Cobalt-iridium nanocrystal, preparation method thereof and water electrolysis catalyst

Abstract

The invention provides a cobalt-iridium nanocrystal, a preparation method thereof and an electrolyzed water catalyst. The preparation method comprises the following steps: mixing an iridium salt, an organic ligand, a reducing solvent and a centrifugate, heating in a protective atmosphere to fully dissolve the iridium salt to form a first precursor, and carrying out heat preservation on the first precursor; and heating the first precursor in a protective atmosphere, mixing the heated first precursor with cobalt salt to form a second precursor, carrying out a reaction on the second precursor at a constant temperature, centrifuging, and washing a centrifugal precipitate to obtain the cobalt-iridium nanocrystal. The invention also provides the preparation method and an electrolyzed water catalyst prepared from the cobalt-iridium nanocrystal. According to the preparation method, the centrifugate is taken as the raw material, so that the yield, the crystallinity and the electrocatalytic activity of the synthesized cobalt-iridium nanocrystal can be improved, and the synthesis cost is further reduced.

Description

Technical Field

[0001] The invention relates to the technical field of PEM water electrolysis anode catalyst preparation, and in particular to a cobalt-iridium nanocrystal and a preparation method thereof and a water electrolysis catalyst. Background Art

[0002] Proton exchange membrane (PEM) water electrolysis hydrogen production technology based on renewable energy is one of the effective methods for large-scale production of green hydrogen in the future. It has the advantages of high working efficiency, high purity of hydrogen production, compact electrolyzer and system structure, high intrinsic safety, large adjustable range of load fluctuation, and suitable for rapid start and stop. The anode reaction is the rate-controlling step. The activity, efficiency and cost of the anode catalyst are currently one of the important factors restricting the large-scale development of PEM water electrolysis hydrogen production. At present, the main commercial anode catalyst is IrO2 or Ir black catalyst. Ir reserves are small and expensive. Therefore, it is imperative to seek an efficient synthesis method that can simultaneously reduce the preparation cost of Ir catalysts and improve catalyst performance.

[0003] Abundant non-precious metal materials, such as nickel, cobalt, and iron, have been widely studied as efficient anodic oxygen evolution reaction catalysts. Although great progress has been made in this field, the main problem faced by these non-precious metal catalysts is that their activity is still generally lower than that of the precious metal Ir and Ru catalysts used as reference benchmarks. In addition, non-precious metal catalysts are generally less efficient under acidic conditions, which greatly limits their application in proton exchange membrane water electrolysis devices, as the latter usually operate in a corrosive and strongly acidic environment. Currently, only Ir and Ru can maintain good OER activity and efficiency in such harsh environments. Compared with Ru, Ir has higher efficiency under acidic conditions and is therefore considered to be the most ideal OER catalyst.

[0004] Compared with other precious metals, the controllable synthesis of Ir-based nanomaterials is still relatively difficult. On the one hand, because the precursors of Ir are usually difficult to reduce and the synthesis conditions are relatively harsh, conventional synthesis and regulation strategies are difficult to apply to the synthesis of Ir-based nanomaterials. In addition, since Ir has a low homogeneous nucleation barrier, during the synthesis process, the newly generated Ir atoms are more inclined to nucleate themselves and grow into small particles, rather than depositing on the surface of existing particles to form larger nanoparticles. Therefore, it is usually difficult to obtain nanocrystals with regular morphology of Ir, and there are relatively few related studies and reports. Since Ir resources are scarce and expensive, it is of utmost importance to develop highly active catalysts to improve the utilization rate of Ir. In order to reduce the amount of Ir used and improve the activity and efficiency of the catalyst, researchers have developed doped and loaded Ir-based catalysts to improve the utilization rate of Ir, improve the performance of the catalyst, and thus reduce the cost of the catalyst.

[0005] In the field of PEM water electrolysis for hydrogen production, in order to reduce the amount of precious metal Ir, researchers are committed to developing core-shell structure catalysts. The core-shell structure usually consists of one substance forming the core and another substance wrapping the shell. Thanks to its surface strain and the influence of atomic proximity on the charge transfer between the core and the shell, the stability and catalytic activity in the OER process are improved. The electrocatalytic process belongs to a surface reaction. Only the active sites distributed on the surface of the catalyst can participate in the reaction. The core-shell structure can be fully utilized to wrap the precious metal on the outside to form a shell, and the core is replaced by other non-precious metal substances, which maximizes the contact between the precious metal and the reactant, while reducing the amount of precious metal used, and enhancing the activity and stability of the catalyst through the synergistic effect of the core-shell. The price of metallic cobalt is much lower than that of metallic iridium. The introduction of some cobalt is conducive to reducing the amount of iridium, thereby reducing the cost of electrolytic water anode catalysts. In view of the important application value of Ir-based nanomaterials in PEM water electrolysis technology, in order to realize the large-scale promotion and application of PEM water electrolysis technology, it is urgent to develop efficient and low-cost Ir-based material preparation methods. Summary of the invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a cobalt-iridium nanocrystal and a preparation method thereof and a water electrolysis catalyst. The preparation method can shorten the reaction time, improve the product yield, and reduce the preparation cost. The prepared cobalt-iridium nanocrystal has high crystallinity and high catalytic activity.

[0007] In order to achieve the above object, the present invention provides a method for preparing cobalt-iridium nanocrystals, the preparation method comprising:

[0008] S1, mixing an iridium salt, an organic ligand, a reducing solvent and a centrifuge liquid, heating the mixture in a protective atmosphere to fully dissolve the iridium salt to form a first precursor, and keeping the first precursor warm;

[0009] S2, heating the first precursor in a protective atmosphere and mixing it with a cobalt salt to form a second precursor, keeping the second precursor warm for reaction, centrifuging, and washing the centrifugal precipitate to obtain the cobalt-iridium nanocrystals; the volume proportion of the centrifugal liquid in the second precursor is greater than or equal to 10% and less than 40%;

[0010] The centrifuge liquid is the centrifuge liquid obtained during the centrifugation of S2, or the preparation method of the centrifuge liquid includes: mixing an iridium salt, an organic ligand and a reducing solvent, heating the mixture in a protective atmosphere to fully dissolve the iridium salt to form a third precursor; mixing the third precursor with a cobalt salt in a protective atmosphere to form a fourth precursor, heating the fourth precursor to react, and centrifuging the mixture to obtain the centrifuge liquid.

[0011] In the above-mentioned method for preparing cobalt-iridium nanocrystals, unreacted raw materials (iridium source, cobalt source, organic ligand and reducing solvent) remain in the centrifugal liquid of the cobalt-iridium reaction product, and discharging the centrifugal liquid will pollute the environment and the waste treatment cost is high; in addition, the iridium salt remaining in the centrifugal liquid and a small amount of iridium atomic clusters that have not been centrifugally separated are reused in the preparation process of cobalt-iridium nanocrystals to improve the product yield. Therefore, the present invention uses the centrifugal liquid as a reaction raw material, and can recycle the centrifugal liquid generated in the preparation process of cobalt-iridium nanocrystals, which can not only reduce the preparation cost and improve the yield of cobalt-iridium nanocrystals, but also shorten the reaction time in the preparation process (reduce the harshness of the reaction) and improve the crystallinity and electrocatalytic activity of the cobalt-iridium nanocrystals obtained thereby.

[0012] In the above-mentioned method for preparing cobalt-iridium nanocrystals, by using the centrifugal liquid of the cobalt-iridium reaction product as one of the reaction raw materials, the following effects are achieved in terms of cost saving: (1) improving the synthesis yield of the catalyst; (2) solving the problem of environmental pollution caused by the centrifugal waste liquid during the preparation process; and (3) improving the utilization rate of the reaction raw materials. The present invention reduces the preparation cost of cobalt-iridium nanocrystals from the above-mentioned raw materials, environmental waste discharge and product yield.

[0013] The inventors have found that in the above-mentioned method for preparing cobalt-iridium nanocrystals, by controlling the proportion of the centrifugal liquid in the reaction system (the second precursor), the morphology and aggregation of the generated cobalt-iridium nanocrystals can be regulated, and then the catalytic activity of the cobalt-iridium nanocrystals can be regulated. Specifically, when too much centrifugal liquid is added, the generated cobalt-iridium nanocrystals are easy to aggregate and produce irregular shapes, and the catalytic activity is low; when too little centrifugal liquid is added, the yield of cobalt-iridium nanocrystals is not significantly improved. However, by controlling the volume proportion of the centrifugal liquid in the second precursor to be greater than 5% and less than 40%, the obtained cobalt-iridium nanocrystals have high dispersibility and morphological regularity, are not easy to aggregate, the yield is significantly improved, and the catalytic activity is improved. The volume proportion of the centrifugal liquid in the second precursor can be specifically controlled to be 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 39%, and other specific values, as well as a range with any two of the above specific values ​​as endpoints. Furthermore, the volume proportion of the centrifugal liquid in the second precursor can be controlled to be greater than or equal to 8% and less than 40%, or greater than or equal to 10% and less than 40%; further, the volume proportion of the centrifugal liquid in the second precursor can be controlled to be 10%-30%.

[0014] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the cobalt salt can be reduced to cobalt, and the catalyst formed with iridium can reduce the cost on the basis of retaining the activity of the iridium catalyst. Specifically, the cobalt salt in the second precursor can include one or a combination of two or more of cobalt acetate, cobalt sulfate, cobalt chloride, cobalt nitrate, and basic cobalt carbonate. In some specific embodiments, the cobalt salt can be basic cobalt carbonate.

[0015] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the iridium salt can generally include a combination of an inorganic salt of iridium and an organic salt of iridium. The iridium element reduced from the inorganic salt of iridium has a high crystallinity and a high catalytic activity; the organic salt of iridium has a similar binding energy to the cobalt salt and can react with the cobalt salt to form a cobalt-iridium alloy, thereby replacing part of the iridium as a catalyst with cobalt and reducing costs. The cobalt-iridium nanocrystals formed by the above-mentioned cobalt salt and iridium salt can have both high catalytic activity and low synthesis cost.

[0016] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the iridium salt in the second precursor may include a combination of at least one of iridium trichloride (IrCl3), iridium tetrachloride (IrCl4), chloroiridic acid (H2IrCl6), and ammonium chloroiridate ((NH4)2IrCl6) and iridium acetate. In some specific embodiments, the iridium salt may also be in the form of a hydrate, for example, the iridium tetrachloride may be iridium tetrachloride hydrate (IrCl4·xH2O).

[0017] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the molar ratio of the organic salt of iridium to the inorganic salt of iridium can be 0.8-2, specifically, it can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar ratio of the organic salt of iridium to the inorganic salt of iridium can be 1-2.

[0018] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the organic ligand can regulate the morphology of cobalt-iridium nanocrystals and the size of cobalt-iridium nanocrystals by limiting the growth of cobalt-iridium nanocrystals. The organic ligand used in the present invention can be dissolved in the reducing solvent. Specifically, the organic ligand in the second precursor can include a long-chain compound with a carbon number of 12-16 and containing a hydroxyl group and / or an amine group. In some specific embodiments, the organic ligand can specifically include one or a combination of two or more of hexadecanediol (e.g., 1,2-hexadecanediol, HDD), dodecanediol, hexadecyltrimethylammonium bromide (CTAB), and hexadecyltrimethylammonium chloride.

[0019] In the above method for preparing cobalt-iridium nanocrystals, the reducing solvent in the first precursor may include oleylamine. Oleylamine has a high boiling point and reducing property, and can be used as a solvent to dissolve various reaction raw materials and perform high-temperature reduction reaction.

[0020] In the above-mentioned method for preparing cobalt-iridium nanocrystals, in the second precursor, the molar ratio of the cobalt salt to the iridium salt can be 0.01-0.8, specifically 0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and other specific values ​​and a range with any two of the above specific values ​​as endpoints. The ratio refers to the molar ratio of the iridium salt added separately in S1 to the cobalt salt added separately in S2, excluding the cobalt salt and iridium salt in the centrifuge. In some specific embodiments, the molar ratio of the cobalt salt to the iridium salt in the second precursor can be 0.01-0.5.

[0021] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the size of cobalt-iridium nanocrystals can be adjusted by adjusting the ratio of organic ligands to iridium salts. In the second precursor, the molar ratio of the organic ligand to the iridium salt is 0.1-5, and can be specifically 0.1, 0.5, 1, 1.5, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.5, 4, 4.5, 5 and other specific values ​​and a range with any two of the above specific values ​​as endpoints. The ratio refers to the molar ratio of the organic ligand and the iridium salt added separately in S1, and does not include the organic ligand and the iridium salt in the centrifuge.

[0022] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the molar ratio of the reducing solvent to the iridium salt can be 350-500, and can be specifically 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500 and other specific values, and a range with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar ratio of the reducing solvent to the iridium salt can be 400-500.

[0023] In the above-mentioned method for preparing cobalt-iridium nanocrystals, in S1, the temperature increase treatment after the iridium salt, organic ligand, reducing solvent and centrifugal liquid are mixed can make the above-mentioned components fully dissolved and mixed. The temperature reached by the heating (also the temperature of the first precursor formed) can be controlled at 150-180°C so that the iridium salt is fully dissolved while avoiding the occurrence of reduction reaction; accordingly, the temperature of the obtained first precursor can also be controlled to be 150-180°C. In some specific embodiments, the temperature reached by the heating can be specific values ​​such as 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, and a range with any two of the above specific values ​​as endpoints. Further, the above temperature can be controlled to be 150-170°C.

[0024] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the heated first precursor can be kept warm for a period of time before being mixed with the cobalt salt.

[0025] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the iridium salt in the first precursor obtained after heating is completely dissolved and can be a clear solution.

[0026] In the above method for preparing cobalt-iridium nanocrystals, the process of heating the mixture of iridium salt, organic ligand, reducing solvent and centrifugal liquid to form the first precursor is carried out in a protective atmosphere to prevent the iridium salt from being reduced prematurely. The protective atmosphere may include nitrogen.

[0027] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the reaction carried out in S2 is a high-temperature reduction reaction of a cobalt salt and an iridium salt under the action of a reducing solvent. The temperature of the reaction can be controlled to be 200-280°C, for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C and other specific values ​​and a range with any two of the above specific values ​​as endpoints. Further, the temperature of the reaction can be controlled to be 230-250°C.

[0028] In the above-mentioned method for preparing cobalt-iridium nanocrystals, in S2, the cobalt salt can be mixed with the first precursor in the form of a solution. The solution of the cobalt salt can be formed by fully mixing the cobalt salt with the reducing solvent, and the reducing solvent is of the same type as the reducing solvent in S1. Furthermore, the cobalt salt and the reducing solvent can also be heated after mixing to ensure that the cobalt salt is completely dissolved. The temperature reached by the heating is generally 100°C-120°C, and can be specific values ​​such as 100°C, 105°C, 110°C, 115°C, 120°C, and a range with any two of the above specific values ​​as endpoints. The cobalt salt solution obtained after heating can be a clear solution.

[0029] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the sum of the insulation time of the first precursor in S1 and the reaction time of the second precursor in S2 is usually controlled to be less than 6 hours, and can be specific values ​​such as 1h, 2h, 3h, 4h, 5h, 6h, and a range with any two of the above specific values ​​as endpoints.

[0030] In the above-mentioned method for preparing cobalt-iridium nanocrystals, by using centrifugal liquid as raw material, the reaction speed can be increased and the reaction time can be shortened. Specifically, the reaction time in S2 is generally 1.5-2h. For example, when the volume of the centrifugal liquid is 15% of the volume of the second precursor, the reaction time can be shortened to 2 hours. When the volume of the centrifugal liquid is 30% of the volume of the second precursor, the reaction time can be shortened to 1.5 hours. The reaction time in S2 can specifically be specific values ​​such as 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, and a range with any two of the above specific values ​​as endpoints.

[0031] In the above-mentioned method for preparing cobalt-iridium nanocrystals, the holding time of the first precursor in S1 can be 1-2 hours, so as to ensure that the iridium salt in the first precursor is fully dissolved.

[0032] In the above method for preparing cobalt-iridium nanocrystals, washing in S2 can be performed with a mixture of alcohol and ketone, specifically ethanol and acetone. After washing, the cobalt-iridium nanocrystals are dried to obtain the cobalt-iridium nanocrystals.

[0033] The centrifuge used in the present invention can be the centrifuge obtained in the centrifugation process of S2 (referred to as centrifuge A); or it can be the centrifuge obtained in the preparation method of cobalt-iridium nanocrystals in which the reaction raw materials do not contain centrifuge (hereinafter referred to as centrifuge B). The preparation method of the centrifuge specifically comprises: mixing an iridium salt, an organic ligand and a reducing solvent, heating the mixture in a protective atmosphere to fully dissolve the iridium salt to form a third precursor; mixing the third precursor with a cobalt salt to form a fourth precursor, heating the fourth precursor in a protective atmosphere to react, and the liquid obtained by centrifugation is the centrifuge.

[0034] In the preparation method of the above-mentioned centrifugal solution B, the iridium salt in the fourth precursor may include a combination of an inorganic salt of iridium and an organic salt of iridium. Further, the iridium salt in the fourth precursor may include a combination of at least one of iridium trichloride (IrCl3), iridium tetrachloride, chloroiridic acid (H2IrCl6), and ammonium chloroiridate ((NH4)2IrCl6) and iridium acetate. In some specific embodiments, the above-mentioned iridium salt may also be in the form of a hydrate, for example, the iridium tetrachloride may be iridium tetrachloride hydrate (IrCl4·xH2O).

[0035] The iridium salt in the fourth precursor may be the same as or different from the iridium salt in the second precursor. The same iridium salt type as that used in the second precursor and the fourth precursor can further improve the yield of cobalt-iridium nanocrystals.

[0036] In the preparation method of the centrifugal solution B, the molar ratio of the organic salt of iridium to the inorganic salt of iridium in the fourth precursor can be 0.8-2, specifically 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar ratio of the organic salt of iridium to the inorganic salt of iridium in the fourth precursor can be 1-2.

[0037] In the preparation method of the centrifugal solution B, the organic ligand in the fourth precursor may include a long-chain compound having a carbon number of 12-16 and containing a hydroxyl group and / or an amine group. In some specific embodiments, the organic ligand may specifically include one or a combination of two or more of hexadecanediol, dodecanediol, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride.

[0038] The type of organic ligand in the fourth precursor may be the same as or different from the type of organic ligand in the second precursor. When the two are the same, the yield of cobalt-iridium nanocrystals can be further improved.

[0039] In the method for preparing the centrifugal solution B, the reducing solvent in the third precursor and the fourth precursor is the same as the reducing solvent in the first precursor and the second precursor. Specifically, the reducing solvent in the third precursor and the reducing solvent in the fourth precursor may include oleylamine.

[0040] In the preparation method of the centrifugal solution B, in the fourth precursor, the molar ratio of the cobalt salt to the iridium salt can be 0.01-0.8, specifically 0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar ratio of the cobalt salt to the iridium salt in the fourth precursor can be 0.01-0.5.

[0041] The molar ratio of the cobalt salt to the iridium salt in the fourth precursor may be the same as or different from the molar ratio of the cobalt salt to the iridium salt in the second precursor. When the molar ratio of the cobalt salt to the iridium salt in the fourth precursor is the same, the yield of the cobalt-iridium nanocrystals may be further improved.

[0042] In the preparation method of the above-mentioned centrifugal liquid B, in the fourth precursor, the molar ratio of the organic ligand to the iridium salt is 0.1-5, specifically 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 and the like, as well as a range with any two of the above-mentioned specific values ​​as endpoints.

[0043] The molar ratio of the organic ligand to the iridium salt in the second precursor may be the same as or different from the molar ratio of the organic ligand to the iridium salt in the second precursor. When the two are the same, the yield of the cobalt-iridium nanocrystals can be further improved.

[0044] In the preparation method of the centrifugal solution B, in the fourth precursor, the molar ratio of the reducing solvent to the iridium salt can be 350-500, specifically 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500 and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, the molar ratio of the reducing solvent to the iridium salt can be 400-500.

[0045] In the preparation method of the above-mentioned centrifugal liquid B, the heating treatment after the iridium salt, organic ligand, reducing solvent and centrifugal liquid are mixed can make the above-mentioned components fully dissolved and mixed. The temperature reached by the heating (also the temperature of the third precursor formed) can be controlled at 150-180°C so that the iridium salt is fully dissolved while avoiding the occurrence of reduction reaction; accordingly, the temperature of the obtained third precursor can also be controlled to be 150-180°C. In some specific embodiments, the temperature reached by the heating can be specific values ​​such as 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, and a range with any two of the above specific values ​​as endpoints. Further, the above temperature can be controlled to be 150-170°C.

[0046] In the preparation method of the above centrifuge B, the third precursor after heating can be kept warm for a period of time before mixing with the cobalt salt. In some specific embodiments, the insulation time is generally controlled to be 1-2h, and can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0047] In the method for preparing the centrifugal solution B, the iridium salt in the third precursor obtained after heating is completely dissolved, and a clear solution can be obtained.

[0048] In the above method for preparing centrifugal solution B, the process of heating the mixture of iridium salt, organic ligand and reducing solvent to form the third precursor is carried out in a protective atmosphere to prevent the iridium salt from being reduced prematurely. The protective atmosphere may include nitrogen.

[0049] In the preparation method of the above centrifugal solution B, the reaction of the fourth precursor is a high-temperature reduction reaction of a cobalt salt and an iridium salt under the action of a reducing solvent. The temperature of the reaction can be controlled to be 200-280°C, for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C and other specific values ​​and a range with any two of the above specific values ​​as endpoints. Further, the temperature of the reaction can be controlled to be 230-250°C.

[0050] In the preparation method of the above-mentioned centrifugal solution B, the cobalt salt can be mixed with the third precursor in the form of a solution. The solution of the cobalt salt can be formed by fully mixing the cobalt salt with the reducing solvent, and the reducing solvent is of the same type as the reducing solvent in the third precursor. Furthermore, the cobalt salt and the reducing solvent can also be heated after mixing to ensure that the cobalt salt is completely dissolved. The temperature reached by the heating is generally 100°C-120°C, and can be specific values ​​such as 100°C, 105°C, 110°C, 115°C, 120°C, and a range with any two of the above specific values ​​as endpoints. The cobalt salt solution obtained after heating can be presented as a clear solution.

[0051] In the preparation method of the centrifugal solution B, the reaction time of the fourth precursor is generally 2-4 hours, for example, it can be 2h, 3h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h, 4h and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, the reaction time can be further controlled to 3h-4h.

[0052] The present invention does not limit centrifugation, and can be a conventional centrifugation method in this area. In some specific embodiments, the centrifugal speed is 15000-2000rpm, and can specifically be 15000rpm, 16000rpm, 17000rpm, 18000rpm, 19000rpm, 20000rpm and other specific values ​​and the scope with any two of the above specific values ​​as endpoints. The centrifugal time is 20min-30min, and can specifically be 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min, 30min and other specific values ​​and the scope with any two of the above specific values ​​as endpoints.

[0053] The present invention also provides cobalt iridium nanocrystals obtained by the above preparation method. The cobalt iridium nanocrystals have good dispersibility, regular morphology, high crystallinity, and high catalytic performance. In some specific embodiments, the particle size of the nanocrystals can be 2-8nm, specifically 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm and other specific values ​​and a range with any two of the above specific values ​​as endpoints.

[0054] The present invention also provides a water electrolysis catalyst, which includes the above cobalt-iridium nanocrystals or is made of the above cobalt-iridium nanocrystals. The above cobalt-iridium nanocrystals have both high catalytic activity and high catalytic stability, have excellent water electrolysis performance, and can be used as a water electrolysis catalyst.

[0055] The beneficial effects of the present invention are:

[0056] The method for preparing cobalt-iridium nanocrystals provided by the present invention has the characteristics of efficient synthesis and low cost, and can recycle the centrifugal waste liquid generated in the synthesis process. By using the centrifugal liquid as the preparation raw material, on the one hand, the amount of raw materials can be saved, the reaction time can be shortened, the synthesis yield of the product can be improved, and the problem of centrifugal waste liquid being discharged and polluting the environment can be solved, thereby reducing the production cost from three aspects of raw materials, environmental waste discharge and product yield; on the other hand, the morphology regularity, monodispersity, crystallinity and catalytic activity of the synthesized cobalt-iridium nanocrystals can be improved, thereby improving the electrolytic water catalytic effect of the cobalt-iridium nanocrystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a TEM image of the cobalt-iridium core-shell water electrolysis catalyst S1 obtained in Example 1 of the present invention.

[0058] Figure 2 This is a TEM image of the cobalt-iridium core-shell water electrolysis catalyst S2 obtained in Example 2 of the present invention.

[0059] Figure 3 This is a TEM image of the cobalt-iridium core-shell water electrolysis catalyst S13 obtained in Comparative Example 1 of the present invention.

[0060] Figure 4 This is a TEM image of the cobalt-iridium core-shell water electrolysis catalyst S14 obtained in Comparative Example 2 of the present invention.

[0061] Figure 5 The XRD diagrams of the catalysts obtained in Example 1 and Comparative Example 1 are shown.

[0062] Figure 6 The polarization curves of the oxygen evolution reaction of the catalysts obtained in Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0063] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0064] Comparative Example 1

[0065] This comparative example provides a cobalt-iridium nanocrystal, and the preparation method thereof comprises:

[0066] (1) Dissolution: 0.2 g of iridium acetate, 0.1 g of iridium trichloride, and 0.50 g of 1,2-hexadecanediol were added to 100 mL of oleylamine, and heated to 150° C. under a N2 atmosphere. The mixture was dissolved to form a clear solution C, i.e., the third precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0067] (2) Reaction: After keeping solution C at 150°C for 1 hour, further heat it to 240°C. Quickly inject the cobalt salt solution into the solution C at 240°C to form a fourth precursor solution. Keep the fourth precursor solution at 240°C for 2 hours. The color of the fourth precursor solution gradually turns black. Finally, cool it to room temperature.

[0068] (3) Separation: The cooled fourth precursor solution was centrifuged at a high speed of 18,000 rpm for 30 min to separate into a centrifuge solution and a centrifuge precipitate. The centrifuge precipitate was washed three times with ethanol and acetone, and dried at 80°C in a vacuum overnight to collect cobalt-iridium nanocrystals S13. TEM characterization of sample S13 is shown in FIG. Figure 3 shown.

[0069] Example 1

[0070] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0071] (1) Dissolution: 0.2 g of iridium acetate, 0.1 g of iridium trichloride, and 0.50 g of 1,2-hexadecanediol were added to 88 mL of oleylamine, and 12 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a basic cobalt carbonate solution.

[0072] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0073] (3) Separation: The cooled second precursor solution was centrifuged at a high speed of 18,000 rpm for 30 min to separate the centrifuge solution and the centrifuge precipitate. The centrifuge precipitate was washed three times with ethanol and acetone, and dried overnight at 80°C in a vacuum oven to collect the cobalt-iridium nanocrystal sample S1. The TEM characterization results of sample S1 are shown in FIG. Figure 1 shown.

[0074] In the above method, the volume of the centrifuge liquid is 10% of the total volume of the second precursor.

[0075] Example 2

[0076] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0077] (1) Dissolution: 0.2 g of iridium acetate, 0.1 g of iridium trichloride, and 0.50 g of 1,2-hexadecanediol were added to 64 mL of oleylamine, and 36 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0078] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0079] (3) Separation: The cooled second precursor solution was centrifuged at a high speed of 18,000 rpm for 30 min to separate the centrifuge solution and the centrifuge precipitate. The centrifuge precipitate was washed three times with ethanol and acetone, and dried overnight at 80°C in a vacuum oven to collect the cobalt-iridium nanocrystal sample S2. The TEM characterization results of sample S2 are shown in FIG. Figure 2 shown.

[0080] In the above method, the volume of the centrifuge liquid is 30% of the total volume of the second precursor.

[0081] Example 3

[0082] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0083] (1) Dissolution: 0.2 g of iridium acetate, 0.12 g of iridium tetrachloride hydrate, and 0.50 g of 1,2-hexadecanediol were added to 88 mL of oleylamine, and 12 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve the mixture to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0084] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0085] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80°C overnight to collect a cobalt-iridium nanocrystal sample S3.

[0086] In the above method, the volume of the centrifuge liquid is 10% of the total volume of the second precursor.

[0087] Example 4

[0088] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0089] (1) Dissolution: 0.2 g of iridium acetate, 0.12 g of iridium tetrachloride hydrate, and 0.50 g of 1,2-hexadecanediol were added to 64 mL of oleylamine, and 36 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0090] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0091] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80° C. overnight to collect a cobalt-iridium nanocrystal sample S4.

[0092] In the above method, the volume of the centrifuge liquid is 30% of the total volume of the second precursor.

[0093] Example 5

[0094] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0095] (1) Dissolution: 0.2 g of iridium acetate, 0.1 g of iridium trichloride, 0.31 g of hexadecyltrimethylammonium bromide, and 0.25 g of 1,2-hexadecanediol were added to 88 mL of oleylamine, and 12 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0096] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0097] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80°C overnight to collect a cobalt-iridium nanocrystal sample S5.

[0098] In the above method, the volume of the centrifuge liquid is 10% of the total volume of the second precursor.

[0099] Example 6

[0100] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0101] (1) Dissolution: 0.2 g of iridium acetate, 0.1 g of iridium trichloride, 0.31 g of hexadecyltrimethylammonium bromide, and 0.25 g of 1,2-hexadecanediol were added to 64 mL of oleylamine, and 36 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0102] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0103] (3) Separation: The cooled second precursor solution was centrifuged at a high speed of 18,000 rpm for 30 min to separate into a centrifuge liquid and a centrifuge precipitate. The centrifuge precipitate was washed three times with ethanol and acetone, and dried overnight at 80°C in a vacuum oven to collect a cobalt-iridium nanocrystal sample S6.

[0104] In the above method, the volume of the centrifuge liquid is 30% of the total volume of the second precursor.

[0105] Example 7

[0106] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0107] (1) Dissolution: 0.2 g of iridium acetate, 0.12 g of iridium tetrachloride hydrate, 0.31 g of hexadecyltrimethylammonium bromide, and 0.25 g of 1,2-hexadecanediol were added to 88 mL of oleylamine, and 12 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0108] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0109] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80° C. overnight to collect a cobalt-iridium nanocrystal sample S7.

[0110] In the above method, the volume of the centrifuge liquid is 10% of the total volume of the second precursor.

[0111] Example 8

[0112] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0113] (1) Dissolution: 0.2 g of iridium acetate, 0.12 g of iridium tetrachloride hydrate, 0.31 g of hexadecyltrimethylammonium bromide, and 0.25 g of 1,2-hexadecanediol were added to 64 mL of oleylamine, and 36 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0114] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0115] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80°C overnight to collect a cobalt-iridium nanocrystal sample S8.

[0116] In the above method, the volume of the centrifuge liquid is 30% of the total volume of the second precursor.

[0117] Example 9

[0118] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0119] (1) Dissolution: 0.2 g of iridium acetate, 0.05 g of iridium trichloride, 0.06 g of iridium tetrachloride hydrate, and 0.50 g of 1,2-hexadecanediol were added to 88 mL of oleylamine, and 12 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0120] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0121] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80°C overnight to collect a cobalt-iridium nanocrystal sample S9.

[0122] In the above method, the volume of the centrifuge liquid is 10% of the total volume of the second precursor.

[0123] Example 10

[0124] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0125] (1) Dissolution: 0.2 g of iridium acetate, 0.05 g of iridium trichloride, 0.06 g of iridium tetrachloride hydrate, and 0.50 g of 1,2-hexadecanediol were added to 64 mL of oleylamine, and 36 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0126] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0127] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80° C. overnight to collect a cobalt-iridium nanocrystal sample S10.

[0128] In the above method, the volume of the centrifuge liquid is 30% of the total volume of the second precursor.

[0129] Embodiment 11

[0130] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0131] (1) Dissolution: 0.2 g of iridium acetate, 0.15 g of ammonium chloroiridate, and 0.50 g of 1,2-hexadecanediol were added to 88 mL of oleylamine, and 12 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0132] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0133] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80° C. overnight to collect a cobalt-iridium nanocrystal sample S11.

[0134] In the above method, the volume of the centrifuge liquid is 10% of the total volume of the second precursor.

[0135] Example 12

[0136] This embodiment provides a cobalt-iridium nanocrystal, and the preparation method thereof includes:

[0137] (1) Dissolution: 0.2 g of iridium acetate, 0.15 g of ammonium chloroiridate, 0.06 g of iridium tetrachloride hydrate, and 0.50 g of 1,2-hexadecanediol were added to 64 mL of oleylamine, and 36 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0138] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0139] (3) Separation: The cooled second precursor solution was subjected to high-speed centrifugation at a centrifugal speed of 18,000 rpm for 30 min to separate into a centrifugal solution and a centrifugal precipitate. The centrifugal precipitate was repeatedly washed with ethanol and acetone for 3 times, and vacuum dried at 80°C overnight to collect a cobalt-iridium nanocrystal sample S12.

[0140] In the above method, the volume of the centrifuge liquid is 30% of the total volume of the second precursor.

[0141] Comparative Example 2

[0142] This comparative example provides a cobalt-iridium nanocrystal, and the preparation method thereof comprises:

[0143] (1) Dissolution: 0.2 g of iridium acetate, 0.1 g of iridium trichloride, and 0.50 g of 1,2-hexadecanediol were added to 52 mL of oleylamine, and 48 mL of the centrifuged liquid in Comparative Example 1 was added, and the mixture was heated to 150° C. under a N2 atmosphere to dissolve the mixture to form a clear solution A, i.e., the first precursor. Then, 0.3 g of basic cobalt carbonate was dissolved in 20 mL of oleylamine at 100° C. to form a clear basic cobalt carbonate solution.

[0144] (2) Reaction: Solution A was kept at 150°C for 1 hour and then further heated to 240°C. The basic cobalt carbonate solution was quickly injected into the above-mentioned solution A at 240°C to obtain a second precursor solution. The second precursor solution was kept at 240°C for 2 hours, and the color of the solution gradually turned black. Finally, it was cooled to room temperature.

[0145] (3) Separation: The cooled second precursor solution was centrifuged at a high speed of 18,000 rpm for 30 min, and the separation was divided into one centrifugation and centrifugal precipitation. The centrifugal precipitation was washed three times with ethanol and acetone, and dried at 80°C in vacuum overnight to collect the cobalt-iridium nanocrystal sample S14. The TEM characterization of sample S14 is shown in FIG. Figure 4shown.

[0146] In the above method, the volume of the centrifuge liquid is 40% of the total volume of the second precursor.

[0147] Comparative Example 3

[0148] This comparative example provides a cobalt-iridium nanocrystal, and its preparation method is similar to that of comparative example 2, except that the volume of the centrifugal liquid in this comparative example is 5% of the total volume of the second precursor.

[0149] Test Case

[0150] The yields of the cobalt-iridium nanocrystal samples of the above-mentioned embodiments and comparative examples were statistically analyzed, and the cobalt-iridium nanocrystal samples were subjected to structural characterization and performance testing.

[0151] 1. Product yield

[0152] Table 1 shows the raw material composition and dosage as well as the product yield during the synthesis of the cobalt-iridium nanocrystal samples in the above examples and comparative examples.

[0153] Table 1

[0154]

[0155]

[0156] As can be seen from Table 1, compared with the preparation method in Comparative Example 1 in which the raw material does not contain centrifugal liquid, the preparation method in Examples 1 to 12 by adding centrifugal liquid to the raw material can improve the product yield of cobalt-iridium nanocrystals, and the improved yield can reach more than 87%, and further can reach more than 90%.

[0157] Furthermore, it can be seen from Comparative Examples 2 and 3 that too little centrifuge liquid is added to the raw material, which has no effect on improving the product yield; too much centrifuge liquid added to the raw material will lead to a significant decrease in the product yield, and the present invention can maintain a high product yield by controlling the addition ratio of the centrifuge liquid within a reasonable range.

[0158] The above results show that the present invention can effectively improve the product yield of cobalt-iridium nanocrystals, improve the utilization rate of raw materials, and save preparation costs by adding centrifugal liquid to the raw materials and controlling the proportion of the centrifugal liquid in the raw materials.

[0159] 2. Structural characterization

[0160] Figure 1 This is a TEM photo of the cobalt-iridium nanocrystal sample of Example 1. Figure 2 This is a TEM photo of the cobalt-iridium nanocrystal sample of Example 2. Figure 3 This is a TEM photo of the cobalt-iridium nanocrystal sample of Comparative Example 1. Figure 4This is the TEM photo of the cobalt-iridium nanocrystal sample of Comparative Example 2.

[0161] from Figure 1 , Figure 2 It can be seen that the particle size of the cobalt-iridium nanocrystals prepared in Example 1 and Example 2 is 3-8 nm.

[0162] The amount of centrifuge added in the preparation process of Comparative Example 2 is higher than the amount of centrifuge added in the preparation method of the present invention. Figure 4 and Figure 1 and Figure 2 By comparison, it can be seen that excessive addition of centrifugal liquid will lead to obvious agglomeration between nanoparticles and irregular morphology of nanoparticles, thereby reducing the dispersibility of nanoparticles and reducing catalytic ability. However, the present invention can obtain nanoparticles with good monodispersity and regular morphology by controlling the amount of centrifugal liquid within a reasonable range, thereby improving the catalytic activity of nanoparticles.

[0163] The cobalt-iridium nanocrystals of Examples 1 to 12 all have a core-shell structure and are cobalt-iridium core-shell nanocrystals, wherein the core is a cobalt-iridium alloy formed by an organic salt of iridium and a cobalt salt, and the shell is an iridium single substance formed by reducing an inorganic salt of iridium.

[0164] Figure 5 The XRD patterns of the cobalt-iridium nanocrystal samples of Comparative Example 1 and Example 1 are shown in FIG. Figure 5 It can be seen that the crystallinity of the cobalt-iridium nanocrystal sample of Example 1 is higher than that of the cobalt-iridium nanocrystal sample of Comparative Example 1. This result can illustrate that the present invention can effectively improve the crystallinity of cobalt-iridium nanocrystals by adding centrifugal liquid during the preparation process of cobalt-iridium nanocrystals, thereby improving the catalytic activity.

[0165] 3. Performance testing

[0166] The catalytic activity of the oxygen evolution reaction of the cobalt-iridium nanocrystal (S1) of Example 1 and the cobalt-iridium nanocrystal (S13) of Comparative Example 1 was tested to obtain polarization curves. The specific testing method is as follows:

[0167] (1) Test samples Weigh 5 mg of the sample to be tested, add 250 μL of isopropanol and 250 μL of nafion diluent in sequence, and sonicate for 30 min to mix the slurry evenly;

[0168] (2) Take an appropriate amount of the dispersed slurry and evenly drop it onto the smooth and clean surface of the disk electrode, let it dry naturally, and use it as the working electrode;

[0169] (3) The test process used a three-electrode system with a rotating disk electrode speed of 1600 rpm. The catalyst was activated by cyclic voltammetry in a suitable voltage range until the catalyst reached a stable state, wherein the measurement was performed in the potential range of 1.23-1.60 V (relative to reversible hydrogen electrode, RHE) at a scan rate of 1 mVs-1.

[0170] Figure 6 is the polarization curve of oxygen evolution reaction of the above sample. Figure 6 It can be seen that when the amount of the sample to be tested is the same, the catalytic activity of the oxygen evolution reaction of the cobalt-iridium nanocrystal sample synthesized using the centrifugal liquid is higher than that of the cobalt-iridium nanocrystal synthesized without the centrifugal liquid. This result shows that the use of the centrifugal liquid as a raw material can effectively improve the activity of the cobalt-iridium nanocrystal.

[0171] Based on the above test results, it can be seen that the present invention can improve the morphological regularity, monodispersity, crystallinity and catalytic activity of oxygen evolution reaction of synthesized cobalt iridium nanocrystals by using the centrifugal liquid produced in the preparation process of cobalt iridium nanocrystals as raw material.

Claims

1. A method for preparing cobalt-iridium nanocrystals, the preparation method comprising: S1, mixing an iridium salt, an organic ligand, a reducing solvent and a centrifuge liquid, heating the mixture in a protective atmosphere to fully dissolve the iridium salt to form a first precursor, and keeping the first precursor warm; S2, heating the first precursor in a protective atmosphere and mixing it with a cobalt salt to form a second precursor, keeping the second precursor warm for reaction, centrifuging, and washing the centrifugal precipitate to obtain the cobalt-iridium nanocrystals; The centrifuge is the centrifuge obtained during the centrifugation of S2, or the preparation method of the centrifuge comprises: mixing an iridium salt, an organic ligand and a reducing solvent, heating the mixture in a protective atmosphere to fully dissolve the iridium salt to form a third precursor, and keeping the third precursor warm; mixing the third precursor with a cobalt salt in a protective atmosphere to form a fourth precursor, heating the fourth precursor to react, and centrifuging to obtain the centrifuge; The volume proportion of the centrifugal liquid in the second precursor is greater than 5% and less than 40%.

2. The preparation method according to claim 1, wherein The volume proportion of the centrifugal liquid in the second precursor is greater than or equal to 8% and less than 40%; The volume proportion of the centrifugal liquid in the second precursor is greater than or equal to 10% and less than 40%; The volume proportion of the centrifuge liquid in the second precursor is 10%-30%.

3. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the iridium salt comprises a combination of an inorganic salt of iridium and an organic salt of iridium; Preferably, the iridium salt comprises a combination of at least one of iridium trichloride, iridium tetrachloride, chloroiridic acid, and ammonium chloroiridate and iridium acetate; Preferably, the molar ratio of the organic salt of iridium to the inorganic salt of iridium is 0.8-2.

4. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the organic ligand comprises a long-chain compound having 12 to 16 carbon atoms and containing a hydroxyl group and / or an amine group; Preferably, the organic ligand includes one or a combination of two or more of hexadecandiol, dodecanediol, hexadecyltrimethylammonium bromide and hexadecyltrimethylammonium chloride.

5. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the reducing solvent includes oleylamine.

6. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the cobalt salt includes one or a combination of two or more of cobalt acetate, cobalt sulfate, cobalt chloride, cobalt nitrate, and basic cobalt carbonate.

7. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the molar ratio of the cobalt salt to the iridium salt is 0.01-0.

8.

8. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the molar ratio of the organic ligand to the iridium salt is 0.1-5.

9. The preparation method according to claim 1, wherein In the second precursor and / or the fourth precursor, the molar ratio of the reducing solvent to the iridium salt is 350-500.

10. The preparation method according to claim 1, wherein: The sum of the holding time of the first precursor in S1 and the reaction time of the second precursor in S2 is less than or equal to 6 hours.

11. The preparation method according to claim 1, wherein: The reaction temperature of the second precursor and / or the fourth precursor is 200-280°C, preferably 230-250°C; The reaction time of the second precursor and / or the fourth precursor is 1.5h-2h.

12. The preparation method according to claim 1, wherein: S1, the heating temperature reaches 150-180°C, preferably 150-170°C.

13. A cobalt-iridium nanocrystal obtained by the preparation method according to any one of claims 1 to 12; Preferably, the particle size of the cobalt-iridium nanocrystals is 2nm-8nm.

14. A water electrolysis catalyst, comprising the cobalt-iridium nanocrystals according to claim 13 or made of the cobalt-iridium nanocrystals according to claim 13.

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