JP2015195193A - Anode electrode material for fuel battery, method of manufacturing the same, electrode for fuel battery, membrane electrode assembly, and solid polymer type fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anode electrode material for a fuel battery suitable for manufacturing an anode electrode of a fuel battery of low temperature operation type.SOLUTION: An anode electrode material for a fuel battery includes a conductive auxiliary material made from at least one kind selected from a fabric carbon and chain-coupled carbon particle whose surface has a graphite structure, a titanium oxide carrier born by the conductive auxiliary material, and an electrode catalyst particle being dispersion-born by the titanium oxide carrier among the conductive auxiliary material and the titanium oxide carrier.

Description

  The present invention relates to a fuel cell anode electrode material and a method for producing the same, a fuel cell electrode, and a polymer electrolyte fuel cell.

Since fuel cells can efficiently convert the chemical energy of hydrogen into electrical energy, the spread of power generation systems using fuel cells is expected. Among the fuel cells, in particular, a polymer electrolyte fuel cell (hereinafter, sometimes referred to as “PEFC”) using a solid polymer membrane as an electrolyte has an operating temperature compared with around 80 ° C. Because of its low temperature, it has been introduced as a small-scale fixed power source for in-vehicle use, home use, and the like. In the polymer electrolyte fuel cell, electric power can be taken out by the following electrochemical reaction.
Anodic reaction: 2H ₂ → 4H ⁺ + 4e ⁻ (reaction 1)
Cathode reaction: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (reaction 2)
Total reaction: 2H ₂ + O ₂ → 2H ₂ O

In PEFC, a membrane electrode assembly (Membrane Electrode Assembly; hereinafter, sometimes referred to as “MEA”) in which a pair of electrodes are arranged on both surfaces of a solid polymer electrolyte membrane is generally used as a gas flow path. It has a structure sandwiched between the formed separators.
An electrode for a fuel cell (especially an electrode for PEFC) is generally composed of an electrode catalyst layer composed of an electrode material having an electrocatalytic activity and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electronic conductivity. The As an electrode material for PEFC, a material in which noble metal particles are dispersed and supported on the surface of a carrier made of a particulate or fibrous carbon-based material is widely used (for example, Patent Documents 1 and 2).

By the way, since the electrolyte membrane of PEFC is acidic (pH = 0-3), the electrode material of PEFC is used in an acidic atmosphere. Further, the cell voltage during normal operation is 0.4 to 1.0 V, but it is known that the cell voltage rises to 1.5 V when starting and stopping. The state of the cathode and the anode under such PEFC operating conditions is a region in which the carbon-based material as a carrier is decomposed as carbon dioxide (CO ₂ ) at the cathode. Therefore, at the cathode, a reaction occurs in which the carbon-based support is electrochemically oxidized and decomposed into CO ₂ (see Non-Patent Document 1). As a result, the carbon-based support is corroded and the noble metal particles that are catalytically active components are dropped off. There is a problem of doing.

  In addition to the cathode, not only the anode but also the fuel gas shortage at the initial stage of operation causes a voltage drop or concentration polarization at that part, resulting in a locally opposite potential and electrochemical oxidative decomposition of carbon. A reaction may occur.

The carbon-based material used as a support for the electrode catalyst particles is electrochemically oxidatively corroded as described above, and becomes a problem particularly when the PEFC is started and stopped or operated for a long time. In order to improve the durability of the carbon-based material against oxidation, there is a method of increasing the crystallization by heat treatment at a high temperature, but the durability against oxidation is still insufficient. Therefore, it is desired to develop a fuel cell electrode that is stable under PEFC operating conditions.
In response to such a demand, the inventors of the present application disclose an electrocatalyst material in which noble metal particles are dispersed in a tin oxide support instead of a carbon-based material, and production thereof. Since this electrocatalyst material is thermodynamically stable under the operating conditions of the PEFC cathode, the cathode produced using the electrocatalyst material can generate power for a long time without being oxidatively corroded.

Japanese Patent Laid-Open No. 2005-87993 Japanese Patent No. 368364 Japanese Patent No. 532110

L. M. Roen, 2 others, “Electrocatalytic Corrosion of Carbon Support in MCFC (Carbon Support in PEMFC Cathes)” and Solid-State letters) ", 2004, Vol. 7 (1), A19-A22.

  However, although the fuel cell electrode material using a tin oxide support has high durability, there is a problem that the tin oxide itself is reduced under a reducing atmosphere in the anode, and the performance deteriorates. In addition, the electrode performance of a fuel cell electrode manufactured using the electrode material is often inferior to that of a fuel cell electrode manufactured using a conventional electrode material using a carbon-based carrier. As a main cause, it is generally predicted that an electron conductive oxide has a lower electron conductivity than a carbon-based carrier.

  Under such circumstances, the object of the present invention is to combine the excellent durability to electrochemical oxidation caused by the electron conductive oxide with the excellent electronic conductivity caused by the carbon-based material, and in the PEFC anode. An object of the present invention is to provide an anode electrode material for a fuel cell that can be used stably even in a reducing atmosphere. Furthermore, it aims at providing the electrode for fuel cells containing the said anode electrode material for fuel cells, a membrane electrode composite_body | complex, and a polymer electrolyte fuel cell.

  As a result of intensive studies to solve the above problems, the present inventor has found that the following inventions meet the above object, and have reached the present invention.

That is, the present invention relates to the following inventions.
<1> One or more kinds of conductive auxiliary materials selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface, a titanium oxide carrier supported on the conductive auxiliary material, the conductive auxiliary material, A fuel cell anode electrode material comprising electrode catalyst particles dispersedly supported on the titanium oxide carrier among the titanium oxide carriers.
<2> The anode electrode material for a fuel cell according to <1>, wherein the conductive auxiliary material is vapor grown carbon fiber (VGCF).
<3> The anode electrode material for a fuel cell according to <1> or <2>, wherein the titanium oxide support is made of niobium-doped titanium oxide doped with 0.1 to 20 mol% of niobium.
<4> The fuel cell anode electrode material according to any one of <1> to <3>, wherein the titanium oxide support is supported on the conductive auxiliary material such that a part of the conductive auxiliary material is exposed.
<5> The anode electrode material for a fuel cell according to any one of <1> to <4>, wherein the electrode catalyst particles are electrode catalyst particles made of an alloy containing Pt and Pt having an average particle diameter of 1 to 30 nm.
<6> A fuel cell electrode comprising the fuel cell electrode material according to any one of <1> to <5> and a proton conductive electrolyte material, wherein the conductive auxiliary material is in contact with each other to form a conductive path. .
<7> A membrane / electrode assembly having a solid polymer electrolyte membrane, a cathode joined to one surface of the solid polymer electrolyte membrane, and an anode joined to the other surface of the solid polymer electrolyte membrane. A membrane electrode assembly in which the anode is an electrode for a fuel cell according to <6>.
<8> A polymer electrolyte fuel cell comprising the membrane electrode assembly according to <7>.

Moreover, the other aspect of this invention concerns on the manufacturing method of the anode electrode material for fuel cells of the following this invention.
<1a> A method for producing an anode electrode material for a fuel cell, comprising the following steps (1) to (3).
(1) A step of supporting a titanium oxide carrier on a conductive auxiliary material comprising at least one selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface. (2) The conductive material supported on the titanium oxide carrier. A step of immersing an auxiliary material in a solution containing an electrode catalyst precursor and supporting the electrode catalyst particles or the electrode catalyst precursor on the titanium oxide support (3) The electrode catalyst particles or the electrode catalyst supported on the titanium oxide support Step of activating precursor <2a> The fuel cell electrode according to <1a>, wherein the method of supporting the titanium oxide support in step (1) is a method of hydrolyzing titanium alkoxide, which is a precursor of the titanium oxide support. Material manufacturing method.
<3a> The method for producing an electrode material for a fuel cell according to <1a> or <2a>, wherein the method for supporting the electrode catalyst precursor in the step (2) is a colloid method.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode material for fuel cells which has the outstanding durability to the electrochemical oxidation resulting from a titanium oxide support | carrier, and the outstanding electronic conductivity resulting from a carbonaceous material is provided. A polymer electrolyte fuel cell including a membrane electrode assembly using a fuel cell electrode containing the electrode material has excellent durability to electrochemical oxidation and can generate power for a long period of time. .

It is a schematic diagram of the electrode material for fuel cells of this invention. It is a cross-sectional schematic diagram of the membrane electrode assembly of this invention. It is a conceptual diagram which shows the typical structure of the polymer electrolyte fuel cell of this invention. It is a FE-SEM image of the electrode material for fuel cells of Experiment example 1 (electrode catalyst particle unsupported), (a) is 600 degreeC baking, (b) is 300 degreeC baking, (c) is no baking. 3 is an XRD profile of a fuel cell electrode material (non-supported electrode catalyst particles) of Experimental Example 1; 3 is an evaluation result of measurement of a BET specific surface area of an electrode material for fuel cells (non-supported electrode catalyst particles) of Experimental Example 1. Is a diagram showing the relationship of the TiO ₂ loading of the BET specific surface area of the fuel cell electrode material (electrode catalyst particles unsupported). A FE-SEM image of the TiO ₂ loading of 10 wt% of the fuel cell electrode material (electrode catalyst particles unsupported, 300 ° C. calcination), (a), (b ) is another field, respectively. A FE-SEM image of the TiO ₂ loading of 20 wt% of the fuel cell electrode material (electrode catalyst particles unsupported, 300 ° C. calcination), (a), (b ) is another field, respectively. A FE-SEM image of the TiO ₂ loading of 50 wt% of the fuel cell electrode material (electrode catalyst particles unsupported, 300 ° C. calcination), (a), (b ) is another field, respectively. Supporting Pt catalyst particles in a colloidal method, a FE-SEM image of the TiO ₂ loading of 10 wt% of the fuel cell electrode material is (a) a low magnification image, (b) high magnification image. Supporting Pt catalyst particles in a colloidal method, a FE-SEM image of the TiO ₂ loading of 20 wt% of the fuel cell electrode material is (a) a low magnification image, (b) high magnification image. Supporting Pt catalyst particles in a colloidal method, a FE-SEM image of the TiO ₂ loading of 50 wt% of the fuel cell electrode material is (a) a low magnification image, (b) high magnification image. Supporting Pt catalyst particles acetylacetonate method, a FE-SEM image of the TiO ₂ loading of 10 wt% of the fuel cell electrode material is (a) a low magnification image, (b) high magnification image. Supporting Pt catalyst particles acetylacetonate method, a FE-SEM image of the TiO ₂ loading of 20 wt% of the fuel cell electrode material is (a) a low magnification image, (b) high magnification image. Supporting Pt catalyst particles acetylacetonate method, a FE-SEM image of the TiO ₂ loading of 50 wt% of the fuel cell electrode material is (a) a low magnification image, (b) high magnification image. It is an evaluation result of the electrochemical effective surface area (ECSA) of the electrode material for fuel cells which supported the Pt catalyst by the colloid method or the acetylacetonate method. It is a mass activity evaluation result of the electrode material for fuel cells which carried Pt catalyst by the colloid method or the acetylacetonate method. It is an evaluation result of Specific activity of the electrode material for fuel cells which carried Pt catalyst by the colloid method or the acetylacetonate method.

  Hereinafter, the present invention will be described in detail with reference to examples and the like, but the present invention is not limited to the following examples and the like, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In the present specification, “to” is used as an expression including numerical values or physical quantities before and after.

<1. Fuel Cell Electrode Material of the Present Invention>
The anode electrode material for fuel cell of the present invention (hereinafter sometimes referred to as “electrode material of the present invention”) is one or more selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface. A conductive auxiliary material comprising: a titanium oxide carrier supported on the conductive auxiliary material; and electrocatalyst particles dispersedly supported on the titanium oxide carrier among the conductive auxiliary material and the titanium oxide carrier. To do.

In the electrode material of the present invention, the electrocatalyst fine particles supported on the titanium oxide support are hardly in contact with the conductive support material of the carbon-based material, so that the electrochemical oxidation generated when the electrode catalyst fine particles are supported on the conventional carbon-based support It is possible to avoid the deterioration of the electrode performance due to the corrosion of the carbon-based support due to. The conductive auxiliary material constituting the electrode material of the present invention has good mutual contact and is a fibrous carbon or chain-connected carbon particle having excellent electronic conductivity. Therefore, the electrode material is used for a fuel cell. When the electrode is configured, the conductive auxiliary materials come into contact with each other to form a low-resistance conductive path, and the electrode has excellent electron conductivity.
Thus, the electrode material of the present invention has both excellent durability to electrochemical oxidation caused by the titanium oxide carrier and excellent electronic conductivity caused by the carbon-based material. Therefore, the fuel cell electrode formed of the electrode material exhibits excellent electrode performance even when used as an anode, has high durability, and can generate power for a long period of time.

  In addition, in the conventional fuel cell electrode catalyst material comprising a particulate electron conductive oxide as a carrier, the particulate electron conductive oxide is a carrier for electrode catalyst fine particles, and the fuel cell electrode. Since it has a role as a skeleton, particles having an average particle size of about 0.1 to 5 μm are used. Since the electron conductive oxide having such a particle size is inferior to the carbon-based material in terms of electron conductivity, it is compared with the fuel cell electrode material using a carbon material having the same particle size as the carrier. Increases electrical resistance. Furthermore, since the electron conductive oxide having the particle size is a secondary particle having an average particle size of about 0.1 to 5 μm in which primary particles of about several nm to several tens of nm are aggregated, As a result, an electrical resistance due to the fuel cell is generated, which is also a major cause of an increase in the electrical resistance of the fuel cell electrode. For this reason, in such a carrier, it is usual to use tin oxide having high electron conductivity as the electron conductive oxide. Titanium oxide, which has poor electron conductivity compared to tin oxide, has electron conductivity. It could not be practically used as an oxide support.

  On the other hand, in the fuel cell catalyst material of the present invention, since the conductive auxiliary material composed of fibrous carbon or chain-connected carbon particles plays a role as the skeleton of the fuel cell electrode, the electrode catalyst fine particles are supported. The particle size (in the case of a thin film) of the electron conductive oxide carrier (titanium oxide carrier) can be reduced. Therefore, in the fuel cell electrode formed using the fuel cell catalyst material of the present invention, the electrical resistance due to the electron conductive oxide carrier can be reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing a typical configuration of the fuel cell electrode material of the present invention. As shown in FIG. 1, a fuel cell electrode material 1 according to the present invention includes a conductive auxiliary material 2, a particulate titanium oxide carrier 3a supported on the conductive auxiliary material 2, and a titanium oxide carrier 3a. The electrode catalyst fine particles 3b are selectively dispersed and supported.

  The conductive auxiliary material 2 is a carbon-based conductive auxiliary material made of fibrous carbon or chain-connected carbon particles having a graphite structure on the surface. Fibrous carbon and chain-linked carbon particles have good mutual contact and excellent electronic conductivity. Therefore, when a fuel cell electrode is formed using the fuel cell electrode material 1, a conductive path is formed. In the present specification, the “conductive auxiliary material” means a material that is included in the fuel cell electrode material and has a role of improving electronic conductivity when the fuel cell electrode is formed. The conductive auxiliary material 2 has excellent electronic conductivity derived from the carbon-based material, and can carry the titanium oxide carrier 3a. Since the fuel cell electrode material 1 uses such a conductive auxiliary material 2, when the fuel cell electrode is formed, the adjacent conductive auxiliary material 2 can be continuously in contact with each other, and the fuel cell electrode material 1 A space capable of smoothly diffusing gas such as hydrogen and oxygen and discharging water (steam) can be formed.

  Fibrous carbon is a hollow or fibrous carbon material, and specifically includes so-called carbon nanotubes (CNT) and carbon nanofibers. In the present invention, “carbon nanotubes” include not only single-walled CNTs but also double-walled CNTs, multi-walled CNTs, and mixtures thereof.

Here, in order to achieve both electrical conductivity and gas diffusibility in the electrode when the fuel cell electrode is formed, it is preferable that the fibrous carbon has a diameter of 2 nm to 20 μm and a total length of 0.03 to 500 μm. is there.
Of the hollow or fibrous carbon materials, as represented by carbon nanotubes, the diameter is 100 nm or less, or the diameter is 100 such as vapor grown carbon fiber (VGCF). In many cases, the diameter of the carbon material is about 1 to 20 nm, such as activated carbon fiber, but there is no clear definition about the length and the name of these carbon materials. These are collectively referred to as fibrous carbon.

  Further, among the fibrous carbons, if the carbon surface has a graphite structure, it is chemically stable and the surface area is small, so that the electrode catalyst fine particles are hardly supported, and most of the electrode catalyst fine particles are the titanium oxide support. Selectively supported. Therefore, the ratio of the electrode catalyst fine particles that directly contact with the fibrous carbon out of all the electrode catalyst fine particles is reduced, and the fibrous carbon is prevented from electrochemical oxidative corrosion when used as a fuel cell electrode. Is done. Examples of the fibrous carbon having a graphite structure on the surface include single-walled CNT, double-walled CNT, multi-walled CNT, and vapor grown carbon fiber (VGCF), and those having high crystallinity and high purity are preferable. Among these, VGCF is particularly preferable.

The chain-linked carbon particles are particles in which carbon particles having a primary particle size of 30 to 300 nm are chain-connected, and have high electron conductivity derived from carbon. In order to achieve both electrical conductivity and gas diffusibility in the electrode when the fuel cell electrode is formed, it is preferable that the chain-connected carbon particles have an aspect ratio of 5 or more, and more preferably the aspect ratio. The ratio is 10 or more.
Among the chain-linked carbon particles, acetylene black (AB) produced by thermal decomposition of acetylene is preferable. Since acetylene black is more graphitized than ordinary carbon black, the effect that electrode catalyst fine particles are not easily supported can be expected as in the case of fibrous carbon whose surface has a graphite structure. In addition, since acetylene black is directly generated from acetylene gas and does not contain impurities such as iron ions that cause deterioration of the electrolyte membrane in PEFC, it is suitable as a conductive auxiliary material used in PEFC.

(Titanium oxide carrier)
Titanium oxide constituting the titanium oxide support 3a has both sufficient durability and electron conductivity in both anode conditions and cathode conditions of a fuel cell (in particular, a polymer electrolyte fuel cell). One feature of the fuel cell electrode material of the present invention is that titanium oxide, which is an electron conductive oxide, can be used stably even in a reducing atmosphere at the anode of PEFC. The PEFC cathode conditions are conditions at the cathode during normal operation of the PEFC, which means a temperature (room temperature to about 150 ° C.) and a condition in which a gas containing oxygen such as air is supplied (oxidizing atmosphere). The conditions are conditions in the anode during normal operation of the PEFC, and mean conditions under which the temperature is room temperature to about 150 ° C. and a fuel gas containing hydrogen is supplied (reducing atmosphere).

Titanium (Ti) is an element, and the oxide TiO ₂ is thermodynamically stable and does not reduce under PEFC anode conditions. Furthermore, an oxide mainly composed of titanium oxide can be used as a cathode because TiO ₂ as an oxide is thermodynamically stable not only under PEFC anode conditions but also under cathode conditions.
Note that the oxide mainly composed of titanium oxide is inferior in electronic conductivity to the oxide mainly composed of tin oxide. However, as described above, the electrode material of the present invention is used as a skeleton of an electrode for a fuel cell. Since the role of the conductive auxiliary material made up of fibrous carbon or chain-connected carbon particles plays a role, the particle size (thickness in the case of a thin film) of the titanium oxide carrier on which the electrode catalyst fine particles are supported can be reduced. An oxide mainly composed of titanium can also be suitably used.

In the present invention, the “titanium oxide carrier” is a particulate or thin film carrier made of an oxide mainly composed of titanium oxide, and the carrier itself is supported on a conductive auxiliary material, and on the surface of the carrier. It means what can carry electrode catalyst particles. A suitable particle size (film thickness in the case of a thin film) of the titanium oxide carrier will be described later.
The “oxide mainly composed of titanium oxide” means (A) titanium oxide, and (B) oxide in which titanium oxide is doped with another element, and titanium oxide as a base oxide is 80 mol%. The oxide contained above is meant.

  The element to be doped is an element having a higher valence than Ti, and specifically includes Sb, Nb, Ta, W, In, V, Cr, Mn, and Mo. Among these, niobium-doped titanium oxide doped with 0.1 to 20 mol% of niobium (Nb) is particularly preferable in that the electronic conductivity of titanium oxide can be particularly improved.

In the fuel cell electrode material 1 of the present invention, since the conductive auxiliary material 2 made of fibrous carbon or chain-connected carbon particles plays a role as the skeleton of the fuel cell electrode, the electron conductivity is higher than that of the carbon-based material. Thus, it is preferable that the small titanium oxide support 3a has a smaller particle size within a range in which the electrode catalyst fine particles 3b can be dispersedly supported. The titanium oxide carrier 3a may be either primary particles or secondary particles. However, the titanium oxide carrier 3a is preferably primary particles. This is because when the titanium oxide support 3a is a secondary particle, the electrical resistance is increased due to the grain boundary resistance between the primary particles constituting the secondary particle.
The titanium oxide carrier 3a is preferably a particulate titanium oxide carrier having an average particle diameter of 3 to 200 nm, and more preferably a titanium oxide carrier having an average particle diameter of 5 to 40 nm which is substantially primary particles. From the viewpoint of the conductivity of the fuel cell electrode material 1, the particulate titanium oxide support 3 a is not concentrated, and a part of the conductive auxiliary material 2 is exposed, and the conductive auxiliary material 2 and other conductive auxiliary materials are exposed. It is preferable that the titanium oxide support 3a is dispersed and supported to the extent that the direct contact with the substrate 2 is not hindered.
The “average particle diameter of the titanium oxide carrier” can be obtained from the average value of the particle diameters of any of the titanium oxide carriers (20) examined from an electron microscope image.

In FIG. 1, the titanium oxide carrier 3 a is a particulate titanium oxide carrier dispersedly supported on the conductive auxiliary material 2, but is not limited thereto, and the titanium oxide carrier 3 a may be supported on the conductive auxiliary material 2. Other forms are possible. As another form, for example, a form in which the conductive auxiliary material 2 is covered with a thin-film titanium oxide carrier can be mentioned. The thin film titanium oxide carrier can be formed, for example, by covering the conductive auxiliary material with a titanium oxide carrier by a dry method such as vapor deposition.
From the viewpoint of the conductivity of the electrode material 1 for fuel cells, the film thickness of the thin film titanium oxide support is preferably as thin as possible within the range where it can be formed. That is, one of the preferred embodiments of the titanium oxide carrier in the fuel cell electrode material of the present invention is that the titanium oxide carrier is a thin-film titanium oxide carrier having an average film thickness of 2 to 50 nm. In this aspect, a part or the whole is supported so as to cover the conductive auxiliary material. If the titanium oxide carrier has an average film thickness of 2 to 50 nm, the electrical resistance due to the titanium oxide carrier is not substantially a problem, so that the exposed portions of the conductive auxiliary material do not need to contact each other. The “average film thickness of the thin film titanium oxide support” can be obtained from the average value of the thicknesses (5 points) at arbitrary positions examined from the cross-sectional electron microscope image in the thickness direction of the thin film titanium oxide support.

It is preferable that the titanium oxide carrier has a large surface property within a range in which the mechanical strength can be maintained in order to increase the amount of the electrode catalyst supported. Specifically, the BET specific surface area is preferably 20 m ² / g or more, more preferably 40 m ² / g or more, and further preferably 60 m ² / g or more.

  In addition, the amount of the titanium oxide carrier supported depends on various conditions such as the physical properties of the titanium oxide carrier such as the particle size (film thickness in the case of a thin film) and the surface area, and the production method of the titanium oxide carrier. It is determined as appropriate as long as the electrode catalyst particles can be supported. The supported amount of the titanium oxide carrier is usually 5 to 95% by weight, preferably 20 to 50% by weight, when the total of the conductive auxiliary material and the titanium oxide carrier is 100% by weight. If the amount of the titanium oxide carrier supported is too small, a sufficient amount of electrode catalyst particles as a fuel cell electrode material cannot be supported. If the amount of the titanium oxide carrier supported is too large, the particle size (or film thickness in the case of a thin film) of the titanium oxide carrier may be too large, and the electric resistance of the fuel cell electrode material may increase.

(Electrocatalyst particles)
The electrode catalyst particles 3b are selectively dispersed and supported on the titanium oxide carrier 3a. Here, “selectively dispersed and supported on the titanium oxide support” means 80% or more, preferably 90% or more, more preferably 95% or more (including 100%) of all the electrode catalyst particles (number). ) Means supported on a titanium oxide support. The ratio of the electrode catalyst particles supported on the titanium oxide support was determined by selecting any electrode catalyst particles (100 or more) obtained by observing the fuel cell electrode material to be evaluated with an electromagnetic microscope. It is possible to evaluate by counting the number of the obtained and the number carried on the carbon-based conductive auxiliary material.

  The electrocatalyst particles 3b may be either a noble metal catalyst or a non-noble metal catalyst as long as it has an electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation), preferably Pt, Ru, It is selected from noble metals such as Ir, Pd, Rh, Os, Au, and Ag, and alloys containing these noble metals. The “alloy containing a noble metal” includes “an alloy consisting only of the noble metal” and “an alloy consisting of the noble metal and another metal and containing 10% by mass or more of the noble metal”. The “other metals” to be alloyed with the noble metal are not particularly limited, but Co, Ni, W, Ta, Nb, and Sn can be cited as suitable examples, and one or more of these may be used. May be. Moreover, you may use the alloy containing two or more types of said noble metals and noble metals in the state which carried out phase separation. The noble metals and alloys containing these noble metals may be hereinafter referred to as “electrode catalyst metals”.

  Among electrocatalyst metals, Pt and alloys containing Pt have high electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) in the temperature range around 80 ° C., which is the operating temperature of a polymer electrolyte fuel cell. Therefore, it can be particularly preferably used.

  The shape of the electrode catalyst particles 3b is not particularly limited, and those having the same shape as known electrode catalyst particles can be used. Specific examples include a spherical shape, an elliptical shape, a polyhedron, and a core-shell structure. The structure of the electrode catalyst particles 3b is not limited to crystals, and may be amorphous or a mixture of crystals and amorphous.

As the size of the electrode catalyst particle 3b is smaller, the effective surface area through which the electrochemical reaction proceeds increases, and therefore the electrochemical catalyst activity tends to increase. However, if the size is too small, the electrochemical reaction activity decreases. Accordingly, the size of the electrode catalyst particles 3b is 1 to 30 nm, more preferably 1.5 to 10 nm, as an average particle diameter.
The “average particle diameter of the electrode catalyst particles” in the present invention can be obtained from the average value of the particle diameters of the electrode catalyst particles (20 particles) examined from an electron microscope image. When calculating the average particle diameter based on the electron microscope image, if the shape of the fine particles is other than a spherical shape, the length in the direction indicating the maximum length of the particles is taken as the particle diameter.
That is, one of the preferred embodiments of the electrode catalyst particles in the fuel cell electrode material of the present invention is electrode catalyst particles made of an alloy containing Pt and Pt having an average particle diameter of 1 to 30 nm.

  The amount of the electrode catalyst particles supported is appropriately determined in consideration of conditions such as the type of catalyst and the size (thickness) of the titanium oxide carrier. If the amount of the catalyst supported is too small, the electrode performance becomes insufficient, and if it is too large, the electrode catalyst particles may aggregate to deteriorate the performance.

  The amount of the electrode catalyst particles supported is preferably 0.1 to 60% by mass, more preferably 0.5 to 20% by mass, based on the total weight of the electrode material for the fuel cell. Excellent electrode reaction activity can be obtained according to the loading amount.

Further, the amount of the electrode catalyst particles supported is usually 3 to 40% by mass with respect to the titanium oxide carrier. If it is such a range, it will be excellent in the catalyst activity per unit mass, and can obtain the desired electrochemical catalyst activity according to the load.
When the loading amount is less than 3% by mass, the electrode reaction activity is insufficient, and when it exceeds 40% by mass, the aggregation of the electrode catalyst particles easily occurs, and the effective surface area for the electrochemical reaction of oxygen or hydrogen is reduced. There is a problem. Note that the amount of electrode catalyst particles supported can be examined by, for example, inductively coupled plasma emission spectrometry (ICP).

<2. Manufacturing Method of Fuel Cell Electrode Material>
The method for producing the fuel cell electrode material of the present invention described above is not particularly limited, and a suitable method is appropriately selected according to the type of the conductive auxiliary material, the titanium oxide support, and the electrode catalyst particles constituting the fuel cell electrode material. do it. Further, after supporting the titanium oxide support on the conductive auxiliary material, the electrode catalyst particles may be supported on the titanium oxide support, or after supporting the electrode catalyst particles on the titanium oxide support, the titanium oxide supported on the electrode catalyst particles. The carrier may be supported on the conductive auxiliary material.
From the viewpoint that the electrode material for a fuel cell of the present invention can be produced with good reproducibility, it is preferable to produce it by the production method described below (hereinafter referred to as “the production method of the invention”).
That is, the manufacturing method of the fuel cell electrode material of the present invention includes the following steps.
(1) A step of supporting a titanium oxide carrier on a conductive auxiliary material composed of one or more kinds selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface (2) The above-mentioned titanium oxide carrier supported A step of immersing a conductive auxiliary material in a solution containing an electrode catalyst precursor and supporting the electrode catalyst particles or the electrode catalyst precursor on the titanium oxide support (3) The electrode catalyst particles or the electrode supported on the titanium oxide support Step of activating catalyst precursor In the production method of the present invention, step (2) and step (3) may be performed simultaneously.

In the production method of the present invention, after supporting a titanium oxide carrier on one or more conductive auxiliary materials selected from fibrous carbon having a graphite structure and chain-linked carbon particles, electrode catalyst particles are supported. There is a special feature.
That is, the fibrous carbon and chain-linked carbon particles having a graphite structure on the surface can carry the titanium oxide carrier, but have the property that the electrode catalyst particles are hardly carried. This originates from the property that when the surface of the carbon material constituting the conductive auxiliary material has a graphite structure, the electrode catalyst particles are weakly bound and the deterioration behavior of the electrode catalyst particles moving and aggregating easily occurs.
When the titanium oxide support is supported on the conductive auxiliary material and then immersed in a solution containing the electrode catalyst precursor, the electrode catalyst precursor is selectively supported on the titanium oxide support and converted into electrode catalyst particles by reduction treatment or the like. The Therefore, according to the production method of the present invention, it is possible to obtain a fuel cell electrode material in which most of the electrode catalyst particles are selectively dispersed and supported on a titanium oxide carrier.

  Hereafter, each process in the manufacturing method of this invention is demonstrated in detail.

"Process (1)"
Step (1) is a step of supporting a titanium oxide carrier on a conductive auxiliary material made of one or more selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface.
The conductive auxiliary material and the titanium oxide support are <1. As described above in the description of the fuel cell electrode material of the present invention, detailed description is omitted here.

As the conductive auxiliary material, fibrous carbon having a graphite structure on the surface is particularly preferable VGCF. The conductive auxiliary material is preferably one in which a part of the surface is oxidized by surface modification and the supportability of the titanium oxide carrier is improved. The method for modifying the surface of the conductive auxiliary material is not particularly limited, but a method of treating with an inert gas (for example, N ₂ ) containing 0.5 to 30% water (water vapor) at a temperature of 200 to 400 ° C. is exemplified. It is done. That is, VGCF whose surface is modified is an example of a suitable conductive auxiliary material used in the production method of the present invention.

  As a method for supporting the titanium oxide carrier, any method can be adopted as long as it can support the titanium oxide carrier on the conductive auxiliary material, but a method of hydrolyzing titanium alkoxide which is a precursor of the titanium oxide carrier (alkoxide method). Is preferred.

In the alkoxide method, titanium alkoxide, which is a titanium oxide support precursor, is brought into contact with water in a solvent to perform hydrolysis, and the resulting titanium oxide support (including titanium hydroxide and the like) is supported on a conductive auxiliary material. Is the method. An advantage of this method is that the reaction rate can be controlled by sequentially reacting while dropping water and changing the dropping rate of water. Titanium alkoxide is an organic titanium compound represented by Ti (OR) ₄ , and examples of R include a methyl group, an ethyl group, a purpyl group, and a butyl group. Among these, Ti (OC ₃ H ₇ ) ₄ in which R is a pullyl group is preferable. When the target titanium oxide support is an oxide doped with not only titanium oxide but also other elements, the alkoxide of the doping element may be allowed to coexist in the solution for hydrolysis.

The solvent is a solvent that can dissolve titanium alkoxide, and may be any solvent that does not substantially contain moisture. Examples thereof include lower anhydrous alcohols such as anhydrous ethanol.
That is, one of the preferred embodiments for supporting the titanium oxide carrier in the production method of the present invention is an alkoxide method, in which anhydrous ethanol is used as a solvent, and further, an embodiment in which VGCF is used as a conductive auxiliary material. It is.

Since the titanium oxide carrier supported on the conductive auxiliary material by the alkoxide method includes those in an amorphous state, a titanium oxide carrier having high crystallinity can be obtained by drying and firing.
The drying method is not particularly limited, and the solvent may be evaporated by a method such as heating, reduced pressure, or natural drying. Also, the atmosphere during drying is not particularly limited, and the atmospheric conditions such as an oxidizing atmosphere containing oxygen or an air atmosphere, an inert atmosphere containing nitrogen or argon, a reducing atmosphere containing hydrogen, etc. Although it can be chosen arbitrarily, it is usually an atmospheric atmosphere.

  A titanium oxide support formed and supported on a conductive auxiliary material by an alkoxide method is heat-treated at 100 to 600 ° C., preferably 250 to 400 ° C. in an oxygen-containing oxidizing atmosphere (for example, in an air atmosphere). By doing so, a titanium oxide carrier having a large surface area and high electron conductivity can be obtained. If the heat treatment temperature is too low, the crystallinity may be low if the heat treatment temperature is lower, and sufficient electron conductivity may not be obtained. If the heat treatment temperature exceeds 800 ° C., the titanium oxide support aggregates and the surface area becomes small. In some cases, the titanium oxide carrier may be detached from the conductive auxiliary material.

The carbon material may be fueled if it exceeds a high temperature (for example, 500 ° C.) in an oxidizing atmosphere. However, the carbon material is used as a conductive auxiliary material in the present invention, and the surface is a fibrous carbon and a chain structure having a graphite structure. The connected carbon particles have high temperature durability. Therefore, the heat treatment temperature may be determined within a range in which the titanium oxide support is not substantially desorbed and the titanium oxide support is not desorbed within the above temperature range.
Particularly suitable VGCF has high crystallinity and is stable in that the titanium oxide carrier is hardly detached from the conductive auxiliary material in an air atmosphere of at least 600 ° C.

"Process (2)"
Step (2) is a step of immersing the conductive auxiliary material supporting the titanium oxide support in a solution containing an electrode catalyst precursor, and supporting the electrode catalyst particles or the electrode catalyst precursor on the titanium oxide support. Electrode catalyst precursors or electrode catalyst particles are hardly supported on fibrous carbon or chain-linked carbon particles (particularly fibrous carbon) having a graphite structure on the surface, and most are supported on a titanium oxide support.

Electrocatalyst precursors are <1. Electrocatalyst precursor described for the electrode catalyst particles in the fuel cell electrode material of the present invention, which is reduced in the solution in step (2) or in step (3) to become a zero-valent electrode catalyst metal. If it is.
Specific examples of the electrode catalyst precursor when the electrode catalyst particles are platinum (Pt) include platinum halides such as platinum chloride, platinum bromide, and platinum iodide; chloroplatinic acid, ammonium tetrachloroplatinate, hexachloro Inorganic acid salts of platinum such as potassium platinumate; organic acid salts of platinum such as platinum acetylacetonate, platinum hexafluoroacetylacetonate, dichloro (1,5-cyclooctadiene) platinum, platinum cyanide and the like. When the electrode catalyst particles are a metal other than Pt, a precursor corresponding to the metal may be used.

As a method for supporting the electrode catalyst precursor or the electrode catalyst particles, a known metal supporting method can be employed.
In the step (2), the method for forming the electrode catalyst fine particles from the electrode catalyst precursor and supporting the electrode catalyst fine particles on the titanium oxide carrier is not particularly limited, but depending on the support method, the particle size and dispersibility of the electrode metal particles may be reduced. The object of the present invention may not be achieved.
Suitable methods capable of obtaining highly dispersed electrocatalyst particles having a small particle diameter include a noble metal acetylacetonate method using a noble metal acetylacetonate and a colloid method using a noble metal colloid described below.

  In the method of using noble metal acetylacetonate as the electrode catalyst precursor (noble metal acetylacetonate method), after the noble metal acetylacetonate, which is an electrode catalyst precursor, is supported on a titanium oxide support, the electrode catalyst precursor is electrocatalyst particles. This is a direct conversion method.

  In the acetylacetonate method, a conductive auxiliary material supporting a titanium oxide carrier is dispersed in a solution in which a noble metal acetylacetonate is dissolved in a suitable solvent such as dichloromethane, and the mixture is stirred and evaporated to remove the electrode. Since the catalyst precursor can be supported, it is possible to avoid impurities such as chlorine and sulfur from being mixed, and it is possible to support the electrocatalyst particles having a uniform nano-size particle size distribution in a highly dispersed state. Further, since a strong oxidizing agent or reducing agent is not used in the solution, there is an advantage that deterioration of the titanium oxide carrier and the carbon-based conductive auxiliary material can be avoided.

  Examples of the noble metal acetylacetonate include acetylacetonates of noble metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, and Ag, and one or more of these can be used. The solvent may be an organic solvent that can disperse the noble metal acetylacetonate. A typical example is dichloromethane.

  When presenting a method for supporting electrocatalyst fine particles by the noble metal acetylacetonate method, the conductive auxiliary material supporting the titanium oxide support and the noble metal acetylacetonate are placed in a predetermined container and cooled with ice using an ultrasonic stirring device. And a method of stirring until all the solvent is volatilized.

  In addition, since the noble metal acetylacetonate method uses an organic solvent, it has a high affinity with a hydrophobic conductive auxiliary material. Compared with the colloid method using an aqueous solvent described later, the electrode catalyst particles on the titanium oxide carrier However, it is useful in that it can easily support highly dispersed electrocatalyst particles.

  On the other hand, the colloid method is a method in which electrocatalyst particles having a small particle size distribution can be obtained using an aqueous solvent without using an organic solvent essential in the noble metal acetylacetonate method. The colloidal method is advantageous in comparison with a supporting method in which an organic solvent is essential because water can be used as a solvent. In the colloidal method, since water is used as a solvent, the generated electrocatalyst particles are selectively supported on the surface of the titanium oxide support because the hydrophobic surface is not particularly supported on the graphite carbon material. It is easy, and by adopting the colloid method, it can be selectively supported on a highly dispersed electrode catalyst on the surface of the titanium oxide carrier.

  The colloid method will be described below. In the colloid method, the conductive auxiliary material supporting the titanium oxide carrier is dispersed in a solution containing a colloid of an electrode catalyst precursor (particularly a noble metal colloid), and the electrode catalyst precursor colloid is reduced to form an electrode on the titanium oxide carrier. This is a method of supporting as catalyst particles. In the colloid method, electrode metal particles having a uniform nano-size particle size distribution can be generated without using a surfactant or an organic solvent.

As a specific method of the colloid method, the conductive auxiliary material supporting a titanium oxide carrier is dispersed in a solution containing a noble metal colloid, and the noble metal colloid is reduced and supported on the titanium oxide carrier as noble metal fine particles.
The conditions for preparing the solution containing the noble metal colloid are not particularly limited, and may be set appropriately according to the selected noble metal precursor and the reducing agent.

  The solvent may be any solvent that can dissolve the precursor of the titanium oxide carrier, and examples thereof include water, lower alcohols such as methanol and ethanol. The ability to use water as a solvent is one of the advantages of the colloid method.

Examples of the reducing agent include sodium bisulfite (NaHSO ₃ ), sodium borohydride, sodium triethylborohydride, hydrogen peroxide, hydrazine, and the like. These may be used alone or in combination of two or more. Furthermore, after reducing with a certain reducing agent, you may reduce with another reducing agent. By performing multistage reduction treatment in the liquid phase in this manner, highly dispersed noble metal fine particles can be supported on the support. As a preferred specific example, the reducing agent is NaHSO ₃ and hydrogen peroxide in this order. The method used in is mentioned.

  The pH of the solution is particularly preferably pH 4-6. When produced in this pH range, a colloid solution in which noble metal colloids are uniformly dispersed without aggregation can be produced. A suitable temperature range is 20 to 100 ° C. (particularly preferably 50 to 70 ° C.). Moreover, since the particle diameter of the noble metal particle | grains to be formed will increase when it is made to contact with a reducing agent for a long time, contact time is about 10 minutes-about 2 hours normally.

"Process (3)"
Step (3) is a step of activating the electrode catalyst particles or electrode catalyst precursor supported on the titanium oxide support. In the step (2), the electrocatalyst particles or electrocatalyst precursor supported on the titanium oxide support may contain a non-stoichiometric metal oxide, and the activity is low as it is. Heat treatment in an atmosphere or a reducing atmosphere containing hydrogen activates the electrochemical catalytic action of the metal serving as the electrode catalyst.

  The heat treatment conditions are appropriately selected depending on the type of the titanium oxide carrier, the metal used as the electrode catalyst, and the precursor. When the electrode catalyst is Pt or a Pt alloy, it is usually 180 to 400 ° C, preferably 200 to 250 ° C. If the temperature is too low, activation of the metal that becomes the electrode catalyst becomes insufficient, and if the temperature is too high, the electrode catalyst particles aggregate and the effective reaction surface area becomes too small. Water vapor may be added to the atmosphere as necessary.

  Further, since the titanium oxide support is stable even in a reducing atmosphere containing hydrogen, the heat treatment can be performed in the presence of hydrogen. Hydrogen is used after being diluted to 0.1 to 50% (preferably 1 to 10%) with an inert gas such as nitrogen, helium or argon. When the electrode catalyst is Pt or a Pt alloy, the heat treatment temperature is usually 180 to 400 ° C, preferably 200 to 250 ° C. If the temperature is too low, activation of the metal that becomes the electrode catalyst becomes insufficient, and if the temperature is too high, the electrode catalyst particles aggregate and the effective reaction surface area becomes too small. Water vapor may be added to the atmosphere as necessary.

<3. Fuel Cell Electrode>
The fuel cell electrode of the present invention includes the above-described fuel cell electrode material and a proton conductive electrolyte material, and the conductive auxiliary material is in contact with each other to form a conductive path.

  In such a configuration, since the conductive auxiliary material constituting the electrode material of the present invention described above is a carbon material that is a carbon material having a long diameter and excellent electronic conductivity, it is a fuel having a chain connected carbon particles. As a whole battery electrode, it is excellent in electronic conductivity. Furthermore, since the gap between the long-diameter conductive auxiliary materials can be formed at least to the extent that air permeability is exhibited, it is excellent in the diffusibility of gases involved in electrode reactions such as hydrogen, oxygen, and water vapor, and sufficient protons. The conductive electrolyte material can be sufficiently retained. Therefore, the fuel cell electrode formed of the electrode material exhibits excellent electrode performance, has high cycle durability, and can generate power for a long period of time.

  Hereinafter, the fuel cell electrode formed using the fuel cell electrode material of the present invention will be described. Specifically, a case where the above-described fuel cell electrode material is used as an electrode in PEFC will be described.

  This fuel cell electrode may be composed only of the above-mentioned fuel cell electrode material, but is usually a proton conductive electrolyte material (hereinafter referred to as “proton conductive electrolyte material”) used for the fuel cell electrolyte. Or simply described as “electrolyte material”). The electrolyte material contained in the fuel cell electrode together with the fuel cell electrode material may be the same as or different from the electrolyte material used in the fuel cell electrolyte membrane. From the viewpoint of improving the adhesion between the fuel cell electrode and the electrolyte membrane, it is preferable to use the same one.

  Examples of the electrolyte material used for the PEFC electrode and the electrolyte membrane include a proton conductive electrolyte material. This proton conductive electrolyte material is roughly classified into a fluorine-based electrolyte material that contains fluorine atoms in all or part of the polymer skeleton, and a hydrocarbon-based electrolyte material that does not contain fluorine atoms in the polymer skeleton. Can be used.

  Specific examples of fluorine-based electrolyte materials 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. Can be mentioned.

  Specific examples of the hydrocarbon electrolyte material include polymers such as polysulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid. In addition, a polymer having a side chain such as an alkyl group can be mentioned as a suitable example.

  The mass ratio between the fuel cell electrode material and the electrolyte material mixed with the fuel cell electrode material provides good proton conductivity in the electrode formed using these materials, and gas diffusion in the electrode. In addition, it may be determined as appropriate so that water vapor can be discharged smoothly. However, if the amount of the electrolyte material mixed with the electrode material for fuel cells is too large, the proton conductivity is improved, but the gas diffusibility is lowered. Conversely, when the amount of the electrolyte material to be mixed is too small, the gas diffusibility is improved, but the proton conductivity is lowered. Therefore, 10-50 mass% is a suitable range for the mass ratio of the electrolyte material to the fuel cell electrode material. When this mass ratio is smaller than 10% by mass, the continuity of the material having proton conductivity is deteriorated, and sufficient proton conductivity as a fuel cell electrode cannot be ensured. On the other hand, when it is larger than 50% by mass, the continuity of the electrode material for the fuel cell is deteriorated, and it may not be possible to have sufficient electronic conductivity as the electrode for the fuel cell. Furthermore, the diffusibility of gas (oxygen, hydrogen, water vapor) inside the electrode may be reduced.

The fuel cell electrode of the present invention may contain components other than the above-described fuel cell electrode material and proton conductive material.
For example, a conductive auxiliary material other than the conductive auxiliary material contained in the above-described fuel cell electrode material (hereinafter referred to as “other conductive auxiliary material”) may be included. By including other conductive auxiliary materials, the number of conductive paths connecting the fuel cell electrode materials increases, and the conductivity of the entire electrode may be improved.
Other conductive auxiliary materials may be the above-mentioned conductive auxiliary materials such as fibrous carbon and chain-linked carbon particles (however, no titanium oxide carrier or electrode catalyst particles are supported), carbon black, activated carbon, etc. Ordinary particulate carbon may be used.

In addition, although the electrode for PEFC was demonstrated as an electrode for fuel cells containing the electrode material for fuel cells of this invention, it uses as an electrode in various fuel cells other than PEFC, such as an alkaline fuel cell and a phosphoric acid fuel cell. be able to. Further, it can also be suitably used as an electrode for a water electrolysis apparatus using a polymer electrolyte membrane similar to PEFC.
The fuel cell electrode containing the fuel cell electrode material of the present invention has excellent electrochemical catalytic activity for oxygen reduction and hydrogen oxidation, and can therefore be used as a cathode and an anode. In particular, it is excellent in electrochemical catalytic activity for the oxidation of hydrogen shown in (Reaction 1), and is particularly suitable as an anode because it does not cause electrochemical oxidative decomposition of a conductive material as a carrier under the operating conditions of a fuel cell. Can be used for

  In addition to PEFC, the fuel cell electrode of the present invention can be used as an electrode in various fuel cells such as alkaline fuel cells and phosphoric acid fuel cells. Further, it can also be suitably used as an electrode for a water electrolysis apparatus using a solid polymer electrolyte membrane similar to PEFC.

<4. Membrane electrode assembly (MEA)>
The membrane electrode assembly of the present invention comprises a solid polymer electrolyte membrane, a cathode joined to one surface of the solid polymer electrolyte membrane, and an anode joined to the other surface of the solid polymer electrolyte membrane. In the membrane electrode assembly, the anode is the fuel cell electrode of the present invention.

As an embodiment of the present invention, a fuel cell electrode including an electrode material using a titanium oxide carrier as an electron conductive oxide and a membrane electrode assembly using the fuel cell electrode of the present invention as an anode will be described.
FIG. 2 schematically shows a cross-sectional structure of the membrane electrode assembly according to the embodiment of the present invention. As shown in FIG. 2, the membrane electrode assembly 10 has a structure in which the cathode 4 and the anode 5 are arranged facing the solid polymer electrolyte membrane 6.

  The cathode 4 includes an electrode catalyst layer 4a and a gas diffusion layer 4b, and a known cathode used in PEFC can be used. In addition, the fuel cell electrode of the present invention can also be used as the cathode 4.

  A conventionally known gas diffusion layer can be used as the gas diffusion layer 4b. For example, a conductive carbon-based sheet member having a pore size distribution of about 100 nm to 90 μm, which has been used as a conventional PEFC gas diffusion layer, is preferably a carbon cloth or carbon with a water repellent treatment. Paper, carbon nonwoven fabric, etc. can be used. Further, a sheet-like member other than a carbon-based material such as stainless steel may be used. The thickness of the gas diffusion layer 4b is not particularly limited, but is usually about 50 μm to 1 mm. The gas diffusion layer 4b may have a microporous layer made of an aggregate of carbon fine particles having an average particle diameter of about 10 to 100 nm and a water repellent on one surface.

  The anode 5 includes an electrode catalyst layer 5a and a gas diffusion layer 5b. Since the electrode catalyst layer 5a uses the electrode for a fuel cell of the present invention as described above, detailed description thereof is omitted. Further, the gas diffusion layer 5 b of the anode 5 can be the same as the gas diffusion layer 4 b described in the cathode 4.

  As the solid polymer electrolyte membrane 6, a known PEFC electrolyte membrane may be used as long as it has proton conductivity, chemical stability, and thermal stability. In FIG. 2, the thickness is emphasized, but the thickness of the solid polymer electrolyte membrane 6 is usually about 0.05 mm in order to reduce the electric resistance.

Examples of the electrolyte material constituting the solid polymer electrolyte membrane 6 include a fluorine-based electrolyte material and a hydrocarbon-based electrolyte material. In particular, an electrolyte membrane formed of a fluorine-based electrolyte material is preferable because of its excellent heat resistance, chemical stability, and the like. Specific examples 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.
Examples of the hydrocarbon polymer electrolyte material include polymers such as polysulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid. These include polymers having side chains such as alkyl groups. Further, as the electrolyte membrane, an electrolyte membrane made of an inorganic proton conductor such as phosphate or sulfate can also be used.

The embodiments of the MEA of the present invention have been described above with reference to the drawings. However, these are examples of the present invention, and various configurations other than those described above can be adopted.
For example, in the above-described embodiment, the fuel cell electrode of the present invention is employed only for the anode, but the fuel cell electrode of the present invention may also be used for the cathode. As a preferred example, a fuel cell electrode including an electrode material using an oxide mainly composed of tin oxide as an electron conductive oxide may be used as a cathode.

<5. Polymer electrolyte fuel cell>
The polymer electrolyte fuel cell (single cell) of the present invention comprises the membrane electrode assembly of the present invention, and usually has a structure in which the membrane electrode assembly is sandwiched between separators having gas flow paths.

FIG. 3 is a conceptual diagram showing a typical configuration of the polymer electrolyte fuel cell of the present invention. As shown in FIG. 3, in the polymer electrolyte fuel cell 20, hydrogen is supplied to the anode 5, and the proton (H ⁺ ) generated by the above-described (reaction 1) 2H ₂ → 4H ⁺ + 4e ⁻ is solid polymer. The supplied electrons are supplied to the cathode 4 through the electrolyte membrane 6, and the generated electrons are supplied to the cathode through the external circuit 21. (Reaction 2) O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O reacts with oxygen. Produce water. A potential difference is generated between the electrodes by the electrochemical reaction between the anode and the cathode. In the polymer electrolyte fuel cell of the present invention, the components other than the membrane electrode assembly of the present invention are the same as those of the known polymer electrolyte fuel cell, and thus detailed description thereof is omitted.
Actually, a fuel cell stack in which the polymer electrolyte fuel cells (single cells) of the present invention are stacked in the number corresponding to the power generation performance is formed, and by assembling other accompanying devices such as a gas supply device and a cooling device. used.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the following examples and description of the drawings, the niobium-doped titanium oxide support may be simply referred to as a titanium oxide support or TiO ₂ particles. In addition, “fibrous carbon carrying a titanium oxide carrier” may be referred to as an electrode material for a fuel cell material (no electrode catalyst is carried).

<Conductive auxiliary material>
As the conductive auxiliary material, fibrous carbon (manufactured by Showa Denko KK, vapor grown carbon fiber, VGCF-H (registered trademark)) having the following physical properties was used.
Fiber diameter: 150 nm
True density: 2.1 g / cm ³
Specific surface area: 11.4m ² / g
Thermal conductivity: 1200W / (m · K)
Conductivity: 1 × 10 ⁻⁴ Ωcm

<Ti precursor>
Ti (OC ₃ H ₇ ) ₄ (Kishida Chemical Co., Ltd., purity 99.0% or more)
<Nb precursor>
Nb (OC ₂ H ₅ ) ₅ (ALDRICH, purity 99.95% or more)

[Evaluation 1] Evaluation of electrode material for fuel cell material (no electrode catalyst supported) [Evaluation 1-1] Influence of calcination temperature In Experimental Example 1, a niobium-doped titanium oxide support is supported on fibrous carbon (VGCF) by the following method. Thus, an electrode material for a fuel cell material (no electrode catalyst supported) was obtained.
Process (1)
A predetermined amount of absolute ethanol was added to the fibrous carbon (0.492 g), and the mixture was stirred with an ultrasonic homogenizer to obtain a dispersion of fibrous carbon. In this dispersion, Ti (OC ₃ H ₇ ) ₄ as a titanium oxide precursor and Nb (OC ₂ H ₅ ) ₅ as a dopant precursor were added, and hydrolysis was performed by adding distilled water dropwise with a burette while stirring. Incidentally, the amount of raw material, the amount of Ti (OC ₃ H _{7) 4} is supported rate for carbon fiber in terms of TiO ₂ (TiO ₂ carrier rate), and 32.5 wt% (charged amount), Nb ( The amount of OC ₂ H ₅ ) ₅ was ₂ mol% with respect to TiO ₂ .
After the distilled water was added dropwise, stirring was continued for 2 hours, and then the dispersion was filtered and washed, and dried at 100 ° C. for 10 hours to obtain fibrous carbon (no calcination) carrying a titanium oxide carrier. Further, the fibrous carbon carrying the titanium oxide carrier (no firing) was heat-treated at 300 ° C. or 600 ° C. for 2 hours in the air atmosphere to obtain fibrous carbon carrying the titanium oxide carrier. Also, using a thermal analyzer (ThermoPlus TG8120, manufactured by Rigaku Corporation), the fibrous carbon carrying the titanium oxide support was heated to 800 ° C. in the air, and the mass difference before and after the temperature increase was reduced by weight. As the weight of the fibrous carbon burned, the support ratio of the titanium oxide support was determined to be 30.9 wt%.

  An FE-SEM image obtained by observing the fibrous carbon carrying the titanium oxide support after firing at 300 ° C. without firing, at 600 ° C. with a scanning electron microscope (FE-SEM, Hitachi High-Technologies Corporation, S-5200). As shown in FIG. Moreover, the result of having evaluated each sample by the X ray diffraction method is shown in FIG.

In the sample after baking at 600 ° C., TiO ₂ particles (titanium oxide support) having a particle size of about 20 to 30 nm were confirmed as shown in FIG. 4A, and anatase type as shown in FIG. A peak indicating a crystal was clearly confirmed. The peak at 2θ of about 27 ° is attributed to fibrous carbon.
In the sample after baking at 300 ° C., TiO ₂ particles (titanium oxide support) having a particle size of less than 10 nm were confirmed as shown in FIG. 4B, and after baking at 600 ° C. as shown in FIG. Compared with the sample, the peak showing anatase type crystals was broad.
In the sample without firing, TiO ₂ particles (titanium oxide support) having a particle size of less than 10 nm were confirmed as shown in FIG. 4 (c), and anatase type crystals were shown as shown in FIG. The peak was further broader than the sample after baking at 300 ° C.

FIG. 6 shows the results of evaluating the BET specific surface area of each sample and fibrous carbon not supporting the titanium oxide carrier. As can be seen from FIG. 6, the sample fired at 600 ° C. has a smaller BET specific surface area than the sample fired at 300 ° C. and not fired. This is considered to be due to the fact that the surface area is reduced at the same TiO ₂ loading because the particle size of the TiO ₂ particles is increased and the crystallinity is high due to firing at a high temperature. Furthermore, when the particle size is large, the electron conduction path in TiO ₂ becomes long, which is disadvantageous as an electrode material.
On the other hand, if the firing temperature is too low, there is a possibility that a hydrated oxide of Ti may remain, which may deteriorate the conductivity.
Note that in the DTA measurement, observed DTA peak at the time beyond 200 ° C., since it is considered that crystallization of the TiO ₂ is performed in this respect, the crystallization of the TiO ₂ rows at 300 ° C. calcination It was judged that Therefore, 300 ° C. firing was employed in the following examination.

[Evaluation 1-2] Relationship between TiO ₂ loading ratio and specific surface area The amount of raw material that is a titanium oxide precursor is 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt% in terms of charged amount of TiO ₂ loading 60 wt%, and the amount of Nb (OC ₂ H ₅ ) ₅ is ₂ mol% with respect to TiO ₂ , and the TiO ₂ loading is different in the same manner as in step (1) of [Evaluation 1-1]. An electrode material for fuel cell material (no electrode catalyst supported) was produced. FIG. 7 shows the result of evaluating the BET specific surface area. FIGS. 8, 9 and 10 show FE-SEM images with TiO ₂ loadings of 10 wt%, 20 wt% and 50 wt%, respectively.

As shown in FIG. 7, the BET specific surface area increases with an increase in the TiO ₂ loading rate, and shows a maximum value at 50 wt%. Also, there is almost no difference between 50 wt% and 60 wt%, but this is due to the fact that TiO ₂ particles aggregated due to excessively increased loading rate and secondary particles with a large particle diameter were formed. It is thought that. Therefore, it was judged that an increase in the specific surface area of the carrier could not be expected even if the TiO ₂ loading rate was further increased. Further, there is a possibility that the TiO ₂ particles are stacked in layers by increasing the TiO ₂ loading rate, and as a result, the surface area is increased. In that case, it is presumed that the electron conduction path in TiO ₂ becomes longer and the catalytic activity tends to be lowered.
8 to 10, it can be seen that many portions where TiO ₂ particles are aggregated or overlapped are seen by increasing the TiO ₂ loading rate.
From the above results, taking into account the state of dispersion of carrier specific surface area and TiO ₂ particles (or TiO ₂ particles are uniformly dispersed in a single layer), hereinafter, 20 wt of TiO ₂ supported rate for fibrous carbon (VGCF) Evaluation was made on the samples with%.

[Evaluation 2] Evaluation of electrode material for fuel cell material (supporting electrode catalyst) Fibrous carbon (VGCF) surface-modified by heat treatment at 300 ° C. for 2 hours with 3% steam humidified N ₂ (N ₂ bubbling) as a conductive auxiliary material And the amount of Nb (OC ₂ H ₅ ) ₅ was 5 mol% with respect to TiO ₂ , and the niobium dope obtained by the same method as in the above evaluation 1 (corresponding to step (1)) Pt catalyst particles were supported by a colloidal method or a Pt acetylacetonate method on an electrode material for a fuel cell material (non-supported electrode catalyst) composed of titanium oxide support / fibrous carbon (Nb—TiO ₂ / VGCF).
In all the catalysts described below, the charge value of Pt was adjusted to 20 wt% with respect to the niobium-doped titanium oxide support / fibrous carbon (Nb—TiO ₂ / VGCF).

[Support of Pt catalyst particles by colloid method]
Step (2)
The Pt catalyst particles were supported by the colloid method on the electrode material for a fuel cell material having a predetermined TiO ₂ support rate obtained in the step (1) (no electrode catalyst supported) by the following procedure.
First, 1 g of H ₂ PtCl ₆ .6H ₂ O was dissolved in 100 mL of distilled water, then 2 g of NaHSO ₃ was added, and the temperature was raised while stirring with a stirrer. Thereafter, the liquid was changed to colorless and transparent, and maintained until there was no irritating odor due to hydrogen chloride. Subsequently, the above-mentioned solution was added to distilled water in which an electrode material for fuel cell material (no electrode catalyst supported) was dispersed, and 45 mL of 35% H ₂ O ₂ aqueous solution was added dropwise with stirring at 40 ° C. using a hot stirrer. At this time, the pH was adjusted by adding an aqueous NaOH solution so that the pH was always in the range of 4.95 to 5.00. After the dropwise addition of 35% H ₂ O ₂ , the slurry obtained by stirring for 24 hours was subjected to filtration and washing three times to remove impurities to obtain a residue.

Process (3)
The residue obtained in step (2) was pulverized after the powder was dried at 100 ° C. for 10 hours and subjected to a reduction treatment at 200 ° C. for 2 hours in a 5% H ₂ —N ₂ atmosphere to obtain a residual sulfur content. Removal of the catalyst and activation of the catalyst yielded the intended electrode material for fuel cell materials (colloid method).

[Support of Pt catalyst particles by acetylacetonate method]
Step (2)
The Pt catalyst particles were supported by the platinum acetylacetonate method on the electrode material for a fuel cell material having a predetermined TiO ₂ support rate obtained in the step (1) (no electrode catalyst supported) by the following procedure.
Add the fuel cell material electrode material (no electrode catalyst supported) and Pt (II) acetylacetonate to the eggplant flask, then dissolve in dichloromethane, and all the solvent is volatilized while applying ultrasonic waves using an ultrasonic stirrer. Stir until obtained powder.

Process (3)
The powder obtained in the step (2) was subjected to reduction treatment at 210 ° C. for 3 hours and at 240 ° C. for 3 hours in an N ₂ atmosphere, whereby the fuel cell electrode material of Example 1 was obtained. The heat treatment is performed in two stages in order to suppress Pt particle growth due to rapid thermal reduction and to carry Pt with a small particle diameter.

11, 12 and 13 show FE-SEM images of 10 wt%, 20 wt% and 50 wt% of TiO ₂ supported on a Pt catalyst by the colloid method.
It can be confirmed that the Pt catalyst particles on TiO ₂ is supported in a highly dispersed than 11-13. Moreover, almost no Pt catalyst particles directly supported on fibrous carbon (VGCF) as a conductive auxiliary material were seen regardless of the supporting rate of TiO ₂ . This is because the surface of VGCF is chemically stable with a graphite structure, and the colloidal method precipitates Pt colloid while stirring in pure water, so that almost no Pt colloid was attached to hydrophobic VGCF. It is done.

FIGS. 14, 15 and 16 show FE-SEM images of 10 wt%, 20 wt% and 50 wt% of TiO ₂ supported on Pt catalyst particles by the acetylacetonate method.
From 14 to 16, it can be seen that the Pt catalyst particles supported on a fibrous carbon (VGCF) as a conductive auxiliary material with a decrease of the TiO ₂ support ratio has increased. In the acetylacetonate method, the Pt catalyst particles are supported while stirring the sample in dichloromethane, which is a hydrophobic organic solvent, so it is considered that the Pt catalyst particles are easily supported on the hydrophobic fibrous carbon (VGCF).

From the above results, it was confirmed that the Pt catalyst particles were supported on the TiO ₂ support by either the colloid method or the acetylacetonate method. However, in the colloid method, almost no Pt catalyst particles directly supported on fibrous carbon (VGCF) were observed regardless of the TiO ₂ loading rate, whereas the acetylacetonate method decreased the TiO ₂ loading rate. Along with this, the number of Pt catalyst particles directly supported on fibrous carbon (VGCF) increased. Therefore, from this result, it is understood that the colloidal method does not support the Pt catalyst particles on the fibrous carbon (VGCF) and can selectively support the Pt catalyst particles on the TiO ₂ support. It was.

[Evaluation 3] Electrochemical measurement Using the above-mentioned electrode material for fuel cell material (TiO ₂ loading rate 20 wt%, Pt charge value 20 wt%), which was supported by Pt by the colloid method and the acetylacetonate method, in an acidic solution The electrochemical surface area (ECSA) and oxygen reduction (ORR) activity of the prepared electrode material for fuel cell materials were quantitatively evaluated. In this evaluation, the ORR activity is evaluated as a simulation evaluation of the electrode activity. However, when H ₂ is saturated in the solution, the hydrogen oxidation (HOR) activity can be evaluated.

(Evaluation of ECSA)
The electrochemical surface area (Pt effective surface area) was calculated from the hydrogen adsorption amount obtained from CV based on the assumption that one hydrogen atom was adsorbed on one Pt atom on the surface. CV measurement conditions are as follows. Assuming that 1 atom of H is adsorbed per 1 atom of Pt, the electric quantity is 210 μC / cm ² .

Measurement: Three-electrode cell (working electrode: electrode material for fuel cell / GC, counter electrode: Pt, reference electrode: Ag / AgCl)
Electrolyte: 0.1M HClO ₄ (pH: about 1)
Measurement potential range: 0.05 to 1.2 V (standard hydrogen electrode standard)
Scanning speed: 50 mV / s
Hydrogen adsorption amount: Calculated from peak area showing hydrogen adsorption of 0.05 to 0.4 V. Electrochemical surface area (ECSA): calculated from the following formula ECSA = (hydrogen desorption electric amount Q _H ) [μC] / 210 [μC / cm ² ]

(ORR activity)
ORR activity is calculated based on the activation-dominated current (i _k ) obtained from the rotating disk electrode method (RDE method). Mass activity (activity per unit Pt mass), Specific activity (activity per unit Pt effective area) Was used as an index.
Mass activity = i _k / Pt mass on electrode
Specific activity = i _k / ECSA

The activation-dominated current (i _k ) is a Koutecky-Levich plot obtained by plotting the current-potential curve obtained by rotating electrode measurement with i ⁻¹ and ω ^−1/2 at an arbitrary potential. The obtained straight line was extrapolated from the intercept.
As a specific procedure, first after the O ₂ was bubbled for 30 minutes at 100mL / min, 2500rpm, 1600rpm, 900rpm, until 1.20 V _RHE at 10 mV / sec in a direction nobler from each 0.05 V _RHE in order 400rpm The potential was scanned and the measurement was performed. Note that O ₂ was always purged at 100 mL / min during the measurement. The calculation of the activation dominant current by the Koutecky-Levich plot was all performed at 0.90 V _RHE .

  FIG. 17 shows the ECSA evaluation results of the fuel cell electrode material carrying a Pt catalyst by the colloid method or the acetylacetonate method. 18 and 19 show the evaluation results of the mass activity and specific activity, respectively, of the fuel cell electrode material supporting the Pt catalyst by the colloid method or the acetylacetonate method. Moreover, the result of the commercially available 46 wt% Pt / C (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) which is a standard catalyst is also shown for comparison.

As can be seen from FIGS. 17 to 19, the fuel cell electrode material loaded with Pt by the colloid method had a smaller ECSA than the electrode material for fuel cell loaded with Pt by the acetylacetonate method. The fuel cell electrode material carrying Pt catalyst particles by the method showed a larger value than the fuel cell electrode material carrying Pt by the acetylacetonate method. In particular activity, the fuel cell electrode material loaded with Pt by the colloidal method showed a value comparable to Pt / C as the standard catalyst.
In the CV measurement, any of the samples loaded with Pt by the colloid method or the acetylacetonate method showed a current peak peculiar to Pt. There is a report that Ct of Pt / TiO ₂ and Pt / Nb—TiO ₂ in which titanium oxide is not supported on a conventional conductive auxiliary material does not show a Pt-specific current peak. Therefore, in the electrode material for fuel cell materials of the present invention in which a titanium oxide carrier is supported on fibrous carbon, which is a conductive auxiliary material, and Pt catalyst particles are supported on the titanium oxide carrier, the electron conduction of TiO ₂ by the conductive auxiliary material. It can be said that the path shortening effect was confirmed.

  According to the fuel cell electrode material of the present invention, a fuel cell electrode having excellent electron conductivity, gas diffusibility, and excellent durability can be provided. The fuel cell electrode is suitable for a polymer electrolyte fuel cell electrode that requires long-term operation.

DESCRIPTION OF SYMBOLS 1 Electrode material for fuel cells 2 Conductive auxiliary material 3a (Particulate) titanium oxide support 3b Electrocatalyst fine particles 4 Fuel cell electrode (cathode)
4a Cathode electrode layer 4b Gas diffusion layer 5 Fuel cell electrode (anode)
5a Cathode electrode layer 5b Gas diffusion layer 6 Solid polymer electrolyte membrane 10 Membrane electrode assembly (MEA)
20 Polymer electrolyte fuel cell 21 External circuit

Claims (9)

  One or more kinds of conductive auxiliary materials selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface, a titanium oxide support carried on the conductive auxiliary material, the conductive auxiliary material, and the titanium oxide An anode electrode material for a fuel cell, comprising electrode catalyst particles dispersedly supported on the titanium oxide support among the supports.   The anode electrode material for a fuel cell according to claim 1, wherein the conductive auxiliary material is vapor grown carbon fiber (VGCF).   The anode electrode material for a fuel cell according to claim 1 or 2, wherein the titanium oxide support is made of niobium-doped titanium oxide doped with 0.1 to 20 mol% of niobium.   The anode electrode material for a fuel cell according to any one of claims 1 to 3, wherein the titanium oxide carrier is supported on the conductive auxiliary material so that a part of the conductive auxiliary material is exposed.   The anode electrode material for a fuel cell according to any one of claims 1 to 4, wherein the electrode catalyst particles are fine particles made of an alloy containing Pt and Pt having an average particle diameter of 1 to 30 nm.   6. A fuel cell comprising the anode electrode material for a fuel cell according to claim 1 and a proton conductive electrolyte material, wherein the conductive auxiliary material is in contact with each other to form a conductive path. electrode.   A membrane electrode assembly comprising: a solid polymer electrolyte membrane; a cathode joined to one surface of the solid polymer electrolyte membrane; and an anode joined to the other surface of the solid polymer electrolyte membrane, A membrane electrode assembly, wherein the anode is the fuel cell electrode according to claim 6.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 7. The manufacturing method of the anode electrode material for fuel cells characterized by including the following processes (1)-(3).
(1) A step of supporting a titanium oxide carrier on a conductive auxiliary material comprising at least one selected from fibrous carbon and chain-linked carbon particles having a graphite structure on the surface. (2) The conductive material supported on the titanium oxide carrier. A step of immersing an auxiliary material in a solution containing an electrode catalyst precursor and supporting the electrode catalyst particles or the electrode catalyst precursor on the titanium oxide support (3) The electrode catalyst particles or the electrode catalyst supported on the titanium oxide support Activating the precursor