JP4187479B2 - Electrocatalyst - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an electrode catalyst, in particular, an electrode catalyst suitable for a gas diffusion electrode, and a method for producing the electrode catalyst, and among others, is applied to an oxygen cathode for salt electrolysis, a metal-air battery, and the like. The present invention relates to an electrode catalyst suitable for an oxygen reducing gas diffusion electrode.
[0002]
[Prior art]
A gas diffusion electrode is a fuel cell or metal-air battery that supplies gas such as hydrogen, oxygen, and air to a porous electrode and causes it to react on the electrode, converting the chemical energy of the gas into electrical energy and taking it out. It is used for etc.
In the field of salt electrolysis, the development of a gas diffusion electrode has been promoted as a cathode that can greatly reduce the electrolysis voltage by converting the cathode reaction from the current hydrogen generation reaction to the oxygen reduction reaction, and can save energy. It has been.
[0003]
Various types of gas diffusion electrodes are known depending on applications. The gas diffusion electrode is a laminated structure of a gas diffusion layer and a reaction layer using an aqueous solution as an electrolytic solution, and a current collector for electrical connection is embedded therein. Oxygen is supplied from the gas diffusion layer side, and the reaction layer is in contact with the electrolytic solution. Oxygen permeates and diffuses inside the gas diffusion layer, and then undergoes a reduction reaction on an oxygen reduction catalyst fixed in the reaction layer.
Conventionally, platinum, silver, organometallic complexes, perovskite oxides, and the like are known as catalysts having high oxygen reduction activity (Japanese Patent Laid-Open No. 2000-212788, FC Anson, et. Al., J. Am. Chem. Soc., 1980, 102, 6027, JP-A-2-257575, JP-A-7-289903), mainly using carbon particles as a carrier and carrying them in a highly dispersed state.
[0004]
Since the gas diffusion electrode for salt electrolysis is a caustic soda solution with an atmosphere of 30% by weight or more, it is a harsh environment that is corroded even by noble metals such as platinum. Only silver is confirmed to be stable during continuous operation. (N. Furuya and H. Aikawa, Electrochim. Acta, 45 , 4251 (2000).) However, the catalytic activity of silver is not sufficient, and the overvoltage when used as a cathode increases. As a result, it has not been able to surpass the current hydrogen cathode system with economic advantages including oxygen cost. Therefore, a catalyst having higher oxygen reduction activity is demanded.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide an electrode catalyst having higher oxygen reduction activity than a conventional silver catalyst.
[0006]
[Means for Solving the Problems]
As a result of intensive research on the above problems, the present inventors combined silver fine particles with at least one kind of rare earth oxide fine particles selected from the group consisting of cerium oxide, holmium oxide, and gadolinium oxide. It has been found that the oxygen reduction activity is improved by the electrode catalyst as compared with the electrode catalyst having only silver fine particles, and the present invention has been made.
That is, the present invention is as follows.
(1) An oxygen-reducing gas diffusion electrode catalyst carrying a catalyst on a conductive carrier, wherein the conductive carrier is carbon fine particles, and the catalyst is made of silver fine particles, cerium oxide, holmium oxide, and gadolinium oxide. An oxygen-reducing gas diffusion electrode catalyst, which is a mixture with at least one kind of rare earth oxide fine particles selected from the compound group.
(2) The oxygen-reducing gas diffusion electrode catalyst according to (1), wherein the molar ratio of silver to rare earth oxide is 1: 0.5 to 1: 2.0.
(3) A gas diffusion electrode for salt electrolysis using the oxygen reducing gas diffusion electrode catalyst according to (1) or (2).
[0007]
Hereinafter, the present invention will be described in detail.
The electrode catalyst of the present invention is an electrode catalyst that supports a catalyst on a conductive carrier, and the catalyst is a mixture of silver fine particles and at least one kind of rare earth oxide fine particles. In the present invention, a combination of silver fine particles and at least one kind of rare earth oxide fine particles provides higher oxygen reduction activity than when only silver fine particles are supported. That is, in the electrode catalyst of the present invention, the interface between the silver fine particles and the rare earth oxide fine particles becomes a reaction active point, and the oxygen reduction activity is improved by the promoter action of the rare earth oxide.
[0008]
In the present invention, it is preferable that the silver fine particles of the main catalyst are smaller as long as they are fixed to the support because the surface area of silver as the main catalyst increases. Specifically, it is preferably 200 nm or less, and more preferably 100 nm or less. If the particle diameter is larger than 200 nm, the surface area of silver as the main catalyst is reduced, and sufficient oxygen reduction activity cannot be obtained. In addition, it is preferable that the fine particles of the rare earth oxide are smaller as long as they are fixed to the support because the active points increase. Specifically, 500 nm or less is preferable. If the particle diameter is too large than 500 nm, an interface serving as an active point is hardly formed, and sufficient oxygen reduction activity cannot be obtained.
[0009]
The electrode catalyst of the present invention is usually carried on a conductive carrier having a large surface area for the purpose of increasing the surface area of the catalyst.
As the conductive carrier, usually fine carbon particles are used. For example, carbon black having a BET specific surface area of 30 to 2000 m ² / g can be mentioned, and those called furnace black, lamp black, acetylene black, channel black, thermal black, and the like can be used. The particle size of the carbon particles is preferably 0.01 μm to 1 μm.
[0010]
The rare earth oxide of the present invention is an oxide of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Preferred are cerium oxide, holmium oxide, and gadolinium oxide.
The composition ratio between the silver fine particles and the at least one kind of rare earth oxide fine particles contained in the electrode catalyst of the present invention is such that the abundance of silver fine particles is A and the abundance of at least one kind of rare earth oxide fine particles. Is B, the molar ratio of B to A (B / A) is preferably 0.5 to 2.0. If the molar ratio is less than 0.5, the amount of rare earth oxide fine particles is too small, and the formation of an interface serving as an active site becomes insufficient. Conversely, if the molar ratio is larger than 2.0, the amount of rare earth oxide is small. However, neither of them can improve the oxygen reduction activity because the interface is reduced because the rare earth oxide covers the silver fine particles.
[0011]
The weight of the electrocatalyst material with respect to the carbon particles is preferably 10 to 90% by weight. If the amount of the electrode catalyst material is too small, the total reaction surface area of the electrode catalyst material becomes small, so that sufficient oxygen reduction activity cannot be obtained. On the other hand, when the amount of the electrode catalyst material is too large, the electrode catalyst material tends to aggregate and the total reaction surface area of the electrode catalyst material becomes small, so that sufficient oxygen reduction activity cannot be obtained.
[0012]
Hereafter, the preparation method of the electrode catalyst of this invention is demonstrated.
(1) Method for supporting silver First, a method for supporting silver fine particles will be described. Since carbon fine particle powder is usually used as the conductive carrier, the case where carbon fine particle powder is used as the conductive carrier will be described below.
In the dispersing step, the carbon fine particle powder is dispersed in a solution in which a silver salt is dissolved. Any silver salt may be used as long as it dissolves. Examples of the silver salt include silver nitrate, chloride, sulfate, carbonate, and acetate. Silver nitrate is preferred because chlorine, sulfur, and the like are unlikely to remain during pyrolysis.
[0013]
As the solvent, water is usually used. If necessary, a small amount of alcohol, organic solvent, acid, alkali or the like can be used. Any solvent may be used as long as it is a solvent in which the silver salt is dissolved.
In order to disperse the carbon fine particle powder in this solution, a method of stirring using a stirrer or a stirring bar, a method of using a kneader, a method of ultrasonic dispersion, a method of using a homogenizer, a method of using an ultrasonic homogenizer, etc. Various methods can be used, but generally a method of stirring using a stirrer is used because it is simple.
In the drying step, the suspension is evaporated to dryness. Any drying method can be used as long as the solvent can be removed. Examples thereof include a method of holding at about 100 ° C. for 12 hours or longer in a dryer or oven, a method using a vacuum dryer, an evaporator, or the like.
[0014]
The firing step is a step of obtaining a silver-supported carbon powder in which silver fine particles are highly dispersed by a thermal decomposition reaction of a catalyst precursor which is a dispersion of silver nitrate and carbon fine particles obtained in the drying step. It is preferable to heat and calcinate in a non-oxidizing atmosphere such as nitrogen so that the oxidation of the carbon particles of the conductive carrier does not proceed. However, if silver fine particles can be formed at a low temperature so that the carbon particles are not oxidized, oxygen or oxygen can be used. Heating and baking can be performed even in an atmosphere containing the same. The baking temperature is a temperature at which silver can be formed by thermal decomposition, and it is preferable to bake at a low temperature as possible. Preferably it is 200-700 degreeC. When fired at a too high temperature, the silver fine particles are aggregated, and the silver particle size is increased. Further, when firing at a low temperature, the silver salt is not completely pyrolyzed and silver fine particles cannot be obtained. The firing pyrolysis time is preferably 1 to 10 hours.
After the heat treatment, the silver-supported carbon powder is pulverized as necessary. The pulverized silver-carrying carbon powder can then be used to produce a gas diffusion electrode or further carry a metal oxide. The pulverization can be performed by various methods such as a mortar and various mills.
[0015]
(2) Rare Earth Oxide Support Method Next, a method for supporting rare earth oxide fine particles will be described.
In the dispersion step, carbon powder is dispersed in a solution in which a rare earth salt is dissolved. The rare earth salt is preferably nitrate. This is because nitrate becomes a rare earth oxide by firing in an inert gas atmosphere in the firing step.
In order to disperse the silver-supported carbon powder in this solution, a method of stirring using a stirrer or a stirring bar, a method of using a kneader, a method of ultrasonic dispersion, a method of using a homogenizer, a method of using an ultrasonic homogenizer, etc. Various methods can be used, but generally a method of stirring using a stirrer is used because it is simple.
[0016]
This solution may be subsequently dried in a drying step, but it can also be evaporated to dryness after forming a hydroxide by adding an alkali such as sodium hydroxide or ammonia.
In the drying step, this suspension is dried. The drying method may be any method as long as the solvent is removed. Examples thereof include a method of holding at about 100 ° C. for 12 hours or longer in a dryer or oven, a method using a vacuum dryer, an evaporator, or the like.
[0017]
In the firing step, the electrode material obtained in the drying step is a step of supporting a rare earth oxide on carbon by a thermal decomposition reaction. It is preferable to heat and calcinate in a non-oxidizing atmosphere such as nitrogen so that the oxidation of the carbon fine particles of the conductive carrier does not proceed. However, if the rare earth oxide fine particles can be formed at a low temperature at which the carbon particles are not oxidized, the air Heating and firing is possible even in an atmosphere containing oxygen or oxygen. Further, the heating and firing temperature is a temperature at which a rare earth oxide can be formed by thermal decomposition, and it is preferable to perform firing at as low a temperature as possible. Preferably it is 200-1000 degreeC. The holding time is preferably 1 to 10 hours. When fired at a too high temperature, the rare earth oxide fine particles aggregate and the particle size becomes large. Further, firing at a low temperature is not good because the rare earth nitrate remains without being completely thermally decomposed.
[0018]
After the heat treatment, the produced powder is pulverized as necessary. The pulverized powder can then be used for the production of a gas diffusion electrode or can further carry a metal or metal oxide. The pulverization can be performed by various methods such as a mortar and various mills.
The electrode catalyst of the present invention can be prepared by any order in which (1) silver fine particles are supported on carbon fine particle powder and (2) rare earth oxide fine particles are supported in any order. After forming, the rare earth oxide fine particles may be supported, or after the rare earth oxide fine particles are formed, silver fine particles may be supported. Further, a mixed solution of silver salt and rare earth salt may be used to simultaneously carry silver fine particles and rare earth oxide fine particles. A plurality of rare earth oxides and silver may be supported.
[0019]
In addition to the above method, a colloidal solution of silver or a rare earth oxide, or a suspension in which powder is dispersed in a solvent can be used to support the conductive carrier.
The electrode catalyst obtained through the above steps can have a crystal structure determined by a powder X-ray diffraction method, and its particle size can be confirmed by observation with an electron microscope.
The electrode catalyst obtained by the above method was evaluated by the channel flow electrode method (hereinafter abbreviated as CFDE method). The measurement cell shown in FIG. 1 was used for the measurement by the CFDE method. The measurement cell of FIG. 1 has a structure in which an oxygen-saturated electrolyte is introduced from an electrolyte introduction port 5 and discharged through an electrolyte solution flow path 6 having a thickness of 0.05 mm. At this time, the flow of the electrolyte solution in contact with the working electrode 1 and the detection electrode 2 only needs to be a laminar flow. A part of the acrylic resin plate has a 2 × 5 mm, 2 mm deep void, and this cavity is filled with an electrode catalyst to form a working electrode 1. There is a detection electrode 2 made of platinum having a smooth surface with a gap of 0.25 mm from the working electrode 1. In order to make an electrical connection, the working electrode 1 and the detection electrode 2 have a working electrode wiring 3 and a detection electrode wiring 4, respectively. Moreover, the liquid junction part 8 with the reference electrode is installed. By changing the flow rate of the electrolytic solution, the diffusion rate of dissolved oxygen in the electrolytic solution can be controlled. An electrolyte solution is flowed at a constant flow rate, and an oxygen reduction reaction is performed at the working electrode 1. Detection electrode 2, HO ₂ ^- and fixed to a potential capable of oxidizing, HO ₂ is a intermediate produced in the working electrode 1 ^- oxidized with the detection electrode 2 is detected as an oxidation current. Measure the potential-current curve of the working electrode 1 with the electrolyte flow rate constant. In this measurement, it can be said that an electrode catalyst in which an oxygen reduction current flows at a more noble potential has a higher oxygen reduction activity. Furthermore, the ratio between the two-electron reaction and the four-electron reaction can be obtained from the current values of the working electrode and the detection electrode.
[0020]
Furthermore, in order to investigate the performance of the electrode catalyst as a gas diffusion electrode, a gas diffusion electrode was prepared and the electrode characteristics were evaluated.
The gas diffusion electrode is a laminated structure of a gas diffusion layer and a reaction layer, and a current collector for electrical connection is embedded inside. Oxygen is supplied from the gas diffusion layer side, and the reaction layer is in contact with the electrolytic solution. Oxygen permeates and diffuses inside the gas diffusion layer, and then undergoes a reduction reaction on an oxygen reduction catalyst fixed in the reaction layer.
[0021]
The gas diffusion layer is required to allow oxygen to permeate through the inside of the reaction layer quickly and uniformly diffuse throughout the reaction layer, and to play a role of suppressing permeation of the electrolyte from the reaction layer side. Any material may be used as long as these two functions are satisfied. Here, carbon particles are mixed and dispersed in a suspension of a fluororesin such as polytetrafluoroethylene having a large water repellency. The particles obtained by filtration, drying can be used. It is preferable to use carbon particles having a high water repellency and a large particle size for the gas diffusion layer.
[0022]
In the reaction layer, the oxygen reduction catalyst is highly dispersed and fixed, and it is necessary to form a sufficiently large area of the three-phase interface composed of oxygen, the oxygen reduction catalyst, and the electrolytic solution. As particles for the reaction layer, carbon particles carrying an electrode catalyst by the production method of the present invention are mixed with a suspension of a fluororesin such as polytetrafluoroethylene and dispersed using a dispersant such as alcohol. Finely pulverized particles after filtration, drying can be used.
The current collector may be any material as long as it has sufficient electrical conductivity for electrical connection and does not dissolve or corrode at the potential at which the oxidation-reduction reaction occurs. A wire mesh such as nickel or silver, a foam, or the like can be used.
[0023]
The gas diffusion electrode is provided with a nickel metal mesh for a current collector in a mold having a predetermined shape, filled with powder particles for the gas diffusion layer on the current collector and cold-pressed, and then the reaction layer It is possible to manufacture by filling the powder particles for use and performing cold pressing, and finally melting and integrating polytetrafluoroethylene by hot pressing.
The gas diffusion electrode obtained by the above method is attached to a cell for electrochemical property evaluation, oxygen or air is supplied from the gas diffusion layer side to perform an oxygen reduction reaction, and the electrode potential at each current density is measured. By doing so, the electrode performance can be evaluated.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in more detail based on examples, but the present invention is not limited to the examples.
[0025]
[Example 1]
(Adjustment of silver-supporting carbon)
A 50% by weight silver-carrying carbon was prepared as follows.
2 g of carbon black (Ketjen Black EC-600JD manufactured by Mitsubishi Chemical) and 3.15 g of silver nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) pulverized using a mill (A10 manufactured by Janke & Kunkel) were dispersed in 200 ml of an aqueous solution. Furthermore, after stirring for 15 minutes using a stirrer, water was evaporated in an oven at 100 ° C. and dried to obtain a powder. Further, this powder was fired in a nitrogen stream at 250 ° C. for 1 hour to thermally decompose silver nitrate, and then pulverized using a mill to obtain 50% by weight of silver-supported carbon.
[0026]
Next, cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O, manufactured by Wako Pure Chemical Industries, Ltd.) 0.434 g was added to 0.216 g of this silver-supported carbon powder so that the molar ratio of silver and cerium was 1: 1. The mixture was added, dispersed in water, and ultrasonic dispersion was performed for 5 minutes. Furthermore, moisture was evaporated in an oven at 100 ° C. and dried to obtain a sample powder. This powder was baked in a nitrogen stream at 800 ° C. for 1 hour and pulverized using a mill to obtain an electrode catalyst powder. The electrode catalyst powder was subjected to powder X-ray diffraction. Specifically, RINT-2500 (manufactured by Rigaku Denki Co., Ltd.) was used, and the radiation source was measured with a copper Kα ray (λ = 1.54184 mm). When the peak was identified, Ag and CeO ₂ were detected.
[0027]
Furthermore, the microstructure was observed with a high-resolution analytical transmission electron microscope (JEM4000FX, manufactured by JEOL Ltd.). As a result, particles of 50 to 100 nm of Ag and CeO ₂ were confirmed.
A small amount of liquid paraffin (manufactured by Kishida Chemical Co., Ltd.) was added to the produced electrode catalyst powder and mixed in a mortar to make a paste. This paste was prepared by filling the working electrode portion of CFDE. A platinum wire was used as a counter electrode, and a silver / silver chloride electrode as a reference electrode. Bubbling was carried out with pure oxygen for 1 hour in a 0.1 M aqueous sodium hydroxide solution, and this aqueous sodium hydroxide solution was saturated with oxygen. Furthermore, after fixing the flow rate of the solution at 83.2 cm / sec and holding at −0.6 V for 10 minutes, the working electrode was swept from +0.1 V to −0.6 V at 10 mV / sec, and the potential-current The curve was measured. The obtained evaluation results are shown in FIG. High oxygen reduction activity.
[0028]
Furthermore, the working electrode is fixed at −0.6 V, the detection electrode is fixed at 0.5 V, and the flow velocity is changed to 41.6, 83.2, 124.8, 166.4. The current value was measured. The number of reaction electrons was calculated from the following equation from the ratio of the current between the working electrode and the detection electrode. The number of reaction electrons is an amount representing how many electrons have flowed per one oxygen at the working electrode. As this value is closer to 4, the oxygen reduction reaction does not pass through the intermediate (HO ₂ ⁻ ), and a higher activity can be expected.
[0029]
Number of reaction electrons = (I (2 electrons) + I (4 electrons)) / (I (2 electrons) / 2 + I (4 electrons) / 4)
However, I (2 electrons) =-detection pole current / capture rate, I (4 electrons) = working pole current-I (2 electrons). Here, the capture rate is a value representing how much the reaction intermediate produced at the working electrode can be captured at the detection electrode. As a result of calculating the number of reaction electrons from the ratio of the current between the working electrode and the detection electrode, the number of reaction electrons was 3.90.
[0030]
[Example 2]
Production and evaluation were performed in the same manner as in Example 1 except that 0.452 g of gadolinium nitrate (Gd (NO ₃ ) ₃ .6H ₂ O, manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of cerium nitrate. As a result of powder X-ray diffraction of the produced electrode catalyst powder, Ag and Gd ₂ O ₃ were detected. The measurement result of the potential-current curve by CFDE evaluation is shown in FIG. Furthermore, the number of reaction electrons was 3.87. Compared with Example 1, the rise of the oxygen reduction current was at a more noble potential, and the oxygen reduction activity was excellent.
[0031]
[Example 3]
Instead of cerium nitrate, holmium nitrate (Ho (NO _{3) 3,} manufactured by Wako Pure Chemical) except for using 0.440 g, prepared as in Example 1 and evaluated.
As a result of powder X-ray diffraction of the produced electrode catalyst powder, Ag and Ho ₂ O ₃ were detected. The measurement result of the potential-current curve by CFDE evaluation is shown in FIG. Furthermore, the number of reaction electrons was 3.91. Compared to Example 2, the rise of the oxygen reduction current was at a more noble potential, and the oxygen reduction activity was superior.
[0032]
[Comparative Example 1]
In the same manner as in Example 1, 50% by weight of silver-supported carbon was produced and evaluated.
As a result of performing powder X-ray diffraction on the produced electrode catalyst powder, Ag was detected. Furthermore, the microstructure was observed with a high-resolution analytical transmission electron microscope. As a result, silver fine particles of 10 to 50 nm were confirmed.
The measurement result of the potential-current curve by CFDE evaluation is shown in FIG. Compared to Examples 1 to 3, the rise of the oxygen reduction current was poor, and the number of reaction electrons was also small, 3.69.
[0033]
[Example 4]
(Preparation of powder for reaction layer)
In the same manner as in Example 1, an electrode catalyst having silver fine particles and cerium oxide fine particles supported on a carbon support was produced. 0.18 g of the obtained carbon particles supporting the electrode catalyst was added to 15 ml of ethanol: water = 1: 60 (weight ratio), and polytetrafluoroethylene dispersin [(POLYFLON (registered trademark) manufactured by Daikin Industries, Ltd.) 0.04 g of TFE D-1 (solid content 60% by weight)) was added, stirred for 1 hour, filtered, and dried at 100 ° C. for 24 hours. Subsequently, after dispersing for 10 minutes with an ultrasonic disperser (US-600T manufactured by Nippon Seiki Seisakusho Co., Ltd.), 30 ml of ethanol was added and stirred for 30 minutes. After filtering this, it dried at 100 degreeC for 24 hours. Subsequently, it was pulverized with a mill to obtain a powder in the reaction layer.
[0034]
(Preparation of powder for gas diffusion layer)
Carbon black (Denka Black AB-7 (registered trademark) manufactured by Denki Kagaku Kogyo): Surfactant (Triton X-100 manufactured by Rohm and Haas): Water = 1: 1: 20 (weight ratio) Polytetrafluoroethylene dispersion (POLYFLON (registered trademark) TFE D-1 (solid content: 60% by weight) manufactured by Daikin Industries) was added so that carbon black: polytetrafluoroethylene = 7: 3 (weight ratio). Then, it was dispersed for 10 minutes with an ultrasonic disperser. Thereafter, ethanol was added to aggregate the particles in the dispersion. Subsequently, suction filtration was performed, and the obtained solid content was dried at 100 ° C. for 24 hours, and then pulverized with a mill to make fine powder. Subsequently, this powder was stirred in ethanol for 1 hour, and the surfactant was removed by washing. Then, the powder for gas diffusion layers was obtained by further pulverizing using a mill.
[0035]
(Production of gas diffusion electrode)
An aluminum foil degreased with acetone is placed on the bottom of a hot press mold having an inner diameter of 20 mm, a nickel mesh with a wire diameter of 0.1 mm and 100 mesh is placed on the aluminum foil, and 0.1 g of powder for the gas diffusion layer is placed. After filling, 0.05 g of the reaction layer powder was filled and cold pressing was performed.
Thereafter, the mold was kept at 370 ° C. and held in a hot press machine (SA-303 manufactured by Tester Sangyo Co., Ltd.), and hot pressing was performed at 60 kg / cm ² for 1 minute to obtain a gas diffusion electrode.
[0036]
(Evaluation of electrochemical characteristics of gas diffusion electrode)
The obtained gas diffusion electrode was attached to a cell for electrochemical property evaluation, and was supplied at a rate of 50 ml / min pure oxygen from the gas diffusion layer in a 33 wt% sodium hydroxide aqueous solution at 80 ° C. Chemical properties were evaluated.
The cell for electrochemical evaluation has oxygen supply and discharge channels formed therein, and has a structure that keeps the gas tight inside the cell by attaching a gas diffusion electrode through an O-ring. This was attached to an electrolytic cell, and oxygen was supplied from the gas diffusion layer side with only the reaction layer side exposed to a 33 wt% sodium hydroxide aqueous solution at 80 ° C. to evaluate the electrochemical characteristics. The effective surface area of the gas diffusion electrode is 3.14 cm ² . As the current pulse generator, HC-113 manufactured by Hokuto Denko Co., Ltd. was used, a platinum wire mesh was used for the counter electrode, and a mercury / mercury oxide electrode was used for the reference electrode.
[0037]
The results of the electrochemical property evaluation are shown in FIG. The horizontal axis represents the current density, and the vertical axis represents the potential with respect to the mercury / mercury oxide electrode. As shown in FIG. 3, the oxygen reduction activity was superior to an electrode catalyst in which only silver fine particles were supported on a carbon fine particle support.
[0038]
[Comparative Example 2]
As in Example 1, 50% by weight of silver-supported carbon was produced. A gas diffusion electrode was prepared and evaluated in the same manner as in Example 4 except that this electrode catalyst was used. The obtained evaluation results are shown in FIG.
[0039]
【The invention's effect】
The electrode catalyst of the present invention exhibits higher oxygen reduction activity as an oxygen reduction electrode catalyst than the conventional carbon electrode catalyst supporting only silver fine particles. If the electrode catalyst of the present invention is used for a gas diffusion electrode, the oxygen reduction overvoltage in electrolysis of an aqueous solution of an alkali metal halide such as saline using an ion exchange membrane can be reduced as compared with the prior art. As a result, electric power used for electrolysis can be reduced, and products such as chlorine and caustic soda can be produced at low cost.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a CFDE evaluation apparatus. FIG. 2 is an explanatory view of CFDE evaluation of electrode catalysts of Examples and Comparative Examples. FIG. 3 is an explanatory view of electrochemical characteristics of gas diffusion electrodes of Examples and Comparative Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Working electrode 2 Detection electrode 3 Working electrode wiring 4 Detection electrode wiring 5 Electrolyte flow path 6 Electrolyte introduction port 7 Electrolyte discharge port 8 Conductive flow path

Claims (3)

An oxygen-reducing gas diffusion electrode catalyst carrying a catalyst on a conductive carrier, wherein the conductive carrier is carbon fine particles, and the catalyst is a silver fine particle, cerium oxide, holmium oxide, and gadolinium oxide. An oxygen reducing gas diffusion electrode catalyst comprising a mixture of at least one rare earth oxide fine particle selected from the group consisting of: Silver and the molar ratio of the rare earth oxide is 1: 0.5 to 1: 2.0 oxygen reducing gas diffusion electrode catalyst according to claim 1, characterized in that. A gas diffusion electrode for salt electrolysis, wherein the oxygen reducing gas diffusion electrode catalyst according to claim 1 or 2 is used.

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