Iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst, preparation method and application

Abstract

The invention relates to the field of electrocatalysts, in particular to an iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst, a preparation method and application. According to the iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst provided by the invention, IrO2 and MoS2 in a heterojunction structure can be mutually adjusted, so that the electrocatalyst has a higher electron transfer rate, excellent hydrophilicity, proper OH * adsorption capacity and a higher deprotonation rate, has better electrochemical performance in catalytic electrolysis of water, and can be used for preparing a high-performance electrocatalyst. In an oxygen evolution reaction, the iridium oxide shows performance far superior to that of commercial iridium oxide, and has relatively low overpotential and relatively high quality activity; good electrochemical performance is shown in the aspect of hydrogen precipitation and is superior to that of commercial Pt / C; and the used material shows relatively low decomposition voltage when being applied to electrolyzed water. Therefore, the IrO2 / MoS2 / CNT heterostructure catalyst can be widely and deeply applied to electrolyzed water.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysts, and in particular to an iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst, a preparation method and application thereof. Background Art

[0002] With the growth of the global economy and population, the demand for fossil energy continues to rise. Its combustion is accompanied by the production of a large amount of greenhouse gases, which leads to an accelerated rise in global temperatures, resulting in adverse effects such as rising sea levels, melting glaciers and frequent severe weather. At the same time, the use of fossil energy is also facing a shortage problem, causing its price to continue to rise, posing a huge challenge to economic development and social stability. Therefore, the search for alternative energy has become a hot topic worldwide. Hydrogen, as a clean energy, only produces water and heat after combustion, without any harmful gases, and H2 is the ideal energy carrier with the highest weight energy density on the earth. Therefore, using hydrogen as an energy source can reduce air pollution and greenhouse gas emissions, thereby protecting the environment. Under the strategic background of the country's implementation of the carbon peak and carbon neutrality goals, the use of excess electricity generated by green energy such as photovoltaics and wind power to produce green hydrogen through water electrolysis technology, without carbon emissions in the process, is regarded as the mainstream direction of the future development of hydrogen energy. However, the strong fluctuation properties of photovoltaic and wind power energy themselves put forward higher requirements on the dynamic adaptability and operational reliability of water electrolysis hydrogen production systems.

[0003] Generally speaking, water electrolysis can be carried out under acidic, neutral and alkaline conditions. According to the properties of the electrolyte, water electrolysis can be divided into three types: proton exchange membrane electrolysis (PEM), alkaline electrolysis (AWE) and solid oxide electrolysis (SOEC). Compared with alkaline electrolyzers, PEM electrolyzers have lower ohmic losses, higher voltage efficiency, higher gas purity, more compact system design, higher current density, faster system response and a larger local load range. However, due to the presence of a large amount of H on the anode side during the hydrolysis process, PEM electrolyzers have a large amount of H + , which keeps the acidity on the anode side at a very high level, resulting in the use of expensive precious metals or their oxides as electrocatalysts in PEM electrolyzers. The scarcity and high cost of precious metal resources have become one of the main factors limiting the large-scale commercialization of PEM water electrolysis technology.

[0004] In the electrolysis of water in an acidic solution, the water electrolysis reaction is carried out by the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. The hydrogen evolution reaction is the simplest electrochemical reaction and a relatively easy process to occur. The oxygen evolution reaction is a slow process. The complexity of the OER involves a four-electron proton coupled electrochemical reaction, which leads to a higher overpotential and slow reaction kinetics in the water splitting process. Compared with the two-electron transfer HER reaction, the OER requires higher energy consumption (i.e., overpotential), making it the dominant factor affecting the overall efficiency of water electrolysis.

[0005] Currently, for the hydrogen evolution reaction (HER) in acidic media, the available electrocatalysts are usually platinum black or carbon-supported platinum nanoparticles; while for the oxygen evolution reaction (OER), IrO2 is currently the most commonly used stable oxygen evolution catalyst in the commercial market. Due to the slow kinetics and high overpotential of the OER on the anode side, it accounts for most of the voltage loss of the electrolyzer. In theory, the standard electrode potential of the cathode HER is 0V, and the overpotential for the Pt / C catalyst is only about 25mV, which can meet the needs of large-scale production. However, for OER, its standard electrode potential is 1.23V. On the one hand, the extremely high electrode potential and severe acid corrosion conditions make most elements unable to exist stably; on the other hand, OER involves 4 electron transfers, which causes kinetic retardation. Even for the IrO2 catalyst with excellent performance, its overpotential is above 300mV, and because the content of metal Ir in nature is very low and the yield is not high, the price of iridium is high (about ￥1500 / g), which greatly limits the commercialization of water electrolysis. In order to realize the large-scale application of PEM water electrolysis to produce hydrogen as soon as possible and develop commercially viable PEM electrocatalysts, it is still necessary to use IrO2 as the main active substance and achieve performance and stability improvements through crystal morphology regulation, impurity doping, construction of heterogeneous structures or introduction of carriers. Therefore, it is urgent to develop a low-Ir oxygen evolution catalyst with both high activity and stability to reduce the amount of precious metal Ir in the electrolytic cell. 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 an iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst, a preparation method and an application thereof.

[0007] The technical solution adopted by the present invention is as follows: an iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst, including a carbon matrix, IrO2 and MoS2 loaded on the carbon matrix.

[0008] Preferably, the MoS2 has a crystal structure phase in which IT phase and 2H phase coexist.

[0009] Preferably, the carbon matrix is ​​carbon nanotubes.

[0010] Preferably, the mass proportion of IrO2 is 30%-40%.

[0011] The method for preparing the iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst as described above comprises the following steps:

[0012] (1) Synthesizing supported molybdenum disulfide nanosheets on a carbon matrix by a solvothermal method to obtain a MoS2 / carbon matrix precursor;

[0013] (2) growing iridium dioxide nanoparticles on the MoS2 / carbon matrix precursor prepared in step (1) by a solvothermal method to prepare an iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst.

[0014] Preferably, in step (1), the molybdate and the carbon matrix are dispersed in water, and then the thiourea solution is added dropwise, stirred and dispersed, and then transferred to a reaction kettle, sealed and placed in an oven, and heated to react to generate molybdenum disulfide nanosheets, and the reaction temperature is 160-200°C.

[0015] Preferably, in step (1), after the heating reaction is completed, the product is washed with distilled water and ethanol, dried, and calcined under an inert gas atmosphere to obtain a MoS2 / carbon matrix precursor.

[0016] Preferably, in step (2), the iridium source and MoS2 / carbon matrix precursor are dispersed in ethanol, transferred to a reaction kettle, sealed and placed in an oven, and heated to react to generate iridium dioxide nanoparticles, and the heating reaction temperature is 80-120°C.

[0017] Application of the iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst as described above in water electrolysis.

[0018] The iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst provided by the present invention has IrO2 and MoS2 in the heterojunction structure that can adjust each other, so that it has a faster electron transfer rate, and has excellent hydrophilicity, suitable OH* adsorption capacity and faster deprotonation rate, has good electrochemical performance in catalytic water electrolysis, and shows performance far superior to commercial iridium dioxide in oxygen evolution reaction, has lower overpotential and higher mass activity; also shows good electrochemical performance in hydrogen evolution, which is better than commercial Pt / C; the material used in water electrolysis also shows a lower decomposition voltage. Therefore, this IrO2 / MoS2 / CNT heterostructure catalyst has a wide and profound application in water electrolysis, and provides material design ideas and research methods for studying water electrolysis catalysts.

[0019] The preparation method of the present invention is simple to operate, safe and easy to synthesize on a large scale, and therefore has prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 TEM (a), HRTEM (b) and EDS (c) images of IrO2 / MoS2 / CNT;

[0022] Figure 2 XRD patterns (a) and Raman patterns (b) of MoS2 / CNT and IrO2 / MoS2 / CNT;

[0023] Figure 3 LSV diagram (a), electrochemical impedance diagram (b), and electrochemical active area diagram (c) of different contents of IrO2 / MoS2 / CNT;

[0024] Figure 4 Results of electrochemical performance tests: (a) polarization curve of oxygen evolution reaction (OER); (b) polarization curve of hydrogen evolution reaction (HER); (c) results of acidic durability test. DETAILED DESCRIPTION

[0025] 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.

[0026] Embodiment 1:

[0027] (1) Preparation of MoS2 / CNT precursor

[0028] The specific process is: first (NH4)6Mo7O 24 ·4H2O and CNT were dissolved in 10ml ultrapure water, stirred at room temperature for 30min, and then an appropriate amount of thiourea was dissolved in 20ml water. The thiourea solution was dropped into the prepared molybdic acid solution and continued to stir for 1 hour. Then, the solution was transferred to a 50mL stainless steel autoclave, sealed, and placed in an oven at 180°C for 24h. The product was collected by centrifugation at 8000rpm for 5 minutes and washed several times with distilled water and ethanol to remove any possible ions. The final product was collected after drying in a vacuum oven at 60°C overnight. The obtained solid mixture was calcined at 800°C in an Ar atmosphere at a rate of 5°C / min for 2h, and cooled to room temperature to obtain a MoS2 / CNT precursor.

[0029] (2) Preparation of IrO2 / MoS2 / CNT catalyst

[0030] Iridium dioxide nanoparticles were grown on molybdenum disulfide precursors using a hydrothermal method. Specifically, the MoS2 / CNT precursor and IrCl3.xH2O in step (1) were accurately weighed at a molar ratio of 3:1, uniformly dispersed in a beaker containing 15 ml of ethanol, magnetically stirred at room temperature for 1 hour, then transferred to a 25 mL stainless steel autoclave, sealed, and placed in an oven at 100°C for 10 hours. After cooling at room temperature, the suspension was filtered, washed, and dried overnight under vacuum at 60°C to obtain an IrO2 / MoS2 / CNT (30%) catalyst with a mass percentage of IrO2 of 30%.

[0031] MoS2 / CNT and IrO2 / MoS2 / CNT were characterized by the following methods: transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and energy dispersive x-ray spectroscopy (EDS) elemental mapping were performed using a JEOL-2100F (200 kV) instrument; Cu Kα radiation (40 kV, 100 mA, ) of the sample; the Raman spectrum was recorded by Raman microscopy using an argon ion laser at a wavelength of 532 nm.

[0032] like Figure 1 As shown in (a), TEM can observe the (200) crystal plane of IrO2 and the (002) crystal plane of MoS2; Figure 1 As shown in (b), HRTEM can observe that MoS2 in IrO2 / MoS2 / CNT material coexists in IT phase and 2H phase; Figure 1 As shown in (c), the EDS spectrum shows that Ir, Mo, O, S, and C are evenly distributed in the synthesized material.

[0033] like Figure 2 As shown in (a), XRD pattern analysis can prove that IrO2 successfully enters the MoS2 / CNT precursor; Figure 2 As shown in (b), Raman image analysis shows that the addition of IrO2 can promote the transformation of part of 2H-MoS2 from 2H phase to 1T phase.

[0034] Embodiment 2:

[0035] This embodiment is substantially the same as embodiment 1, the main difference being the molar ratio of the MoS2 / CNT precursor to IrCl3.xH2O, specifically 1.6:1, to obtain an IrO2 / MoS2 / CNT (20%) catalyst in which the mass ratio of IrO2 is 20%.

[0036] Embodiment 3:

[0037] This embodiment is substantially the same as embodiment 1, the main difference being the molar ratio of the MoS2 / CNT precursor to IrCl3.xH2O, specifically 3.3:1, to obtain an IrO2 / MoS2 / CNT (40%) catalyst in which the mass ratio of IrO2 is 40%.

[0038] Test example Electrochemical test:

[0039] All electrochemical measurements were performed on Shanghai Chenhua chi760e electrochemical workstation. The electrochemical performance of oxygen evolution was tested in a three-electrode system and the electrochemical performance of water electrolysis was tested in a two-electrode system. In the three-electrode system, in 0.5M H2SO4 electrolyte, a platinum mesh was used as the counter electrode, calomel was used as the reference electrode, and a self-prepared catalyst was used as the working electrode. Similarly, in the two-electrode system, the reference electrode and the counter electrode were replaced with the same electrode, which was the self-prepared working electrode. In this system, the water electrolysis decomposition voltage was tested by linear voltammetric scanning.

[0040] like Figure 3 As shown, compared with IrO2, the addition of MoS2 and CNT can significantly improve the OER and HER activities. Among them, the IrO2 / MoS2 / CNT (30%) catalyst with an IrO2 mass proportion of 30% exhibits the best OER and HER activities.

[0041] IrO2 / MoS2 / CNT (30%) was further tested for its electrochemical performance in water electrolysis. Figure 4 As shown in (a) and (b), in 0.5M H2SO4 solution, it can be found that the HER and OER performances of MoS2 / CNT are poor, the HER and OER performances of IrO2 / CNT are slightly better than those of commercial IrO2 and commercial Pt / C, and the IrO2 / MoS2 / CNT catalyst exhibits significantly excellent HER and OER performances. By comparison, it can be seen that IrO2 and MoS2 have a synergistic effect. Figure 4 As shown in (c), the acid durability test using IrO2 / MoS2 / CNT catalyst can be maintained for more than 100 h, far exceeding MoS2 / CNT, commercial IrO2, and IrO2 / CNT.

[0042] 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. An iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst, characterized in that: It includes a carbon matrix, and IrO2 and MoS2 loaded on the carbon matrix.

2. The iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst according to claim 1, characterized in that: The MoS2 has a crystal structure phase in which an IT phase and a 2H phase coexist.

3. The iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst according to claim 1, characterized in that: The carbon matrix is ​​carbon nanotubes.

4. The iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst according to claim 1, characterized in that: The mass proportion of IrO2 is 30%-40%.

5. The method for preparing the iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst according to any one of claims 1 to 4, characterized in that The following steps are involved: (1) Synthesizing supported molybdenum disulfide nanosheets on a carbon matrix by a solvothermal method to obtain a MoS2 / carbon matrix precursor; (2) Growing iridium dioxide nanoparticles on the MoS2 / carbon matrix precursor prepared in step (1) by a solvothermal method to prepare an iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst.

6. The preparation method according to claim 5, characterized in that: In step (1), molybdate and carbon matrix are dispersed in water, thiourea solution is added dropwise, stirred and dispersed, and then transferred to a reaction kettle, sealed and placed in an oven, and heated to react to generate molybdenum disulfide nanosheets, and the reaction temperature is 160-200°C.

7. The preparation method according to claim 6, characterized in that: In step (1), after the heating reaction is completed, the product is washed with distilled water and ethanol, dried, and calcined under an inert gas atmosphere to obtain a MoS2 / carbon matrix precursor.

8. The preparation method according to claim 6, characterized in that: In step (2), the iridium source and MoS2 / carbon matrix precursor are dispersed in ethanol, transferred to a reaction kettle, sealed and placed in an oven, and heated to react to generate iridium dioxide nanoparticles at a heating reaction temperature of 80-120°C.

9. Use of the iridium dioxide / molybdenum disulfide / carbon matrix heterostructure electrocatalyst as described in any one of claims 1 to 4 in water electrolysis.

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