Preparation method and application of iridium-based electrocatalyst

Abstract

The application belongs to the technical field of electrocatalysts, and discloses a preparation method of an iridium-based electrocatalyst and application thereof. The preparation method comprises the following steps: mixing a triblock polymer, a metal salt containing anions, and a solvent to obtain a mixture; adding soluble Ir salt and other metal salts into the mixture, stirring, adding a reducing agent solution containing the triblock polymer, reacting, separating, obtaining a pre-synthesized iridium-based oxide, and calcining to obtain the iridium-based electrocatalyst; the triblock polymer contains polyethylene glycol and polypropylene glycol structural units; the anions in the metal salt containing anions are selected from at least one of NO3 ‑ , SO4 2‑ , HPO4 2‑ , COOH ‑ , F ‑ , Cl ‑ , I ‑ , Br ‑ , ClO4 ‑ , and SCN ‑ . The iridium-based electrocatalyst has ideal controllable morphology and crystal structure, can realize high porosity and large specific surface area, and further improves the electrocatalytic activity and stability of the iridium-based electrocatalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysts, and particularly relates to a preparation method of an iridium-based electrocatalyst and application thereof. BACKGROUND

[0002] As an ideal secondary energy, hydrogen can be prepared, stored, transported and used in a zero-carbon emission environment, and has a high energy density (140 MJ / Kg), which is the most potential energy carrier in the twenty-first century. The proton exchange membrane water electrolysis (PEMWE) hydrogen production technology has also been highly concerned in the hydrogen production field due to its compact system design, fast reaction speed, and the advantages of producing high-purity hydrogen at high pressure to reduce hydrogen compression cost. Among them, iridium oxide is widely used as an oxygen evolution side electrocatalyst in electrolytic cells due to its excellent stability and high oxygen evolution catalytic activity. However, as a noble metal element, iridium is difficult to smelt due to its low content in the earth's crust, which restricts its more extensive application. Therefore, it is urgent to optimize and control the preparation process of the iridium-based electrocatalyst to improve the utilization rate and unit mass activity of iridium, thereby reducing the loading amount of iridium, improving the electrocatalytic efficiency, reducing the cost of hydrogen production, and promoting the commercialization development of water electrolysis.

[0003] The triblock polymer (TBP) surfactant soft template method is a reasonable and effective method for preparing electrocatalysts. This method provides a limited size of dynamic synthesis space for the reaction through the TBP soft template, so that the electrocatalyst material is synthesized and assembled in an integrated manner in a controllable region. However, because of the short-range order and limitations of TBP itself, the structure of the finally generated electrocatalyst cannot still maintain order in a large range, and the stability of the catalyst is poor; at the same time, in order to accommodate the template, the catalyst structure cannot be accurately designed according to the designer's intention.

[0004] Therefore, it is urgent to provide a new preparation method of a water electrolysis catalyst, which has high catalytic efficiency and good stability. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a preparation method of an iridium-based electrocatalyst and application thereof, which can controllably prepare the iridium-based electrocatalyst, so that the prepared iridium-based electrocatalyst has the advantages of high catalytic efficiency and good stability.

[0006] The inventive concept of the present application is that the preparation method introduces Hofmeister type anions, utilizes the Hofmeister effect and the difference in anion lyophilicity and hydrophobicity, and realizes the regulation of the micro-nano structure and morphology of the iridium-based electrocatalyst through the modification of the anions and the covalent or non-covalent interaction between the triblock polymer (TBP) and the iridium-based electrocatalyst, thereby solving the problem that the structure of the iridium-based catalyst material generated when the triblock polymer (TBP) is used as a surfactant soft template cannot be completely controlled due to the limitation of the template, so as to controllably prepare the iridium-based electrocatalyst, and the prepared iridium-based electrocatalyst has the advantages of high catalytic efficiency and good stability.

[0007] The first aspect of the present application provides a preparation method of an iridium-based electrocatalyst.

[0008] Specifically, the preparation method of the iridium-based electrocatalyst comprises the following steps:

[0009] (1) mixing a triblock polymer, a metal salt containing anions and a solvent to obtain a mixture;

[0010] (2) adding soluble Ir salt and other metal salts to the mixture in step (1), stirring and dissolving, then adding a reducing agent solution, reacting, separating, obtaining a pre-synthesized iridium-based oxide, and calcining to obtain the iridium-based electrocatalyst;

[0011] In step (1), the triblock polymer in step (1) contains polyethylene glycol and polypropylene glycol structural units.

[0012] In step (1), the anions in the metal salt containing anions are selected from at least one of NO3 - , SO4 2- , HPO4 2- , COOH - , F - , Cl - , I - , Br - , ClO4 - or SCN - .

[0013] The triblock polymer in step (1) is a non-ionic surfactant, and the anions in the metal salt containing anions in step (1) belong to Hofmeister type anions. The role of step (1) is to allow the triblock polymer to self-assemble into micelles with different structures under the regulation of the introduced anions.

[0014] Preferably, in step (1), the triblock polymer is selected from at least one of polyethylene glycol-polypropylene glycol-polyethylene glycol (PEG-PPG-PEG), polypropylene glycol-polyethylene glycol-polypropylene glycol (PPG-PEG-PPG), polyethylene glycol-polypropylene glycol-polyethylene glycol diacrylate, O,O'-bis(2-aminopropyl)polypropylene glycol-polyethylene glycol-polypropylene glycol.

[0015] Preferably, in step (1), the metal salt containing anions refers to alkali metal salt or alkaline earth metal salt containing anions.

[0016] Preferably, in step (1), the molar ratio of the triblock polymer and the metal salt containing anions is 1 / (500-5000); preferably 1 / (1000-3000).

[0017] Preferably, in step (1), the solvent is water, preferably deionized water.

[0018] Preferably, in step (1), the triblock polymer is Pluronic® developed by BASF. L31, L35, L61, L64, L121, P123, F68, F127 or F108.

[0019] wherein NO3 - , I - , Br - , ClO4 - and SCN - are called Chaotropic anions, because they have hydrophobicity and are not easy to adsorb the hydrophilic PEG shell in the triblock polymer, so that the hydrophilicity of the triblock polymer micelles is stronger. 2- , HPO4 2- , COOH - , F - and Cl - are called Kosmotropic anions, because they have hydrophilicity and can adsorb the hydrophilic PEG shell in the triblock polymer, so that the hydrophobicity of the triblock polymer micelles is stronger.

[0020] Specifically, wherein NO3 - , I - , Br - , ClO4 - and SCN - are called Chaotropic anions, when dispersed into the bulk water, because they have high polarizability and hydrophobicity, they can destroy hydrogen bonds and repel water molecules, which helps to increase the combination of interfacial water molecules and bulk water layer water molecules, enhance the hydration effect of the triblock polymer, promote the dispersion and solubility of the triblock polymer micelles.2- , HPO4 2- , COOH - , F - and Cl - are called Kosmotropic anions, because of their hydrophilicity, which can adsorb water molecules at the interface of the triblock copolymer, and weaken the binding force between the water molecules in the bulk and the water molecules in the hydration layer, and thus decrease the dispersion and solubility of the triblock copolymer micelles.

[0021] The different structure micelles in step (1) refer to micelles with different structures, such as spherical, sheet-like, nanorod-like, etc., which are formed due to the influence of different anions on the morphological structure, system stability, solution viscosity and surface tension of the triblock copolymer, which follows the Hofmeister sequence.

[0022] Preferably, in step (2), the soluble Ir salt is at least one selected from IrCl3, IrCl4, H2IrCl6 or K2IrCl6. The soluble Ir salt can also contain crystal water.

[0023] Preferably, in step (2), the other metal salt is an organic or inorganic salt of Sn, Ru, Pt, Mn, Fe, Co, Ni, Se, Mo or W. The other metal salt can also contain crystal water.

[0024] Further preferably, in step (2), the other metal salt is SnCl4 or CoCl2, which can or can not contain crystal water.

[0025] Preferably, in step (2), the total molar concentration of the soluble Ir salt and the other metal salt in the mixture is 0.001-0.5 mol / L, preferably 0.001-0.1 mol / L.

[0026] Preferably, in step (2), the molar ratio of Ir to the other metal in the mixture is 1:(0.1-5); preferably 1:(1-2).

[0027] Preferably, in step (2), the stirring temperature is 5-95°C, and the stirring time is 0.5-24 hours; further preferably, the stirring temperature is 25-85°C, and the stirring time is 2-20 hours.

[0028] Preferably, in step (2), the reducing agent solution is selected from NaBH4 or KBH4 solution.

[0029] Preferably, in step (2), the reducing agent solution can also contain the triblock copolymer.

[0030] Preferably, in step (2), the reducing agent solution is added to the reaction mixture to form a reaction mixture, and the BH4- The molar ratio of Ir to other metal is 10: (0.2-2), preferably 10:1.

[0031] Preferably, in step (2), the reaction temperature is 5-95℃, and the reaction time is 0.5-24 hours; further preferably, the reaction temperature is 25-85℃, and the reaction time is 2-20 hours.

[0032] Preferably, in step (2), the calcination temperature is 250-800℃, and the calcination time is 0.5-6 hours; further preferably, the calcination temperature is 450-550℃, and the calcination time is 1.5-2.5 hours.

[0033] In step (2), soluble Ir salt and other metal salt are added to the mixture in step (1), stirred and dissolved, and an initial iridium-based oxide seed Ir-Sn or Ir-M (M is selected from one of Ru, Pt, Mn, Fe, Co, Ni, Se, Mo, and W) is formed.

[0034] Preferably, in step (2), the separation process is as follows: after the reaction, the reacted substance is allowed to stand, separated, washed (the washing solution is anhydrous ethanol, water, isopropanol, or a mixture of two of them), dried, and ground to obtain the pre-synthesized iridium-based oxide.

[0035] Preferably, in step (2), the calcination process is carried out in an air or oxygen atmosphere. The purpose of calcination is to remove the triblock polymer (surfactant) and effectively control the crystallization degree and structure of the iridium-based oxide, and ultimately generate an anion-regulated iridium-based electrocatalyst (or iridium-based oxide powder).

[0036] The iridium-based electrocatalyst is named: SY-IrSnO x , S represents a surfactant (Surfactant), Y = N, S, P, C, F, Cl, I, Br, ClO, SCN, and the added metal salt anion is NO3 - , SO4 2- , HPO4 2- , COOH - , F - , Cl - , I - , Br - , ClO4 - , or SCN - .

[0037] The second aspect of the present application provides an iridium-based electrocatalyst.

[0038] An iridium-based electrocatalyst prepared by the preparation method.

[0039] The third aspect of the present application provides an application of the preparation method of the iridium-based electrocatalyst.

[0040] Specifically, the application of the preparation method of the iridium-based electrocatalyst in the field of electrochemistry.

[0041] Preferably, the field of electrochemistry includes any one of the fields of proton exchange membrane electrolysis, alkaline electrolysis, photoelectrocatalysis, and electrochemical reduction of carbon dioxide.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] (1) The present application starts from the hydrophobicity and hydrophilicity of polypropylene glycol (PPG) and polyethylene glycol (PEG) units in the triblock polymer, utilizes the Hofmeister effect, and adds specific anions according to the requirements to change the structure and micellar aggregation state of the PPG and PEG units, and thus controllably changes the morphology and performance of the prepared iridium-based electrocatalyst. The obtained iridium-based electrocatalyst forms structures with different morphological characteristics under the regulation and modification of different anions on the triblock polymer. Therefore, adding appropriate anions to the triblock polymer can make the iridium-based electrocatalyst have an ideal controllable morphology and crystal structure, and can realize the advantages of high porosity and large specific surface area, and thus improve the electrocatalytic activity and stability of the iridium-based electrocatalyst.

[0044] (2) The raw material triblock polymer used in the preparation method of the present application is a mature commercial product, which is economically feasible, has little environmental pollution, and is biocompatible. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The structure diagram of the micelles of the triblock polymer in the aqueous solution when no anion is added in Comparative Example 1 is shown in the figure;

[0046] Figure 2 The structure diagram of the micelles of the triblock polymer in the aqueous solution after modification by the Chaotropic type anion in Example 1 is shown in the figure;

[0047] Figure 3 The structure diagram of the micelles of the triblock polymer in the aqueous solution after modification by the Kosmotropic type anion in Example 2 is shown in the figure;

[0048] Figure 4 The transmission electron microscope (TEM) images of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2 are shown in the figures;

[0049] Figure 5Cyclic voltammetry (CV) curves of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2;

[0050] Figure 6 Linear sweep (LSV) curves of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2;

[0051] Figure 7 The percentage decrease in oxygen evolution activity of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2 after accelerated stability testing;

[0052] Figure 8 Linear sweep (LSV) curves of the iridium-based electrocatalysts prepared in Comparative Example 2 and Example 3 before and after accelerated stability testing. Detailed Implementation

[0053] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0054] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0055] Example 1

[0056] A method for preparing an iridium-based electrocatalyst includes the following steps:

[0057] Take a certain amount of triblock polymer TBP ( F108)(PEG132PPG50PEG132, molecular weight 14600g / mol) and NaNO3 were dissolved in deionized water and stirred until completely dissolved to obtain a mixture. The mixture was transferred to an oil bath at 60°C, and H2IrCl6 and SnCl4 hydrates were added to allow the triblock polymer TBP ( The molar concentrations of F108, NaNO3, and total metal ions (Ir+Sn) reached 0.001 mol / L, 2 mol / L, and 0.1 mol / L, respectively, with a molar ratio of Ir / Sn = 1 / 1. After stirring at high speed in an oil bath at 60℃ for 6 hours, a 1 mol / L NaBH4 reducing agent solution was slowly added dropwise, with a molar ratio of BH4... - After stirring and reacting for 10 hours with a ratio of Ir + Sn = 10, the mixture was allowed to cool to room temperature and then centrifuged. The resulting solid was thoroughly washed with anhydrous ethanol / water, vacuum dried, and then carefully ground in an agate mortar to obtain a pre-synthesized iridium-based oxide. This pre-synthesized oxide was then transferred to a tube furnace and calcined at 500°C for 2 hours. Calcination removed residual surfactants and promoted the formation of the Ir-Sn composite oxide. Finally, the iridium-based electrocatalyst IrSnO was obtained.x (denoted as SN-IrSnO) x ).

[0058] Example 2

[0059] Compared with Example 1, in Example 2, NaCl was used instead of NaNO3 in Example 1, and the rest of the process was the same as in Example 1. In Example 2, an iridium-based electrocatalyst IrSnO was prepared. x (denoted as SCl-IrSnO) x ).

[0060] Example 3

[0061] Compared with Example 1, Example 3 used equimolar amounts F127 (PEO100PPO65PEO100, molecular weight 12600g / mol) was used instead of the one in Example 1. F108 was prepared by replacing SnCl4 hydrate in Example 1 with an equimolar amount of CoCl2 hydrate, with the remaining procedures being the same as in Example 1. Example 3 yielded the iridium-based electrocatalyst IrCoO. x (denoted as SN-IrCoO) x ).

[0062] Comparative Example 1

[0063] Compared to Example 1, Comparative Example 1 did not add NaNO3 solution, but the rest of the process was the same as in Example 1. The iridium-based electrocatalyst IrSnO prepared in Comparative Example 1 was... x (denoted as S-IrSnO) x ).

[0064] Comparative Example 2

[0065] Compared to Example 3, Comparative Example 2 did not add NaNO3 solution, but the rest of the process was the same as in Example 3. The iridium-based electrocatalyst IrCoO2 prepared in Comparative Example 2 was... x (denoted as S-IrCoO) x ).

[0066] Product effectiveness test

[0067] Figure 1 This is a schematic diagram of the micelle structure of the triblock polymer in aqueous solution without the addition of anions in Comparative Example 1. Figure 2 This is a schematic diagram of the micelle structure of the triblock polymer modified with Chaotropic anions in Example 1 in aqueous solution; Figure 3 This is a schematic diagram of the micelle structure of the triblock polymer modified with Kosmotropic anions in Example 2 in aqueous solution.

[0068] from Figures 1-3Hofmeister effect of anions. The triblock copolymer (polyethylene glycol-polypropylene glycol-polyethylene glycol, PEG-PPG-PEG) surfactant self-assembled into micelles with certain structure in aqueous solution without any anions added. The addition of Chaotropic anion NO3 - After modification, the micelle size of the triblock copolymer surfactant increased. This is because the addition of NO3 - reduces the repulsive force between the triblock copolymer micelles, reduces the critical micelle concentration (CMC), and promotes the growth of micelles. The iridium-based electrocatalyst synthesized via this micelle as a template has a more uniform spherical structure. The micelles of the triblock copolymer modified by Kosmotropic anion Cl - , compared with NO3 - , Cl - has a smaller ionic radius and polarity, can compete with water molecules with the hydrophilic group PEG of the triblock copolymer, increases the mutual adsorption and hydrophobicity of the triblock copolymer micelles. The iridium-based electrocatalyst synthesized by this micelle template has a larger particle size and is easy to agglomerate.

[0069] Figure 4 The transmission electron microscope (TEM) images of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2; Figure 4 (a) in FIG. 1 corresponds to the transmission electron microscope (TEM) image of the iridium-based electrocatalyst prepared in Comparative Example 1, Figure 4 (b) in FIG. 1 corresponds to the transmission electron microscope (TEM) image of the iridium-based electrocatalyst prepared in Example 1, Figure 4 (c) in FIG. 1 corresponds to the transmission electron microscope (TEM) image of the iridium-based electrocatalyst prepared in Example 2, Figure 4 λ in FIG. 1 represents the average particle size of the iridium-based electrocatalyst.

[0070] Figure 4 directly reflects Figures 1-3 the change in the structure and size of the triblock copolymer surfactant due to the difference in the added anions, leading to the change in the particle structure and size of the iridium-based electrocatalyst. It can be seen that, compared with the iridium-based electrocatalyst S-IrSnO x , the addition of Hofmeister anions significantly increases the particle size of the iridium-based electrocatalyst, the average particle size, and the iridium-based electrocatalyst S-IrSnO x <iridium-based electrocatalyst SN-IrSnO x <iridium-based electrocatalyst SC-IrSnO x . The addition of NO3 - and Cl -The sodium salts had average particle diameters of 13.1 and 78.3 nm, respectively. It is worth noting that, due to NO3... - The introduction of iridium-based electrocatalyst SN-IrSnO x The interparticle dispersion is better than that of the iridium-based electrocatalyst SCl-IrSnO x There have been significant improvements.

[0071] Figure 5 Cyclic voltammetry (CV) curves of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2; Figure 5 The test conditions were a scan rate of 50 mV·s. -1 The electrolyte solution is a 0.5 mol / L H₂SO₄ solution saturated with N₂. From... Figure 5 It can be seen that Ir is found at approximately 0.7V SCE (saturated calomel electrode). 3+ / Ir 4+ Redox peaks, iridium-based electrocatalyst SN-IrSnO in Example 1 x The larger peak current response value indicates that it has more electrochemical active sites.

[0072] Figure 6 Linear sweep (LSV) curves of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2; Figure 6 The test conditions were a scan rate of 2 mV·s. -1 The electrolyte solution is a 0.5 mol / L H₂SO₄ solution saturated with N₂. From... Figure 6 It can be seen that the addition of anions significantly affects the oxygen evolution activity of iridium-based electrocatalysts, with the oxygen evolution activity order being: iridium-based electrocatalyst SN-IrSnO x >Iridium-based electrocatalyst S-IrSnO x >Iridium-based electrocatalyst SCl-IrSnO x This indicates that, compared to the comparative example without added anions, iridium-based electrocatalyst S-IrSnO... x Example 1: NO3 was added - Anions can significantly reduce the oxygen evolution overpotential and improve the efficiency of the prepared iridium-based electrocatalyst SN-IrSnO. x The oxygen evolution electrocatalytic activity.

[0073] Figure 7 The percentage decrease in oxygen evolution activity of the iridium-based electrocatalysts prepared in Comparative Example 1, Example 1, and Example 2 after accelerated stability testing. Figure 7 The results show that the iridium-based electrocatalyst was tested under the following electrochemical stability conditions: 2000 cycles of CV, scan potential 0.4–1.4 V, and scan rate 100 mV·s. -1, electrolyte solution is N2 saturated 0.5 mol / L H2SO4 solution. Figure 7 It is shown that the oxygen evolution activity of the comparative example 1 iridium-based electrocatalyst S-IrSnOx, the example 1 iridium-based electrocatalyst SN-IrSnOx, and the example 2 iridium-based electrocatalyst SCl-IrSnOx is attenuated by -8.6%, 4.0%, and 4.1% respectively after the electrochemical stability test, wherein "-" represents an increase in performance. It is shown that the iridium-based electrocatalysts do not have obvious attenuation and have excellent oxygen evolution electrocatalytic stability.

[0074] Figure 8 Linear sweep (LSV) curves of the iridium-based electrocatalysts prepared in the comparative example 2 and the example 3 before and after the accelerated stability test. Figure 8 The linear sweep (LSV) curves in the accelerated stability test conditions of Figure 7 The corresponding accelerated stability test conditions are the same. Figure 8 The linear sweep (LSV) curves in the accelerated stability test conditions of Figure 6 The corresponding linear sweep (LSV) curves are tested under the same conditions, i.e., a scan rate of 2 mV·S -1 , and an electrolyte solution of N2 saturated 0.5 mol / L H2SO4 solution. From Figure 8 It can be seen that, due to the strong modification effect of the anion on the structure of the prepared iridium-based electrocatalyst, the addition of the anion NO3 - The example 3 iridium-based electrocatalyst SN-IrCoO x prepared with the assistance of the anion has a significantly higher oxygen evolution electrocatalytic activity compared to the comparative example 2 iridium-based electrocatalyst S-IrCoO x prepared without the addition of the anion. Moreover, the oxygen evolution electrochemical stability of the example 3 iridium-based electrocatalyst SN-IrCoO x has also been greatly improved.

Claims

1. A method for preparing an iridium-based electrocatalyst, characterized by, The method comprises the following steps: (1) mixing a triblock polymer, a metal salt containing anions and a solvent to obtain a mixture; (2) adding a soluble Ir salt and other metal salts to the mixture of step (1), stirring, then adding a reducing agent solution, reacting, separating, obtaining a pre-synthesized iridium-based oxide, and calcining to obtain the iridium-based electrocatalyst. In step (1), the metal salt containing anions refers to an alkali metal salt containing anions, and the anions are NO3 - ; In step (1), the triblock polymer is polyethylene glycol-polypropylene glycol-polyethylene glycol. In step (2), the other metal salt is selected from organic or inorganic salts of Sn, Mn, Fe, Co and Ni.

2. The production method according to claim 1, characterized by, In step (2), the soluble Ir salt is selected from at least one of IrCl3, IrCl4, H2IrCl6 and K2IrCl6.

3. The preparation method according to claim 1, characterized in that, In step (2), the total molar concentration of the soluble Ir salt and the other metal salt in the mixture is 0.001-0.5 mol / L.

4. The method of claim 1, wherein, In step (2), the reducing agent solution is selected from NaBH4 or KBH4 solution in which the triblock polymer of step (1) is dissolved.

5. The preparation method according to claim 1, characterized in that, In step (2), the reaction temperature is 5-95℃, and the reaction time is 0.5-24 hours.

6. The method of claim 1, wherein, In step (2), the calcination temperature is 250-800℃, and the calcination time is 0.5-6 hours.

7. An iridium-based electrocatalyst characterized in that, The iridium-based electrocatalyst is prepared by the method of any one of claims 1-6.

8. The iridium-based electrocatalyst prepared by the method of any one of claims 1-6 or the iridium-based electrocatalyst of claim 7 for use in the field of electrolysis of water.

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