JP2007257888A - Oxygen pole catalyst for solid polymer fuel cell, oxygen reduction electrode using it, and manufacturing method of those - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen pole catalyst for a solid polymer fuel cell superior in catalyst activity of oxygen reduction which does not contain a noble metal such as platinum at all and which does not bring about efficiency deterioration of the fuel cell due to crossover, and an oxygen reduction electrode using the same, and a manufacturing method of these. <P>SOLUTION: The oxygen pole catalyst for solid polymer fuel cell is a catalyst of oxygen reduction electrode used for a solid polymer fuel cell which arranges an ion exchange membrane between a pair of electrodes, and the catalyst of the oxygen reduction electrode is a cubic titanium carbon nitride powder containing nitrogen 2.0-15.5 wt.%, carbon 6.0-19.0 wt.%, and free carbon 0.1-5.9 wt.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oxygen reduction electrode suitable for use as an electrode of a polymer electrolyte fuel cell.

  Conventionally, noble metals such as platinum are stable and have high catalytic ability even at high potentials, and are therefore used as catalysts for electrodes in various electrochemical systems. However, since platinum is expensive and limited in terms of resources, a highly active catalyst that can replace platinum has been demanded and various proposals have been made (for example, Patent Documents 1, 2, 3, and 4). reference).

  First, in Patent Document 1, at least one of boron, oxygen, and nitrogen is added to a face-centered cubic or rhombohedral crystal catalyst containing Al, Cu, Group VIII elements, and La series elements, and then carbon, silicon At least one of zirconium, titanium, hafnium is added, and is made of an alloy selected from platinum and iron, further palladium, ruthenium, rhodium and gold, and then at least one of chromium, molybdenum and tungsten is added. Then, a catalyst is disclosed in which at least one of vanadium, niobium and tantalum is added, and further platinum is added.

Further, in Patent Document 2, a catalyst material (Pm _X Me _Y ) made of an alloy of a noble metal component (Pm) made of an alloy containing platinum and a transition metal component (Me, eg, Fe) is subjected to nitriding treatment on the surface of the catalyst material. electrode catalyst is disclosed of forming a transition metal four nitride structures (Me-N _4).

  Further, in Patent Document 3, at least one selected from ruthenium oxide, titanium oxide, vanadium oxide, manganese oxide, cobalt oxide, nickel oxide, tungsten oxide, or a metal oxide or metal nitride electrode catalyst of molybdenum nitride, A catalyst of a mixture of at least one inorganic oxide selected from platinum, palladium, ruthenium, rhodium, silver, nickel, iron, copper, cobalt, and molybdenum has been proposed.

As mentioned above, no technology that does not contain expensive platinum has been developed.

  Further, in Patent Document 4, when an organic liquid fuel such as methanol having high affinity for water is used, a fuel cell by crossover in which the organic liquid fuel diffuses into a solid electrolyte membrane containing moisture and reaches the oxygen reduction electrode. As a technique for solving the decrease in efficiency, it is disclosed that a layer containing a hydrogen-containing heteropoly acid salt is formed between a fuel electrode or an oxygen reduction electrode and a solid electrolyte membrane.

  Such conventional catalysts contain platinum and are expensive and resource-constrained. Furthermore, as the platinum content decreased, the catalytic activity also decreased, and there was no satisfactory oxygen electrode catalyst for polymer electrolyte fuel cells.

  In addition, since platinum is contained, there is a problem that the efficiency of the fuel cell is reduced due to crossover.

JP 2003-187812 A JP 2005-44659 A JP 2005-63677 A JP 2003-317737 A

  The present invention solves the above-mentioned problems, and its technical problem is an oxygen electrode catalyst for a polymer electrolyte fuel cell that does not contain any precious metal such as platinum and has excellent catalytic activity for oxygen reduction. It is an object of the present invention to provide an oxygen electrode catalyst for a polymer electrolyte fuel cell that does not cause a decrease in the efficiency of the fuel cell due to the above, an oxygen reduction electrode for a polymer electrolyte fuel cell using the same, and a method for producing them.

  In order to realize a high-performance fuel cell, the solution according to the present invention for solving this problem is that the titanium carbonitride powder and the composite titanium carbonitride powder have crystallinity depending on the contents of nitrogen and carbon and the processing conditions. Is to control. Further, in an oxygen reduction electrode for a polymer electrolyte fuel cell in which a mixture of conductive carbon black powder is coated on a carbon-based substrate to form an electrolyte membrane of Nafion (registered trademark, hereinafter simply referred to as Nafion), In order to prevent the efficiency of the fuel cell from being reduced due to over, the problem is solved by using a catalyst of titanium carbonitride powder and composite titanium carbonitride powder that do not have an action of catalyzing the decomposition reaction of fuel.

  That is, according to the present invention, there is provided a catalyst for an oxygen reduction electrode used in a polymer electrolyte fuel cell in which an ion exchange membrane is disposed between a pair of electrodes. Solid polymer characterized in that it is a cubic titanium carbonitride powder containing -15.5% by mass, carbon 6.0-19.0% by mass and free carbon 0.1-5.9% by mass An oxygen electrode catalyst for a fuel cell is obtained.

Further, according to the present invention, in the oxygen electrode catalyst for a catalyst solid polymer fuel cell, the titanium carbonitride powder is JCPDS file 42-1489 (C _0.7 N _0.3 Ti) or 42-1488 (C _0.3 N _0.7 Ti), a solid polymer having a lattice constant measured by Miller's index (hkl) 511 of 4.260 to 4.317Å An oxygen electrode catalyst for a fuel cell is obtained.

  Further, according to the present invention, in the above-mentioned catalytic oxygen electrode catalyst for a polymer electrolyte fuel cell, the catalyst is further divided into group IVa zirconium, hafnium, group Va vanadium, niobium, tantalum, group VIa chromium, molybdenum. Thus, an oxygen electrode catalyst for a polymer electrolyte fuel cell is obtained, which is a composite titanium carbonitride powder to which 0.1 to 20% by mass of at least one element of tungsten is added. Here, in the present invention, the IVa group element, the Va group element, and the VIa group element respectively correspond to the Group 4, Group 5, and Group 6 elements according to the revised IUPAC inorganic chemical nomenclature (1989).

  Moreover, according to the present invention, there is provided an oxygen reduction electrode for a polymer electrolyte fuel cell that does not cause a decrease in efficiency due to crossover, comprising: the catalyst according to claim 1 or 2; and a conductive carbon black powder. The mixture is coated on a glassy carbon substrate on a carbon-based substrate, and a polymer electrolyte Nafion electrolyte membrane is formed on the coating membrane, thereby obtaining an oxygen reduction electrode for a solid polymer fuel cell.

Further, according to the present invention, in the oxygen reduction electrode for a polymer electrolyte fuel cell, a potential is scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. using a platinum foil as a counter electrode. When the current value in the oxygen atmosphere measured between the two electrodes at 0.4 V on the basis of the reversible hydrogen electrode potential is I _O2 and the current value in the nitrogen atmosphere is I _N2 , R = (I _O2 −I A value represented by _N2 ) / _IN2 is 0.5 or more, and an oxygen reduction electrode for a polymer electrolyte fuel cell is obtained.

  Further, according to the present invention, in the oxygen reduction electrode for a polymer electrolyte fuel cell, a potential is scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. using a platinum foil as a counter electrode. In this case, an oxygen reduction electrode for a polymer electrolyte fuel cell is obtained in which the potential between both electrodes when the oxygen reduction current starts to flow is 0.5 V or more on the basis of the reversible hydrogen electrode potential.

  Moreover, according to the present invention, there is provided a method for producing a titanium carbonitride powder used for the oxygen electrode catalyst for a polymer electrolyte fuel cell, wherein the carbon content of the titanium carbonitride powder is 6.0 to 19.0% by mass. So that at least one of titanium oxide, titanium hydride, and metal titanium as a titanium raw material is mixed with carbon black powder, and the amount of nitrogen in the mixed powder is 15.5-2. A first heat treatment step in which heat treatment is performed in nitrogen or a mixed atmosphere of nitrogen and hydrogen at 1400 to 1800 ° C. so as to be 0% by mass, and titanium carbonitride powder subjected to the first heat treatment is 1200 A second heat treatment step in which heat treatment is further performed in each of the above-described atmospheres or vacuum at ˜1600 ° C., and a titanium carbonitride powder subjected to the first heat treatment, or a second heat treatment was performed. Charcoal Method for producing a polymer electrolyte fuel cell oxygen electrode catalyst, characterized in that the titanium powder and a grinding step of grinding in a ball mill or an impact pulverizer or a jet mill can be obtained.

  According to the present invention, there is also provided a method for producing a composite titanium carbonitride powder used for an oxygen electrode catalyst for a polymer electrolyte fuel cell, wherein at least one of titanium oxide, titanium hydride, and titanium metal as a titanium raw material. An oxide powder, a metal powder, or a carbide powder in which at least one element of zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten is 0.1 to 20% by mass; and 6.0 A mixing step of mixing carbon black powder so as to contain ˜19.0% by mass of carbon and 0.1 to 5.9% by mass of free carbon, and the amount of nitrogen in the composite titanium carbonitride powder is 15. 1st heat processing process which heat-processes the said mixed powder in 1400-1800 degreeC nitrogen or the mixed atmosphere of nitrogen and hydrogen so that it may become 5-2.0 mass% A second heat treatment step of further heat-treating the composite titanium carbonitride powder subjected to the first heat treatment in the respective atmosphere or vacuum at 1200 to 1600 ° C., and the first heat treatment A pulverizing step of pulverizing the composite titanium carbonitride powder subjected to the above or the composite titanium carbonitride powder subjected to the second heat treatment with at least one pulverizing means of a ball mill, an impact pulverizer, and a jet mill. A method for producing an oxygen electrode catalyst for a polymer electrolyte fuel cell is provided.

  Moreover, according to this invention, it is a method of manufacturing the said oxygen reduction electrode for polymer electrolyte fuel cells, Comprising: The process of mixing the catalyst of Claim 1 or Claim 3, and electroconductive carbon black powder. And a step of mixing the mixed powder with a binder Teflon to form a paste, applying the paste to the surface of the glassy carbon substrate and drying to form a coating film made of a catalyst and a conductive material on the carbon-based substrate; And a step of coating the coating film with Nafion, a polymer electrolyte, to obtain a method for producing an oxygen reduction electrode for a polymer electrolyte fuel cell.

  ADVANTAGE OF THE INVENTION According to this invention, the oxygen electrode catalyst for polymer electrolyte fuel cells which can substitute for the catalyst using platinum with an expensive and resource restrictions can be provided.

  Further, according to the present invention, the titanium carbonitride powder and the composite titanium carbonitride powder catalyst containing no platinum have the advantage that the efficiency of the fuel cell is not reduced by crossover, and oxygen in the acidic electrolyte. An oxygen electrode catalyst and an oxygen reduction electrode for a polymer electrolyte fuel cell excellent in reducing oxygen can be provided.

  The present invention will be described in more detail.

  The oxygen electrode catalyst for a polymer electrolyte fuel cell of the present invention is a catalyst for an oxygen reduction electrode used in a polymer electrolyte fuel cell in which an ion exchange membrane is disposed between a pair of electrodes, The catalyst is a cubic titanium carbonitride powder containing 2.0 to 15.5% by mass of nitrogen, 6.0 to 19.0% by mass of carbon and 0.1 to 5.9% by mass of free carbon. Have

In this polymer electrolyte fuel cell oxygen electrode catalyst, titanium carbonitride powder is either JCPDS file 42-1489 (C _0.7 N _0.3 Ti) or 42-1488 (C _0.3 N _0.7 Ti). It is preferable that the lattice constant measured by the Miller index (hkl) 511 satisfies 4.260 to 4.317４.

  In the present invention, the oxygen electrode catalyst for a polymer electrolyte fuel cell is further added to group IVa zirconium (Zr), hafnium (Hf), group Va vanadium (V), niobium (Nb), tantalum (Ta). , And VIa group chromium (Cr), molybdenum (Mo), tungsten (W) is preferably a composite titanium carbonitride powder to which at least one element of at least one element is added. Here, the IVa group element, the Va group element, and the VIa group element respectively correspond to the Group 4, Group 5, and Group 6 elements according to the revised IUPAC inorganic chemical nomenclature (1989).

  An oxygen reduction electrode for a polymer electrolyte fuel cell according to the present invention is an oxygen reduction electrode for a polymer electrolyte fuel cell that does not cause a decrease in efficiency due to crossover, and is provided with any one of the above-described catalyst and a conductive material. A carbon black powder mixture was applied onto a glassy carbon substrate on a carbon-based substrate, and a polymer electrolyte Nafion electrolyte membrane was formed on the coating membrane.

Here, in this oxygen reduction electrode for a polymer electrolyte fuel cell, a reversible hydrogen electrode was obtained when a platinum foil was used as a counter electrode and a potential scan was performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. When the current value in an oxygen atmosphere measured between both electrodes at 0.4 V with reference to the potential is I _O2 and the current value in a nitrogen atmosphere is I _N2 , R = (I _O2 −I _N2 ) / I _N2 It is preferable that the value represented by is 0.5 or more.

  Further, in this oxygen reduction electrode for polymer electrolyte fuel cell, when a platinum foil was used as the counter electrode and the potential was scanned at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., the oxygen reduction current was It is preferable that the potential between both electrodes when starting to flow has 0.5 V or more based on the reversible hydrogen electrode potential.

  In addition, in one production method of the titanium carbonitride powder used for the oxygen electrode catalyst for the polymer electrolyte fuel cell of the present invention, the titanium carbonitride powder has a titanium content such that the carbon content is 6.0 to 19.0% by mass. A mixing step of mixing one of titanium oxide, titanium hydride, and titanium metal as a raw material with carbon black powder, and so that the nitrogen content of the mixed powder is 15.5 to 2.0% by mass. 1st heat processing process which heat-processes in 1400-1800 degreeC nitrogen or the mixed atmosphere of nitrogen and hydrogen, and said 1st-1600 degreeC said titanium carbonitride powder which performed said 1st heat processing A second heat treatment step for further heat treatment in an atmosphere or a vacuum, and a titanium carbonitride powder subjected to the first heat treatment, or a titanium carbonitride powder subjected to the second heat treatment in a ball mill or And a pulverizing step of pulverizing in a hammer crusher or a jet mill.

  Further, another method for producing a composite titanium carbonitride powder used for the oxygen electrode catalyst for a polymer electrolyte fuel cell of the present invention includes titanium oxide, titanium hydride, titanium metal as a titanium raw material, zirconium , Hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, an oxide powder, a metal powder, or a carbide powder in which at least one element is 0.1 to 20% by mass; and carbon of claim 1 Mixing step of mixing carbon black powder so as to be an amount, and nitrogen or nitrogen and hydrogen at 1400 to 1800 ° C. so that the amount of nitrogen of the composite titanium carbonitride powder is 15.5 to 2.0% by mass A first heat treatment step in which heat treatment is performed on the mixed powder in a mixed atmosphere, and a composite titanium carbonitride powder that has been subjected to the first heat treatment is 1200 to 1200 The second heat treatment step for further heat treatment in the respective atmosphere or vacuum at 600 ° C. and the composite titanium carbonitride powder subjected to the first heat treatment, or the second heat treatment was performed. A pulverizing step of pulverizing the composite titanium carbonitride powder with a ball mill, an impact pulverizer, or a jet mill.

  Further, the method for producing an oxygen reduction electrode for a polymer electrolyte fuel cell according to the present invention comprises a step of mixing any one of the catalyst and conductive carbon black powder, and a binder Teflon mixed with the mixed powder. Coating the paste onto the glassy carbon substrate surface and drying to form a coating film comprising a catalyst and a conductive material on the carbon-based substrate, and coating the coating film with Nafion, a polymer electrolyte. And a process of performing.

  Next, the reason for the numerical limitation in the present invention will be described.

  In the present invention, the amount of nitrogen was limited to 2.0 to 15.5% by mass because the oxygen reduction electrode and the platinum foil were made from titanium carbonitride powder changed to 0.08 to 18.4% nitrogen. As a result of measuring the R value between the two electrodes of the counter electrode using N, the nitrogen content of the titanium carbonitride powder having an R value of 0.5 or more that gives a practical fuel cell is 2.0 to 15.5% by mass Because.

  In the present invention, the carbon content was limited to 6.0 to 19.0 mass% because the oxygen reduction electrode made from titanium carbonitride powder changed to 5.2 to 21.0% carbon content, As a result of measuring the R value between both electrodes of the counter electrode using the platinum foil, the carbon content of the titanium carbonitride powder having an R value of 0.5 or more that gives a practical fuel cell is 6.0 to 19.0% by mass. Because.

In the present invention, free carbon was limited to 0.1 to 5.9% by mass,
As a result of measuring the R value between both electrodes of an oxygen reduction electrode made of titanium carbonitride powder changed to 0.08 to 7.9% free carbon and a counter electrode using platinum foil, a practical fuel cell was obtained. This is because the free carbon of the titanium carbonitride powder having an R value of 0.5 or more obtained from 0.1 to 5.9% by mass.

  In the present invention, the lattice constant of the cubic titanium carbonitride powder was limited to 260 to 4.317%, and the oxygen reduction produced from the titanium carbonitride powder changed to 4.247 to 4.324%. As a result of measuring the R value between the electrode and the counter electrode using the platinum foil, the lattice constant of the cubic titanium carbonitride powder having an R value of 0.5 or more that gives a practical fuel cell is 4.260. This is because it is 4.317 mm.

  Further, in the present invention, 0.1 to 20% by mass of at least one element selected from zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten is added as an element to be used in addition to the raw material titanium. ing.

The reason is that the R value is measured between the oxygen reduction electrode produced from the produced composite titanium carbonitride powder and the counter electrode using the platinum foil, and a practical fuel cell of 0.5 or more can be obtained. This is because the value was obtained.

  Next, the electrochemical characteristics of the electrode will be described.

  In the present invention, it is preferable that the electrochemical characteristics of the electrode using the carbonitride are as follows. This rule is for evaluating the oxygen reduction current per unit amount of the catalyst. If this value is equal to or greater than a predetermined value, the oxygen reduction current is sufficient. That is, an electrode having the following electrochemical characteristics using the titanium carbonitride powder of the present invention is further excellent in oxygen reducing ability and stability in an acidic electrolyte.

As an electrochemical characteristic of the above electrode, in an 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., when an electric potential scan was performed at a scanning speed of 5 mV / s, the current value and _{I O2,} when the current value in a nitrogen atmosphere was _{I N2,} it is preferable that the value represented by _{R = (I O2 -I N2)} / I N2 is 0.5 or more.

  Here, the reason why the R value is limited to 0.5 or more in the present invention will be described.

Even when the potential scan is performed in an inert and reaction-free state, an electric double layer is generated at the interface between the electrode catalyst and the electrolyte, so that a current flows when the potential is scanned. This corresponds to a so-called charging / discharging current of the capacitor. Therefore, when evaluating the oxygen reduction current (current associated with the oxygen reduction reaction), it is necessary to exclude the charge / discharge current of this capacitor. Therefore, the electrolysis current I _N2 is measured in a nitrogen atmosphere as an inactive state, and this is subtracted from the current I _O2 in the oxygen atmosphere, thereby obtaining a net oxygen reduction current (I _O2 −I _N2 ). Next, it is necessary to convert the obtained oxygen reduction current into a value per unit amount of catalyst. Here, since it is the electrode surface that actually acts as an electrode catalyst, it is necessary to normalize the reaction area rather than the absolute amount of the catalyst. However, the adsorption area required by the gas phase method does not necessarily match the electrochemical area in contact with the electrolyte. Therefore, by utilizing the fact that the charge / discharge current (I _N2 ) of the electric double layer is proportional to the electrochemical reaction area of the electrode, and dividing the net oxygen reduction current by I _N2 , It can be used as an index of the catalytic ability. In this way, even if the catalyst is a powder, the catalytic ability can be easily evaluated by measuring the current in a nitrogen atmosphere and an oxygen atmosphere.

  Here, the reason why the current value at 0.4 V is adopted is that an actual fuel cell is not used as an air electrode at a potential lower than 0.4 V, and therefore there is no oxygen reduction catalytic ability at a potential of 0.4 V or higher. This is because it is not practical as an electrode.

The larger the R value, the larger the oxygen reduction current per unit electrode surface area and the higher the catalytic ability. R = 0.5 indicates that the oxygen reduction current is ½ or more of the charge / discharge current of the double layer. This is because if R is less than 0.5, there is no catalytic ability and it is not suitable for practical use as an oxygen reduction electrode.

  By the way, as a method for evaluating catalytic ability, in addition to the above method using the reduction current value at a predetermined potential as an index, the magnitude of the potential (oxygen reduction current start potential) when the oxygen reduction current starts to flow is used as an index. There is a way.

  As the oxygen reduction current starts to flow from a higher potential, the activation energy of the reaction may be smaller, and in this case, the reduction current value can be increased by engineering improvement that increases the surface area of the catalyst. In practice, the oxygen reduction current starting potential is preferably 0.5 V or more based on the reversible hydrogen electrode. In an oxygen reduction electrode for a polymer electrolyte fuel cell, when a platinum foil is used as a counter electrode and an oxygen reduction current starts to flow when a potential scan is performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. This is because the potential between the two electrodes is preferably 0.5 V or more on the basis of the reversible hydrogen electrode potential.

  It is preferable to employ either or both of the oxygen reduction current value based on the R value and the oxygen reduction starting potential as an index for evaluating catalytic ability.

  Next, examples relating to an oxygen electrode catalyst for a polymer electrolyte fuel cell, an oxygen reduction electrode for a polymer electrolyte fuel cell, and a method for producing the same according to the present invention will be described, but the present invention is not limited thereto. Of course not.

  In Examples 1 to 9 of the present invention, preparation of carbonitrided powder will be described.

Example 1
After mixing titanium oxide with an average particle size of 0.5 μm and acetylene black so that the ratio of nitrogen to carbon in the titanium carbonitride powder is 72:28, this is mixed with a Henschel mixer whose stirring blades rotate at high speed. Ethyl alcohol was added to 1 to 2 mm granules. The granular mixed powder was passed through a nitrogen atmosphere maintained at 1600 ° C. twice using a rotary graphite tube furnace and subjected to first and second heat treatments. A titanium nitride powder was obtained.

Nitrogen and carbon of the obtained titanium carbonitride powder are measured by LECO measuring device (nitrogen amount is TC600 type, carbon amount is WR112 type), and free carbon is not dissolved by strong acid. The crystal system and the lattice constant were measured using Geiger Flex manufactured by Rigaku Corporation, and the specific surface area was measured using MONOSOB manufactured by Yuasa Ionics Co., Ltd. As a result, as shown in Example 1 of Table 1 below, the amount of nitrogen was 15.5% by mass, the amount of carbon was 6.0% by mass, the amount of free carbon was 1.9% by mass, the crystal system was cubic, the lattice The constant was 4.260 Å and the specific surface area was 3.29 m ² / g.

(Example 2)
Granular titanium hydride and acetylene black were mixed so that the ratio of nitrogen to carbon in the titanium carbonitride powder was 39:61, and then mixed in a ball mill. The mixed powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1400 ° C. using a tunnel furnace, subjected to a first heat treatment, and the heat-treated product was pulverized with a ball mill.

The pulverized powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1500 ° C. using a tunnel furnace, and subjected to a second heat treatment to obtain a titanium carbonitride powder. Nitrogen, carbon, and free carbon of the obtained titanium carbonitride powder were measured in the same manner as in Example 1. As a result, as shown in Example 2 in Table 1 below, the amount of nitrogen was 8.8% by mass, the amount of carbon was 13.9% by mass, the amount of free carbon was 2.8% by mass, the crystal system was cubic, the lattice The constant was 4.290 Å and the specific surface area was 2.68 m ² / g.

(Example 3)
Metal titanium powder and acetylene black were prepared so that the ratio of nitrogen to carbon in the titanium carbonitride powder was 28:72, and then mixed by a ball mill. The mixed powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1600 ° C. using a tunnel furnace, subjected to a first heat treatment, and the heat-treated product was pulverized with a ball mill.

  The pulverized powder was filled in a graphite tray, passed through a nitrogen atmosphere at 1200 ° C. using a tunnel furnace, and subjected to a second heat treatment to obtain a titanium carbonitride powder.

Nitrogen, carbon, and free carbon of the obtained titanium carbonitride powder were measured in the same manner as in Example 1. As a result, as shown in Example 3 in Table 1 below, the amount of nitrogen was 5.4% by mass, the amount of carbon was 14.1% by mass, the amount of free carbon was 0.10% by mass, the crystal system was cubic, and the lattice The constant was 4.304 Å and the specific surface area was 1.14 m ² / g.

(Examples 4 to 9)
In the same manner as in Examples 1 to 3, the mixing ratio of the titanium raw material and acetylene black, the heat treatment temperature, and the heat treatment atmosphere were changed so that the target titanium carbonitride powder containing nitrogen, carbon, and free carbon was obtained. Titanium carbonitride powders of Examples 4 to 9 shown in Table 1 below were produced.

The specific surface area of the titanium carbonitride powder shown in Table 1 below was obtained in the range of 1.1 to 8.1 m ² / g. When the titanium carbonitride powders of Examples 1 to 9 were examined by X-ray diffraction, all of them were cubic titanium carbonitride powders. As an example, the results of X-ray diffraction of the powders of Example 7 are shown in the figure.

Also, with respect to the characteristics of the target titanium carbonitride powder, the case where nitrogen is high and carbon is low is shown in Comparative Example 1, the case where nitrogen is high and free carbon is high is shown in Comparative Example 2, and the case where nitrogen is low and free carbon is low Table 1 below shows Comparative Example 3 as a comparative example 4 where nitrogen is low and carbon is high, and Comparative Example 5 is a case where carbon is high and free carbon is high.

  Next, preparation of composite titanium carbonitride powder will be described.

Under the conditions of the titanium carbonitride powder obtained in Example 7 of the present invention, at least one element of zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten is 0. The composite titanium carbonitride powder prepared by adding at least one element of the oxide powder, metal powder, and carbide powder of the element so as to be 1 to 20% by mass when mixed with acetylene black is shown in the following table. It is shown in 2. Many combinations that can be expected to have a catalytic activity for complexation with the above-described additives are conceivable, and the present invention is not limited thereto.

  Next, oxygen electrode electrodes were prepared for Examples 1 to 9 of the characteristics of the titanium carbonitride powder and Examples 10 to 19 and Comparative Examples 1 to 5 of the composite titanium carbonitride powder, and the oxygen reduction current was measured. In the above electrolysis, any anode may be used as the counter electrode. For example, carbon, Pt, or the like can be used. However, carbon is preferable because Pt may be dissolved in a minute amount.

  Next, manufacture of an electrode is demonstrated.

Said oxygen reduction electrode can be manufactured as follows, for example. First, the above-described titanium carbonitride powder is mixed with a powder of a conductive substance such as tungsten oxide, iridium oxide, etc., and mixed with a known binder to form a paste, and this paste is applied to the surface of the carrier. An electrode is manufactured by drying. For the titanium carbonitride powder and composite titanium carbonitride powder catalyst, it is preferable to use carbon black as the conductive powder. The titanium carbonitride powder and composite titanium carbonitride powder are more preferable for fine particles, and the specific surface area depends on the preparation conditions. In the range of 1.1 to 8.1 m ² / g, a fine titanium carbonitride powder is preferable because the catalytic ability can be exhibited even with a small amount of catalyst.

  The potentials used in the following description, figures, and tables were based on the reversible hydrogen electrode potential reference, and this was indicated as RHE. A reference electrode obtained by coating Nafion on a carbon-based substrate made of cylindrical glassy carbon having a diameter of 5.2 mm was designated as GC.

  When the titanium carbonitride powder of the present invention was used for an oxygen reduction electrode, the electrode did not dissolve and was stable if it was 0.8 V or less even when used in an acidic electrolyte. Further, the inventors' research has revealed that a stable electrode in an acidic electrolyte has catalytic activity (oxygen reduction catalytic ability). Below, the advantage of using titanium carbonitride powder as a catalyst for a polymer electrolyte fuel cell will be described.

  First, production of an electrode will be described using the titanium carbonitride powder of Example 5. The electrode was prepared by using cylindrical glassy carbon having a diameter of 5.2 mm as a base material, applying a catalyst to the bottom surface, and coating Nafion. When applying the catalyst, 0.1 g of the catalyst was mixed in 5 ml of water so that it could be applied in an equal amount. Thereafter, 30 μl of the solution prepared by stirring and suspending with ultrasonic waves was applied to uniformly disperse the catalyst.

A glassy carbon electrode coated with a catalyst was immersed in a 0.1 mol / dm ³ sulfuric acid solution, and an experiment was conducted at 30 ° C. and atmospheric pressure. The gas atmosphere was nitrogen and oxygen. A reversible hydrogen electrode in the same concentration sulfuric acid solution was used as a reference electrode. The display of current density was per geometric area.

  An electrolytic cell was prepared using the above electrode as a cathode, a platinum foil as a counter electrode, and a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. as an electrolytic solution in a nitrogen atmosphere. As the reference electrode, a reversible hydrogen electrode having the same sulfuric acid concentration as described above was used. Using this electrolytic cell, a cyclic voltammogram (CV) was measured at a potential scanning speed of 50 mV / s. The potential range was 0.05 to 0.8V. This will be described with reference to FIG. 2 showing a cyclic voltammogram (CV) of an electrode in an acidic electrolyte.

  FIG. 2 is a diagram showing the CV of the electrode according to the present invention using the titanium carbonitride powder of Example 5 of the present invention. Referring to FIG. 2, in the case of the electrode according to the present invention, it can be seen that the shape of the CV curve hardly changes even when the potential scan is repeated several tens of times, and the carbonitride is stable in the acidic electrolyte.

The oxygen reduction current was measured in an oxygen atmosphere measured at 0.4 V on the basis of the reversible hydrogen electrode potential when the potential scan was performed at a scanning speed of 5 mV / s in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. using the electrolytic cell. Current value I _O2 and current value I _N2 in a nitrogen atmosphere were measured. Next, to determine the value represented by the equation _{R = (I O2 -I N2)} / I N2. The higher the reduction current, the higher the catalytic ability.

  3 and 4 are diagrams showing measurement results of the reduction current of the electrode using the titanium carbonitride powder of Example 7 and calculation results of the index R. FIG. FIG. 3 shows that a slight reduction current flows in the nitrogen atmosphere and that the reduction current is large in the oxygen atmosphere. Further, FIG. 4 shows that the index R is 0.5 or more at a potential of 0.55 V or less.

An electrode was prepared from the titanium carbonitride and composite titanium carbonitride powders of Table 1 and Table 2 in the same manner as the titanium carbonitride powder of Example 5, and the reduction current and oxygen reduction start potential were measured. A result of 3 was obtained.

  FIG. 5 shows the R index obtained from the reduction current for Examples 1 and 6 and Comparative Examples 1 and 4.

Next, measurement of the oxygen reduction start potential will be described. Using the above electrolytic cell, the potential at which I _O2 started flowing at the time of measurement of the reduction current was determined on the basis of the reversible hydrogen electrode potential, with the potential of I _O2 = -1 μA / cm ² being the oxygen reduction start potential. . The higher the oxygen reduction starting potential, the higher the catalytic ability. The oxygen reduction starting potential of the electrode using the titanium carbonitride powder of Example 7 was 0.66V.

Cubic titanium carbonitride powder having 2.0 to 15.5% by mass of nitrogen, 6.0 to 19.0% by mass of carbon and 0.1 to 5.9% by mass of free carbon, and zirconium, hafnium, vanadium , Niobium, Tantalum, Chromium, Molybdenum, Tungsten and mixed with conductive carbon black powder using titanium carbonitride powder composed of titanium carbonitride and the above-mentioned element added with up to 20% by mass of at least one element The paste is mixed with a binder Teflon to form a paste, and the paste is applied to the surface of a carrier (carbon paper) and dried to form a coating film of a catalyst and a conductive material on the carbon-based substrate. Using an oxygen electrode for a polymer electrolyte fuel cell coated with Nafion, a polymer electrolyte, in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C., a scanning speed of 5 When the potential scan at V / s, when the current value in an oxygen atmosphere to be measured at 0.4V with a reversible hydrogen electrode potential reference and I _O2, a current value in a nitrogen atmosphere was I _N2, R = (I _O2- I _N2 ) / I _N2 has a value of 0.5 or more and a potential when the oxygen reduction current starts to flow is 0.5 V or more on the basis of the reversible hydrogen electrode potential. It was.

  FIG. 6 shows a case where the titanium carbonitride powder of Example 7 was used, in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. in an oxygen atmosphere and in a 0.1 mol / L sulfuric acid + 0.1 mol / L methanol aqueous solution, at a scanning speed of 5 mV / It is a figure which shows the CV curve when the electric potential scan is carried out by s. As shown in FIG. 6, the activity of methanol decomposition catalyst was not recognized in the titanium carbonitride powder, and the same oxygen reduction current was exhibited both in the sulfuric acid aqueous solution and in the sulfuric acid + methanol aqueous solution. Therefore, the titanium carbonitride powder does not have the action of catalyzing the reaction of the fuel that crosses over from the fuel electrode. Therefore, the titanium carbonitride powder is an oxygen electrode catalyst for a polymer electrolyte fuel cell that does not cause a decrease in fuel cell efficiency due to fuel crossover It turned out to be.

  Furthermore, the oxygen reduction electrode of the present invention can be suitably used as a cathode electrode for an electrochemical system using an acidic electrolyte such as water, an inorganic substance, an organic substance, or a fuel cell.

  The oxygen reduction electrode of the present invention is suitable as an oxidizer electrode when an acidic electrolyte is used, such as a phosphoric acid fuel cell or a polymer electrolyte fuel cell. Accordingly, the present invention is not limited to the above-described embodiments.

  As described above, the oxygen electrode catalyst and the oxygen reduction electrode using the same according to the present invention are most suitable as an oxygen electrode catalyst and an oxygen reduction electrode for excellent polymer electrolyte fuel cells that reduce oxygen in an acidic electrolyte. is there.

It is a figure which shows the X-ray-diffraction figure of the titanium carbonitride powder by Example 7 of this invention. It is a cyclic voltammogram (CV) figure of the electrode using the titanium carbonitride powder by Example 5 of this invention. It is a figure which shows the measurement result of the reduction current of the electrode using the titanium carbonitride powder by Example 7 of this invention. It is a figure which shows R parameter | index from the reduction current of the electrode using the titanium carbonitride powder by Example 7 of this invention. It is a figure which shows R parameter | index from the reduction current of the electrode using the titanium carbonitride powder by the Example and comparative example of this invention. It is a figure which shows the measurement result of the reduction current in the presence of methanol of the electrode using the titanium carbonitride powder by Example 7 of this invention.

Claims (9)

  A catalyst for an oxygen reduction electrode used in a polymer electrolyte fuel cell in which an ion exchange membrane is disposed between a pair of electrodes, wherein the oxygen reduction electrode catalyst contains 2.0 to 15.5% by mass of nitrogen, carbon Is a cubic titanium carbonitride powder containing 6.0 to 19.0% by mass and 0.1 to 5.9% by mass of free carbon. 2. The oxygen electrode catalyst for a polymer electrolyte fuel cell according to claim 1, wherein the titanium carbonitride powder is 42-1489 (C _0.7 N _0.3 Ti) or 42-1488 (C _0.3 N) of JCPDS file. Oxygen for polymer electrolyte fuel cell, characterized by having a cubic system conforming to _0.7 Ti) and having a lattice constant measured by Miller's index (hkl) 511 of 4.260 to 4.317Å Polar catalyst.   2. The oxygen electrode catalyst for a polymer electrolyte fuel cell according to claim 1, wherein the catalyst is further selected from among group IVa zirconium, hafnium, group Va vanadium, niobium, tantalum, group VIa chromium, molybdenum, and tungsten. An oxygen electrode catalyst for a polymer electrolyte fuel cell, which is a composite titanium carbonitride powder to which at least one element of 0.1 to 20% by mass is added.   An oxygen reduction electrode for a polymer electrolyte fuel cell that does not cause a decrease in efficiency due to crossover, wherein a mixture of the catalyst according to claim 1 or 2 and a conductive carbon black powder is added to a glassy substrate on a carbon-based substrate. An oxygen reduction electrode for a polymer electrolyte fuel cell, characterized in that it is coated on a carbon substrate, and a polymer electrolyte Nafion (registered trademark) electrolyte film is formed on the coating film. 5. The oxygen reduction electrode for a polymer electrolyte fuel cell according to claim 4, wherein a platinum foil is used as a counter electrode, and the potential is scanned in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. at a scanning speed of 5 mV / s. When the current value in an oxygen atmosphere measured between both electrodes at 0.4 V with respect to the hydrogen electrode potential is I _O2 and the current value in a nitrogen atmosphere is I _N2 , R = (I _O2 −I _N2 ) / An oxygen reduction electrode for a polymer electrolyte fuel cell, wherein the value represented by I _N2 is 0.5 or more.   5. The oxygen reduction electrode for a polymer electrolyte fuel cell according to claim 4, wherein a platinum foil is used as a counter electrode, and oxygen scanning is performed in a 0.1 mol / L sulfuric acid aqueous solution at 30 ° C. at a scanning speed of 5 mV / s. An oxygen reduction electrode for a polymer electrolyte fuel cell, wherein a potential between both electrodes when a reduction current starts to flow has 0.5 V or more on the basis of the reversible hydrogen electrode potential. It is a manufacturing method of the titanium carbonitride powder used for the oxygen electrode catalyst for polymer electrolyte fuel cells of Claim 1, Comprising: The carbon amount of the said titanium carbonitride powder is set to 6.0-19.0 mass%. A mixing step of mixing carbon black powder with at least one of titanium oxide, titanium hydride, and titanium metal as a titanium raw material;
A first heat treatment step in which heat treatment is performed in a mixed atmosphere of nitrogen or nitrogen and hydrogen at 1400 to 1800 ° C. so that the amount of nitrogen in the mixed powder is 15.5 to 2.0% by mass;
A second heat treatment step of further heat-treating the titanium carbonitride powder subjected to the first heat treatment in the respective atmosphere or vacuum at 1200 to 1600 ° C .;
A pulverizing step of pulverizing the titanium carbonitride powder subjected to the first heat treatment or the titanium carbonitride powder subjected to the second heat treatment with a ball mill, an impact pulverizer, or a jet mill. A method for producing an oxygen electrode catalyst for a polymer electrolyte fuel cell. A method for producing a composite titanium carbonitride powder used for an oxygen electrode catalyst for a polymer electrolyte fuel cell, comprising at least one of titanium oxide, titanium hydride, and titanium metal as a titanium raw material, zirconium, hafnium, vanadium, Oxide powder or metal powder or carbide powder in which at least one element of niobium, tantalum, chromium, molybdenum, and tungsten is 0.1 to 20% by mass, and 6.0 to 19.0% by mass Mixing the carbon black powder so as to contain carbon and 0.1-5.9 mass% free carbon;
1st heating which heat-processes the said mixed powder in 1400-1800 degreeC nitrogen or the mixed atmosphere of nitrogen and hydrogen so that the nitrogen amount of the said composite titanium carbonitride powder may be 15.5-2.0 mass% Processing steps;
A second heat treatment step of further subjecting the composite titanium carbonitride powder subjected to the first heat treatment to heat treatment in the respective atmosphere or vacuum at 1200 to 1600 ° C .;
The composite titanium carbonitride powder subjected to the first heat treatment or the composite titanium carbonitride powder subjected to the second heat treatment is subjected to at least one kind of pulverization means among a ball mill, an impact pulverizer, and a jet mill. A method for producing an oxygen electrode catalyst for a polymer electrolyte fuel cell, comprising a pulverizing step. A method for producing an oxygen reducing electrode for a polymer electrolyte fuel cell according to claim 5, wherein the catalyst according to claim 1 or 3 and a conductive carbon black powder are mixed, A step of forming a coating film composed of a catalyst and a conductive material on a carbon-based substrate by coating the mixed powder with a binder Teflon to form a paste, applying the paste to a glassy carbon substrate surface, and drying the coating; And a step of coating the membrane with Nafion (registered trademark) as a polymer electrolyte. A method for producing an oxygen reduction electrode for a polymer electrolyte fuel cell, comprising:

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