JP2016062826A - Electrode catalyst and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalyst having chemical stability under conditions from an acidic condition to a basic condition and excellent in catalyst activity under the conditions.SOLUTION: An electrode catalyst includes a metal nitride containing molybdenum (Mo) or tungsten (W), and the metal nitride may be a ternary compound nitride containing transition metal. The electrode catalyst is manufactured using a method in which a catalyst material containing molybdenum or tungsten and/or transition metal is fired to obtain a precursor oxide, and a metal nitride is obtained by firing the precursor oxide in the presence of a nitrogen-containing material to be nitrided.SELECTED DRAWING: None

Description

  The present invention relates to an electrode catalyst, and more particularly to an electrode catalyst having chemical stability from an acidic condition to a basic condition and having excellent catalytic activity under the above condition.

The air battery uses oxygen as a positive electrode active material, and does not need to have a positive electrode active material in the battery. Therefore, it is possible to contain more negative electrode active materials than other batteries such as lead-acid batteries, nickel-metal hydride batteries, lithium ion batteries, etc., and the energy density is high and the size and weight can be reduced. Have advantages. Therefore, it is expected to be used as a next-generation automobile power source.
As the air battery, for example, a metal air battery such as a lithium air battery, a magnesium air battery, or a zinc air battery is known.

  An air battery is composed of a positive electrode, an electrolytic solution, a negative electrode, a separator, and the like. The positive electrode has a function of taking in oxygen from the outside and reacting during discharge, and a gas diffusion electrode is often used. In general, the gas diffusion electrode contains a catalyst that promotes the oxidation-reduction reaction.

Further, when the electrolyte is an aqueous electrolyte, it is considered that the following discharge reaction proceeds.
(During discharge)
Negative electrode: M → M ⁺ + e ⁻
Positive electrode: O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻

As described above, since the concentration of hydroxide ions generated from the positive electrode increases as the discharge proceeds, the pH of the electrolytic solution increases. In addition, since there is a possibility of using an acidic solution as the electrolytic solution, the catalyst is required to have stable and catalytic activity in a wide range of pH as well as neutral, and platinum (Pt) or platinum An alloy is used.
However, since platinum is very expensive and is a rare metal in terms of resources, development of a non-Pt catalyst is required.

  In Patent Document 1, as an oxygen reduction catalyst using a transition metal oxide into which oxygen defects are introduced, an electrolytic solution having any properties of an acidic solution, an alkaline solution, a neutral solution, and an organic solvent can be used. The effect is disclosed.

JP 2012-200633 A

  However, those using transition metal oxides as oxygen reduction catalysts have insufficient oxygen reducing ability, and there is room for further improvement.

  The present invention has been made in view of such problems of the prior art. The object of the present invention is to have chemical stability from acidic conditions to basic conditions, and to be excellent under the above conditions. It is to provide an electrocatalyst having high activity.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that metal nitrides containing molybdenum (Mo) or tungsten (W) as essential components as metal components are under acidic to alkaline electrolytes. The present invention was found to be chemically stable and have excellent catalytic activity.

  That is, the electrode catalyst of the present invention is characterized by having a metal nitride containing molybdenum (Mo) or tungsten (W).

  The method for producing an electrode catalyst according to the present invention is a method for producing the above electrode catalyst via a precursor oxide, characterized by nitriding a precursor oxide obtained by firing a catalyst material containing molybdenum or tungsten. To do.

  According to the present invention, since a metal nitride containing molybdenum (Mo) or tungsten (W) is used, an electrode catalyst that is chemically stable under an acidic to alkaline electrolyte and has excellent catalytic activity is provided. Can be provided.

  In addition, according to the present invention, since the catalyst material is a precursor oxide and the precursor oxide is nitrided, it not only has chemical stability under acidic to alkaline electrolytes, but also has excellent catalytic activity. Can be produced.

It is a schematic cross section of the gas diffusion electrode produced in the Example. It is a schematic diagram of the apparatus used in order to measure the reduction current of the gas diffusion electrode produced in the Example. The XRD pattern before and behind immersion of 1M-HCl aqueous solution of the nitride produced in Example 9 is shown.

The electrode catalyst of the present invention will be described in detail.
The electrode catalyst of the present invention has a metal nitride, and the metal nitride contains at least molybdenum (Mo) or tungsten (W).
The metal nitride may contain not only molybdenum or tungsten but also other metal elements, and may be a binary or ternary metal nitride.

  The metal nitride does not elute even in a strongly acidic atmosphere such as a strongly acidic electrolyte (for example, pH 4 or less), is chemically stable, and has excellent catalytic activity in a wide pH range from acidic to alkaline.

  As said metal nitride, the metal nitride represented by the following general formula (I) can be mentioned.

但し、一般式（Ｉ）中、Ａは遷移金属元素、Ｂはモリブテン（Ｍｏ）又はタングステン（Ｗ）を表し、ｘ、ｙは、０≦ｘ≦１０、０＜ｙ≦１０である。

However, in general formula (I), A represents a transition metal element, B represents molybdenum (Mo) or tungsten (W), and x and y are 0 ≦ x ≦ 10 and 0 <y ≦ 10.

  Examples of the ternary metal nitride include ternary composite metal nitrides represented by the following general formula (II).

但し、一般式（ＩＩ）中、Ａ’Ａ’’は、互いに異なる遷移金属元素、Ｂはモリブテン（Ｍｏ）又はタングステン（Ｗ）を表し、ｘ、ｙは、０≦ｘ≦１０、０＜ｙ≦１０であり、αは、０＜α＜１である。

In general formula (II), A′A ″ represents different transition metal elements, B represents molybdenum (Mo) or tungsten (W), and x and y are 0 ≦ x ≦ 10 and 0 <y. ≦ 10 and α is 0 <α <1.

Further, when the metal element other than the molybdenum (Mo) or tungsten (W) is a transition element, the oxygen reduction activity is improved.
Examples of the transition element include iron (Fe), nickel (Ni), cobalt (Co), manganese (Mn), titanium (Ti), chromium (Cr), copper (Cu), zinc (Zn), zirconium ( Zr), niobium (Nb), tantalum (Ta), rhenium (Re), osmium (Os), iridium (Ir), silver (Ag), indium (In), gadolinium (Gd), tin (Sn), lead ( Pb), vanadium (V), gallium (Ga), lanthanum (La) and the like can be mentioned, among which iron (Fe), nickel (Ni), cobalt (Co), and manganese (Mn) are preferable.

The metal nitride is preferably an interstitial compound in which nitrogen enters between lattices of metal atoms. The interstitial compound may be not only a stoichiometric compound but also a non-stoichiometric solid solution.
What forms an interstitial compound is generally limited to those having a transition metal element of Group 4-6.

  The reason why the metal nitride of the present invention has an excellent catalytic activity has not been clarified, but the nitrogen atom has a smaller electronegativity than the oxygen atom and does not easily become an anion, so it does not become an ionic crystal. It is considered that the formation of an interstitial compound and low electric resistance also contributes to the excellent electrochemical catalytic activity.

  The composition of the metal nitride in the electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

In the electrode catalyst of the present invention, the shape and size of the metal nitride described above are not particularly limited, and the same shape and size as known metal nitrides can be used. However, the metal nitride may be granular. preferable.
The smaller the average particle size of the metal nitride, the higher the catalytic activity because the effective electrode area where the electrochemical reaction proceeds increases, which is preferable, but in fact, if the average particle size is too small, there is a phenomenon that the catalytic activity decreases. It can be seen. Therefore, the average particle diameter of the metal nitride is preferably several nm to several hundred nm.

  The “average particle diameter of metal nitride” in the present invention refers to the crystallite diameter determined from the half-value width of the diffraction peak of metal nitride in X-ray diffraction, or metal nitride particles determined from a transmission electron microscope image. It can be measured by the average value of the diameters.

The electrode catalyst of the present invention can contain a conductive material in addition to the metal nitride that promotes the electrode reaction. By including the conductive material, a gap for sufficiently diffusing a reaction gas such as oxygen can be secured in the electrode catalyst layer produced using the electrode catalyst.
Therefore, the oxygen reduction activity of the obtained electrode catalyst can be further improved. Further, by using a conductive material having sufficient electronic conductivity as a current collector, the electrode reaction is not hindered.

  In the electrode catalyst of the present invention, the metal nitride and the conductive material may be simply mixed and used, but the metal nitride is preferably supported on a conductive material. By using the conductive material as a catalyst carrier, the metal nitride can be highly dispersed, and high catalytic activity can be obtained over a long period of time.

Any conductive material may be used as long as it has a specific surface area for supporting the metal nitride in a desired dispersed state and has sufficient electronic conductivity as a current collector. It is preferably composed of atoms.
In the present invention, that the main component is a carbon atom means that it does not exclude the mixing of impurities other than about 2 to 3% by mass or less of carbon atoms.

  Examples of the conductive material include acetylene black, vulcan, ketjen black, black pearl, graphitized acetylene black, graphitized vulcan, graphitized ketjen black, graphitized black pearl, carbon nanotube, carbon nanofiber, and carbon nanohorn. , Carbon fibrils, fullerenes, graphenes, and the like. These may be used alone or in combination of two or more.

The BET specific surface area of the conductive material only needs to have a specific surface area sufficient for highly dispersing and supporting the metal nitride, preferably 5 to 1600 m ² / g, more preferably 50 to 1300 m ² / g. is there.
If the specific surface area is less than 20 m ² / g, the dispersibility of the metal nitride in the conductive material may be reduced, and sufficient power generation performance may not be obtained. If the specific surface area exceeds 1600 m ² / g, metal nitridation may occur. The effective utilization rate of things may decrease.

  Further, the size of the conductive material is not particularly limited, but from the viewpoint of controlling the ease of loading and the catalyst utilization rate within an appropriate range, the average diameter is 5 to 200 nm, preferably about 10 to 100 nm. It is good to do.

In the electrode catalyst of the present invention, the metal nitride content is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, based on the total amount of the electrode catalyst. If the content exceeds 80% by mass, the degree of dispersion of the metal nitride on the conductive material may be reduced, and the improvement in power generation performance may be small compared to the loading amount and the economic advantage may be reduced. is there. Further, if the supported amount is less than 10% by mass, the catalytic activity per unit mass may be reduced, and a large amount of electrode catalyst may be required to obtain the desired catalytic activity.
Note that the content of metal nitride can be examined by inductively coupled plasma emission spectroscopy (ICP).

<Manufacturing method>
The metal nitride can be produced by nitriding a catalyst material containing molybdenum or tungsten. The catalyst material may be a binary or ternary catalyst material containing molybdenum alone and a salt thereof, or tungsten alone and a salt thereof, and other metals other than molybdenum or tungsten.

  The binary or ternary catalyst material is prepared by mixing a solution containing a water-soluble molybdenum salt or a water-soluble tungsten salt with a solution containing another water-soluble metal material, and adjusting the pH to produce a solid. By separating, a catalyst material can be obtained.

  Specifically, solids such as precipitates are generated by adjusting the pH of the solution containing the water-soluble metal material to be acidic. As said pH, it is 0 or more and less than 7, Preferably it is 0-4. In order to adjust the acidity, an acid such as hydrochloric acid (HCl), sulfuric acid, nitric acid, and acetic acid may be added.

  Further, the mixing speed when mixing the solution containing water-soluble molybdenum or water-soluble tungsten and the solution containing other water-soluble metal material is preferably 0.1 to 5 mL / min, and preferably 1 to 2 mL / min. More preferably. If the mixing speed is less than 0.1 mL / min, it takes too much time and is not efficient, and if it exceeds 5 mL / min, the composition of the catalyst material may become non-uniform.

  Prior to the nitriding treatment, the solid material may be dried using a known method such as natural drying, evaporation to dryness, rotary evaporator, spray dryer, drum dryer or the like. What is necessary is just to select a drying time and drying temperature suitably according to the method to be used.

  Examples of the salts and water-soluble metal materials include nitrates, ammonium salts, sulfates, amines, carbonates, bicarbonates, halogen salts such as chlorides, inorganic salts such as nitrites and oxalic acid, and formic acid containing the above metal elements. Examples thereof include carboxylates such as salts and hydroxides, alkoxides, hydroxides, and the like. These may be used alone or in combination of two or more, and may be appropriately selected depending on the type and pH of the solvent in which these are dissolved. can do.

  The nitriding treatment for nitriding the catalyst material can be performed by performing heat treatment together with a material containing nitrogen. For example, it may be a solid such as urea, acetamide, thioacedamide, methylacetamide, dimethylacetamide, ammonium carbonate, EDTA, a liquid such as hydrazine, or a gas containing nitrogen such as nitrogen gas or ammonia gas.

When heating together with a solid, nitriding proceeds more in the atmosphere of nitrogen gas or ammonia gas during heating, but nitriding can be performed even in the presence of an inert gas such as Ar or He. For example, urea decomposes when heated to generate gaseous ammonia. Nitriding can be performed by reacting with the ammonia gas. Further, it may be dissolved in water together with the water-soluble metal material. In that case, the resulting nitride becomes finer, and the effect of becoming a highly active catalyst can be expected.
Moreover, when using gas, it can nitride by performing the heat processing in the gas flow atmosphere of nitrogen containing gas, such as nitrogen gas and ammonia gas. When nitrogen gas is used, nitriding can be promoted by using it as a mixed gas with hydrogen.

  Examples of the nitriding treatment conditions include heating in a temperature range of 600 ° C. to 1000 ° C. for about 5 hours to 20 hours, depending on the metal catalyst material and the amount ratio thereof. Moreover, as flow volume of nitrogen or ammonia gas, about 100 mL / min-1000 mL / min can be illustrated at normal temperature.

The metal nitride of the present invention may be subjected to direct nitriding treatment of the catalyst material. However, it is preferable that the catalyst material is calcined to be a precursor oxide, and the precursor oxide is nitrided.
Those that have passed through the precursor oxide have superior catalytic activity as compared with those obtained by directly nitriding the catalyst material without passing through the precursor oxide. In the reaction between the precursor oxide and ammonia, oxygen is released with the progress of nitriding, so ammonia acts as a reducing agent and a nitriding agent.

  The firing temperature when the catalyst material is fired to form a precursor oxide can be performed in the temperature range of 300 ° C. or more and 1000 ° C. or less in the air, depending on the composition of the catalyst material. Examples of the time include baking for about 5 hours to 100 hours. Further, by performing a refinement process such as pulverization with a mortar or the like before the nitriding process, nitriding proceeds further, and a nitride having excellent catalytic activity can be obtained.

  As described above, the electrode catalyst of the present invention can be used in combination with a metal nitride and a conductive material, and the metal nitride and the conductive material may be used simply as a mixture. You may use as an electrode catalyst which made the material carry | support metal nitride.

  In the electrode catalyst in which the conductive material and the catalyst material are simply mixed, the metal nitride and the conductive material may be mixed. In addition, an electrode catalyst in which a metal nitride is supported on a conductive material can be obtained by a conventionally known method, such as an impregnation method, a liquid phase support method, an evaporation to dryness method, a colloid adsorption method, or a spray pyrolysis method. , Reverse micelles (microemulsion method), and the like.

  That is, after the pH of the dispersion in which the catalyst material is dispersed is adjusted to be acidic, the conductive material is mixed and stirred to disperse, and reacted at 10 to 60 ° C. for 1 to 10 hours to form the catalyst material on the conductive material. Is supported. Thereafter, the dispersion / mixed liquid is filtered, and the obtained solid is subjected to nitriding treatment, whereby an electrocatalyst having a metal nitride supported on the conductive material can be obtained.

  The electrode catalyst of the present invention can be used for an electrode catalyst layer of an air battery, a fuel cell or the like, and is particularly preferably used for an air battery using an aqueous electrolyte or a catalyst layer of a positive electrode of a fuel cell.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Reference Examples, but the present invention is not limited to these.

[Example 1]
In pure water, ammonium molybdate hydrate _{(NH 4) 6 Mo 7 O} 24 · 4H 2 O was added, was prepared by stirring the solution (A). Similarly, nickel nitrate hydrate Ni (NO ₃ ) ₂ .4H ₂ O was added to pure water and stirred (B) and cobalt nitrate hydrate was added with Co (NO ₃ ) ₂ .4H ₂ O and stirred. Solution (C) was prepared.

The solution (B) is dropped while stirring the solution (A) so that the molar ratio is Mo: Ni: Co = 2: 1: 1, and then the solution (C) is dropped similarly. A suspension of catalyst material was obtained.
The above suspension was suction filtered, and the obtained solid was dried at 120 ° C. for 12 hours, pulverized in a mortar, baked at 650 ° C. for 9 hours, cooled to room temperature, taken out, and pulverized in a mortar. The precursor oxide was obtained.

The precursor oxide is fired at 700 ° C. for 6 hours while flowing ammonia gas (purity 99.8% or more) at 200 mL / min, and has a composition of Ni _1.5 Co _1.5 Mo ₃ N. A nitride was obtained.

  0.4 g of carbon black (Ketjen Black EC) as a conductive material was mixed with 0.3 g of the metal nitride to obtain an electrode catalyst.

[Example 2]
A metal nitride having a composition of Co ₃ Mo ₃ N in the same manner as in Example 1 except that nickel nitrate is not used and mixing is performed so that the molar ratio is Mo: Co = 1: 1. An electrode catalyst containing was obtained.

[Example 3]
In Example 1, Ni ₂ Mo ₃ N was used in the same manner as in Example 1 except that cobalt nitrate was not used and the molar ratio was Mo: Ni = 3: 2 and the mixture was fired at 750 ° C. An electrode catalyst containing a metal nitride having a composition was obtained.

[Example 4]
In Example 1, instead of nickel nitrate and cobalt nitrate, iron nitrate hydrate was used, mixed so that the molar ratio was Mo: Fe = 1: 1, and fired at 750 ° C. Example 1 In the same manner as above, an electrode catalyst containing a metal nitride having a composition of Fe ₃ Mo ₃ N was obtained.

[Example 5]
In Example 1, an electrode catalyst containing a metal nitride having a Mo ₂ N composition was obtained in the same manner as in Example 1 except that nickel nitrate and cobalt nitrate were not used and calcination was performed at 700 ° C. for 9 hours.

[Example 6]
In Example 1, except that nickel nitrate and cobalt nitrate were not used, there was no step of obtaining a precursor oxide by baking at 650 ° C. for 9 hours, and nitriding was carried out by baking at 700 ° C. for 9 hours. In the same manner as in Example 1, an electrode catalyst containing a metal nitride having a composition of Mo ₂ N was obtained.

[Example 7]
In pure water, and stirred added ammonium tungstate hydrate _{(NH 4) 10 W 12 O} 41 · 4H 2 O, the solution (D) was prepared. Similarly, manganese nitrate hydrate Mn (NO ₃ ) ₂ .4H ₂ O added to pure water and stirred was prepared as a solution (E).

The solution (E) was dropped while stirring the solution (D) so that the molar ratio was W: Mn = 1: 1, thereby obtaining a mixed solution of catalyst materials. The mixture was concentrated in the atmosphere until the total amount was 30 ml or less, then transferred to an alumina boat and dried at 120 ° C. for 12 hours.
The obtained solid was heated to 800 ° C., calcined for 9 hours while flowing ammonia gas (purity 99.8% or more) at 200 mL / min, and an electrode catalyst containing a metal nitride having a composition of MnWN ₃ was obtained. Obtained.

[Example 8]
An electrocatalyst containing a metal nitride having a composition of MnWN ₃ by burning a commercially available manganese tungstate MnWO ₄ powder at 750 ° C. for 9 hours while flowing ammonia gas (purity 99.8% or more) at 200 mL / min. Got.

[Example 9]
In pure water, it added and stirred ammonium tungstate hydrate _{(NH 4) 10 W 12 O} 41 · 4H 2 O, the solution (F) was prepared. Similarly, a solution obtained by adding cobalt nitrate hydrate Co (NO ₃ ) ₂ .4H ₂ O to pure water and stirring the solution (G), a solution obtained by adding 4H-EDTA to pure water and stirring the solution (H), pure A solution obtained by adding polyethylene imide (PEI) to and stirring was prepared as solution (I).

While the solution (F) is being stirred, the solution (G) is added dropwise so that the molar ratio of Co: W: EDTA = 1: 1: 2 EDTA is half the weight of PEI. H) and solution (I) were added dropwise in the same manner to obtain a mixed solution.
The mixture was concentrated in the atmosphere until the total amount became 30 ml or less, then transferred to an alumina boat and dried at 120 ° C. for 12 hours. The obtained solid was heated to 800 ° C. and baked at 200 mL / min for 15 hours in a nitrogen flow. As a result, an electrode catalyst having a composition of Co ₃ W ₃ N was obtained.
The nitride obtained above was washed with water and then immersed in 1M HCl aqueous solution for 12 hours. The XRD pattern before and after immersion is shown in FIG.

[Comparative Example 1]
Carbon black (Ketjen Black EC) 0.4 g as a conductive material was mixed with 0.3 g of manganese dioxide manufactured by High Purity Chemical Co., Ltd. to obtain an electrode catalyst.
In order to confirm the acid resistance of this oxide, it was confirmed that it was dissolved when immersed in 1M HCl.

[Comparative Example 2]
Pure water of ammonium molybdate hydrate _{(NH 4)} was dissolved _{10 M 7 O 24 · 4H 2} O, 650 ℃ After drying 70 ° C., to obtain a MoO ₂ and heated for 3 hours.
In order to confirm the acid resistance of the obtained oxide, it was confirmed that it was dissolved when immersed in 1M HCl.

[Comparative Example 3]
In Example 1, ammonium molybdate hydrate, nickel nitrate, instead of cobalt nitrate, using iron nitrate hydrate, except that the calcined for 9 hours at 800 ° C., the Fe 3 _N in the same manner as in Example 1 An electrode catalyst containing a metal nitride having a composition was obtained.
In order to confirm the acid resistance of the obtained nitride, it was confirmed that it was dissolved when immersed in 1M-HCl.

<Evaluation>
The catalytic activity of the electrode catalyst prepared above was measured and evaluated according to the following procedure.

1. Fabrication of gas diffusion electrode
Carbon black (acetylene black) 6g, surfactant (Triton X-100) 6g, and pure water 180mL were mixed. Further, PTFE dispersion (Daikin Kogyo Polyflon D-1E, PTFE 60 wt%) was added with 0.3 g in terms of solid content, mixed and pulverized with a homogenizer, suction filtered, and dried at 120 ° C. for 12 hours.
The dried product was pulverized and atomized, and heat treated at 280 ° C. for 3 hours to remove Triton X-100 and pulverized to obtain a gas diffusion layer forming powder.

After adding 0.4 g of the electrode catalyst of Example 1 above to a mixed solution of 10 mL of 1-butanol and 100 mL of pure water, the mixture was stirred for 1 hour, and then a PTFE dispersion (Daikin Industries, Ltd. Polyflon D-1E, PTFE 60 wt%). ) Was added in an amount of 0.3 g in terms of solid content, and the mixture was further stirred for 1 hour.
This was suction filtered, dried at 120 ° C. for 12 hours, and further pulverized to obtain a powder for forming a catalyst layer.

  Moreover, except having used the electrode catalyst of the said Examples 2-9 and Comparative Examples 1-3, the powder for catalyst layer formation was obtained similarly.

Ni mesh is placed on a hot press mold, and 120 mg of the gas diffusion layer forming powder is uniformly filled thereon, and further 60 mg of the catalyst layer forming powder is uniformly filled, and this is filled at 30 MPa for 10 minutes. Pressed.
The molded body taken out from the mold is sandwiched between metal plates, placed in an electric furnace heated to 550 ° C., the internal temperature of the molded body is raised to 380 ° C., taken out again, and pressed at 60 MPa for 10 minutes. Thus, a gas diffusion electrode in which a current collector, a gas diffusion layer, and a catalyst layer were laminated was produced.

A cross-sectional view of the gas diffusion electrode is shown in FIG. In FIG. 1, 101 is a Ni mesh, 102 is a gas diffusion layer, and 103 is a catalyst layer.
The gas diffusion layer had a thickness of 0.2 mm and a diameter of 15 mmφ, and the electrode catalyst layer had a thickness of 0.2 mm and a diameter of 15 mmφ.

2. Evaluation of gas diffusion electrodes
The reduction current of the gas diffusion electrode produced above was measured at 70 ° C. using the apparatus shown in FIG.
The gas diffusion electrode 100 produced above is attached to a cell, a platinum plate is used as the counter electrode 130, a hydrogen electrode is used as the reference electrode (RHE) 140 in the 2N—H ₂ SO ₄ aqueous solution 110, and the reaction gas is pure. Oxygen was flowed at 80 mL / min. Using a potentiostat 150, a stable potential (rest potential, RP) was confirmed after several minutes. After passing a current of 10 mA for 10 minutes, the potential was swept in the negative direction, the reduction current was measured, and recorded by the XT recorder 160.

In addition, a current density I ₇₀₀ (mA / cm ² ) at a positive electrode potential of 700 mV when a 5N-KOH aqueous solution is used as an electrolytic solution and a current density I ₄₀₀ at a positive electrode potential of 400 mV when a H ₂ SO ₄ aqueous solution is used as an electrolytic solution. (MA / cm ² ) was measured. The measurement results are shown in Table 1.

※―の項目については未実施、×については酸に溶解するため実施できず。

* Items marked with-are not implemented, and those marked with x cannot be implemented because they dissolve in acid.

100 gas diffusion electrode 101 Ni mesh 102 gas diffusion layer 103 catalyst layer 110 _2N-H 2 SO ₄ aqueous 120 bath 130 counter 140 reference electrode 150 potentiostat 160 X-T Recorder 170 Luggin capillary

Claims (8)

  An electrode catalyst comprising a metal nitride containing molybdenum (Mo) or tungsten (W). The electrode catalyst according to claim 1, wherein the metal nitride is represented by the following general formula (I).

However, in general formula (I), A represents a transition metal element, B represents molybdenum (Mo) or tungsten (W), and x and y are 0 ≦ x ≦ 10 and 0 <y ≦ 10. The electrode catalyst according to claim 1, wherein the metal nitride is a ternary composite metal nitride represented by the following general formula (II).

In general formula (II), A′A ″ represents different transition metal elements, B represents molybdenum (Mo) or tungsten (W), and x and y are 0 ≦ x ≦ 10 and 0 <y. ≦ 10 and α is 0 <α <1.   The transition metal element is iron (Fe), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), titanium (Ti), copper (Cu), zinc (Zn), niobium (Nb) , Zirconium (Zr), tantalum (Ta), rhenium (Re), osmium (Os), iridium (Ir), silver (Ag), indium (In), gadolinium (Gd), tin (Sn), lead (Pb) The electrode catalyst according to claim 2, wherein the electrode catalyst is selected from vanadium (V), gallium (Ga), and lanthanum (La).   The electrode catalyst according to any one of claims 1 to 4, wherein a precursor oxide obtained by calcining a catalyst material containing molybdenum or tungsten is nitrided.   A method for producing an electrode catalyst according to any one of claims 1 to 5, wherein a precursor oxide obtained by firing a catalyst material containing molybdenum or tungsten is subjected to nitriding treatment. Method.   The method for producing an electrode catalyst according to claim 6, wherein the nitriding treatment is performed by baking in the presence of a nitrogen-containing material.   The method for producing an electrode catalyst according to claim 6, wherein the nitriding treatment is performed in an atmosphere of a gas containing nitrogen.

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