An ultrathin iridium-based nanosheet catalyst, a preparation method and application thereof

Abstract

The application discloses a simple preparation method of an iridium-based (Ir-M, M=Fe, Co, Ni) ultrathin nanosheet catalyst, which comprises the following steps: preparing a metal precursor solution; generating nanosheets through high-temperature hydrothermal reaction; and washing and drying the catalyst to obtain an ultrathin nanosheet structure catalyst. The obtained iridium-based nanosheet has excellent anode and cathode water electrolysis catalytic performance in an acidic medium. Compared with commercial catalysts (Pt / C-η10=30 mV, IrO2-η10=313 mV), the nanosheet structure has a much lower overpotential (η OER =223 mV; η HER =19 mV) and a stable water electrolysis capacity (over 30 hours) when catalyzing HER and OER reactions. The high-efficiency iridium-based nanosheet with a water electrolysis nearly 100% energy conversion efficiency makes it possible to realize large-scale production of water electrolysis of high-energy-density hydrogen energy.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation and application in electrocatalytic water electrolysis for hydrogen production, and particularly to an ultrathin iridium-based nanosheet catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen is widely considered a practical alternative energy source to polluting fossil fuels, and an attractive and simple method for producing hydrogen from abundant renewable resources is through water electrolysis. This involves two related electrochemical reactions in the electrolyzer: the oxygen evolution reaction (OER) at the anolyte and the hydrogen evolution reaction (HER) at the catholyte. Proton exchange membrane (PEM) water electrolyzers offer significant advantages over alkaline electrolyzers, including higher voltage and higher gas purity. To achieve efficient overall water electrolysis for hydrogen production in a PEM electrolyzer, OER and HER electrocatalysts need to be coupled in an acidic environment. Despite significant progress in developing bifunctional water-splitting electrocatalysts for alkaline electrolytes, acidic environments remain a challenge. While many transition metal derivatives exhibit high efficiency for both OER and HER in alkaline environments, a significant drawback is their dissolution in acidic environments, leading to limited long-term water-splitting capabilities.

[0003] Two-dimensional metals are a class of nanomaterials that are not yet fully developed, but due to their excellent electrical conductivity and the ability to achieve the highest material utilization efficiency by utilizing the interfacial electronic effects of exposed surface atoms in their structures, they have become a highly attractive target for catalytic applications in recent years. Iridium (Ir) metal is an important electrocatalyst in the oxygen evolution reaction (OER) under acidic conditions because it can operate at low overpotentials while still maintaining high stability. Therefore, various Ir-based materials, such as nanoframeworks and core-shell structures, have been studied in OER applications, but there are relatively few reports on Ir-based two-dimensional nanosheet materials.

[0004] Based on the above reasons, it is necessary to design and apply two-dimensional ultrathin iridium-based nanosheets to address the current design and synthesis problems of iridium-based acidic water electrolysis catalysts. Summary of the Invention

[0005] Based on the above reasons, and in view of the problems or defects existing in the prior art, the purpose of this invention is to provide an ultrathin iridium-based nanosheet catalyst, its preparation method and application, so as to solve the technical problems of efficient energy conversion and long-term stability of water electrolysis in harsh acidic environments in the prior art.

[0006] In a first aspect, in order to achieve the first objective of the present invention, the technical solution adopted by the present invention is as follows:

[0007] An ultrathin iridium-based nanosheet catalyst, wherein the catalyst is any one or more of Ir-Fe, Ir-Co, or Ir-Ni.

[0008] Secondly, the present invention provides a method for preparing the above-described ultrathin iridium-based nanosheet catalyst, comprising the following steps:

[0009] The precursors of noble metal Ir and non-noble metal M are mixed and dissolved in deionized water to obtain metal precursor solution A.

[0010] The metal precursor solution A is mixed with the reducing agent solution B, and then a surfactant is added to obtain a mixture C.

[0011] The mixture C was transferred to a hydrothermal reactor and reduced using a hydrothermal method.

[0012] The hydrothermal reactor was naturally cooled to room temperature, the product was removed, centrifuged, washed, and dried to obtain the ultrathin iridium-based nanosheet catalyst.

[0013] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the type of precursor of the noble metal Ir is not limited, and can be at least one of iridium acetylacetonate, iridium chloride, iridium acetate or chloroiridium acid.

[0014] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the precursor of the non-noble metal M includes at least one of ferric chloride or ferric nitrate, cobalt chloride or cobalt nitrate, nickel chloride or nickel nitrate, etc.

[0015] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the molar ratio of the noble metal Ir precursor to the non-noble metal M precursor is 1.

[0016] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the reducing agent in the reducing agent solution B includes an organic alcohol, an aqueous solution of glyoxal, and sodium citrate; wherein the ratio of the organic alcohol, the aqueous solution of glyoxal, and sodium citrate is 6 parts by volume: 0.2 parts by volume: (30-50) parts by mass, and the ratio of parts by volume to parts by mass is based on mL: mg.

[0017] Specifically, the reducing agent solution B used in this invention plays the role of dispersing metal ions to reduce them under hydrothermal conditions to form an alloy.

[0018] More preferably, in the above technical solution, the organic alcohol is at least one of isopropanol, glycerol, isobutanol, or benzyl alcohol.

[0019] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the reducing agent solution B is prepared as follows: organic alcohol, glyoxal aqueous solution and sodium citrate are mixed according to the ratio and ultrasonically dispersed evenly to obtain reducing agent solution B.

[0020] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the surfactant is polyvinylpyrrolidone (PVP-K30).

[0021] More preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the mass ratio of the noble metal Ir precursor to the surfactant is 1:(2-3).

[0022] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the specific conditions for the hydrothermal reduction are: heating from room temperature to 180-200℃ at a rate of 5-10℃ / min and holding at that temperature for 7-10 hours.

[0023] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the washing specifically uses a mixed washing solution composed of acetone and ethanol or directly washes with ethanol three or more times to ensure complete removal of the surfactant.

[0024] Preferably, the volume ratio of acetone to ethanol is 20:1.

[0025] Preferably, in the preparation method of the ultrathin iridium-based nanosheet catalyst, the hydrothermal reactor should be selected to maintain the reaction solution accounting for 50-70% of the volume, more preferably 60%.

[0026] Thirdly, the present invention provides the application of the ultrathin iridium-based nanosheet catalyst described above, which can be used as a HER and / or OER catalyst for electrocatalytic water electrolysis in an acidic environment.

[0027] The present invention relates to an ultrathin iridium-based nanosheet catalyst, its preparation method, and its application, which has the following advantages over the prior art:

[0028] (1) The preparation method of the ultrathin iridium-based nanosheet catalyst of the present invention is achieved by a one-pot solvothermal method with medium-low temperature liquid phase control. The process is relatively simple and complete crystalline nanosheets can be obtained without high-temperature treatment. The preparation method of this application is simple in preparation process, relatively reduces energy consumption, and the closed condition helps to avoid toxic reaction systems (glyoxal, etc.) and minimizes environmental pollution.

[0029] (2) The ultrathin iridium-based nanosheet catalyst prepared by the present invention has a higher specific surface area and more active area compared with bulk particle catalysts, which can improve catalytic activity and material utilization efficiency. Therefore, the nanosheet catalyst prepared by the present invention is extremely active in HER and OER in acidic environment, can effectively reduce the cell voltage of water electrolysis for hydrogen production in acidic environment, and has excellent stability, which can save energy costs.

[0030] (3) The transition metal-doped ultrathin iridium nanosheet catalyst prepared by the present invention improves the activity of each active site by means of electronic structure and physicochemical properties, thereby enhancing the bifunctional activity in acidic media.

[0031] (4) The iridium-based nanosheet catalyst obtained in this invention possesses excellent catalytic performance for anode and cathode water electrolysis in acidic media, and is comparable to commercial catalysts (Pt / C-η). 10 =30mV, IrO2-η 10 Compared to 313 mV, this nanosheet structure exhibits a much lower overpotential (η) when catalyzing HER and OER reactions. OER =223mV; η HER =19mV) and a continuous and stable water electrolysis capability (over 30 hours). The highly efficient iridium-based nanosheets with a near 100% energy conversion efficiency in water electrolysis enable the large-scale production of high-energy-density hydrogen through water electrolysis. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the preparation method of the ultrathin iridium-based nanosheet catalyst of the present invention;

[0033] Figure 2 The XRD patterns of the ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention and the Ir nanosheets prepared in Comparative Example 1 are shown.

[0034] Figure 3 The images show SEM, TEM, and HR-TEM images of the surface morphology of the ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention and the Ir nanosheets prepared in Comparative Example 1.

[0035] Figure 4 The elemental distribution EDS-mapping diagram of the ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention;

[0036] Figure 5 The ultrathin iridium-based nanosheet catalyst IrNi nanosheets prepared in Example 1 of this invention, the Ir nanosheets prepared in Comparative Example 1, and commercial IrO2 were subjected to a three-electrode system in an acidic electrolyte at a scan rate of 5 mV / s.-1 The oxygen evolution reaction curve;

[0037] Figure 6 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention, the Ir nanosheets prepared in Comparative Example 1, and commercial Pt / C were compared in an acidic electrolyte three-electrode system at a scan rate of 5 mV / s. -1 The hydrogen evolution reaction curve;

[0038] Figure 7 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention and Pt / C-IrO2 were tested in an acidic electrolyte under a two-electrode system at a scan rate of 5 mV / s. -1 The reaction curve of the complete electrolysis of water was tested;

[0039] Figure 8 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention was tested at a known current density (0.15 A cm⁻¹). -2 The volumes of H2 (gray line) and O2 (black line) produced by water splitting in the theoretical (hollow diagram) and actual (solid diagram) scenarios are shown below. Detailed Implementation

[0040] Please refer to Figure 1 This invention provides a method for preparing an ultrathin iridium-based nanosheet catalyst, comprising: a step of preparing a metal precursor solution; a step of high-temperature hydrothermal generation of nanosheets; and a step of washing and drying the catalyst. The specific steps described above are as follows:

[0041] S1. Prepare precursor solutions A of noble metal (Ir) and non-noble metal M (M = one of Fe, Co, Ni, etc.);

[0042] S2. Mixed reducing agent solution B (organic alcohol, glyoxal aqueous solution and sodium citrate);

[0043] S3. Sonicately mix solutions A and B and add a surfactant to obtain mixture C;

[0044] S4. Preparation of nanosheets by hydrothermal reduction;

[0045] S5. Allow to cool naturally to room temperature, then centrifuge, wash with the washing liquid and dry to obtain the nanosheet catalyst.

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0047] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless otherwise stated, the numerical parameters listed in the specification are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0048] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0049] Example 1

[0050] This embodiment provides a method for preparing an ultrathin iridium-based nanosheet catalyst (IrNi nanosheets), including the following steps:

[0051] S1.1. Weigh out the following quantities of metal precursors: iridium acetylacetone (acac)3 (0.1 mmol, approximately 48.9 mg) and NiCl2 (0.1 mmol, approximately 25 mg), respectively. Add 12 mL of deionized water to dissolve and mix them. Sonicate at room temperature for 5 minutes to dissolve and disperse the metal precursor solution A.

[0052] S1.2. Measure 6 mL of benzyl alcohol B, 0.2 mL of glyoxal aqueous solution (mass percentage concentration of 40%), and 48 mg of sodium citrate monohydrate to obtain reducing agent solution B; mix metal precursor solution A and reducing agent solution B, add 100 mg of PVP-K30, and sonicate to obtain mixture C;

[0053] S1.3. Transfer the mixture C to a hydrothermal reactor and reduce it using a hydrothermal method; wherein: during the hydrothermal reduction, the temperature is increased from room temperature (about 25°C) to 180°C at a rate of 5°C / min and held for 10 hours; the hydrothermal reactor should be selected to maintain the reaction solution at 60% of its volume.

[0054] S1.4. After the reaction is completed, the hydrothermal reactor is naturally cooled to room temperature, the product is removed, centrifuged, washed, and dried to obtain the ultrathin iridium-based nanosheet catalyst (IrNi nanosheets); wherein: the washing solution is a mixture of acetone and ethanol in a volume ratio of 20 / 1, and washing is performed more than three times to ensure that PVP is completely removed; the drying is carried out in a drying oven at a drying temperature of 60℃.

[0055] Comparative Example 1

[0056] The preparation method of this comparative example of Ir nanosheets is basically the same as that of the IrNi nanosheets in Example 1, except that the non-noble metal precursor NiCl2 is not added in step S1.1 of this comparative example.

[0057] Structural and performance analysis:

[0058] Figure 2 The images show the XRD patterns of the ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 and the Ir nanosheets prepared in Comparative Example 1. Figure 2 It can be seen that IrNi nanosheets and Ir nanosheets have the same diffraction peaks, and Ni doping improves the cell parameters of Ir. Compared with Ir, Ni has a smaller atomic radius. Ni doping will make the cell parameters of Ir smaller, the lattice spacing smaller, and the diffraction peaks shift to the right. The test results are consistent with the theoretical results. Figure 2 The above matches perfectly.

[0059] Figure 3 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention... Figure 3 df) and Ir nanosheets prepared in Comparative Example 1 ( Figure 3 The surface morphology of IrNi nanosheets is shown in SEM (a, d), TEM (b, e) and HR-TEM (c, f). It can be seen that the obtained IrNi nanosheet catalyst is a wrinkled nanosheet. Compared with pure Ir nanosheets, the doping of Ni makes the Ir lattice slightly smaller, which is also in complete agreement with the XRD diffraction pattern.

[0060] Figure 4 The image shows the elemental distribution EDS-mapping diagram of the ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention. It can be seen that Ir and Ni elements are uniformly distributed on the nanosheets.

[0061] Figure 5The ultrathin iridium-based nanosheet catalyst IrNi nanosheets prepared in Example 1 of this invention, the Ir nanosheets prepared in Comparative Example 1, and commercial IrO2 (model I102673, >99.99%) were tested in an acidic electrolyte (0.5M H2SO4) under a three-electrode system (working electrode - glassy carbon electrode; counter electrode - graphite rod; reference electrode - saturated calomel electrode, with the catalyst to be tested coated on the surface of the glassy carbon electrode), at a scan rate of 5 mV / s. -1 The oxygen evolution reaction curve. (See the graph.) Figure 5 As shown, commercial IrO2, Ir-NS, and IrNi nanosheets at 10 mA cm⁻¹ -2 The overpotentials at these locations were 313 mV, 256 mV, and 223 mV, respectively, demonstrating the excellent electrocatalytic oxygen evolution reaction (OER) catalytic activity of the Ir and IrM (M = Fe, Co, Ni) ultrathin nanosheet structures. Moreover, the corresponding Tafel slopes showed that the IrNi nanosheets had the fastest OER reaction kinetics.

[0062] Figure 6 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention, the Ir nanosheets prepared in Comparative Example 1, and commercial Pt / C (model HPTO20, 20% Pt / C) were tested in an acidic electrolyte (0.5M H2SO4) under a three-electrode system (working electrode - glassy carbon electrode; counter electrode - graphite rod; reference electrode - saturated calomel electrode, wherein the catalyst to be tested was coated on the surface of the glassy carbon electrode) at a scan rate of 5 mV s. -1 The hydrogen evolution reaction curve. From Figure 6 As can be seen from the data, commercial Pt / C and nanosheet-structured Ir and IrNi ultrathin nanosheet structures exhibit performance at 10 mA cm⁻¹. -2 The overpotentials at the locations were 30 mV, 25 mV, and 19 mV, respectively. Compared to commercial electrocatalysts, the IrNi nanosheet catalyst prepared in Example 1 of this application has better hydrogen evolution activity.

[0063] Figure 7 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention and Pt / C-IrO2 were subjected to a two-electrode system in an acidic electrolyte (0.5 M H2SO4) at a scan rate of 5 mV / s. -1 The reaction curves for the complete water electrolysis test are shown. Specifically, in testing the water electrolysis performance of the catalyst nanosheets in Example 1, IrNi nanosheets were used for both the anode and cathode; in testing the water electrolysis performance of Pt / C-IrO2, a commercial Pt / C catalyst (model HPT020, 20% Pt / C) was used as the cathode and a commercial IrO2 (model I102673, >99.99%) was used as the anode. The polarization curves and stability test graphs are shown below. Figure 7 As shown.

[0064] from Figure 7 It can be seen that the commercially available catalyst Pt / C-IrO2, when applied to proton exchange membrane water electrolysis for hydrogen production, requires 1.69V to drive the entire water electrolysis process to 10mA cm⁻¹. -2 The IrNi nanosheet catalyst obtained in this embodiment only requires 1.54V to achieve the same current density.

[0065] Figure 8 The ultrathin iridium-based nanosheet catalyst (IrNi nanosheets) prepared in Example 1 of this invention was tested at a known current density (0.15 A cm⁻¹). -2 The figures show the volumes of H2 (gray line) and O2 (black line) produced by water splitting in both theoretical (hollow diagram) and actual (solid diagram) scenarios. Comparative analysis shows that when IrNi nanosheets are used as electrocatalysts to promote water splitting, the volumes of the cathode (hydrogen) and anode (oxygen) match the theoretical volume ratio (2 / 1) with minimal deviation. This implies that the energy utilization efficiency is nearly 100%.

[0066] In summary, the ultrathin iridium-based nanosheet catalyst prepared in this application has a nanosheet thickness of approximately 2 nm. Compared to pure iridium nanosheets, the introduction of transition metals into the IrM (M = Fe, Co, Ni) ultrathin nanosheets allows for a relative reduction in the content of the noble metal iridium in acidic environments while maintaining or even improving electrocatalytic activity and durability. The introduction of base metals regulates the arrangement of iridium atoms in the nanosheets and adjusts the electronic structure of the alloy nanosheets, providing unlimited possibilities for maximizing catalytic activity. The IrM (M = Fe, Co, Ni) ultrathin nanosheet catalyst prepared in this application combines superior performance and stability compared to commercial Pt / C and commercial IrO2, effectively reducing the high cost of noble metal catalysts used in industrial acidic water electrolysis processes.

Claims

1. A method for preparing an ultrathin iridium-based nanosheet catalyst, characterized in that: Includes the following steps: A precursor of noble metal Ir is mixed with a precursor of non-noble metal M in a molar ratio of 1:

1. The precursor of noble metal Ir is at least one of iridium acetylacetonate, iridium chloride, iridium acetate or chloroiridium acid. The non-noble metal M is any one or more of Fe, Co or Ni. After dissolving in deionized water, metal precursor solution A is obtained. The metal precursor solution A is mixed with the reducing agent solution B, wherein the reducing agent solution B contains an organic alcohol, glyoxal and sodium citrate; then the surfactant polyvinylpyrrolidone PVP-K30 is added to obtain a mixture C; wherein the mass ratio of the precursor of the noble metal Ir to the surfactant is 1:(2-3). The mixture C was transferred to a hydrothermal reactor and reduced using a hydrothermal method. The specific conditions for the hydrothermal reduction were: heating from room temperature to 180-200℃ at a rate of 5-10℃ / min and holding at that temperature for 7-10 hours. The hydrothermal reactor was naturally cooled to room temperature, the product was removed, centrifuged, washed, and dried to obtain the ultrathin iridium-based nanosheet catalyst. The catalyst is any one or more of Ir-Fe, Ir-Co, or Ir-Ni.

2. The method according to claim 1, characterized in that: The precursor of the non-precious metal M includes at least one of ferric chloride or ferric nitrate, cobalt chloride or cobalt nitrate, and nickel chloride or nickel nitrate.

3. The application of the ultrathin iridium-based nanosheet catalyst prepared by the method according to any one of claims 1 to 2 as a HER and / or OER catalyst in the electrocatalytic water electrolysis in an acidic environment.

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