JP2007250366A - Catalyst layer of fuel cell electrode - Google Patents

Abstract

[PROBLEMS] To improve the power generation characteristics of a fuel cell by suppressing aggregation of catalyst powder particles and forming more three-phase interfaces in the catalyst layer when forming a catalyst layer of a fuel cell electrode from a catalyst powder. Let
A catalyst-carrying particle 610 in which a catalyst for a fuel cell reaction is carried on conductive particles, a fibrous substance 630, and an electrolyte material 620 are prepared. The prepared catalyst-carrying particles 610, the fibrous material 630, and the electrolyte material 620 are granulated to generate catalyst powder. And the catalyst layer comprised with the catalyst powder is formed so that an electrolyte membrane may be contacted, and the electrode for fuel cells is manufactured.
[Selection] Figure 3

Description

  The present invention relates to a technique for forming a catalyst layer of a fuel cell electrode.

  The fuel cell reaction in the fuel cell proceeds at the interface (referred to as “three-phase interface”) between the catalyst of the catalyst-supported particles, the reaction gas used in the fuel cell reaction, and the electrolyte. Therefore, the power generation characteristics of the fuel cell are improved by increasing the amount of formation of this three-phase interface. Therefore, conventionally, in order to increase the formation amount of the three-phase interface, a powder is generated by granulating the catalyst-supporting particles and the electrolyte material, and a catalyst layer including the catalyst-supporting particles and the electrolyte material is formed by granulation. Forming from the produced | generated powder (catalyst powder) is performed (for example, refer patent document 1).

JP 2001-185163 A Japanese Patent Laid-Open No. 11-126615 JP 2003-123769 A Japanese Patent Laid-Open No. 10-223233

  However, when a catalyst layer is formed with a catalyst powder produced by granulating catalyst-carrying particles and an electrolyte material, the particles of the catalyst powder may aggregate in the formed catalyst layer. When the catalyst powder particles are aggregated, it is difficult to supply the reaction gas to the aggregated catalyst powder particles. Therefore, even if the catalyst layer is formed from the granulated powder, a sufficient three-phase interface is not formed, and sufficient power generation performance may not be obtained.

  The present invention has been made to solve the above-described conventional problems, and improves the power generation characteristics of the fuel cell by suppressing the aggregation of the particles of the catalyst powder and forming more three-phase interfaces. The purpose is to let you.

  In order to achieve at least a part of the above object, the method of the present invention is a method for producing a fuel cell electrode having a catalyst layer provided in contact with an electrolyte membrane, the method comprising: A step of producing a catalyst powder by granulating a catalyst-carrying particle having a catalyst supported on conductive particles, a fibrous material, and an electrolyte material; and (b) the catalyst powder so as to be in contact with the electrolyte. Forming the configured catalyst layer.

  According to this configuration, the aggregation of the particles of the catalyst powder is suppressed by the fibrous substance contained in the catalyst powder. As a result, the pore volume in the catalyst layer increases and more three-phase interfaces can be formed, so that the power generation characteristics of the fuel cell can be enhanced.

  The step (a) includes a step of preparing a catalyst ink containing the catalyst-supporting particles, the fibrous substance, the electrolyte material, and a solvent, and removing the solvent from the catalyst ink to thereby form the catalyst powder. And a step of generating.

  According to this configuration, the distribution of the fibrous substance and the catalyst-carrying particles is made more uniform, so that the aggregation of the catalyst-carrying particles in the particles of the catalyst powder is suppressed, and the power generation characteristics of the fuel cell can be further improved. it can.

  The step (b) may include a step of spraying the catalyst powder on the electrolyte membrane.

  According to this configuration, by forming the catalyst layer from the catalyst powder dispersed on the electrolyte membrane, the interface between the electrolyte membrane and the catalyst layer can be kept clean, thereby suppressing deterioration in power generation characteristics of the fuel cell. can do.

  The ratio of the weight of the fibrous material to the weight of the conductive particles may be in the range of 2% to 10% by weight.

  The ratio of the weight of the electrolyte material to the weight of the conductive particles may be in the range of 80 wt% to 120 wt%.

  The fibrous material may be conductive.

  According to this configuration, since the particles of the catalyst powder are joined by the conductive fibrous substance, the electrical conductivity of the catalyst layer is increased. Therefore, the internal loss of the fuel cell is reduced, and the power generation characteristics of the fuel cell can be further improved.

  The conductive fibrous substance may be fibrous carbon.

  Since fibrous carbon is difficult to corrode, deterioration of the fuel cell due to corrosion of the fibrous substance can be suppressed.

  The present invention can be realized in various modes. For example, a catalyst layer of a fuel cell and a manufacturing method thereof, a fuel cell using the catalyst layer, a power generation device using the fuel cell, and This can be realized in the form of an electric vehicle or the like equipped with the fuel cell.

Next, the best mode for carrying out the present invention will be described in the following order based on examples.
A. Embodiment:
B. Example:

A1. Fuel cell structure:
FIG. 1 is a schematic cross-sectional view showing the structure of a cell 100 constituting a fuel cell as an embodiment of the present invention. The fuel cell has a fuel cell stack in which a plurality of cells 100 are stacked. The cell 100 includes an electrolyte membrane 110, and a cathode 200 and an anode 300 that sandwich the electrolyte membrane 110 from both sides.

  The cathode 200 includes a cathode catalyst layer 210, a cathode diffusion layer 220, and a cathode separator 230. The anode 300 includes an anode catalyst layer 310, an anode diffusion layer 320, and an anode separator 330. The cathode catalyst layer 210, the anode catalyst layer 310, the laminate of the cathode catalyst layer 210 and the cathode diffusion layer 220, and the laminate of the anode catalyst layer 310 and the anode diffusion layer 320 are generally referred to as an “electrode”. be called.

  The electrolyte membrane 110 is a proton conductive ion exchange membrane made of a fluorine resin material such as Nafion (trademark of DuPont) and having good conductivity in a wet state. The cathode catalyst layer 210 and the anode catalyst layer 310 include an electrolyte material and conductive particles carrying a catalyst (generally called “catalyst carrying particles”). The gas diffusion layers 220 and 320 are made of a conductive porous material (for example, carbon paper or foam metal).

  The cathode catalyst layer 210 and the anode catalyst layer 310 contain a fibrous substance in addition to the electrolyte material and the catalyst-supporting particles. In addition, the process of forming these catalyst layers 210 and 310 will be described later.

The separators 230 and 330 are formed by press-molding a material having gas impermeability and conductivity such as carbon. The separators 230 and 330 are provided with recesses on the sides facing the gas diffusion layers 220 and 320, respectively. An oxidant gas containing oxygen (O ₂ ) is supplied to a space (cathode flow path) 232 formed by the recess provided in the cathode separator 230 and the cathode diffusion layer 220. A fuel gas containing hydrogen (H ₂ ) is supplied to a space (anode channel) 332 formed by a recess provided in the anode separator 330 and the anode diffusion layer 320.

  The hydrogen molecules supplied to the anode flow path 332 pass through the anode diffusion layer 320 and reach the anode catalyst layer 310. In the anode catalyst layer 310, hydrogen molecules are dissociated into electrons and protons. Protons generated by the dissociation move to the cathode catalyst layer 210 through the electrolyte membrane 110. Electrons generated by the dissociation are supplied to an external conductor via the anode diffusion layer 320 and the anode separator 330. Power generation in the cell 100 is performed by moving electrons from the anode 300 to the cathode 200 through an external conductor as the protons move.

  The oxygen molecules supplied to the cathode channel 232 pass through the cathode diffusion layer 220 and reach the cathode catalyst layer 210. In the cathode catalyst layer 210, a fuel cell of oxygen molecules supplied through the cathode diffusion layer 220, protons supplied through the electrolyte membrane 110, and electrons supplied from an external conductor through the cathode separator 230 and the cathode diffusion layer 220. Water is produced by the reaction.

A2. Production of catalyst layer in this embodiment:
FIG. 2 is an explanatory diagram showing an outline of the manufacturing process of the catalyst layer. In the present embodiment, first, catalyst ink is prepared as shown in FIG. The catalyst ink is a liquid in which catalyst-carrying particles, a fibrous substance, and an electrolyte material are dispersed in a solvent containing water and a hydrophilic organic solvent. By carrying out the granulation treatment of the prepared catalyst ink, a powder (hereinafter referred to as “catalyst powder”) in which the catalyst-carrying particles, the fibrous substance, and the electrolyte material are granulated is obtained.

  FIG. 3 is an explanatory view schematically showing states of catalyst-supporting particles, fibrous substances, and electrolyte materials constituting the catalyst powder in the production process of the catalyst layer. In the catalyst powder production process, first, catalyst-carrying particles 610 in which a catalyst for a fuel cell reaction is carried on conductive particles, an electrolyte solution in which an electrolyte material 620 is dissolved in alcohol or the like (for example, a Nafion solution made by DuPont), water, Are mixed with an organic solvent. At this time, the ratio of the weight of the electrolyte material to the weight of the conductive particles is preferably 80 to 120% by weight.

  Any catalyst-supported particles may be used as long as the fuel cell reaction catalyst is supported on conductive particles. Catalysts for the fuel cell reaction include platinum group catalyst metals such as platinum, rhodium, iridium, ruthenium and palladium, base metal catalyst metals such as copper, nickel, cobalt, iron, manganese, chromium, molybdenum and vanadium, and these An alloy of these metals can be used. This catalyst is supported on conductive particles having a particle size of 10 to 50 nm. As the conductive particles carrying the catalyst, fine particles of carbon or various metals can be used. The amount of the catalyst supported on the conductive particles can be appropriately determined within the range of 40 to 80% by weight of the catalyst supported particles.

  As the organic solvent, any hydrophilic organic solvent such as methanol, ethanol, propanol and acetone can be used.

  The mixed liquid of the catalyst-carrying particles 610, the electrolyte solution, water, and the organic solvent is subjected to a dispersion treatment. By the dispersion treatment, a dispersion liquid in which the catalyst-carrying particles 610 and the electrolyte material 620 shown in FIG. 3A are dispersed in the solvent 600 is generated. The dispersion treatment may be any method in which the catalyst-carrying particles 610 and the electrolyte material 620 are dispersed in the solvent 600 by applying strong energy to the mixture, such as ultrasonic dispersion that applies ultrasonic vibration to the mixture. It can be done in any way. 3A shows a colloidal dispersion liquid in which the electrolyte material 620 is precipitated in the solvent 600, the non-colloidal state in which the electrolyte material is dissolved in the solvent by appropriately changing the composition of the solvent. It is also possible to use a dispersion.

  After generation of the dispersion, a fibrous material 630 is added to the dispersion to prepare a catalyst ink. Specifically, the catalyst ink is prepared by adding the fibrous material 630 while stirring the dispersion. By preparing the catalyst ink in this way, as shown in FIG. 3B, a catalyst ink in which the catalyst-carrying particles 610, the fibrous material 630, and the electrolyte material 620 are dispersed can be obtained. In this embodiment, the fibrous substance 620 is added to the dispersion liquid after the dispersion treatment. However, the catalyst-supporting particles 610, the fibrous substance 630, the electrolyte solution, water, and an organic solvent are mixed, and the dispersion treatment is performed. It is also possible to prepare a catalyst ink by application.

  The fibrous substance added to the dispersion may be any fibrous substance that does not dissolve in water or an organic solvent contained in the catalyst ink having a diameter of 10 to 300 nm and a length of 1 to 5 μm. In addition, it is more preferable that the diameter of the fibrous substance is approximately equal to the particle diameter of the conductive particles. As the fibrous material, for example, ceramic or metal whisker or fibrous carbon can be used, but those having conductivity are preferable.

  When the amount of the fibrous substance added is too large, the power generation characteristics of the fuel cell may be reduced due to an increase in concentration polarization caused by an increase in the thickness of the catalyst layer. The addition amount of the fibrous substance is appropriately determined in consideration of such characteristics. Specifically, the fibrous material is preferably added so that the ratio of the weight of the fibrous material to the weight of the conductive particles (fiber weight ratio) is in the range of 1 to 20% by weight. More preferably, the ratio is added in the range of 2 to 10% by weight.

  In addition, various things can be used for the fibrous carbon as a fibrous substance. As the fibrous carbon, vapor growth carbon fiber (for example, VGCF manufactured by Showa Denko), carbon nanotube, pitch-based carbon fiber, PAN-based carbon fiber, or the like can be used. In addition, those obtained by subjecting these fibrous carbons to surface modification treatment such as water repellent treatment can also be used.

  From the catalyst ink obtained by adding the fibrous substance, the solvent in the catalyst ink is removed by a spray dryer to produce catalyst powder. The spray drying conditions are determined in consideration of the composition of the catalyst ink so that the average particle diameter of the produced catalyst powder has a predetermined size in the range of 1 to 20 μm. In this embodiment, the catalyst powder is granulated from the catalyst ink using a spray dryer. However, the catalyst powder can be obtained by granulation by other methods. The catalyst powder can also be obtained by removing the solvent from the catalyst ink, for example, by vacuum freeze granulation. Further, catalyst powder can be obtained by directly granulating the catalyst-supporting particles, the fibrous substance, and the electrolyte material by dry preparation such as granulation using a mechanochemical effect. The catalyst powder is produced by removing the solvent from the catalyst ink because the distribution of the fibrous substance and the catalyst-carrying particles becomes uniform and the aggregation of the catalyst-carrying particles in the catalyst powder particles is suppressed. Is more preferable.

  As shown in FIG. 3C, the catalyst powder 612 generated from the catalyst ink to which the fibrous substance 630 has been added has substantially spherical particles in which the catalyst-carrying particles 610 are bound together by the electrolyte 620, and the catalyst-carrying particles 610. And the fibrous substance 630 are combined with the electrolyte 620. Projections formed by the fibrous material 630 are formed on the particles of the catalyst powder 612 in which the catalyst-carrying particles 610 and the fibrous material 630 are combined.

  When a catalyst layer is formed using the catalyst powder 612 thus obtained (FIG. 3C), as shown in FIG. 3D, the protrusion of the catalyst powder 612 is formed by the protrusions formed by the fibrous material 630. Aggregation of particles is suppressed. Therefore, the interval between the particles of the catalyst powder 612 is widened, and the pore volume of the catalyst layer is increased. In addition, the particles of the catalyst powder 612 constituting the catalyst layer are joined to each other by the fibrous substance 630. Therefore, the electrical conductivity of the catalyst layer can be improved by using a conductive material as the fibrous material.

  In the step of forming the catalyst layer from the catalyst powder, first, the catalyst powder is dispersed on the electrolyte membrane 110 as shown in FIG. The catalyst powder is sprayed onto the electrolyte membrane 110 by a general powder coating method such as an electrostatic spraying method or an electrostatic screen method. The electrostatic screen method is preferable to other powder coating methods because most of the catalyst powder used for spraying can be attached to the electrolyte membrane 110. By the dispersion of the catalyst powder, a first powder coating film 410 is formed on the electrolyte membrane 110.

  The first powder coating film 410 formed on the electrolyte membrane 110 is assumed so that the first powder coating film 410 does not peel from the electrolyte membrane 110 in a later step. For example, as shown in FIG. 2 (c), the assumed attachment is performed by heat compression using a flat press machine. The conditions such as heating temperature, compression pressure, and compression time at the time of heat compression are appropriately determined depending on the type of electrolyte, the particle size of the catalyst powder, and the like. In the hypothetical wearing shown in FIG. 2 (c), heat compression is performed by a flat press machine, but heat compression may be performed by using a roll press machine or the like. Further, depending on the type of electrolyte, it can be assumed by performing only heating and compression.

  Next, as shown in FIG. 2 (d), the electrolyte membrane 110 to which the first powder coating 410 is supposedly applied is turned upside down. On the inverted electrolyte membrane 110, a second powder coating 420 is formed by spraying catalyst powder in the same manner as the first powder coating 410. The electrolyte membrane 110 on which the second powder coating film 420 is formed is heated and compressed by a flat press machine together with the assumed first powder coating film 410, as shown in FIG. 2 (e). This is fixed. In the main fixing, the catalyst layers 412 and 422 are formed from the powder coating films 410 and 420 by making the heating temperature and the compression pressure higher than the assumed values, respectively. Note that, as in the hypothetical attachment, the main fixing can be performed by heat compression using a roll press or the like. In addition, depending on the type of electrolyte, the main fixing can be performed only by heating or compression.

  As shown in FIG. 1, the gas diffusion layers 220 and 320 and the separators 230 and 330 are stacked on the electrolyte membrane 110 having the catalyst layers 412 and 422 formed on both sides, and the fuel cell 100 is formed. Created.

  In this embodiment, as shown in FIG. 2, the catalyst layers 412 and 422 are formed by spraying the catalyst powder on the electrolyte membrane 110. However, the catalyst layer in contact with the electrolyte membrane is a powder of the catalyst powder. Any catalyst layer formed from a coating film may be used. For example, one of the catalyst layers sandwiching the electrolyte membrane can be formed by catalyst powder dispersed on the gas diffusion layer, and the other can be formed by catalyst powder dispersed on the electrolyte membrane. In this case, the hypothetical attachment is achieved by heat-compressing the gas diffusion layer, the catalyst powder coating on the gas diffusion layer, the electrolyte membrane, and the catalyst powder coating on the electrolyte membrane together and fixing the film. Can be omitted.

  In this embodiment, the catalyst layer formed of the catalyst powder is formed on both surfaces of the electrolyte membrane 110. However, the catalyst layer formed of the catalyst powder is formed on one surface of the electrolyte membrane, and the electrolyte membrane 110 The catalyst layer may be formed on the other surface by a different method. For example, a powder coating film is formed on one surface of the electrolyte membrane, and the catalyst layer formed on the substrate is brought into contact with the other surface of the electrolyte membrane 110, so that the substrate, the catalyst layer, the electrolyte membrane, and the powder coating are contacted. A catalyst layer can be formed on both surfaces of the electrolyte membrane by combining the membrane and heating and compressing.

B. Example:
[Example 1]
In Example 1, first, catalyst-supporting carbon in which 50% by weight of platinum was supported on carbon particles having an average particle diameter of about 20 nm, a Nafion solution, water, and ethanol were prepared. Then, a catalyst-supporting carbon, a Nafion solution, water, and ethanol were mixed, and dispersion treatment was performed using ultrasonic waves to prepare a dispersion. The dispersion was prepared so that the weight of the electrolyte in the Nafion solution was 0.5, the weight of water was 3, and the weight of ethanol was 3 with respect to 1 of the weight of the catalyst-supporting carbon. To this prepared dispersion, VGCF having a weight of 0.025 with respect to 1 of the catalyst-supporting carbon was added to prepare a catalyst ink having a fiber weight ratio of 5% by weight with respect to the carbon weight. Next, catalyst powder was granulated from the prepared catalyst ink by a spray dryer. The average particle size of the obtained catalyst powder was about 3 μm.

  Thus, the obtained catalyst powder was sprayed on the electrolyte membrane 110 (FIG. 2) by the electrostatic screen method, and the 1st powder coating film 410 (FIG. 2) was formed. The first powder coating film 410 was applied on the assumption of the first powder coating film 410 by a flat press machine. Assuming that the heating temperature is 100 ° C., the compression pressure is 10 kgf, and the compression time is 3 minutes.

  Next, the second powder coating 420 (see FIG. 5) is formed on the back surface of the electrolyte membrane 110 on the surface on which the first powder coating 410 is formed, by the electrostatic screen method in the same manner as the formation of the first powder coating 410. 2) was formed. After the formation of the second powder coating film 420, the powder coating films 410 and 420 on both surfaces of the electrolyte membrane 110 were permanently fixed by a flat press machine. The main fixing conditions were a heating temperature of 130 ° C., a compression pressure of 30 kgf, and a compression time of 3 minutes. As shown in FIG. 1, gas diffusion layers 220 and 320 and separators 230 and 330 were stacked on the electrolyte membrane 110 having the catalyst layers 412 and 422 formed on both surfaces, thereby forming the cell 100.

[Example 2]
Example 2 is different from Example 1 in that the weight of VGCF added to the dispersion is 0.05 with respect to the weight 1 of the catalyst-supporting carbon, and the fiber weight ratio with respect to the carbon weight of the catalyst ink is 10% by weight. Is different. Others are the same as the first embodiment.

[Example 3]
Example 3 is different from Example 1 in that the weight of VGCF added to the dispersion is 0.10 with respect to the weight 1 of the catalyst-supporting carbon, and the fiber weight ratio with respect to the carbon weight of the catalyst ink is 20% by weight. Is different. Others are the same as the first embodiment.

[Comparative example]
The comparative example differs from Example 1 in that no fibrous carbon was added. Others are the same as the first embodiment.

[Evaluation of catalyst layer structure]
FIG. 4 shows electron microscope images of the catalyst layers prepared in Comparative Example and Example 3. In the electron microscope image shown in FIG. 4, the shape of the catalyst powder used for forming the catalyst layer can be observed. As shown in FIG. 4A, in the catalyst powder obtained in the comparative example, the shape of the particles was almost spherical. On the other hand, in the catalyst powder obtained in Example 3, as shown in FIG. 4 (b), the particles having the protrusions indicated by the broken lines in FIG. 4 (b) and the substantially spherical particles were mixed. It was. As shown in FIG. 4B, in the catalyst layer of Example 3, it was observed that the particles of the catalyst powder were joined by protrusions formed by fibrous carbon.

[Evaluation of pore volume of catalyst layer]
FIG. 5 shows the evaluation results of the amount of pores of the catalyst layers prepared in the comparative example and Examples 1-3. The evaluation of the amount of pores was performed by a well-known mercury (Hg) press-fitting method (porosimetry). The porosity by this porosimetry is a parameter having a correlation with the pore volume, and the pore volume increases as the pore volume increases. As shown in FIG. 5, the amount of pores increased monotonously as the fiber weight ratio to carbon weight increased. The amount of pores in the catalyst layers of Examples 1 to 3 prepared using the catalyst ink added with fibrous carbon is the pores in the catalyst layer of the comparative example prepared using the catalyst ink not added with fibrous carbon. More than the amount.

[Evaluation of electrical conductivity of catalyst powder]
In order to evaluate the electrical conductivity of the obtained catalyst powder, pressure was applied to the catalyst powder and the conductivity was measured. The pressure applied to the catalyst powder was six points of 1.6, 3.2, 6.4, 12.7, and 25.5 MPa, and the conductivity at each pressure was measured.

  FIG. 6 shows the relationship between the pressure applied to the catalyst powder and the conductivity of the catalyst powders obtained in Examples 1 to 3 and the comparative example. The squares (□) in FIG. 6 indicate the relationship between the pressure applied to the catalyst powder obtained in Example 1 and the electrical conductivity. The triangles (Δ) in FIG. 6 indicate the relationship between the pressure applied to the catalyst powder obtained in Example 2 and the conductivity. Similarly, the circle (◯) in FIG. 6 shows the relationship between the pressure applied to the catalyst powder obtained in Example 3 and the electrical conductivity, and the diamond (◇) in FIG. 6 shows the catalyst obtained in the comparative example. The relationship between the pressure applied to the powder and the conductivity is shown.

  As shown in FIG. 6, the catalyst powders obtained in Examples 1 to 3 to which fibrous carbon was added applied the same pressure as the catalyst powders obtained in Comparative Examples to which fibrous carbon was not added. In this case, the conductivity was high. In addition, the conductivity increased as the amount of fibrous carbon added was increased.

[Evaluation of electric conductivity of catalyst layer]
Next, a catalyst layer was formed from the obtained catalyst powder, and the electrical conductivity of the catalyst layer was evaluated by an impedance spectrum method. The impedance spectrum method is a well-known electrical conductivity evaluation method that measures the frequency characteristics of complex impedance between a catalyst layer and an electrolyte solution that is in contact with the electrolyte layer provided in contact with the catalyst layer. For the electrical conductivity evaluation of the catalyst layer by the impedance spectrum method, Jia et al., “Modification of carbon supported catalysts to improve performance in gas diffusion electrodes” (Electrochimica Acta, 2001, Vol. 46, 2863-2869) Etc. are described.

  FIG. 7 shows the results of evaluating the electrical conductivity of the catalyst layers prepared in Comparative Example and Examples 1 and 3 by the impedance spectrum method. In the graph of FIG. 7 (referred to as “Cole-Cole plot”), of the measured complex impedance, the real part is drawn as the value on the horizontal axis, and the imaginary part is drawn as the value on the vertical axis. This Cole-Cole plot indicates that the conductivity by electron conduction is higher as the tangent slope in the high impedance region (upper right of the graph) is larger. Moreover, it has shown that the electrical conductivity by ionic conduction is so low that the value of the intersection of the tangent in a high impedance area | region and a horizontal axis is large.

The evaluation of the electrical conductivity of the catalyst layer was performed by supplying gases having different dew points to the catalyst layer. Specifically, humidified gases at different dew points (dp = 55, 70, 80 ° C.) were supplied to the catalyst layers of Examples 1 and 3 and the comparative example. Nitrogen (N ₂ ) was supplied to the cathode and hydrogen was supplied to the anode. Then, electrical conductivity was evaluated by an impedance spectrum method under each condition.

  The shapes of the Cole-Cole plot graphs under high humidification conditions in which a gas having a high dew point (d.p. = 70, 80 ° C.) was supplied are the comparative example (FIG. 7A) and Example 1 (FIG. There was no significant difference between b)) and Example 3 (FIG. 7C).

  Under the low humidification condition in which a gas having a low dew point (d.p. = 55 ° C.) was supplied, the shape of the graph of the comparative example (FIG. 7 (a)) is such that the high impedance region is the graph of Examples 1 and 3. The shape shifted to the right from the high impedance region. The intersection of the tangent and the horizontal axis in the high impedance region increased in the order of Example 3, Example 1, and Comparative Example. Thus, the electrical conductivity by ionic conduction under low humidification conditions was greatly improved by adding fibrous carbon to the catalyst ink for forming the catalyst layer. Moreover, the electrical conductivity by ionic conduction increased as the amount of fibrous carbon added increased.

  As described above, in Examples 1 and 3, ion conductivity under low humidification conditions was improved by adding fibrous carbon to the catalyst ink for forming the catalyst layer. This is presumably because the network structure of Nafion coated with fibrous carbon was developed by adding fibrous carbon to the catalyst ink.

[Evaluation of power generation characteristics]
FIG. 8 is an explanatory diagram showing an evaluation apparatus used for evaluating the power generation characteristics of the cell 100. The power generation characteristics of the cell 100 are evaluated by connecting a current-voltage characteristic measuring device 510 having a constant current load 512 and a voltmeter 514 between the cathode separator 230 and the anode separator 330 of the cell 100 via wirings 502 and 504. Made by connecting. In the evaluation of the power generation characteristics, the current flowing through the constant current load 512 was set to a predetermined value, and the voltage (cell voltage) between the separators 230 and 330 was measured using a voltmeter 514.

FIG. 9 shows the power generation characteristics of the cell 100 created in Example 1 and the comparative example. In the evaluation of power generation characteristics, the cell voltage at the output current density of the cell 100 at 8 points (0, 50, 100, 200, 400, 600, 800, 1000 mA / cm ² ) was measured. The squares (□) in FIG. 9 indicate the relationship between the output current density of the cell 100 created in Example 1 and the cell voltage. In addition, diamonds (形) in FIG. 9 indicate the relationship between the output current density and the cell voltage of the cell 100 created in the comparative example.

As shown in FIG. 9, the electromotive forces (cell voltages at a current density of 0 mA / cm ² ) of the cells 100 prepared in Example 1 and the comparative example were almost the same. On the other hand, in the state in which the cell 100 is outputting current, the cell voltage of the cell 100 created in Example 1 is higher than the cell voltage of the cell 100 created in the comparative example, and the power generation characteristics of the cell 100 are improved. did.

[Evaluation of gas diffusivity]
FIG. 10 shows the results of evaluating the gas diffusivity of the catalyst layers prepared in Comparative Example and Examples 1 and 3. The gas diffusivity is evaluated by supplying a mixed gas of oxygen and nitrogen having different oxygen concentrations (5%, 10%) to the cathode channel 232 of the evaluation apparatus shown in FIG. The relationship between the output current density of the cell 100 and the cell voltage (current-voltage characteristics) was evaluated.

  The graph of FIG. 10 shows the current-voltage characteristics of the cell 100 when a mixed gas of oxygen and nitrogen is supplied to the cathode channel 232. As shown in FIG. 10, the cell voltage decreases in a region where the current density is large. The current density at which the cell voltage obtained by extrapolating the current-voltage characteristic graph is 0 V is generally called the limiting current density. It is considered that the cell voltage becomes 0 V at the limit current density when the supply of gas (oxygen) is cut off. Therefore, it can be determined that the larger the limit current density value, the higher the gas diffusibility of the catalyst layer.

  As shown in FIG. 10, when the oxygen concentration was 5%, the limiting current densities of Example 1 and Example 3 were both larger than the limiting current density of the comparative example. Therefore, it can be judged that the catalyst layers prepared in Examples 1 and 3 are catalyst layers excellent in gas diffusibility.

[The invention's effect]
According to the present invention, a catalyst layer having a large pore volume can be generated from a catalyst powder obtained by granulating catalyst-carrying particles, a fibrous substance, and an electrolyte material. By using a catalyst layer having a large pore volume, gas diffusibility is increased and more three-phase interfaces are formed, so that power generation characteristics of the fuel cell can be improved. Further, by using a conductive fibrous substance as the fibrous substance, the particles of the catalyst powder are joined by the conductive fibrous substance, and the conductivity of the catalyst layer can be increased. By configuring the fuel cell using a catalyst layer having a high conductivity, the loss of the fuel cell can be reduced and the power generation characteristics of the fuel cell can be improved.

The cross-sectional schematic diagram which shows the structure of the cell 100 which comprises the fuel cell as one Embodiment of this invention. Explanatory drawing which shows the outline of the manufacturing process of a catalyst layer. Explanatory drawing which shows typically the state of the catalyst support particle | grains, fibrous substance, and electrolyte material which comprise catalyst powder in the manufacturing process of a catalyst layer. The electron microscope image of the catalyst layer produced in the comparative example and Example 3. FIG. The porosity amount evaluation result of the catalyst layer produced in the comparative example and Examples 1-3. The graph which shows the relationship between the pressure added to catalyst powder, and the electrical conductivity of catalyst powder. The electrical conductivity evaluation result of the catalyst layer created in the comparative example and Examples 1 and 3 by the impedance spectrum method. Explanatory drawing which shows the evaluation apparatus used for the electric power generation characteristic evaluation of the cell 100. FIG. The power generation characteristic evaluation result of the cell 100 created in Example 1 and the comparative example. The gas-diffusion evaluation result of the catalyst layer produced in the comparative example and Examples 1 and 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Cell 110 ... Electrolyte membrane 200 ... Cathode 210 ... Cathode catalyst layer 220 ... Cathode diffusion layer 230 ... Cathode separator 232 ... Cathode flow path 300 ... Anode 310 ... Anode catalyst layer 320 ... Anode diffusion layer 330 ... Anode separator 332 ... Anode flow Road 410, 420 ... Powder coating film 412, 422 ... Catalyst layer 502, 504 ... Wiring 510 ... Voltage characteristic measuring device 512 ... Constant current load 514 ... Voltmeter 600 ... Solvent 610 ... Catalyst supporting particle 620 ... Electrolyte material 630 ... Fiber Matter

Claims (7)

A method for producing a fuel cell electrode having a catalyst layer provided in contact with an electrolyte membrane,
(A) producing a catalyst powder by granulating catalyst-carrying particles carrying a catalyst for fuel cell reaction on conductive particles, a fibrous material, and an electrolyte material;
(B) forming a catalyst layer composed of the catalyst powder so as to be in contact with the electrolyte membrane;
A method comprising: The method of claim 1, comprising:
The step (a)
Preparing a catalyst ink containing the catalyst-carrying particles, the fibrous material, the electrolyte material, and a solvent;
Generating the catalyst powder by removing the solvent from the catalyst ink;
Including the method. The method according to claim 1 or 2, comprising:
The step (b) includes a step of spraying the catalyst powder on the electrolyte membrane. A method according to any one of claims 1 to 3,
The method wherein the ratio of the weight of the fibrous material to the weight of the conductive particles is in the range of 2 wt% to 10 wt%. A method according to any one of claims 1 to 4, comprising
The method wherein the ratio of the weight of the electrolyte material to the weight of the conductive particles is in the range of 80 wt% to 120 wt%. A method according to any of claims 1 to 5, comprising
The method wherein the fibrous material has electrical conductivity. The method of claim 6, comprising:
The method, wherein the conductive fibrous material is fibrous carbon.

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