Preparation method of in-situ loaded low-iridium electrocatalyst and application of in-situ loaded low-iridium electrocatalyst as OER catalyst in electrolyzed water

Abstract

The invention belongs to the field of electrocatalysts, and particularly relates to a preparation method of an in-situ loaded low-iridium electrocatalyst and application of the in-situ loaded low-iridium electrocatalyst as an OER catalyst in electrolyzed water. The method comprises the following steps: dispersing (NH4) 3IrCl6 into methanol to obtain a reaction solution, and transferring the reaction solution into a high-pressure kettle; immersing the carbon cloth into the reaction solution, and sealing the autoclave for hydrothermal reaction; the in-situ loaded low-iridium N-Ir catalyst material is directly synthesized through a hydrothermal method, so that the iridium-based material grows on the carbon cloth in situ, the synthesis operation is simple, and the catalyst has relatively high quality activity and excellent stability; n is introduced into the material, so that the synergistic effect between the materials is improved, the catalytic activity of the material can be improved, and in the oxygen precipitation process, the addition of N can promote better charge transfer and faster deprotonation ability of the material, and the catalytic kinetics of OER is improved.

Description

Technical Field

[0001] The invention belongs to the field of electrocatalysts, and in particular relates to a preparation method of an in-situ loaded low-iridium electrocatalyst and an application of the in-situ loaded low-iridium electrocatalyst as an OER catalyst in water electrolysis. Background Art

[0002] In recent years, the overuse of fossil fuels has brought about a series of problems such as environmental pollution, energy crisis, and climate change, forcing people to seek new, more sustainable and environmentally friendly energy to replace traditional fossil fuels. Hydrogen (H2) is an efficient clean energy carrier with high energy density and is expected to become an ideal substitute for fossil fuels. Building a hydrogen society is a potential way to solve these challenges.

[0003] Electrolysis of water to produce hydrogen is a mature traditional method of hydrogen production that meets the expectations of low carbon emissions and is currently the best way to obtain hydrogen energy. Electrochemical water splitting includes two half reactions, namely the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Compared with HER with two electron transfers, the reaction barrier of OER with four electron transfers is much higher, making it significantly slower. It is necessary to apply a potential far exceeding the 1.23V (vs. SHE) required by thermodynamics to decompose water molecules into their main components (hydrogen and oxygen). For example, in order to achieve at least 10mA / cm 2 To achieve a high current density, an overpotential of several hundred millivolts above the OER equilibrium potential must be applied, which greatly reduces the process efficiency. Therefore, the efficiency of OER is very important for the entire water electrolysis.

[0004] At present, the more mature water electrolysis technologies are alkaline water electrolysis (AWE) and proton exchange membrane water electrolysis (PEMWE). Compared with AWE, PEMWE has faster system response, higher current density, higher gas purity, more compact design, etc. However, in PEMWE, due to the use of acidic PEM, OER needs to operate under acidic conditions. The main challenge at this stage is to improve the electrochemical stability of OER catalysts in acid, because most transition metal-based oxides will be severely degraded under such oxidative and corrosive OER conditions. Although many promising OER catalysts have been developed, the OER catalysts available in acidic media are still limited to ruthenium or iridium-based oxides.

[0005] Ruthenium-based materials have high OER activity, but their rapid dissolution due to the formation of volatile ruthenium tetroxide (RuO4) in the OER potential region makes durability issues necessary to ensure their practical use. In contrast, Ir-based materials have balanced electrochemical activity and stability and are currently the most suitable electrocatalysts for OER in acidic media. However, even Ir-based electrocatalysts dissolve in acidic environments, especially in high potential regions, and the development of highly active OER and durable acid electrocatalysts with low Ir is indeed essential. Although efforts have been made recently to develop low-Ir materials for acidic OER, their success has been quite limited. Crucially, the iridium content in the materials is often too high to guarantee sufficient Ir mass activity, which is the most important factor for the practical application of acidic OER. The development of Ir-based nanoparticle catalysts provides a direct route to maximize the Ir mass activity. In addition, obtaining good durability without significant surface reconstruction during the acidic OER process is another challenging issue. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing an in-situ loaded low iridium electrocatalyst and its application as an OER catalyst in electrolysis of water.

[0007] The technical solution adopted by the present invention is as follows: a method for preparing an in-situ loaded low-iridium electrocatalyst, comprising the following steps: dispersing (NH4)3IrCl6 in methanol to obtain a reaction solution, and transferring it to an autoclave; immersing carbon cloth in the reaction solution, sealing the autoclave and maintaining it at 180-220°C for 10-20 hours.

[0008] Preferably, the carbon cloth is pretreated before reacting, and the pretreatment process is as follows: the carbon cloth is ultrasonically treated in acetone, deionized (DI) water and anhydrous ethanol in sequence, and then dried.

[0009] Preferably, after (NH4)3IrCl6 is added to methanol, it is stirred on a heated stirrer at 40-50°C for 15-45 minutes to obtain a reaction solution.

[0010] Preferably, the stirring speed of the heating stirrer is 100-600 r / min.

[0011] Preferably, after the reaction, the carbon cloth is cooled, taken out, rinsed several times with ethanol and deionized water, and dried.

[0012] The in-situ loaded low iridium electrocatalyst is prepared by the method for preparing the in-situ loaded low iridium electrocatalyst as described above.

[0013] The in situ supported low iridium electrocatalyst as described above is used as an OER catalyst in water electrolysis.

[0014] The beneficial effects of the present invention are as follows: the present invention directly synthesizes an in-situ loaded low-iridium N-Ir catalyst material through a hydrothermal method, so that the iridium-based material is in-situ grown on the carbon cloth and can be more firmly distributed on the base material, which solves the problem of material shedding and dissolution during the reaction to a certain extent, improves the stability of the material, has simple synthesis operation, high catalytic efficiency, and the synthesis process meets the requirements of green chemical production and does not pollute the environment; the catalyst has high mass activity and excellent stability; the introduction of N into the material improves the synergistic effect between the materials and can improve the catalytic activity of the material. In the process of oxygen evolution, the addition of N can promote better charge transfer and faster deprotonation ability of the material, improve the catalytic kinetics of OER, and increase the reaction rate; compared with commercial IrO2 electrocatalysts, it exhibits excellent performance in oxygen evolution and hydrogen evolution reactions, has a lower overpotential, and also exhibits a lower decomposition voltage in water electrolysis, which is more conducive to the electrolysis of water to produce hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0016] Figure 1 :HAADF-STEM image of N-Ir material;

[0017] Figure 2 : Element mapping of N-Ir materials;

[0018] Figure 3 :(a) XRD patterns of N-Ir and comparative samples (b) Ir 4f XPS spectrum of N-Ir (c) N 1s XPS spectrum of N-Ir;

[0019] Figure 4 :(a) LSV of N-Ir and other materials; (b) Tafel slope of N-Ir and other materials; (c) Comparison of electrochemical active areas of different materials; (d) N-Ir at 10 mA cm -2 it under current density; (e) Stability of N-Ir under multiple-step current density;

[0020] Figure 5 :N-Ir material at 100mA cm -2 Test stability at current density of ;

[0021] Figure 6 :(a) LSV of N-Ir in fully electrolyzed water (b) Stability test of N-Ir in fully electrolyzed water. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Example 1 Preparation of N-Ir electrocatalyst:

[0024] (1) Pretreatment of carbon cloth: Cut the carbon cloth into 1×2 cm 2 The size was then ultrasonically treated in acetone, deionized (DI) water and anhydrous ethanol for 30 minutes in sequence and dried in an oven at 60°C for 12 hours before use.

[0025] (2) Synthesis of N-Ir catalytic material: Weigh (NH4)3IrCl6 and place it in a polytetrafluoroethylene liner, add 5 ml of methanol solution, stir it on a heated stirrer at 45°C and 600 r / min for 40 min, place the treated 1*2 cm carbon cloth vertically into the solution, ensure that the immersed area is not less than 1*1 cm, then place it in a stainless steel reactor, seal it and keep it at 200°C for 15 h, and obtain an in-situ N-Ir electrocatalyst loaded on the carbon cloth. The amount of reactant (NH4)3IrCl6 added is 0.06 mmol, and the amount of solvent methanol added is 1 / 4 of the volume of the reactor.

[0026] Test Example 1 Structural Characterization of N-Ir Material:

[0027] High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images and corresponding energy dispersive X-ray spectroscopy (EDX) elemental mapping were obtained on a FEI Themis Z TEM / STEM equipped with a correction stage, a high-angle annular dark field detector and an EDX detector at 200 kV. Surface investigations of the materials were performed on an X-ray diffractometer (XRD, D / MAX-2400) and an X-ray photoelectron spectrometer (XPS, Thermo Fisher Scientific K-Alpha), and Raman spectra were recorded by Raman microscopy using an argon ion laser at a wavelength of 532 nm.

[0028] exist Figure 1 TEM can observe that the iridium-based nanoparticles are uniformly distributed, and the lattice spacing of the nanoparticles is observed to be 0.22 nm, corresponding to the (111) crystal plane of Ir. Figure 2 The EDX spectrum shows that Ir, O, and N are evenly distributed. Figure 3The XRD pattern of (a) shows that after a series of synthesis, the crystallinity and crystal size of different iridium-based precursors are different, but they all correspond to the PDF card of single substance Ir(111). Figure 3 (b) and Figure 3 In the XPS graph (c), it is observed that the chemical states of Ir and N in the synthesized N-Ir material have changed compared with the precursor. In the 4f spectrum of Ir, several peaks are observed, mainly peaks of Ir 0 and its satellite peaks. Compared with the precursor, Ir 3+ was reduced; at the same time, in the 1s spectrum of N, it was observed that N was oxidized, and electron transfer may have occurred between Ir and N.

[0029] Test Example 2 Characterization of electrochemical properties of N-Ir materials:

[0030] (1) Preparation of electrolyte: Add 27.1 mL of concentrated sulfuric acid to 1 L of deionized water, stir evenly, and cool to room temperature to obtain 0.5 M H2SO4 electrolyte.

[0031] (2) The obtained in-situ loaded catalyst on carbon cloth was used as the working electrode, the platinum mesh was used as the counter electrode, and the calomel electrode was used as the reference electrode. The three electrodes were placed in a 0.5 M H2SO4 solution to evaluate the OER performance of the electrocatalyst. The OER test window was 0.9-1.4 V, and the scan rate was 0.005-0.01 V / s.

[0032] The oxygen evolution performance was tested in a three-electrode system. In 0.5 M H2SO4, a platinum mesh was used as the counter electrode, calomel was used as the reference electrode (the calomel electrode was calibrated with a reversible hydrogen electrode (RHE), E vs. RHE = E vs. SCE + 0.269), and the self-supporting carbon cloth material was used as the working electrode. The system was connected to an electrochemical workstation to test its linear voltammetry (LSV) curve and other electrochemical properties.

[0033] The linear sweep voltammetry (LSV) potential range was 0.9 V–1.4 V (vs. SCE) with a scan rate of 10 mV s -1 The LSV data were 90% iR compensated. The Tafel plot was calculated by the formula η = blog j + a, where b is the Tafel slope. All data are from LSV. The CV was used to calculate the different scan rates (10, 20, 30, 40 and 50 mV s -1 ) under electrochemically active surface area (ECSA). At 10 mA cm -2 Chronopotentiometry was performed at a continuous current density (10, 20, 50, 100, 10 mA cm -2 ) was carried out to evaluate the stability of the prepared electrocatalysts.

[0034] The activity and stability of different materials were tested. Figure 4 (a) The LSV performance of different materials was measured. N-Ir at 10 mA cm -2 The overpotential at the current density is only 212mV, indicating that the material has high activity; Figure 4 (b) It can be seen that N-Ir has the smallest Tafel slope of 56.92 mV dec -1 , indicating that its reaction kinetics is the fastest. Figure 4 (c) In the ECSA diagram of N-Ir, the linear fitting slope of N-Ir is greater than that of other catalysts, indicating that the N-Ir catalyst has more abundant active sites and a larger electrochemical active area. Figure 4 (d) and (e) used different methods to determine the stability of the materials. N-Ir can not only maintain good stability at different current densities, but also maintain good stability at 10 mA cm -2 The stability of different materials at a higher current density (100 mA cm-2) was also tested. Figure 5 ), the N-Ir material can still maintain stability for at least 250 h at high current density, which is better than other comparative materials and commercial iridium dioxide.

[0035] Test Example 3: Water electrolysis performance test of N-Ir material:

[0036] The electrochemical performance of water electrolysis was tested in a two-electrode system, in which the reference electrode and the counter electrode were the same electrode, i.e., a self-prepared working electrode. In this system, the water electrolysis decomposition voltage was tested by linear voltammetric scanning, and the electrochemical window was 1.2-2.0 V / s.

[0037] exist Figure 6 In (a), N-Ir was used as the anode and cathode catalyst, while commercial IrO2 and commercial 20% Pt / C were used as the anode and cathode catalyst groups as control experiments. The bifunctional electrolytic cell assembled with N-Ir catalyst was -2 The water decomposition voltage under the current density is only 1.492V, which is lower than the decomposition voltage of the commercial control group (1.61V). Figure 6 In the full-battery stability test (b), N-Ir can catalyze decomposition relatively stably and can operate normally for more than 320 hours with little potential decay.

[0038] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing an in-situ loaded low iridium electrocatalyst, characterized in that The following steps are involved: (NH4)3IrCl6 is dispersed in methanol to obtain a reaction solution, which is transferred to an autoclave; the carbon cloth is immersed in the reaction solution, and the autoclave is sealed and maintained at 180-220°C for 10-20 hours.

2. The method for preparing an in-situ loaded low iridium electrocatalyst according to claim 1, characterized in that: The carbon cloth is pretreated before the reaction, and the pretreatment process is as follows: the carbon cloth is ultrasonically treated in acetone, deionized (DI) water and anhydrous ethanol in sequence, and then dried.

3. The method for preparing an in-situ loaded low iridium electrocatalyst according to claim 1, characterized in that: After (NH4)3IrCl6 is added to methanol, the mixture is stirred on a heating stirrer at 40-50°C for 15-45 minutes to obtain a reaction solution.

4. The method for preparing an in-situ loaded low iridium electrocatalyst according to claim 3, characterized in that: The stirring speed of the heating stirrer is 100-600r / min.

5. The method for preparing an in-situ loaded low iridium electrocatalyst according to claim 1, characterized in that: After the reaction, the carbon cloth was cooled, taken out, rinsed with ethanol and deionized water several times, and dried.

6. An in-situ loaded low iridium electrocatalyst prepared by the method for preparing an in-situ loaded low iridium electrocatalyst as described in any one of claims 1 to 5.

7. Use of the in-situ loaded low iridium electrocatalyst as claimed in claim 6 as an OER catalyst in water electrolysis.

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