JP2015129347A - Electrode catalyst for water electrolysis and water electrolyzer using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalyst for water electrolysis which is stable even under a high potential and is capable of exhibiting sufficient catalytic activity even if it contains a reduced amount of noble metal or no noble metal.SOLUTION: The electrode catalyst for water electrolysis of the present invention contains: a carrier containing an oxide which contains at least one element selected from the group consisting of Sn, Sb, Nb, Ta, and Ti and has electron conductivity; and an oxide catalyst which is carried on the carrier, contains at least one element selected from the group consisting of group 4 elements and group 5 elements, and has an oxygen defect.

Description

  The present invention relates to an electrode catalyst for water electrolysis and a water electrolysis apparatus using the electrode catalyst for water electrolysis.

  Examples of the electrochemical device used under a high potential include a water electrolysis apparatus.

For example, in a polymer electrolyte water electrolysis apparatus, it is possible to generate hydrogen and oxygen from water by the reactions shown in the following formulas (1) and (2). This reaction theoretically requires a voltage of 1.23 V or higher under standard conditions (25 ° C., 1 atm).
H ₂ O → 2H ⁺ + 2e ⁻ + 1 / 2O ₂ ↑ (1)
2H ⁺ + 2e ⁻ → H ₂ ↑ (2)

In solid polymer water electrolyzers, in general, the anode contains platinum (Pt), iridium oxide (IrO ₂ ), etc. that are stable in a wide potential range and have high catalytic ability for the electrochemical reaction of the anode. It is used as a catalyst, and platinum or the like is used as a catalyst for the cathode.

  However, since noble metals such as platinum and iridium have limited resources and are expensive, conventionally, methods for reducing the amount of noble metal used and catalysts that replace noble metals have been developed.

Patent Document 1 discloses using a metal oxide of a non-noble metal as an electrode catalyst as an alternative to a noble metal catalyst. Specifically, an electrode catalyst containing at least one transition metal oxide as a main catalyst among ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O _5, TiO _{2 and the} like provided with oxygen defects and gold as a promoter. Is disclosed. This electrode catalyst is stable even in an acidic electrolyte, and realizes high activity by providing a promoter. It is also disclosed that these catalysts are supported on an electron conductive carrier such as carbon, iridium oxide and tungsten oxide.

Patent Document 2 discloses a catalyst for water electrolysis in which iridium oxide is supported on an inorganic oxide having a high BET surface area. Specifically, a catalyst containing an inorganic oxide having a high BET specific surface area such as titania (TiO ₂ ), silica (SiO ₂ ), alumina (Al ₂ O ₃ ), and iridium oxide is disclosed. The inorganic oxide is present in an amount of less than 20% by mass with respect to the total mass of the catalyst. Patent Document 2 discloses that this catalyst exhibits a higher catalytic activity than that of iridium oxide alone.

International Publication No. 2006/019128 Special table 2007-514520 gazette

  In studying an electrocatalyst for water electrolysis that is stable even under high potential (water electrolysis conditions of 1.23 V or more), the catalyst is required to have stability under high potential and catalytic activity for each electrochemical reaction. It is done. Precious metals such as platinum and iridium oxide have catalytic activity for electrochemical reaction of water electrolysis, but are limited in resources and expensive. Therefore, the catalyst is preferably a catalyst with a reduced amount of noble metal used or a non-noble metal. Further, the carrier supporting the catalyst is required to be stable at a high potential and to have high electron conductivity because electrons contributing to the reaction move in the carrier. Furthermore, for the same reason as in the case of the catalyst, it is desired that the support does not contain a noble metal element.

The catalyst disclosed in Patent Document 1 uses, as an electron conductive carrier, carbon that dissolves as CO ₂ by reaction under high potential, expensive iridium oxide, and the like, and is stable even under water electrolysis conditions. Problems remain in examining the electrocatalyst for water electrolysis.

  The catalyst disclosed in Patent Document 2 has a configuration in which iridium oxide having catalytic activity is supported on a support made of an inorganic oxide. In the catalyst having this configuration, since the inorganic oxide as a carrier does not have electronic conductivity, iridium oxide bears the electronic conductivity of the entire catalyst. Therefore, in order to ensure electronic conductivity, the amount of inorganic oxide must be suppressed to less than 20% by mass, and as a result, the amount of expensive iridium oxide used must be increased.

  Therefore, the present invention provides an electrode catalyst for water electrolysis that is stable even at a high potential and that can exhibit sufficient catalytic activity even when the amount of noble metal is reduced or no noble metal is contained. For the purpose.

The electrocatalyst for water electrolysis which is one embodiment of the present invention,
A support containing an oxide having at least one element selected from the group consisting of Sn, Sb, Nb, Ta and Ti and having an electron conductivity;
An oxide catalyst having at least one element selected from the group consisting of Group 4 elements and Group 5 elements supported on the carrier and having oxygen defects;
including.

  In the electrode catalyst for water electrolysis that is one embodiment of the present invention, the oxide contained in the support can have a relatively high surface area and electron conductivity while being a non-noble metal oxide, and even at a high potential. It is stable. Further, the catalyst supported on the carrier is an oxide in which an oxygen defect serving as an active site of reaction is provided in an oxide containing at least one element selected from the group consisting of Group 4 elements and Group 5 elements. It is a catalyst and exhibits a sufficient activity for water oxidation reaction while being stable at a high potential. Therefore, the electrode catalyst for water electrolysis is stable even at a high potential, and can further exhibit sufficient catalytic activity even if the amount of noble metal is reduced or no noble metal is contained.

Schematic sectional view showing a configuration example of a water electrolysis apparatus according to Embodiment 2 of the present invention X-ray diffraction patterns of Sb-doped tin oxide (ATO) used as a support in the electrode catalyst powder for water electrolysis of Examples 1 to 4 and the electrode catalyst powder for water electrolysis of Examples 1 to 4 X-ray diffraction patterns of Sb-doped tin oxide (ATO) used as a support in the electrocatalyst powder for water electrolysis of Examples 6 to 8 and the electrocatalyst powder for water electrolysis of Examples 6 to 8

The first aspect of the present invention is:
A support containing an oxide having at least one element selected from the group consisting of Sn, Sb, Nb, Ta and Ti and having an electron conductivity;
An oxide catalyst having at least one element selected from the group consisting of Group 4 elements and Group 5 elements supported on the carrier and having oxygen defects;
An electrode catalyst for water electrolysis is provided.

  In the electrode catalyst for water electrolysis according to the first aspect, the oxide contained in the support can have a relatively high surface area and electronic conductivity while being a non-noble metal oxide, and is stable even at a high potential. It is. Further, the catalyst supported on the carrier is an oxide in which an oxygen defect serving as an active site of reaction is provided in an oxide containing at least one element selected from the group consisting of Group 4 elements and Group 5 elements. It is a catalyst and exhibits a sufficient activity for water oxidation reaction while being stable at a high potential. Therefore, the electrode catalyst for water electrolysis according to the first aspect is stable even at a high potential, and can further exhibit a sufficient catalytic activity even when the amount of noble metal is reduced or no noble metal is contained. It is.

According to a second aspect of the present invention, in the first aspect,
The catalyst ratio of the oxide catalyst in the electrode catalyst for water electrolysis (weight of the oxide catalyst / (weight of the oxide catalyst + weight of the support)) is more than 0 wt% and not more than 42 wt%.
An electrode catalyst for water electrolysis is provided.

  When the catalyst ratio is 42 wt% or less, the reduction of the surface area due to the aggregation of the catalysts is reduced, and the amount of the catalyst with poor electron conductivity is reduced, so that electrical contact between the carriers and the collecting electrode is achieved. The number of points increases, electrons generated by the reaction are more easily moved, and high electron conductivity can be realized. Thereby, the electrode catalyst for water electrolysis which concerns on a 2nd aspect can implement | achieve the stability and high catalyst activity under high potential more reliably.

According to a third aspect of the present invention, in the first or second aspect,
The carrier includes Sn and an oxide having electronic conductivity.
An electrode catalyst for water electrolysis is provided.

  A carrier containing Sn and an oxide having electron conductivity is likely to have oxygen defects at the interface with the oxide catalyst. Therefore, the electrode catalyst for water electrolysis according to the third aspect can realize higher electron conductivity. Thereby, the electrode catalyst for water electrolysis which concerns on a 3rd aspect can implement | achieve the stability and high catalyst activity under high potential more reliably.

According to a fourth aspect of the present invention, in the third aspect,
The carrier includes an oxide obtained by doping SnO ₂ with at least one element selected from the group consisting of Sb, Nb and Ta.
An electrode catalyst for water electrolysis is provided.

An oxide obtained by doping SnO ₂ with at least one element selected from the group consisting of Sb, Nb, and Ta can maintain stable oxygen defects. Therefore, oxygen diffusion occurs at the interface between the support and the oxide catalyst, and the decrease in the amount of oxygen defects in the oxide catalyst due to the electrochemical reaction is suppressed, so that the oxide catalyst can maintain high catalytic activity for a long period of time. It becomes possible. Thereby, the electrode catalyst for water electrolysis which concerns on a 4th aspect can implement | achieve stability and high catalyst activity under high potential more reliably.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects,
The oxide catalyst further comprises at least one element selected from the group consisting of N and C;
An electrode catalyst for water electrolysis is provided.

  Examples of the electrode catalyst for water electrolysis according to the fifth aspect include a configuration example in which part of oxygen in the oxide catalyst is substituted with N (nitrogen), C (carbon), or both. According to this configuration, the oxide catalyst has an increased amount of free electrons as the trivalent nitrogen or tetravalent carbon is substituted for the divalent oxygen, so that the electron conductivity of the catalyst itself is improved. Further, as another configuration example of the electrode catalyst for water electrolysis according to the fifth aspect, carbon or a substance in which a part of carbon is substituted with nitrogen covers at least a part of the surface of the oxide catalyst. A configuration is also mentioned. In this configuration example, carbon itself or a substance in which a part of carbon is substituted with nitrogen has conductivity, so that these become an electron conduction path when the catalyst undergoes a surface reaction. Thereby, the electronic conductivity of the catalyst itself is improved.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects,
The Group 4 elements are Ti and Zr;
An electrode catalyst for water electrolysis is provided.

  The oxides of Ti and Zr are stable even in an acidic electrolyte, and the oxides provided with oxygen defects have activity for water oxidation reaction. Therefore, according to the electrode catalyst for water electrolysis according to the sixth aspect, higher catalytic activity can be realized.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects,
The Group 5 elements are Nb and Ta,
An electrode catalyst for water electrolysis is provided.

  The oxides of Nb and Ta are stable even in an acidic electrolyte, and the oxides provided with oxygen defects have activity for water oxidation reaction. Therefore, according to the electrode catalyst for water electrolysis according to the seventh aspect, higher catalytic activity can be realized.

According to an eighth aspect of the present invention, in any one of the first to seventh aspects,
And further comprising a promoter containing at least one element selected from the group consisting of Pt, Ir, Ni and Co.
An electrode catalyst for water electrolysis is provided.

  A substance containing at least one element selected from the group consisting of Pt, Ir, Ni and Co has a high activity for water oxidation reaction. Therefore, according to the electrode catalyst for water electrolysis according to the eighth aspect, higher catalytic activity can be realized.

The ninth aspect of the present invention provides
An anode containing the electrocatalyst for water electrolysis according to any one of the first to eighth aspects;
A cathode,
A water electrolysis apparatus comprising:

  The water electrolysis apparatus according to the ninth aspect includes the electrode catalyst for water electrolysis according to any one of the first to eighth aspects having catalytic activity for water oxidation reaction as an anode catalyst. Therefore, the water electrolysis apparatus according to the ninth aspect can improve the efficiency of the water electrolysis apparatus and the system including the water electrolysis apparatus, and can reduce the amount of noble metal or reduce the cost by not using the noble metal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiment is an example, and the present invention is not limited to the following embodiment.

(Embodiment 1)
An embodiment of the electrode catalyst for water electrolysis of the present invention will be described. The electrode catalyst for water electrolysis according to the present embodiment includes a support and an oxide catalyst supported on the support. The carrier includes an oxide having at least one element selected from the group consisting of Sn, Sb, Nb, Ta, and Ti and having electron conductivity (hereinafter referred to as electron conductive oxide). Yes.) The electron conductive oxide is desirably an oxide containing Sn. The oxide catalyst includes at least one element selected from the group consisting of Group 4 elements and Group 5 elements, and has an oxygen defect.

  First, the support | carrier contained in the electrode catalyst for water electrolysis of this embodiment is demonstrated.

  The carrier supporting the catalyst is, for example, in the form of powder. Hereinafter, the carrier of this embodiment will be described by taking the case where the carrier is a powder as an example.

  Since the carrier powder is responsible for the movement of electrons involved in the electrochemical reaction on the catalyst, the carrier itself needs to have electron conductivity. In particular, when the catalyst itself has poor electronic conductivity, the carrier becomes the main electron transfer path, so the electron conductivity of the carrier is important. As a method for increasing the electron conductivity of the carrier, there are mainly a method of positively introducing oxygen defects into an oxide contained in the carrier and a method of doping with other elements.

By positively introducing oxygen vacancies, the electrons of the metal element are surplus, and the electrons become carrier electrons, thereby improving the electron conductivity. For example, when tin oxide (SnO ₂ ) is contained in the carrier, two electrons are left due to oxygen deficiency.

Further, by doping with other elements having different valences, it is possible to increase carrier electrons and increase electron conductivity. For example, when the support contains an oxide containing a tetravalent element (eg, tin oxide (SnO ₂ )), the oxide containing a tetravalent element is at least one of pentavalent elements (Sb, Nb, Ta). By doping one element, a tetravalent element is replaced by the element. Therefore, since one carrier electron is injected, the obtained oxide has electron conductivity. When the electron conductive oxide contained in the carrier of the present embodiment is an oxide containing a tetravalent element, the content of the pentavalent element doped in the oxide containing the tetravalent element is 0.1 to 25 at% is preferable with respect to the element, and more preferably 1 to 15 at%. As will be described later, when other element doping is used as a means for increasing the electronic conductivity, the obtained oxide can maintain stable oxygen defects, so that oxygen diffusion occurs at the interface between the support and the oxide catalyst. The oxide catalyst can maintain high catalytic activity for a long period of time. Therefore, it is desirable that the electron conductive oxide has electron conductivity realized by doping with other elements.

The electron conductivity of the carrier can be measured by a four-probe method or the like by pressing the carrier powder into a pellet by pressing with a hand press or the like. Electronic conductivity of the carrier is preferably 0.01 Scm ^-1 or more, 0.1Scm ^-1 or more is more preferable. The electron conductivity of the carrier is, for example, 10 Scm ⁻¹ or less.

Regarding the surface area of the carrier powder, it is preferable that the area capable of supporting the catalyst is large from the viewpoint of the reaction area. The BET specific surface area of the carrier powder is preferably 10 m ² / g or more, more preferably 100 m ² / g or more. The BET specific surface area of the carrier powder is, for example, 500 m ² / g or less.

  The shape of the carrier powder is not particularly limited, and it is possible to use a spherical powder, an aggregate shape in which spheres are fused, a square shape, a column shape, a needle shape, or the like.

The carrier powder in the present embodiment only needs to contain the electron conductive oxide, desirably contains 20% by mass or more of the electron conductive oxide, and more desirably contains 50% by mass or more. It is that you are. The carrier powder in the present embodiment may be made of the electron conductive oxide. Further, the electron conductive oxide may be coated with a substance serving as a base material. For example, the base material made of SiO ₂ , Al ₂ O ₃ or the like contains an oxide having at least one element selected from the group consisting of Sn, Sb, Nb, Ta, and Ti and having electron conductivity. It may be covered with an electron conductive layer.

  Next, the oxide catalyst supported on the carrier will be described.

  As described above, the oxide catalyst in the present embodiment includes at least one element selected from the group consisting of Group 4 elements and Group 5 elements, and has an oxygen defect. In this oxide catalyst, since the oxygen defect contained acts as an active site of the reaction, it becomes highly active for electrochemical reaction, particularly water oxidation reaction. However, since the structural change is induced when the amount of oxygen defects is too large, the oxygen defects in the oxide catalyst are preferably 1 to 10 at%. Note that the amount of oxygen defects can be calculated by elemental analysis using an inert gas melting infrared absorption method, whereby the presence or absence of oxygen defects can also be determined.

  In addition, the amount of oxygen defects may decrease and the catalyst activity may decrease with the electrochemical reaction at a high potential and in an oxidizing atmosphere at an anode or the like in a water electrolysis apparatus, for example. However, in the electrode catalyst for water electrolysis of the present embodiment, it is possible to use a carrier containing an electron conductive oxide that can maintain stable oxygen defects by doping with other elements, and has oxygen defects on the carrier. An oxide catalyst can be supported. According to such a configuration, oxygen diffusion occurs at the interface between the support and the oxide catalyst, and a reduction in the amount of oxygen defects in the catalyst due to the electrochemical reaction is suppressed. Thus, the oxide catalyst in the present embodiment can maintain high catalytic activity for a long period of time.

  The oxide catalyst in the present embodiment can be produced by supporting a precursor of an organometallic compound-derived catalyst on a support and heat-treating it. In the heat treatment of the precursor of the oxide catalyst, the precursor becomes an oxide (oxide catalyst) while depriving oxygen on the surface of the oxide as a support. Therefore, oxygen defects occur at the interface between the oxide catalyst and the support. Due to the presence of oxygen vacancies at the interface between the oxide catalyst and the support, the electrode catalyst for water electrolysis of the present embodiment can realize high electronic conductivity. For the electrode catalyst for water electrolysis of the present embodiment, for example, a support containing tin oxide that is easily reduced and oxygen is easily released can be used. Therefore, according to the electrode catalyst for water electrolysis of the present embodiment, it is possible to easily generate oxygen defects at the interface between the oxide catalyst and the carrier, and as a result, high electron conductivity can be obtained. Further, the surface of the electron conductive oxide contained in the carrier is slightly reduced by re-heat treatment at 100 to 300 ° C. in a vacuum atmosphere or a reducing atmosphere such as hydrogen or ammonia after the heat treatment. The conductivity can be improved. Thereby, the electrode catalyst for water electrolysis of this embodiment can further improve the catalytic ability. In this case, sintering of the electrode catalyst for water electrolysis and high temperature heat treatment accompanied by a decrease in surface area are not required.

  Further, the oxide catalyst in the present embodiment may further contain nitrogen, carbon, or both elements of nitrogen and carbon. For example, a part of oxygen of the oxide catalyst may be substituted with nitrogen, carbon, or both, or at least a part of the surface of the oxide catalyst is substituted with nitrogen. It may be coated with a different material. In particular, the electron conductivity on the catalyst surface is improved by including a part of oxygen substituted on the catalyst surface with nitrogen, or containing carbon or a substance in which a part of carbon is substituted with nitrogen in the vicinity of the catalyst surface. The electron transfer on the catalyst surface is promptly performed.

As a method of substituting part of oxygen of the oxide catalyst with nitrogen, a method of heat-treating the oxide catalyst in a nitrogen stream or an ammonia stream, urea, melamine, pyrazine, purine, bipyridine, in which ammonia is generated by thermal decomposition, Examples thereof include a method in which acetanilide or piperazine is premixed with an oxide catalyst and heat-treated. As a method for containing a substance in which carbon or a part of carbon is substituted with nitrogen in the vicinity of the surface of the oxide catalyst, a transition metal carbide or transition metal carbonitride is heated in a mixed gas containing oxygen, and the oxide A method of depositing fine carbon on the catalyst, a method of depositing carbon on the oxide catalyst by a chemical vapor deposition method using an appropriate carbon source, an organic substance is decomposed by hydrothermal synthesis, etc. A method of depositing carbon or the like can be used.

  The oxide catalyst only needs to be supported on a carrier, and the supported form is not particularly limited. For example, oxide catalyst particles may be supported on the surface of the carrier powder, or a film made of an oxide catalyst may be formed in an island shape so as to cover at least a part of the surface of the carrier powder. Good. The entire surface of the carrier powder may be covered with a film made of an oxide catalyst.

  The oxide catalyst is desirably a finer powder from the viewpoint of the reaction area. For example, the oxide catalyst is preferably nanoparticles having a particle size of 100 nm or less, and more preferably nanoparticles having a particle size of 50 nm or less. The particle size of the oxide catalyst is, for example, 1 nm or more.

  When a Group 4 element is included in the oxide catalyst, the Group 4 element is preferably Ti and / or Zr. In addition, when a Group 5 element is included in the oxide catalyst, the Group 5 element is preferably Nb and / or Ta. The oxide containing these elements is stable even in an acidic electrolyte, and the oxide provided with an oxygen defect has activity for an oxygen reduction reaction and a water oxidation reaction. Therefore, higher catalytic activity can be realized.

  The catalyst ratio of the oxide catalyst in the electrode catalyst for water electrolysis of the present embodiment (weight of oxide catalyst / (weight of oxide catalyst + weight of support)) is more than 0 wt% and not more than 42 wt%. Desirably, 32 wt% or less is more desirable, 23 wt% or less is particularly desirable, and 12 wt% or less is even more desirable. When the catalyst ratio is 42 wt% or less (desirably 32 wt% or less), the reduction in the surface area due to aggregation of the catalysts is reduced, and the amount of the catalyst with poor electron conductivity is reduced, so that the carriers and current collectors are collected. The number of electrical contact points with the electrode is increased, electrons generated by the reaction are more easily moved, and high electron conductivity can be realized. Therefore, by setting the catalyst ratio within the above range, it is possible to provide an electrode catalyst for water electrolysis that can more reliably realize stability under high potential and high catalytic activity.

  In the electrode catalyst for water electrolysis of the present embodiment, the catalyst included as the main catalyst is the oxide catalyst, but the promoter includes at least one element selected from the group consisting of Pt, Ir, Ni and Co. May further be included. In the water electrolysis electrode catalyst of the present embodiment, noble metals such as Pt are included not only as a main catalyst but as a cocatalyst. Therefore, when viewed as a whole water electrolysis electrode catalyst, the noble metal is used as a main catalyst. Compared with the conventional electrode catalyst for water electrolysis that is used, the amount of noble metal used can be greatly reduced while having high catalytic activity.

  Moreover, since the electrode catalyst for water electrolysis of this embodiment is composed of an oxide for both the carrier and the main catalyst, it is stable in the electrolyte even under water electrolysis conditions (1.23 V or more).

(Embodiment 2)
An embodiment of the water electrolysis apparatus of the present invention will be described. FIG. 1 shows a solid polymer water electrolysis apparatus 100 which is an example of the configuration of the water electrolysis apparatus of the present embodiment.

  A water electrolysis apparatus 100 shown in FIG. 1 includes a cathode, an anode, and a solid polymer electrolyte membrane (electrolyte layer) 110 disposed between the cathode and the anode. The cathode includes a cathode catalyst layer 120 disposed on one surface of the solid polymer electrolyte membrane 110 and a power supply body 140-1 disposed on the cathode catalyst layer 120. The anode is composed of an anode catalyst layer 130 disposed on the other surface of the solid polymer electrolyte membrane 110 and a power feeder 140-2 disposed on the anode catalyst layer 130. The laminate of the cathode, the solid polymer electrolyte membrane 110, and the anode is sandwiched between a separator 150-1 provided with a fluid channel 160-1 and a separator 150-2 provided with a fluid channel 160-2. Has been. In the figure, 170 indicates a gasket.

  For the cathode catalyst layer 120, a known catalyst such as platinum can be used as the cathode catalyst of the solid polymer water electrolysis apparatus.

  The anode catalyst layer 130 is an electrode catalyst for water electrolysis described in Embodiment 1 instead of a catalyst conventionally used as an anode catalyst of a solid polymer water electrolysis apparatus (for example, a noble metal catalyst such as platinum or iridium oxide). Is used.

  Water is supplied from the anode-side fluid flow path 160-2, and the water oxidation reaction shown in the above reaction formula (1) occurs on the anode catalyst layer 130 to generate oxygen and hydrogen ions. On the cathode catalyst layer 120, hydrogen ions are supplied from the anode side through the solid polymer electrolyte membrane 110, and hydrogen is generated by the reaction shown in the above reaction formula (2). As described above, the water electrolysis apparatus 100 can generate hydrogen and oxygen from water.

  Since the water electrolysis apparatus 100 according to the present embodiment uses the water electrolysis electrode catalyst according to the first embodiment as an anode catalyst, the efficiency of the water electrolysis apparatus and a system including the water electrolysis apparatus can be improved and the cost can be reduced.

  The constituent elements other than the anode catalyst layer 130 may be the corresponding known constituent elements used in the known solid polymer water electrolysis apparatus, and thus detailed description thereof is omitted here. To do.

  Here, the solid polymer type water electrolysis device has been described as an example, but the water electrolysis device of the present embodiment is not limited to this, and can be applied to various types of devices for electrolyzing water.

[Method for producing carrier for electrode catalyst for water electrolysis]
Tin chloride dihydrate (SnCl ₂ .2H ₂ O) and antimony chloride (SbCl ₃ ), niobium chloride (NbCl ₅ ) or tantalum chloride (TaCl ₅ ) were dissolved in a solvent (ethanol). While maintaining the resulting solution at a low temperature, diluted aqueous ammonia was added to the solution, and then this was filtered. The obtained filtrate was dried at 100 ° C. After drying, it is subjected to atmospheric heat treatment at 900 ° C., and an oxide in which SnO ₂ is doped with Sb (Sb-doped tin oxide (hereinafter referred to as ATO)) and an oxide in which SnO ₂ is doped with Nb (Nb-doped) Tin oxide (hereinafter referred to as NTO) and an oxide in which Ta was doped with SnO ₂ (Ta-doped tin oxide (hereinafter referred to as TTO)) were prepared. In the carrier produced in the example, the molar ratio of the oxide of the dopant element to SnO ₂ was 5 mol%. The carrier made of SnO ₂ used in Comparative Example 1 was prepared by using the same heat treatment using only tin chloride dihydrate.

[Method for producing electrode catalyst for water electrolysis]
An oxide catalyst containing Zr and having an oxygen defect is obtained by thermally decomposing it in the atmosphere using zirconium tetrapropoxide as an organic zirconium compound or tantalum ethoxide as an organic tantalum compound as a starting material ( ZrO _2-x catalyst) or an oxide catalyst containing Ta and having oxygen defects (Ta ₂ O _5-x catalyst) was prepared. The specific method is as follows.

  600 mg of zirconium tetrapropoxide or tantalum ethoxide was dissolved in 200 mL of 1-methyl-2-pyrrolidone placed in an Erlenmeyer flask and stirred with a stirrer for 12 hours or more. Thereafter, ATO, NTO or TTO as a carrier is mixed with the phthalocyanine solution so as to have an arbitrary ratio with respect to the oxide weight which is considered to be obtained after the oxidation treatment of zirconium tetrapropoxide or tantalum ethoxide. And stirred for 12 hours or longer. After removing the solvent while maintaining at 85 ° C. with an evaporator, vacuum drying was performed for 12 hours or more while maintaining at 85 ° C. with a vacuum dryer. After drying, the recovered material was pulverized with an agate mortar to obtain a starting material powder for an electrode catalyst for water electrolysis.

  After placing the starting material powder on an alumina boat, an air catalyst for water electrolysis was obtained by subjecting the muffle furnace to atmospheric heat treatment at a predetermined temperature (550 to 700 ° C.) for 1 h.

Example 1
The starting material powder using ATO as the carrier and the weight ratio of the ZrO _2-x catalyst to the water electrocatalyst electrode catalyst (oxide catalyst + carrier) of 58 wt% is described in [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 1, an electrode catalyst powder for ZrO _2-x / ATO water electrolysis was produced by atmospheric heat treatment at 550 ° C. for 1 h.

(Example 2)
A ZrO _2-x / ATO water electrolysis electrode catalyst powder was prepared in the same manner as in Example 1 except that the heat treatment temperature was 600 ° C.

(Example 3)
An electrode catalyst powder for ZrO _2-x / ATO water electrolysis was prepared in the same manner as in Example 1 except that the heat treatment temperature was 650 ° C.

Example 4
An electrode catalyst powder for ZrO _2-x / ATO water electrolysis was prepared in the same manner as in Example 1 except that the heat treatment temperature was 700 ° C.

(Example 5)
The starting material powder using ATO as the carrier and the weight ratio of the ZrO _2-x catalyst to the electrode catalyst for water electrolysis (oxide catalyst + carrier) being 42 wt% is explained in the above [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 5, an electrode catalyst powder for ZrO _2-x / ATO water electrolysis was produced by atmospheric heat treatment at 700 ° C. for 1 h.

(Example 6)
The starting material powder using ATO as the carrier and the weight ratio of the ZrO _2-x catalyst to the electrocatalyst for water electrolysis (oxide catalyst + carrier) being 32 wt% is described in [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 6, an electrode catalyst powder for ZrO _2-x / ATO water electrolysis was produced by atmospheric heat treatment at 700 ° C. for 1 h.

(Example 7)
The starting material powder using ATO as the carrier and the weight ratio of the ZrO _2-x catalyst to the water electrocatalyst electrode catalyst (oxide catalyst + carrier) being 23 wt% is described in [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 7, an electrode catalyst powder for ZrO _2-x / ATO water electrolysis was produced by atmospheric heat treatment at 700 ° C. for 1 h.

(Example 8)
The starting material powder using ATO as the carrier and the weight ratio of the ZrO _2-x catalyst to the electrode catalyst for water electrolysis (oxide catalyst + carrier) being 12 wt% is explained in the above [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 8, an electrode catalyst powder for ZrO _2-x / ATO water electrolysis was produced by atmospheric heat treatment at 700 ° C. for 1 h.

Example 9
The starting material powder using NTO as the carrier and the weight ratio of the ZrO _2-x catalyst to the water electrocatalyst electrode catalyst (oxide catalyst + carrier) being 12 wt% is described in [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 9, an electrode catalyst powder for ZrO _2-x / NTO water electrolysis was prepared by atmospheric heat treatment at 700 ° C. for 1 h.

(Example 10)
The starting material powder using TTO as the carrier and the weight ratio of the ZrO _2-x catalyst to the electrode catalyst for water electrolysis (oxide catalyst + carrier) being 12 wt% is explained in the above [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 10, an electrode catalyst powder for ZrO _2-x / TTO water electrolysis was produced by atmospheric heat treatment at 700 ° C. for 1 h.

(Example 11)
Starting material powder using NTO as a support and having a weight ratio of Ta ₂ O _5-x catalyst to an electrode catalyst for water electrolysis (oxide catalyst + support) of 12 wt% is described in [Method for preparing electrode catalyst for water electrolysis]. It was produced using the method described in 1. In Example 11, an electrode catalyst powder for Ta ₂ O _5-x / NTO water electrolysis was prepared by atmospheric heat treatment at 700 ° C. for 1 h.

(Example 12)
The starting material powder using NTO as the carrier and the weight ratio of the ZrO _2-x catalyst to the water electrocatalyst electrode catalyst (oxide catalyst + carrier) being 12 wt% is described in [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 12, after an atmospheric heat treatment at 700 ° C. for 1 h, a reduction heat treatment was further performed at 200 ° C. for 1 h in a 1% hydrogen atmosphere to produce an electrode catalyst powder for ZrO _2-x / NTO water electrolysis.

(Example 13)
The starting material powder using NTO as the carrier and the weight ratio of the ZrO _2-x catalyst to the water electrocatalyst electrode catalyst (oxide catalyst + carrier) being 12 wt% is described in [Method for producing electrode catalyst for water electrolysis]. It was produced using the method described above. In Example 13, after carrying out atmospheric heat treatment at 700 ° C. for 1 h, the obtained substance was dispersed in an IrO ₂ colloidal solution and then subjected to atmospheric heat treatment at 500 ° C. for 1 h, thereby supporting 1 wt% of IrO ₂ . An electrode catalyst powder for ZrO _2-x / NTO water electrolysis was produced.

(Comparative Example 1)
Starting material powder using SnO ₂ as a support and the weight ratio of the ZrO _2-x catalyst to the electrocatalyst for water electrolysis (oxide catalyst + support) of 58 wt% was obtained in the above-mentioned [Method for preparing electrocatalyst for water electrolysis]. Prepared using the method described. In Comparative Example 1, an electrode catalyst powder for ZrO _2-x / SnO ₂ water electrolysis was produced by atmospheric heat treatment at 550 ° C. for 1 h.

  Evaluation of the electrocatalyst for water electrolysis obtained in Examples and Comparative Examples was performed as follows.

[Measurement of oxygen defects]
About the electrode catalyst for water electrolysis of Examples 1-13 and the comparative example 1, when the amount of oxygen defects was measured by the elemental analysis by an inert gas fusion infrared absorption method, all were about 5-7 at%.

[Composition analysis by X-ray diffraction]
The electrode catalyst powder for water electrolysis of Examples 1 to 4 and 6 to 8 was subjected to powder X-ray diffraction measurement. CuKα rays were used for the measurement. The X-ray diffraction patterns of Examples 1 to 4 and 6 to 8 are shown in FIGS. In all the electrocatalyst powders for water electrolysis of Examples 1 to 4 and 6 to 8, the peak of ATO derived from the support (ICDDPDF01-075-8093) and the tetragonal ZrO ₂ derived from the oxide catalyst (t-ZrO ₂ : ICDD) -PDF01-072-7115) was confirmed. Furthermore, in all the electrocatalyst powders for water electrolysis of Examples 1 to 4 and 6 to 8, it was confirmed that there was no decomposition of the support and that the starting material was crystallized from the atmospheric heat treatment temperature of 550 ° C. to t-ZrO ₂ . . It was also confirmed that the peak intensity of t-ZrO ₂ was changed according to the ratio of the oxide catalyst.

[Electrochemical measurement for activity evaluation]
(Preparation of catalyst ink and working electrode)
To 10 mg of the electrocatalyst powder for water electrolysis obtained in the examples or comparative examples, a mixed solvent obtained by adding 1 mL each of 2-propanol and distilled water and 5 wt% perfluorosulfonic acid ionomer were added and ultrasonically dispersed. Was used as a catalyst ink. Next, the working electrode was obtained by repeatedly applying and drying the catalyst ink so that the supported amount was 1.5 mgcm ⁻² on the current collecting electrode having a diameter of 6 mm.

(Electrochemical measurement)
Electrochemical measurement was performed using a three-electrode cell. The working electrode produced by the above method was used, a platinum net was used for the counter electrode, and a silver / silver chloride (Ag / AgCl, 3M NaCl) electrode was used for the reference electrode. Hereinafter, the potential is based on a silver / silver chloride electrode (Ag / AgCl). As the solution, a 0.1 M sulfuric acid solution degassed by argon bubbling was used, and the measurement was performed at room temperature. The electrochemical measurement, scanning range 0.4～1.0V, after the cyclic voltammograms were 40 cycles measured at a scan rate 50 mVs ^-1, scan range 0.8V~1.8V as activity evaluation, a scanning rate of 5MVs ^-1 The cyclic voltamgram was measured for 7 cycles, and the current density at 1.8 V in the 7th cycle was used for activity evaluation.

(Activity evaluation result)
Table 1 shows the activity evaluation results of the water electrolysis electrode catalysts of Examples 1 to 4 and Comparative Example 1, Table 2 shows the activity evaluation results of the water electrolysis electrode catalysts of Examples 4 to 8, and Table 3 shows the activity evaluation results of Example 8. The activity evaluation result of the electrode catalyst for water electrolysis of -13 is shown, respectively. In Tables 1 to 3, the configurations of the electrocatalysts for water electrolysis of each Example and Comparative Example, the catalyst ratio (wt%), the catalyst ratio (at%), and the heat treatment temperature when preparing the electrocatalyst for water electrolysis are also shown. It is shown. Here, the catalyst ratio (at%) is calculated by the number of catalyst element atoms / (the number of catalyst element atoms + the number of Sn atoms) × 100.

  As is apparent from Table 1, the water electrolysis electrode catalyst having a higher heat treatment temperature during the production of the water electrolysis electrode catalyst had higher activity. This is considered that the crystallinity of the catalyst due to the heat treatment temperature affects the activity. Moreover, as shown in Tables 1 to 3, the water electrolysis electrode catalysts of all Examples had higher activity than the water electrolysis electrode catalyst of Comparative Example 1 in which the carrier did not satisfy the requirements of the present invention. . This is considered to be due to the electron conductivity of the carrier. This is because tin oxide that is not doped with other elements has few oxygen defects and low electron conductivity, so that it is insufficient as an electron conduction path for electrons generated in the reaction.

  As is apparent from Table 2, when the catalyst ratio (catalyst loading) is 42 wt% or less, the catalyst has a high activity, and this is because the decrease in the surface area due to the aggregation of the catalysts is reduced. This is because the amount of the catalyst loaded with poor properties is reduced, so that the number of electrical contact points between the carriers and the collecting electrode is increased, and electrons generated by the reaction are more easily moved.

Moreover, as shown in Table 3, according to the comparison of Examples 8 to 10, the activity was highest when NTO was used as the carrier, followed by ATO and then TTO. Further, according to a comparison between Example 9 and Example 11, the activity of ZrO _2-x was higher than that of Ta ₂ O _5-x as a catalyst. Moreover, the activity of the electrode catalyst for water electrolysis of Example 12 subjected to the reduction treatment was greatly improved as compared with the electrode catalyst for water electrolysis of Example 9 that was not subjected to the reduction treatment. Furthermore, from the results of Example 13, it was confirmed that the activity was further improved by adding IrO ₂ as a promoter.

  From the above results, the superiority of the electrode catalyst for water electrolysis of the present invention was demonstrated.

[Water electrolysis test]
A water electrolysis test was performed on the electrode catalyst for water electrolysis of Example 12 and Comparative Example 1. In the water electrolysis test, the water electrolysis apparatus 100 having the configuration shown in FIG. For the solid polymer electrolyte membrane 110, Nafion 112 (registered trademark, manufactured by DuPont) was used. The cathode catalyst layer 120 is made of 20 wt% platinum-supported carbon (Pt / C), and the anode catalyst layer 130 is the electrode catalyst for water electrolysis of Example 11 or the electrode catalyst for water electrolysis of Comparative Example 1 that is the object of evaluation. Using. As separators 150-1 and 150-2, a titanium (Ti) surface coated with gold was used. In addition, titanium meshes whose surfaces were coated with gold were used for the power feeding bodies 140-1 and 140-2. A rubber packing was used for the gasket 170. Pure water was supplied to the anode (anode-side fluid flow path 160-2), and a current-voltage curve was measured. Table 4 shows the current density at 2.0 V in the obtained results. As is clear from the results in Table 4, the performance as a water electrolysis apparatus was greatly improved by using the water electrolysis electrode catalyst according to the present invention. It was also found that the electrocatalyst for water electrolysis according to the present invention has catalytic activity even at a high potential of 2V.

[Durability test]
About the electrode catalyst for water electrolysis of Example 12, the durability test was done using the apparatus similar to a water electrolysis test. The current density was 0.5 Acm ⁻² and constant current measurement was performed for 1000 hours. Table 5 shows the result of comparing the initial characteristics (after 1 hour) and the characteristics after 1000 hours. As is apparent from the results in Table 5, it can be seen that even after 1000 hours, there is no significant decrease in the catalyst performance, and the stability of the catalyst activity under a high potential and oxidizing atmosphere is very high.

  The electrode catalyst for water electrolysis according to the present invention has stability and high activity under a high potential. Especially in energy devices such as water electrolysis devices, it is useful in that it can lead to a significant reduction in costs by replacing a conventional electrocatalyst for water electrolysis that contains precious metals, and may promote the spread to society. .

DESCRIPTION OF SYMBOLS 100 Water electrolysis apparatus 110 Solid polymer electrolyte membrane 120 Cathode catalyst layer 130 Anode catalyst layer 140-1, 140-2 Feed body 150-1, 150-2 Separator 160-1, 160-2 Fluid flow path 170 Gasket

Claims (9)

A support containing an oxide having at least one element selected from the group consisting of Sn, Sb, Nb, Ta and Ti and having an electron conductivity;
An oxide catalyst having at least one element selected from the group consisting of Group 4 elements and Group 5 elements supported on the carrier and having oxygen defects;
An electrode catalyst for water electrolysis, comprising: The catalyst ratio of the oxide catalyst in the electrode catalyst for water electrolysis (weight of the oxide catalyst / (weight of the oxide catalyst + weight of the support)) is more than 0 wt% and not more than 42 wt%.
The electrode catalyst for water electrolysis according to claim 1. The carrier includes Sn and an oxide having electronic conductivity.
The electrode catalyst for water electrolysis according to claim 1 or 2. The carrier includes an oxide obtained by doping SnO ₂ with at least one element selected from the group consisting of Sb, Nb and Ta.
The electrode catalyst for water electrolysis according to claim 3. The oxide catalyst further comprises at least one element selected from the group consisting of N and C;
The electrode catalyst for water electrolysis according to any one of claims 1 to 4. The Group 4 elements are Ti and Zr;
The electrode catalyst for water electrolysis according to any one of claims 1 to 5. The Group 5 elements are Nb and Ta,
The electrode catalyst for water electrolysis according to any one of claims 1 to 6. And further comprising a promoter containing at least one element selected from the group consisting of Pt, Ir, Ni and Co.
The electrode catalyst for water electrolysis according to any one of claims 1 to 7. An anode comprising the electrocatalyst for water electrolysis according to any one of claims 1 to 8,
A cathode,
Water electrolyzer with

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