JP2016148074A - Cathode for hydrogen generation and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode low in hydrogen overvoltage and hardly generating deterioration of a catalyst layer by reverse current generated during stopping an electrolyte tank.SOLUTION: There is provided a cathode for hydrogen generation consisting of a conducive substrate and a catalyst layer on the conducive substrate, where the catalyst layer contains a ruthenium element, a cerium element, an element of a transition metal which may take trivalence excluding ruthenium and cerium and an aluminum element.SELECTED DRAWING: None

Description

  The present invention relates to a hydrogen generating cathode used for electrolysis of water or an aqueous alkali metal compound solution, and more particularly to a hydrogen generating cathode suitably used for ion exchange membrane salt electrolysis and a method for producing the same.

The cathode for hydrogen generation is used for the purpose of producing hydrogen, chlorine, caustic soda, etc. by electrolyzing an aqueous solution of water or an alkali metal compound (typically alkali metal chloride). In the electrolysis industry, reduction of energy consumption, specifically, reduction of electrolysis voltage is a major issue. In recent years, the ion exchange membrane method has been the mainstream as an electrolysis method for an aqueous solution of alkali metal chloride such as saline, and various studies have been made so far. In actual electrolysis, in addition to the voltage required for electrolysis of salt, which is theoretically required, the overvoltage of the anodic reaction (chlorine generation), the overvoltage of the cathodic reaction (hydrogen generation), and the ion exchange membrane A voltage due to resistance and a voltage due to the distance between the anode and the cathode are further required. Among these voltages, focusing on the overvoltage due to the electrode reaction, the chlorine evolution for anodic been developed noble metal electrode, called the so-called DSA (D imensionally S table A node ), chlorine overvoltage is greatly reduced to below 50mV ing.

  On the other hand, as for cathodes with hydrogen generation, in recent years, from the viewpoint of energy saving, there is a demand for cathodes with low hydrogen overvoltage and durability. In the past, mild steel, stainless steel, and nickel have been used as cathodes for hydrogen generation. Then, it has been studied to activate the surfaces of these cathodes to reduce hydrogen overvoltage, and many patent applications have been filed so far. Examples of the catalyst for activating the surface of the hydrogen generating cathode include nickel, nickel oxide, an alloy of nickel and tin, a combination of activated carbon and oxide, ruthenium oxide, platinum and the like. The catalyst layer containing these catalysts is formed by alloy plating, dispersion / composite plating, thermal decomposition, thermal spraying, or a combination thereof.

  In Patent Document 1, a cathode having a low overvoltage is formed by forming a catalyst layer made of a lanthanum metal compound and a platinum group compound on a conductive substrate. In Patent Document 2, ruthenium nitrate and a lanthanum carboxylate are coated on a conductive substrate and fired in the air to form a catalyst layer, which is stable for a long time even in operation at high current density. A catalyst layer is obtained.

  On the other hand, it is known that a reverse current is generated when the electrolytic cell is stopped, and that the catalyst layer is oxidized and deteriorated by this reverse current. In order to prevent the deterioration of the catalyst layer due to the reverse current, a method of passing a corrosion-proof current when the electrolytic cell is stopped is taken.

  Patent Document 3 proposes a technique for forming an electrode catalyst layer having a coating made of ruthenium oxide, nickel, and a rare earth metal having a hydrogen storage capability. In this technique, a hydrogen storage alloy is introduced into the catalyst layer to prevent oxidation due to a reverse current generated when the electrolytic cell is stopped.

  Platinum has a low hydrogen overvoltage, is an electrochemically stable material, and is relatively stable against reverse currents. Therefore, a cathode with a low hydrogen overvoltage that has been supported by platinum on a catalyst layer has been proposed. Yes. However, the price of platinum is very high, and an increase in electrode cost accompanying use is a major problem. Moreover, the deterioration due to the reverse current occurs not a little.

  As described above, many efforts have been made for the purpose of reducing power consumption, and various cathodes for hydrogen generation have been proposed. However, a hydrogen generating cathode having a low hydrogen overvoltage and sufficient resistance against a reverse current when the electrolytic cell is stopped has not been obtained yet.

JP 2000-239882 A JP 2008-133532 A JP-A-11-140680

  An object of the present invention is to provide a cathode that has a low hydrogen overvoltage and is unlikely to deteriorate the catalyst layer due to a reverse current generated when the electrolytic cell is stopped.

  The inventors of the present invention have made extensive studies on the above problems. As a result, the present inventors have found that the above problems can be solved by a cathode having a catalyst layer in which a specific metal compound coexists with a combination of a ruthenium compound and a cerium compound, and the present invention has been completed.

That is, the present invention is as follows.
(1) A hydrogen generating cathode comprising a conductive substrate and a catalyst layer on the conductive substrate,
The cathode for hydrogen generation, wherein the catalyst layer contains a ruthenium element, a cerium element, a transition metal element capable of taking trivalence (excluding ruthenium and cerium), and an aluminum element.
(2) The cathode for hydrogen generation according to (1), wherein the trivalent transition metal is a rare earth metal.

(3) The hydrogen generating cathode according to (2), wherein the trivalent transition metal is at least one metal selected from the group consisting of lanthanum, praseodymium, neodymium, and samarium.
(4) The content of the cerium element is 1/20 to 1/2 mol with respect to 1 mol of the ruthenium element,
The content of the transition metal element capable of taking the trivalent is 1/100 to 1/2 mol with respect to 1 mol of the ruthenium element, and the content of the aluminum element is 1 with respect to 1 mol of the ruthenium element. The cathode for hydrogen generation as described in any one of (1)-(3) which is / 100-1 / 2 mol.

(5) The ruthenium element is an element that forms at least one compound of ruthenium oxide and ruthenium hydroxide,
The cerium element is an element forming at least one compound of cerium oxide and cerium hydroxide;
At least a part of the transition metal element capable of taking trivalence is an element forming at least one compound of transition metal oxide and transition metal hydroxide, and the aluminum element is oxidized The cathode for hydrogen generation according to any one of (1) to (4), which is an element that forms at least one compound of aluminum and aluminum hydroxide.
(6) The hydrogen generating cathode according to (5), wherein at least a part of the transition metal element is doped with at least one of the cerium oxide and cerium hydroxide.

(7) The conductive substrate is made of nickel,
At least a part of the cerium element in the catalyst layer is an element that forms cerium oxide,
At least a part of the ruthenium element is an element that forms ruthenium oxide, and 2θ = 47.3 ° attributed to cerium oxide when the catalyst layer is X-ray diffracted together with the conductive substrate. The cathode for hydrogen generation according to (5) or (6), wherein the peak intensity is 1/40 or less with respect to the peak intensity of 2θ = 35.1 ° attributed to ruthenium oxide.
(8) The cathode for hydrogen generation as described in any one of (1)-(7) whose content of the ruthenium element contained in the said catalyst layer is 1-20 g / m < ² >.

(9) On the conductive substrate,
After applying a solution containing a ruthenium compound, a cerium compound, a trivalent transition metal compound (except ruthenium and cerium), and an aluminum compound, it is dried to form a coating film, and then in the coating film A method for producing a hydrogen generating cathode, wherein the catalyst group is formed by thermally decomposing the compound group contained in the catalyst.
(10) The method for producing a cathode for hydrogen generation according to (9), wherein the trivalent transition metal compound is a rare earth metal compound.

(11) The hydrogen according to (9) or (10), wherein the trivalent transition metal compound is at least one selected from the group consisting of a lanthanum compound, a praseodymium compound, a neodymium compound, and a samarium compound. A method for producing a cathode for generation.
(12) In the solution,
The content of the cerium compound is 1/20 to 1/2 mol as a ratio of the cerium element to 1 mol of the ruthenium element in the ruthenium compound,
The content of the transition metal compound capable of taking the trivalence is 1/100 to 1/2 mol as a ratio of the transition metal element to 1 mol of the ruthenium element in the ruthenium compound, and the content of the aluminum compound is The method for producing a cathode for hydrogen generation according to any one of (9) to (11), wherein the ratio of aluminum element to 1 mol of ruthenium element in the ruthenium compound is 1/100 to 1/2 mol. .

(13) The method for producing a cathode for hydrogen generation according to any one of (9) to (12), wherein the ruthenium compound is a chloride.
(14) The method for producing a cathode for hydrogen generation according to any one of (9) to (13), wherein the transition metal compound capable of taking trivalence is a chloride.

(15) Drying after applying the solution on the conductive substrate is performed at a temperature of less than 150 ° C.,
The method for producing a hydrogen generating cathode according to any one of (9) to (14), wherein the thermal decomposition is performed at a temperature of 350 ° C. or higher and 600 ° C. or lower.
(16) The method for producing a cathode for electrolysis according to any one of (9) to (15), wherein temporary baking is performed at a temperature of 150 ° C. or higher and lower than 350 ° C. for 1 to 60 minutes before the thermal decomposition. .

  According to the present invention, a cathode for hydrogen generation that can be used for electrolysis of an aqueous solution of an alkali metal compound, particularly suitable for a zero gap electrolytic cell, has a low hydrogen overvoltage, and is resistant to a reverse current generated when the electrolytic cell is stopped. A sufficiently high cathode for hydrogen generation is provided.

It is a graph which shows the cathode potential rise behavior in the reverse current application test of the cathode for hydrogen generation obtained by the Example and the comparative example. It is a cross-sectional SEM image (magnification: 10,000 times) after supplying with electricity to the cathode for hydrogen generation obtained in comparative example 4 for 7 days.

The cathode for hydrogen generation of the present invention comprises a conductive substrate and a catalyst layer on the conductive substrate.
<Conductive substrate>
As the conductive substrate in the hydrogen generating cathode of the present invention, for example, nickel, nickel alloy, stainless steel or the like can be used. However, when stainless steel is used in a high-concentration alkaline aqueous solution, considering that elution of iron and chromium and that the electrical conductivity of stainless steel is about 1/10 that of nickel, the conductive base material is Is preferably nickel.

  The shape of the conductive substrate is not particularly limited, and an appropriate shape can be selected depending on the purpose. For example, a so-called woven mesh produced by knitting a perforated plate, an expanded shape, or a nickel wire is preferably used. About the shape of an electroconductive base material, there exists a suitable specification with the distance of the anode and cathode in an electrolytic cell. When the anode and the cathode have a finite distance, a perforated plate or an expanded shape is used. In the case of a so-called zero gap electrolytic cell where the ion exchange membrane and the electrode are in contact with each other, a woven mesh knitted with a thin line is used. Used.

In the present invention, it is preferable to relieve the residual stress during processing by annealing the conductive substrate in an oxidizing atmosphere. Further, in order to improve the adhesion with the catalyst layer coated on the surface of the conductive substrate, irregularities are formed using a steel grid, alumina powder, etc., and the surface area is increased by subsequent acid treatment. It is preferable to increase.
The substrate is preferably a woven mesh knitted with fine nickel wires. The wire diameter of the nickel fine wire is preferably 0.05 to 0.3 mm, and more preferably 0.1 to 0.2 mm. Moreover, as a mesh number, 10-60 mesh is preferable, It is more preferable that it is 20-50 mesh, More preferably, it is 25-45 mesh.

<Catalyst layer>
The catalyst layer in the cathode for hydrogen generation of the present invention contains a ruthenium element, a cerium element, a trivalent transition metal element (except for ruthenium and cerium), and an aluminum element.

(Ruthenium element)
The ruthenium element contained in the catalyst layer is a component that functions as a catalyst in hydrogen generation electrolysis. The ruthenium element is preferably an element that forms at least one compound or metal of ruthenium oxide, ruthenium hydroxide, and metal ruthenium, and at least one of ruthenium oxide and ruthenium hydroxide. The element that forms a compound is more preferable, and the element that forms ruthenium oxide is particularly preferable. That is, the catalyst layer in the cathode for hydrogen generation of the present invention particularly preferably contains ruthenium oxide.
The larger the content of ruthenium element contained in the catalyst layer, the longer the time during which a low overvoltage can be maintained, which is preferable. However, since ruthenium element is expensive, it is necessary to suppress the amount of use from the viewpoint of obtaining appropriate cost merit. In view of these facts, the content of ruthenium element contained in the catalyst layer is preferably from 1 to 20 g / ^{m 2,} more preferably from 5 to 20 g / ^{m 2,} more preferably 5 to 15 g / a m ^2.

(Cerium element)
The cerium element contained in the catalyst layer is preferably an element that forms at least one compound or metal of cerium oxide, cerium hydroxide, and metal cerium, and includes cerium oxide and cerium hydroxide. Of these, an element that forms at least one compound is more preferable, and an element that forms cerium oxide is particularly preferable. That is, the catalyst layer in the cathode for hydrogen generation of the present invention particularly preferably contains cerium oxide.

  When hydrogen generation electrolysis is carried out in a cathode electrolyte (for example, an aqueous sodium hydroxide solution), cerium oxide is reduced to trivalent cerium hydroxide and changes into a needle crystal. As a result, the ruthenium compound functioning as a catalyst is prevented from falling off the base material, and the catalyst layer has an effect of changing to a structure with more voids and increasing the surface area.

When the amount of the cerium element is 1/20 mol or more with respect to 1 mol of the ruthenium element, it is easy to hold the ruthenium compound in the catalyst layer, and physical dropout hardly occurs. On the other hand, when this value is ½ mol or less, the cerium compound having no catalytic activity does not completely cover the surface of the ruthenium compound having catalytic activity in the catalyst layer formed by thermal decomposition of the coating solution as described later. Therefore, a low overvoltage cathode can be obtained.
The content of the cerium element in the catalyst layer is more preferably in the range of 1/8 to 1/4 with respect to 1 mol of ruthenium element.

  As described above, the catalyst layer in the hydrogen generating cathode of the present invention preferably contains both ruthenium oxide and cerium oxide. In this case, when the catalyst layer is X-ray diffracted together with the conductive substrate, the peak intensity of 2θ = 47.3 ° attributed to cerium oxide is 2θ = 35.1 ° attributed to ruthenium oxide. It is preferable that it is 1/40 or less with respect to peak intensity. When the strength ratio of cerium oxide and ruthenium oxide is larger than 1/40, there are few amorphous cerium oxides, and cerium oxide is difficult to be reduced, so that the effects of the present invention may not be sufficiently obtained. The intensity ratio is more preferably 1/50 or less, further preferably 1/60 or less, and particularly preferably 1/65 or less. The smaller the intensity ratio is, the more preferable it is due to the presence of more amorphous cerium.

(Transition metal element)
The catalyst layer in the cathode for hydrogen generation of the present invention further contains a transition metal element capable of taking trivalence. From this transition metal element, ruthenium element and cerium element are excluded. In the present specification, the transition metal capable of taking trivalence (except ruthenium and cerium) may be simply referred to as “transition metal” hereinafter.
The transition metal element is preferably selected from rare earth metal elements excluding cerium,
More preferably, it is at least one metal element selected from the group consisting of lanthanum, praseodymium, neodymium, and samarium.
It is preferable that at least a part of the transition metal element is an element that forms at least one compound or metal of a transition metal oxide, a transition metal hydroxide, and a metallic transition metal. More preferably, it is an element that forms at least one compound of a transition metal oxide and a transition metal hydroxide.

  When a transition metal element is added to a catalyst layer containing a cerium compound (preferably at least one of cerium oxide and cerium hydroxide, particularly preferably cerium oxide), a trivalent transition metal element is added to the cerium compound. Is doped. When the cerium compound is, for example, cerium oxide, the doping of the transition metal element improves the conductivity of the cerium oxide and facilitates reduction, and promotes acicular crystallization. As a result, formation of voids in the catalyst layer is promoted and the surface area is increased. Therefore, it is preferable that at least a part of the transition metal element is doped in the cerium compound. The dope amount is preferably 1 to 20 mol%, more preferably 3 to 15 mol%, based on the cerium atom contained in the cerium compound.

  When the content of the transition metal element in the catalyst layer is 1/100 or more with respect to 1 mol of ruthenium, the reduction rate of cerium oxide by electrolysis increases, and when it is 1/2 mol or less, as described later, the coating solution In the catalyst layer formed by thermal decomposition, the transition metal compound does not completely cover the surface of the ruthenium compound, and a low overvoltage cathode can be obtained. The content of the transition metal element in the catalyst layer is more preferably 1/50 to 1/5 with respect to 1 mole of the ruthenium element.

(Aluminum element)
The catalyst layer in the cathode for hydrogen generation of the present invention further contains an aluminum element.
When an aluminum element is added to the catalyst layer, the aluminum compound is eluted by the cathode electrolyte (for example, sodium hydroxide aqueous solution), and the surface area of the catalyst layer is increased.
The aluminum element is preferably an element that forms at least one compound or metal of aluminum oxide, aluminum hydroxide, and metal aluminum, and at least one of aluminum oxide and aluminum hydroxide. The element that forms a compound is more preferable, and the element that forms aluminum oxide is particularly preferable. That is, the catalyst layer in the cathode for hydrogen generation of the present invention particularly preferably contains aluminum oxide.

  When the content of the aluminum element in the catalyst layer is 1/100 or more with respect to 1 mol of the ruthenium element, an effect of increasing the surface area is obtained. When the content of the aluminum element is 1/2 mol or less, the catalyst after the aluminum compound is eluted Since the physical strength of the layer is maintained, the catalyst component is difficult to fall off. The content of aluminum element is more preferably in the range of 1/20 to 1/2, and still more preferably in the range of 1/15 to 1/4 with respect to 1 mole of ruthenium element.

(Catalyst layer thickness, etc.)
The thicker the catalyst layer, the longer the period during which a low overvoltage can be maintained. However, if the catalyst layer is excessively thick, the physical strength of the cathode may decrease. Considering both of these, the thickness of the catalyst layer is preferably 1 to 10 μm, and more preferably 2 to 5 μm.
Even weight per unit area of the catalyst layer, heavier, but the period to maintain a low overvoltage is long, considering also the viewpoint of economy, is preferably ^{1~20g / m 2, 3~15g / m} 2 It is more preferable that

(Mechanism for suppressing cathode deterioration)
In the hydrogen generating cathode of the present invention, the deterioration of the cathode is suppressed by increasing the surface area of the catalyst layer. The mechanism by which this effect appears will now be described.
When a reverse current flows after the electrolytic cell is stopped, the potential rises while the oxidation reaction proceeds on the cathode. On the cathode, various oxidation reactions of various substances proceed in the order of the redox potential. Specifically, first, oxidation reaction (1) of hydrogen adsorbed on the cathode proceeds in the vicinity of −1.0 V (vs. Ag | AgCl). Next, the oxidation reaction (2) of Ni metal (Ni substrate surface) proceeds in the vicinity of −0.9 V (vs. Ag | AgCl). Next, in the vicinity of −0.1 V (vs. Ag | AgCl), the oxidation elution reaction (3) of Ru, which is a catalytically active component in the catalyst layer, proceeds, and the Ru catalyst layer deteriorates.

As described above, the oxidation elution reaction (3) of Ru, which is a catalytically active component in the catalyst layer, does not start immediately when a reverse current flows, but starts after the oxidation reaction of a substance having a lower redox potential is completed. . That is, the oxidation elution reaction (3) of Ru in the catalyst layer is suppressed by increasing the amount of electricity consumed in other oxidation reactions such as hydrogen and nickel having a lower redox potential than Ru in the catalyst layer. be able to.
Here, by increasing the surface area of the catalyst layer, the amount of reverse current electricity used for these other oxidation reactions also increases, so it is speculated that the oxidation elution (3) of Ru can be suppressed.

The specific surface area of the catalyst layer can be estimated from the measurement result of the electric double layer capacity.
If the electric double layer capacity is 0.01 C / V · cm ² , the catalyst layer can be considered to have a sufficient specific surface area. Electric double layer capacity of the catalyst layer is more preferably 0.05C / V · cm ² or more, further preferably 0.08C / V · cm ² or more. The upper limit is preferably 0.35 C / V · cm ² or less as a practical value.
The electric double layer capacity can be measured as follows.
The cathode having the catalyst layer was immersed in a 32 wt% NaOH aqueous solution at 90 ° C., and the sweep rate was 10, 30, 50, 80, between −0.75 and −0.55 V (vs. Ag | AgCl). Sweeps were varied as 100 and 150 mV / s, and the current value at −0.65 V (vs. Ag | AgCl) was read. Then, the slope of the straight line obtained by plotting the sweep speed on the horizontal axis and the current value of −0.65 V (vs. Ag | AgCl) on the vertical axis is evaluated as the electric double layer capacity.

In the present invention, the surface area of the catalyst layer is increased by adding a transition metal element and an aluminum element to the catalyst layer in addition to the ruthenium element and the cerium element. For this reason, it is possible to suppress an increase in cathode potential when a reverse current flows.
The surface area of the catalyst layer can also be increased by adding a large amount of only one of the transition metal element and the aluminum element. However, in this case, layered peeling occurs in the catalyst layer, which causes a problem in durability during normal use.
By adding the elements of the predetermined combination of the present invention preferably in the range of the contents described above, a cathode having low hydrogen overvoltage, high reverse current resistance, and high durability during normal use can be obtained. It can be done.

<Method for producing cathode for hydrogen generation>
The hydrogen generating cathode of the present invention is, for example,
On the conductive substrate
After applying a solution (coating solution) containing a ruthenium compound, a cerium compound, a transition metal compound, and an aluminum compound, it is dried to form a coating film, and then the compound group contained in the coating film is pyrolyzed. It can manufacture by forming a catalyst layer. The transition metal compound is selected from trivalent transition metal compounds, except for ruthenium and cerium.

(Coating solution)
The coating liquid is a liquid composition containing a ruthenium compound, a cerium compound, a transition metal compound, and an aluminum compound.

The ruthenium compound used as a component of the coating solution may be in any form of chloride, sulfate, nitrate, and carboxylate. However, chlorides are preferably used because of the ease of thermal decomposition and the availability of raw material salts.
The concentration of the ruthenium compound in the coating solution is not particularly limited, but is preferably in the range of 10 to 200 g / L as the concentration in terms of ruthenium element in consideration of the coating thickness per time when forming the catalyst layer, A range of 50 to 120 g / L is more preferable.

  The cerium compound, transition metal compound, and aluminum compound may be in any form, but metal salts such as nitrates, sulfates, and chlorides are preferred, and further, thermal decomposition is facilitated, and raw material salts are readily available. From the standpoint of ease, chloride is preferably used.

The ratio of the metal element in the catalyst layer in the cathode for hydrogen generation of the present invention preferably reflects the ratio of the metal element in the coating solution used. Therefore, the content of each metal compound contained in the coating solution is as follows from the viewpoint of enabling the formed catalyst layer to sufficiently exhibit the effect.
Cerium compound: The ratio of cerium element to 1 mol of ruthenium element in ruthenium compound is preferably 1/20 to 1/2 mol, more preferably 1/8 to 1/4 mol Transition metal compound: ruthenium element in ruthenium compound As a ratio of transition metal element to 1 mol, preferably 1/100 to 1/2 mol, more preferably 1/50 to 1/10 mol Aluminum compound: As a ratio of aluminum element to 1 mol of ruthenium element in ruthenium compound, Preferably 1/100 to 1/2 mole, more preferably 1/15 to 1/4 mole

The above coating liquid contains the metal compounds as described above and the solvent described below as essential components, but may optionally contain other components.
Examples of other components used here include a pH adjuster, a surfactant, a viscosity adjuster, and a chelating agent.
These other components can be contained in the coating solution as long as they exhibit their functions and do not impair the effects of the present invention.

The coating solution is preferably prepared as a solution in which each metal compound as described above and other components optionally used as necessary are dissolved in a suitable solvent.
As a solvent used here, water, an organic solvent (for example, alcohol etc.) etc. can be mentioned, for example, It is preferable to use 1 or more types selected from these. Particularly preferred is water.

  As a method of applying the above-mentioned coating solution on the conductive substrate, a dipping method in which the substrate is immersed in the coating solution, a method of coating the coating solution with a brush, a roll that is coated by impregnating the coating solution with a sponge-like roll For example, an electrostatic coating method in which the coating liquid and the substrate are charged to opposite charges and sprayed using a spray or the like is preferably used. Among them, the roll method or the electrostatic coating method is suitably used from the viewpoint of productivity and that the coating liquid can be uniformly applied to the electrode surface.

After coating the coating solution on the substrate, it is dried at an appropriate temperature to form a coating film.
The drying temperature after coating at this time is preferably less than 150 ° C, and more preferably about 30 to 100 ° C. As drying time, 1 to 60 minutes are preferable, More preferably, it is 5 to 30 minutes, More preferably, it is 5 to 15 minutes.

Next, the coating film formed as described above is heated and thermally decomposed.
Thermal decomposition is a reaction that heats a metal compound in a coating film to accelerate its decomposition. Here, it refers to a reaction in which a metal salt is heated to decompose into a metal and a gaseous substance. For example, if the metal salt is a chloride, it decomposes into a metal and hydrogen chloride and / or chlorine gas,
If the metal salt is a nitrate compound, it decomposes into a metal and NOx gas and / or nitrogen,
If the metal salt is a sulfuric acid compound, it decomposes into a metal and SOx gas and / or sulfur. In many cases, the metal produced by the above decomposition tends to form an oxide in combination with oxygen in the environment.

  In order to accelerate the thermal decomposition of the coating film containing the mixture of metal compounds, it is preferable to employ a temperature range of 350 ° C. or higher and 600 ° C. or lower as the thermal decomposition temperature, and a temperature range of 450 to 550 ° C. is more preferable. When the temperature is lower than 350 ° C., the rate of thermal decomposition of the metal compound is slow, while when the temperature exceeds 600 ° C., the nickel base is rapidly softened. A temperature range of 500 to 550 ° C. is most preferable from the viewpoint of achieving both thermal decomposition acceleration of the metal compound and maintaining the strength of the nickel base material. As the thermal decomposition time, a longer time is preferable for sufficient thermal decomposition. However, considering the productivity of the electrode, the thermal decomposition time is preferably in the range of 5 to 60 minutes, more preferably in the range of 10 to 30 minutes.

  After drying and forming a coating film, before the thermal decomposition, calcination may be carried out in a temperature range of 150 ° C. or more and less than 350 ° C., which is a temperature at which water of crystallization of each metal compound disappears. By carrying out calcination, rapid evaporation of moisture and crystal water is suppressed in the thermal decomposition step, so that the catalyst layer can easily have a dense structure. In addition, since the preliminary calcination facilitates the formation of crystal nuclei and crystal growth of ruthenium oxide in the thermal decomposition step, a dense catalyst layer can be formed. The temperature range of pre-baking is preferably 200 ° C. or higher and lower than 350 ° C., more preferably 250 ° C. or higher and 320 ° C. or lower. The pre-baking time is preferably 1 to 60 minutes, more preferably 1 to 30 minutes, and still more preferably 1 to 15 minutes.

  The cycle of forming the catalyst layer including the application, drying, and thermal decomposition may be performed only once, or may be repeated a plurality of times. By repeating the coating / drying / pyrolysis cycle as necessary, a thick catalyst layer can be obtained.

In order to form a thick catalyst layer, the coating amount per time may be increased, or the ruthenium compound concentration in the coating solution may be increased. However, if the coating amount per time is large, unevenness may occur at the time of coating, and it is difficult to form the coating layer uniformly. Therefore, it is preferable to perform the coating / drying / pyrolysis cycle multiple times. When pre-baking is included, it is preferable to perform a plurality of cycles of coating, drying, pre-baking, and thermal decomposition. Preferably, the content of the ruthenium element in the formed catalyst layer is 0.1 to ² g / m ² per cycle, and the above cycle is repeated. The ruthenium element content in the catalyst layer formed per cycle is more preferably 0.3 to 1.8 g / m ² , further preferably 0.5 to 1.5 g / m ² .

  After the formation of the catalyst layer having a predetermined thickness, it is desirable to perform firing for a longer period of time in order to completely decompose the catalyst layer and stabilize the catalyst layer. As firing conditions in this case, the temperature range is preferably 500 to 650 ° C, more preferably 500 to 550 ° C. If the time for thermal decomposition of the catalyst layer is short, the thermal decomposition of the catalyst layer does not proceed sufficiently, and if it is too long, the oxidation of cerium in the catalyst layer proceeds excessively and the effect of adding a transition metal is manifested. Neither is desirable because it is difficult. Therefore, the firing time is preferably about 30 minutes to 8 hours, more preferably 1 hour to 3 hours.

The present embodiment will be described in more detail based on examples. However, the present invention is not limited to the following examples.
Various measurements in the following examples and comparative examples were performed by the following methods, respectively.
(Crystal structure analysis of ruthenium oxide and cerium oxide)
Crystal structure analysis of ruthenium oxide and cerium oxide was performed using an X-ray diffractometer (UltraX18, manufactured by Rigaku Corporation) under the following conditions.
X-ray source: CuKα ray (λ = 1.54184Å)
Acceleration voltage: 50 kV
Acceleration current: 200 mA
Scanning axis: 2θ / θ
Step interval: 0.02 °
Scan speed: 2.0 ° / min
Measurement range: 2θ = 20-60 °

(Measurement of peak intensity ratio of ruthenium oxide and cerium oxide)
In the X-ray chart obtained under the above conditions, the intensities of the 35.1 ° peak attributed to ruthenium oxide and the 47.3 ° peak attributed to cerium oxide were compared. The ruthenium oxide diffraction line position was determined with reference to JCPDS card number 431027, and the cerium oxide diffraction line position was determined with reference to JCPDS card number 340394. The peak intensity ratio between the two was calculated by the following formula.
(a formula)
Peak intensity ratio = peak intensity (count) around 47.3 ° / peak intensity (count) around 35.1 °

(Ruthenium element content)
The content of ruthenium element contained in the test cathode was calculated as follows.
The increase in the weight of the cathode before and after coating was measured, and it was assumed that the breakdown of the weight increase was the same as the composition of the coating solution, and that the metal element formed an oxide. However, in the case where an organic substance is contained, it is assumed that the organic substance is thermally decomposed into CO ₂ , H ₂ O and the like in the baking process and does not contribute to the increase in the weight of the cathode.

(Reverse current application test)
Evaluation of resistance to reverse current was performed according to the following procedure.
The test cathode cut out to 30 mm × 30 mm was fixed to the electrolytic cell with a nickel screw. The counter electrode was a platinum plate, in 32 wt% sodium hydroxide aqueous solution, at 80 ° C., the electrolysis current density 1 kA / ^{m 2} at 20 min, 3 min each at 2 kA / ^{m 2} and 3 kA / ^{m 2,} and 4 kA / m ^Then , positive electrolysis was performed sequentially for ² minutes so that the test cathode generated hydrogen. Thereafter, reverse electrolysis was performed at a current density of reverse current of 0.05 kA / m ² while measuring the cathode potential using Ag / AgCl as the reference electrode, and the cathode potential was the ruthenium dissolution potential (−0.1 V vs. Ag / Ag / The time required to reach (AgCl) was measured, and this value was defined as the reverse current durability time.
FIG. 1 shows the potential rise behavior during the reverse current application test of the test cathode. The horizontal axis of FIG. 1 is a relative value with 1.0 as the time until the cathode of Comparative Example 1 reaches the ruthenium dissolution potential. The reverse current durability time in Table 1 is the time (relative value) until each test cathode reaches the ruthenium dissolution potential.

(Cross section SEM observation)
The cross section of the catalyst layer after energization was observed according to the following procedure.
The test cathode was cut out to a size of 48 mm × 58 mm, and two holes were made to fix it to the small electrolytic cell with nickel screws. This was fixed on a nickel expanded substrate. As the anode, so-called DSA in which ruthenium oxide, iridium oxide and titanium oxide were formed on a titanium base material was used. Salt electrolysis was performed in a state where the anode cell and the cathode cell were separated by an ion exchange membrane sandwiched by a rubber gasket made of EPDM (ethylene propylene diene rubber). As the ion exchange membrane, “Aciplex” (registered trademark) F6801 (manufactured by Asahi Kasei Chemicals Corporation) was used. The anode and the ion exchange membrane were brought into close contact, and a gap of 2 mm was provided between the cathode and the ion exchange membrane. The solution concentration in the cathode tank was adjusted so that the sodium chloride concentration in the anode chamber was 205 g / L and the sodium hydroxide concentration in the cathode chamber was 32 wt%. In addition, the temperature in the cathode tank was adjusted so that the temperature in the electrolytic cell was 90 ° C. Electrolysis was carried out for one week with an electrolytic current density of a constant value of 4 kA / m ² .

  Cut out a part of the test cathode after energization as described above, embed it in an epoxy resin, and then perform cross-section processing with an Ar ion beam accelerated at 6 kV using a cross section polisher (manufactured by Hitachi). Thus, a sample for observing the cross section of the catalyst layer was prepared. After mounting this on the SEM sample stage, the backscattered electron image was observed at an acceleration voltage of 5 kV using FE-SEM “S-4700” (manufactured by Hitachi).

[Examples 1 to 6 and Comparative Examples 2 to 4]
As the conductive substrate, a woven mesh obtained by knitting a fine nickel wire having a diameter of 0.15 mm with an opening of 40 mesh was used. This was blasted with JIS R6001 (1998) standard No. 320 alumina particles, then acid-treated with 6N hydrochloric acid at room temperature for 5 minutes, washed with water and dried.

  Next, a rare earth chloride and an aluminum compound (aluminum chloride) so that the content of each metal element has the composition shown in Table 1 with respect to an aqueous ruthenium chloride solution (made by Tanaka Kikinzoku, ruthenium element concentration 100 g / L). Was added to prepare a coating solution.

The coating solution was placed in a bat, and an EPDM coating roll was placed on the bat so that the coating solution was always in contact with the coating solution, and the coating solution was immersed in the coating roll. On top of that, an EPDM roll was placed so as to be always in contact with the coating roll, and a PVC roll was placed on the upper EPDM coating roll. The conductive substrate was passed between the upper EPDM coating roll and the PVC roll, and a coating solution was applied onto the substrate (roll method). If necessary, quickly pass the conductive substrate after coating between two EPDM sponge rolls before the coating solution dries, and suck the coating solution that accumulates at the intersection of the mesh of the conductive substrate. Removed. Thereafter, it was dried at 50 ° C. for 10 minutes to form a coating film.
Further, using a muffle furnace (KM-600, manufactured by Advantech Co., Ltd.), pre-baking is performed at 300 ° C. for 10 minutes in the atmosphere, and then baking is performed at 500 ° C. for 10 minutes to thermally decompose the coating film. It was. After repeating this roll coating, drying, and thermal decomposition cycle 11 times, the test cathode was finally obtained by firing at 500 ° C. for 1 hour.

About said test cathode, the measurement of X-ray diffraction and reverse current durability time was implemented by the above-mentioned method. The results of Examples 1 to 6 are shown in Table 1, and the results of Comparative Examples 2 to 4 are shown in Table 2, respectively. Moreover, the potential behavior of the cathode during the reverse current application test is shown in FIG.
Furthermore, about the comparative example 4, SEM observation of the catalyst layer cross section after electricity supply was performed by the above-mentioned method. The SEM image obtained by the observation is shown in FIG.

[Comparative Examples 1, 5, and 6]
As the conductive substrate in these comparative examples, the same woven mesh as in Examples 1 to 6 and Comparative Examples 2 to 4 was used after being treated in the same manner.

Using the above conductive substrate,
In Comparative Example 1, by the method of Example 6 described in Patent Document International Publication No. 2003/076694, page 13, line 7 and thereafter,
In Comparative Example 5, the method of Example 1 described in Paragraph 0034 and subsequent paragraphs of Japanese Patent Laid-Open No. 2006-299395 is used, and in Comparative Example 6, Paragraph 0039 and thereafter of Japanese Patent Laid-Open Publication No. 2009-215580. According to the method of Example 7 described in
Test cathodes were respectively prepared.

  About each said test cathode, the measurement of the X-ray diffraction and reverse current durability time was implemented by the above-mentioned method. Table 2 shows the results of X-ray diffraction and reverse current durability time. FIG. 1 shows the potential behavior of the cathode during the reverse current application test.

From Tables 1 and 2 above and FIGS. 1 and 2, the following is understood.
In Examples 1 to 6, when reverse electrolysis was performed, the time until the cathode potential reached −0.1 V vs. Ag / AgCl, which is the dissolution potential of ruthenium, which is a catalyst component (reverse current durability time), Compared to Comparative Example 1, it was 3.1 to 6.7 times larger. That is, it is difficult for the cathode potential to rise during reverse current generation, and reverse current resistance is improved. This is also clear from FIG.

  In Comparative Examples 2, 3 and 6, the reverse current endurance time is 2.3 to 2.8 times longer than that of Comparative Example 1, respectively. However, these values are all smaller than those of Examples 1-6. From this, it is understood that even if the same amount of ruthenium element as in the example is contained, a sufficient effect cannot be obtained in the catalyst layer having the predetermined configuration of the present invention.

In Comparative Example 4, the reverse current endurance time was 5.7 times that of Comparative Example 1, indicating that a large reverse current resistance can be obtained by adding a large amount of lanthanum. However, in the cathode of Comparative Example 4, layered peeling occurs in the coating layer as shown in FIG. That is, the cathode of Comparative Example 4 is not practical because it has low coating strength and the catalyst layer falls off during electrolysis.
In Comparative Example 5, the reverse current endurance time is 0.8 times that of Comparative Example 1, and the reverse current resistance is insufficient.

Claims (16)

A cathode for hydrogen generation comprising a conductive substrate and a catalyst layer on the conductive substrate,
The cathode for hydrogen generation, wherein the catalyst layer contains a ruthenium element, a cerium element, a transition metal element capable of taking trivalence (excluding ruthenium and cerium), and an aluminum element.   2. The cathode for hydrogen generation according to claim 1, wherein the trivalent transition metal is a rare earth metal.   The hydrogen generating cathode according to claim 2, wherein the trivalent transition metal is at least one metal selected from the group consisting of lanthanum, praseodymium, neodymium, and samarium. The content of the cerium element is 1/20 to 1/2 mol with respect to 1 mol of the ruthenium element,
The content of the transition metal element capable of taking the trivalent is 1/100 to 1/2 mol with respect to 1 mol of the ruthenium element, and the content of the aluminum element is 1 with respect to 1 mol of the ruthenium element. The cathode for hydrogen generation as described in any one of Claims 1-3 which is / 100-1 / 2 mol. The ruthenium element is an element that forms at least one compound of ruthenium oxide and ruthenium hydroxide;
The cerium element is an element forming at least one compound of cerium oxide and cerium hydroxide, and at least a part of the transition metal element capable of taking trivalent is a transition metal oxide and The element forming at least one compound of transition metal hydroxides, and the aluminum element is an element forming at least one compound of aluminum oxide and aluminum hydroxide. The cathode for hydrogen generation as described in any one of 1-4.   The cathode for hydrogen generation according to claim 5, wherein at least a part of the transition metal element is doped with at least one of the cerium oxide and cerium hydroxide. The conductive substrate is made of nickel;
At least a part of the cerium element in the catalyst layer is an element that forms cerium oxide,
At least a part of the ruthenium element is an element that forms ruthenium oxide, and 2θ = 47.3 ° attributed to cerium oxide when the catalyst layer is X-ray diffracted together with the conductive substrate. The cathode for hydrogen generation according to claim 5 or 6, wherein the peak intensity is 1/40 or less with respect to the peak intensity of 2θ = 35.1 ° attributed to ruthenium oxide. The cathode for hydrogen generation as described in any one of Claims 1-7 whose content of the ruthenium element contained in the said catalyst layer is 1-20 g / m < ² >. On the conductive substrate
After applying a solution containing a ruthenium compound, a cerium compound, a trivalent transition metal compound (except ruthenium and cerium), and an aluminum compound, it is dried to form a coating film, and then in the coating film A method for producing a hydrogen generating cathode, wherein the catalyst group is formed by thermally decomposing the compound group contained in the catalyst.   The method for producing a cathode for hydrogen generation according to claim 9, wherein the transition metal compound capable of taking trivalence is a rare earth metal compound.   The production of a cathode for hydrogen generation according to claim 9 or 10, wherein the trivalent transition metal compound is at least one selected from the group consisting of a lanthanum compound, a praseodymium compound, a neodymium compound, and a samarium compound. Method. In the solution,
The content of the cerium compound is 1/20 to 1/2 mol as a ratio of the cerium element to 1 mol of the ruthenium element in the ruthenium compound,
The content of the transition metal compound capable of taking the trivalence is 1/100 to 1/2 mol as a ratio of the transition metal element to 1 mol of the ruthenium element in the ruthenium compound, and the content of the aluminum compound is The method for producing a cathode for hydrogen generation according to any one of claims 9 to 11, wherein the ratio of aluminum element to 1 mol of ruthenium element in the ruthenium compound is 1/100 to 1/2 mol.   The manufacturing method of the cathode for hydrogen generation as described in any one of Claims 9-12 whose said ruthenium compound is a chloride.   The method for producing a cathode for hydrogen generation according to any one of claims 9 to 13, wherein the transition metal compound capable of taking trivalence is a chloride. Drying after applying the solution on the conductive substrate at a temperature of less than 150 ° C .;
The manufacturing method of the cathode for hydrogen generation as described in any one of Claims 9-14 which performs the said thermal decomposition at the temperature of 350 to 600 degreeC.   The method for producing a cathode for electrolysis according to any one of claims 9 to 15, wherein pre-baking is performed at a temperature of 150 ° C or higher and lower than 350 ° C for 1 to 60 minutes before the thermal decomposition.