Iridium-based alloy catalysts, methods of synthesis and use thereof

Abstract

The application discloses an iridium-based alloy catalyst and a synthesis method and application thereof. The iridium-based alloy catalyst comprises an iridium-based alloy active component and a carrier; the iridium-based alloy active component comprises iridium and at least one transition metal selected from iron, cobalt and nickel; and the carrier is a conductive oxide carrier; wherein the iridium-based alloy active component is a polyhedral nanocrystal with (111) crystal face exposure. The catalyst provided by the application has high activity and stability in water electrolysis and anode oxygen evolution reaction in carbon dioxide electro-reduction under alkaline conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrocatalysis, and particularly relates to an iridium-based alloy catalyst, a synthesis method thereof, and an application thereof in oxygen evolution reaction. BACKGROUND

[0002] Electrolysis of water to produce hydrogen is a common renewable energy storage and utilization technology, and the anode catalyst plays a key role in its efficiency and stability. Among them, iridium catalysts have attracted much attention due to their high activity and good corrosion resistance. Iridium catalysts have many advantages in oxygen evolution reaction, showing excellent electrocatalytic activity, excellent corrosion resistance and stability. However, iridium catalysts also have some problems. As a rare and expensive metal, the cost of iridium limits its popularity in large-scale applications.

[0003] Currently, there are many synthesis methods for iridium-based alloy catalysts. For example, CN110453256B discloses a method for preparing polyhedral cobalt-iridium nanoparticle catalyst by electrochemical deposition, but this method has high cost and the obtained catalyst particle size is large, which is not conducive to providing electrochemical active sites; CN113215616B uses freeze-drying to prepare IrCoFe@MXene nanofiber catalyst, which has the problem of being limited by equipment and is not suitable for large-scale production; CN115058729A discloses an iridium-based high-entropy alloy nanocatalyst, which uses an oil phase synthesis method, but the uniformity of the nanoparticle size cannot be guaranteed, which affects the stability of different batches of catalyst production.

[0004] There is a need in the art to provide an iridium-based alloy catalyst with high catalytic activity and outstanding stability, as well as a new preparation method. SUMMARY

[0005] To solve the problems existing in the prior art, the present application provides an iridium-based alloy catalyst, a synthesis method thereof and an application thereof. The catalyst has outstanding electrocatalytic activity and stability for oxygen evolution reaction under alkaline conditions.

[0006] The first aspect of the present application provides an iridium-based alloy catalyst, which comprises an iridium-based alloy active component and a carrier; the iridium-based alloy active component comprises iridium and at least one transition metal selected from iron, cobalt and nickel; and the carrier is a conductive oxide carrier.

[0007] Further, the iridium-based alloy active component is a polyhedral nanocrystal with (111) crystal plane exposure.

[0008] Further, the proportion of the (111) crystal plane exposed by the polyhedral nanocrystal is greater than 80%, preferably greater than 85%.

[0009] Further, the proportion of tetrahedrons in the polyhedral nanocrystal is greater than 60%, preferably greater than 72%.

[0010] Further, the polyhedral nanocrystal has a grain size of 2-15 nm, preferably 3.8-12.0 nm.

[0011] Further, the atomic ratio of iridium to transition metal is 1:(0.1-5), preferably 1:(0.1-3), more preferably 1:(0.2-3).

[0012] Further, the conductive oxide carrier is selected from at least one of indium tin oxide and antimony tin oxide.

[0013] Further, the catalyst comprises 10-95 parts by weight of the iridium-based alloy active component and 5-90 parts of the conductive oxide carrier, preferably 20-90 parts of the iridium-based alloy active component and 10-80 parts of the conductive oxide carrier.

[0014] The second aspect of the present application provides a synthesis method of the above-mentioned iridium-based alloy catalyst, comprising the following steps:

[0015] (1) mixing an iridium source and a transition metal source, a surfactant, a crystal face coordination reagent, a reducing agent and an organic alcohol, adjusting the pH to be acidic, and performing a heating reaction to obtain an iridium-based polyhedral nanocrystal;

[0016] (2) mixing the iridium-based polyhedral nanocrystal with a conductive oxide carrier and performing a thermal treatment in an oxidizing atmosphere to obtain the catalyst.

[0017] Further, the iridium source in step (1) is selected from at least one of iridium chloride, iridium acetylacetonate, iridium carbonyl, hexachloroiridic acid, sodium hexachloroiridate, and ammonium hexachloroiridate.

[0018] Further, the transition metal source in step (1) is selected from at least one of soluble chlorides, bromides, nitrates, sulfates, carbonates, acetates, and acetylacetonates of transition metals iron, cobalt, and nickel.

[0019] Further, the surfactant in step (1) is polyvinylpyrrolidone.

[0020] Further, the crystal face coordination reagent in step (1) is an oxalate salt; preferably, at least one of sodium oxalate, potassium oxalate, and ammonium oxalate.

[0021] Further, the reducing agent in step (1) is at least one of methanol, formaldehyde, ascorbic acid, citric acid, hydrazine hydrate, and sodium borohydride.

[0022] Further, the organic alcohol in step (1) is preferably a polyhydric alcohol, more preferably dihydric and / or trihydric alcohol; preferably, the polyhydric alcohol is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, diethylene glycol, triethylene glycol.

[0023] Further, the pH value in step (1) is 3-5, and an acid regulator such as but not limited to hydrochloric acid, nitric acid, etc. is usually used.

[0024] Further, the molar ratio of the iridium source, transition metal source, crystal face coordination reagent, and reducing agent in step (1) is 1:(0.1-5):(10-30):(10-50).

[0025] Further, the mass ratio of the iridium source (calculated on the basis of iridium chloride hydrate), surfactant, and polyhydric alcohol solvent in step (1) is 1:(8-12):(1500-1800).

[0026] Further, the heating reaction in step (1) is preferably carried out in a sealed state; optionally, the organic alcohol solvent is subjected to a hydrothermal reaction under heating conditions; optionally, the heating temperature is 130-230°C, preferably 160-200°C; the time is 1-12 h, preferably 2-8 h; and the pressure is 0.8-1.5 bar, preferably 0.8-1.2 bar.

[0027] Further, after the heating reaction in step (1), a conventional post-treatment step (such as centrifugation, washing, and drying) can be used to obtain the purified iridium-based polyhedral nanocrystals. The centrifugation operation step is, for example but not only, that the obtained product after the heating reaction is added with acetone and centrifuged; the washing and drying operation step is, for example but not only, that the black precipitate after centrifugation is ultrasonically dispersed with ethanol, added with acetone and centrifugally washed, and the above steps are repeated for several times, and the purified iridium-based polyhedral nanocrystals are obtained by drying.

[0028] Further, in step (2), the iridium-based polyhedral nanocrystals in step (1) are first prepared into a dispersion liquid and then mixed with a conductive oxide carrier. Optionally, after mixing, a conventional treatment means can be used for washing and drying. For example but not limited to, a solid powder is obtained by ultrasonic dispersion, centrifugation, and drying. The ultrasonic time is 8-24 h; and the drying temperature is 60-120°C, and the time is 4-12 h.

[0029] Further, the dispersion liquid is an ethanol solution containing iridium-based polyhedral nanocrystals, and the mass fraction of the iridium-based polyhedral nanocrystals in the dispersion liquid is 0.2%-2%.

[0030] Further, the conductive oxide carrier in step (2) is selected from at least one of indium tin oxide and antimony tin oxide.

[0031] Further, the indium tin oxide and / or antimony tin oxide in step (2) is preferably in a nano-powder state.

[0032] Further, the mass ratio of the iridium-based polyhedral nanocrystal to the conductive oxide carrier in step (2) is 10-95:5-90.

[0033] Further, the atmosphere heat treatment in step (2) is a treatment in an oxidation atmosphere at 200-350℃ for 0.5-4h.

[0034] Further, the oxygen content in the oxidation atmosphere in step (2) is 5vol%-20vol%.

[0035] Further, in the oxidation atmosphere in step (2), in addition to oxygen, the remaining is at least one of nitrogen or / and an inert gas, wherein the inert gas is selected from at least one of argon and helium.

[0036] The third aspect of the present application provides an application of the above-mentioned iridium-based alloy catalyst in an oxygen evolution reaction under alkaline conditions.

[0037] Further, the oxygen evolution reaction under alkaline conditions can be an anode oxygen evolution reaction in the electrolysis of water or the electro-reduction of carbon dioxide under alkaline conditions. Further, the alkaline oxygen evolution reaction includes an oxygen evolution reaction occurring on the surface of a polymer electrolyte membrane and in an alkaline solution.

[0038] Further, the polymer electrolyte membrane includes one of a polyether and a derivative thereof, a polyaromatic hydrocarbon and a derivative thereof, a polyethylene and a derivative thereof, or a composite membrane; and the alkaline solution is at least one of a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution, and a potassium carbonate solution.

[0039] Further, the concentration of the alkaline solution is 0.01-15mol·L -1 .

[0040] Further, the alkaline solution is an alkaline solution saturated with oxygen at 20-80℃.

[0041] The present application includes the following beneficial effects:

[0042] In the iridium-based alloy catalyst of the present application, the active component is a polyhedral nanocrystal with (111) crystal plane exposure, which can significantly improve the oxidation dissolution resistance of the iridium-based alloy catalyst in an alkaline solution, improve the stability of the catalyst, and reduce the amount of noble metal iridium, and the catalyst has excellent oxygen evolution reaction catalytic activity. At the same time, the preparation method provided by the present application is simple, has little impact on the environment, the prepared iridium-based catalyst has uniform size, and is suitable for large-scale production. DETAILED DESCRIPTION

[0043] The application will be further described in connection with specific examples, but does not constitute any limitation to the application.

[0044] In the following examples, the oxygen saturation is 1.0 mol·L-1 at 25℃. -1 The test is carried out in a three-electrode system using Ag / AgCl electrode as reference electrode, platinum sheet electrode as counter electrode and rotating disc electrode with a rotation speed of 1600 rpm as working electrode. The catalyst and Nafion solution are dispersed into water / ethanol / isopropanol to obtain catalyst slurry by ultrasonic dispersion. The catalyst slurry is dropped on the surface of the rotating disc electrode and dried to obtain thin film electrode. The oxygen evolution reaction current at 0.25 V overpotential is used as reference to compare the oxygen evolution reaction activity of the catalyst. The time for the catalyst to stably operate at a current density of 10 mA·cm-2 is used as the evaluation standard of the stability of the catalyst. -2 The test is carried out in a three-electrode system using Ag / AgCl electrode as reference electrode, platinum sheet electrode as counter electrode and rotating disc electrode with a rotation speed of 1600 rpm as working electrode. The catalyst and Nafion solution are dispersed into water / ethanol / isopropanol to obtain catalyst slurry by ultrasonic dispersion. The catalyst slurry is dropped on the surface of the rotating disc electrode and dried to obtain thin film electrode. The oxygen evolution reaction current at 0.25 V overpotential is used as reference to compare the oxygen evolution reaction activity of the catalyst. The time for the catalyst to stably operate at a current density of 10 mA·cm-2 is used as the evaluation standard of the stability of the catalyst.

[0045] In the application, the particle size of the iridium-based alloy nanocrystal is measured by transmission electron microscopy (TEM) photograph, TEM acceleration voltage is 200-300 kV, magnification is 200-1500 kx. The diameter of the nanocrystal in the TEM photograph is measured by using Nano Measurer software, 200 measurement results at different positions are counted, and the average value and standard deviation are calculated, so as to obtain the particle size of the alloy nanocrystal. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 TEM image of the active component iridium-based nanocrystal in Example 1;

[0047] Figure 2 TEM image of the active component iridium-based nanocrystal in Comparative Example 3.

[0048] Example 1

[0049] 2.5 g of PVP, 1 mmol of hydrated iridium chloride and 0.5 mmol of nickel chloride hexahydrate are added into 475 g of ethylene glycol, stirred until completely dissolved, then 15 mmol of sodium oxalate and 15 mmol of formaldehyde aqueous solution are added, stirred for 0.5 h, then concentrated hydrochloric acid (concentration is 37%) and water with a volume ratio of 1:1 are added, the pH is adjusted to 3.5 to obtain a clear solution. It is added into a 800 mL autoclave, reacted at 200℃ and 1 bar for 8 h, the obtained product is added into acetone and centrifuged to obtain black precipitate, which is ultrasonically dispersed with ethanol, added into acetone and centrifuged, the above steps are repeated for several times, and dried to obtain the purified iridium-nickel alloy polyhedral nanocrystal, the diameter is 5.1±0.3 nm. The ratio of iridium atom to nickel atom is 1:0.5. The TEM image of the iridium-nickel alloy polyhedral nanocrystal is shown in Figure 1 Figure 1 ​It can be seen that the proportion of exposed (111) crystal planes in polyhedral nanocrystals is about 94%, of which the proportion of tetrahedral nanocrystals is about 80%.

[0050] 52 mg of iridium-nickel alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, and 97 mg of indium tin oxide nanoparticles were added. The mixture was ultrasonically treated for 12 h, centrifuged to obtain a black precipitate, and dried in an oven at 80 °C for 8 h to obtain a black solid powder. The solid powder was then treated at 250 °C in an oxidizing atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium-nickel alloy catalyst.

[0051] At 25℃, oxygen saturation is 1.0 mol·L⁻¹ -1 In a sodium hydroxide solution, using an Ag / AgCl electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a rotating disk electrode at 1600 rpm as the working electrode, a three-electrode system exhibits a specific catalyst activity of 57.5 μA / cm² at a reaction overpotential of 0.25 V. 2 At 10mA·cm -2 It operated stably for 29 hours at the specified current density.

[0052] Example 2

[0053] 3.5 g PVP, 1 mmol iridium acetylacetone, and 2 mmol cobalt sulfate heptahydrate were added to 500 g ethylene glycol and stirred until completely dissolved. Then, 10 mmol potassium oxalate and 30 mmol ascorbic acid were added, and the mixture was stirred for 0.5 h. Concentrated hydrochloric acid (37% concentration) and water (1:1 volume ratio) were added to adjust the pH to 3, resulting in a clear solution. This solution was added to an 800 mL hydrothermal reactor and reacted at 190 °C and 0.8 bar for 6 h. The resulting product was centrifuged with acetone, and the resulting black precipitate was dispersed ultrasonically with ethanol, washed with acetone, and the process was repeated several times. After drying, purified polyhedral nanocrystals of the iridium-cobalt alloy were obtained. TEM images were obtained. Figure 1 Similarly, the diameter is 7.8 ± 0.6 nm. The ratio of iridium atoms to cobalt atoms is 1:2. The proportion of exposed (111) crystal planes in the nanocrystals is approximately 87%, of which tetrahedrons account for approximately 72%.

[0054] 65 mg of iridium-cobalt alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, and 97 mg of antimony-tin oxide nanoparticles were added. The mixture was ultrasonically treated for 10 h, centrifuged to obtain a black precipitate, and dried in an oven at 70 °C for 6 h to obtain a black solid powder. The solid powder was then treated at 220 °C in an oxidizing atmosphere containing 15 vol% oxygen and 85 vol% helium for 1.5 h to obtain an iridium-cobalt alloy nanocatalyst.

[0055] At 25℃, oxygen saturation is 1.0 mol·L⁻¹ -1In a sodium hydroxide solution, using an Ag / AgCl electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a rotating disk electrode at 1600 rpm as the working electrode, a three-electrode system exhibits a specific catalyst activity of 46.1 μA / cm² at a reaction overpotential of 0.25 V. 2 At 10mA·cm -2 It operates stably for 24 hours at a current density.

[0056] Example 3

[0057] 3 g PVP, 1 mmol tetrairidium dodecylcarbonyl, and 0.2 mmol ferric bromide hexahydrate were added to 525 g glycerol and stirred until completely dissolved. Then, 12 mmol sodium oxalate and 10 mmol sodium borohydride were added, and the mixture was stirred for 0.5 h. Concentrated hydrochloric acid (37%) and water (1:1 volume ratio) were added to adjust the pH to 3.2, resulting in a clear solution. This solution was added to an 800 mL hydrothermal reactor and reacted at 180 °C and 0.9 bar for 4 h. The resulting product was centrifuged with acetone, and the resulting black precipitate was dispersed ultrasonically with ethanol, washed with acetone, and the process was repeated several times. After drying, purified polyhedral nanocrystals of the iridium-iron alloy were obtained. TEM images were obtained. Figure 1 Similarly, the diameter is 4.4 ± 0.2 nm. The ratio of iridium atoms to iron atoms is 1:0.2. The proportion of exposed (111) crystal planes in the nanocrystals is approximately 96%, of which tetrahedrons account for approximately 75%.

[0058] 24 mg of iridium-iron alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, and 97 mg of indium tin oxide nanoparticles were added. The mixture was ultrasonically treated for 20 h, centrifuged to obtain a black precipitate, and dried in an oven at 120 °C for 12 h to obtain a black solid powder. The solid powder was then treated at 270 °C in an oxidizing atmosphere containing 15 vol% oxygen and 85 vol% helium for 2 h to obtain an iridium-iron alloy nanocatalyst.

[0059] At 25℃, oxygen saturation is 1.0 mol·L⁻¹ -1 In a sodium hydroxide solution, using an Ag / AgCl electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a rotating disk electrode at 1600 rpm as the working electrode, a three-electrode system exhibits a catalyst specific activity of 53.8 μA / cm² at a reaction overpotential of 0.25 V. 2 At 10mA·cm -2 It operated stably for 26 hours at the specified current density.

[0060] Example 4

[0061] Into 550 g of glycerol, 3 g of PVP, 1 mmol of acetylacetone iridium and 0.7 mmol of basic ferrous carbonate were added, stirred until completely dissolved, then 20 mmol of potassium oxalate and 17 mmol of hydrazine hydrate were added, stirred for 0.5 h, then 1:1 volume ratio of concentrated hydrochloric acid (concentration of 37%) and water were added, the pH was adjusted to 3.7 to obtain a clear solution. It was added to an 800 mL autoclave, reacted at 160°C and 1.1 bar for 2 h, the obtained product was added to acetone and centrifuged to obtain a black precipitate which was dispersed with ethanol by ultrasonic, added to acetone and centrifuged, the above steps were repeated several times, and dried to obtain the purified iridium-iron alloy polyhedral nanocrystals, and the TEM image was similar to Figure 1 The diameter was 5.8±0.3 nm, and the proportion of nanocrystals exposing (111) crystal surface was about 92%, of which the proportion of tetrahedron was about 85%. The proportion of iridium atoms to iron atoms was 1:0.7.

[0062] 32 mg of iridium-iron alloy polyhedral nanocrystals were dispersed with 50 mL of ethanol, 97 mg of antimony tin oxide nanometer powder was added, and ultrasonic treatment was carried out for 15 h, centrifugation was carried out to obtain a black precipitate, and the black solid powder was dried in an oven at 100°C for 10 h to obtain an iridium-iron nanocatalyst.

[0063] At 25°C, 1.0 mol·L -1 -1 was saturated with oxygen, and a three-electrode system of a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode, an Ag / AgCl electrode as a reference electrode, and a platinum sheet electrode as a counter electrode was used to carry out the reaction at an overpotential of 0.25 V. The specific activity of the catalyst was 60.6 μA / cm 2 at a current density of 10 mA·cm -2 for 34 h.

[0064] Example 5

[0065] Into 560 g of 1,2-propanediol, 3.8 g of PVP, 1 mmol of iridium chloride hydrate and 3 mmol of cobalt acetylacetone were added, stirred until completely dissolved, then 18 mmol of sodium oxalate and 40 mmol of citric acid were added, stirred for 0.5 h, then 1:1 volume ratio of concentrated hydrochloric acid (concentration of 37%) and water were added, the pH was adjusted to 4 to obtain a clear solution. It was added to an 800 mL autoclave, reacted at 170°C and 1 bar for 3 h, the obtained product was added to acetone and centrifuged to obtain a black precipitate which was dispersed with ethanol by ultrasonic, added to acetone and centrifuged, the above steps were repeated several times, and dried to obtain the purified iridium-cobalt alloy polyhedral nanocrystals, and the TEM image was similar to Figure 1Similarly, the diameter of 9.2±1.1nm, nanocrystals exposed (111) crystal surface ratio of about 85%, of which the proportion of tetrahedron is about 83%. The ratio of iridium atoms to cobalt atoms is 1:3.

[0066] The 388 mg of iridium-cobalt alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, 97 mg of indium tin oxide nanometer powder was added, and ultrasonic treatment was performed for 18 h. A black precipitate was obtained by centrifugation, and a black solid powder was obtained by drying in an oven at 100℃ for 10 h. The solid powder was treated in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium at 320℃ for 3 h to obtain an iridium-cobalt nanocatalyst.

[0067] The 1.0 mol / L NaOH solution was saturated with oxygen at 25℃, and the catalyst was obtained by the method of Example 1. -1 The specific activity of the catalyst was 50.9 μA / cm2at a reaction overpotential of 0.25 V in a three-electrode system using an Ag / AgCl electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode. 2 The current density was 10 mA / cm2, and the catalyst was stable for 35 h. -2 The current density was 10 mA / cm2, and the catalyst was stable for 35 h.

[0068] Example 6

[0069] 2.75 g of PVP, 1 mmol of acetylacetone iridium, and 1 mmol of carbonyl nickel were added to 570 g of 1,2-propanediol, and stirred until completely dissolved. Then, 30 mmol of potassium oxalate and 20 mmol of formaldehyde aqueous solution were added, and stirred for 0.5 h. Then, concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added, and the pH was adjusted to 4.2 to obtain a clear solution. The solution was added to an 800 mL autoclave, and reacted at 180℃ and 1 bar for 4 h. The obtained product was added to acetone and centrifuged to obtain a black precipitate. The black precipitate was dispersed in ethanol by ultrasonic treatment, and acetone was added for centrifugal washing. The above steps were repeated several times, and the purified iridium-nickel alloy polyhedral nanocrystals were obtained by drying. Figure 1 Similarly, the diameter of 6.4±0.4nm, nanocrystals exposed (111) crystal surface ratio of about 90%, of which the proportion of tetrahedron is about 92%. The ratio of iridium atoms to nickel atoms is 1:1.

[0070] The 146 mg of iridium-nickel alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, 97 mg of antimony tin oxide nanometer powder was added, and ultrasonic treatment was performed for 22 h. A black precipitate was obtained by centrifugation, and a black solid powder was obtained by drying in an oven at 60℃ for 4 h. The solid powder was treated in an oxidation atmosphere containing 15 vol% oxygen and 85 vol% helium at 250℃ for 3.5 h to obtain an iridium-nickel nanocatalyst.

[0071] The 1.0 mol / L NaOH solution was saturated with oxygen at 25℃, and the catalyst was obtained by the method of Example 1. -1In a sodium hydroxide solution, using an Ag / AgCl electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a rotating disk electrode at 1600 rpm as the working electrode, a three-electrode system exhibits a specific catalyst activity of 65.0 μA / cm² at a reaction overpotential of 0.25 V. 2 At 10mA·cm -2 It operated stably for 38 hours at the specified current density.

[0072] Example 7

[0073] 2.75 g PVP, 1 mmol dodecyltetrairidium, and 1.5 mmol cobalt chloride hexahydrate were added to 480 g ethylene glycol and stirred until completely dissolved. Then, 24 mmol sodium oxalate and 24 mmol hydrazine hydrate were added, and the mixture was stirred for 0.5 h. Concentrated hydrochloric acid (37% concentration) and water (1:1 volume ratio) were added to adjust the pH to 4.5, resulting in a clear solution. This solution was added to an 800 mL hydrothermal reactor and reacted at 160 °C and 1.2 bar for 2 h. The resulting product was centrifuged with acetone, and the resulting black precipitate was dispersed ultrasonically with ethanol, washed with acetone, and the process was repeated several times. The purified iridium-cobalt alloy polyhedral nanocrystals were obtained after drying. TEM images were obtained. Figure 1 Similarly, the diameter is 7.1±0.5nm, and the proportion of exposed (111) crystal planes of the nanocrystals is about 88%, of which the proportion of tetrahedrons is about 87%. The ratio of iridium atoms to cobalt atoms is 1:1.5.

[0074] 226 mg of iridium-cobalt alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, and 97 mg of indium tin oxide nanoparticles were added. The mixture was ultrasonically treated for 24 h, centrifuged to obtain a black precipitate, and dried in an oven at 90 °C for 12 h to obtain a black solid powder. The solid powder was then treated at 200 °C in an oxidizing atmosphere containing 20 vol% oxygen and 80 vol% helium for 1 h to obtain an iridium-cobalt nanocatalyst.

[0075] At 25℃, oxygen saturation is 1.0 mol·L⁻¹ -1 In a sodium hydroxide solution, using an Ag / AgCl electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a rotating disk electrode at 1600 rpm as the working electrode, a three-electrode system exhibits a specific catalyst activity of 57.1 μA / cm² at a reaction overpotential of 0.25 V. 2 At 10mA·cm -2 It operated stably for 31 hours at the specified current density.

[0076] Example 8

[0077] Into 500 g of glycerol, 3.5 g of PVP, 1 mmol of hydrated iridium chloride and 2.5 mmol of nickel acetate were added, stirred until completely dissolved, then 26 mmol of potassium oxalate and 35 mmol of citric acid were added, stirred for 0.5 h, then concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added, the pH was adjusted to 4.7, and a clear solution was obtained. It was added to an 800 mL autoclave, reacted at 190℃ and 1.5 bar for 6 h, the obtained product was added to acetone and centrifuged to obtain a black precipitate which was dispersed with ethanol by ultrasonic treatment, added to acetone and centrifuged, the above steps were repeated several times, and dried to obtain the purified iridium-nickel alloy polyhedral nanocrystals, and the TEM image was similar to Figure 1 The diameter was 8.5±0.7 nm, and the proportion of nanocrystals exposing (111) crystal surface was about 86%, of which the proportion of tetrahedron was about 90%. The proportion of iridium atoms to nickel atoms was 1:2.5.

[0078] The 97 mg of iridium-nickel alloy polyhedral nanocrystals were dispersed with 50 mL of ethanol, 97 mg of antimony tin oxide nanometer powder was added, and ultrasonic treatment was performed for 8 h. A black precipitate was obtained by centrifugation, and a black solid powder was obtained by drying in an oven at 80℃ for 8 h. The solid powder was treated at 300℃ in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 3 h to obtain an iridium-nickel nanocatalyst.

[0079] In a 1.0 mol·L -1 The specific activity of the catalyst was 58.8 μA / cm 2 at a current density of 10 mA·cm -2 for 32 h.

[0080] Example 9

[0081] Into 475 g of ethylene glycol, 2.5 g of PVP, 1 mmol of hydrated iridium chloride and 0.1 mmol of nickel chloride hexahydrate were added, stirred until completely dissolved, then 15 mmol of sodium oxalate and 10 mmol of sodium borohydride were added, stirred for 0.5 h, then concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added, the pH was adjusted to 5, and a clear solution was obtained. It was added to an 800 mL autoclave, reacted at 200℃ and 1 bar for 8 h, the obtained product was added to acetone and centrifuged to obtain a black precipitate which was dispersed with ethanol by ultrasonic treatment, added to acetone and centrifuged, the above steps were repeated several times, and dried to obtain the purified iridium-nickel alloy polyhedral nanocrystals, and the TEM image was similar to Figure 1Similarly, the diameter of the nanocrystals is 4.0 ± 0.2 nm, and the proportion of the nanocrystals exposing (111) crystal surface is about 84%, of which the proportion of tetrahedron is about 78%. The proportion of iridium atom to nickel atom is 1:0.1.

[0082] The 11 mg of iridium-nickel alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, 97 mg of indium tin oxide nanometer powder was added, and ultrasonic treatment was performed for 12 h. A black precipitate was obtained by centrifugation, and a black solid powder was obtained by drying in an oven at 80°C for 8 h. The solid powder was treated in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium at 250°C for 2.5 h to obtain an iridium-nickel nanocatalyst.

[0083] The 1.0 mol / L of oxygen-saturated NaOH solution was prepared at 25°C. -1 The specific activity of the catalyst was 51.2 μA / cm2at a reaction overpotential of 0.25 V in a three-electrode system using an Ag / AgCl electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode. 2 The current density was 10 mA / cm2. -2 The catalyst was stably operated for 24 h.

[0084] Example 10

[0085] 2.5 g of PVP, 1 mmol of hydrated iridium chloride, and 5 mmol of nickel chloride hexahydrate were added to 475 g of ethylene glycol, and stirred until completely dissolved. Then, 15 mmol of potassium oxalate and 50 mmol of ascorbic acid were added, and stirred for 0.5 h. Subsequently, concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added, and the pH was adjusted to 3.5 to obtain a clear solution. The solution was added to an 800 mL autoclave, and reacted at 200°C and 1 bar for 8 h. The obtained product was added to acetone and centrifuged to obtain a black precipitate. The black precipitate was dispersed in ethanol by ultrasonic treatment, and acetone was added for centrifugal washing. The above steps were repeated several times, and the dried product was obtained as purified iridium-nickel alloy polyhedral nanocrystals. The TEM image is shown in FIG. 6. Figure 1 Similarly, the diameter of the nanocrystals is 9.9 ± 1.5 nm, and the proportion of the nanocrystals exposing (111) crystal surface is about 80%, of which the proportion of tetrahedron is about 79%. The proportion of iridium atom to nickel atom is 1:5.

[0086] The 1843 mg of iridium-nickel alloy polyhedral nanocrystals were dispersed in 50 mL of ethanol, 97 mg of antimony tin oxide nanometer powder was added, and ultrasonic treatment was performed for 12 h. A black precipitate was obtained by centrifugation, and a black solid powder was obtained by drying in an oven at 80°C for 8 h. The solid powder was treated in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium at 250°C for 2.5 h to obtain an iridium-nickel nanocatalyst.

[0087] The 1.0 mol / L of oxygen-saturated NaOH solution was prepared at 25°C. -1The specific activity of the catalyst was 39.8 μA / cm2at 0.25 V overpotential in a three-electrode system using an Ag / AgCl electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode. 2 at a current density of 10 mA·cm-2for 25 h. -2 at a current density of 10 mA·cm-2for 25 h.

[0088] Comparative Example 1

[0089] A commercial iridium / carbon catalyst with a loading of 40% was saturated with oxygen at 25°C at a concentration of 1.0 mol·L-1. -1 The specific activity of the catalyst was 20.6 μA / cm2at 0.25 V overpotential in a three-electrode system. 2 at a current density of 10 mA·cm-2for 12 h. -2 at a current density of 10 mA·cm-2for 12 h.

[0090] Comparative Example 2

[0091] 2.5 g of PVP, 1 mmol of hydrated iridium chloride, and 0.5 mmol of nickel chloride hexahydrate were added to 475 g of ethylene glycol, stirred until completely dissolved, 15 mmol of sodium oxalate was then added, and after stirring for 0.5 h, concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added, the pH was adjusted to 3.5, and a clear solution was obtained. This was added to an 800 mL autoclave, and reacted at 200°C and 1 bar for 8 h. The product obtained was added to acetone and centrifuged to obtain a black precipitate, which was dispersed with ethanol by ultrasonic treatment, and then added to acetone and centrifuged for washing, and the above steps were repeated several times, and the purified iridium-nickel alloy nanocrystals were dried to obtain a black solid powder. The solid powder was treated at 250°C in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium-nickel nanocatalyst. The diameter of the nanocrystals was 0.5±0.1 nm, and the proportion of the (111) crystal plane exposed by the nanocrystals was about 64%, of which the proportion of tetrahedrons was about 23%. The proportion of iridium atoms to nickel atoms was 1:0.005.

[0092] 52 mg of the nanocrystals were dispersed in 50 mL of ethanol, 97 mg of indium tin oxide nanometer powder was added, and ultrasonic treatment was performed for 12 h. The black precipitate was obtained by centrifugation, and was dried in an oven at 80°C for 8 h to obtain a black solid powder. The solid powder was treated at 250°C in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium-nickel nanocatalyst.

[0093] at 25°C, saturated with oxygen at a concentration of 1.0 mol·L-1. -1 The specific activity of the catalyst was 30.9 μA / cm2at 0.25 V overpotential in a three-electrode system using an Ag / AgCl electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode. 2 at a current density of 10 mA·cm-2for 25 h. -2at a current density of 10 mA·cm

[0094] Comparative Example 3

[0095] Into 475 g of ethylene glycol, 2.5 g of PVP, 1 mmol of hydrated iridium chloride and 0.5 mmol of nickel chloride hexahydrate were added and stirred until completely dissolved. Then 15 mmol of aqueous formaldehyde solution was added, and after stirring for 0.5 h, concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added. The pH was adjusted to 3.5 with acid to obtain a clear solution. The solution was added to an 800 mL autoclave and reacted at 200℃ and 1 bar for 8 h. The obtained product was centrifuged with acetone to obtain a black precipitate which was dispersed with ethanol by ultrasonic treatment. The black precipitate was washed by centrifugation with acetone, and the above steps were repeated several times. The purified iridium-nickel alloy nanocrystals were dried to obtain a black solid powder. The diameter of the nanocrystals was 6.3±0.4 nm, and the proportion of the (111) crystal plane exposed by the nanocrystals was about 78%, as shown in FIG. 1. The proportion of tetrahedrons was about 15%. The proportion of iridium atoms to nickel atoms was 1:0.5. Figure 2

[0096] The 52 mg of nanocrystals were dispersed with 50 mL of ethanol, and 97 mg of indium tin oxide nanometer powder was added. The mixture was ultrasonically treated for 12 h, and the black precipitate was obtained by centrifugation. The black precipitate was dried in an oven at 80℃ for 8 h to obtain a black solid powder. The solid powder was treated at 250℃ in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium-nickel nanocatalyst.

[0097] The oxygen saturation of the 1.0 mol·L -1 The specific activity of the catalyst was 26.2 μA / cm 2 at a current density of 10 mA·cm -2 and stably operated for 23 h.

[0098] Comparative Example 4

[0099] ​1 mmol iridium chloride hydrate and 0.5 mmol nickel chloride hexahydrate were added into 475 g ethylene glycol, stirred until completely dissolved, then 15 mmol sodium oxalate and 15 mmol formaldehyde aqueous solution were added, after stirring for 0.5 h, concentrated hydrochloric acid (concentration of 37%) and water with a volume ratio of 1:1 were added, the pH was adjusted to 3.5 to obtain a clear solution. It was added to an 800 mL autoclave, reacted at 200℃ and 1 bar for 8 h, the obtained product was added to acetone and centrifuged to obtain a black precipitate which was dispersed with ethanol by ultrasonic, added to acetone and centrifuged, the above steps were repeated several times, and dried to obtain the purified iridium-nickel alloy nanocrystals, with a diameter of 286±52 nm, the proportion of nanocrystals exposing (111) crystal surface was about 32%, and the proportion of tetrahedron was about 0%. The proportion of iridium atoms to nickel atoms was 1:0.5.

[0100] 52 mg of nanocrystals were dispersed with 50 mL of ethanol, 97 mg of indium tin oxide nanometer powder was added, and ultrasonic treatment was performed for 12 h. A black precipitate was obtained by centrifugation, and a black solid powder was obtained by drying in an oven at 80℃ for 8 h. The solid powder was treated at 250℃ in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium-nickel nanocatalyst.

[0101] The oxygen saturation of 1.0 mol·L -1 The specific activity of the catalyst was 8.6 μA / cm 2 at a current density of 10 mA·cm -2 for 11 h.

[0102] Comparative Example 5

[0103] 1 mmol iridium chloride hydrate and 0.5 mmol nickel chloride hexahydrate were added into 475 g ethylene glycol, stirred until completely dissolved, then 15 mmol sodium oxalate and 15 mmol formaldehyde aqueous solution were added, after stirring for 0.5 h, concentrated hydrochloric acid (concentration of 37%) and water with a volume ratio of 1:1 were added, the pH was adjusted to 3.5 to obtain a clear solution. It was added to an 800 mL autoclave, reacted at 200℃ and 1 bar for 8 h, the obtained product was added to acetone and centrifuged to obtain a black precipitate which was dispersed with ethanol by ultrasonic, added to acetone and centrifuged, the above steps were repeated several times, and dried to obtain the purified iridium-nickel alloy nanocrystals, with a diameter of 286±52 nm, the proportion of nanocrystals exposing (111) crystal surface was about 32%, and the proportion of tetrahedron was about 0%. The proportion of iridium atoms to nickel atoms was 1:0.5.

[0104] The 52 mg nanocrystals were dispersed with 50 mL ethanol, 97 mg indium tin oxide nano powder was added, and ultrasonic treatment was performed for 12 h. Centrifugation was performed to obtain a black precipitate. The black solid powder was dried in an oven at 80°C for 8 h. The solid powder was treated at 250°C in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium nanocatalyst.

[0105] The 1.0 mol·L-1 NaOH solution was saturated with oxygen at 25°C. -1 The catalyst specific activity of the catalyst was 24.9 μA / cm2at 0.25 V overpotential in a three-electrode system using an Ag / AgCl electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode. 2 The catalyst was stably operated at a current density of 10 mA·cm-2for 19 h. -2

[0106] Comparative Example 6

[0107] The 2.5 g PVP, 1 mmol iridium chloride hydrate, and 0.5 mmol nickel chloride hexahydrate were added to 475 g ethylene glycol, and stirred until completely dissolved. Then, 15 mmol sodium oxalate and 15 mmol formaldehyde aqueous solution were added, and stirred for 0.5 h. Subsequently, concentrated hydrochloric acid (concentration of 37%) and water in a volume ratio of 1:1 were added, and the pH was adjusted to 3.5 to obtain a clear solution. The solution was added to an 800 mL autoclave, and reacted at 200°C and 1 bar for 8 h. The obtained product was added to acetone, and centrifuged to obtain a black precipitate. The black precipitate was dispersed with ethanol by ultrasonic treatment, and added to acetone for centrifugal washing. The above steps were repeated several times, and the purified iridium-nickel alloy nanocrystals were dried to obtain a black solid powder. The diameter of the nanocrystals was 5.1±0.3 nm, and the proportion of the (111) crystal plane exposed by the nanocrystals was about 94%. The proportion of tetrahedrons was about 80%. The proportion of iridium atoms to nickel atoms was 1:0.5.

[0108] The 52 mg nanocrystals were dispersed with 50 mL ethanol, 97 mg indium tin oxide nano powder was added, and ultrasonic treatment was performed for 12 h. Centrifugation was performed to obtain a black precipitate. The black solid powder was dried in an oven at 80°C for 8 h. The solid powder was treated at 250°C in an oxidation atmosphere containing 10 vol% oxygen and 90 vol% helium for 2.5 h to obtain an iridium nanocatalyst.

[0109] The 1.0 mol·L-1 NaOH solution was saturated with oxygen at 25°C. -1 The catalyst specific activity of the catalyst was 24.9 μA / cm2at 0.25 V overpotential in a three-electrode system using an Ag / AgCl electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a rotating disc electrode with a rotation speed of 1600 rpm as a working electrode. 2 The catalyst was stably operated at a current density of 10 mA·cm-2for 19 h. -2 ​​

[0110] Physical and catalytic properties of various examples and comparative examples

[0111]

[0112]

[0113] The examples described above are intended to be illustrative only and are not intended to limit the present application in any way. The present application has been described with reference to the preferred embodiments. Modifications and alterations can occur to others upon reading and understanding the preceding detailed description. It is intended to include all such modifications and alterations insofar as they come within the scope and spirit of the present application. Although the present application has been described in some detail with reference only to the preferred embodiments, it should be appreciated that the application is not limited to the disclosed embodiments, but rather, changes and modifications can be made to the disclosed embodiments by those having ordinary skill in the art without departing from the spirit and scope of the application.

Claims

1. An iridium-based alloy catalyst, the catalyst comprising an iridium-based alloy active component and a support; the iridium-based alloy active component comprising iridium and at least one transition metal selected from iron, cobalt, and nickel; the support being a conductive oxide support; in, The active component of the iridium-based alloy is a polyhedral nanocrystal with (111) crystal planes exposed. The proportion of exposed (111) crystal faces in the polyhedral nanocrystals is greater than 80%; the proportion of tetrahedral faces in the polyhedral nanocrystals is greater than 60%.

2. The iridium-based alloy catalyst according to claim 1, characterized in that, The grain size of the polyhedral nanocrystals is 2~15nm.

3. The iridium-based alloy catalyst according to claim 1, characterized in that, The atomic ratio of iridium to transition metal is 1:(0.1~5).

4. The iridium-based alloy catalyst according to claim 1, characterized in that, The conductive oxide carrier is selected from at least one of indium tin oxide and antimony tin oxide.

5. The iridium-based alloy catalyst according to claim 1, characterized in that, The catalyst comprises, by weight, 10-95 parts iridium-based alloy active component and 5-90 parts conductive oxide support.

6. A method for synthesizing the iridium-based alloy catalyst according to any one of claims 1-5, comprising the following steps: (1) Iridium source and transition metal source, surfactant, crystal plane coordination agent, reducing agent and organic alcohol are mixed, pH is adjusted to acidic, and heated reaction is carried out to obtain iridium-based polyhedral nanocrystals; (2) The iridium-based polyhedral nanocrystals were mixed with a conductive oxide support and subjected to heat treatment in an oxidizing atmosphere to obtain the catalyst.

7. The synthesis method according to claim 6, characterized in that, The iridium source mentioned in step (1) is selected from at least one of iridium chloride, iridium acetylacetonate, iridium carbonyl, hexachloroiridic acid, sodium hexachloroiridate, and ammonium hexachloroiridate.

8. The synthesis method according to claim 6, characterized in that, The transition metal source mentioned in step (1) is selected from at least one of the soluble chlorides, bromides, nitrates, sulfates, carbonates, acetates, and acetylacetone salts corresponding to the transition metals iron, cobalt, and nickel.

9. The synthesis method according to claim 6, characterized in that, The surfactant mentioned in step (1) is polyvinylpyrrolidone.

10. The synthesis method according to claim 6, characterized in that, The crystal plane coordination reagent mentioned in step (1) is oxalate.

11. The synthesis method according to claim 6, characterized in that, The reducing agent mentioned in step (1) is at least one of methanol, formaldehyde, ascorbic acid, citric acid, hydrazine hydrate, and sodium borohydride.

12. The synthesis method according to claim 6, characterized in that, The organic alcohol mentioned in step (1) is a polyol.

13. The synthesis method according to claim 6, characterized in that, The molar ratio of the iridium source, transition metal source, crystal plane coordination reagent and reducing agent in step (1) is 1:(0.1~5):(10~30):(10~50).

14. The synthesis method according to claim 6, characterized in that, The iridium source mentioned in step (1) is based on hydrated iridium chloride, wherein the mass ratio of iridium source, surfactant and polyol is 1:(8~12):(1500~1800).

15. The synthesis method according to claim 6, characterized in that, The heating temperature in step (1) is 130~230℃; the time is 1~12h; and the pressure is 0.8~1.5bar.

16. The synthesis method according to claim 6, characterized in that, The atmosphere heat treatment in step (2) is to treat in an oxidizing atmosphere at 200~350°C for 0.5~4h; the oxygen content in the oxidizing atmosphere in step (2) is 5vol%~20vol%.

17. The synthesis method according to claim 6, characterized in that, The oxygen content in the oxidizing atmosphere in step (2) is 5 vol% to 20 vol%; in the oxidizing atmosphere in step (2), apart from oxygen, the remaining gas is at least one of nitrogen and / or an inert gas, wherein the inert gas is selected from at least one of argon and helium.

18. The use of the iridium-based alloy catalyst according to any one of claims 1-5 in the oxygen evolution reaction under alkaline conditions.

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