JP2007250214A - Electrode catalyst and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst keeping a constant proton concentration and maintaining power generating performance by the use of a hydrogen storage material, in order to solve a problem that, when fuel shortage occurs, water electrolysis or carbon corrosion takes place at an anode side to make the degradation of anode catalyst progress. <P>SOLUTION: The electrode catalyst has a catalyst component and a hydrogen storage material carried on the surface of a conductive carrier, with a particle occupancy parameter α<SB>P</SB>as defined in a formula within a range of 0.01<α<SB>P</SB><2.0. Provided that S<SB>s</SB>is a specific surface area of the conductive carrier (cm<SP>2</SP>/g), m<SB>A</SB>is a catalyst component carrying volume (g) per 1g of the conductive carrier, d<SB>A</SB>is a mean particle diameter (cm) of the catalyst component, p<SB>A</SB>is a specific gravity of the catalyst component (g/cm<SP>3</SP>), m<SB>H</SB>is a hydrogen storage material carrying volume per 1g of the conductive carrier, d<SB>H</SB>is a mean particle diameter (cm) of the hydrogen storage material, and p<SB>H</SB>is a specific gravity (g/cm<SP>3</SP>) of the hydrogen storage material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode catalyst for a battery, particularly an electrode catalyst for a fuel cell, and more particularly to an electrode catalyst excellent in hydrogen storage capacity, particularly an electrode catalyst for a fuel cell.

  In recent years, in view of the social situation against the background of energy and environmental problems, there has been an increasing demand for the practical use of polymer electrolyte fuel cells that can operate at room temperature and obtain high output density. In such a polymer electrolyte fuel cell, the hydrogen gas of the fuel is converted into protons at the anode by the electrode catalyst, and oxygen is reduced at the cathode to be combined with protons that have passed through the electrolyte layer to become water. Thus, the polymer electrolyte fuel cell directly obtains electric energy from the reaction energy obtained by the chemical reaction. However, the practical application of the polymer electrolyte fuel cell has many problems in terms of technology and cost.

  As a major technical issue, solid polymer fuel cells use precious metal catalysts such as Pt and polymer electrolytes, but the catalyst and polymer electrolyte deteriorate due to adsorption of oxygen, etc. There is a problem of lowering. On the other hand, it has been known for a long time that there is a property of taking in hydrogen depending on the type of metal, and a battery utilizing this property has been studied.

In Patent Document 1, hydrogen storage alloys having excellent corrosion resistance capable of adsorbing oxygen on the negative electrode side are concentrated on the outermost negative electrode plate, and the activity of the outermost negative electrode, which is reduced by this, is more electrochemical than corrosion resistance. It discloses an invention that supplements by intensively locating an alloy having enhanced activity on the inner negative electrode plate, which requires more reactivity. In the invention according to Patent Document 1, when the negative electrode is exposed to a high potential, the electrochemical corrosion reaction itself is not suppressed, and thus there is a problem that the effect of suppressing the deterioration of the negative electrode cannot be obtained for a long time.
JP 2003-168422 A

  In view of this, the present invention supplies protons to the cathode side when a fuel deficiency such as hydrogen occurs on the anode side during power generation, so that water electrolysis or carbon corrosion as shown in the following reaction formula occurs on the anode side and the anode catalyst deteriorates. In order to solve the problem that the power generation performance of the fuel cell decreases, the use of a hydrogen storage material can suppress a rapid decrease in the proton concentration and suppress / prevent deterioration of the catalyst and the polymer electrolyte membrane. Another object of the present invention is to provide an electrode catalyst that maintains the power generation performance of the fuel cell.

  In order to solve the above-mentioned problems, the present invention comprises a catalyst component and a hydrogen storage material supported on the surface of a conductive carrier.

However, in the formula, _{S s:} conductive carrier specific surface area _{^{(cm 2 / g), m}} A: catalyst component carrying amount per conductive support 1g (g / (g)) , d A: catalyst component average particle size (Cm), ρ _A : specific gravity of catalyst component (g / cm ³ ), m _H : hydrogen storage material loading per 1 g of conductive support (g / (g)), d _H : hydrogen storage material average particle diameter ( cm), ρ _H : specific gravity (g / cm ³ ) of the hydrogen storage material,
The electrode occupancy parameter α ^P defined by the following is provided: 0.01 <α _P <2.0.

  A fuel deficiency such as hydrogen occurs on the anode side, the potential increases, and at the same time, the hydrogen stored in Pd is released, and the shortage of hydrogen is supplied to alleviate the instantaneous fuel deficiency and Deterioration can be suppressed. Further, even when a local fuel deficiency occurs in a minimal region in the electrode plane, the stored hydrogen is released from Pd only in the local region, and the fuel deficiency can be alleviated.

  The electrode catalyst according to the present invention comprises a catalyst component and a hydrogen storage material supported on the surface of a conductive carrier.

(Formula 1)
However, in the formula, _{S s:} conductive carrier specific surface area _{^{(cm 2 / g), m}} A: catalyst component carrying amount per conductive support 1g (g / (g)) , d A: catalyst component average particle size (Cm), ρ _A : specific gravity of catalyst component (g / cm ³ ), m _H : hydrogen storage material loading per 1 g of conductive support (g / (g)), d _H : hydrogen storage material average particle diameter ( cm), ρ _H : specific gravity (g / cm ³ ) of the hydrogen storage material,
The particle occupancy parameter α _P defined by is preferably 0.01 <α _P <2.0.

  The particle occupancy parameter is defined by the above Equation 1, and this parameter value is a value indicating the area occupancy rate of the catalyst component and the hydrogen storage material supported on the conductive support surface. That is, the larger the particle occupancy parameter value, the higher the area occupancy of the catalyst component and the hydrogen storage material on the surface of the carrier, indicating that the fuel oxidation electrode catalyst material and the hydrogen storage material are closer to each other.

The particle occupation parameter α _P is preferably 0.01 to 2.0, more preferably 0.02 to 1.5, still more preferably 0.03 to 1.2, and particularly preferably 0.05 to 1.0.

When the particle occupancy parameter α _P is 0.01 <α _P <2.0, hydrogen is released from the hydrogen storage material, and then reacts (protons are generated) on the catalyst surface, thereby generating hydrogen from the hydrogen storage material. Since hydrogen is efficiently supplied to the electrode catalyst, it is possible to suppress and prevent a rapid decrease in the proton production concentration. As a result, since water electrolysis and carbon corrosion reaction do not occur, electrode corrosion and catalyst deterioration can be suppressed / prevented.

  The case where the particle occupancy parameter value is 0.01 or less indicates a state where the hydrogen storage material is small or a distance between the catalyst component and the hydrogen storage material is large. A sufficient amount of hydrogen cannot be supplied to the catalyst component due to the release of the catalyst, so that a sufficient effect cannot be obtained. On the other hand, when the particle occupancy parameter value is 2 or more, the overlap between the catalyst component and the hydrogen storage material is too much, for example, as described above, the alloy is completely alloyed so that hydrogen atoms cannot enter and exit, thereby reducing the hydrogen storage capacity, A sufficient catalytic activity cannot be obtained.

  The definition of each parameter of the above formula 1 and the measurement method thereof will be described below.

“S _s : Conductive carrier specific surface area (cm ² / g)” is calculated from the specific surface area measurement result by the BET method, and the conductive carrier specific surface area (cm ² / g) is preferably 1 × 10 ^{5 to} 1.6 × 10 ⁷ (cm ² / g), more preferably 2 × 10 ^{5 to} 1.2 × 10 ⁷ (cm ² / g), and even more preferably 5 × 10 ⁵ to 1 × 10 ⁷ (Cm ² / g).

“ _{M A} : catalyst component loading per g of conductive support (g / (g))” is calculated from the measurement result of ICP (inductively coupled plasma emission spectroscopy), preferably 0.1 4 (g), more preferably 0.2 to 2.5 (g), still more preferably 0.4 to 1.5 (g).

“D _A : catalyst component average particle diameter (cm)” is measured using a crystallite diameter determined by observation of a TEM (transmission electron microscope) image or XRD (X-ray diffraction), preferably 2 ×. 10 ^{−7 to} 5 × 10 ⁻⁶ (cm), more preferably 2 × 10 ⁻⁷ to 2 × 10 ⁻⁶ (cm), and further preferably 2 × 10 ⁻⁷ to 1 × 10 ⁻⁶ (cm). .

The “specific gravity (g / cm ³ ) of the catalyst component” is the true specific gravity at room temperature of the material, and a known true specific gravity measurement method can be used. The range of the specific gravity (g / cm ³ ) of the catalyst component is preferably 2 to 22 (g / cm ³ ), more preferably 5 to 22 (g / cm ³ ), and still more preferably 10 to 22 (g / cm ^3). ).

“ _{M H} : hydrogen storage material loading per gram of conductive support (g / (g))” is calculated from the measurement result of ICP (inductively coupled plasma emission spectroscopy), preferably 0.01 -2 (g), More preferably, it is 0.02-1.5 (g), More preferably, it is 0.05-1 (g).

“D _H : hydrogen storage material average particle diameter (cm)” uses a crystallite diameter determined by observation of a TEM (transmission electron microscope) image or XRD (X-ray diffraction). The range of the hydrogen storage material average particle size (cm) is preferably 2 × 10 ^{−7 to} 5 × 10 ⁻⁶ (cm), more preferably 2 × 10 ⁻⁷ to 2 × 10 ⁻⁶ (cm), and still more preferably. Is 2 × 10 ⁻⁷ to 1 × 10 ⁻⁶ (cm), “ρ _H : specific gravity of hydrogen storage material (g / cm ³ )” is the true specific gravity at room temperature of the material, and a known true specific gravity measurement method Can be used. The range of ρH: specific gravity (g / cm ³ ) of the hydrogen storage material is preferably 2 to 22 (g / cm ³ ), more preferably 5 to 18 (g / cm ³ ), and still more preferably 10 to 15 (g / Cm ³ ).

  The “catalyst component” according to the present invention is a component that exhibits catalytic activity for a reaction in which a fuel such as hydrogen supplied to the anode electrode is electrochemically oxidized to generate protons.

  As the catalyst component used in the electrode catalyst according to the present invention, the cathode catalyst is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. The catalyst component used for the anode catalyst is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like, and alloys thereof. Is done. Among these, those containing at least platinum (Pt) are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide, heat resistance, and the like. This is because Pt shows high oxidation activity.

  The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. The composition of the alloy when the alloy is used as a cathode catalyst varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 It is preferable to set it to -70 atomic%. In general, an alloy is a generic term for an element obtained by adding one or more metal elements or non-metal elements to a metal element and having metallic properties. In addition, only palladium is excluded from the catalyst component.

  The alloy structure consists of a eutectic alloy, which is a mixture of component elements that form separate crystals, a component element that completely dissolves into a solid solution, and a component element that is an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. Under the present circumstances, the catalyst component used for a cathode catalyst and the catalyst component used for an anode catalyst can be suitably selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the cathode catalyst and the anode catalyst have the same definition for both, and are collectively referred to as “catalyst components”. However, the catalyst components for the cathode catalyst and the anode catalyst do not have to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  Pt alloy catalysts based on Pt and noble metal-base metal mixture catalysts also show high activity. Therefore, it is possible to provide a high-performance anode having sufficient oxidation activity and durability as an electrode catalyst.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. At this time, the smaller the average particle size of the catalyst component used in the electrode catalyst, the higher the effective electrode area where the electrochemical reaction proceeds, which is preferable because the oxygen reduction activity is also high, but actually the average particle size is too small On the other hand, a phenomenon in which the oxygen reduction activity decreases is observed. Therefore, the average particle diameter of the catalyst component contained in the electrode catalyst is preferably 2 to 50 nm, more preferably 2 to 20 nm, even more preferably 2 to 10 nm, and particularly preferably 2 to 8 nm.

  When the average particle size of the catalyst component contained in the electrode catalyst is less than 2 nm, the durability is low, such as sintering is likely to occur. On the other hand, when the average particle size of the catalyst component contained in the electrode catalyst exceeds 50 nm, the catalyst specific surface area is low. Thus, the electrode performance obtained with respect to the amount of the catalyst component to be used becomes low, and the electrode becomes expensive to obtain a certain performance. The “average particle diameter of the catalyst component” in the present invention is the average value of the particle diameter of the catalyst component determined from the crystallite diameter or transmission electron microscope image obtained from the half width of the diffraction peak of the catalyst component in X-ray diffraction. Can be measured.

The specific gravity (g / cm ³ ) of the catalyst component according to the present invention is preferably 2 to 22 (g / cm ³ ), more preferably 5 to 22 (g / cm ³ ), and still more preferably 10 to 22 ( g / cm ³ ). When the specific gravity of the catalyst component according to the present invention is in the range of 2 to 22 (g / cm ³ ), it is possible to contain a necessary amount of the catalyst component even in a thin electrode catalyst layer. In other words, when the specific gravity of the catalyst component is small, the required amount of catalyst is used, so that the thickness of the electrode catalyst layer becomes significantly thick, and the mass transfer of reactants, the increase in electron conduction resistance, the increase in cell thickness, etc. It is disadvantageous.

  The “hydrogen storage material” according to the present invention is a material that can not only adsorb hydrogen on the surface of the material but also absorb and store it inside the solid.

  As a hydrogen storage material used in the electrode catalyst according to the present invention, in any of the cathode electrode catalyst layer and the anode electrode catalyst layer, a material that can not only adsorb hydrogen on the material surface but also absorb and store it in the solid interior If it is, there is no restriction | limiting in particular and a well-known material can be used similarly. For example, any material that can suitably maintain the hydrogen storage / release characteristics in the usage environment of the anode electrode of a fuel cell using an electrolyte can be used. Specifically, transition metals such as titanium, manganese, zirconium, nickel, and alloys thereof, and alloys having a hexagonal structure such as Laves phase, rare earth elements, niobium, zirconium Examples include alloys containing transition metal 5 with respect to 1, vanadium and vanadium-based alloys, body-centered cubic alloys, magnesium, magnesium-based alloys, palladium (Pd), palladium-based alloys, and the like. Of these, palladium (Pd) and palladium-based alloys having a hydrogen storage capacity of 935 times their own volume are preferred.

  Examples of the palladium-based alloy include alloys such as Pd—Ni, Pd—V, Pd—Co, Pd—Fe, Pd—Ag, Pd—Cr, Pd—Mn, Pd—Pt, and Pd—Zr. Containing at least atomic percent).

For example, when the invention according to the present invention is used for a fuel cell, Pd occludes hydrogen in the vicinity of 0 V that is the normal operating potential range of the anode electrode. From this state, if the anode potential becomes higher than that during normal operation due to the lack of fuel such as hydrogen, the stored hydrogen is released from Pd. Further, since the catalyst component and the hydrogen storage material are close to each other, the released hydrogen quickly reaches the catalyst component, and the fuel deficiency state such as hydrogen can be alleviated. Therefore, it is considered that the use of a Pd-based material as the hydrogen storage material is most suitable for the purpose of the present invention. In addition to Pd, Ti ₂ CoFe, LaNi _{5 and the} like are known as materials having hydrogen storage properties, but they may be difficult to use because they dissolve in the strong acid / high potential environment used in the present invention. .

  Further, the hydrogen storage material in the electrode catalyst according to the present invention preferably has a current peak potential of 0 to 1.0 V, more preferably 0 to 1.0 V resulting from the release of hydrogen in the hydrogen storage material. 0.5V, more preferably 0-0.2V.

  When the current peak potential resulting from the release of hydrogen in the hydrogen storage material is in the range of 0 to 1.0 V, the potential at which carbon corrosion becomes noticeable when fuel depletion such as hydrogen occurs at the anode electrode. This is because hydrogen release occurs before the anode potential rises to the region. Thereby, when a fuel deficiency such as hydrogen occurs at the anode electrode, hydrogen release occurs before the potential at which carbon corrosion becomes significant, and the fuel deficiency can be mitigated.

  The measurement of the current peak potential resulting from the release of stored hydrogen from the hydrogen storage material is performed by cyclic voltammetry. Specifically, in the case of a polymer electrolyte fuel cell, humidified nitrogen is allowed to flow through an anode electrode containing a hydrogen storage material at room temperature (20 to 30 ° C.), and humidified hydrogen is allowed to flow through the cathode electrode. The potential-current characteristics of the anode electrode as a reference electrode are measured. At this time, the absolute potential (V vs. standard hydrogen electrode) of the humidified hydrogen flow cathode used as the reference electrode must be known.

  The shape of the hydrogen storage material is preferably granular, and the average particle size of the hydrogen storage material used in the electrode catalyst is preferably 2-50 nm, more preferably the average particle size of the hydrogen storage material contained in the electrode catalyst. Is preferably 2 to 40 nm, more preferably 2 to 30 nm, particularly preferably 2 to 20 nm.

  When the particle size of the hydrogen storage material is less than 2 nm, the ratio of the surface of each hydrogen storage material particle is too large, so that the amount of hydrogen stored in the bulk is smaller than the amount of hydrogen storage material used. If it exceeds 50 nm, the degree of dispersion is not sufficient on the surface of the carrier, and the suppression effect obtained with respect to the amount of the hydrogen storage material to be used becomes low. Therefore, in order to obtain a certain performance, the electrode becomes expensive. Similarly to the catalyst component, the particle size of the hydrogen storage material can also be determined from the crystallite size obtained from the half width of the peak of the profile obtained by X-ray diffraction or the particle size estimated from the transmission electron microscope image.

  Moreover, it is preferable that Pd content in the electrode catalyst which concerns on this invention is 10-80 atomic% with respect to a catalyst component. For example, when the catalyst component is Pt and the hydrogen storage material is Pd, it is preferable that 10 to 80 atom% of Pd is present with respect to 100 atoms of Pt. The Pd content is more preferably 20 to 70 atomic% with respect to the catalyst component, and further preferably 30 to 60 atomic% with respect to the catalyst component.

  When the amount of Pd used is less than 10% with respect to the catalyst component, a sufficient suppression effect cannot be obtained even with an optimum particle size. On the other hand, when it exceeds 80% with respect to the catalyst component, Pd covers the catalyst component, and the oxidation activity of the anode electrode decreases.

Moreover, the specific gravity (g / cm < ³ >) of the hydrogen storage material which concerns on this invention becomes like this. Preferably it is 2-22 (g / cm < ³ >), More preferably, it is 5-18 (g / cm < ³ >), More preferably, it is 10-15. (G / cm ³ ). When the specific gravity (g / cm ³ ) of the hydrogen storage material is in the range of 2 to 22 (g / cm ³ ), it is possible to contain a necessary amount of catalyst components even in a thin electrode catalyst layer. In other words, when the specific gravity of the catalyst component is small, the required amount of catalyst is used, so that the thickness of the electrode catalyst layer becomes significantly thick, and the mass transfer of reactants, the increase in electron conduction resistance, the increase in cell thickness, etc. It is disadvantageous.

  The conductive carrier according to the present invention is used in the present invention as long as it has a specific surface area for supporting the catalyst component in a desired dispersed state and has sufficient electronic conductivity as a current collector. It is preferable that the main component is a carbon material. By using a carbon material for the conductive support according to the present invention, a high-performance anode electrode with little electrical resistance loss and material diffusion loss can be obtained. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. Further, as such carbon materials, more specifically, acetylene black, Vulcan, Ketjen black, black pearl, graphitized acetylene black, graphitized Vulcan, graphitized Ketjen black, graphitized carbon, graphitized black pearl , Carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils as main components. In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed. By using the carbon materials listed above for the electrode according to the present invention as the conductive support, a high performance anode electrode with less loss can be obtained.

BET specific surface area of the conductive support, the catalyst component may be a sufficient specific surface area to be highly dispersed supported but is preferably 10~1600m ² / g, more preferably 20~1200m ² / g, more preferably Is preferably 50 to 1000 m ² / g. If the specific surface area is less than 10 m ² / g, the dispersibility of the catalyst component and the polymer electrolyte on the conductive support may be reduced, and sufficient power generation performance may not be obtained, and the specific surface area exceeds 1600 m ² / g. In addition, the effective utilization rate of the catalyst component and the polymer electrolyte may decrease instead.

  Further, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the average primary particle size is 10 ˜100 nm, preferably 15 to 60 nm, more preferably about 15 to 40 nm.

  The electrode catalyst according to the present invention is an electrode including a conductive carrier carrying a catalyst component and a hydrogen storage material. The catalyst component and the hydrogen storage material are preferably dispersed and supported on the surface of the conductive carrier.

  In the reaction in power generation, hydrogen is oxidized and protonated on the anode side, but since the hydrogen storage material is dispersed and exists on the surface of the conductive carrier, hydrogen is released from the hydrogen storage material when there is a shortage of fuel. It is possible to suppress / prevent a rapid decrease in the amount of sucrose. As a result, for example, when hydrogen is locally deficient during power generation, water electrolysis and carbon corrosion occur on the anode side to supply protons to the cathode side, and it is only necessary to suppress / prevent degradation of anode electrode performance. In addition, the corrosion of the electrode and the deterioration of the catalyst due to oxygen generated by water electrolysis can be suppressed / prevented.

  In view of the above, an electrode including a conductive carrier carrying a catalyst component and a hydrogen storage material according to the present invention is provided on both the anode side and the cathode side, or on either the anode side or the cathode side. However, the anode side, which is preferably a reaction of oxidizing hydrogen to protons, is preferred.

  The ratio (mass ratio) of the catalyst component, the hydrogen storage material, and the conductive support, which are components of the electrode catalyst according to the present invention, is preferably 0 when the conductive support is 1 g. 0.1 to 4 (g), more preferably 0.2 to 2.5 (g), still more preferably 0.4 to 1.5 (g), and the amount of hydrogen storage material supported (g) is preferably It is 0.01-2 (g), More preferably, it is 0.02-1.5 (g), More preferably, it is 0.05-1 (g).

  If the amount of the catalyst component supported is too small, only insufficient electrode performance can be obtained. If it is too large, sufficient electrode performance can be obtained, but the cost becomes high. Similarly, for the hydrogen storage material, if the supported amount is too small, the amount of hydrogen stored per electrode decreases, so the amount of hydrogen supplied at the time of fuel shortage becomes insufficient, and a sufficient deterioration suppressing effect cannot be obtained. Although a sufficient deterioration suppressing effect can be obtained, the cost is increased and the catalyst surface is covered, and the progress of the hydrogen oxidation reaction during normal power generation is hindered, so the electrode performance is rather lowered.

  The hydrogen storage material is preferably present in the vicinity of the catalyst component. This is because when hydrogen is reduced during power generation, hydrogen atoms released from the hydrogen storage material due to diffusion, electric potential, etc. are vapor diffusion or electrolyte in the surface diffusion of adsorbed hydrogen atoms or in the state of hydrogen molecules. It is considered that the catalyst surface is reached by dissolving and diffusing inside, but if the distance between the hydrogen storage material and the catalyst component is too large, hydrogen cannot be effectively supplied to the catalyst surface in such a process. is there.

  If it explains in detail based on the principle of a hydrogen storage material, hydrogen storage is divided roughly into two, a solid solution phenomenon and a chemical bond. The “solid solution phenomenon” means that another element enters a solid crystal and occupies a stable position in the form of substitution between atoms constituting the crystal or atoms constituting the crystal. In particular, the former is called interstitial solid solution and the latter is called substitutional solid solution, but it is considered that an interstitial solid solution is formed with hydrogen and an alloy. In addition, the storage of hydrogen requires taking into consideration the opposite of hydrogen release, and in order to achieve both hydrogen release and storage, first the hydrogen storage material has a hydrogen structure in the crystal structure. There is a void into which hydrogen atoms can exist in a metastable state and hydrogen must exit from this void. Furthermore, unless the hydrogen released from the hydrogen storage material collides with (reacts with) the catalyst components present in the vicinity of the hydrogen storage material without any restrictions, protons cannot be effectively supplied as a result. It causes carbon corrosion.

  Therefore, if the catalyst component and the hydrogen storage material are completely alloyed by heat or the like, and the crystal structure of the catalyst component and the hydrogen storage material changes, it is not preferable because hydrogen atoms cannot enter and exit the void. It is done. However, in the case where a part of the catalyst component and the hydrogen storage material are alloyed and joined, there are sufficient voids into and out of the crystal structure so that hydrogen storage ability can be expected.

  Although it is difficult to clearly express the ratio of alloying of the catalyst component and the hydrogen storage material with numbers, it is 1 to 20%, more preferably 1 to 10%, based on the total mass of the catalyst component and the hydrogen storage material. In this range, since there is a void through which hydrogen can enter and exit in a sufficient crystal structure, the effect of the present invention can be sufficiently expected. The electrode catalyst according to the present invention is a generic term for an anode side electrode catalyst and a cathode side electrode catalyst. In the present invention, the electrode catalyst is formed by supporting a catalyst component and a hydrogen storage material on a conductive carrier.

The electrode catalyst according to the present invention is a method for producing an electrode catalyst in which a catalyst component and a hydrogen storage material are supported on the surface of a conductive carrier.
Supporting a catalyst for dispersing and supporting the catalyst component on the conductive carrier;
A step of dispersing and supporting the hydrogen storage material on the conductive carrier;
And a step of firing a conductive support carried by the catalyst component and the hydrogen storage material.

  In the step of supporting the catalyst component and the hydrogen storage material on the conductive support, the respective materials must be supported in a highly dispersed state on the conductive support. As a method for supporting the conductive carrier, a liquid phase chemical reduction method in which a metal salt or metal complex is reduced with a reducing agent in a liquid phase, a wet support method such as an impregnation method using a metal salt or metal complex, CVD, or A dry support method using a spray pyrolysis method can be used. Preferably, a liquid phase chemical reduction method capable of supporting a catalyst component and a hydrogen storage material at a low cost and in a highly dispersed manner is used.

  The order in which the catalyst component and the hydrogen storage material are supported on the conductive carrier may be that the catalyst component is supported first, or the hydrogen storage material may be supported first. Moreover, the carrying | support process to an electroconductive support | carrier may perform a catalyst component and a hydrogen storage material separately, respectively, and may carry | support them simultaneously.

  In the firing step, the catalyst component and the hydrogen storage material particles are brought close to each other, and the metal component, particularly the Pd component, contained in the catalyst component and the hydrogen storage material is partially alloyed to further enhance the durability of the hydrogen storage material. There is an effect of improving, and this step can provide a fuel electrode catalyst having a desired particle diameter and a supported form.

  The firing temperature in the firing step is preferably 200 to 800 ° C, more preferably 300 to 700 ° C, and more preferably 400 to 600 ° C.

  If it is lower than 200 ° C, the catalyst component and the hydrogen storage material are difficult to adhere to each other, and the durability effect cannot be obtained. End up.

  In the firing step, the catalyst component and the hydrogen storage material are brought close to each other, and the durability of the hydrogen storage material is further improved by partially alloying the catalyst component and the metal component contained in the hydrogen storage material, particularly the Pd component. However, if the heat treatment temperature is too high, alloying proceeds too much, and not only the catalyst component and the hydrogen storage material become both large, but also the crystal structure changes due to alloying, and the above-described voids through which hydrogen can enter and exit Disappears, and the hydrogen storage and release characteristics of metal components, particularly Pd, are lost, so that effects such as suppression and prevention of electrode corrosion and catalyst deterioration due to water electrolysis cannot be obtained. Accordingly, a second aspect of the present invention relates to a cell.

  The present invention sandwiches an electrode catalyst layer containing an electrode catalyst in which a catalyst component and a hydrogen storage material according to the present invention are supported on the surface of a conductive support on both sides of a polymer electrolyte membrane, and further on both sides of the electrode catalyst layer. A membrane electrode assembly (MEA) comprising a gas diffusion layer containing a gas diffusion substrate in between can be provided.

  The electrode catalyst according to the present invention is a generic term for an anode-side electrode catalyst and a cathode-side electrode catalyst, and when used for an electrode of a fuel cell or the like, it is preferably used by forming a layer. In this case, the electrode catalyst layer according to the present invention includes an electrode catalyst, a proton conductive polymer, and, if necessary, a water repellent material. In the present invention, the electrode catalyst is formed by supporting a catalyst component and a hydrogen storage material on a conductive carrier.

  The catalyst component, hydrogen storage material, and conductive carrier used in the present invention are the same as the catalyst component, hydrogen storage material, and conductive carrier described above, and are omitted here.

  The proton conductive polymer in the electrode catalyst layer according to the present invention is not particularly limited and known ones can be used, but the same materials as those used for the polymer electrolyte described later can be used, and at least high protons can be used. Any material having conductivity may be used. The cathode electrode catalyst layer / anode electrode catalyst layer (hereinafter also simply referred to as “electrode catalyst layer” or “catalyst layer”) of the present invention includes a polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  The catalyst component can be supported on the conductive carrier by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. Alternatively, a commercially available electrode catalyst may be used.

  The polymer electrolyte used in the polymer electrolyte membrane and the electrode layer may be different, but it is preferable to use the same polymer electrolyte considering the contact resistance between the membrane and the electrode.

  The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that functions as an adhesive. Thereby, while being able to maintain the structure of an electrode stably, the sufficient three-phase interface where an electrode reaction advances can be ensured, and high catalyst activity can be obtained. Although content of the said solid polymer electrolyte contained in an electrode is not specifically limited, It is good to set it as 30-70 mass% with respect to the whole quantity of an electroconductive support | carrier.

  The porosity of the electrode catalyst layer is preferably 30 to 70%, more preferably 40 to 60%. If the porosity is less than 30%, gas diffusion is not sufficient, and the cell voltage in the high current region decreases. On the other hand, when the porosity exceeds 70%, the strength of the electrode catalyst layer is not sufficient, and the porosity decreases in the transfer process.

  As the material having water repellency according to the present invention, known materials can be used. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene Fluorine resin such as copolymer (FEP), polypropylene, polyethylene and the like can be mentioned. Among these, PTFE is more preferably used because of excellent water repellency and corrosion resistance during electrode reaction.

  The composition ratio of the electrode including the electrode catalyst according to the present invention is such that the catalyst component, the hydrogen storage material, the conductive carrier, the proton conductive polymer, and the water repellent material and the solvent as needed are 10 to 30 parts by mass, respectively. Parts, 5 parts by mass to 20 parts by mass, 10 parts by mass to 30 parts by mass, 5 parts by mass to 20 parts by mass, and 0 parts by mass to 5 parts by mass are preferable.

  1-50 micrometers is preferable and, as for the thickness of the electrode catalyst layer containing the electrode catalyst which concerns on this invention, 1-20 micrometers is more preferable.

  The polymer electrolyte membrane used in the present invention is not particularly limited and a known one can be used, but the same materials as those used for the electrode catalyst layer can be used, and at least a material having high proton conductivity is used. I just need it. The “electrolyte” used in the present invention may be a liquid, solid, gel-like material having high proton conductivity, and is a liquid strong acid such as phosphoric acid or sulfuric acid, antimonic acid, stannic acid, heteropoly Solid acids such as acids, polyelectrolytes typified by perfluorosulfonic acid polymers, etc., doped with inorganic acids such as phosphoric acid to hydrocarbon polymer compounds, some of which are proton conductive functional groups Illustrative examples include substituted organic / inorganic hybrid polymers and gel proton conductivity obtained by impregnating a polymer matrix with a phosphoric acid solution or a sulfuric acid solution. As the proton conductive member, a mixed conductor having electronic conductivity can be used.

  The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  As a material used for the gas diffusion substrate according to the present invention, a sheet-like material made of carbon paper, nonwoven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. When the gas diffusion base material has excellent electron conductivity, efficient transport of electrons generated by the power generation reaction is achieved, and the performance of the fuel cell is improved. If the gas diffusion base material has excellent water repellency, the generated water is efficiently discharged.

  In order to ensure high water repellency, a technique for forming a gas diffusion layer by subjecting a material constituting the gas diffusion base material to water repellency has also been proposed. For example, a solution containing a fluororesin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting a gas diffusion base material such as carbon paper, and dried in the air or an inert gas such as nitrogen. In some cases, a hydrophilic treatment may be performed on the material constituting the gas diffusion base material.

  Hereinafter, a manufacturing method will be described with respect to an embodiment according to the present invention.

  The electrode catalyst of the present invention is reduced and supported on a conductive carrier such as carbon black after being dispersed with a homogenizer or the like in addition to an ion aqueous solution containing a catalyst component such as platinum and a hydrogen storage material such as palladium. Next, after heating and drying, heat treatment is performed at 200 ° C. to 800 ° C. to prepare. Thereafter, a catalyst carrier is prepared by adding a conductive carrier carrying a catalyst component and a hydrogen storage material, and a proton conductive polymer such as Nafion to a solvent such as water or alcohol as necessary.

  The catalyst slurry of the present invention is applied to a transfer mount and dried to form an electrode catalyst layer. In this case, as the transfer mount, a known sheet such as a PTFE (polytetrafluoroethylene) sheet, a PET (polyethylene terephthalate) sheet, or a polyester sheet can be used. The transfer mount is appropriately selected according to the type of catalyst slurry used (particularly, a conductive carrier such as carbon in ink). In the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). Thickness can be used. Specifically, the thickness of the electrode catalyst layer is 1 to 50 μm, more preferably 1 to 20 μm.

  The catalyst slurry on the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. The applied electrode catalyst layer drying conditions are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the coating layer (electrode catalyst layer) of the catalyst slurry is dried at room temperature to 100 ° C., more preferably 50 to 80 ° C. for 30 to 60 minutes in a vacuum dryer. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, the process proceeds to the following steps.

  That is, after sandwiching the solid polymer electrolyte membrane thus produced, hot pressing is performed on the laminate. In this case, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the solid polymer electrolyte membrane can be joined sufficiently closely, but are 100 to 170 ° C., more preferably 100 to 150 ° C., with respect to the electrode surface. The press pressure is preferably 1 to 5 MPa. Thereby, bondability with a solid polymer electrolyte membrane and an electrode catalyst layer can be improved.

  After hot pressing, the electrode including the electrode catalyst layer and the solid polymer electrolyte membrane can be obtained by removing the transfer mount.

  Next, the gas diffusion layer is produced by impregnating carbon paper, carbon non-woven fabric or carbon cloth in a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) as necessary, and in the atmosphere or inert such as nitrogen. After drying in gas, a gas diffusion layer is prepared.

  Then, the membrane electrode assembly is produced by sandwiching the electrode including the electrode catalyst layer and the solid polymer electrolyte membrane using the two gas diffusion layers produced above.

  The catalyst slurry of the present invention has a water repellency such as polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, if necessary, in addition to the electrode catalyst, proton conductive polymer, and solvent. Polymers, thickeners and the like may be included. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged.

  The use of a thickener is effective when the catalyst slurry or the like cannot be successfully applied onto the transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, (EG (ethylene glycol), PVA (polyvinyl alcohol)), and the like. The amount of the thickener added when the thickener is used is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 0.1 with respect to the total mass of the catalyst slurry. -10 mass%. Furthermore, the solvent constituting the catalyst slurry used in the present invention is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used.

  The catalyst slurry of the present invention may be used for only one or both of the cathode side electrode catalyst layer and the anode side electrode catalyst layer, but the cathode side is particularly affected by changes in the amount of water produced due to output fluctuations. At least the anode-side electrode catalyst layer because there is a high risk that the porous structure of the electrode catalyst layer in the initial state collapses due to changes in dryness and moisture, the porosity decreases, and the amount of reaction gas supplied to the electrode catalyst layer decreases. It is preferable to be used for.

  This invention uses the membrane electrode assembly which is 3rd invention for a fuel cell.

  The fuel cell using the electrode according to the present invention generally further includes a gas diffusion layer as described in detail below. At this time, the gas diffusion layer is a transfer mount in the above method. It is preferable that the electrode assembly is further bonded to each electrode catalyst layer after the electrode catalyst layer and the solid polymer electrolyte membrane are bonded, by further sandwiching the obtained bonded body with a gas diffusion layer. Alternatively, after an electrode catalyst layer is formed on the surface of the gas diffusion layer in advance to produce an electrode catalyst layer-gas diffusion layer assembly, the electrode catalyst layer-gas diffusion layer assembly is solid as described above. It is also preferable to sandwich and bond the polymer electrolyte membrane by hot pressing. In addition to the hot pressing method, a method of laminating an electrode catalyst layer, a polymer electrolyte membrane, an electrode catalyst layer, and a gas diffusion layer on the gas diffusion layer by sequential coating may be used.

  In the present invention, an electrode (membrane electrode assembly) can be produced by a heat treatment similar to a conventionally known method. For example, by applying and drying the prepared catalyst slurry on a transfer mount with a desired thickness, an electrode catalyst layer on the cathode side and the anode side is formed, and the electrode catalyst layer is placed so that the electrode catalyst layer is on the inside. After sandwiching the molecular electrolyte membrane between the electrode catalyst layers and joining them by hot pressing or the like, the catalyst layer was attached to the electrolyte membrane by peeling off the transfer mount.

  The catalyst layer-coated electrolyte membrane thus prepared and the gas diffusion layer (the carbon layer side of the carbon paper coated with the carbon layer) were bonded together to produce an electrode (MEA: membrane electrode assembly).

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a solid polymer electrolyte fuel cell is preferable because it is small in size 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. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, moving bodies such as automobiles that are susceptible to corrosion of the carbon support due to the high output voltage required after a relatively long shutdown, and deterioration of the polymer electrolyte due to the high output voltage being taken out during operation. It is particularly preferred to be used as a power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be used as appropriate. Generally, the fuel cell has a structure in which an electrode (membrane electrode assembly) is sandwiched between separators.

  The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Further, in order to prevent the gas supplied to each catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion where the catalyst layer is not formed on the gasket layer. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. The thickness of the gas seal portion may be 2 mm to 50 μm, preferably about 1 mm to 100 μm.

  Furthermore, a stack in which a plurality of electrodes (membrane electrode assemblies) are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. 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.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. In the examples, “%” represents a mass percentage unless otherwise specified.

(1) Pt-supported carbon prepared carbon black powder 1.0 g (Cabot Corporation, Vulcan XC-72: a specific surface area of 250m ² / g) a homogenizer in an aqueous solution of chloroplatinic acid 250g containing platinum 0.4% Then, 3 g of sodium citrate was added thereto, and the mixture was heated at 85 ° C. for 6 hours using a reflux reactor to carry out reduction loading of platinum. And after standing to cool to room temperature, platinum carrying | supported carbon was separated by filtration and Pt carrying | support carbon powder was obtained by fully wash | cleaning with a pure water. The average Pt particle diameter of the Pt-supported carbon was about 3.1 nm from the result of observation with a transmission electron microscope. Further, as a result of examining the amount of Pt supported by inductively coupled plasma emission spectroscopy, it was confirmed that 48.6% of Pt was supported.

(2) Preparation of Pt—Pd-supported carbon (1) Using a homogenizer, 100 g of Pt-supported carbon prepared by the method (1) above was added to 100 g of a chloropalladium acid aqueous solution containing 0.1% palladium. Then, 2 g of sodium citrate was added thereto, and heated at 85 ° C. for 6 hours using a reflux reactor to carry out reduction loading of palladium as a hydrogen storage material. And after standing to cool to room temperature, the Pt-Pd carrying | support carbon powder was obtained by filtering and wash | cleaning. Further, this Pt—Pd-supported carbon powder was calcined at 700 ° C. for 4 hours in a nitrogen stream. From the result of observation of this Pt—Pd-supported carbon (1) by a combined transmission electron microscope image and characteristic X-ray surface analysis using a transmission electron microscope, the average Pt particle size is 5.2 nm and the average Pd particle size is 7. Estimated at 6 nm. The amounts of Pt and Pd supported were quantified by inductively coupled plasma emission spectroscopy, and were found to be Pt: 44.6% and Pd: 8.3%.

Each parameter is described below.
S _s: conductive carrier specific surface area ^(cm 2 ^{/g)=2.5×10 6} m _A: catalyst component carrying amount per conductive support 1g (g / (g)) = 0.947, d A: catalyst Component average particle diameter (cm) = 5.2 nm, ρ _A : Specific gravity of catalyst component (g / cm ³ ) = 21.45, m _H : Amount of hydrogen storage material supported per 1 g of conductive support (g / (g) ) = 0.176, d _H : hydrogen storage material average particle diameter (cm) = 7.6 nm, ρ _H : specific gravity of hydrogen storage material (g / cm ³ ) = 12.16.
The particle occupation parameter α _P of this Pt—Pd-supported carbon was 0.06.

(3) Preparation of Pt—Pd-supported carbon (2) It was prepared by the same preparation method as in the above (1) and (2) except that ketjen black EC (specific surface area 800 m ² / g) was used as the carrier carbon. From the result of observation of this Pt—Pd-supported carbon (2) by a combined transmission electron beam image and characteristic X-ray surface analysis using a transmission electron microscope, the average Pt particle size is 7.2 nm, and the average Pd particle size is 9. Estimated at 6 nm. Further, the amounts of Pt and Pd supported were quantified by inductively coupled plasma emission spectroscopy, and were found to be Pt: 28.3% and Pd: 5.7%. The particle occupation parameter α _P of this Pt—Pd-supported carbon was 0.007.

Each parameter is described below.
S _s: conductive carrier specific surface area ^(cm 2 ^{/g)=8.0×10 6} m _A: catalyst component carrying amount per conductive support 1g (g / (g)) = 0.429, d A: catalyst Component average particle diameter (cm) = 7.2 nm, ρ _A : Specific gravity of catalyst component (g / cm ³ ) = 21.45, m _H : Amount of hydrogen storage material supported per 1 g of conductive support (g / (g) ) = 0.086, d _H : hydrogen storage material average particle size (cm) = 9.6 nm, ρ _H : specific gravity of hydrogen storage material (g / cm ³ ) = 12.16.

(Production of MEA)
About production of MEA (membrane electrode assembly), it performed as follows about all.

  After adding 5 times the amount of purified water to the mass of the catalyst-supporting carbon powder, 0.5 times the amount of isopropyl alcohol is added, and the mass of Nafion (registered trademark) is 0.8 times the amount. Nafion (registered trademark) solution (containing 5 wt.% Nafion manufactured by Aldrich) was added. The mixed slurry was well dispersed with an ultrasonic homogenizer, followed by addition of a vacuum degassing operation to prepare a catalyst slurry. The catalyst slurry is printed on one side of the Teflon sheet by a screen printing method so as to have a predetermined Pt amount, dried at 60 ° C. for 3 hours, and then the surface on which the electrode catalyst layer is applied is matched with the electrolyte membrane at 130 ° C. The catalyst layer was attached to the electrolyte membrane by hot pressing at 1.5 MPa for 10 minutes.

These MEAs had an amount of Pt used of 0.3 mg on the anode side and 0.5 mg on the cathode side per apparent electrode area of 1 cm ² , and the electrode area was 25 cm ² . In addition, Nafion (registered trademark) 112 (thickness: about 50 μm) was used as the polymer electrolyte membrane.

  In the examples, anode electrode: Pt-Pd-supported carbon 1) was used, and cathode electrode: Pt-supported carbon prepared by (1) was used.

In Comparative Example 1, the anode electrode: Pt-supported carbon prepared by (1) was used, and the cathode electrode: Pt-supported carbon prepared by (1) was used.
In (Comparative Example 2), an anode electrode: Pt—Pd-supported carbon 2) was used, and a cathode electrode: Pt-supported carbon prepared by (1) was used.

〔Evaluation methods〕
(Single cell evaluation)
A fuel cell single cell was constructed using the produced MEA, and performance degradation of the anode electrode against hydrogen fuel deficiency was evaluated by the following method.

  Hydrogen was supplied as fuel to the anode electrode of the fuel cell, and air was supplied to the cathode electrode side. The supply pressure for both gases is atmospheric pressure, the temperature of the fuel cell body is set to 70 ° C., the hydrogen utilization rate is 67%, the anode supply gas dew point is 70 ° C., the air utilization rate is 40%, and the cathode supply gas dew point is 50%. Electric power was generated at a current density of 0.5 A / cm 2 constant current density. During power generation operation at a constant current density, the supply of hydrogen to the anode electrode was cut every 5 minutes for 1 second, and a fuel-deficient state was simulated in the anode electrode. Such a fuel depletion cycle at the anode electrode was generated 100 times. In order to evaluate the deterioration degree of the anode electrode by this test, cyclic voltammetry was performed to determine the electrochemically effective Pt surface area of Pt of the anode electrode before and after the test. In cyclic voltammetry measurement, the cell temperature is set to room temperature, hydrogen at room temperature dew point is circulated at 100 cc / min on the cathode side, and nitrogen at room temperature dew point is circulated at 200 cc / min on the anode side. The anode electrode potential was set to 0 to 1.1 V and scanned at a constant sweep rate. The electrochemically effective Pt surface area of the anode electrode was determined from the amount of electricity of the hydrogen adsorption wave observed by this measurement.

  Table 1 shows changes in the electrochemical effective Pt area of the anode electrode due to the hydrogen depletion operation. When the electrocatalysts of Comparative Examples 1 and 2 were used, the electrochemically effective Pt area was significantly reduced due to the progress of corrosion of the catalyst component support carbon of the anode electrode due to the occurrence of hydrogen deficiency. On the other hand, when the catalyst component and the hydrogen storage agent of the examples in the present invention were used, the amount of decrease in the electrochemical effective Pt area was remarkably reduced even for the same operation. It was found that an anode having high resistance to fuel deficiency such as hydrogen can be obtained by using the anode.

Claims (12)

The catalyst component and the hydrogen storage material are supported on the surface of the conductive support, and the following formula 1:

However, in the formula, _{S s:} conductive carrier specific surface area _{^{(cm 2 / g), m}} A: catalyst component carrying amount per conductive support 1g (g / (g)) , d A: catalyst component average particle size (Cm), ρ _A : specific gravity of catalyst component (g / cm ³ ), m _H : hydrogen storage material loading per 1 g of conductive support (g / (g)), d _H : hydrogen storage material average particle diameter ( cm), ρ _H : specific gravity (g / cm ³ ) of the hydrogen storage material,
An electrode catalyst characterized in that the particle occupancy parameter α _P defined by is 0.01 <α _P <2.0.   The electrode catalyst according to claim 1, wherein the catalyst component of the electrode contains at least Pt.   The electrode catalyst according to claim 1 or 2, wherein the particles of the catalyst component are particles having an average particle diameter of 2 to 50 nm.   The electrode catalyst according to claim 1, wherein the hydrogen storage material is Pd or a Pd-based alloy.   The electrode catalyst according to claim 1, wherein the hydrogen storage material has an average particle diameter of 2 to 50 nm.   The electrode according to claim 1, wherein the hydrogen storage material is Pd or a Pd-based alloy, and the Pd content in the hydrogen storage material is 10 to 80 atomic% with respect to the catalyst component. catalyst.   The electrode catalyst according to claim 1, wherein the conductive support contains a carbon material as a main component.   The electrode catalyst according to any one of claims 1 to 7, wherein a current peak potential resulting from the release of hydrogen in the hydrogen storage material is 0 to 1.0V. In the method for producing an electrode catalyst in which a catalyst component and a hydrogen storage material are supported on a conductive carrier surface,
Supporting a catalyst for dispersing and supporting the catalyst component on the conductive carrier;
A step of dispersing and supporting the hydrogen storage material on the conductive carrier;
And a step of calcining a conductive carrier supported by the catalyst component and the hydrogen storage material.   The method for producing an electrode catalyst according to claim 9, wherein a firing temperature in the firing step is 200 to 800 ° C.   The membrane electrode assembly using the said electrode catalyst of Claims 1-8.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 11.