JP2003512520A - Catalyst powder and electrodes made therefrom - Google Patents

Abstract

(57) Abstract: A porous coating (12) is a catalyst powder comprising a plurality of support metal particles surrounding a support metal particle (11), wherein the porous coating is an electrode catalyst metal or The above catalyst powder comprising any one of the electrocatalyst metal continuous phases in a mixed state with the particulate matter (14). Electrodes made from the catalyst powder, as well as methods for making the electrodes, are also disclosed. The present invention is advantageous because the porous coating mixture is first applied to the powder rather than directly to the metal substrate, which results in a large internal surface area on the electrode and thus lower overpotential requirements. It is.

Description

Detailed Description of the Invention

The present invention is directed to electrocatalytically reactive electrodes. More particularly, the present invention is directed to cathodes useful in electrolytic cells such as chloralkali cells.

Chlorine and caustic soda are typically produced by electrolysis of an aqueous solution of sodium chloride, a process commonly referred to as the chloroalkali process.

The most widely used chloralkali process uses either a diaphragm (“diaphragm”) or a membrane (“membrane”) type of electrolytic cell. In a diaphragm cell, an alkali metal halide brine solution is fed into the anolyte compartment, where the halide ions are oxidized to produce halogen gas. Alkali metal ions migrate into the catholyte compartment through a hydraulically permeable microporous membrane located between the anolyte compartment and the catholyte compartment. Hydrogen gas and an aqueous alkali metal hydroxide solution are produced at the cathode. Due to the hydraulically permeable diaphragm, brine can flow into the catholyte compartment and mix with the alkali metal hydroxide solution.

Membrane electrolyzers function similarly to diaphragm electrolyzers, except that the membrane is provided with a hydraulically impermeable cation-selective membrane that selectively allows the passage of hydrated alkali metal ions into the catholyte compartment. Will be replaced. The membrane electrolyzer produces an aqueous alkali metal hydroxide solution that is essentially uncontaminated with brine.

Electrodes are usually manufactured by applying an electrocatalyst coating on a conductive substrate.
Useful catalytic coatings include, for example, platinum group metals such as ruthenium, rhodium, osmium, iridium, palladium and platinum. Useful conductive substrates include, for example, nickel, iron and steel.

The production of chlorine gas at the anode and the simultaneous production of hydroxide ions and production of hydrogen gas at the cathode almost always require a cell voltage higher than the thermodynamic energy for the next reaction. 2NaCl + 2H ₂ O → Cl ₂ + H ₂ + 2NaOH

The extra energy or overvoltage is, among other parameters,
It is provided to overcome electrolytic resistance and overpotentials associated with chlorine gas evolution at the anode and hydrogen gas evolution and hydroxide ion formation at the cathode.

Various methods have been proposed to reduce electrode overpotential requirements by altering surface properties. The term "overvoltage" is used herein to refer to the overvoltage required for an electrolyser, while the term "overpotential" refers to the overvoltage required for individual electrodes within an electrolyzer. Used herein to refer.

The overpotential for an electrode is a function of its chemical properties and current density. Current density is defined as the current applied to an electrode per unit of effective surface area. Techniques that increase the effective surface area of the electrode, such as acid etching or sandblasting the surface of the electrode, will result in a substantial reduction in current density for a given amount of applied current and will also reduce overpotential requirements. .

Efforts to reduce overpotential requirements have been made, for example, in US Pat. No. 4,668,370 and US Pat. No. 4,79, which disclose electrodes useful as cathodes in electrolytic cells.
Including those described in No. 8,662. These are produced by coating a conductive substrate such as nickel with a catalyst coating containing one or more platinum group metals from a solution containing a platinum group metal salt. Both of these patents disclose electrodes designed to reduce the operating voltage of the electrolytic cell by reducing the overpotential requirements of the electrodes. In addition, US Pat. No. 5,035,789 and US Pat. No. 5,227,03
No. 0 and US Pat. No. 5,066,380 disclose cathode coatings that exhibit low hydrogen overpotential.

A desirable property of cathode coatings is high porosity with a large internal surface area. A large internal surface area will result in a lower effective current density and thus a lower overpotential. Another outcome of porous electrodes is higher resistance to the toxic effects of impurities. The rough outer surface of a typical porous electrode makes electrodeposition of metal ions as impurities difficult, and the large internal electroactive surface area is readily available for impurity ions present in the electrolyte due to the long path for diffusion. Not. Such properties are described in US Pat. No. 5,645,930.

Metal plating is often used to form a reinforcing layer on electrodes. For example, US Pat. No. 4,061,802 and US Pat. No. 4,764,401 describe the use of palladium chloride to activate a plastic or metal substrate prior to nickel plating by electroless deposition. .

In one aspect, the present invention is a catalyst powder comprising a plurality of support metal particles containing a transition metal or an alloy thereof, and a coating surrounding the support metal particles, the coating comprising: The above catalyst powder, either comprising an electrocatalyst metal coating or comprising a coating having a metal continuous phase in a mixed state with particulate matter.

In a second aspect, the present invention is an electrode comprising a conductive metal substrate and a first layer comprising a matrix in which catalyst powder is dispersed, the matrix comprising a platinum group metal oxide. Or a mixture of platinum group metal oxides and valve metal oxides, the catalyst powder being either an electrocatalyst metal coating or a coating comprising electrocatalyst metal in admixture with particulate matter. The above electrode comprising support metal particles covered with.

In a third aspect, the present invention relates to a method of making an electrode, comprising the steps of forming a catalyst powder, mixing the catalyst powder with a dispersion medium to form a mixture, and making the mixture conductive. Comprising the steps of applying to a metal substrate to form a coated substrate, baking the coated substrate in the presence of oxygen, and optionally enhancing the adhesion and strength of the coating with an alloy coating process. Is the way.

The present invention is advantageous because the porous coating mixture is applied first to the powder, rather than directly to the metal substrate, which results in a larger internal surface area with respect to the prior art. A large internal surface area will result in a lower effective current density and thus a lower overpotential. Therefore, since the surface area is increased using the present invention, the overpotential required for electrodes made according to the present invention is also reduced with respect to the prior art electrodes cited above.

FIG. 1 shows an enlarged view of catalyst powder particles 10 of the present invention. As shown, the catalyst powder particles 10 comprise support metal particles 11 surrounded by a porous coating comprising a continuous phase 12 having particulate material 13 dispersed therein.

The support metal particles 11 are preferably transition metals or alloys thereof. Preferred transition metals include nickel, cobalt, iron, steel, stainless steel or copper. Preferred transition metal alloys are nickel alloyed with phosphorus, boron or sulfur,
Includes cobalt or copper.

Preferably, the support metal particles are at least 0.2 micron, more preferably at least about 1 micron, even more preferably at least 2 micron, even more preferably at least 3 micron before the porous coating is applied thereto. Has an average diameter of. Preferably, the metal particles are up to 20.0 microns, more preferably 10
． It has an average diameter of up to 0 microns and even more preferably up to 6.0 microns.

The support metal particles 11 are coated either with the electrocatalytic metal or with a porous coating comprising the electrocatalytic metal continuous phase 12 in admixture with the particulate material 13. Due to the porous and dendritic nature of the coating on the support metal particles, the resulting catalyst powder particles 10 have a large internal surface area with pores 14 present throughout.

Preferably, the electrocatalytic metal continuous phase 12 is ruthenium, iridium, osmium, platinum, palladium, rhodium, rhenium, or an alloy of any one or more of these.

In one embodiment, continuous phase 12 has particulate matter 13 dispersed therein.
Have. Preferably, the particulate matter 13 comprises a metal oxide of ruthenium, iridium, osmium, platinum, palladium, rhodium, rhenium, technetium, molybdenum, chromium, niobium, tungsten, tantalum, manganese or lead, whereby ruthenium. More preferred are oxides of iridium, iridium, osmium, platinum, palladium and rhodium.

In order to produce the catalyst powder, a plurality of support metal particles may be used in combination with the electrocatalyst metal alone or in a mixture with a particulate material comprising either a metal or a metal oxide. It is covered with a porous coating comprising either. Generally, the first step in making the catalyst powder is to make a precipitation solution containing at least a palladium promoter and an organic or inorganic acid.

It is noted that the presence of palladium metal ions in the deposition solution in addition to the metal ions of the electrocatalyst metal precursor compound promotes the deposition of the electrocatalyst metal on the metal particles. US Pat. Known from No. 066,380. Examples of suitable palladium metal compounds are palladium halides and palladium nitrate. The concentration of palladium metal ions in the porous coating solution should be sufficient to promote improved electrocatalyst loading on the metal particles. The palladium precursor compound, when present, is generally included in an amount sufficient to provide a palladium metal ion concentration in the coating solution of at least 0.001 weight percent based on the weight of the coating solution. The palladium metal ion concentration may suitably be from 0.001% to 5% by weight of the coating solution, preferably 0.005% to 2% and most preferably 0.01% to 0.05% by weight. Weight percentages less than 0.001 percent are generally insufficient to promote electrocatalyst metal deposition. Weight percentages greater than 5 percent will result in the deposition of excess electrocatalytic metal major phase of the coating on the substrate.

The pH of the precipitation solution can be adjusted by including an organic or inorganic acid therein. Examples of suitable inorganic acids are hydrobromic acid, hydrochloric acid, sulfuric acid, perchloric acid and phosphoric acid. Examples of organic acids are acetic acid, oxalic acid and formic acid. Hydrobromic acid and hydrochloric acid are preferred. The pH range of the precipitation solution is generally pH 0 to pH 2.8.
Precipitation of hydrous platinum group metal oxides will occur at relatively high pH. A low pH may help to compete with side reactions such as substrate dissolution.

At least one electrocatalytic metal compound that is soluble in water or aqueous acid is added to the deposition solution. Suitable electrocatalytic metals are generally those that are more noble than the metals used for the metal particles, i.e., the electrocatalytic metal precursor compound has a Gibbs free energy that is greater than the Gibbs free energy of the metal compound from dissolution of the metal particles. And thus non-electrolytic reduction deposition occurs on the metal particles. Preferably, the electrocatalyst metal is a platinum group metal. Further details on non-electrolytic reduction deposition can be found in US Pat. No. 5,645,930.

The electrocatalytic metal precursor compound may be present in the deposition solution in an amount sufficient to deposit an effective amount of metal on the metal particles. The concentration of the electrode catalyst metal ion in the deposition solution is
Expressed in weight percent, it is generally from 0.01 percent to 5 percent by weight of the solution, preferably from 0.1 percent to 3 percent, and most preferably from 0.2 percent to 1 percent. Electrocatalytic metal ion concentrations of greater than 5 percent are not desirable because unnecessarily high amounts of platinum group metal are used to make the coating solution. Electrocatalytic metal ion concentrations of less than 0.01 percent are not desirable because undesirably long contact times are required.

The optional particulate material is suspended in the precipitation solution at a concentration of 0.002 to 2 percent, preferably 0.005 to 0.5 percent, and most preferably 0.01 to 0.2 percent.

After the deposition solution containing the palladium promoter, the acid and the optional particulate matter is prepared, it is kept at elevated temperature and stirred at high speed while the powder comprising the support metal particles. Is added to it. After a period of time, the electrocatalytic metal precursor compound is added and the electrocatalytic metal is formed and deposited on the support metal particles, with simultaneous partial dissolution of the support metal particles.

The rate at which the electrocatalytic metal deposits to form a porous coating on the metal particles is a function of solution temperature. The temperature is generally in the range 25 ° C to 90 ° C. Low temperatures are not practical because uneconomically long times are required to deposit an effective amount of electrocatalytic metal on the metal particles. Temperatures above 90 ° C are operable, but will generally result in excess metal deposition and side reactions. Temperatures in the range between 40 ° C and 80 ° C are preferred, therefore 45 ° C to 65 ° C.
Is most preferred.

In general, the time allowed for contact between the deposition solution and the metal particles can vary from 1 minute to 60 minutes. However, it should be understood that the required contact time varies with the deposition solution temperature, the electrocatalyst metal concentration and the palladium ion concentration. Contact times of 5 to 60 minutes are preferred, with 10 to 40 minutes being most preferred. In general, if a relatively short contact time is desired, the method described herein can be repeated multiple times until an effective amount of the platinum group electrocatalyst metal is deposited on the surface of the metal particles.

The catalyst powder 10 is advantageously used to form electrodes for an electrolytic cell. FIG. 2 shows an enlarged view of a portion of the electrode 20 of the present invention. The electrode 20 is a conductive metal substrate 21.
And a first layer, wherein the first layer comprises a matrix 22 in which the catalyst powder 10 described above is dispersed. The porous dendritic nature of the catalyst powder provides a porous surface on the electrode, which in turn reduces the overpotential required for efficient operation of the electrode and electrolyzer.

Preferably, the conductive metal substrate 21 is nickel, iron, steel, stainless steel, cobalt, copper or silver. The shape of the substrate is not critical and can be, for example, a flat plate, a curved surface, a perforated plate, a wire mesh screen or a mesh plate.

The first layer matrix 22 comprises either a platinum group metal oxide or a mixture of platinum group metal oxides and valve metal oxides. Platinum group metal oxides include oxides of ruthenium, iridium, rhodium, osmium, platinum, palladium, or mixtures of any one or more of these. Valve metal oxides include oxides of titanium, zirconium, tantalum, tungsten, niobium, bismuth, or mixtures of any one or more of these.

To prepare the electrodes of the present invention, the catalyst powders described above are mixed with a dispersion medium to form a mixture, and the mixture is applied to a conductive metal substrate to form a coated substrate. To be done. The coated substrate is then baked in the presence of oxygen.

The dispersion medium forms the matrix of the electrode and comprises either a platinum group metal oxide precursor or a mixture of platinum group metal oxide precursor and valve metal oxide precursor. A platinum group metal oxide precursor is a substance that forms a platinum group metal oxide when baked in the presence of oxygen. A preferred platinum group metal oxide precursor is
Includes platinum group metal halides, sulfates, nitrates, nitrites and phosphates. More preferred are platinum group metal halides, nitrates and phosphates, with platinum group metal chlorides being most preferred. A valve metal oxide precursor is a material that forms a valve metal oxide when baked in the presence of oxygen.
Preferably, the valve metal oxide precursor is a titanium alkoxide, tantalum alkoxide, zirconium acetylacetonate or niobium alkoxide.

Preferably, the dispersion medium further comprises a solvent. Suitable solvents include methanol, ethanol, 1-propanol, 2-propanol, butanol, or mixtures of any of these.

[0038] Preferably, the dispersion medium further comprises a compound soluble in the alkaline solution. Examples of such soluble compounds include aluminum chloride and zinc chloride. Such alkali-soluble compounds are useful in creating pores in the coating after they are dissolved in the alkaline solution.

Any suitable method can be used to disperse the catalyst powder in the dispersion medium.
Examples include mechanical agitation, sonication or combinations thereof.

Application of the catalyst powder / dispersion medium mixture can be accomplished using any suitable method. An example is spraying through a nozzle. Spraying generally to 50 ug / cm ² without the 2000 ug / cm ^2, forming a platinum group metal loading in the resulting electrode was calculated as the metal "atoms" form. The amount of metal in the electrodes is measured by X-ray fluorescence. The preferred loading for both elemental metals and compound oxides is 40.
A 0ug / cm ² from 1500ug / cm ^2, a Thus the most preferred loading is 1000 ug / cm ² from 500 ug / cm ^2. Loadings of less than 50 ug / cm ² are generally insufficient to provide a satisfactory reduction in cell overvoltage. 20
Loadings greater than 00 ug / cm ² do not significantly reduce applied overvoltage when compared to relatively low loadings within the preferred range. The deposition effective amount noted above refers only to the loading of platinum group electrocatalyst metal and metal oxide in the electrode, and the palladium metal promoter or any optional secondary metal that can be used to provide the increased loading. It does not include the amount of electrocatalyst metal or metal particles.

In a preferred embodiment, the substrate is protected before the mixture is applied to it, for example by electroless nickel plating. Such a method is described in US Pat.
No. 1,802.

The baking step is used to convert the platinum group metal oxide precursor and the valve metal oxide precursor to the oxide form. The coated substrate is preferably baked in the presence of oxygen at a temperature of at least 350 ° C, more preferably at least 420 ° C and even more preferably at least 450 ° C. Preferably, the coated substrate is 55
No higher than 0 ° C, more preferably no higher than 500 ° C, even more preferably 48
Baking at a temperature not higher than 0 ° C. Preferably, the baking step is
It takes between 30 and 90 minutes. The coated substrate is oxygen (air or some other substance containing oxygen, such that the platinum group metal oxide precursor and the valve metal oxide precursor are converted to the platinum group metal oxide and the valve metal oxide. It is important to be baked in the presence of). The result is a two-phase first layer of the electrode,
Thus one phase is the matrix and the second phase is the catalyst powder particles dispersed in the matrix.

In a preferred embodiment, the electrode of the present invention further comprises a reinforcing layer 23. The reinforcing layer 23 preferably comprises a transition metal or its alloy. More preferably, the strengthening layer is nickel, cobalt, copper or alloys thereof with boron, phosphorus or sulfur.

The second electroless plating step consists of plating the coated substrate with a transition metal or transition metal alloy to create an optional reinforcing layer. Such a toughening layer helps hold the catalyst powder and matrix together and helps ensure that the first layer adheres to the substrate. Further details on forming a toughening layer can be found in US Pat. No. 5,645,930.

All parts and percentages are by weight unless otherwise specified. The following example
It is not intended to be restrictive.

Examples 1-3 : Preparation of catalyst powder with metal particulates Porous coating solutions were prepared using PdCl ₂ as palladium promoter and 0.5N-HCl as acid. The solution was heated to reaction temperature and stirred continuously. RuCl ₃ .H ₂ O was added as an electrocatalyst platinum group metal compound. The resulting solution was maintained at the reaction temperature and stirred using a COWLES high speed disperser while 3
Micron nickel powder (Aldrich) was added. After stirring this mixture at the elevated temperature for the desired contact time, the resulting Ru-coated nickel powder was collected on a filter paper,
It was dried at 90 ° C. for several hours and weighed. The amount of Ru in this powder was determined using X-ray fluorescence. Table I lists variables and results.

[0047]

[Table 1]

Examples 4-6 : Preparation of catalyst powders with metal / metal oxide agglomerates as particulate matter PdCl ₂ as palladium promoter and 0.5N-HCl as acid, for porous coatings. A solution was prepared. The solution was heated to reaction temperature and stirred continuously. RuO ₂ was added as a platinum group metal oxide. The resulting solution was held at the reaction temperature and stirred using a COWLES high speed disperser operating at 3000 rpm, while 3 micron nickel powder (Aldrich) was added. Then, RuCl ₃ .H ₂ O was added as an electrocatalyst platinum group metal compound. After stirring this mixture at the elevated temperature for the desired contact time, the resulting Ru-coated nickel powder is dried,
And weighed. The amount of Ru in this powder was determined using X-ray fluorescence. Table II
Enumerates variables and results.

[0049]

[Table 2]

Examples 7-9-Preparation of Cathode with Metallic Particulates A 5 inch x 6 inch (12.7 cm x 15.24 cm) plate according to the procedure described in US Pat. No. 4,061,802. Electroless nickel plated. Then, on this plate, a dispersion medium and Ru-coated nickel powder (Ru = 3.1) dispersed therein.
%) And sprayed the mixture. The weight percentage of powder in the spray mixture was about 10 percent. The platinum group metal oxide precursor in the dispersion medium is Ru
Cl ₃ and the valve metal oxide precursor compound in the dispersion medium was titanium isopropoxide. The solvent in the dispersion medium is a combination of methanol and 2-propanol, the compound soluble in the alkaline solution is aluminum chloride or zinc chloride, and the acid used to adjust the pH is It was HCl gas.

The sprayed samples were dried at 90 ° C. for 20 minutes and baked at 490 ° C. for 60 minutes. The X-ray fluorescence of this sample was used to determine the loading of metal on the substrate. Table III lists the parameters and results.

[0052]

[Table 3]

Examples 10-13 Preparation of Cathodes with Metal / Metal Oxide Aggregate Particulate Matter According to the procedure described in US Pat. No. 4,061,802, 5 inches by 6 inches (12.7 cm). X 15.24 cm) plate was electroless nickel plated. Then, a dispersion medium and Ru / RuO ₂ coated nickel powder (R
u = 25.86 percent). The weight percentage of powder in the mixture for spraying is about 10 percent. The dispersion medium is 2.37 weight percent RuCl ₃ .H ₂ O as a platinum group metal oxide precursor, 2.87 weight percent titanium isopropoxide as a valve metal oxide precursor, and 8. as a solvent.
86 weight percent methanol and 83.80 weight percent 2-propanol, as well as AlCl ₃ · 6H ₂ O of 2.10 wt% as soluble compounds in an alkaline solution.

The sprayed samples were dried at 90 ° C. for 20 minutes and baked at 490 ° C. for 60 minutes. The X-ray fluorescence of this sample was used to determine the loading of metal on the substrate. Table IV lists the parameters and results.

[0055]

[Table 4]

Examples 14-16-Preparation of Electrodes with Second Reinforcement Layer The samples from Examples 7-9 above are coated with a second reinforcement layer of Ni-P by the following steps. The plate was immersed in a mixture of the following solutions for 5 minutes at ambient temperature. That is, 25 cc
Of, in methanol 0.01M- of _{(NH 4) 2 PdCl 4,} 50cc, 0.1M poly (4-vinylpyridine) in methanol, and 425cc methanol.
Then, these coated plates were dried at 90 ° C. in a horizontal position. These dipping and drying steps were repeated.

Thereafter, these coated plates were placed in a plastic horizontal container with the screw threads of the plate fitted to the fitting part at the bottom of the container. The vessel was first charged with 3 at pH = 2.95.
It meets 5-10 minutes with an aqueous solution containing NaH ₂ PO ₂ · H ₂ O of 6 g / l, P
d (II) was reduced to Pd °. The solution is then poured out and then 500
ml electroless nickel plating solution was added to the vessel and electroless plating was performed for 20 minutes. The composition of the electroless plating solution is as follows. That is,

NiCl ₂ .6H ₂ O 17.4 g / l sodium citrate 30.24 g / l NaH ₂ PO ₂ .H ₂ O 25.2 g / l NH ₄ Cl 21.26 g / l NH ₄ OH pH = 8. Add until 8

The weight gains for Example 4 (Example 7), Example 5 (Example 8) and Example 6 (Example 9) are 2.63 mg / cm ² , 3.26 mg / cm ² and It was 2.69 mg / cm ² .

To measure the hydrogen potential, the plate was connected to a nickel rod and placed in a caustic bath at elevated temperature. A platinum plate welded to a nickel rod was used as the anode. 0.46 amps per square inch (ASI), 1.0 AS
A current density of I and / or 1.09 ASI was applied to the cathode sample and anode from the rectifier. The cathode potential was measured using a LUGGIN probe with a Hg / HgO reference electrode. The parameters and results are listed in Table V.

[0061]

[Table 5]

Examples 17-20-Preparation of Electrodes with Second Reinforcement Layer The samples from Examples 10-13 above were coated with a second reinforcement layer of Ni-P by the following steps.

The starting operation was carried out at ambient temperature for 2-3 minutes at 0.8-0.9 amps. The plate was then placed in the electroless plating solution for 20-30 minutes. The composition of the electroless plating solution is as follows. That is, NiCl ₂ .6H ₂ O 17.4 g / l sodium citrate 30.24 g / l NaH ₂ PO ₂ .H ₂ O 25.2 g / l NH ₄ Cl 21.26 g / l NH ₄ OH pH = 8.8 Add until

The weight gains for Example 10 (Example 17), Example 11 (Example 18), Example 12 (Example 19) and Example 13 (Example 20) were each 0.5.
50 g, 0.578 g, 0.683 g and 0.489 g.

Examples 20-23- Measurement of Hydrogen Potential To measure the hydrogen potential of the plates produced in Examples 17-20,
The plate was connected to a nickel rod and placed in an 11.75 percent caustic bath at 70 ° C. A platinum plate welded to a nickel rod was used as the anode. A current density of 0.46 ASI was applied from the rectifier to the cathode plate and anode. The cathode potential was measured with a LUGGIN probe against a Hg / HgO reference electrode. Example 17 (Example 20), Example 18 (Example 21), Example 1
The hydrogen potential measurements for 9 (Example 22) and Example 20 (Example 23) are -0.956 Volt, -0.960 Volt, -0.949 Volt and -0.956 Volt, respectively.

[Brief description of drawings]

[Figure 1]   FIG. 1 is an enlarged cross-sectional view of catalyst powder particles of the present invention.

[Fig. 2]   FIG. 2 is an enlarged cross-sectional view of a part of the electrode of the present invention.

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Claims (27)

[Claims] 1. A catalyst powder comprising: A plurality of support metal particles comprising a transition metal or an alloy thereof, and Porous coating surrounding the metal particles And a catalyst powder containing the electrocatalyst metal continuous phase, wherein the porous coating further comprises 2. The catalyst powder according to claim 1, wherein the porous coating further contains a particulate material in a mixed state with the electrocatalyst metal continuous phase. 3. The powder according to claim 1, wherein the electrocatalyst metal in the porous coating is ruthenium, iridium, osmium, platinum, palladium, rhodium, rhenium or an alloy thereof. 4. The particulate matter in the porous coating is rhenium oxide, technetium oxide, molybdenum oxide, chromium oxide, niobium oxide, tungsten oxide, tantalum oxide, manganese oxide, lead oxide. Powder. 5. The powder according to claim 1, wherein the support metal particles are nickel, cobalt, iron, steel, stainless steel or copper. 6. A powder according to claim 5, wherein the support metal particles have an average diameter of 0.2 to 20.0 microns. 7. An electrode comprising a first layer comprising a conductive metal substrate and a matrix having a catalyst powder dispersed therein, the matrix comprising a platinum group metal oxide or a platinum group metal oxide. And a valve metal oxide, wherein the catalyst powder comprises support metal particles covered with a porous coating, the porous coating comprising an electrocatalytic metal. 8. The electrode of claim 7, wherein the porous coating further comprises particulate matter in admixture with the electrocatalytic metal. 9. The electrode according to claim 7, wherein the conductive metal substrate is nickel, iron, steel, stainless steel, cobalt, copper or silver. 10. The electrode according to claim 7, wherein the support metal particles in the catalyst powder are nickel, cobalt, iron, steel, stainless steel or copper. 11. The electrode according to claim 7, wherein the electrocatalytic metal in the porous coating film of the first layer is ruthenium, iridium, rhodium, osmium, platinum, palladium, rhenium or a mixture thereof. 12. The particulate matter in the porous coating of the first layer comprises platinum group metal oxide, rhenium oxide, technetium oxide, molybdenum oxide, chromium oxide, niobium oxide, tungsten oxide, tantalum oxide, manganese oxide and oxides. 9. The electrode of claim 8 which is a metal oxide particulate material selected from the group consisting of lead. 13. The platinum group metal oxide in the matrix is ruthenium oxide,
Iridium oxide, osmium oxide, platinum oxide, palladium oxide or a mixture thereof, and the valve metal oxide in the matrix is titanium oxide, zirconium oxide, tantalum oxide, tungsten oxide, niobium oxide, bismuth oxide or a mixture thereof. The electrode according to claim 7, wherein 14. The electrode of claim 7, further comprising a second reinforcing layer consisting essentially of a transition metal or alloy thereof. 15. The electrode according to claim 14, wherein the transition metal or its alloy is nickel, cobalt, copper, or an alloy thereof with phosphorus, boron or sulfur. 16. A method of making an electrode, comprising: Forming a catalyst powder, Mixing the catalyst powder with a dispersion medium to form a mixture, Applying the mixture to a conductive metal substrate to form a coated substrate, and Baking the coated substrate in the presence of oxygen The above method comprising. 17. The method according to claim 16, wherein the catalyst powder is formed by covering a plurality of support metal particles with a porous coating film containing an electrode catalyst metal in a mixed state with a particulate matter. . 18. The method according to claim 17, wherein the porous coating film is formed by a non-electrolytic reduction deposition method, an electrodeposition method or a sintering method. 19. The method of claim 17, wherein the electrocatalytic metal in the porous coating is ruthenium, iridium, rhodium, osmium, platinum, palladium or mixtures thereof. 20. The particulate material in the porous coating is a platinum group metal oxide, rhenium oxide, technetium oxide, molybdenum oxide, chromium oxide, niobium oxide, tungsten oxide, tantalum oxide, manganese oxide, lead oxide and their compounds. 18. The method of claim 17 which is a metal oxide particulate material selected from the group consisting of mixtures. 21. The method of claim 16 wherein the application step is performed using solvent spraying, electrostatic spraying, plasma spraying or melt spraying. 22. The method of claim 16, wherein the dispersion medium comprises a mixture of a platinum group metal oxide precursor and a valve metal oxide precursor. 23. The platinum metal oxide precursor is ruthenium chloride and the valve metal oxide precursor is a titanium alkoxide, tantalum alkoxide, zirconium acetylacetonate or niobium alkoxide. the method of. 24. The dispersion medium further comprises aluminum chloride or zinc chloride.
23. The method of claim 22. 25. The method of claim 24, wherein the dispersion medium further comprises a solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, butanol and mixtures thereof. 26. The method of claim 16 further comprising the step of plating the coated substrate with a transition metal or transition metal alloy to form a reinforcing layer. 27. The method of claim 26, wherein the transition metal is nickel, cobalt, copper, or an alloy thereof with phosphorus, boron or sulfur.