Preparation method of low-iridium-content catalyst for PEM electrolytic water anode oxygen evolution

Abstract

The invention discloses a preparation method of a low-iridium-content catalyst for PEM electrolyzed water anode oxygen evolution, and belongs to the field of PEM electrolyzed water. The method comprises the following steps: (1) dissolving a manganese salt, potassium permanganate and a cerium salt in water, adding an acid, adjusting the pH value to 3-7, uniformly stirring, and aging to form a uniform suspension; then transferring into a reaction kettle, and carrying out hydrothermal reaction; roasting by using a muffle furnace to obtain a cerium-manganese-based metal oxide carrier; (2) adding iridium salt into deionized water, stirring, and carrying out ultrasonic dispersion to obtain an iridium-containing precursor solution; and adding the iridium-containing precursor solution into the cerium-manganese-based metal oxide carrier suspension, stirring and mixing, then carrying out ball milling treatment, washing and drying to obtain the supported low-iridium-content catalyst, namely the low-iridium-content catalyst for PEM electrolytic water anode oxygen evolution. The use amount of Ir is reduced, more active sites of Ir are exposed, and the performance of the catalyst is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of PEM water electrolysis, in particular to a catalyst for anodic oxygen evolution in PEM water electrolysis, and more particularly to a preparation method of a catalyst for anodic oxygen evolution in PEM water electrolysis with low iridium content. BACKGROUND

[0002] With the rapid development of sustainable energy, green and clean hydrogen energy has become a research hotspot. As a kind of secondary clean energy, it has a wide source, high calorific value, is clean and carbon-free, can store energy, generate electricity and heat, is flexible and efficient, and has rich application scenarios. It is an important part of carbon neutral energy system and is considered as an ideal energy carrier to promote the clean and efficient use of traditional energy and the industrialization development of renewable energy. It is also the most promising energy to replace fossil fuels.

[0003] Through previous research, it is found that proton exchange membrane (PEM) water electrolysis is a very promising technology that can efficiently produce high-purity hydrogen. Therefore, developing high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts is the key to promoting the large-scale application of proton exchange membrane water electrolysis (PEMWE) for hydrogen production. So far, the best option for OER catalysts is still the noble metals iridium (Ir) and ruthenium (Ru), but the stability of Ru oxide is poor due to the formation of higher valence Ru oxide during the OER process. As a commercial electrocatalyst for anodic oxygen evolution reaction (OER) in proton exchange membrane (PEM) water electrolysis cells, IrO2 not only exhibits excellent catalytic performance, but also can maintain stability under strong acid and high corrosion conditions. However, it still has problems such as insufficient activity and scarcity of reserves, which increases the cost of the material. Due to the scarcity and high price of Ir, it is crucial to improve the OER activity and stability of Ir-based catalysts and develop low-Ir-loading catalysts. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a catalyst for anodic oxygen evolution in PEM water electrolysis with low iridium content. This method not only reduces the amount of Ir used, but also exposes more active sites to Ir, improving the performance of the catalyst.

[0005] The technical solution adopted by the present application is as follows:

[0006] A preparation method of a catalyst for anodic oxygen evolution in PEM water electrolysis with low iridium content, comprising the following steps:

[0007] (1) Synthesis of cerium-manganese-based metal oxide carrier;

[0008] Dissolve manganese salt, potassium permanganate and cerium salt in water, add acid to adjust the pH value to 3-7, stir uniformly, and age to form a uniform suspension;

[0009] Then, the hydrothermal reaction is carried out in a reaction kettle;

[0010] After the completion, the hydrothermal product is taken out after cooling, centrifuged, washed for multiple times, dried, calcined in a muffle furnace, and then a cerium-manganese-based metal oxide carrier is obtained.

[0011] (2) preparing a supported catalyst with low iridium content;

[0012] The cerium-manganese-based metal oxide carrier obtained in step (1) is dissolved in a solvent and ultrasonically dispersed to obtain a cerium-manganese-based metal oxide carrier suspension;

[0013] The iridium salt is added to deionized water and stirred and ultrasonically dispersed to obtain an iridium-containing precursor solution;

[0014] The iridium-containing precursor solution is added to the cerium-manganese-based metal oxide carrier suspension, stirred and mixed, then subjected to ball milling treatment, and then washed to obtain a supported catalyst with low iridium content, i.e., a low-iridium-content catalyst for PEM electrolytic water anode oxygen evolution.

[0015] Preferably, in step (1), the manganese salt is selected from any one or more than two combinations of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate; the cerium salt is selected from cerium nitrate; and the acid is one or more of acetic acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid.

[0016] Preferably, in step (1), the hydrothermal reaction temperature is 100-180℃, and the time is 1-12h.

[0017] Preferably, in step (1), the calcination is carried out in an air atmosphere, the calcination temperature is 350-380℃, and the calcination time is 3-4h.

[0018] Preferably, in step (1), the molar ratio of Ce / Mn in the cerium-manganese-based metal oxide carrier is Ce:Mn=0.1-2:10.

[0019] Preferably, in step (2), the iridium salt is selected from one or more of iridium chloride, chloroiridic acid and potassium chloroiridate.

[0020] Preferably, in step (2), after the iridium salt is added to deionized water and stirred, the pH value is adjusted to 3-4 by adding an acid, and then ultrasonic dispersion is carried out for 1-2h to obtain an iridium-containing precursor acidic solution.

[0021] Preferably, in step (2), the ball milling treatment is carried out in a ball mill, and the ball milling speed is controlled to be 100-500rmp for 2-12h.

[0022] Preferably, in step (2), the molar ratio of iridium to the total amount of cerium and manganese in the supported low-iridium-content catalyst is 3-30%. That is, the molar content of iridium in the catalyst accounts for 3%-30% of the molar content of the metal oxide.

[0023] Preferably, in step (2), the particle size of iridium oxide in the supported low-iridium-content catalyst is 10-15 nm.

[0024] The beneficial technical effects of the present application are as follows:

[0025] The present application provides a preparation method of a low-iridium-content catalyst for PEM electrolytic water anode oxygen evolution, which comprises the following steps: first, preparing a metal oxide carrier through aging, hydrothermal treatment and calcination; then, loading and ion exchanging through high-temperature high-speed ball milling to uniformly load / embed Ir atoms into the crystal lattice of the metal oxide, replace Mn atoms, and make the crystal lattice distorted to expose more sites, thereby improving the OER electrochemical performance.

[0026] The present application fully disperses the cerium-manganese-based metal oxide substrate through high-speed ball milling, increases the specific surface area of the substrate, fully exposes the sites, makes the ion exchange of iridium and metal more uniform, and solves the problem of iridium agglomeration. Moreover, the present application greatly reduces the iridium content in the catalyst, and the obtained catalyst has better performance than pure iridium oxide, can greatly reduce the cost of PEM electrolytic water catalyst, and improve the stability and electrochemical activity of the catalyst.

[0027] In the low-iridium-content acidic oxygen evolution electrocatalyst prepared by the present application, the metal oxide carrier is an alpha-CeMnO2 nanorod, and the particle size of the iridium oxide loaded on the surface is 10-15 nm.

[0028] The present application uses Ce as a local electronic structure regulator of Ir species and one-dimensional alpha-CeMnO2 nanorods as a carrier, and uses iridium ion exchange to prepare Ir highly dispersed IrCeMnO@Ir nanorods, and applies the same to acidic OER. The characterization and experimental results show that the ordered iridium atomic chain and randomly distributed iridium clusters in the IrCeMnO@Ir nanorods cause the destruction of structural symmetry and the reconstruction of spin electrons, resulting in more oxygen vacancies and active sites. Since Ce optimizes the electronic structure of iridium (Ir) to form a rich Ir(Ⅲ) surface, and inhibits the dissolution of active components by stabilizing the oxidation state of iridium during the OER process, and Mn accelerates the supply of electrons to Ir atoms through O bridge atoms, which is conducive to the adsorption of active oxygen intermediates, the IrCeMnO@Ir nanorods exhibit high activity and stable performance in acidic OER. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 SEM image of the catalyst IrCeMnO@Ir prepared in Example 1 of the present application;

[0030] Figure 2 SEM image of the catalyst IrMnO@Ir prepared for Comparative Example 1;

[0031] Figure 3 XRD image of the catalyst prepared for Example 1, Comparative Example 1 and metal oxide carrier. DETAILED DESCRIPTION

[0032] According to the existing research direction and technical development, in order to reduce the amount of Ir and improve the performance of the catalyst, the application provides a preparation method of a low-iridium-content catalyst for PEM electrolytic water anode oxygen evolution.

[0033] The application uses cerium (Ce) as an electron structure regulator of iridium and one-dimensional alpha-CeMnO2 nanorod as a carrier to prepare an Ir highly-dispersed IrCeMnO@Ir electrocatalyst by using iridium ion exchange method.

[0034] The application will be further described below in combination with the drawings and specific examples.

[0035] Example 1: Preparation of the catalyst IrCeMnO@Ir-20.

[0036] Preparation of the metal oxide carrier (alpha-CeMnO2 nanorod):

[0037] 0.2g of manganese sulfate monohydrate (MnSO4·H2O), 0.2g of Ce(NO3)3·6H2O and 0.5g of potassium permanganate (KMnO4) were dissolved in 50mL of deionized water, 2.5mL of HNO3 was added, and the mixture was stirred and aged at room temperature for 1h to form a uniform suspension, i.e., a mixed solution. Then the mixed solution was transferred into a reaction kettle, and hydrothermal reaction was carried out at 130℃ for 12h. After cooling, centrifugation was performed, and the sample was washed with deionized water three times and centrifuged, and then dried in an oven at 80℃. Then, the sample was calcined in a muffle furnace under air atmosphere at 350℃ for 3h to obtain alpha-CeMnO2 powder, which was used as a catalyst carrier.

[0038] Preparation of the IrCeMnO@Ir catalyst:

[0039] 60 mg of α-CeMnO2 powder was dispersed in 20 ml of ethanol, 25 mg of IrCl3·3H2O was dissolved in 20 ml of H2O, and then the two solutions were ultrasonically treated for 30 min, respectively. The aqueous solution of IrCl3 was injected into the suspension of α-CeMnO2 nanorods under vigorous stirring at room temperature, and then transferred into a 50-ml ball mill tank, 20 ZrO2 beads with Ф=25 mm were added into the ball mill tank, and high-temperature high-speed ball milling was performed at 350 rpm for 10 h. The product was collected by vacuum filtration and repeatedly washed with deionized water to obtain an iridium-based OER catalyst IrCeMnO@Ir with an iridium content of 20 wt.%.

[0040] Example 2: Preparation of the catalyst IrCeMnO@Ir-10.

[0041] The metal oxide carrier (α-CeMnO2 nanorods) was prepared as in Example 1.

[0042] Preparation of the IrCeMnO@Ir catalyst:

[0043] 60 mg of α-CeMnO2 powder was dispersed in 20 ml of ethanol, 12.5 mg of IrCl3·3H2O was dissolved in 20 ml of H2O, and then the two solutions were ultrasonically treated for 30 min, respectively. The aqueous solution of IrCl3 was injected into the suspension of α-CeMnO2 nanorods under vigorous stirring at room temperature, and then transferred into a 50-ml ball mill tank, 20 ZrO2 beads with Ф=25 mm were added into the ball mill tank, and high-temperature high-speed ball milling was performed at 350 rpm for 10 h. The product was collected by vacuum filtration and repeatedly washed with deionized water to obtain an iridium-based OER catalyst IrCeMnO@Ir with an iridium content of 10 wt.%.

[0044] Example 3:

[0045] The preparation method was the same as in Example 1, except that α-CeMnO2 powders with different Ce / Mn molar ratios were prepared by changing the amount of manganese salt and cerium salt added, and the Ce:Mn molar ratio was 0.1-2:10.

[0046] Comparative Example 1:

[0047] An Ir uniformly exchanged Mn low-iridium-content manganese-based oxide catalyst, the catalyst comprising Ir and Mn, and the carrier being a metal oxide MnO2, wherein the Ir content is 10 wt.%.

[0048] The preparation method is as follows:

[0049] Take 40 ml of deionized water in a beaker, weigh 1 g of manganese sulfate in a beaker, dissolve in deionized water, add 0.5M sulfuric acid, adjust the pH value range to 4-5 (about 8 ml of 0.5M sulfuric acid solution is added), ultrasonic and stir evenly. Take 40 ml of deionized water in another beaker, weigh 0.5 g of potassium permanganate in 40 ml of water, ultrasonic stirring for 1 h, pour the above potassium permanganate solution into the manganese sulfate solution, stir evenly, and place in a 100 ml polytetrafluoroethylene reactor at 120℃ for 12 h of high-temperature hydrothermal treatment. After reaction, take out and wash with deionized water and ethanol several times and separate. After drying in an oven, calcine in a muffle furnace at 350℃ in air atmosphere for 3 h to obtain α-MnO2 powder.

[0050] The oxide powder is added with water to prepare a suspension. Weigh 100 mg of iridium chloride in a beaker, add 50 ml of deionized water to the beaker, and add 0.5M hydrochloric acid solution to adjust the pH value range to 3-4 (about 12 ml of 0.5M hydrochloric acid is added), ultrasonic for 1 h to make it fully dissolved, pour it into the above manganese oxide suspension, stir vigorously, and place in a 100 ml ball mill tank, add 20 ZrO2 beads with Ф=25 mm to the 100 ml ball mill tank, set 350 rpm, time for 10 h, and perform high-temperature high-speed ball milling. Then wash with water, filter and dry to obtain IrMnO@Ir catalyst.

[0051] Figure 1 SEM image of the catalyst IrCeMnO@Ir prepared in Example 1 of the application. Figure 2 SEM image of the catalyst IrMnO@Ir prepared in Comparative Example 1. Figure 3 XRD image of the catalysts prepared in Example 1 and Comparative Example 1, and the metal oxide carrier. Figures 1-2 From the SEM images of IrMnO@Ir and IrCeMnO@Ir NRs electrocatalysts, it can be seen that the nanorod structure of manganese dioxide is well maintained in the ion exchange reaction, but due to the embedding of Ir elements in the MnO2 lattice, surface element reorganization and Ir cluster deposition occur, and IrMnO@Ir forms a rougher surface. Due to the ion exchange reaction, the whiskers on the surface of the α-CeMnO2 nanorods dissolve and coarsen, forming an irregular rough surface. These rough surfaces can act as bubble nucleation points, while the accumulated one-dimensional nanorod pore structure is conducive to the rapid release of oxygen bubbles during the OER process, which is conducive to mass transfer and diffusion at high current density.

[0052] Figure 3The powder XRD patterns of metal oxide support α-MnO2, α-CeMnO2 and comparative examples and the Ir-based catalysts IrMnO@Ir and IrCeMnO@Ir NRs prepared by the respective examples were compared. No characteristic peaks related to Ir or Ce were detected in the XRD patterns of the α-CeMnO2, IrMnO@Ir and IrCeMnO@Ir NRs electrocatalysts, demonstrating that the Ir / Ce elements were doped into the crystal lattice of the MnO2 crystals, or were supported on the surface of the MnO2 crystals in the form of extremely small nanoparticles, and no phase separation or mixed phase was produced due to ion exchange.

[0053] Electrochemical performance analysis:

[0054] The electrochemical performance test of the catalyst was evaluated using an electrochemical workstation (CHI760e) and a rotating disk electrode. A glassy carbon electrode, a saturated calomel electrode (SCE) and a graphite rod formed a three-electrode system, and the electrolyte was 0.1M HCIO4, and the test temperature was 25℃. The OER test was carried out in 0.1M HCIO4 solution saturated by oxygen bubbling treatment. Test method: in the test interval of 0.7-1.7V vs. SCE, the scanning activation was carried out by cyclic voltammetry (CV) at a scanning rate of 50mV·s -1 , and a rotation speed of 1600rpm. Then CV test was carried out in the same interval (scanning rate: 5.0mV·s -1 ) to test the polarization curve of the working electrode. The OER performance of the IrMnO@Ir and IrCeMnO@Ir catalysts was evaluated by linear sweep voltammetry, and commercial IrO2 was used as a reference. The results are shown in Table 1. Table 1 is the electrochemical characterization results of the OER of the electrocatalyst samples prepared in Example 1 and Comparative Example 1.

[0055] Table 1

[0056]

[0057] As seen from Table 1, the OER polarization curve onset potentials of IrCeMnO@Ir and IrMnO@Ir are 1.43 and 1.45 V vs. RHE, respectively, which are significantly lower than that of commercial IrO2(1.49 V vs. RHE). The charge transfer resistance (Rct) of IrCeMnO@Ir (~6.8 Ω) and IrMnO@Ir (~12.4 Ω) are significantly lower than that of commercial IrO2(~65.8 Ω). This is because Ir is doped into the MnO2lattice by ion exchange and forms Ir nanoclusters on the surface, thus reducing the activation energy barrier, so that IrMnO@Ir and IrCeMnO@Ir have superior OER kinetics and electrochemical activity. In order to understand the intrinsic electrocatalytic activity of the catalyst, the electrochemically active surface area is also evaluated in Table 1. According to the commonly used specific capacitance value (C*≈35 μF cm -2 ), the ECSA of IrCeMnO@Ir, IrMnO@Ir and commercial IrO2are ~60.9, ~24.7 and ~59.2 m 2 g -1 , respectively. From the comprehensive comparison of the data in Table 1, the IrCeMnO@Ir prepared in the embodiments of the present application has excellent performance.

[0058] Finally, it should be noted that: the above description of the embodiments is only applicable to help understand the method of the present application and its core idea, and is not limited to the technical solutions described in the present application. Therefore, although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present application can still be modified or replaced by equivalents, and the obvious changes or variations derived therefrom should be covered in the scope of the claims of the present application.

Claims

1. A method for the preparation of a low iridium content catalyst for the anodic oxygen evolution in PEM electrolysis of water, characterized in that The method comprises the following steps: (1) synthesizing a cerium-manganese-based metal oxide carrier; Dissolve manganese salt, potassium permanganate and cerium salt in water, add acid to the solution to adjust the pH value to 3-7, stir uniformly, and age to form a uniform suspension; Then transfer to a reaction kettle to perform hydrothermal reaction; After completion, take out the hydrothermal product, centrifugal filter, wash repeatedly, dry, and then calcine in a muffle furnace to obtain the cerium-manganese-based metal oxide carrier; (2) preparing a supported low-iridium-content catalyst; Dissolve the cerium-manganese-based metal oxide carrier obtained in step (1) in a solvent, ultrasonic disperse to obtain a cerium-manganese-based metal oxide carrier suspension; Stir and ultrasonic disperse iridium salt in deionized water to obtain an iridium-containing precursor solution; Add the iridium-containing precursor solution to the cerium-manganese-based metal oxide carrier suspension, stir and mix, then perform ball milling treatment, and then wash to obtain the supported low-iridium-content catalyst, i.e. a low-iridium-content catalyst for PEM electrolytic water anode oxygen evolution.

2. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (1), the manganese salt is selected from any one or more than two combinations of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate; the cerium salt is selected from cerium nitrate; and the acid is one or more of acetic acid, sulfuric acid, hydrochloric acid, nitric acid and perchloric acid.

3. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (1), the hydrothermal reaction temperature is 100-180℃, and the time is 1-12h.

4. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (1), the calcination is performed in an air atmosphere, the calcination temperature is 350℃-380℃, and the calcination time is 3-4h.

5. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (1), the molar ratio of Ce / Mn in the cerium-manganese-based metal oxide carrier is Ce:Mn=0.1-2:

10.

6. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (2), the iridium salt is selected from one or more of iridium chloride, chloroiridic acid and potassium chloroiridate.

7. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (2), after the iridium salt is added to deionized water and stirred, the pH value is adjusted to 3-4 by adding acid, and then ultrasonic dispersion is performed for 1-2h to obtain an iridium-containing precursor acidic solution.

8. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (2), the ball milling treatment is performed in a ball mill, and the ball milling speed is controlled to be 100-500rmp for 2-12h.

9. A method for preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (2), the molar ratio of iridium to the total amount of cerium and manganese in the supported low-iridium-content catalyst is 3-30%.

10. A method of preparing a low iridium content PEM electrolyzer anode oxygen evolution catalyst according to claim 1, characterized by, In step (2), the particle size of iridium oxide in the supported low-iridium-content catalyst is 10-15nm.

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