-side gas flow path and the exhaust-side gas flow path was 1 mm in the same comb-shaped flow path, and a battery test was performed. The current-voltage characteristic and its change with time were not so different from those in the case where the interval between the flow paths was 2 mm, but the gas pressure loss in the battery was the same.
About 0.03kgf /
cm ² , which was significantly reduced.

As an embodiment of the fuel cell system according to the present invention, a 5 kW polymer electrolyte fuel cell using the comb separator shown in FIG. 8, a metal hydride cylinder as an hydrogen gas supply device, an air supply device Input as 1k
A W blower and a DC / AC converter were used as basic components. It should be noted that the conventional battery having a gas flow path as shown in FIG.
To construct a fuel cell system of 0.5 kgf / cm ² ) and 5 kW, a compressor of 2 to 3 kW and a special blower were required. "Example 2" other types of gas passages of the first embodiment of the present invention is shown in Figure 1 also examined, a prototype collector separator having a gas flow path in FIG. 9, FIG. 10, similarly batteries The test was performed. The other components of the fuel cell and the cell test conditions were the same as in Example 1. 9 and 10, the gas flow path on the supply side and the gas flow path on the discharge side are each composed of one flow path groove without branch, and are opposed to each other at a constant interval. FIG.
In FIG. 10, the electrode layer 3 has a meandering curve, and in FIG.
Is formed. Also in this flow path structure, the gas supplied from the supply gas flow path is forcibly sent to the electrode layer 3 and pushed out to the opposite discharge gas flow path after the electrode reaction. Further, even if gas passes through any part of the electrode layer 3, the pressure loss is equal, so that the gas can flow more uniformly over the entire area of the electrode layer 3. According to the results of the actual battery test, the performance of the battery having this type of gas flow path was higher than that of the comb-shaped gas flow path. However, even at the same gas flow rate, the pressure loss was slightly higher than in the comb channel. It is considered that the gas flow path has been lengthened, but the usefulness is further enhanced by optimizing the fuel cell system, such as by using an air supply blower for higher pressure.

In the present invention, the shapes and relationships of the supply-side gas passage portion and the discharge-side gas passage portion are not limited to the example described in the above embodiment, and may have other shapes and relationships. Needless to say, it is only necessary to be separated from each other.

Further, the battery according to the present invention can be applied to many electric appliances such as a notebook personal computer, a portable terminal, an outdoor power supply, and a lighting power supply.

[0032]

As described above, in the present invention, relatively low pressure,
Since high efficiency battery performance can be obtained by supplying a small amount of gas,
High efficiency can be maintained as a battery system.

Further, the effects of preventing the electrolyte membrane from being overly wetted and overdried and the suppression of carbon monoxide poisoning enhance the durability of the polymer electrolyte fuel cell and the battery system.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view of a comb-shaped gas flow channel according to an embodiment of the present invention.

FIG. 2 is a diagram showing the dependence of current-voltage characteristics on oxygen utilization.

FIG. 3 is a diagram showing the dependence of current-voltage characteristics on hydrogen utilization.

FIG. 4 is a cross-sectional view illustrating a gas flow through a gas flow channel according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a gas flow in a conventional gas flow path.

FIG. 6 is a diagram showing a change over time in initial performance of the fuel cell according to one embodiment of the present invention;

FIG. 7 is a diagram showing the durability of a fuel cell according to an embodiment of the present invention to poisoning with carbon monoxide.

FIG. 8 is a plan view of a gas flow channel having an interval of 1 mm according to an embodiment of the present invention.

FIG. 9 is a plan view of another type of gas flow channel according to an embodiment of the present invention.

FIG. 10 is a plan view of another type of gas flow channel according to an embodiment of the present invention.

FIG. 11 is a cross-sectional view of a conventional polymer electrolyte fuel cell.

FIG. 12 is a plan view of a conventional gas flow path.

FIG. 13 is a plan view of another conventional gas flow path.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 polymer electrolyte membrane 2 catalyst layer 3 electrode layer 4 gas flow path 5 current collector separator 6 manifold hole 7 sealing material 8 gas flow path trunk 9 gas flow path engagement section 10 main flow of gas 11 water droplet 12 gas supply comb Channel 13 Comb-shaped channel for gas discharge

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Eiichi Yasumoto 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A polymer electrolyte membrane, a pair of electrode layers having both conductivity and gas permeability disposed opposite to each other with a catalyst layer interposed therebetween on both surfaces of the polymer electrolyte thin film; A conductive current collector having a gas flow path for supplying a gas or discharging the gas from the electrode layer; a gas flow path portion for supplying a gas, which constitutes the gas flow path; A solid polymer fuel cell, wherein a gas flow path portion for the fuel cell is separated on the current collector and is not connected to each other. 2. The gas flow path for gas supply and the gas flow path for gas discharge are each formed in a comb shape, and are formed on the current collector so as to mesh with each other. The polymer electrolyte fuel cell according to claim 1, wherein 3. The gas flow path for gas supply and the gas flow path for gas discharge each constitute a single gas flow path having no branch point. 2. The polymer electrolyte fuel cell according to claim 1, wherein the gas flow path and the gas discharge gas flow path are formed in a meandering, curved, or spiral shape while approaching and facing each other. 4. A polymer electrolyte fuel cell, comprising: the polymer electrolyte fuel cell according to claim 1; and a gas blower for blowing gas in the gas flow path. system. 5. An electric apparatus comprising the polymer electrolyte fuel cell according to claim 1 as a power source.