Iridium and / or iridium oxide microsphere-based porous material, preparation method therefor, and uses thereof

Abstract

The invention relates to a porous material in the form of microspheres based on iridium and/or iridium oxide, its preparation process, its use as anodic catalyst in a water electrolyser based on a solid polymer electrolyte, also called PEM water electrolyser (with PEM meaning “Proton Exchange Membrane” or “Polymer Electrolyte Membrane”) or for the manufacture of light-emitting diodes for various electronic devices or for cars, and a PEM water electrolyser comprising such a material as an anode catalyst.

Claims

1. Inorganic material comprising iridium, wherein: said inorganic material comprises at least 90% by weight of iridium, relative to the total weight of said inorganic material, or said inorganic material comprises at least 90% by weight of iridium and a metal M, relative to the total weight of said inorganic material, wherein said inorganic material is macroporous and is in the form of micron or sub-micron spheres having a mean diameter ranging from 100 nm to 40 μm, and wherein said metal M is chosen from ruthenium, osmium, strontium, tin, tantalum, niobium, antimony, nickel, calcium, barium, copper, cobalt, platinum, titanium, indium, molybdenum, tungsten, gold, manganese and chromium, and said metal M represents at most 70% by mole, relative to the total number of moles of iridium and M metal in said inorganic material.

2. The inorganic material according to claim 1, wherein the spheres are individual.

3. The inorganic material according to claim 1, wherein the spheres have an external wall with a thickness varying from 5 nm to 6 μm.

4. The inorganic material according to claim 1, wherein said material has a specific surface, calculated by the B.E.T. method, varying from 20 to 200 m.sup.2/g.

5. The inorganic material according to claim 1, wherein said inorganic material has a macroporous volume ranging from 0.15 to 2 cm.sup.3/g.

6. The inorganic material according to claim 1, wherein the spheres are chosen from macroporous solid spheres with a macroporous outer wall, macroporous hollow spheres with a dense outer wall and macroporous hollow spheres with macroporous inner and outer double walls.

7. Process for the preparation of the inorganic material as defined in claim 1, wherein said process comprises at least the following steps: i) the preparation of an aqueous solution or suspension comprising at least one iridium precursor and at least one pore-forming agent chosen from organic polymers and copolymers and one of their mixtures, ii) atomizing the aqueous solution or suspension obtained in step i) to form solid composite beads comprising iridium and the porogen or pore-forming agent; or said material; or solid composite beads comprising iridium, the pore-forming agent, and said inorganic material, iii) the calcination of the solid composite beads obtained in the preceding step ii) if said solid composite beads exist.

8. Process according to claim 7, wherein in the solution or suspension obtained at the end of step i), the molar ratio number of moles of aqueous solvent/number of moles of iridium precursor is between 20 and 10000.

9. Process according to claim 7, wherein in the solution or suspension obtained at the end of step i), the molar ratio number of moles of monomer units of the porogen or pore-forming agent/number of moles of iridium ranges from 0.0005 to 7.

10. Process according to claim 7, wherein the porogen or pore-forming agent is chosen from homopolymers and copolymers of acrylate, methacrylate, ethylene oxide, methylene oxide, propylene oxide, epichlorohydrin, allyl glycidyl ether, styrene, butadiene and a mixture thereof.

11. Process according to claim 7, wherein the porogen or pore-forming agent is a polymethyl methacrylate, a block copolymer of ethylene oxide and propylene oxide or a mixture thereof.

12. Process according to claim 7, wherein the atomizing step ii) comprises the following substeps: ii-1) spraying the aqueous solution or suspension obtained in step i), to form droplets of said aqueous solution or suspension, ii-2) drying the droplets in the presence of a flow of a hot gas, to form solid composite beads comprising iridium and the porogen or pore-forming agent, and ii-3) collecting solid composite beads and/or said inorganic material.

13. Process according to claim 12, wherein the temperature during the drying of sub step ii-2) varies from 35° C. to 1000° C.

14. Process according to claim 7, wherein the calcination step iii) is carried out at a temperature of at least 300° C. and at most 600° C.

15. An anode catalyst in a water electrolyser based on Proton Exchange Membrane, wherein said anode catalyst comprises the inorganic material as defined in claim 1.

16. Light emitting diodes for electronic devices or for electroluminescent diodes or for cars, wherein said light emitting diode comprises the inorganic material as defined in claim 1.

17. Water electrolyser based on Proton Exchange Membrane comprising, at the anode, the inorganic material as defined in claim 1.

18. The inorganic material according to claim 1, wherein the inorganic material comprising iridium is an inorganic material comprising Iridium Oxide.

19. The inorganic material according to claim 1, wherein the inorganic material comprising iridium is an inorganic material comprising a combination of Iridium and Iridium Oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B show SEM images of the material M.sub.1 obtained in the example at scales 1 μm (FIG. 1a) and 100 nm (FIG. 1b);

(2) FIG. 2 shows an X-ray diffractogram of material M.sub.1 obtained in the example 1.

(3) FIG. 3 shows an SEM image of the M.sub.2 material obtained in Example 2 at the 200 nm scale:

(4) FIGS. 4A and 4B show SEM images of the material M.sub.3 obtained in example 3 at the 2 μm scale (FIG. 4a) and at the 300 nm scale (FIG. 4b);

(5) FIGS. 5A-5C show SEM images of the material M.sub.4 obtained in example 4 at the 2 μm scale (FIG. 5a), at the 1 μm scale (FIG. 5b) and at the 100 nm scale (FIG. 5c);

(6) FIGS. 6A-6F shows SEM images of the M.sub.A metal iridium marketed by Alfa-Aesar at the 1 μm scale (FIG. 6a), at the 200 nm scale (FIG. 6b) and at the 100 nm scale. (FIG. 6c) and an SEM image of the M.sub.B iridium oxide marketed by Alfa-Aesar at the 300 nm scale (FIG. 6d), at the 200 nm scale (FIG. 6e) and at the 250 nm scale (FIG. FIG. 6f);

(7) FIGS. 7A-7B show SEM images of the M.sub.5 material obtained in the example at 2 μm (FIG. 7a) and 250 nm (FIG. 7b);

(8) FIG. 8 shows an X-ray diffractogram of the material M.sub.5 obtained in Example 5.

(9) FIGS. 9a and 9b show the curve of the current density j (in mA.Math.cm 2.Math.mg-1) as a function of the voltage U (in volts V) of the materials according to the invention M.sub.1, M.sub.2, M′.sub.2, M.sub.3, M.sub.4 and M.sub.5, and for comparison commercial materials M.sub.A and M.sub.B not in conformity with the invention;

(10) FIG. 10 shows the curve of the voltage U (in millivolts, mV) as a function of the current I (in ampere per square centimeter, A/cm.sup.2) of the materials in accordance with the invention M.sub.2 (curve with the filled diamonds, load in catalyst of 2 mg/cm.sup.2), M.sub.2 (curve with full triangles, loading of 1.3 mg/cm.sup.2) and M.sub.5 (curve with solid circles, load of 1.8 mg/cm.sup.2);

(11) FIGS. 11A-11B show SEM images of the M.sub.6 material obtained in Example 7 at the 2 μm (FIG. 11a) and 250 nm (FIG. 11b) scales;

(12) FIG. 12 shows an X-ray diffractogram of material M.sub.6 obtained in Example 7;

(13) FIGS. 13A-13B shows SEM images of the M.sub.7 material obtained in Example 8 at the 2 μm (FIG. 13a) and 100 nm (FIG. 13a) scales;

(14) FIG. 14 shows an X-ray diffractogram of material M.sub.7 obtained in Example 8;

(15) FIGS. 15A-15B shows SEM images of the material M.sub.8 obtained in Example 9 at scales 2 μm (FIG. 15a) and 100 nm (FIG. 15b);

(16) FIG. 16 shows an X-ray diffractogram of material M.sub.8 obtained in Example 9;

(17) FIGS. 17A-17B shows SEM images of material M.sub.9 obtained in example 10 at the 2 μm (FIG. 17a) and 100 nm (FIG. 17b) scales; and

(18) FIG. 18 shows an X-ray diffractogram of material M.sub.9 obtained in Example 10.

(19) FIG. 19 shows the curve of the current density J (in mA.Math.cm.sup.2.Math.mg.sup.−1) as a function of the voltage U (in volts V) of the materials according to the invention M.sub.6, M.sub.7, M.sub.8, and M.sub.9, and for comparison of commercial material M.sub.B not in accordance with the invention

DETAILED DESCRIPTION

Examples

(20) Materials's characterization:

(21) The specific surface of the materials was measured by adsorption-desorption of nitrogen and the B.E.T method, using an apparatus sold under the trade name Belsorp-max by MicrotracBEL.

(22) The materials were analyzed by scanning electron microscopy (SEM) using an apparatus sold under the trade name ZEISS supra 40 by ZEISS using a field effect gun.

(23) The materials were also analyzed by X-ray diffraction using a diffractometer sold under the trade name Panalytical X'pert pro by Panalytical and equipped with a cobalt anode and X'celerator detector.

(24) The materials were tested by cyclic voltammetry using a potentiostat sold under the trade name Autolab PGSTAT 12 by the company Metrohm (ex-situ tests). The working electrode was a 5 mm diameter rotating disk glassy carbon electrode (Pine Instrument), gently polished and rinsed in ethanol in the presence of ultrasound before use. The counter-electrode was a platinum wire and the reference electrode an aqueous calomel electrode. All the experiments were carried out under argon at 20° C. at a rotation speed of 1600 rpm. A solution of sulfuric acid at 0.05 mol/l was prepared and used as electrolyte. To manufacture the electrode, an electrode ink comprising 1 mg of material based on iridium and/or iridium oxide, 2 mg of carbon black marketed under the reference Vulcan XC72R by Cabot, 250 μL of a solution of Nafion® 5% by mass marketed by Alfa Aesar and 250 μL of deionized water (conductivity of 0.059 μS.Math.cm.sup.−2) was prepared. 8.8 μL of this ink of electrode were deposited on the surface of the working electrode to form a catalytic layer, then the whole was dried in air and left for 30 min at 100° C. in a furnace.

(25) The materials were also characterized using an electrolytic test bench. The catalytic layers were prepared by the offset-transfer technique. The material according to the invention and a solution of perfluorosulfonated ionomer (sold under the reference Nafion®) in the form of a dispersion at 5% by weight, were mixed in a water/isopropanol solution (⅓ volume ratio) to obtain a final mass ratio: mass material according to the invention/mass (material according to the invention+ionomer) of between 10 and 50%, and preferably between 20 and 30%. The resulting solution was then deposited on a Teflon® sheet by spray. After preparation of the catalytic layers, a hot pressing step was carried out at 135° C., at a pressure of 160 kg/cm.sup.2 for 90 seconds, to transfer the catalytic layers to a perfluorosulfonated membrane (sold under the reference Nafion® 115). The membrane and the anode were then again pressed at 135° C., at a pressure of 160 kg/cm.sup.2 for 5 minutes with a diffusion-layer electrode constituting the cathodic catalytic layer, comprising a carbon paper on which 0.5 m/cm.sup.2 of platinum is deposited. The prepared membrane-electrode assemblies were inserted into a 6.25 cm.sup.2 monolayer having titanium monopolar plates coated with gold at the anode.

Example 1

Process for the Preparation of Materials According to the Invention M.SUB.1 .and M′.SUB.1

(26) An aqueous solution A comprising 1 g of IrCl.sub.3.xH.sub.2O in 27 ml of water was prepared.

(27) An aqueous suspension B comprising 0.33 g of polymethyl methacrylate in the form of beads 300 nm in diameter in 3 ml of water was prepared.

(28) The polymethyl methacrylate beads were prepared beforehand by radical polymerization in emulsion of methyl methacrylate according to the method described in Hatton et al., PNAS, 2010, 107, 23, 10354.

(29) 28 g of solution A were mixed with 3.33 g of suspension B to form an aqueous suspension comprising 3.2% by weight of IrCl.sub.3.xH.sub.2O and 1% by weight of polymethyl methacrylate, relative to the total mass of the aqueous suspension.

(30) This aqueous suspension was sprayed using an atomizer sold under the trade name B290 by the company Buchi.

(31) The droplets formed were dried under a stream of hot air. The inlet temperature of the atomizer was about 220° C. and its outlet temperature was about 145° C.

(32) The composite beads obtained were then calcined according to the following substeps:

(33) heating the composite beads in air using a heating ramp ranging from 20° C. to 450° C. for 10 minutes, and then

(34) their heating in air at 450° C. for 15 minutes.

(35) FIG. 1 shows SEM images of the material M.sub.1 obtained in the example at scales 1 μm (FIG. 1a) and 100 nm (FIG. 1b).

(36) FIG. 2 shows an X-ray diffractogram of material M.sub.1 obtained in the example 1.

(37) In this example, the material M.sub.1 consisted essentially of metallic iridium, it was in the form of macroporous and mesoporous microporous and mesoporous sub-micron solid spheres with a macroporous and mesoporous outer wall, mixed with macroporous hollow and mesoporous hollow spheres. outer macroporous and mesoporous. The M.sub.1 material had a specific surface area of 37 m.sup.2/g. The spheres had an average diameter of 1.164 μm. The macropores had an average size of about 260 nm. The material M.sub.1 comprised a mixture of amorphous and crystalline phases.

(38) When the calcination as described above was carried out at 550° C. instead of 450° C., under the same conditions as above (ramp from 20 to 550° C. in 10 minutes in the air, then 550° C. for 15 minutes in air), the material obtained M′.sub.1 consisted essentially of metallic iridium and iridium oxide with a metal iridium/iridium oxide molar ratio of approximately 80/20. The material M′.sub.1 comprised a mixture of amorphous and crystalline phases. It was in the form of macroporous and mesoporous microporous and mesoporous submicron solid spheres with macroporous and mesoporous outer walls, mixed with macroporous and mesoporous hollow spheres with macroporous and mesoporous outer walls. The spheres had an average diameter of 1.164 μm. The macropores had an average size of about 260 nm.

Example 2

Process for the Preparation of Materials According to the Invention M.SUB.2 .and M′.SUB.2

(39) An aqueous solution A comprising 1 g of IrCl.sub.3.xH.sub.2O in 27 ml of water was prepared.

(40) An aqueous solution B comprising 0.33 g of polymethyl methacrylate in the form of beads 300 nm in diameter as prepared according to the process described in Example 1, in 3 ml of water was prepared.

(41) 28 g of solution A were mixed with 3.33 g of suspension B to form an aqueous suspension comprising 3.2% by weight of IrCl.sub.3.xH.sub.2O and 1% by weight of polymethyl methacrylate, relative to the total mass of the aqueous suspension.

(42) This aqueous suspension was sprayed with an atomizer as described in Example 1 and using the same sputtering and atomizing parameters.

(43) The droplets formed were dried under a stream of hot air.

(44) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30, and then

(45) Their heating in air at 450° C. for 10 minutes.

(46) FIG. 3 shows an SEM image of the M.sub.2 material obtained in Example 2 at the 200 nm scale.

(47) The material M.sub.2 obtained in Example 2 comprised 20 mol % of metal iridium and 80 mol % of iridium oxide. The M.sub.2 material comprised a mixture of amorphous and crystalline phases.

(48) In this example, the material M.sub.2 was in the form of macroporous and mesoporous microporous and mesoporous submicron solid spheres with a macroporous and mesoporous outer wall, mixed with macroporous and mesoporous hollow spheres with a macroporous and mesoporous outer wall. Small crystallites were present on the surface of the solid spheres and in particular of the outer wall. The macropores had a mean size (in number) of about 250 nm. M.sub.2 material had a surface area of about 68 m.sup.2/g. The spheres had a mean diameter (in number) of about 1.029 μm.

(49) When the calcination as described above was carried out according to the following substeps:

(50) heating the composite beads in air using a heating ramp ranging from 20° C. to 450° C. for 10 minutes, and then their heating in air at 450° C. for 3 hours 35 minutes,

(51) The material obtained M′.sub.2 consisted essentially of metal iridium and iridium oxide with a metal iridium/iridium oxide molar ratio of about 60/40. The material M′.sub.2 comprised a mixture of amorphous and crystalline phases. It was in the form of macroporous and mesoporous microporous and mesoporous submicron solid spheres with macroporous and mesoporous outer walls, mixed with macroporous and mesoporous hollow spheres with macroporous and mesoporous outer walls. The spheres had an average diameter of 1.029 μm. The macropores had an average size of about 250 nm.

Example 3

Process for the Preparation of a Material According to the M.SUB.3 .Invention

(52) An aqueous solution A comprising 1 g of IrCl.sub.3.xH.sub.2O in 27 ml of water was prepared.

(53) An aqueous solution B comprising 0.33 g of a block copolymer of ethylene oxide and propylene oxide sold under the reference Pluronic® F-127 in 3 ml of water was prepared.

(54) 28 g of solution A were mixed with 3 ml of solution B to form an aqueous solution comprising 3.2% by weight of IrCl.sub.3.xH.sub.2O and 1% by weight of block copolymer of ethylene oxide and propylene oxide, relative to the total mass of the aqueous solution.

(55) This aqueous solution was sprayed with an atomizer as described in Example 1 and using the same sputtering and atomizing parameters.

(56) The droplets formed were dried under a stream of hot air.

(57) The composite beads obtained were then calcined according to the following substeps:

(58) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30, and then

(59) Their heating in air at 450° C. for 10 minutes.

(60) FIG. 4 shows a SEM image of the material M.sub.3 obtained in example 3 at the 2 μm scale (FIG. 4a) and at the 300 nm scale (FIG. 4b).

(61) In this example, the material M.sub.3 was in the form of macroporous micron and sub-micron hollow spheres with a dense outer wall. The spheres had an average diameter of 1.780 μm. The central macropores had an average size of approximately 1.480 μm. The material M.sub.3 very largely consisted of an amorphous phase.

Example 4

Process for the Preparation of a Material According to the M.SUB.4 .Invention

(62) An aqueous solution A comprising 1 g of IrCl.sub.3.xH.sub.2O in 27 ml of water was prepared.

(63) An aqueous suspension B comprising 0.17 g of a block copolymer of ethylene oxide and propylene oxide sold under the reference Pluronic® F-127 and 0.17 g of polymethyl methacrylate in the form of 300 nm in diameter as prepared according to the method described in Example 1, in 3 ml of water was prepared.

(64) 28 g of solution A were mixed with 3.33 g of suspension B to form an aqueous suspension comprising 3.2% by weight of IrCl.sub.3.xH.sub.2O, 0.5% by weight of polymethyl methacrylate and 0.5% by weight of mass of block copolymer of ethylene oxide and propylene oxide, based on the total mass of the aqueous suspension.

(65) This aqueous suspension was sprayed with an atomizer as described in Example 1 and using the same sputtering and atomizing parameters.

(66) The droplets formed were dried under a stream of hot air.

(67) The composite beads obtained were then calcined according to the following substeps:

(68) heating the composite beads in air using a heating ramp ranging from 20° C. to 450° C. for 10 minutes, and then

(69) their heating in air at 450° C. for 15 minutes.

(70) FIG. 5 shows an SEM image of the material M.sub.4 obtained in example 4 at the 2 μm scale (FIG. 5a), at the 1 μm scale (FIG. 5b) and at the 100 nm scale (FIG. 5c).

(71) In this example, the M.sub.4 material was in the form of macroporous and mesoporous micron and sub-micron hollow spheres with macroporous and mesoporous inner and outer double walls. The macropores of the inner and outer walls had an average size of about 175 nm. The central macropores had an average size of about 500 nm. The spheres had an average diameter of 1.280 μm.

(72) For comparison purposes, FIG. 6 shows a SEM image of the M.sub.A metal iridium marketed by Alfa-Aesar at the 1 μm scale (FIG. 6a), at the 200 nm scale (FIG. 6b) and at the 100 nm scale. (FIG. 6c) and an SEM image of the M.sub.B iridium oxide marketed by Alfa-Aesar at the 300 nm scale (FIG. 6d), at the 200 nm scale (FIG. 6e) and at the 250 nm scale (FIG. FIG. 6f).

(73) These materials M.sub.A and M.sub.B are mainly in the form of crystallites. In particular, they are not macroporous and are not in the form of micron or sub-micron spheres. M.sub.A and M.sub.B materials are materials in the form of nanoparticles.

Example 5

Process for the Preparation of a Material According to the M.SUB.5 .Invention

(74) An aqueous solution A comprising 0.2 g of IrCl.sub.3.xH.sub.2O and 0.075 g of RuCl.sub.3.xH.sub.2O in 8.4 ml of water was prepared.

(75) An aqueous suspension B comprising 0.11 g of polymethyl methacrylate in the form of beads 300 nm in diameter as prepared according to the method described in Example 1, in 0.89 ml of water was prepared.

(76) 8.675 g ml of solution A were mixed with 1 g of suspension B to form an aqueous suspension comprising 2.07% by weight of IrCl.sub.3.xH.sub.2O, 0.78% by weight RuCl.sub.3.xH.sub.2O and 1.14% by weight of polymethyl methacrylate, based on the total mass of the aqueous suspension.

(77) This aqueous suspension was sprayed using an atomizer sold under the trade name B290 by the company Buchi.

(78) The droplets formed were dried under a stream of hot air. The inlet temperature of the atomizer was about 220° C. and its outlet temperature was about 145° C.

(79) The composite beads obtained were then calcined according to the following substeps:

(80) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30 min, then

(81) their heating in air at 450° C. for 15 minutes.

(82) FIG. 7 shows SEM images of the M.sub.5 material obtained in the example at 2 μm (FIGS. 7a) and 250 nm (FIG. 7b).

(83) FIG. 8 shows an X-ray diffractogram of the material M.sub.5 obtained in Example 5.

(84) In this example, the material M.sub.5 consisted essentially of a metal part and an oxide part. It was in the form of macroporous and mesoporous microporous and mesoporous submicron solid spheres with macroporous and mesoporous outer walls, mixed with macroporous and mesoporous hollow spheres with macroporous and mesoporous outer walls. The spheres had an average diameter of about 1.190 μm. The macropores had an average size of about 250 nm.

Example 6

Electrochemical Characterizations of the Materials in Accordance with the Invention

(85) FIGS. 9a and 9b show the curve of the current density j (in mA.Math.cm 2.Math.mg−1) as a function of the voltage U (in volts V) of the materials according to the invention M.sub.1, M.sub.2, M′.sub.2, M.sub.3, M.sub.4 and M.sub.5, and for comparison commercial materials M.sub.A and M.sub.B not in conformity with the invention.

(86) In FIG. 9a, materials M.sub.1 and M.sub.2 have cyclic voltammetry properties comparable to those of commercial materials. Moreover, these materials have the additional advantages of being more economical, less toxic and easier to handle because they are not in nanometric form as commercial materials M.sub.A and M.sub.B. In addition, they are obtained from a simple process, not requiring complex and expensive equipment.

(87) FIG. 10 shows the curve of the voltage U (in millivolts, mV) as a function of the current I (in ampere per square centimeter, A/cm.sup.2) of the materials in accordance with the invention M.sub.2 (curve with the filled diamonds, load in catalyst of 2 mg/cm.sup.2), M.sub.2 (curve with full triangles, loading of 1.3 mg/cm.sup.2) and M.sub.5 (curve with solid circles, load of 1.8 mg/cm.sup.2).

Example 7

Process for the Preparation of a Material in Accordance with the Invention M.SUB.6

(88) Aqueous solution A comprising 1.0 g of IrCl.sub.3.xH.sub.2O and 0.102 g of CoCl.sub.2.6H.sub.2O in 29.04 ml of water was prepared.

(89) An aqueous suspension B comprising polymethyl methacrylate in the form of beads 300 nm in diameter as prepared according to the method described in Example 1, 11% by weight was prepared.

(90) 30142 g of solution A were mixed with 3.267 g of suspension B to form an aqueous suspension comprising 3% by weight of IrCl.sub.3.xH.sub.2O, 0.3% by weight CoCl.sub.2.6H.sub.2O and 11% by weight of polymethyl methacrylate, relative to to the total mass of the aqueous suspension.

(91) This aqueous suspension was sprayed with an atomizer as described in Example 1.

(92) The droplets formed were dried under a stream of hot air. The inlet temperature of the atomizer was about 220° C. and its outlet temperature was about 110° C. The composite beads obtained were then calcined according to the following substeps:

(93) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30, and then

(94) their heating in air at 450° C. for 15 minutes.

(95) FIG. 11 shows SEM images of the M.sub.6 material obtained in Example 7 at the 2 μm (FIGS. 11a) and 250 nm (FIG. 11b) scales.

(96) FIG. 12 shows an X-ray diffractogram of material M.sub.6 obtained in Example 7.

(97) In this example, the material M.sub.6 consisted essentially of an oxide part. It comprised 13.7 mol % of cobalt and 86.3 mol % of iridium, based on the total number of moles of metal.

(98) The main peaks are characteristic of iridium oxide, they are shifted to large angles, which means that there is incorporation of cobalt within the structure of iridium oxide. It was in the form of macroporous and mesoporous microporous and mesoporous submicron solid spheres with macroporous and mesoporous outer walls, mixed with macroporous and mesoporous hollow spheres with macroporous and mesoporous outer walls. The spheres had a mean diameter of about 2.2 μm. The macropores had an average size of about 250 nm.

Example 8

Process for the Preparation of a Material According to the M.SUB.7 .Invention

(99) Aqueous solution A comprising 1.0 g of IrCl.sub.3.xH.sub.2O and 0.289 g of CoCl.sub.2.6H.sub.2O in 34.85 ml of water was prepared.

(100) An aqueous suspension B comprising polymethyl methacrylate in the form of beads 300 nm in diameter as prepared according to the method described in Example 1, at 11% by weight was prepared.

(101) 34.85 ml of solution A were mixed with 3.935 g of suspension B to form an aqueous suspension comprising 2.50% by weight of IrCl.sub.3.xH.sub.2O, 0.72% by mass CoCl.sub.2.6H.sub.2O and 1.1% by weight of polymethyl methacrylate, based on the total mass of the aqueous suspension.

(102) This aqueous suspension was sprayed with an atomizer as described in Example 1.

(103) The droplets formed were dried under a stream of hot air. The inlet temperature of the atomizer was about 220° C. and its outlet temperature was about 110° C. The composite beads obtained were then calcined according to the following substeps:

(104) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30, and then

(105) their heating in air at 450° C. for 15 minutes.

(106) FIG. 13 shows SEM images of the M.sub.7 material obtained in Example 8 at the 2 μm (FIGS. 13a) and 100 nm (FIG. 13a) scales.

(107) FIG. 14 shows an X-ray diffractogram of material M.sub.7 obtained in Example 8.

(108) In this example, the material M.sub.7 consisted essentially of an oxide part. It comprised 31 mol % of cobalt and 69 mol % of iridium, based on the total number of moles of metal.

(109) The main peaks are characteristic of iridium oxide, they are shifted towards the large angles, which means that there is incorporation of cobalt. It was in the form of macroporous and mesoporous microporous and mesoporous submicron solid spheres with macroporous and mesoporous outer walls, mixed with macroporous and mesoporous hollow spheres with macroporous and mesoporous outer walls. The spheres had a diameter of between about 200 nm and about 10 μm. The macropores had an average size of about 250 nm.

Example 9

Process for the Preparation of a Material According to the Invention M.SUB.8

(110) Aqueous solution A comprising 1.0 g of IrCl.sub.3.xH.sub.2O and 0.086 g of MoCl.sub.5 in 29.335 ml of water was prepared.

(111) An aqueous suspension B comprising polymethyl methacrylate in the form of beads 300 nm in diameter as prepared according to the method described in Example 1, 11% by weight was prepared.

(112) 29.335 ml of solution A were mixed with 3.265 g of suspension B to form an aqueous suspension comprising 2.97% by weight of IrCl.sub.3.xH.sub.2O, 0.26% by mass MoCl.sub.5 and 1.1% by weight of polymethyl methacrylate, relative to the total mass of the aqueous suspension.

(113) This aqueous suspension was sprayed with an atomizer as described in Example 1.

(114) The droplets formed were dried under a stream of hot air. The inlet temperature of the atomizer was about 220° C. and its outlet temperature was about 110° C. The composite beads obtained were then calcined according to the following substeps:

(115) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30, and then

(116) their heating in air at 450° C. for 15 minutes.

(117) FIG. 15 shows SEM images of the material Mg obtained in Example 9 at scales 2 μm (FIGS. 15a) and 100 nm (FIG. 15b).

(118) FIG. 16 shows an X-ray diffractogram of material M.sub.8 obtained in Example 9.

(119) In this example, the material M.sub.8 consisted essentially of an oxide part. It comprised 10 mol % of molybdenum and 90 mol % of iridium, based on the total number of moles of metal.

(120) The main peaks are characteristic of iridium oxide, they are shifted to large angles, which means that molybdenum is incorporated into the iridium oxide structure. It was in the form of solid macroporous and mesoporous micronic and sub-micronic spheres with macroporous and mesoporous outer walls, mixed with macroporous and mesoporous hollow spheres with macroporous and mesoporous outer walls. The spheres had an average diameter of about 1.0 μm The macropores had an average size of about 250 nm.

Example 10

Process for the Preparation of a Material According the M.SUB.9 .Invention

(121) Aqueous solution A comprising 1.0 g of IrCl.sub.3.xH.sub.2O and 0.331 g of MoCl.sub.5 in 35.967 ml of water was prepared.

(122) An aqueous suspension B comprising polymethyl methacrylate in the form of beads 300 nm in diameter as prepared according to the method described in Example 1, 11% by weight was prepared.

(123) 35.967 ml of solution A were mixed with 4.001 g of suspension B to form an aqueous suspension comprising 2.42% by weight of IrCl.sub.3.xH.sub.2O, 0.80% by mass MoCl.sub.5 and 1.4% by weight of polymethyl methacrylate, relative to the total mass of the aqueous suspension.

(124) This aqueous suspension was sprayed with an atomizer as described in Example 1.

(125) The droplets formed were dried under a stream of hot air. The inlet temperature of the atomizer was about 220° C. and its outlet temperature was about 110° C. The composite beads obtained were then calcined according to the following substeps:

(126) heating the composite balls in air using a heating ramp ranging from 20° C. to 450° C. for 3 h 30, and then

(127) their heating in air at 450° C. for 15 minutes.

(128) FIG. 17 shows SEM images of material Mg obtained in example 10 at the 2 μm (FIGS. 17a) and 100 nm (FIG. 17b) scales.

(129) FIG. 18 shows an X-ray diffractogram of material M.sub.9 obtained in Example 10.

(130) In this example, the material M.sub.9 consisted essentially of a portion of amorphous iridium oxide. It comprised 30 mol % molybdenum and 70 mol % iridium, based on the total number of moles of metal.

(131) It was in the form of microporous macroporous sub-micron solid spheres with a macroporous outer wall mixed with macroporous hollow spheres with a macroporous outer wall. The spheres had a mean diameter of about 1.0 μm. The macropores had an average size of about 260 nm.

(132) FIG. 19 shows the curve of the current density J (in mA.Math.cm.sup.2.Math.mg.sup.−1) as a function of the voltage U (in volts V) of the materials according to the invention M.sub.6, M.sub.7, M.sub.8, and M.sub.9, and for comparison of commercial material M.sub.B not in accordance with the invention.