JP2010015940A - Method for manufacturing electrolyte layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrolyte layer for forming it of high quality to have a desired thickness. <P>SOLUTION: By preparing a paste for electrolyte layer formation by mixing stable particles and binder against an electrolyte, and by controlling the pH value within a pH control range B by adjusting dissolved carbon dioxide gas concentration of the paste for the electrolyte layer formation, viscosity of the paste for electrolyte layer formation is prepared within a viscosity adjusting range A, and by coating the paste for the electrolyte layer formation after viscosity preparation on a fuel electrode or an air electrode, the electrolyte layer is formed. In the case the viscosity of the paste for the electrolyte layer formation is lower than a set value, it is preferable that the dissolved carbon dioxide gas concentration is increased by aeration of the carbon dioxide gas in the paste for electrolyte layer formation. In the case the paste for electrolyte layer formation is higher than the set value, it is preferable that the dissolved concentration of the carbon dioxide gas is decreased by aerating an inert gas except the dissolved carbon dioxide concentration of the carbon dioxide gas in the paste for the electrolyte layer formation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an electrolyte layer used for holding an electrolyte of a fuel cell.

  The fuel cell has a configuration in which an electrolyte is disposed between a fuel electrode and an air electrode. In addition to supplying a hydrogen-containing gas to the fuel electrode side, an oxygen-containing gas is supplied to the air electrode side, and an electromotive force is obtained using an electrochemical reaction that occurs between the two electrodes.

  By the way, phosphoric acid is used as an electrolyte in phosphoric acid fuel cells. However, phosphoric acid has a low viscosity, and therefore, phosphoric acid alone can be disposed between the fuel electrode and the air electrode to form a fuel cell. Can not. For this reason, in a fuel cell using an electrolyte having a low viscosity, such as a phosphoric acid fuel cell, the electrolyte is held in an electrolyte layer, and the electrolyte layer holding the electrolyte is disposed between both electrodes to form a fuel cell. Yes.

  In a fuel cell using such an electrolyte layer, protons generated on the fuel electrode side move to the air electrode side through the electrolyte layer and combine with oxygen ions, thereby realizing an electrochemical reaction necessary for power generation. The Therefore, in order to improve the power generation capability of the fuel cell, it is important to reduce the electric resistance (ion transfer resistance) in the electrolyte layer between the fuel electrode and the air electrode so that the power generation reaction is performed more efficiently. Come.

  As a method for reducing the electric resistance of the electrolyte layer, it is possible to reduce the thickness of the electrolyte layer and increase its porosity. However, if the electrolyte layer is too thin or the porosity is too high, it becomes difficult to maintain airtightness even when the inside of the electrolyte layer is filled with the electrolyte solution, and the hydrogen-containing gas and the oxygen-containing gas are caused to pass through the electrolyte layer. It reacts directly and the power generation capacity of the fuel cell is significantly reduced. In addition, there is a risk of fever and ignition.

  From such a point, it is desirable that the electrolyte layer has a thickness of about 30 μm to 80 μm and a porosity of about 40% to 60%. Further, in order to obtain a more stable power generation capability, it is desirable that the electrolyte layer surface is smooth and no recesses or defects are formed therein.

As one method for forming an electrolyte layer, a method is known in which a paste serving as a precursor of an electrolyte layer is applied to an electrode surface (catalyst layer surface), and then dried and heat-treated to form an electrolyte layer.
For example, in a phosphoric acid fuel cell, a mixture mainly containing fine particles of silicon carbide (SiC) and a binder such as polytetrafluoroethylene (PTFE) is used as the paste. Such a binder is usually obtained by mixing SiC in a suitable solvent with a stirring blade or mixing the solvent and SiC using a mortar, ball mill, pot mill or the like, and then adding PTFE or the like to the resulting slurry. It is prepared by mixing a binder.

However, the paste prepared in this way does not always have a uniform viscosity, and changes every time the preparation is performed.
If the paste viscosity is too low, the thickness of the formed electrolyte layer tends to be thin, and the possibility of being less than 30 μm is high. For this reason, it becomes difficult to ensure the airtightness of the reaction gas. In addition, when applied to the electrode surface, the paste may be repelled due to the influence of the binder contained in the catalyst layer, the applicability may deteriorate, or dripping from the roll may occur when a coating roll is used. . If the paste viscosity is too low in this way, it is very likely that the electrolyte layer formed will be too thin or the coating thickness on the electrode surface will be uneven. Then, it is easy to form an electrolyte layer having a non-uniform thickness.

  On the other hand, if the paste viscosity is too high, the formed electrolyte layer tends to be thick, which is disadvantageous for reducing electric resistance. In addition, the binder contained in the paste solidifies due to an increase in the shear stress in the coating roll, and when the paste is applied, aggregated particles that greatly exceed the thickness of the electrolyte layer and the paste on the electrode surface are generated. Transcriptional defects may occur. Also, the coating roll is often formed with grooves with a pitch of about 1 mm to hold the paste. However, if the paste viscosity is high, its fluidity is relatively low, so the pitch is almost the same as the groove pitch after application. May be left on the coating film or the electrolyte layer, and a subsequent process such as smoothing may be required. For example, a high-viscosity paste having a thickness of more than 3000 mPa · s may be thinned to 20 μm or less, and the concave portion having a reduced thickness sometimes becomes a deficient portion, which contributes to significantly reducing the airtightness of the reaction gas.

  As described above, in the method of forming the electrolyte layer using the paste, the paste viscosity greatly affects the fuel cell characteristics, and therefore management of the paste viscosity is important.

  In adjusting the paste viscosity, there is a method of adjusting the paste viscosity to an appropriate range by adjusting the solid content concentration of SiC or the like in the paste.

Patent Document 1 listed below describes that the viscosity of the paste serving as the precursor of the electrolyte layer has a correlation with the pH value. By adding an alkaline solution or an acidic solution, the pH value of the paste is adjusted. A method of controlling and thereby changing the dispersion state of the particles in the paste to adjust the paste viscosity is disclosed.
JP-A-2005-294179 (paragraph numbers 0028 to 0031, FIG. 3)

  When the viscosity is adjusted by changing the solid content concentration in the paste, the thickness of the coating film changes when applied to the electrode surface. The thickness of the electrolyte layer is different, and it is difficult to control the thickness of the electrolyte layer.

  Moreover, in the said patent document 1, the paste viscosity is adjusted so that it may become a setting range by adding an alkaline solution and an acidic solution and controlling the pH value of a paste. With the method of Patent Document 1, since the solid content concentration in the paste does not fluctuate greatly, the thickness of the electrolyte layer finally formed is unlikely to vary. However, a compound contained in an alkaline solution or an acidic solution used for pH adjustment may remain in the electrolyte layer. These residues may react with an electrolyte or the like to form a salt or the like that becomes an inhibitor of the electrode reaction, which may adversely affect the characteristics of the battery. For example, Patent Document 1 discloses an example in which pH of a paste is adjusted using aqueous ammonia (paragraph number 0029). However, when ammonia remains in the electrolyte layer, phosphoric acid and ammonia as electrolytes are mixed. May react to form ammonium phosphate which may adversely affect battery characteristics.

  Accordingly, an object of the present invention is to provide a method for producing an electrolyte layer capable of forming a high quality electrolyte layer with a desired thickness.

  In order to achieve the above object, the method for producing an electrolyte layer according to the present invention is stable to the electrolyte in the method for producing an electrolyte layer for holding an electrolyte disposed between a fuel electrode and an air electrode of a fuel cell. By preparing a paste for forming an electrolyte layer by mixing a fine particle and a binder, adjusting the carbon dioxide dissolved concentration of the paste for forming an electrolyte layer and controlling the pH value to be a set value, The viscosity of the electrolyte layer forming paste is adjusted, and the electrolyte layer forming paste is applied to the fuel electrode or the air electrode to form the electrolyte layer.

  According to the present invention, by adjusting the carbon dioxide dissolved concentration of the electrolyte layer forming paste and controlling the pH value to be a set value, the dispersion state of the particles in the paste is changed and the viscosity is adjusted. be able to. For this reason, the electrolyte layer forming paste having a predetermined viscosity range can be easily adjusted without substantially changing the solid content concentration in the paste. Therefore, it is possible to form a uniform coating film with a desired thickness on the electrode surface with no irregularities or defects, and the effect of reducing electrical resistance in the electrolyte layer is excellent. Further, even if carbon dioxide gas is contained in the electrolyte layer forming paste, carbon dioxide gas is degassed by an operation such as heat treatment at the time of forming the electrolyte layer, so that impurities hardly remain in the electrolyte layer. In addition, since it does not react with the electrolyte or the like to form a salt or the like that inhibits the electrode reaction, there is little possibility of damaging the cell characteristics of the fuel cell, and the fuel cell using the electrolyte layer thus formed is Stable power generation output can be obtained over a long period of time.

  When the viscosity of the electrolyte layer forming paste is lower than a set value, the electrolyte layer manufacturing method of the present invention increases the dissolved concentration of carbon dioxide gas by aeration of carbon dioxide gas to the electrolyte layer forming paste. When the viscosity of the layer forming paste is higher than the set value, it is preferable to aerate an inert gas other than carbon dioxide gas to the electrolyte layer forming paste to lower the dissolved concentration of carbon dioxide gas. When the viscosity of the electrolyte layer forming paste is lower than the set value, aeration of carbon dioxide gas to the electrolyte layer forming paste increases the dissolved concentration of carbon dioxide gas and lowers the pH value. To rise. In addition, when the viscosity of the electrolyte layer forming paste is higher than the set value, the dissolved concentration of carbon dioxide gas is lowered and the pH value is increased by aerating inert gas other than carbon dioxide gas to the electrolyte layer forming paste. As a result, the paste viscosity decreases. Thus, according to the viscosity of the electrolyte layer forming paste, the paste viscosity can be adjusted to a predetermined viscosity range by aeration of carbon dioxide gas or inert gas to the electrolyte layer forming paste.

  In the method for producing an electrolyte layer of the present invention, it is preferable to use one or more selected from nitrogen, helium and argon as the inert gas. If these inert gases remain in the electrolyte layer, they do not adversely affect the cell characteristics of the fuel cell.

  The method for producing an electrolyte layer of the present invention is preferably adjusted so that the electrolyte layer forming paste has a viscosity of 1,500 to 3,000 mPa · s. According to this aspect, it is possible to form an electrolyte layer having a smooth surface, no recesses and defects, and an appropriate thickness and porosity.

  According to the present invention, since the viscosity of the electrolyte layer forming paste can be easily adjusted, it is possible to form a uniform coating film having a concavo-convex portion and a defect portion on the electrode surface with a desired thickness. In addition, impurities are unlikely to remain in the formed electrolyte layer, so that it does not react with the electrolyte or the like to form a salt or the like that becomes an inhibitor of the electrode reaction, and stable power generation output can be achieved over a long period of time. Obtainable.

  The method for producing an electrolyte layer according to the present invention includes a step of preparing an electrolyte forming paste, a viscosity adjusting step of adjusting the viscosity of the obtained electrolyte forming paste, and a viscosity-adjusted electrolyte forming paste as a fuel electrode of a fuel cell. Or it is mainly comprised by the electrolyte layer formation process of apply | coating to an air electrode, heating and drying and forming an electrolyte layer.

(Preparation process of electrolyte forming paste)
In the step of preparing the electrolyte forming paste, particles that are stable with respect to the electrolyte and a binder are mixed to prepare the electrolyte forming paste.

  The particles used for the preparation of the electrolyte forming paste are not particularly limited as long as they are not decomposed by the electrolyte and can maintain the chemical structure even when in contact with the electrolyte, and SiC fine particles and the like are preferable. For example, when phosphoric acid is used as the electrolyte, SiC fine particles are preferably used for reasons of heat resistance and acid resistance.

  Moreover, 0.1-20 micrometers is preferable and, as for the particle size of the said particle | grain, 0.5-5 micrometers is more preferable. If the particle diameter is less than 0.1 μm, the porosity for holding the electrolyte is lowered, and if the particle diameter exceeds 20 μm, the particles themselves may damage other components of the battery.

  The particles are preferably used by being dispersed in a solvent. Examples of the dispersion solvent include solvents such as diethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, ethylene glycol, and benzyl alcohol. These solvents may be mixed with water and used as an aqueous solution. Examples of the method for dispersing the particles in the solvent include ultrasonic dispersion.

  Preferred examples of the binder used for preparing the electrolyte forming paste include polytetrafluoroethylene (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA). For example, when using phosphoric acid as an electrolyte, PTFE is preferably used for the reasons of heat resistance and acid resistance.

  The electrolyte forming paste can be prepared, for example, as follows. That is, SiC fine particles are mixed with a solvent such as an ethylene glycol aqueous solution, and stirred while applying ultrasonic waves to disperse the SiC fine particles in the solvent to prepare a slurry. Subsequently, an electrolyte forming paste is prepared by mixing the slurry-like material thus formed with a binder such as PTFE.

(Viscosity adjustment process)
Next, the viscosity of the electrolyte forming paste thus prepared is adjusted to a predetermined viscosity. In the present invention, the pH value is controlled by adjusting the carbon dioxide dissolved concentration of the electrolyte forming paste. By doing so, the paste viscosity is adjusted to be within the set range.

  FIG. 1 shows a relationship diagram between the pH value and the viscosity of the electrolyte forming paste. In FIG. 1, the horizontal axis indicates the pH value of the electrolyte forming paste, and the vertical axis indicates the viscosity (mPa · s) of the electrolyte forming paste. The paste viscosity is a value measured with a B-type rotational viscometer.

  As shown in FIG. 1, the electrolyte forming paste has a tendency to decrease in viscosity as the pH value increases. This seems to be because by changing the pH value of the electrolyte forming paste, the zeta potential of the particles in the paste changes and the degree of aggregation of the particles changes, which appears in the paste viscosity. . The characteristics shown in FIG. 1 showed the same tendency regardless of the paste composition.

  The electrolyte forming paste incorporates carbon dioxide in the atmosphere at the time of preparing the paste, and the carbon dioxide is dissolved. Therefore, the pH value can be easily adjusted by adjusting the concentration of carbon dioxide dissolved in the electrolyte forming paste. Can be adjusted.

  In the present invention, when the viscosity of the electrolyte forming paste is below the set range, carbon dioxide gas is aerated on the electrolyte forming paste to increase the dissolved concentration of carbon dioxide gas in the electrolyte forming paste. As the dissolved concentration of carbon dioxide increases, the pH value decreases, and accordingly, the viscosity of the electrolyte forming paste increases. On the other hand, when the viscosity of the electrolyte forming paste exceeds the set range, the electrolyte forming paste is aerated with an inert gas other than carbon dioxide (preferably nitrogen, helium, argon) to reduce the dissolved concentration of carbon dioxide. Reduce. Since the pH value increases when the dissolved concentration of carbon dioxide gas decreases, the viscosity of the electrolyte forming paste decreases accordingly.

  In the present invention, it is preferable to adjust the viscosity by adjusting the dissolved concentration of carbon dioxide gas so that the viscosity of the electrolyte forming paste is 1500 mPa · s to 3000 mPa · s to control the pH value of the paste. When the viscosity is 1500 mPa · s or more, it is possible to suppress the formation of a thin electrolyte layer and the occurrence of repellency and dripping on the electrode surface. In addition, if the viscosity is 3000 mPa · s or less, the formed electrolyte layer is less likely to be thick, resulting in high electrical resistance, generation of aggregated particles, occurrence of paste transfer defects, etc., uneven portions due to coating roll grooves And the occurrence of defects can be suppressed. If the viscosity of the paste is within the above range, an electrolyte layer having a porosity of about 40% to 60% is formed with a thickness of about 30 μm to 80 μm by applying to the electrode surface using a natural roll coater or the like. It becomes easy.

(Electrolyte layer forming process)
After adjusting the viscosity of the electrolyte forming paste to a predetermined viscosity, it is applied to the fuel electrode or air electrode of the fuel cell, and heated and dried to form an electrolyte layer.

  The method for applying the electrolyte forming paste is not particularly limited, and preferred examples include coating using a natural roll coater, screen printing, spray coating, and coating using a reverse roll coater.

(Manufacture of fuel cells)
Then, an electrolyte layer formed on one electrode surface is impregnated with an electrolyte such as phosphoric acid, and this one electrode is joined and integrated with the other electrode sandwiching the electrolyte layer, so that a single cell of the fuel cell A fuel cell can be manufactured by stacking a plurality of battery single cells obtained in this way via a separator.

  In the present invention, by adjusting the carbon dioxide dissolved concentration of the electrolyte layer forming paste and controlling the pH value to be a set value, the dispersion state of the particles in the paste can be changed and the viscosity can be adjusted. it can. For this reason, an electrolyte layer forming paste having a predetermined viscosity range can be easily adjusted with almost no change in the solid content concentration in the paste, and in application to the electrode surface using a coating roll, etc., excellent fluidity after application A coating film having a smooth and uniform thickness can be obtained over the entire electrode surface. Further, impurities are unlikely to remain in the electrolyte layer, and further, a salt that does not react with the electrolyte or the like and becomes an inhibitor of the electrode reaction is not formed, which may impair the battery characteristics of the fuel cell. Few. Therefore, according to the present invention, it is possible to easily and stably manufacture a high-quality electrolyte layer having a desired thickness, improve the power generation capability of the fuel cell, and manufacture a highly reliable fuel cell. It becomes possible to do.

Example 1
A SiC fine particle powder having an average particle size of about 1 μm was put into a 70% diethylene glycol aqueous solution, and this was stirred and dispersed for 1 hour using a stirring blade while applying an ultrasonic wave of 28 kHz and 1200 W to obtain a slurry. Then, a dispersion of PTFE was added to the slurry thus obtained and stirred for 5 minutes to prepare an electrolyte layer forming paste. The obtained paste for forming an electrolyte layer had a pH value of 6 and a viscosity of 1000 mPa · s. When this electrolyte layer forming paste was aerated with carbon dioxide gas for 15 minutes, the pH value was 5.8 and the viscosity was 1580 mPa · s.
The electrolyte layer forming paste thus adjusted in viscosity is applied to the electrode surface using a natural roll coater, dried in a drying furnace controlled at a temperature of about 45 ° C. for 15 hours, and then in a nitrogen atmosphere at a temperature of about A heat treatment was performed at 270 ° C. for 20 minutes to form an electrolyte layer having a thickness of 40 μm. This electrolyte layer was smooth throughout, and had no unevenness, and had a uniform thickness. Further, when applying the paste to the electrode surface, there was no dripping or the like, and the application workability was good.
Then, the electrolyte layer thus formed on one electrode surface is impregnated with phosphoric acid, and this one electrode is joined and integrated with the other electrode sandwiching the electrolyte layer, so that a single unit of the phosphoric acid fuel cell is obtained. A cell was formed, and about 30 cells were stacked via a separator to manufacture a phosphoric acid fuel cell.
When the phosphoric acid fuel cell thus manufactured was evaluated, an open circuit voltage of 950 mV or more was obtained for all cells.

(Example 2)
A SiC fine particle powder having an average particle size of about 1 μm was put into a 70% diethylene glycol aqueous solution, and this was stirred and dispersed for 1 hour using a stirring blade while applying an ultrasonic wave of 28 kHz and 1200 W to obtain a slurry. Then, a dispersion of PTFE was added to the slurry thus obtained and stirred for 5 minutes to prepare an electrolyte layer forming paste. The obtained electrolyte layer forming paste had a pH value of 5.1 and a viscosity of 3500 mPa · s. When this electrolyte layer forming paste was aerated with nitrogen gas for 15 minutes, the pH value was 5.2 and the viscosity was 3000 mPa · s.
The electrolyte layer forming paste thus adjusted in viscosity is applied to the electrode surface using a natural roll coater, dried in a drying furnace controlled at a temperature of about 45 ° C. for 15 hours, and then in a nitrogen atmosphere at a temperature of about A heat treatment was performed at 270 ° C. for 20 minutes to form an electrolyte layer having a thickness of 40 μm. This electrolyte layer was smooth throughout, and had no unevenness, and had a uniform thickness.
Then, the electrolyte layer thus formed on one electrode surface is impregnated with phosphoric acid, and this one electrode is joined and integrated with the other electrode sandwiching the electrolyte layer, so that a single unit of the phosphoric acid fuel cell is obtained. A cell was formed, and about 30 cells were stacked via a separator to manufacture a phosphoric acid fuel cell.
When the phosphoric acid fuel cell thus manufactured was evaluated, an open circuit voltage of 950 mV or more was obtained for all cells.

It is a relationship figure of pH value and viscosity of a paste.

Claims (4)

In a method for producing an electrolyte layer for holding an electrolyte disposed between a fuel electrode and an air electrode of a fuel cell,
A paste for forming an electrolyte layer is prepared by mixing particles that are stable with respect to the electrolyte and a binder,
By adjusting the carbon dioxide dissolved concentration of the electrolyte layer forming paste and controlling the pH value to be a set value, the viscosity of the electrolyte layer forming paste is adjusted,
A method for producing an electrolyte layer, wherein the electrolyte layer is formed by applying the electrolyte layer-forming paste after viscosity adjustment to the fuel electrode or the air electrode.   When the viscosity of the electrolyte layer forming paste is lower than a set value, carbon dioxide gas is aerated on the electrolyte layer forming paste to increase the dissolved concentration of carbon dioxide gas, and the viscosity of the electrolyte layer forming paste is lower than the set value. 2, the method for producing an electrolyte layer according to claim 1, wherein an inert gas other than carbon dioxide gas is aerated on the electrolyte layer forming paste to lower the dissolved concentration of carbon dioxide gas.   The method for producing an electrolyte layer according to claim 1 or 2, wherein at least one selected from nitrogen, helium and argon is used as the inert gas.   The manufacturing method of the electrolyte layer of any one of Claims 1-3 adjusted so that the viscosity of the said paste for electrolyte layer formation may be set to 1,500-3,000 mPa * s.

Images