WO2018069979A1

WO2018069979A1 - Catalyst layer production method, catalyst layer, catalyst precursor, and catalyst precursor production method

Info

Publication number: WO2018069979A1
Application number: PCT/JP2016/080147
Authority: WO
Inventors: 大間　敦史; 一樹在原; 佳久古谷; 高橋　真一; 吉田　雅夫; 江藤　正和
Original assignee: 日産自動車株式会社
Priority date: 2016-10-11
Filing date: 2016-10-11
Publication date: 2018-04-19

Abstract

The present invention provides a means for suppressing direct contact between a catalyst and an electrolyte. This catalyst layer production method comprises: preparing a catalyst precursor 1 obtained by having a platinum-containing catalyst metal supported on a conductive carrier; preparing a catalyst precursor 2 by cladding the catalyst precursor 1 with an inorganic material that adheres to the platinum-containing catalyst metal; forming a catalyst precursor layer by mixing the catalyst precursor 2 with an electrolyte; and further removing the inorganic material from the catalyst precursor layer.

Description

Method for producing catalyst layer, catalyst layer, catalyst precursor, and method for producing catalyst precursor

The present invention relates to a method for producing a catalyst layer, a catalyst layer, a catalyst precursor, and a method for producing the catalyst precursor.

A solid polymer fuel cell using a proton conductive solid polymer membrane operates at a lower temperature than other types of fuel cells such as a solid oxide fuel cell and a molten carbonate fuel cell. For this reason, the polymer electrolyte fuel cell is expected as a stationary power source or a power source for a moving body such as an automobile, and its practical use has been started.

In order to reduce the cost of fuel cell vehicles (FCV), it is necessary to simplify the FC system and stack (reduction in the number of parts / materials) and further reduce the cost of parts / materials. Particularly for the latter, reducing the amount of noble metal used such as platinum used in the FC stack has a very large impact. This is because the amount of precious metals cannot be expected to reduce costs by mass production even during the full-scale diffusion of FCV. Therefore, development of electrode catalyst materials and catalyst layers for reducing the amount of precious metal used per FCV is required.

For the purpose of solving the above problems, for example, Patent Document 1 discloses a catalyst layer in which direct contact between a catalyst and a solid proton conductive material (electrolyte) is suppressed.

International Publication No.2012-053638

According to the membrane electrode assembly (MEA) and the fuel cell having the catalyst layer described in Patent Document 1, the utilization efficiency of the catalyst is improved, and the amount of the catalyst used can be reduced while maintaining the power generation performance. On the other hand, Patent Document 1 requires the use of a conductive carrier having a hole for arranging a catalyst.

From the viewpoint of improving the performance of FCV, it may be preferable to use a conductive support having no or few such pores. In such a case, the above-mentioned Patent Document 1 may not always be suitably used. . For this reason, there is a need for means for suppressing direct contact between the catalyst and the electrolyte regardless of the form and properties of the constituent members of the catalyst layer, such as the presence or absence of pores in the conductive carrier.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide means for suppressing direct contact between a catalyst and an electrolyte.

The present inventors have conducted intensive research to solve the above problems. As a result, the catalyst metal previously coated with an inorganic substance having catalytic metal adsorptivity was mixed with an electrolyte to form a catalyst layer, and then the removal of the inorganic substance was found to be an effective means, and the present invention was completed. .

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell containing the catalyst layer which concerns on one Embodiment of this invention. The power generation test evaluation results (IV curve) under wet conditions of MEA 1 to 3 obtained in Example 4 and Comparative Examples 3 to 4 are shown. The power generation test evaluation results (IV curve) under the dry conditions of MEA 1 to 3 obtained in Example 4 and Comparative Examples 3 to 4 are shown.

The method for producing a catalyst layer of the present invention includes the following steps (a) to (d) (first embodiment):
(A) preparing a catalyst precursor 1 in which a platinum-containing catalyst metal is supported on a conductive carrier (step (a));
(B) The catalyst precursor 1 is coated with an inorganic substance adsorbed on a platinum-containing catalyst metal to prepare a catalyst precursor 2 (step (b));
(C) The catalyst precursor 2 is mixed with an electrolyte to form a catalyst precursor layer (step (c)); and (d) the inorganic substance is removed from the catalyst precursor layer (step (d)). According to the said structure, the direct contact with a catalyst and electrolyte can be suppressed irrespective of the form and property of the structural member of a catalyst layer. Therefore, a membrane electrode assembly and a fuel cell excellent in power generation performance can be provided.

In this specification, the catalyst precursor 1 obtained by supporting a platinum-containing catalyst metal on a conductive support is also simply referred to as “catalyst precursor 1 according to the present invention” or “catalyst precursor 1”. The inorganic substance adsorbed on the platinum-containing catalyst metal is also simply referred to as “inorganic substance according to the present invention” or “inorganic substance”. Further, the platinum-containing catalyst metal is also simply referred to as “catalyst metal according to the present invention” or “catalyst metal”.

So far, electrocatalytic materials have been in competition not only in Japan but also at the world level. For example, in Japan, a polymer electrolyte fuel cell commercialization development project (up to FY2014) led by NEDO, a core-shell catalyst with palladium as the core and platinum as the shell, and a platinum skin layer on the surface of the platinum-cobalt alloy A PtCo skin catalyst is being developed. These catalysts have high activity and durability compared to conventional platinum catalysts in the evaluation of a single electrode catalyst. In addition, in the FC project led by the US Department of Energy (DOE), highly active electrocatalyst materials such as nano-frame catalysts made from platinum nickel have been developed. These single unit evaluations are mainly based on evaluation results in a half cell such as a rotating disk electrode (RDE) method. However, the evaluation with an actual MEA has a problem that the activity and durability are generally lower than that of a half cell.

The causes of the above problems are broadly divided into differences in operating conditions (temperature, humidity, etc.) between MEA and half-cell, and differences due to things such as electrode catalyst materials and catalyst layer structural changes. Has been implemented. Under such circumstances, as a result of intensive studies, the present inventors have, as one of the causes caused by things, an electrolyte (ionomer) contained in the catalyst layer coats a catalyst metal such as platinum particles. It has been discovered that the ratio is an important factor governing the activity as a catalyst layer. That is, it has been found that the apparent oxygen reduction (ORR) activity decreases as the ionomer catalytic metal coverage increases. This is because the ionomer has a poisoning effect on the catalytic metal, and since the interaction between the ionomer and the catalytic metal is strong, the chance that the oxygen molecule as the ORR reactant is adsorbed on the catalytic metal surface decreases. As a result, the apparent ORR activity is lowered. The influence of this phenomenon on the ORR activity can be confirmed by evaluating the ORR area specific activity (A / cm ² —Pt) (see Non-Patent Document 1 above). Here, the ORR area specific activity is the ORR activation dominant current per unit mass of platinum (for example, a current value at 0.9 V), that is, the ORR mass specific activity (A / g_Pt) is expressed as the electrochemical per unit mass of platinum. It is a value divided by the effective surface area (m ² / g_Pt). Moreover, it has been found that this phenomenon can be observed not only by MEA but also by RDE based on recent research results (see Non-Patent Document 2 above).

From the above, the present inventors considered that when an electrode catalyst was mixed with an electrolyte to form a catalyst layer, the electrolyte caused a poisoning action on the catalyst metal and reduced the catalytic activity. That is, it was considered that the apparent ORR activity (ORR specific activity) was improved as the coverage of the catalyst metal by the electrolyte was lower. Here, “poisoning action” means that the interaction between the electrolyte and the catalyst metal is strong, so that the opportunity for the reaction gas (especially oxygen) to contact the surface of the catalyst metal is reduced. Based on the above findings, the present inventors have intensively studied a means for reducing the coverage of the catalyst metal by the electrolyte, that is, a means for reducing the poisoning effect received by the catalyst metal. As a result, a catalyst (catalyst precursor 2) previously coated with an inorganic material that exhibits adsorptivity to the platinum-containing catalyst metal is mixed with an electrolyte to form a layer (catalyst precursor layer), and then the inorganic material is removed from the layer. We found that the measures are effective. According to this method, in the catalyst precursor layer, the catalyst precursor 2 (particularly a catalyst metal) in a state of being coated with an inorganic substance is mixed with the electrolyte. For this reason, an inorganic substance intervenes between the catalyst precursor 2 (particularly the catalyst metal) and the electrolyte. Next, when the inorganic substance is removed from the catalyst precursor layer in this state, the electrolyte in contact with the inorganic substance (that is, covering the catalyst precursor 2) is removed together with the inorganic substance. For this reason, in the obtained catalyst layer, the catalyst metal is not coated or hardly coated with the electrolyte, and is in a state of being directly exposed on the conductive support or in a state of being covered with water. Thus, the catalytic metal that is not in contact with the electrolyte is less likely to receive the poisoning action of the electrolyte. Therefore, the opportunity for the reactive gas (especially oxygen) to come into contact with the catalytic metal surface is increased, and the formation of the three-phase interface of the reactive gas (especially oxygen), catalytic metal particles and water is promoted, and the catalytic activity (especially ORR specific activity) Will improve. Therefore, according to the above method, a catalyst layer exhibiting high catalytic activity (particularly oxygen reduction reaction (ORR) specific activity) can be obtained. Further, in the method of the present invention, since the catalyst (catalyst precursor 1) is previously coated with an inorganic substance, the structure of the catalyst (catalyst precursor 1) such as the presence or absence of pores of the conductive support and the shape of the catalyst metal, the electrolyte The type is not limited. Therefore, the method of the present invention can be applied to various forms of catalysts (conductive supports and catalytic metals) and electrolytes. In addition, the said mechanism is estimation and the technical scope of this invention is not restrict | limited by the said estimation.

Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited only to the following embodiment. Further, in this specification, “X to Y” indicating a range includes X and Y, and means “X or more and Y or less”. Unless otherwise specified, measurements such as operation and physical properties are performed under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50% RH.

[Step (a)]
In this step, a catalyst precursor 1 obtained by supporting a platinum-containing catalyst metal on a conductive support is prepared.

Here, the conductive carrier functions as a carrier for supporting a catalyst metal, which will be described later, and an electron conduction path involved in the transfer of electrons between the catalyst particles and other members. The conductive support only needs to have a specific surface area for supporting the catalyst metal in a desired dispersed state, and may be either a carbon support or a non-carbon support. Here, the “carbon carrier” refers to a carrier containing a carbon atom as a main component. “Containing carbon atoms as a main component” is a concept including both “consisting only of carbon atoms” and “substantially consisting of carbon atoms”, and may contain elements other than carbon atoms. “Substantially consists of carbon atoms” means that 2 to 3% by weight or less of impurities can be mixed. The non-carbon carrier refers to a material not corresponding to the definition of the above carbon carrier, and examples thereof include metal oxides.

Specific examples of the carbon support include acetylene black, ketjen black, thermal black, oil furnace black, channel black, lamp black, graphitized carbon, and the like. More specifically, Vulcan (registered trademark) XC-72R, Vulcan (registered trademark) P, Black Pearls (registered trademark) 880, Black Pearls (registered trademark) 1100, Black Pearls (registered trademark) 1300, Black Pearls (registered) Trademark) 2000, Regal (registered trademark) 400 (above, manufactured by Cabot Japan Co., Ltd.), Ketjen Black (registered trademark) EC300J, Ketjen Black (registered trademark) EC600JD (above, manufactured by Lion Specialty Chemicals Co., Ltd.), # 3150, # 3250 (made by Mitsubishi Chemical Corporation), Denka Black (registered trademark) (made by Denka Corporation), and the like.

The shape of the conductive carrier can have an arbitrary shape such as a particle shape, a plate shape, a column shape, a tubular shape, or an indefinite shape.

The size of the conductive carrier is not particularly limited. From the viewpoint of controlling the ease of loading, the catalyst utilization rate, and the thickness of the electrode catalyst layer within an appropriate range, the average diameter of the conductive support is preferably 100 to 2000 nm, and preferably 200 to 1000 nm. More preferably, it is 300 to 500 nm. When primary particles are connected or aggregated to form a conductive carrier, the average primary particle diameter is preferably 5 to 30 nm, and more preferably 10 to 20 nm. As the average primary particle diameter, a value measured by SEM or TEM is adopted. The “average diameter of the conductive carrier” is the crystallite diameter determined from the half-value width of the diffraction peak of the conductive carrier in X-ray diffraction (XRD), or the particle diameter of the conductive carrier examined by a transmission electron microscope (TEM). It can be measured as an average value of. In the present specification, the “average diameter of the conductive carrier” means the maximum diameter of the conductive carrier, which is examined from a transmission electron microscope image of a statistically significant number (for example, at least 200, preferably at least 300) of samples. Is the average value.

The BET specific surface area of the conductive support may be a specific surface area sufficient to carry the catalyst metal and the spacer in a highly dispersed manner, but is preferably 10 to 5000 m ² / g, more preferably 50 to 2000 m ² / g. Even more preferably, it is 100 to 1000 m ² / g, and particularly preferably 300 to 800 m ² / g. With such a specific surface area, a sufficient catalytic metal can be supported on the conductive support, and high catalytic activity can be exhibited.

The “BET specific surface area (m ² / g carrier)” of the carrier is measured by a nitrogen adsorption method. Specifically, about 0.04 to 0.07 g of catalyst powder is precisely weighed and sealed in a sample tube. This sample tube is preliminarily dried at 90 ° C. for several hours in a vacuum dryer to obtain a measurement sample. For weighing, an electronic balance (AW220) manufactured by Shimadzu Corporation is used. In the case of a coated sheet, a net weight of about 0.03 to 0.04 g of the coated layer obtained by subtracting the Teflon (registered trademark) (base material) weight of the same area from the total weight of the coated sheet is used as the sample weight. . Next, the BET specific surface area is measured under the following measurement conditions. On the adsorption side of the adsorption / desorption isotherm, a BET specific surface area is calculated from the slope and intercept by creating a BET plot from a relative pressure (P / P ₀ ) range of about 0.00 to 0.45.

Also, the platinum-containing catalyst metal (catalyst metal) has a function of catalyzing an electrochemical reaction. The catalytic metal includes at least platinum. For this reason, catalytic activity, poisoning resistance to carbon monoxide, heat resistance, etc. can be improved. That is, the catalytic metal is platinum or contains a metal component other than platinum and platinum.

The metal component other than platinum is not particularly limited and can be used in the same manner as a known catalyst component. Specifically, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, Examples thereof include metals such as cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and zinc. One or more metal components other than platinum may be used. Especially, it is preferable that it is a transition metal from a viewpoint of catalyst performance. Here, the transition metal atom refers to a Group 3 element to a Group 12 element, and the type of the transition metal atom is not particularly limited. From the viewpoint of catalytic activity, the transition metal atom is preferably selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, copper, zinc and zirconium.

The composition of the alloy depends on the type of metal to be alloyed. For example, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal alloyed with platinum is preferably 10 to 70 atomic%. . In general, an alloy is a general term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be sufficient.

The shape of the catalyst metal is not particularly limited, and may be spherical (including particles, powders, granules), plates, needles, columns, squares, polyhedrons, and the like. Preferably, the catalytic metal is spherical.

The size of the catalyst metal is not particularly limited. For example, the average particle diameter of the catalyst metal is preferably 1 nm to 30 nm, more preferably 2 nm to 10 nm, and even more preferably 3 nm to 5 nm. If it is such a range, melt | dissolution and aggregation of a catalyst metal can be suppressed, raising the activity per unit weight (weight specific activity) of a catalyst metal. In the present specification, the “average particle diameter of the catalyst metal” represents the maximum diameter of the catalyst metal. The above-mentioned “average particle diameter” is an average value of particle diameters of particles observed in several to several tens of fields using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The

The supported amount (support rate) of the catalyst metal is not particularly limited, but is preferably 2 to 60% by weight when the weight of the catalyst precursor 1 (total weight of the conductive support and the catalyst metal) is 100% by weight. . By setting it as such a range, since aggregation of catalyst metals is suppressed and the increase in the thickness of an electrode catalyst layer can be suppressed, it is preferable. More preferably, it is 5 to 50 weight%. If it is in such a range, the balance between the dispersibility of the catalytic metal on the conductive support and the catalytic activity can be appropriately controlled. The amount of catalyst metal supported can be examined by a conventionally known method such as inductively coupled plasma emission spectrometry (ICP-atomic emission spectroscopy), inductively coupled plasma mass spectrometry (ICP mass-spectrometry), or fluorescent X-ray analysis (XRF). .

The method for producing the catalyst precursor 1 (a method for supporting the catalyst metal on the conductive support) is not particularly limited, and a conventionally known method can be used. For example, methods such as a liquid phase reduction method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used.

Examples of the liquid phase reduction method include a method in which a catalytic metal is deposited on the surface of a conductive support and then heat treatment is performed. Specifically, for example, a method in which a conductive support is immersed in a catalyst metal precursor solution for reduction and then heat treatment is performed.

Here, the catalyst metal precursor is not particularly limited and is appropriately selected depending on the type of catalyst metal used. Specific examples include chlorides, nitrates, sulfates, chlorides, acetates, and amine compounds of the catalyst metals such as platinum. More specifically, platinum chloride (hexachloroplatinic acid hexahydrate), palladium chloride, rhodium chloride, ruthenium chloride, cobalt chloride and other nitrates, palladium nitrate, rhodium nitrate, iridium nitrate and other nitrates, palladium sulfate, sulfuric acid Preferred examples include sulfates such as rhodium, acetates such as rhodium acetate, and ammine compounds such as dinitrodiammineplatinum nitrate and dinitrodiammine palladium. Moreover, the solvent used for preparation of a catalyst metal precursor solution will not be restrict | limited especially if a catalyst metal precursor can be melt | dissolved, According to the kind of catalyst metal precursor used, it selects suitably. Specifically, water, an acid, an alkali, an organic solvent, etc. are mentioned. The concentration of the catalyst metal precursor in the catalyst metal precursor solution is not particularly limited, but is preferably 0.1 wt% or more and 50 wt% or less, more preferably 0.5 wt% or more and 20 wt% in terms of metal. % Or less.

Examples of the reducing agent include hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like. . Note that a gaseous substance at room temperature such as hydrogen can be supplied by bubbling. The amount of the reducing agent is not particularly limited as long as it can reduce the catalyst metal precursor to the catalyst metal, and a known amount can be similarly applied.

The deposition conditions are not particularly limited as long as the catalyst metal can be deposited on the conductive support. For example, the precipitation temperature is preferably around the boiling point of the solvent (solvent boiling point ± 10 ° C., more preferably solvent boiling point ± 5 ° C.), more preferably from room temperature to 100 ° C. The deposition time is preferably 1 to 10 hours, more preferably 2 to 8 hours. In addition, you may perform the said precipitation process, stirring and mixing if necessary. As a result, the catalytic metal precursor is reduced, and catalytic metal is generated on the conductive support.

As the heat treatment conditions, for example, the heat treatment temperature is preferably 300 to 1200 ° C., more preferably 500 to 1150 ° C., and still more preferably 700 to 1000 ° C. The heat treatment time is preferably 0.02 to 3 hours, more preferably 0.1 to 2 hours, and even more preferably 0.2 to 1.5 hours. From the viewpoint of the effect of promoting the reduction of the catalytic metal precursor, the heat treatment step is preferably performed in an atmosphere containing hydrogen gas, more preferably in a hydrogen atmosphere.

Alternatively, the catalyst precursor 1 may be manufactured by preparing a catalyst metal in advance and then supporting it on a conductive carrier. In the case of this method, a highly active catalytic metal having a special form can be supported on a conductive support while maintaining its activity.

Alternatively, a commercially available catalyst precursor 1 may be used. Specifically, a platinum catalyst manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. (for example, TEC10E40E, TEC10E50E, TEC10E50E-HT, TEC10E60TPM, TEC10E70TPM, TEC10V40E, TEC10V40E, TEC10V50E, etc.), platinum / ruthenium catalyst manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. TEC66E50, TEC61E54, TEC62E58), a platinum catalyst manufactured by Johnson Massey (for example, HiSPEC series), a platinum catalyst manufactured by Ishifuku Metal Industry Co., Ltd., and the like.

[Step (b)]
In this step, the catalyst precursor 1 prepared in the step (a) is coated with an inorganic substance adsorbed on the platinum-containing catalyst metal to prepare the catalyst precursor 2. By this step, the catalyst precursor 1, particularly the catalyst metal 2, in which the catalyst metal is coated with an inorganic substance, is obtained.

The inorganic substance is not particularly limited as long as it has an adsorptivity to the metal constituting the catalyst metal, but an inorganic substance that selectively adsorbs to the metal (particularly platinum) constituting the catalyst metal is preferable. Considering the high selective adsorption property to the metal (especially platinum) constituting the catalyst metal, specifically, the inorganic substance is not particularly limited to the following, but is carbon monoxide; iodine (including ionic form), iodide Iodine compounds such as metal iodides such as lithium, sodium iodide, potassium iodide and cesium iodide; and bromine such as bromides (including ionic forms), metal bromides such as sodium bromide, potassium bromide and cesium bromide Compound etc. are mentioned. Here, the inorganic substance may be used alone or in the form of a mixture of two or more. Among these, it is preferable that an inorganic substance is an iodine compound, a bromine compound, and carbon monoxide. That is, according to a preferred embodiment of the present invention, the inorganic substance is at least one selected from the group consisting of iodine compounds, bromine compounds, and carbon monoxide. More preferably, the inorganic substance is at least one selected from the group consisting of iodine compounds and bromine compounds. Particularly preferably, the inorganic substance is at least one selected from the group consisting of iodine (including iodine ions) and bromine (including bromine ions). Since such an inorganic substance can be specifically chemically adsorbed to the catalyst metal (particularly platinum), it can be strongly adsorbed to the catalyst metal due to the influence of the charge interaction. Therefore, in the next step (c), when the catalyst precursor 2 is mixed with the electrolyte, the inorganic substance is more efficiently interposed between the catalyst metal and the electrolyte. For this reason, the catalyst metal (especially ORR specific activity) can be more effectively improved by more effectively reducing the coating of the catalyst metal with the electrolyte by the following step (d).

In this embodiment, the inorganic substance is preferably selected from compounds that can be ionized in an aqueous solution. Thus, when an inorganic substance ionizes in aqueous solution, an inorganic substance can adsorb | suck more strongly to the catalyst precursor 1 (especially catalyst metal) by an electrostatic interaction. The said form is especially effective when coat | covering the catalyst precursor 1 with an inorganic substance by immersing the catalyst precursor 1 in an inorganic substance solution. Therefore, in the next step (c), when the catalyst precursor 2 is mixed with the electrolyte, the inorganic substance is more efficiently interposed between the catalyst metal and the electrolyte. For this reason, the catalyst metal (especially ORR specific activity) can be more effectively improved by more effectively reducing the coating of the catalyst metal with the electrolyte by the following step (d). From the above viewpoint, the inorganic substance is at least one selected from the group consisting of iodine compounds and bromine compounds. Particularly preferably, the inorganic substance is at least one selected from the group consisting of iodine (including iodine ions) and bromine (including bromine ions).

The method for coating the catalyst precursor 1 with an inorganic substance is not particularly limited, but it is preferable to mix the catalyst precursor 1 with a coating agent. That is, the present invention comprises preparing a catalyst precursor 1 formed by supporting a platinum-containing catalyst metal on a conductive support, and mixing the catalyst precursor 1 with a coating agent that adsorbs the platinum-containing catalyst metal. A method for producing the catalyst precursor of the invention is also provided (third aspect). Here, the coating agent is not particularly limited as long as it has adsorptivity to the metal constituting the catalyst metal, and may be an inorganic compound or an organic compound. The coating agent is preferably one that selectively adsorbs to the metal (particularly platinum) constituting the catalyst metal. In view of the high selective adsorption property to the metal (particularly platinum) constituting the catalyst metal, specifically, although not particularly limited to the following, carbon monoxide, iodine, lithium iodide, sodium iodide, potassium iodide, Iodine compounds such as cesium iodide, inorganic compounds such as bromine compounds such as bromine, sodium bromide, potassium bromide and cesium bromide, quaternary ammoniums such as tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide Examples include iodine salts of compounds, and organic compounds such as bromine salts of quaternary ammonium compounds such as tetraalkylammonium bromide, pyridinium bromide, and imidazolium bromide. The said coating agent may be used independently or may be used with the form of 2 or more types of mixtures. Of these, the coating agent is preferably an inorganic compound, and more preferably an iodine compound, a bromine compound, and carbon monoxide. That is, according to a preferred embodiment of the present invention, the coating agent is at least one selected from the group consisting of iodine compounds, bromine compounds, and carbon monoxide. More preferably, the coating agent is at least one selected from the group consisting of iodine compounds and bromine compounds. Particularly preferably, the coating agent is at least one selected from the group consisting of sodium iodide, potassium iodide, sodium bromide and potassium bromide. Since such a coating agent can be specifically chemically adsorbed to a catalyst metal (particularly platinum), it can be strongly adsorbed to the catalyst metal due to the influence of charge interaction. Therefore, in the next step (c), when the catalyst precursor 2 is mixed with the electrolyte, the coating agent is more efficiently interposed between the catalyst metal and the electrolyte. For this reason, the catalyst metal (especially ORR specific activity) can be more effectively improved by more effectively reducing the coating of the catalyst metal with the electrolyte by the following step (d). The catalyst precursor 1 is mixed with a coating agent to obtain the catalyst precursor 2 in which the catalyst precursor 1 (particularly the catalyst metal) is coated with an inorganic substance. At this time, the coating form of the catalyst precursor 1 with an inorganic material includes both cases where the inorganic material and the coating agent are the same and different. For example, when the catalyst precursor 1 is coated using sodium iodide as a coating agent as in the following examples, the reduced iodine (I) or iodide ion (I ⁻ ) is converted into an inorganic substance as the catalyst precursor. 1 is assumed to be coated.

In this embodiment, the coating agent is preferably selected from compounds that can be ionized in an aqueous solution. As described above, when the coating agent is ionized in the aqueous solution, the coating agent (and hence the inorganic substance) can be more strongly adsorbed to the catalyst precursor 1 (particularly the catalyst metal) by electrostatic interaction. This form is particularly effective when the catalyst precursor 1 is coated with an inorganic substance by immersing the catalyst precursor 1 in a coating solution. Therefore, in the next step (c), when the catalyst precursor 2 is mixed with the electrolyte, the inorganic substance is more efficiently interposed between the catalyst metal and the electrolyte. For this reason, the catalyst metal (especially ORR specific activity) can be more effectively improved by more effectively reducing the coating of the catalyst metal with the electrolyte by the following step (d). From the above viewpoint, the coating agent is particularly preferably at least one selected from the group consisting of sodium iodide, potassium iodide, sodium bromide and potassium bromide.

The method for coating the catalyst precursor 1 with an inorganic material is not particularly limited, and a normal coating method can be used in the same manner or appropriately modified. Specifically, a method in which the catalyst precursor 1 is immersed in a coating solution; a method in which the coating solution is applied to the catalyst precursor 1 by a known means such as a screen printing method, a deposition method, or a spray method; Examples thereof include a method in which the catalyst precursor 1 is placed in an atmosphere containing a gaseous coating agent (when the inorganic substance is carbon monoxide). Among these, in consideration of more uniform coating and ease of operation, a method of immersing the catalyst precursor 1 in a coating solution is preferable.

As described above, the solvent that can be used when the coating agent is used in the form of a solution is not particularly limited as long as it can dissolve the coating agent, and can be appropriately selected according to the type of the coating agent. Specifically, water such as distilled water, ion-exchanged water, pure water, and ultrapure water; nitriles such as acetonitrile, methoxyacetonitrile, and propionitrile; carbonates such as ethylene carbonate; ethers such as diethyl ether and tetrahydrofuran Alcohols such as methanol, ethanol, propanol, isopropanol and the like can be mentioned. Here, the concentration of the coating agent is not particularly limited, but is usually about 0.1 to 1 (w / v)%.

Further, the amount of the coating agent added is not particularly limited as long as it is an amount that can sufficiently cover the catalyst precursor 1 (particularly the catalyst metal). Usually, 1 mol of the inorganic substance is bonded to one metal atom (for example, 1 mol of Pt) adsorbed by the inorganic substance among the metals constituting the catalyst metal. For this reason, it is preferable that the addition amount of a coating agent is substantially more than a reaction equivalent with the metal which an inorganic substance (coating agent) adsorb | sucks. Specifically, the coating agent is preferably used in an amount of 1 to 2 moles, more preferably more than 1 mole and 1.5 moles or less with respect to 1 mole of the catalyst metal adsorbed by the inorganic substance (coating agent). It is preferable to mix with the precursor 1. For this reason, for example, when the catalyst metal is platinum alone, it is preferable to mix the coating agent at a ratio as described above with respect to 1 mol of platinum constituting the catalyst precursor 1. Moreover, 1 mol of coating agents may adsorb | suck with respect to metal 2 atom or 3 atom (2 or 3 mol) depending on the adsorption | suction form of the inorganic substance to a metal. In that case, a coating agent obtained by multiplying the reaction ratio by the above 1-2 times may be added. In addition, when using 2 or more types of coating agents, the addition (mixing) amount of the said coating agent is these total amounts.

The coating conditions (for example, immersion conditions) of the catalyst precursor 1 with the coating agent are not particularly limited as long as the catalyst precursor 1 (particularly the catalyst metal) can be sufficiently coated with an inorganic substance. For example, the coating (for example, immersion) temperature is preferably 10 to 50 ° C., more preferably 15 to 40 ° C. The coating (for example, dipping) time is preferably 10 minutes to 10 hours, more preferably 30 minutes to 2 hours. In addition, when the catalyst precursor 1 is immersed in a coating solution, the coating solution may be stirred.

The coating of the catalyst precursor 1 with an inorganic substance is preferably performed under acidic conditions. That is, according to a preferred embodiment, the catalyst precursor 1 is coated with the inorganic material under acidic conditions, or the catalyst precursor 1 and the coating agent are mixed under acidic conditions. Thereby, impurities adhering to the surface of the catalyst precursor 1 (especially catalyst metal) can be removed, and the catalyst precursor 1 (particularly catalyst metal) having a smooth surface with few impurities can be obtained. Therefore, the inorganic substance covers the catalyst metal more directly, and the catalyst precursor 2 having a dense film can be reliably obtained. The means for achieving this preferred form is not particularly limited, but for example, an acidic coating solution is used. The pH of the coating solution (liquid temperature: 25 ° C.) at this time is not particularly limited, but is preferably 1 or more and less than 6, and more preferably 2 to 4. By using a coating solution having such a pH, impurities adhering to the surface of the catalyst precursor 1 (particularly the catalyst metal) can be more efficiently removed while suppressing elution of the catalyst metal. For this reason, an inorganic substance coat | covers a catalyst metal more directly, and the catalyst precursor 2 which has a denser film is obtained reliably. The acid that can be used to make the coating solution into the acidic solution as described above is not particularly limited, and examples thereof include hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid (HClO ₄ ). The addition amount of the acid is not particularly limited, but is preferably an amount that makes the pH of the coating solution as described above.

After the coating treatment as described above, if necessary, the catalyst precursor 2 may be separated and washed to remove excess inorganic substances or acids (when used). Here, the separation means of the catalyst precursor 2 is not particularly limited, and known methods such as filtration, centrifugation, and decantation can be used. Further, the solvent (cleaning solution) used for cleaning the catalyst precursor 2 is not particularly limited, but can be used in the same manner as the solvent exemplified in the preparation of the inorganic solution. Here, the solvent (cleaning liquid) used for cleaning the catalyst precursor 2 may be the same as or different from the solvent used in the preparation of the inorganic solution. From the viewpoints of suppression of side reactions and industrial viewpoints (simplification of prepared solvent), the same is preferable. Further, at the time of cleaning, the catalyst precursor 2 may be stirred and dispersed in the cleaning liquid using a homogenizer, an ultrasonic dispersion device, a magnetic stirrer, or the like. Moreover, you may repeat the said washing | cleaning process as needed.

The catalyst precursor 2 after the coating treatment or the washing step as described above may be separated and dried if necessary. Here, since the separation means is the same as described above, the description thereof is omitted here. As drying conditions, for example, the drying temperature is preferably 20 to 80 ° C., more preferably 40 to 60 ° C. The drying time is preferably 15 minutes to 10 hours.

Thus, the catalyst precursor 1 (in particular, the catalyst metal) coated with the inorganic substance is obtained. The catalyst precursor 2 of the said form is hard to receive the direct influence from an external environment by the film by an inorganic substance. For example, elution of a metal catalyst can be suppressed even in an acidic environment (see the following examples). That is, the catalyst precursor 2 is excellent in storage stability (deterioration during storage can be suppressed). Therefore, the present invention also provides a catalyst precursor in which a platinum-containing catalyst metal coated with an inorganic substance adsorbed on a platinum-containing catalyst metal is supported on a conductive support (second aspect). Here, the catalyst precursor (particularly catalyst metal) is sufficiently coated to an extent that the direct contact between the catalyst precursor (particularly catalyst metal) and the electrolyte can be sufficiently suppressed when mixed with the electrolyte. What is necessary is just to be coat | covered with the inorganic substance. Specifically, the catalyst precursor is coated with an inorganic substance with a platinum surface area of 20% or more (upper limit: 100%). Preferably, the catalyst precursor is coated with the inorganic material in a proportion of 30-90% platinum surface area, more preferably more than 40% and less than 70%. In addition, the value measured by the method described in [Verification of iodine covering ratio / catalyst powder] in the following examples is adopted as the covering ratio of the catalyst precursor. In addition, in the following method, although an inorganic substance is iodine, those skilled in the art can understand that even if it is other inorganic substances (including inorganic compound ions), it can be measured by the same method.

In addition, since each structural requirement in the 2nd and 3rd aspect other than the said structural requirement is the same as that of the said 1st aspect, description is abbreviate | omitted here.

[Step (c)]
In this step, the catalyst precursor 2 prepared in the above step (b) is mixed with an electrolyte to form a catalyst precursor layer.

Here, the electrolyte is not particularly limited, but is preferably a polymer (polymer electrolyte) from the viewpoint of difficulty in covering the electrode catalyst.

The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material. Of these, fluorine-based polymer electrolytes are preferred. That is, the electrolyte is preferably a fluorine-based polymer electrolyte.

Examples of the ion exchange resin constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Examples thereof include fluorocarbon sulfonic acid polymers. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. Is used.

Specific examples of hydrocarbon polymer electrolytes include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, sulfone. Polyether ether ketone (S-PEEK), sulfonated polyphenylene (S-PPP), and the like. These hydrocarbon polymer electrolytes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

The polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, and is also called a proton conductive polymer. For this reason, proton conductivity is important in polymer electrolytes responsible for proton transmission. Here, when the EW of the polymer electrolyte is too large, the ionic conductivity in the entire catalyst layer is lowered. Therefore, it is preferable that the catalyst layer of this embodiment contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of the present embodiment preferably contains a polymer electrolyte having an EW of 1500 g / mol or less, more preferably a polymer electrolyte having 1200 g / mol or less, and particularly preferably a high electrolyte of 1100 g / mol or less. Contains molecular electrolytes.

On the other hand, if the EW is too small, the hydrophilicity is too high and it becomes difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 g / mol or more. Note that EW (Equivalent Weight) represents an equivalent weight of an exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of ion exchange group, and is expressed in units of “g / mol”.

The catalyst precursor layer includes two or more types of polymer electrolytes having different EWs in the power generation surface. At this time, the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of 90% in the gas in the flow path. It is preferable to use in the region below RH. By adopting such a material arrangement, the resistance value becomes small regardless of the current density region, and the battery performance can be improved. The polymer electrolyte used in the region where the relative humidity of the gas in the flow channel is 90% RH or less, that is, the EW of the polymer electrolyte having the lowest EW is desirably 900 g / mol or less. Thereby, the above-mentioned effect becomes more reliable and remarkable.

Furthermore, it is desirable to use a polymer electrolyte with the lowest EW in a region higher than the average temperature of the cooling water inlet and outlet. As a result, the resistance value is reduced regardless of the current density region, and the battery performance can be further improved.

Furthermore, from the viewpoint of reducing the resistance value of the fuel cell system, the polymer electrolyte having the lowest EW is within 3/5 from the gas supply port of at least one of the fuel gas and the oxidant gas with respect to the flow path length. It is desirable to use it in the range area.

If necessary, the catalyst precursor layer may be a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol ( Additives such as thickeners such as EG), polyvinyl alcohol (PVA), and propylene glycol (PG), and pore-forming agents may be included.

Further, the electrolyte contained in the catalyst precursor layer of the present invention may contain a non-polymer within a range that does not impair the effects of the present invention. The non-polymer is a low molecular weight compound having a weight average molecular weight (Mw) of 10,000 or less, for example, a raw material (for example, a monomer) or an intermediate product (for example, an oligomer) of a polymer electrolyte such as Nafion (registered trademark). Etc., but is not limited to this.

The method for producing the catalyst precursor layer is not particularly limited. For example, a catalyst ink is prepared by mixing the catalyst precursor 2, an electrolyte, a solvent, and other additives as required, and this is applied and dried. can get.

The amount of the electrolyte in the catalyst ink is not particularly limited, but is preferably 0.1 parts by weight or more and 2 parts by weight or less with respect to 1 part by weight of the conductive carrier in the catalyst precursor 2, and 0.2 weight. More preferably, it is at least 1.5 parts by weight.

The solvent used for preparing the catalyst ink is not particularly limited as long as the catalyst precursor 2 and the electrolyte can be uniformly dispersed or dissolved and can be removed after coating. Specifically, water, n-hexanol, cyclohexanol, methanol, ethanol, 1-propanol (n-propyl alcohol), isopropanol, n-butanol, sec-butanol, isobutanol, tert-butanol, etc. -4 lower alcohols, propylene glycol, benzene, toluene, xylene and the like. Besides these, butyl alcohol acetate, dimethyl ether, ethylene glycol, and the like can be given. These may be used alone or in the form of a mixture of two or more.

The solid concentration of the catalyst ink (total concentration of the catalyst precursor 2 and the electrolyte in the ink) is not particularly limited, but is preferably about 1 to 50% by weight, more preferably about 5 to 30% by weight.

In the catalyst ink, additives such as a water repellent, a dispersant, a thickener, and a pore-forming agent may be mixed as necessary. When these additives are used, the amount added is preferably 5 to 20% by weight based on the total amount of the catalyst ink.

In addition, the catalyst ink may be separately provided with a mixing promoting step for mixing well after mixing the above desired components, if necessary. Here, the mixing promotion step is not particularly limited, but the catalyst ink is well dispersed with an ultrasonic homogenizer, or the catalyst ink is well pulverized with an apparatus such as a sand grinder, a circulating ball mill, or a circulating bead mill. Preferable examples include a defoaming operation such as a defoaming operation using a vacuum degassing operation or a hybrid mixer.

Next, a catalyst ink is applied to the surface of the substrate. The application method to the substrate is not particularly limited, and a known method can be used. Specifically, it can be performed using a known method such as a spray (spray coating) method, a gulliver printing method, a die coater method, a screen printing method, or a doctor blade method.

In this case, as the base material to which the catalyst ink is applied, a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion base material (gas diffusion layer) described in detail below can be used. In such a case, a catalyst precursor layer is formed on the surface of a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion base material (gas diffusion layer), and then the obtained laminate is used as it is to produce a membrane electrode assembly. Can be used. Alternatively, a peelable substrate such as a polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as the substrate, and after the catalyst precursor layer is formed on the substrate, the catalyst precursor layer portion is removed from the substrate. The catalyst precursor layer may be obtained by peeling.

Finally, the coating layer (film) of the catalyst ink is dried at room temperature (25 ° C.) to 150 ° C. for 1 to 60 minutes in an air atmosphere or an inert gas atmosphere. Thereby, a catalyst precursor layer is formed.

In the catalyst precursor layer thus formed, at least a part of the catalyst precursor 2 (especially the catalyst metal) is coated with an inorganic substance. As described above, the catalyst precursor 2 is not easily affected by the external environment due to the inorganic coating. For example, elution of a metal catalyst can be suppressed even in an acidic environment (see the following examples). For this reason, the catalyst precursor layer containing the catalyst precursor 2 is also excellent in storage stability (deterioration during storage can be suppressed). Therefore, this invention also provides the catalyst precursor layer containing the catalyst precursor and electrolyte of this invention (4th aspect). Here, the coating degree with the inorganic substance in the catalyst precursor layer may be such that direct contact between the catalyst precursor (particularly the catalyst metal) and the electrolyte can be sufficiently suppressed in the layer. Specifically, in the catalyst precursor layer, the catalyst precursor is coated with an inorganic substance at a ratio of platinum surface area of 20% or more (upper limit: 100%). Preferably, in the catalyst precursor layer, the catalyst precursor is coated with an inorganic substance at a platinum surface area of 30 to 100%, more preferably more than 50% and 100% or less. In addition, the value measured by the method described in [Verification of iodine coating ratio / catalyst layer] in the following examples is adopted as the coverage of the catalyst precursor. In addition, in the following method, although an inorganic substance is iodine, those skilled in the art can understand that even if it is other inorganic substances (including inorganic compound ions), it can be measured by the same method. In addition, since an inorganic substance is not added from step (b) to (c), the coverage ratio of the catalyst precursor layer with the inorganic substance is substantially the same as the coverage ratio of the catalyst precursor with the inorganic substance defined in the second aspect. .

In addition, since each constituent element in the fourth aspect other than the above constituent elements is the same as that in the first aspect, the description thereof is omitted here.

The film thickness (dry film thickness) of the catalyst precursor layer is not particularly limited, but is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, still more preferably 1 to 15 μm, and particularly preferably 1 to 10 μm.

[Step (d)]
In this step, the inorganic substance is removed from the catalyst precursor layer in the step (c). In the catalyst precursor layer formed in the step (c), the catalyst precursor 2 is maintained in a state of being coated with an inorganic substance. In this step, the inorganic material covering the catalyst precursor layer, particularly the catalyst precursor 2 (catalyst metal) is removed, and the electrolyte in contact (coating) with the catalyst precursor 2 is removed. This process reduces the coating (poisoning action) of the catalytic metal with the electrolyte, and the contact between the reactive gas (especially oxygen) and the catalytic metal surface, and hence the three-phase interface of the reactive gas (especially oxygen), catalytic metal particles and water. Promote the formation of Therefore, the catalytic activity (especially oxygen reduction reaction (ORR) specific activity) of the catalyst layer can be improved.

For example, when the inorganic substance is carbon monoxide (CO), a method of supplying an oxygen-containing gas to oxidize CO by a chemical reaction, a method of increasing the temperature to promote CO desorption, or the like can be used.

For example, when the inorganic substance is an iodine compound or a bromine compound, the removal of the inorganic substance is preferably performed by a haloform reaction. That is, according to a preferred embodiment of the present invention, the inorganic substance is at least one of an iodine compound and a bromine compound, and the inorganic substance is removed from the catalyst precursor layer by a haloform reaction.

Hereinafter, the preferable mode will be described in detail.

In this embodiment, the inorganic material present in the catalyst precursor layer is reacted with a compound having an acetyl group or a compound that has an acetyl group by oxidation, and a base (haloform reaction), whereby the catalyst precursor layer, particularly the catalyst precursor. Chemical removal from 2 (catalytic metal). For example, in Example 3 below, it is assumed that the removal of inorganic substances is due to iodoform reaction. Hereinafter, a compound having an acetyl group or a compound having an acetyl group by oxidation is collectively referred to as an “acetyl group-containing compound”.

Here, the compound having an acetyl group is a compound represented by the formula: R—C (═O) —CH ₃ . In the above formula, R is a hydrogen atom (H), an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms. Here, examples of the alkyl group having 1 to 12 carbon atoms include, but are not limited to, for example, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert- Examples include linear or branched alkyl groups such as butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and 2-ethylhexyl. It is done. The aryl group having 6 to 20 carbon atoms is not limited to the following, but includes, for example, phenyl group, benzyl group, phenethyl group, o-, m- or p-tolyl group, 2,3- or 2,4. -Xylyl group, mesityl group, naphthyl group, anthryl group, phenanthryl group, biphenylyl group, benzhydryl group, trityl group and pyrenyl group.

A compound that has an acetyl group by oxidation is a compound that generates a compound having an acetyl group as described above by being oxidized. Specific examples include ethanol and isopropyl alcohol. The compound having an acetyl group and the compound having an acetyl group by oxidation may be used alone or in a mixture of two or more. Further, the compound having an acetyl group and the compound having an acetyl group by oxidation may be used in combination of two or more.

The addition amount of the compound having an acetyl group or the compound that has an acetyl group by oxidation is not particularly limited as long as it is an amount capable of removing a sufficient amount of the inorganic substance, and can be appropriately selected according to the amount of the inorganic substance. The addition amount of the compound having an acetyl group or the compound that has an acetyl group by oxidation is preferably larger than the amount of the inorganic substance charged in the step (b) (molar conversion). Specifically, the amount added is preferably more than 1 mole and not more than 10 moles and about 2 to 8 moles with respect to 1 mole of the inorganic charge in step (b). In addition, the said quantity in the case of using the compound which has an acetyl group by oxidation and the compound which has an acetyl group by oxidation as 2 or more types of mixtures is these total amounts.

The base used in this embodiment is not particularly limited, and examples thereof include sodium hydroxide and potassium hydroxide. The above bases may be used alone or in a mixture of two or more. The base may be used in the form of a solution such as an aqueous solution.

The amount of the base added is not particularly limited as long as a sufficient amount of the inorganic substance can be removed, and can be appropriately selected according to the amount of the inorganic substance. It is preferable that the amount of the base added is larger than the amount of the inorganic material charged in the step (b) (in terms of mole). Specifically, the amount added is preferably more than 1 mole and not more than 10 moles and about 2 to 8 moles with respect to 1 mole of the inorganic charge in step (b). In addition, the said amount in the case of using a base as a 2 or more types of mixture is these total amounts.

The addition form of the acetyl group-containing compound and the base to the catalyst precursor layer is not particularly limited, but the acetyl group-containing compound and the base are preferably in the form of a solution in consideration of the removal efficiency of inorganic substances, operability, and the like. The addition method is not particularly limited, and conventionally known methods such as a coating / printing method, a dipping method, and a spraying method can be applied. Of these, it is preferable to immerse the catalyst precursor layer in a solution containing an acetyl group-containing compound and a base and degas the system by reducing the pressure in the state. By this operation, the base and the acetyl group-containing compound can be uniformly and quickly permeated throughout the catalyst precursor layer and into the inside. Therefore, according to the said form, an inorganic substance can be removed more efficiently. In addition, you may perform the said immersion and / or pressure reduction operation, stirring. Or you may stir the solution which put the catalyst precursor layer after the said immersion and / or pressure reduction operation. By such an operation, the haloform reaction proceeds more efficiently over the inside of the catalyst precursor layer. Therefore, according to the said form, an inorganic substance can be removed more efficiently. The stirring conditions are not particularly limited, but the stirring temperature (solution temperature) is preferably 20 to 80 ° C., more preferably 40 to 70 ° C. in consideration of the further improvement effect of the removal efficiency of inorganic substances. The stirring time is preferably 20 minutes to 3 hours, more preferably 30 minutes to 2 hours.

The order of adding the acetyl group-containing compound and the base to the catalyst precursor layer is not particularly limited. Specifically, (1) an acetyl group-containing compound and a base are collectively added to the catalyst precursor layer; (2) an acetyl group-containing compound is added to the catalyst precursor layer, and then a base is added; (3 ) After adding a base to the catalyst precursor layer, any of adding an acetyl group-containing compound may be used. Among these, the order of the above (3) is preferable. Particularly preferred is the order of (3) above in which the base is in the form of an aqueous solution and the acetyl group-containing compound is ethanol. According to this embodiment, since ethanol has a lower surface tension than water, the base and the acetyl group-containing compound (ethanol) can be uniformly permeated into the entire catalyst precursor layer and into the inside thereof. Therefore, according to the said form, an inorganic substance can be removed still more efficiently.

After the inorganic substance removing operation as described above, if necessary, the catalyst precursor layer may be washed to remove inorganic substances, excess acetyl group-containing compounds and bases. Here, the solvent (cleaning solution) used for cleaning the catalyst precursor layer is not particularly limited, and examples thereof include water such as distilled water, ion-exchanged water, pure water, and ultrapure water. Further, during the cleaning, the catalyst precursor layer may be immersed in the cleaning liquid while stirring using a homogenizer, an ultrasonic dispersing device, a magnetic stirrer, or the like. Moreover, you may immerse in a washing | cleaning liquid under pressure reduction during washing | cleaning. By these operations, the cleaning liquid can penetrate into the catalyst precursor layer. The stirring operation and the decompression operation may be performed in combination. Moreover, you may repeat the said washing | cleaning process as needed. The cleaning conditions are not particularly limited, but considering the further improvement effect of the removal efficiency of inorganic substances, the cleaning temperature (cleaning liquid temperature) is preferably 20 to 80 ° C., more preferably 40 to 70 ° C. The washing (for example, stirring) time is preferably 20 minutes to 3 hours, more preferably 30 minutes to 2 hours. In addition, you may repeat the said washing | cleaning process as needed.

Further, after the above washing operation, the catalyst precursor layer may be separated and dried if necessary. Here, since the separation means is the same as that in the step (b), the description is omitted here. As drying conditions, for example, the drying temperature is preferably 20 to 80 ° C., more preferably 40 to 60 ° C. The drying time is preferably 15 minutes to 10 hours.

In this way, inorganic substances can be removed from the catalyst precursor layer. On the other hand, as described above, when a part of the catalyst (particularly the catalyst metal) is coated with an inorganic substance, it is difficult to be directly affected by the external environment. For example, elution of a metal catalyst can be suppressed even in an acidic environment (see the following examples). For this reason, a catalyst layer containing a catalyst (particularly a catalyst metal) coated with an inorganic substance to some extent is excellent in durability and storage stability. That is, the present invention includes a catalyst and an electrolyte in which a platinum-containing catalyst metal is supported on a conductive support, and the platinum is coated with an inorganic substance that adsorbs to the platinum-containing catalyst metal in a proportion of more than 0% and less than 10%. (5th aspect) is also provided. Hereinafter, the “ratio of platinum in the catalyst layer covered with an inorganic substance adsorbed on the platinum-containing catalyst metal” is also referred to as “platinum coverage of the catalyst layer”. When the coverage of the catalyst with the inorganic substance is 0%, the catalyst layer (and hence the MEA or fuel cell having such a catalyst layer) is durable and storage stable (especially the elution of the catalyst metal in an acidic environment). ). On the contrary, when the coating ratio of the catalyst with the inorganic substance is 10% or more, a sufficient amount of the catalyst metal is not directly exposed on the conductive support, so that the reaction gas (particularly oxygen) cannot sufficiently contact the surface of the catalyst metal, The catalyst layer is inferior in catalytic activity. In consideration of a better balance between catalyst activity and durability and storage stability, the ratio of platinum covered with an inorganic substance in the catalyst layer (platinum coverage of the catalyst layer) is preferably 1% or more and 8% or less. Preferably it is more than 2% and less than 7%. Such a catalyst layer having a platinum coating ratio can exhibit catalyst activity, durability and storage stability in a better balance. In addition, although the catalyst layer which concerns on a 5th aspect can be manufactured by a 1st aspect, you may manufacture by another method. The platinum coverage of the catalyst layer is determined by the fluorescent X-ray (XRF) in the coverage ratio of platinum inorganic substance (iodine) calculated by the method described in [Verification of iodine coverage / catalyst layer] in the following examples. The value multiplied by the quantified iodine removal rate is adopted. The above-mentioned “coating ratio (%) of platinum with inorganic substance (iodine)” is expressed by the formula: 100− (CO chemical adsorption surface area of Pt of catalyst precursor layer) / (CO chemical adsorption surface area of Pt of inorganic additive-free layer)] Sought by. In addition, in the following method, although an inorganic substance is an iodine, those skilled in the art can understand that it can measure by the same method even if it is another inorganic substance.

Further, the coverage can be substituted by quantifying the amount of iodine and the amount of platinum in the catalyst layer by fluorescent X-rays (XRF). When calculating the coverage (%), it can be estimated by making several assumptions. That is, assuming that the X-ray intensity ratio is a molar ratio, the volume of iodine contained in 1 g of platinum (from the obtained iodine / platinum molar ratio, the charged weight and density of platinum, and the charged amount and density of iodine ( m ³ ) is obtained. Further, since the total area (m ² ) that can be covered with iodine can be calculated if the average coating thickness (m) of iodine is known, what percentage is covered with respect to the surface area (m ² / g) of Pt is obtained. be able to. This time, it was estimated that the platinum coverage of iodine was 6% as described in the examples, but this was also reproduced by the above calculation method by assuming the average coating thickness of iodine to be 15 μm. can do. Therefore, the platinum coverage (%) by XRF can be substituted by the above calculation method.

In the present specification, the catalyst layer produced by the method of the present invention and the catalyst layer according to the fifth aspect are collectively referred to as “catalyst layer according to the present invention”.

The film thickness (dry film thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, still more preferably 1 to 10 μm, and particularly preferably 1 to 5 μm. The above film thickness is applied to both the cathode catalyst layer and the anode catalyst layer. The cathode catalyst layer and the anode catalyst layer may be the same or different.

When an alkali metal salt is used as the base when removing the inorganic substance from the catalyst precursor layer, the proton (H ⁺ ) of the electrolyte is replaced with an alkali metal ion (for example, Na ⁺ ). For example, when a sulfonic acid polymer is used as an electrolyte and sodium hydroxide is used as a base, a sulfonic acid group (—SO ₃ H) is converted into a sodium salt of sulfonic acid (—SO ₃ Na). For this reason, acid treatment is performed after the above-described inorganic removal operation, and an operation is performed to return alkali metal ions to protons (for example, sulfonate (for example, —SO ₃ Na) to sulfonic acid group (—SO ₃ H)). It is preferable. That is, according to a preferred embodiment of the present invention, acid treatment is performed after removing the inorganic substance.

Hereinafter, the acid treatment after removing the inorganic substance will be specifically described.

The acid used in the acid treatment is not particularly limited, may be mentioned hydrochloric acid, sulfuric acid, nitric acid, perchloric acid (HClO _4). The above acids may be used alone or in a mixture of two or more. The acid is preferably used in the form of a solution such as an aqueous solution. The amount of the acid added is not particularly limited as long as the alkali metal ion of the electrolyte can be sufficiently substituted with protons, and is appropriately selected according to the electrolytic mass. Preferably, the acid is present in excess relative to the electrolyte. The acid concentration of the aqueous acid solution is preferably 3 to 20% by weight, more preferably 5 to 15% by weight.

The acid treatment method is not particularly limited. Specifically, a conventionally known method such as a coating / printing method, a dipping method, or a spraying method can be applied. Among these, it is preferable to immerse the catalyst precursor layer in an acid solution and degas the system by reducing the pressure in the state. By this operation, the acid can be uniformly and quickly permeated throughout the catalyst precursor layer and into the inside thereof. Therefore, according to the said form, the alkali metal ion of electrolyte can be substituted by a proton efficiently and more rapidly. In addition, you may perform the said immersion and / or pressure reduction operation, stirring. Or after the said immersion and / or pressure reduction operation, you may stir the acid solution which put the catalyst precursor layer. By such an operation, the substitution reaction proceeds more efficiently over the catalyst precursor layer. Therefore, according to the said form, the alkali metal ion of electrolyte can be substituted by a proton efficiently and more rapidly. The stirring conditions are not particularly limited, but the stirring temperature (solution temperature) is preferably 20 to 80 ° C., more preferably 40 to 70 ° C. in consideration of the further improvement effect of substitution efficiency. The stirring time is preferably 20 minutes to 3 hours, more preferably 30 minutes to 2 hours.

After the acid treatment as described above, if necessary, the catalyst precursor layer may be washed to remove excess acid. Here, the solvent (cleaning solution) used for cleaning the catalyst precursor layer is not particularly limited, and examples thereof include water such as distilled water, ion-exchanged water, pure water, and ultrapure water. Further, during the cleaning, the catalyst precursor layer may be stirred and dispersed in the cleaning liquid using a homogenizer, an ultrasonic dispersion device, a magnetic stirrer, or the like. Further, the cleaning liquid may be depressurized during the cleaning. By these operations, the cleaning liquid can penetrate into the catalyst precursor layer. The stirring operation and the decompression operation may be performed in combination. Moreover, you may repeat the said washing | cleaning process as needed. The cleaning conditions are not particularly limited, but considering the further improvement effect of the removal efficiency of inorganic substances, the cleaning temperature (cleaning liquid temperature) is preferably 20 to 80 ° C., more preferably 40 to 70 ° C. The washing (for example, stirring) time is preferably 20 minutes to 3 hours, more preferably 30 minutes to 2 hours. In addition, you may repeat the said washing | cleaning process as needed.

The catalyst precursor layer may be dried after the cleaning treatment as described above. Here, as drying conditions, for example, the drying temperature is preferably 30 to 100 ° C., and more preferably 50 to 90 ° C. The drying time is preferably 5 minutes to 1 hour.

As described above, a catalyst layer containing an electrolyte having a sufficient amount of protons can be provided. Further, in the catalyst layer obtained as described above, the catalyst metal is not coated or hardly coated with the electrolyte, and is in a state of being directly exposed on the conductive support. Here, the coating ratio of the catalyst metal with the electrolyte may be sufficiently low, but is specifically 0.6 or less, preferably less than 0.5, more preferably 0.45 or less (lower limit: 0). is there. With such a low coverage, the catalytic metal is not in contact with the electrolyte, and the poisoning action by the electrolyte can be sufficiently suppressed. Therefore, the opportunity for the reactive gas (especially oxygen) to come into contact with the catalytic metal surface is increased, and the formation of the three-phase interface of the reactive gas (especially oxygen), catalytic metal particles and water is promoted, and the catalytic activity (especially the ORR specific activity). Will improve. Further, the coating of the catalyst metal with the electrolyte can be reduced, and the reaction gas (especially O ₂ ) can be supplied more quickly and more efficiently by the catalyst metal without going through the electrolyte, and the gas transportability can be further improved. In addition, the value measured by the method described in [Measurement of Electrolyte (Ionomer) Coverage] in the Examples below is adopted as the coating ratio of the catalyst metal with the electrolyte.

Further, the above method can be applied regardless of the form and properties of the components constituting the catalyst layer such as a catalyst (conductive carrier, catalyst metal) and an electrolyte. Therefore, since a catalyst and an electrolyte can be selected according to a desired effect, it is preferable from an industrial viewpoint.

The catalyst layer according to the present invention is excellent in catalyst activity (particularly ORR specific activity). Moreover, the catalyst layer according to the present invention is excellent in durability and storage stability. For this reason, the catalyst layer according to the present invention can be suitably applied to fuel cell applications that require higher performance than household and mobile power sources. That is, the membrane / electrode assembly and the fuel cell included in the catalyst layer according to the present invention are excellent in power generation performance. The membrane / electrode assembly and the fuel cell in the catalyst layer according to the present invention are excellent in durability.

Hereinafter, a membrane electrode assembly (MEA) including a catalyst layer and a fuel cell according to the present invention will be described.

<Membrane electrode assembly (MEA)>
As described above, the catalyst layer according to the present invention can be suitably used for a membrane electrode assembly (MEA). That is, the present invention also provides a membrane electrode assembly (MEA) having a catalyst layer according to the present invention, particularly a fuel cell electrode assembly (MEA). Such a membrane electrode assembly (MEA) can exhibit high power generation performance. Moreover, the membrane electrode assembly (MEA) having the catalyst layer according to the present invention is excellent in durability.

The membrane electrode assembly (MEA) having the catalyst layer according to the present invention can be applied with the same configuration except that the catalyst layer according to the present invention is used instead of the conventional catalyst layer. Although the preferable form of MEA of this invention is demonstrated below, this invention is not limited to the following form.

The MEA is composed of an electrolyte membrane, an anode catalyst layer and an anode gas diffusion layer, a cathode catalyst layer and a cathode gas diffusion layer which are sequentially formed on both surfaces of the electrolyte membrane. In this membrane electrode assembly (MEA), the catalyst layer according to the present invention is used for at least one of the cathode catalyst layer and the anode catalyst layer.

[Electrolyte membrane]
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane. For example, the solid polymer electrolyte membrane has a function of selectively allowing protons generated in the anode catalyst layer during operation of a fuel cell (such as PEFC) to permeate the cathode catalyst layer along the film thickness direction. The solid polymer electrolyte membrane also has a function as a partition for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

The electrolyte material constituting the solid polymer electrolyte membrane is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, the above-mentioned fluorine-based polymer electrolyte or hydrocarbon-based polymer electrolyte can be used. In this case, it is not always necessary to use the same polymer electrolyte used for the catalyst layer.

The thickness of the electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte membrane is usually about 5 to 300 μm. When the thickness of the electrolyte membrane is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[Catalyst layer]
The catalyst layer is a layer where the battery reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer, and the reduction reaction of oxygen proceeds in the cathode catalyst layer. Although the catalyst layer according to the present invention can be applied to both the cathode catalyst layer and the anode catalyst layer, it is preferably applied at least to the cathode catalyst layer in view of the necessity for improving the oxygen reduction activity. Needless to say, the present invention may be applied only to the anode catalyst layer or to both the cathode and the anode catalyst layer. For this reason, when the catalyst layer according to the present invention is used for only one side, a conventional catalyst layer can be used for the catalyst layer on the other side.

[Gas diffusion layer]
The gas diffusion layer (anode gas diffusion layer, cathode gas diffusion layer) promotes diffusion of gas (fuel gas or oxidant gas) supplied through the gas flow path of the separator to the catalyst layer, and electronic conduction. It has a function as a path.

The material constituting the base material of the gas diffusion layer is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing flooding. The water repellent is not particularly limited, but fluorine-based high repellents such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include molecular materials, polypropylene, and polyethylene.

In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent agent on the catalyst layer side of the substrate. You may have.

The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

Examples of the water repellent used for the carbon particle layer include the same water repellents as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

The mixing ratio of the carbon particles to the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) by weight in consideration of the balance between water repellency and electronic conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

[Production method of membrane electrode assembly (MEA)]
A method for producing a membrane electrode assembly (MEA) is not particularly limited, and a conventionally known method can be used. For example, a method of joining a gas diffusion layer to a catalyst layer transferred or applied to an electrolyte membrane by hot pressing and drying it, or a microporous layer side of the gas diffusion layer (when a microporous layer is not included) First, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of a base material layer in advance and drying, and then bonding the gas diffusion electrodes to both sides of a solid polymer electrolyte membrane by hot pressing. Application and bonding conditions such as hot pressing can be adjusted as appropriate according to the type of polymer electrolyte (perfluorosulfonic acid type or hydrocarbon type) in the solid polymer electrolyte membrane or catalyst layer. Good.

<Fuel cell>
The membrane electrode assembly (MEA) described above can be suitably used for a fuel cell. That is, the present invention also provides a fuel cell using the electrolyte membrane electrode assembly (MEA) including the catalyst layer according to the present invention. Such a fuel cell can exhibit high power generation performance (particularly weight specific activity) and durability.

Here, the fuel cell includes a pair of a membrane electrode assembly (MEA), an anode side separator having a fuel gas flow path through which fuel gas flows, and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. And a separator. The fuel cell of the present invention is excellent in durability and can exhibit high power generation performance.

Hereinafter, an embodiment of a membrane electrode assembly (MEA) having a catalyst layer and a fuel cell according to the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited only to the following embodiments. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one. Further, in the case where the embodiments of the present invention are described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and duplicate descriptions are omitted.

FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

In the embodiment shown in FIG. 1, the separators (5a, 5c) are formed in an uneven shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

[Separator]
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

Furthermore, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies (MEAs) are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

The above-described PEFC and membrane electrode assembly (MEA) use a catalyst layer having excellent power generation performance and durability. Therefore, the PEFC and membrane electrode assembly (MEA) are excellent in power generation performance and durability.

The PEFC of this embodiment and the fuel cell stack using the same can be mounted on a vehicle as a driving power source, for example.

The fuel cell as described above exhibits excellent power generation performance. Here, the type of the fuel cell is not particularly limited. In the above description, the solid polymer fuel cell has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. Among them, it is particularly preferable to use as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

Further, the application application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The membrane electrode assembly including the catalyst layer according to the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

The effect of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. In the following examples, the operation was performed at room temperature (25 ° C.) unless otherwise specified. Unless otherwise specified, “%” and “part” mean “% by weight” and “part by weight”, respectively.

Example 1 Preparation of Catalyst Precursor A 1.27 g of sodium iodide (NaI) was mixed with 300 cc of ultrapure water whose temperature was controlled at 10 ° C., and stirred for 60 minutes with a magnetic stirrer. Thereafter, stirring was temporarily stopped, and 3 g of the following catalyst precursor 1 powder was added to prepare a precursor liquid. After adding perchloric acid (HClO ₄ ) so that the pH of the precursor solution was 3, stirring was further performed for 60 minutes. Then, it filtered using the filter paper and obtained catalyst precursor 2 powder. As catalyst precursor 1 powder, platinum catalyst (Pt / C): Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E-HT, platinum loading: 50% by weight) was used.

Thereafter, the filtered catalyst precursor 2 powder was added to 300 cc of ultrapure water, stirred for 30 minutes with a magnetic stirrer, and then filtered to wash the catalyst precursor 2 powder. After repeating this step twice, the filtered catalyst precursor 2 powder was dried at 60 ° C. for 30 minutes in a drying furnace to obtain catalyst precursor A in which platinum was covered with iodine.

Comparative Example 1 Preparation of Catalyst Precursor B A platinum catalyst (Pt / C) (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E-HT) was used as it was to prepare catalyst precursor B.

[Verification of iodine coating ratio / catalyst powder]
For the catalyst precursors A and B obtained in Example 1 and Comparative Example 1, the iodine coating ratio was evaluated by the following method. Specifically, for each catalyst precursor powder, carbon monoxide (CO) was adsorbed to verify how much of the Pt surface area was covered with iodine.

That is, in order to adsorb CO to each catalyst precursor, the pretreatment of the catalyst precursor was performed, and then the CO adsorption amount was measured. Pretreatment was performed as follows. First, each catalyst precursor was purged with a nitrogen atmosphere at 25 ° C. (room temperature) for 3 minutes, and then switched to a hydrogen atmosphere. Next, the ambient temperature was raised to 100 ° C. over 30 minutes, and the temperature was further maintained at that temperature for 30 minutes. Thereafter, the catalyst precursor was pretreated by switching to a nitrogen atmosphere and lowering the temperature to 50 ° C. over 30 minutes.

After the pretreatment, CO adsorption on the catalyst precursor was started in the following manner. That is, after the above pretreatment, carbon monoxide (CO) is applied to the catalyst precursor (30 mg) exposed in a nitrogen (N ₂ ) atmosphere at a pulse rate of 50 μl / time 20 times or more until equilibrium is reached. Supplied. Here, when CO is adsorbed on the platinum (Pt) surface, the CO concentration in the nitrogen atmosphere decreases. Therefore, by measuring the change in CO concentration in the nitrogen atmosphere with a mass spectrometer, it is possible to quantify how much CO has been adsorbed (CO adsorption rate). The CO adsorption amount (μl) was converted into the number of moles, and the CO chemical adsorption surface area (m ² / g_Pt) of Pt was determined on the assumption that one molecule of CO was adsorbed per Pt atom. The results are shown in Table 1 below. From Table 1 below, the CO chemisorption surface area of Pt of the catalyst precursor A of Example 1 to which iodine was added was 47 (= 20 × 100 /) of the surface area of the catalyst precursor B of Comparative Example 1 to which iodine was not added. 43) It turns out that it is%. From this, it is considered that 53 (= 100-47)% of the total surface area of platinum was coated.

Example 2 Formation of Catalyst Precursor Layer A 5 g of ultrapure water was added to 5 g of catalyst precursor A obtained in Example 1 and mixed with a hybrid mixer. An ionomer dispersion (Nafion (registered trademark) D2020, EW =) so that the mixing weight ratio (in terms of solid content) of the conductive carrier (carbon) in the catalyst precursor A and the electrolyte (ionomer) is 1: 1. (1000 g / mol, manufactured by DuPont) was added (mixture 1). Separately, a mixed solvent 1 having a mixing weight ratio of water and 1-propanol (NPA) of 8/2 was prepared. The mixed solvent 1 was added to the mixture 1 so that the solid content (Pt + carbon carrier + ionomer) was 21% by weight to prepare catalyst ink 1. The catalyst ink 1 was pulverized for 10 minutes at a rotation speed of 1500 rpm using a bead mill. At this time, beads (made by zirconia, diameter: 1.5 mm) were used. Thereafter, the pulverized catalyst ink 1 is again defoamed with a hybrid mixer, and then applied onto a transfer substrate (Teflon (registered trademark) sheet) using a screen printer, and dried at 80 ° C. for 10 minutes to obtain a catalyst precursor. Layer A (thickness: 10 μm) was formed.

Example 3: Formation of catalyst layer A A catalyst precursor layer A was formed in the same manner as in Example 2.

This catalyst precursor layer A was subjected to iodine removal treatment according to the following method.

1.5 g of sodium hydroxide (NaOH) was added to 300 ml of ultrapure water to prepare an aqueous sodium hydroxide solution (NaOH concentration: 0.125 mol / l).

The catalyst precursor layer A formed on the Teflon (registered trademark) sheet was immersed in this aqueous sodium hydroxide solution, and the aqueous solution was stirred with a magnetic stirrer for about 30 minutes. 25 drops (about 2.5 ml) of ethanol were put into this aqueous solution, and after stirring, evacuation was performed for 30 minutes (pressure after decompression: −0.09 MPa), and sodium hydroxide was permeated into the catalyst precursor layer A. . Next, this aqueous solution was warmed to 60 ° C., stirred for 1 hour, and then washed with pure water.

Further, the catalyst precursor layer A was taken out from the aqueous solution, immersed in 300 ml of ultrapure water, heated to 60 ° C. and stirred for 1 hour, and then evacuated for 30 minutes (pressure after decompression: −0.09 MPa). Further, the catalyst precursor layer A is taken out from the ultrapure water and washed with pure water to remove inorganic substances (iodine (I) or iodide ions (I ⁻ )) from the catalyst precursor layer A (particularly platinum) (catalyst). Layer A ′).

The catalyst layer A ′ was immersed in a perchloric acid solution (HClO ₄ 25 g + ultra pure water 300 g), warmed to 60 ° C., stirred at the same temperature for 1 hour, and then evacuated for 30 minutes (pressure after decompression: − 0.09 MPa). Next, the catalyst layer A ′ is taken out from the perchloric acid solution, immersed in pure water, heated to 60 ° C., stirred for 1 hour, and then evacuated for 30 minutes (pressure after decompression: −0.09 MPa). went. Further, the catalyst layer A ′ was taken out from pure water, washed with pure water, and then dried at 80 ° C. for 10 minutes to obtain a catalyst layer A (thickness: 10 μm). By this perchloric acid treatment, the ionomer sodium ion (Na ⁺ ) contained in the catalyst layer A was replaced with protons (H ⁺ ).

For the catalyst layer A thus obtained, the amount of iodine in the catalyst layer A was quantified using fluorescent X-rays (XRF) to verify whether iodine was removed from platinum. As a result, in the catalyst layer A, it was confirmed that 89.7% by weight of the iodine present in the catalyst precursor layer A before the removal of iodine was removed. In addition, the amount of iodine and platinum in the catalyst layer is quantified by X-ray fluorescence (XRF), and the iodine coverage [= (iodine amount) × 100 / (iodine amount + platinum amount)] is calculated from these values. As a result, it was 6%.

Comparative Example 2: Formation of catalyst layer B In Example 2, except that the catalyst precursor B was used instead of the catalyst precursor A, the catalyst layer B (thickness: 10 μm) was made of Teflon (thickness: 10 μm). It was formed on a (registered trademark) sheet.

[Verification of iodine coating ratio / catalyst layer]
Each of the catalyst precursor layer A obtained in Example 2 and the catalyst layer B obtained in Comparative Example 2 was subjected to the same procedure as in [Verification of iodine coverage / catalyst powder] performed for the catalyst precursor. The catalyst layer was verified for iodine coating. In addition, each catalyst layer is scraped off from a Teflon (registered trademark) sheet and used in place of the catalyst precursor in the above [Verification of Iodine Covering Ratio / Catalyst Powder]. Similarly to [Powder], the surface area was measured by CO chemical adsorption. The results are shown in Table 2 below. In the results of Table 2 below, the CO chemical adsorption surface area of Pt in the catalyst precursor layer A was slightly reduced with respect to the catalyst precursor A (that is, a large amount of iodine was adsorbed), but this difference is considered to be within the error range. Thus, it is considered that iodine is significantly present in the catalyst layer B of Comparative Example 2. Moreover, although the CO chemical adsorption surface area of Pt in the catalyst layer B of Comparative Example 2 is the same value as that of the catalyst precursor B of Comparative Example 1, this is because CO cannot pass iodine but ionomer can pass. It is guessed that.

Moreover, from the following Table 2, the CO chemical adsorption surface area of Pt of the catalyst precursor layer A of Example 2 is 40 (= 17 × 100/43)% of the surface area of the catalyst layer B of Comparative Example 2 to which iodine is not added. It turns out that it is. From this, it is considered that 60 (= 100-40)% of the total surface area of platinum was covered with iodine. On the other hand, in Example 3, it was confirmed that 89.7 wt% of the iodine present in the catalyst precursor layer A before the iodine removal was removed in the catalyst layer A. Therefore, in the catalyst layer A, it is considered that platinum is covered with iodine at a ratio of about 6 (= 60 × (1−0.897))%.

[Measurement of electrolyte (ionomer) coverage]
For the catalyst precursor layer A obtained in Example 2 above, the catalyst layer A obtained in Example 3 and the catalyst layer B obtained in Comparative Example 2, the catalyst metal was prepared according to the methods described in References 1 and 2 below. The electrolyte (ionomer) coverage on (Pt) was measured. References 1 and 2 are as follows:
Reference 1: International Publication No. 2012/053638 Reference 2: Hiroshi Iden, Atsushi Ohma, “An in situ technique for analyzing ionomer coverage in catalyst layers”, Journal of Electroanalytical Chemistry 693, (2013) 34-41.

Specifically, the coverage of the catalyst (ionomer coverage) by the electrolyte is calculated using measurement of the electric double layer capacity formed at the interface between the catalyst electrolyte (ionomer) and water. In calculating the coverage, the coverage is calculated from the ratio of the electric double layer capacity in the low humidification state (5% RH) to the high humidification state (100% RH). As the equipment used, an electrochemical measurement system HZ-3000 manufactured by Hokuto Denko Co., Ltd. and a frequency response analyzer FRA5020 manufactured by NF Circuit Design Block Co., Ltd. were used and the following measurement conditions were adopted.

First, each battery was heated to 30 ° C. with a heater, and the electric double layer capacity was measured in a state where nitrogen gas and hydrogen gas adjusted to the humidified state were supplied to the working electrode and the counter electrode, respectively. When measuring the electric double layer capacity, as shown in the above measurement conditions, the electric potential of the working electrode was oscillated at a frequency of 20 kHz to 10 mHz with an amplitude of ± 10 mV while maintaining at 0.45 V. Here, the real part and imaginary part of the impedance at each frequency are obtained from the response when the working electrode potential vibrates. Since the relationship between the imaginary part (Z ″) and the angular velocity ω (converted from the frequency) is expressed by the following formula 1, the reciprocal of the imaginary part is arranged with respect to −2 to the angular velocity, and Is extrapolated to obtain the electric double layer capacitance C _dl .

Such measurement was performed in a low humidified state (5% RH) and a high humidified state (100% RH). Furthermore, after deactivating the Pt catalyst by flowing nitrogen gas containing CO at a concentration of 1% by volume to the working electrode at a rate of 1 NL / min for 15 minutes or more, the electric gas in the high humidification and low humidification states as described above is obtained. The multi-layer capacity is similarly measured. The electric double layer capacity is shown in terms of a value per area (mF / cm ² ) of the catalyst layer.

Based on the electric double layer capacity in the high humidification and low humidification state calculated in this way, calculated from the ratio of the electric double layer capacity in the low humidification state (5% RH) to the high humidification state (100% RH), Ionomer coverage.

The results are shown in Table 3 below. From the results in Table 3 below, it can be seen that the ionomer coverage in the catalyst layer A of Example 3 is significantly lower than that of the catalyst layer B of Comparative Example 2. Therefore, it is considered that the coating of the catalyst metal by the electrolyte can be effectively suppressed by the method of the present invention.

Example 4: Preparation of MEA1 5 g of ultrapure water was added to 5 g of the catalyst precursor A obtained in Example 1, and mixed with a hybrid mixer. An ionomer dispersion (Nafion (registered trademark) D2020, EW =) so that the mixing weight ratio (in terms of solid content) of the conductive carrier (carbon) in the catalyst precursor A and the electrolyte (ionomer) is 1: 1. (1000 g / mol, manufactured by DuPont) was added (mixture 1). Separately, a mixed solvent 1 having a mixing weight ratio of water and 1-propanol (NPA) of 8/2 was prepared. The mixed solvent 1 was added to the mixture 1 so that the solid content (Pt + carbon carrier + ionomer) was 21% by weight to prepare a cathode catalyst ink 1.

The cathode catalyst ink 1 prepared above was pulverized for 10 minutes at a rotation speed of 1500 rpm using a bead mill. At this time, beads (made by zirconia, diameter: 1.5 mm) were used. Thereafter, the cathode catalyst ink 1 after pulverization is again defoamed with a hybrid mixer, and then applied to a transfer substrate (Teflon (registered trademark) sheet) by a screen printing method so that a platinum carrying amount becomes 0.35 mg / cm ^2. And dried at 80 ° C. for 15 minutes. Thereby, the cathode catalyst precursor layer 1 ′ (thickness: 10 μm) was formed on the transfer substrate.

In Example 3, the cathode catalyst layer 1 (thickness: 10 μm) was formed in the same manner as in Example 3 except that the cathode catalyst precursor layer 1 ′ thus obtained was used instead of the catalyst precursor layer A. did.

5 g of the catalyst precursor B obtained in Comparative Example 1 was added to 5 g of ultrapure water and mixed with a hybrid mixer. An ionomer dispersion (Nafion (registered trademark) D2020, EW =) so that the mixing weight ratio (in terms of solid content) of the conductive support (carbon) and the electrolyte (ionomer) in the catalyst precursor B is 1: 1. (1000 g / mol, manufactured by DuPont) was added (mixture 2). Separately, a mixed solvent 1 having a mixing weight ratio of water and 1-propanol (NPA) of 8/2 was prepared. The mixed solvent 1 was added to the mixture 2 so that the solid content (Pt + carbon carrier + ionomer) was 21% by weight to prepare an anode catalyst ink 1.

The anode catalyst ink 1 prepared above was pulverized for 10 minutes at a rotation speed of 1500 rpm using a bead mill. At this time, beads (made by zirconia, diameter: 1.5 mm) were used. Thereafter, the pulverized anode catalyst ink 1 is again defoamed with a hybrid mixer, and then applied to a transfer substrate (Teflon (registered trademark) sheet) by a screen printing method so that the amount of platinum supported is 0.35 mg / cm ^2. And dried at 80 ° C. for 15 minutes. Thereby, the anode catalyst layer 1 (thickness: 10 μm) was formed on the transfer substrate.

The cathode catalyst layer 1 (size: 5 cm × 5 cm) and the anode catalyst layer 1 (size: 5 cm × 5 cm) produced as described above were combined with a polymer electrolyte membrane (manufactured by Dupont, NAFION (registered trademark) XL, (Thickness: 27.5 μm). Subsequently, this was hot-pressed at 150 ° C. and 2 MPa for 10 minutes to obtain a membrane catalyst layer assembly (CCM: catalyst-coated membrane) 1. Both sides of the obtained membrane catalyst layer assembly (CCM) 1 were sandwiched between gas diffusion layers (24BC, manufactured by SGL Carbon Co., Ltd.) to obtain a membrane electrode assembly 1 (MEA1).

Comparative Example 3: Production of MEA 2 In the same manner as in Example 4, a cathode catalyst precursor layer 1 ′ and an anode catalyst layer 1 were formed on a transfer substrate.

The cathode catalyst layer 1 ′ (size: 5 cm × 5 cm) and the anode catalyst layer 1 (size: 5 cm × 5 cm) produced as described above were formed into a polymer electrolyte membrane (manufactured by Dupont, NAFION (registered trademark) XL). , Thickness: 27.5 μm). Next, this was hot-pressed at 150 ° C. and 2 MPa for 10 minutes to obtain a membrane catalyst layer assembly (CCM: catalyst-coated membrane) 2. Both surfaces of the obtained membrane catalyst layer assembly (CCM) 2 were sandwiched between gas diffusion layers (24BC, manufactured by SGL Carbon Co.) to obtain membrane electrode assembly 2 (MEA2). That is, Comparative Example 3 is the same as Example 4 except that iodine removal treatment and acid treatment were not performed in the formation of the cathode catalyst layer in Example 4.

Comparative Example 4: Production of MEA 3 To 5 g of the catalyst precursor B obtained in Comparative Example 1, 5 g of ultrapure water was added and mixed with a hybrid mixer. Ionomer dispersion (Nafion (registered trademark) D2020, DuPont) so that the mixing weight ratio (in terms of solid content) of the conductive support (carbon) in the catalyst precursor B and the electrolyte (ionomer) is 1: 1. (Mixture 2). Separately, a mixed solvent 1 having a mixing weight ratio of water and 1-propanol (NPA) of 8/2 was prepared. The mixed solvent 1 was added to the mixture 2 so that the solid content (Pt + carbon carrier + ionomer) was 21% by weight to prepare catalyst ink 3.

The catalyst ink 3 prepared above was applied to a transfer substrate (Teflon (registered trademark) sheet) by a screen printing method so that the amount of platinum supported was 0.35 mg / cm ² and dried at 80 ° C. for 15 minutes. The above operation was repeated twice to form a cathode catalyst layer 3 (thickness: 10 μm) and an anode catalyst layer 3 (thickness: 10 μm) on the transfer substrate.

The cathode catalyst layer 3 and the anode catalyst layer 3 (each size: 5 cm × 5 cm) produced as described above were formed into a polymer electrolyte membrane (manufactured by Dupont, NAFION (registered trademark) XL, thickness: 27.5 μm). Arranged on both sides. Next, this was hot-pressed at 150 ° C. and 2 MPa for 10 minutes to obtain a membrane catalyst layer assembly (CCM: catalyst-coated membrane) 3. Both surfaces of the obtained membrane catalyst layer assembly (CCM) 3 were sandwiched between gas diffusion layers (24BC, manufactured by SGL Carbon Co., Ltd.) to obtain a membrane electrode assembly 3 (MEA3).

[Evaluation of ORR activity and surface area]
With respect to MEAs 1 to 3 obtained in Example 4 and Comparative Examples 3 to 4, battery performance (ORR activity) and electrochemical effective surface area (ECA) were evaluated. Cell performance (ORR activity) and electrochemical effective surface area (ECA) were published by the Fuel Cell Practical Use Promotion Council (FCCJ). (Proposal (January 2011)) III-3-2 and III-3-4.

Specifically, the fuel cell is maintained at 80 ° C., oxygen gas conditioned to 100% RH is passed through the cathode, and hydrogen gas conditioned to 100% RH is passed through the anode, and the current density is 1.0 A. The electronic load was set to be / cm ² and held for 15 minutes. Thereafter, the current density was gradually reduced until the cell voltage became 0.9 V or higher. At this time, each current density was held for 15 minutes to obtain the relationship between the current density and the potential. Then, using the electrochemical effective surface area (ECA) obtained under 100% RH conditions, the current density per catalyst surface area (“ORR area specific activity (Is) (μA / cm ² _Pt)” in the table below) and The current density per weight of platinum (“ORR mass specific activity (Im) (A / g_Pt)” in the table below) was converted to a current density at 0.9 V.

The electrochemical effective surface area (ECA) is obtained by using the electrochemical measurement system HZ-3000, sweeping the potential of the measurement object under the following conditions, and the amount of electricity and electrode due to proton adsorption on the catalyst Pt. From the weight of platinum, the electrochemical effective surface area (ECA) (m ² / g_Pt) was calculated.

Results are shown in Table 4 below. From the results shown in Table 4 below, the MEA 1 of Example 4 has a catalyst surface area and current density per platinum weight (ORR area ratio) as compared with MEA 2 of Comparative Example 3 that does not remove iodine and MEA 3 of Comparative Example 4 without treatment. It can be seen that both activity and ORR mass specific activity) are significantly higher. Therefore, the MEA having a catalyst layer obtained by the method of the present invention is expected to exhibit excellent power generation performance.

Further, from comparison between MEA 1 of Example 4 having catalyst layer A of Example 3 and MEA 3 of Comparative Example 4 having catalyst layer B of Comparative Example 2, a high reverse phase relationship is observed in ionomer coverage and ORR activity. . For this reason, the difference in ORR activity (especially ORR area specific activity) originates from the difference in ionomer coverage, and it is considered that the performance of MEA (and hence fuel cell) can be improved by suppressing the coating of the catalytic metal by the ionomer. The

[IV evaluation]
For the MEAs 1 to 3 obtained in Example 4 and Comparative Examples 3 to 4, power generation test evaluation was performed under the following Wet conditions and Dry conditions. Under the following conditions, the load current density was swept in the range of 0 to 2.0 A / cm ² to obtain a current potential (IV) curve. The power generation test evaluation results (IV curves) under the wet and dry conditions are shown in FIGS. 2 and 3, respectively. 2 and 3, it can be seen that the MEA 1 of Example 4 can maintain a high potential even in a high current density region as compared with the MEA 2 of Comparative Example 3 that does not remove iodine and the MEA 3 of Comparative Example 4 without any treatment. In addition, the above features are observed especially under Dry conditions.

Example 5: Preparation of catalyst precursor C Catalyst precursor 2 powder was prepared according to the following method. That is, ² g of carbon support (Ketjen Black (registered trademark) KetjenBlackEC300J, average particle size: 40 nm, BET specific surface area: 800 m ² / g, manufactured by Lion Corporation) is added to 500 mL of 0.5 M HNO ₃ solution in a beaker. The mixture was added and stirred and mixed with a stirrer at 300 rpm for 30 minutes at room temperature (25 ° C.). Subsequently, a carbon support was obtained by performing a heat treatment at 80 ° C. for 2 hours under stirring at 300 rpm. Then, after filtering the carbon support, it was washed with ultrapure water. The above filtration and washing operations were repeated a total of 3 times. After the carbon support was dried at 60 ° C. for 24 hours, an acid-treated carbon support A (BET specific surface area = 850 m ² / g, average particle diameter = 40 nm) was obtained.

Next, 0.2 g of the acid-treated carbon carrier A prepared above was added to 100 ml of ultrapure water placed in a beaker, and sonication was performed for 15 minutes to obtain a carrier suspension A. The carrier suspension A was continuously stirred at 150 rpm at room temperature (25 ° C.) until it was added to the catalyst precursor particles.

To 1000 ml ultrapure water placed in a beaker, 0.36 mL of 0.105 M cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution (9 mg in Co amount), 1.32 M chloroplatinic acid (H ₂ [PtCl ₆ ]. 6H ₂ O) aqueous solution 0.13 mL (91 mg in terms of platinum) was added. This was stirred and mixed with a stirrer at room temperature (25 ° C.) for 5 minutes to prepare a mixed solution.

Separately, 1.2 g of trisodium citrate dihydrate and 0.4 g of sodium borohydride were dissolved in 100 mL of ultrapure water to prepare a reducing agent solution.

100 mL of the reducing agent solution prepared above is added to the mixed solution obtained above, stirred and mixed with a stirrer at room temperature (25 ° C.) for 30 minutes, and reduced and precipitated to obtain catalyst precursor particles (Pt—Co mixed). A solution containing particles) was obtained. Next, the carrier suspension A containing 0.2 g of the acid-treated carbon carrier A was added to this solution, and stirred and mixed with a stirrer at room temperature (25 ° C.) for 48 hours to carry the catalyst precursor particles on the carrier. . Thereafter, the catalyst precursor particle-supported carrier was filtered and washed with ultrapure water. The filtration and washing operations were repeated a total of 3 times, followed by filtration to obtain a catalyst particle-supporting carrier. The catalyst particle-supported carrier was dried at 60 ° C. for 12 hours, and then a heat treatment step was performed at 600 ° C. for 60 minutes in an argon atmosphere. Thereby, the catalyst precursor 2 was obtained. The catalyst particle 2 support concentration (supported amount) of the catalyst precursor 2 was 33% by weight (platinum supported amount: 30% by weight, cobalt supported amount: 3% by weight) with respect to the support. The supported concentration was measured by ICP analysis. The same applies hereinafter.

In Example 1, a catalyst precursor C was obtained in the same manner as in Example 1 except that the catalyst precursor 2 powder prepared above was used instead of the catalyst precursor 1 powder (Pt / C). .

Comparative Example 5: Preparation of catalyst precursor D Catalyst precursor 2 (platinum supported amount: 30% by weight, cobalt supported amount: 3% by weight) was prepared in the same manner as in Example 5 above. This catalyst precursor 2 was used as it was to obtain a catalyst precursor D.

[Elution test of catalytic metal components with or without iodine coating]
For the catalyst precursors C and D obtained in Example 5 and Comparative Example 5, elution of the catalyst metal component was evaluated by the following method. Specifically, each catalyst precursor was immersed in 0.5 mol / L of a perchloric acid (HClO ₄ ) aqueous solution so as to have the same conductive carrier (carbon) weight, and left for 30 hours. After standing for a predetermined time, Pt and Co dissolved in the perchloric acid aqueous solution were quantified by ICP-MS.

The results are shown in Table 5 below. From the results of Table 5, it can be seen that the catalyst precursor C coated with iodine has a suppressed elution amount of both Pt and Co compared to the uncoated catalyst precursor D. From this result, it is considered that the catalyst precursor of the present invention can suppress deterioration due to catalyst elution when stored. Moreover, it is thought that the same effect is acquired by also covering the catalyst layer formed using the catalyst precursor of this invention with an iodine.

1 ... Polymer electrolyte fuel cell (PEFC),
2 ... Solid polymer electrolyte membrane,
3 ... Catalyst layer,
3a ... anode catalyst layer,
3c ... cathode catalyst layer,
4a ... anode gas diffusion layer,
4c ... cathode gas diffusion layer,
5, ... Separator,
5a ... anode separator,
5c ... cathode separator,
6a ... anode gas flow path,
6c ... cathode gas flow path,
7: Refrigerant flow path,
10: Membrane electrode assembly (MEA).

Claims

Preparing a catalyst precursor 1 comprising a platinum-containing catalyst metal supported on a conductive carrier;
The catalyst precursor 1 is coated with an inorganic substance adsorbed on a platinum-containing catalyst metal to prepare a catalyst precursor 2,
The catalyst precursor 2 is mixed with an electrolyte to form a catalyst precursor layer, and the inorganic substance is removed from the catalyst precursor layer.
A method for producing a catalyst layer.
The method according to claim 1, wherein the catalyst precursor 1 is coated with the inorganic substance under acidic conditions.
The method according to claim 1 or 2, wherein the inorganic substance is at least one selected from the group consisting of iodine compounds, bromine compounds and carbon monoxide.
The method according to claim 3, wherein the inorganic substance is at least one of an iodine compound and a bromine compound, and the inorganic substance is removed from the catalyst precursor layer by a haloform reaction.
The method according to claim 4, wherein the catalyst precursor layer is acid-treated after removing the inorganic substance.
The method according to any one of claims 1 to 5, wherein the inorganic substance is selected from compounds that can be ionized in an aqueous solution.
A catalyst layer comprising a catalyst and an electrolyte in which a platinum-containing catalyst metal is supported on a conductive support, and the platinum being coated with an inorganic substance that adsorbs to the platinum-containing catalyst metal in a proportion of more than 0% and less than 10%.
A catalyst precursor in which a platinum-containing catalyst metal coated with an inorganic substance adsorbed on a platinum-containing catalyst metal is supported on a conductive carrier.
The catalyst precursor according to claim 8, wherein the inorganic substance is at least one selected from the group consisting of an iodine compound, a bromine compound, and carbon monoxide.
The catalyst precursor according to claim 8 or 9, wherein the inorganic substance is selected from compounds that can be ionized in an aqueous solution.
A catalyst precursor layer comprising the catalyst precursor according to any one of claims 8 to 10 and an electrolyte.
The catalyst precursor 1 comprising a platinum-containing catalyst metal supported on a conductive carrier is prepared, and the catalyst precursor 1 is mixed with a coating that adsorbs the platinum-containing catalyst metal. A method for producing the catalyst precursor according to claim 1.
The method according to claim 12, wherein the catalyst precursor 1 and the coating agent are mixed under acidic conditions.
The method according to claim 12 or 13, wherein the coating agent is at least one selected from the group consisting of iodine compounds, bromine compounds and carbon monoxide.
The method according to any one of claims 12 to 14, wherein the coating agent is ionized in an aqueous solution.