JP4919005B2 - Method for producing electrode for fuel cell - Google Patents

Description

  The present invention relates to a method for manufacturing a fuel cell electrode using a catalyst ink, and more particularly to a method for manufacturing a fuel cell electrode with improved utilization efficiency of a catalyst metal.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually configured by laminating a plurality of single cells each having a basic structure of a membrane / electrode assembly (MEA) in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for the body.

In a solid polymer electrolyte fuel cell using hydrogen as a fuel and oxygen as an oxidant, the reaction of formula (1) proceeds at the anode (fuel electrode).
H ₂ → 2H ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the cathode (oxidant electrode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves in the solid polymer electrolyte membrane from the anode side to the cathode side by electroosmosis while being hydrated with water.
On the other hand, the reaction of the formula (2) proceeds at the cathode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)

  In order to promote the reaction of the above formula (1) or (2), each electrode (fuel electrode, oxidant electrode) is provided with a catalyst layer containing a catalyst metal. As the catalyst metal, platinum, a platinum alloy, or the like is awarded and is generally contained in the catalyst layer by being supported on a conductive material such as carbon particles. Platinum, which is used as a metal catalyst, is a very expensive material. Therefore, for practical use of fuel cells, it is desired to improve the utilization rate and to develop fuel cells that exhibit excellent power generation performance even with a small amount of use. .

In a solid polymer electrolyte fuel cell, the catalyst layer generally includes a catalyst ink obtained by dispersing carbon particles supporting a catalyst metal and an electrolyte resin in a suitable solvent, and then polymer electrolyte membrane or gas diffusion. It is formed by a method of applying to a support such as a gas diffusion sheet to be a layer, and drying and solidifying, thereby forming a matrix in which carbon particles (such as carbon black) supporting a catalyst metal and a polymer electrolyte are mixed. The electrode reaction of the above formulas (1) and (2) in the catalyst layer is performed at a three-phase interface that can exchange protons (H ⁺ ) and electrons (e ⁻ ) in addition to the reaction gas (fuel or oxidant). Progress actively. That is, the utilization rate of the catalyst metal can be improved by arranging more catalyst metal near the three-phase interface.

  As a method for producing a catalyst layer (electrode), for example, Patent Document 1 discloses a first step of stirring a solid material supporting a catalyst and a second step of mixing the solid material and a resin having hydrogen ion conductivity. The paste is prepared through the steps described above, and then the paste is applied to a conductive substrate to produce an electrode, and the electrode is adhered to both surfaces of the polymer electrolyte membrane to produce a unit cell. A method of manufacturing a fuel cell, wherein the shear rate of stirring in the first step is higher than the shear rate of mixing in the second step is disclosed.

  Patent Document 2 discloses that an average of particles dispersed in this mixed solution is obtained by stirring and mixing carbon black on which a catalyst metal is supported, a polymer electrolyte, and an organic solvent into fine particles. Stirring until the particle diameter reaches a predetermined value, and then adding a dispersant to the mixed solution and stirring and mixing to obtain a paste in which particles having a predetermined average particle diameter are uniformly dispersed A method for producing an electrode paste is disclosed. The manufacturing method of Patent Document 2 controls the average particle diameter of dispersed particles such as carbon black and the adsorption of the dispersant to the dispersed particles by adjusting the timing of adding the dispersant, while maintaining the storage stability. An electrode paste capable of forming a catalyst layer having a sufficient pore volume to obtain good power generation performance is to be manufactured.

JP 2003-59505 A Japanese Patent Laying-Open No. 2005-50726

  However, when a catalyst layer is formed using a catalyst ink prepared by a conventional method such as Patent Documents 1 and 2, the catalyst ink is prepared or applied to a support such as an electrolyte membrane and dried. At this time, the surface of the catalyst metal is covered with the polymer electrolyte (see FIG. 9). Thus, when the surface of the catalytic metal is covered with the polymer electrolyte, the supply of the reactive gas (fuel gas or oxidant gas) to the catalytic metal surface is delayed, and the reactive gas reaching the catalytic metal is reduced. As a result, the obtained fuel cell has a low utilization rate of the catalyst metal, and high power generation performance and cost reduction are difficult.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel cell electrode having a high utilization rate of a catalyst metal and excellent power generation performance.

The method for producing an electrode for a fuel cell of the present invention comprises a catalyst ink preparing step of preparing a catalyst ink by stirring and mixing conductive particles carrying a catalyst metal, a polymer electrolyte, and a solvent, and the catalyst ink on a support. A method for producing a fuel cell electrode comprising a catalyst ink coating / drying step for coating and drying on the surface of the catalyst metal in the catalyst ink preparation step or a step performed prior thereto. Adhering at least one adhesive substance selected from CO, SO ₂ , NO, NO ₂ , H ₂ S, and alcohols, which inhibits the adhesion of the polymer electrolyte;
After the catalyst ink coating / drying step, the formed catalyst layer is used as a working electrode, and a potential difference is generated between the electrode and the counter electrode, so that the adhesive substance attached to the surface of the catalyst metal is electrochemically applied. It is characterized by removing.

The method for producing an electrode for a fuel cell according to the present invention provides an adhesive substance that prevents the adhesion of a polymer electrolyte to the surface of the catalyst metal at an appropriate time when the coating of the catalyst metal surface with the polymer electrolyte can be suppressed. By adhering to and removing from the catalyst metal catalyst surface, the coating of the catalyst metal surface with the polymer electrolyte is suppressed. As a result, the amount of reaction gas that reaches the surface of the catalytic metal increases, and the utilization rate of the catalytic metal can be increased.
When the potential difference is 1.0 V or more, or 1.5 V or more, the adhesive substance can be more reliably removed.
In the present invention, it is preferable to apply a potential from the outside by a voltage applying means to generate the potential difference. This is because a desired potential can be applied and the adhesive substance can be more reliably removed.

The adhering substance easily attaches to the surface of the catalyst metal and can be removed intentionally, so that it is an inorganic compound having 3 or less atoms having an unshared electron pair, or the number of carbon atoms having an unshared electron pair. Is preferably a low molecular compound selected from 3 or less organic compounds (including formaldehyde).
Specifically, at least one low molecular compound selected from the group consisting of CO, SO ₂ , NO, NO ₂ , H ₂ S, and alcohols can be used as the adhesive substance.

In the catalyst ink preparation process, from the viewpoint of more reliably suppressing the polymer electrolyte from adhering to the surface of the catalyst metal, an adhesive substance is attached to the surface of the catalyst metal before the catalyst ink preparation process. It is preferable to carry out the process.
In addition, after the catalyst ink coating / drying step, a step of removing the adhering substance attached to the surface of the catalyst metal is performed to more effectively suppress the adhesion of the polymer electrolyte to the surface of the catalyst metal. be able to.

  According to the method for producing an electrode for a fuel cell of the present invention, a sufficient amount of reaction gas can be supplied to the catalytic metal surface by preventing the catalytic metal surface from being coated with the polymer electrolyte. Therefore, according to the method for producing a fuel cell electrode of the present invention, it is possible to provide a fuel cell electrode having a high utilization rate of the catalyst metal and excellent power generation performance.

  The method for producing an electrode for a fuel cell of the present invention comprises a catalyst ink preparing step of preparing a catalyst ink by stirring and mixing conductive particles carrying a catalyst metal, a polymer electrolyte, and a solvent, and the catalyst ink on a support. A method for producing a fuel cell electrode comprising a catalyst ink coating / drying step for coating and drying on the surface of the catalyst metal in the catalyst ink preparation step or a step performed prior thereto. In the step performed after the catalyst ink preparation step, the adhesive material adhered to the surface of the catalyst metal is removed in a step performed after the catalyst ink preparation step.

Here, the structural example of the single cell containing the electrode for fuel cells provided by the manufacturing method of this invention is demonstrated, referring a figure. FIG. 4 is a cross-sectional view schematically showing an embodiment (unit cell 100) of a unit cell including an electrode for a fuel cell.
The unit cell 100 includes a membrane / electrode assembly 5 in which a fuel electrode (anode) 4 a and an oxidant electrode (cathode) 4 b are provided on one surface side of the electrolyte membrane 1. The fuel electrode 4a is configured by laminating a fuel electrode side catalyst layer 2a and a fuel electrode side gas diffusion layer 3a in this order from the side closer to the electrolyte membrane 1. Similarly, the oxidant electrode 4b is formed by laminating the oxidant electrode side catalyst layer 2b and the oxidant electrode side gas diffusion layer 3b in this order from the side close to the electrolyte membrane 1. In this embodiment, each electrode (fuel electrode, oxidant electrode) has a structure in which a catalyst layer and a gas diffusion layer are laminated, but has a single-layer structure composed of only the catalyst layer. Alternatively, a structure in which a functional layer is provided in addition to the catalyst layer and the gas diffusion layer may be used.

  The membrane / electrode assembly 5 is sandwiched between two separators 6 a and 6 b to constitute a single cell 100. On one side of each separator 6a, 6b, grooves for forming a flow path of the reaction gas (fuel gas, oxidant gas) are provided, and fuel is formed between these grooves and the outer surfaces of the fuel electrode 4a and the oxidant electrode 4b. A gas flow path 7a and an oxidant gas flow path 7b are defined. The fuel gas channel 7a is a channel for supplying fuel gas (a gas containing hydrogen or generating hydrogen) to the fuel electrode 4a, and the oxidant gas channel 7b is oxidant gas to the oxidant electrode 4b. It is a flow path for supplying (a gas containing or generating oxygen).

  In the conventional method for producing an electrode for a fuel cell, in which a catalyst ink in which conductive particles supporting a catalyst metal, a polymer electrolyte, and a solvent are mixed with stirring is applied and dried, the process for preparing the catalyst ink, especially the catalyst ink, In the step of coating the catalyst film on a support such as an electrolyte membrane and drying, the polymer electrolyte adheres to the surface of the catalyst metal and coats the catalyst metal. When the polymer electrolyte coats the surface of the catalyst metal in this way, the reaction gas (fuel gas, oxidant gas) does not reach the catalyst metal sufficiently (see FIG. 9), which reduces the utilization rate of the catalyst metal. Invite.

  On the other hand, in the present invention, in the catalyst ink preparation step or a step performed prior thereto, an adhesive substance that prevents the adhesion of the polymer electrolyte is attached to the surface of the catalyst metal, and the catalyst ink preparation In the step or a step performed after the step, by removing the adhesive substance attached to the surface of the catalytic metal (see FIG. 1), the coating of the catalytic metal surface with the polymer electrolyte can be suppressed. . Therefore, the fuel cell electrode provided by the production method of the present invention has a larger surface area of the catalytic metal to which the reaction gas reaches compared to the fuel cell electrode produced by the conventional method (see FIG. 2). The utilization rate of catalytic metals is high. As a result, the amount of catalytic metal used can be reduced and the power generation performance of the fuel cell can be improved.

  Here, the adhering substance is a substance that can prevent the polymer electrolyte from adhering to the surface of the catalytic metal by adhering to the surface of the catalytic metal. Under the environmental conditions where the catalyst metal is exposed from the preparation process to the coating / drying process of the catalyst ink, it is hardly detached from the surface of the catalyst metal but can be intentionally removed.

  Regarding the “adhesiveness” of the adhesive substance, that is, the property that it hardly desorbs from the surface of the catalytic metal under the environmental conditions where the catalytic metal is exposed from the catalyst ink preparation process to the catalyst ink coating / drying process. For example, when the effective surface area A of a single catalyst metal to which no adhering substance is attached is 100%, the adhering substance before removing the adhering substance from the surface of the catalytic metal, preferably immediately before removing the adhering substance. It can be defined by the effective surface area B of the deposited catalytic metal. Specifically, the ratio (B / A × 100%) of the effective surface area B of the catalytic metal before removing the adhesive substance to the effective surface area A of the catalytic metal is 0 to 80%, particularly 10 to 60%. Further, 30 to 50% is preferable.

  At this time, the effective surface areas A and B of the catalyst metal can be determined according to a general CO adsorption method. That is, after leaving at 80 ° C. in a hydrogen gas atmosphere (hydrogen gas circulated at 0.03 ml / min) for 10 to 15 minutes, 80 ° C. in a CO atmosphere (CO gas circulated at 0.03 ml / min) for 10 to 10 minutes. Let stand for about 15 minutes to adsorb CO to Pt. At this time, CO adsorbs only on the Pt surface, and does not adsorb on the surface to which the adhesive substance has already adhered. Therefore, the CO outflow amount can be measured, and the CO adsorption amount by Pt can be calculated from the difference between the CO inflow amount and the CO outflow amount. Thus, by measuring the effective surface area before and after adhesion of the adhesive substance, the adhesion of the adhesive substance can be defined. When Pt is supported on carbon particles, CO is not adsorbed on the carbon particles as the carrier.

  Alternatively, “adhesiveness” of an adhesive substance is defined by the catalytic activity of the catalytic metal to which the adhesive substance is attached, when the catalytic activity of the catalyst metal to which the adhesive substance is not attached is 100%. You can also Specifically, it is preferable that the catalytic activity of the catalytic metal to which an adhesive substance is attached to the catalytic activity of the single catalytic metal is 0 to 80%, particularly 10 to 60%, and further 30 to 50%.

The catalytic activity of the catalytic metal with or without the adhering substance attached can be evaluated, for example, by the following method. That is, a catalyst dispersion liquid in which a catalytic metal with or without an adhesive substance is dispersed in a solvent such as water is cast on an electrode made of a conductive material such as a conductive carbon material such as glassy carbon. After drying, it can be evaluated using a tripolar electrochemical measuring device. Specifically, an oxygen gas is saturated in a 0.05 MH ₂ SO ₄ aqueous solution, an electrode coated with the catalyst dispersion is immersed in the solution, and the potential of the electrode is changed from 1.2 V to 0.4 V ( vs. RHE), oxygen reduction is performed, and evaluation can be made based on the obtained limiting current value. Ratio of the limit current value (I _LB ) of the electrode using the catalyst metal with the adherent substance to the limit current value (I _LA ) of the electrode using the catalyst metal support to which no adherent substance is attached [(I _LB / I _LA ) × 100] is preferably 0 to 80%, more preferably 10 to 60%, and further preferably 30 to 50%.

The specific adhesive substance is not particularly limited, and examples thereof include those generally known as toxic substances that poison catalyst metals. Among them, since it easily adheres to the surface of the catalytic metal and can be intentionally removed from the surface of the catalytic metal, the adhering substance includes an inorganic compound having 3 or less atoms having an unshared electron pair, or A low molecular compound selected from organic compounds having 3 or less carbon atoms having an unshared electron pair is preferable.
Examples of the inorganic compound having 3 or less atoms having an unshared electron pair include gas components such as CO, SO ₂ , NO, NO ₂ , and H ₂ S.

Examples of the organic compound having 3 or less carbon atoms having an unshared electron pair include organic compounds having a functional group such as a hydroxyl group or a formyl group. For example, alcohols such as methanol, ethanol, and propanol, formaldehyde Aldehydes such as acetaldehyde and propionaldehyde.
These adhesive substances may be used alone or in combination of two or more.

Since the adhesion of the polymer electrolyte to the catalyst metal surface is likely to occur particularly in the catalyst ink preparation process, the adhesion of the adhesive substance to the catalyst metal surface is performed in the catalyst ink preparation process or a process performed prior thereto. . Even if an adhesive substance is attached after the catalyst ink preparation process, the adhesion of the polymer electrolyte to the surface of the catalyst metal has already progressed, so that the coating of the catalyst metal surface with the polymer electrolyte cannot be sufficiently suppressed. It is.
The timing of attaching the adhesive substance to the catalyst metal surface may be during the catalyst ink preparation process (for example, FIGS. 1B and 1D) or before the catalyst ink preparation process (for example, FIGS. 1A and 1C). In order to more reliably prevent the polymer electrolyte from adhering to the surface of the catalyst metal, it is preferable to attach an adhesive substance to the surface of the catalyst metal before the step of preparing the catalyst ink (for example, FIG. 1A, FIG. 1C).

  In the case where an adhesive substance is attached to the catalyst metal before the catalyst ink preparation step, after the adhesive substance is previously attached to the surface of the catalyst metal, the catalyst metal may be supported on conductive particles such as carbon particles. Alternatively, after the catalyst metal is supported on the conductive particles, the adhesive substance may be attached to the surface of the catalyst metal. From the viewpoint of preventing the adhesive substance from peeling off in the step of supporting the catalyst metal on the conductive particles, it is preferable to support the catalyst metal on the conductive particles and then attach the adhesive substance to the catalyst metal.

Examples of the method of attaching the adhesive substance to the surface of the catalyst metal include a method of bringing the catalyst metal into contact with the adhesive substance. Specifically, when a gaseous substance is used as the adhesive substance, a gas that is an adhesive substance is sprayed on the catalyst metal surface, or when a liquid substance is used as the adhesive substance, Examples thereof include a method of spraying a liquid that is an adhesive substance and a method of immersing a catalytic metal in a solution containing the liquid. In the case of attaching a gaseous adhesive substance, a method of enclosing a catalytic metal in an airtight container capable of replacing the gas and supplying the adhesive substance gas is exemplified.
When adhering an adhesive substance to the catalyst metal during the catalyst ink preparation process, the conductive particles carrying the catalyst metal, the polymer electrolyte, and the solvent are stirred and mixed, and a gas as the adhesive substance is sprayed onto the mixture. Alternatively, a method of dispersing an adhesive substance in a solvent in the catalyst ink can be used.

  On the other hand, the removal of the adhering substance adhered to the catalyst metal surface is a catalyst ink preparation step from the viewpoint of at least suppressing the adhesion of the polymer electrolyte in the catalyst ink preparation step in which the polymer electrolyte is likely to adhere to the catalyst metal surface. This is performed in a later process. If the adhesive substance is removed during the catalyst ink preparation process, the adhesion of the polymer electrolyte to the catalyst metal surface cannot be sufficiently prevented.

  There is no particular limitation on the timing of removing the adhesive substance adhered to the catalyst metal surface as long as it is after the catalyst ink preparation step. However, since it is possible to prevent the adhesion of the polymer electrolyte in the coating / drying step of the catalyst ink in which the adhesion of the polymer electrolyte to the catalyst metal surface is likely to proceed together with the step of preparing the catalyst ink, It is preferable to be after the ink coating / drying step (for example, FIGS. 1A and 1B). The specific time after the coating / drying step of the catalyst ink is not particularly limited. For example, the catalyst ink may be formed in a state where a catalyst layer is formed on a support such as an electrolyte membrane, a gas diffusion layer sheet, or a transfer substrate. Further, these supports on which the catalyst layer is formed may be joined to other layers (gas diffusion layer sheet, electrolyte membrane, etc.) to form MEA. Further, it may be after a single cell is formed or after a plurality of single cells are stacked to form a stack.

The method for removing the adhering substance attached to the surface of the catalyst metal is not particularly limited, and examples thereof include an electrochemical method and a chemical method described below.
As an electrochemical method, for example, an electrode including a catalytic metal from which an adhesive substance is to be removed is used as a working electrode, an electrode provided on the opposite side of the electrolyte membrane is used as a counter electrode, hydrogen is used as a counter electrode, and nitrogen or oxygen is used as a working electrode. The adhesive substance adhering to the surface of the catalyst metal can be removed by flowing and generating a potential difference between the counter electrode and the working electrode. As for the potential difference between the counter electrode and the working electrode, a potential difference may be generated by using a voltage applying means in addition to using a potential due to an electrode reaction when hydrogen is supplied to the counter electrode and oxygen is supplied to the working electrode. At this time, the potential due to the electrode reaction may be used, and a voltage application unit may be used, or a potential difference may be generated between the counter electrode and the working electrode only by the voltage application unit. The potential difference between the counter electrode and the working electrode as described above is preferably applied for 1 minute or more, particularly 5 minutes or more. Usually, it is preferably about 5 to 10 minutes.
When nitrogen gas is allowed to flow to the counter electrode, the open circuit voltage is usually 0.2 V or less, so that a voltage applying means is required to obtain a potential necessary for removing the adhering substance, particularly 1.0 V or more. Thus, a potential is applied from the outside.

  When CO is attached as an adhering substance, the voltage between the counter electrode and the working electrode is set to 0.8 V or more, preferably 1.0 V or more, and particularly 1.2 V or more, so that CO on the surface of the catalytic metal is increased. Can be removed. At this time, in order to maintain the voltage between the counter electrode and the working electrode at about 0.8V to 1.2V, only the electrode reaction caused by supplying hydrogen to the counter electrode and oxygen to the working electrode without using the voltage applying means. It can also be used.

In the case where SO ₂ , H ₂ S, NO, or the like is adhered as an adhering substance, the voltage between the counter electrode and the working electrode is 1.2 V or more, preferably 1.5 V or more, so that the catalyst metal It is possible to remove these adhesive substances on the surface. At this time, in order to maintain the voltage between the counter electrode and the working electrode at 1.2 V or higher, it is usually necessary to use a voltage applying means.

As a chemical method, for example, an adhesive substance attached to the surface of the catalyst metal can be removed by heating a fuel cell electrode including the catalyst layer obtained by the above production method in an oxygen atmosphere. Here, under an oxygen atmosphere is an environment of 0.1 MPa or more containing 20 vol% or more of O ₂ and may be in the air, but the higher the oxygen concentration, the better. The heating temperature may be appropriately set in consideration of the heat resistance of the polymer electrolyte membrane to be used, the oxidation reactivity of the adhesive substance, the prevention of increase in the catalyst particle size, etc., but is usually 150 to 200 ° C. In particular, it is preferably 160 to 200 ° C, more preferably 180 to 200 ° C.
The heating in an oxygen atmosphere is usually performed for 10 to 60 minutes, preferably 30 to 60 minutes, particularly preferably about 45 to 60 minutes, although it depends on the heating temperature and the oxidation reactivity of the adhesive substance.

  As described above, according to the production method of the present invention, it is possible to prevent the catalytic metal from being coated with the polymer electrolyte by attaching and removing the adhesive substance on the catalytic metal surface at an appropriate time. For example, when Pt is used as a catalyst metal, a fuel cell electrode having a Pt effective surface area ratio determined by a CO adsorption method and cyclic voltammetry (CV) of 50% or more, and further 75% or more is provided. It is also possible.

  Here, the Pt effective surface area ratio is defined as 100% of the surface area A ′ (measured by a CO adsorption method) of Pt (single Pt / C in a state where no adhering substance is attached) in the Pt / C catalyst. This is the ratio [(S / A ′) × 100] of the surface area S (measured by CV) of Pt in the Pt / C catalyst in a state in which the catalyst layer is formed together with the electrolyte resin, and the general CO adsorption method and cyclic voltammetry It can be determined according to the surface area measurement by (CV).

  As a specific method for measuring the surface area A ′ of Pt (single Pt / C in a state where no adhering substance is adhered) in the Pt / C catalyst by the CO adsorption method, first, Pt / C alone is measured at 80 ° C. In a hydrogen gas atmosphere (circulate hydrogen gas at 0.03 ml / min), leave it for about 10 to 15 minutes. Then, at 80 ° C., it is allowed to stand for about 10 to 15 minutes in a CO atmosphere (CO gas is circulated at 0.03 ml / min) to adsorb CO to Pt. At this time, CO is adsorbed only on Pt and not adsorbed on C as a carrier. The CO outflow amount is measured, and the CO adsorption amount by Pt is calculated from the difference between the CO inflow amount and the CO outflow amount. The Pt effective surface area A ′ of the single Pt / C can be calculated from the obtained CO adsorption amount.

Moreover, as a measuring method of the surface area S of Pt in the Pt / C catalyst in a state where the catalyst layer is formed together with the electrolyte resin by CV, for example, the same amount of Pt / C as that when the surface area A ′ was obtained was used. When the CV curve as shown in FIG. 3 is obtained for the Pt / C catalyst in the catalyst layer forming state, the area S ′ of the oxidation current of 0.05 to 0.4 V (the amount of electricity: the hatched portion in FIG. 3) And the value (S ′ / E) obtained by dividing the area S ′ of the obtained oxidation current by the amount of electricity E (210 μC / cm ² ) of hydrogen desorption from Pt at 0.05 to 0.4 V. Becomes the Pt surface area S in the Pt / C catalyst in the catalyst layer formation state.

  In the present invention, the catalyst metal is not particularly limited as long as it has a catalytic action on the hydrogen oxidation reaction at the fuel electrode or the oxygen reduction reaction at the oxidant electrode. For example, platinum, ruthenium, iron And alloys of platinum and metals such as nickel and manganese. Among them, platinum, platinum-ruthenium alloy, and platinum-iron alloy having high catalytic activity are preferable. The catalyst metal contained in one electrode may be only one type, or may be a combination of two or more types such as a combination of platinum and a platinum alloy, or a combination of different types of platinum alloys.

  The conductive particles supporting the catalyst metal are not particularly limited in material and shape as long as they can support the catalyst metal and have conductivity, carbon materials such as carbon black and carbon nanotubes, and tungsten oxide And metal oxides such as titanium oxide. Among these, carbon particles are preferable, and carbon black is particularly preferable because it has a surface area capable of supporting many catalytic metals and good electronic conductivity. Examples of carbon black include ketjen black, furnace black, channel black, lamp black, thermal black, and acetylene black.

Examples of the method for supporting the catalyst metal on the conductive particles include the following methods. First, conductive particles such as carbon black are dispersed in water, and a necessary amount of a chloroplatinic acid aqueous solution is added thereto, followed by thorough stirring. Next, after adding a reducing agent such as NaBH ₄ , an oxidizing agent such as H ₂ O ₂ is added to remove excess NaBH ₄ to obtain Pt / C in which platinum is supported on carbon black. Can do. The method for supporting the catalyst metal on the conductive particles is not limited to the above method. A commercial product in which a catalytic metal is supported on conductive particles can also be used.

  As a polymer electrolyte, what is used as an electrolyte membrane of a general fuel cell can be used without particular limitation. For example, perfluorocarbon sulfonic acid such as Nafion (trade name, manufactured by DuPont). Examples thereof include fluorine-based electrolyte resins typified by resins and hydrocarbon-based polymer electrolytes.

  Here, the hydrocarbon-based polymer electrolyte resin typically does not contain any fluorine, but may be partially fluorine-substituted because the effects of the present invention can be sufficiently obtained. Specific examples of the hydrocarbon polymer electrolyte include engineering plastics such as polyether ether ketone, polyether ketone, polyether sulfone, polyphenylene sulfide, polyphenylene ether, and polyparaphenylene, and general-purpose plastics such as polyvinyl, polypropylene, and polystyrene. Incorporating proton conductive groups such as sulfonic acid group, carboxylic acid group, phosphoric acid group and boronic acid group into the base, and basic polymers such as polybenzimidazole, polypyrimidine and polybenzoxazole doped with strong acid And a composite electrolyte of a conductive polymer and a strong acid.

  As the solvent for the catalyst ink, any solvent can be used as long as it can prepare a catalyst ink in which a polymer electrolyte and conductive particles carrying a catalyst metal are dispersed. For example, methanol, ethanol, propanol, propylene glycol, Alcohols such as isopropanol, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, etc., or mixtures thereof A mixture with water or water can be used, but is not limited thereto. Of these, ethanol and water are preferably used because they do not poison the catalyst metal.

  In the catalyst ink preparation step, the above components are stirred in the catalyst ink preparation step in which the conductive particles carrying the catalyst metal with or without the adhering substance attached thereto, the polymer electrolyte, and the solvent are stirred and mixed. The mixing method is not particularly limited, and may be a method generally used when preparing a catalyst ink. For example, rotational stirring, homogenizer, ball mill, ultrasonic pulverization, mortar kneading and the like can be mentioned.

  The mixing ratio of each component of the catalyst ink is not particularly limited. For example, when the platinum-supporting carbon (Pt / C) is 1, the polymer electrolyte is 0.1 to 2.0 (weight ratio) and the solvent is 10 It is preferable to be about ˜30 (weight ratio).

  The catalyst ink thus obtained is coated on a support and dried to form a catalyst layer. Here, the support is an electrolyte membrane, an electrode substrate such as a gas diffusion layer sheet constituting the gas diffusion layer, a substrate film of a transfer film, or the like. That is, the catalyst ink is applied directly to the electrolyte membrane and dried, or directly applied to the gas diffusion layer sheet and dried, or is applied onto the substrate film to form a transfer film, and the electrolyte membrane. Alternatively, the catalyst layer can be formed by thermal transfer to a gas diffusion layer sheet. Examples of the base film for the transfer film include polytetrafluoroethylene (PTFE) and polypropylene.

  When the catalyst layer is formed by applying and drying catalyst ink on the electrolyte membrane, the electrolyte membrane on which the catalyst layer is formed and the gas diffusion layer sheet are overlapped with the catalyst layer sandwiched, and hot press or the like is performed. By joining, a membrane / electrode assembly can be formed. When a catalyst ink is applied to a gas diffusion layer sheet and dried to form a catalyst layer, the gas diffusion layer sheet on which the catalyst layer is formed and the electrolyte membrane are stacked so as to sandwich the catalyst layer, and hot A membrane / electrode assembly can be formed by bonding with a press or the like. In addition, when a transfer film is formed using a catalyst ink, the catalyst layer is transferred to the electrolyte membrane or the gas diffusion layer sheet, and the gas diffusion layer and the electrolyte membrane are overlapped and bonded so as to sandwich the catalyst layer. By this, a membrane / electrode assembly can be formed.

The method for applying the catalyst ink is not particularly limited, and general methods such as an inkjet method, a spray method, a doctor blade method, a gravure printing method, and a die coating method can be used. From the viewpoint of workability, the spray method is preferable.
The drying method of the catalyst ink is not particularly limited, and examples thereof include vacuum drying, heat drying, combined use of vacuum drying and heat drying. Usually, it is preferable to dry on the conditions of 50-150 degreeC and 0.1 atmosphere or less.
Although the film thickness of a catalyst layer is not specifically limited, What is necessary is just to be about 5-50 micrometers in a dry state. The catalyst layer may contain other materials such as a water-repellent polymer and a binder as required in addition to the conductive particles supporting the catalyst metal and the polymer electrolyte.

  As the electrolyte membrane, those used in general fuel cells can be used. For example, Nafion (trade name, manufactured by DuPont), Flemion (trade name, manufactured by Asahi Glass), Aciplex (trade name) Fluorine electrolyte resin membranes typified by perfluorocarbon sulfonic acid resins such as Asahi Kasei Co., Ltd.) and hydrocarbon polymers having proton conductive groups such as sulfonic acid groups, carboxylic acid groups, and boronic acid groups in the side chain Examples thereof include an electrolyte resin film such as an electrolyte film, and a composite electrolyte film of a basic polymer and a strong acid obtained by doping a basic polymer such as polybenzimidazole, polypyrimidine, and polybenzoxazole with a strong acid. The thickness of the electrolyte membrane is not particularly limited, but it may usually be about 5 to 500 μm.

  The gas diffusion layer has gas diffusibility, conductivity, and strength required as a material constituting the gas diffusion layer, for example, carbon paper, carbon cloth, carbon, which can efficiently supply gas to the catalyst layer. Carbonaceous porous body such as felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium, tantalum, iron, stainless steel, gold Further, it can be formed using a gas diffusion layer sheet made of a conductive porous material such as a metal mesh composed of a metal such as platinum or a metal porous material. The thickness of the conductive porous body is preferably about 50 to 300 μm.

  The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The water-repellent layer is not always necessary, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.

  The method for forming the water repellent layer on the conductive porous body is not particularly limited. For example, water repellent obtained by mixing conductive particles such as carbon particles, water repellent resin, and other components as necessary with an organic solvent such as ethanol, propanol, propylene glycol, water or a mixture thereof. The layer ink may be applied to at least the side of the conductive porous body facing the catalyst layer, and then dried and / or fired. Examples of the method for applying the water repellent layer ink to the conductive porous body include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.

  In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater, etc. You may process so that it may be discharged well.

  The membrane / electrode assembly provided with a pair of electrodes on the electrolyte membrane is further sandwiched between separators to form a single cell (see FIG. 4). As the separator, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with a resin, a metal separator using a metal material, or the like can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

Example 1
<Preparation of catalyst ink>
A commercially available Pt / C catalyst (Pt loading: 45 wt%) was treated at 80 ° C. under a hydrogen atmosphere (hydrogen gas 0.03 ml / min flow) for 10 minutes, and then at 80 ° C. under a CO atmosphere (CO gas was added). (Circulated at 0.03 ml / min) to allow CO to adhere to Pt.

  A catalyst ink was prepared by stirring and mixing 1 g of the Pt / C catalyst with CO attached thereto, 0.225 g of a hydrocarbon polymer electrolyte, and 30 g of a solvent (ethanol).

The catalyst ink was spray-coated on both surfaces of the hydrocarbon-based polymer electrolyte membrane. At this time, the catalyst ink was applied so that the amount of Pt per unit area of the catalyst layer was 0.5 mg / cm ² . The ink was dried (80 ° C., 0.1 atm or less) to form a catalyst layer.
The obtained electrolyte membrane with a catalyst layer was sandwiched between carbon diffusion layer gas diffusion layers and thermocompression bonded (press pressure: 1.0 MPa, press temperature: 120 ° C.) to obtain a membrane / electrode assembly. This membrane / electrode assembly was sandwiched between two separators (made of carbon) to produce a single cell.

Hydrogen was applied to one electrode of the obtained single cell as a counter electrode, and nitrogen was supplied to the other as a working electrode. A voltage was applied from the outside so that the working electrode voltage was 1.5 V with respect to the counter electrode, and 10 minutes. By holding, CO adhering to the Pt surface in the working electrode was removed. Next, the counter electrode and the working electrode were exchanged, and the same operation was performed to remove CO adhering to the Pt surface in the other electrode, and a single cell including the fuel cell electrode of Example 1 was obtained.
With respect to the electrode of Example 1, the Pt effective surface area ratio was calculated by the above-described CO adsorption method and CV, and was 78.2%. The CV result of the electrode of Example 1 is shown in FIG.

(Comparative Example 1)
In Example 1 above, a unit cell containing the fuel cell electrode of Comparative Example 1 was obtained in the same manner as in Example 1 except that CO deposition and CO removal on the Pt surface of commercially available Pt / C were not performed. It was.
With respect to the electrode of Comparative Example 1, the Pt effective surface area ratio was calculated by the above-described CO adsorption method and CV. As a result, it was 68.9%. The CV result of the electrode of Comparative Example 1 is shown in FIG.

(Power generation evaluation)
The cells obtained in Example 1 and Comparative Example 1 were evaluated for power generation under the following conditions, and the limiting current was measured. The results are shown in Table 1 together with the Pt effective surface area ratio.
<Power generation evaluation conditions>
・ Fuel (hydrogen gas) and oxidizer (air) flow rate: stoichiometric ratio 4.0 (1.0 A / cm ² hour)
・ Hydrogen gas humidification condition: RH100%
・ Air humidification condition: RH100%
Here, the stoichiometric ratio is an air-fuel ratio (so-called theoretical air-fuel ratio, air / hydrogen gas) when oxygen and hydrogen react without excess or deficiency.

  The cell of Example 1 provided with a CO adhesion / removal process so that the polymer electrolyte does not cover the Pt surface has a higher Pt effective surface area ratio and a larger limit current than the cell of Comparative Example 1. It was excellent in performance. Specifically, with respect to the Pt effective surface area ratio and limit current of Comparative Example 1, the Pt effective surface area ratio of Example 1 was about 113%, and the limit current of Example 1 was about 110%.

(Example 2)
<Preparation of catalyst ink>
In the same manner as in Example 1, 1 g of Pt / C catalyst with CO attached thereto, 0.45 g of fluorine-based polymer electrolyte (substance name: perfluorocarbon sulfonic acid) (trade name: Nafion, manufactured by Dupont), and solvent (ethanol) 30 g) was stirred and mixed with an ultrasonic homogenizer to prepare a catalyst ink.
The catalyst ink was spray-coated on both sides of a fluorine-based polymer electrolyte membrane (trade name Nafion, manufactured by Dupont). At this time, the catalyst ink was applied so that the amount of platinum per unit area of the catalyst layer was 0.5 mg / cm ² . The ink was dried (80 ° C., 0.1 atm or less) to form a catalyst layer.

The obtained electrolyte membrane with a catalyst layer was sandwiched between carbon diffusion layer gas diffusion layers and thermocompression bonded (press pressure: 1.0 MPa, press temperature: 120 ° C.) to obtain a membrane / electrode assembly.
The obtained membrane / electrode assembly was heated in an oxygen atmosphere [0.1 MPa (1 atm), 100 vol% O ₂ atmosphere] at 150 ° C. for 1 hour to remove CO adhering to the Pt surface of the Pt / C catalyst. did. Thereafter, the obtained membrane electrode assembly was sandwiched between two separators (made of carbon) to produce a single cell.
With respect to the electrode of Example 2, the Pt effective surface area ratio was calculated by the above-described CO adsorption method and CV. As a result, it was 35.1%. The CV result of the electrode of Example 2 is shown in FIG.

(Comparative Example 2)
In Example 2 above, a unit cell containing the fuel cell electrode of Comparative Example 2 was obtained in the same manner as Example 2 except that CO deposition and CO removal on the Pt surface of commercially available Pt / C were not performed. It was.
With respect to the electrode of Comparative Example 2, the Pt effective surface area ratio was calculated by the above-described CO adsorption method and CV. As a result, it was 28.8%. The CV result of the electrode of Comparative Example 2 is shown in FIG.

(Power generation evaluation)
For the cells obtained in Example 2 and Comparative Example 2, as in Example 1 and Comparative Example 1, power generation evaluation was performed and the limit current was measured. The results are shown in Table 2 together with the Pt effective surface area ratio.

  The cell of Example 2 provided with a CO adhesion / removal process so that the polymer electrolyte does not cover the Pt surface has a higher Pt effective surface area ratio and a larger limit current than the cell of Comparative Example 2. It was excellent in high voltage power generation performance. Specifically, with respect to the Pt effective surface area ratio and limit current of Comparative Example 2, the Pt effective surface area ratio of Example 2 was about 122%, and the limit current of Example 1 was about 105%.

  Further, from the comparison between Example 1 and Comparative Example 1 and the comparison between Example 2 and Comparative Example 2, in Example 2 and Comparative Example 2 using a fluorine-based polymer electrolyte, the limiting current of Example 2 was obtained. Was 105% of the limit current of Comparative Example 2, whereas in Example 1 and Comparative Example 1 using the hydrocarbon-based polymer electrolyte, the limit current of Example 1 was the limit current of Comparative Example 1. 110%.

It is a figure which shows the process example of the manufacturing method of the electrode for fuel cells which concerns on this invention. It is a figure which shows the state of the catalyst metal surface in the electrode obtained by the manufacturing method of the electrode for fuel cells which concerns on this invention. It is a figure explaining the calculation method of the Pt effective surface area of a catalyst layer state by CV method. It is a figure which shows one example of a single cell provided with the electrode for fuel cells obtained by this invention. It is a figure which shows the result of CV measurement of the electrode of Example 1. It is a figure which shows the result of the CV measurement of the electrode of the comparative example 1. It is a figure which shows the result of CV measurement of the electrode of Example 2. It is a figure which shows the result of the CV measurement of the electrode of the comparative example 2. It is a figure which shows the state of the catalyst metal surface in the electrode manufactured by the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Catalyst layer (2a: Fuel electrode side catalyst layer, 2b: Oxidant electrode side catalyst layer)
3. Gas diffusion layer (3a: fuel electrode side gas diffusion layer, 3b: oxidant electrode side gas diffusion layer)
4 ... Electrode (4a: fuel electrode, 4b: oxidant electrode)
5 ... Membrane / electrode assembly 6 ... Separator (6a: fuel electrode side separator, 6b: oxidant electrode side separator)
7 ... Reaction gas channel (7a: Fuel gas channel, 7b: Oxidant gas channel)
100 ... Single cell

Claims (5)

A catalyst ink preparation step for preparing a catalyst ink by stirring and mixing conductive particles carrying a catalyst metal, a polymer electrolyte, and a solvent; and a catalyst ink coating method in which the catalyst ink is applied on a support and dried. A method for producing a fuel cell electrode comprising a drying step,
In the catalyst ink preparation step or a step performed prior thereto, the catalyst metal surface is selected from CO, SO ₂ , NO, NO ₂ , H ₂ S, and alcohols that prevent the polymer electrolyte from adhering to the surface of the catalyst metal. Attaching at least one adhesive substance,
After the catalyst ink coating / drying step, the formed catalyst layer is used as a working electrode, and a potential difference is generated between the electrode and the counter electrode, so that the adhesive substance attached to the surface of the catalyst metal is electrochemically applied. A method for producing an electrode for a fuel cell, characterized in that it is removed. The method for producing a fuel cell electrode according to claim 1, wherein the potential difference is 1.0 V or more. The method for producing a fuel cell electrode according to claim 1, wherein the potential difference is 1.5 V or more. The method for producing an electrode for a fuel cell according to any one of claims 1 to 3, wherein a potential is applied from the outside by a voltage applying means to generate the potential difference. 5. The method for producing an electrode for a fuel cell according to claim 1 , wherein a step of attaching an adhesive substance to the surface of the catalyst metal is performed before the step of preparing the catalyst ink.

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