CN114921808B - Vanadium-doped iridium dioxide electrocatalyst, and preparation method and application thereof - Google Patents

Abstract

The invention discloses a preparation method of a vanadium doped iridium dioxide electrocatalyst, which adopts the technical scheme that an iridium compound and a vanadium compound are prepared into the vanadium doped iridium dioxide electrocatalyst by a sol-gel method, and the molar ratio of the iridium compound to the vanadium compound is 1-10. Vanadium doped IrO prepared by sol-gel pyrolysis method ₂ The nano composite material has uniform morphology and controllable particle size (realized by adjusting the content of doped vanadium (V) and the pyrolysis temperature), and finally the nano amorphous doped vanadium iridium dioxide has higher activity by adjusting the crystallinity of the catalyst. The obtained vanadium-doped iridium dioxide has high-efficiency catalytic activity in electrocatalytic hydrogen and oxygen evolution, and can be used as a good difunctional electrolyzed water catalyst.

Description

Vanadium-doped iridium dioxide electrocatalyst and its preparation method and application

technical field

The invention relates to the field of inorganic functional materials, in particular to a vanadium-doped iridium dioxide electrocatalyst and a preparation method and application thereof.

Background technique

Hydrogen production by electrolysis of water is in line with the requirements of green energy development. Under the background of energy and environmental friendliness, the development of hydrogen energy is very important. Hydrogen energy is a clean secondary energy source, which has the advantages of high energy density, zero pollution, and zero carbon emissions. It is known as the "ultimate energy source" for human beings. At present, the main devices for electrolysis of water are alkaline electrolyzer (AEM) and proton exchange membrane electrolyzer (PEM). Alkaline (AWE) electrolyzer is the water electrolysis device with the most mature technology application, the lowest cost and the highest degree of industrialization at present, and it has been commercially available on a large scale. In a typical AEM electrolytic cell, the electrolyte is 10-30% sodium hydroxide or potassium hydroxide solution, the working temperature of the electrolytic cell is 70-90°C, the gas pressure is less than 0.3 atmospheric pressure, the working electrode is nickel alloy, and the diaphragm The main component is asbestos, which can separate the gases generated at the poles. The disadvantages of alkaline electrolyzers are: low current density, low conversion efficiency and working pressure, low gas purity, high maintenance costs and potential safety hazards. Compared with the AEM electrolyzer, the PEM electrolyzer can solve the above problems well, but it cannot be used on a large scale at present. The main reason for limiting its application is the price of the proton exchange membrane and available electrocatalysts (iridium, platinum, etc.) High, causing the cost of the electrolytic cell is too high.

In order to sustainably produce hydrogen and oxygen from electrolyzed water, commercial IrO ₂ is currently used as the anode catalyst and Pt/C as the cathode catalyst, both of which contain noble metal catalysts. The high cost and scarcity of resources limit their wide application in commerce. In addition, IrO ₂ is easily dissolved during the OER process, resulting in instability under acidic conditions. The main reason for its dissolution is that IrO ₂ dissolves to form IrO ₂ OH as the potential increases during the reaction. The process of dissolving _IrO2 is decomposed into three steps. The first step is that the Ir-O bond of _IrO2 is broken after applying a voltage, which easily causes the Ir in the intermediate structure to form a new bond with the nearest structural oxygen atom; the second step is to dissolve Ir is easily attacked by H ₂ O in the solution, forming IrO ₂ OH on the surface; the third step is that the bond between the dissolved Ir and the surface oxygen atoms is broken, resulting in the release of IrO ₂ OH to the solution. The stability of IrO ₂ is one of the main reasons that limit its use as an anode catalyst for proton exchange membrane water electrolyzers. Therefore, how to solve the stability of IrO ₂ under acidic conditions and simultaneously improve its activity has become a very important issue.

Contents of the invention

The object of the present invention is to provide a vanadium-doped iridium dioxide electrocatalyst and its preparation method and application in order to overcome the shortcomings and deficiencies of the prior art.

In order to achieve the above object, the technical solution of the present invention is to prepare a vanadium-doped iridium dioxide electrocatalyst by using an iridium compound and a vanadium compound through a sol-gel method, and the molar ratio of the iridium compound to the vanadium compound is 1-10.

It is further provided that the iridium compound is iridium trichloride hydrate, H ₂ IrCl ₆ , K ₂ IrCl ₆ , (NH ₄ ) ₃ IrCl ₆ , (NH ₄ ) ₂ IrCl ₆ or Ir ₄ (CO) ₁₂ .

The further setting is that the vanadium compound adopts vanadium trichloride hydrate and its precursor vanadium oxide.

The further setting is that the sol-gel method is specifically: heating and stirring the iridium compound and the vanadium compound to dissolve in deionized water, then adding citric acid and ethylene glycol, stirring under heating until the gel microbubble, and then carrying out high temperature Pyrolysis.

Further setting is that the molar ratio of the amount of citric acid added to the iridium compound is 0.3-40, and the molar ratio of the amount of ethylene glycol to citric acid is 2-1.

It is further provided that the stirring temperature in the heating state is 100-150° C., and the stirring speed range is 100-600 r/min.

It is further set that the pyrolysis temperature is 300-700° C., and the heating rate is 1.5-10° C./min.

The second aspect of the present invention is to provide a vanadium-doped iridium dioxide electrocatalyst prepared by the preparation method.

In addition, the present invention also provides an application of the vanadium-doped iridium dioxide electrocatalyst as a bifunctional electrocatalyst for oxygen evolution and hydrogen evolution reactions in electrolyzed water.

Its application method is:

a. Using the prepared vanadium-doped iridium dioxide electrocatalyst (referred to as V/IrO ₂ catalyst), further prepare a V/IrO ₂ catalyst-loaded test electrode as a working electrode. First weigh 1-8mg of the catalyst, ultrasonically disperse it for 0.5-2h, use 0.5mL-2mL of dispersant (add water, methanol, ethanol, Nafion aqueous solution, etc.), and drop-coat 10uL of the catalyst suspension on the glassy carbon electrode, carbon On paper, dry naturally in the incubator.

b. The electrochemical performance of the catalyst was detected by an electrochemical workstation. The electrode obtained in (a) was used as the working electrode, the platinum wire was used as the counter electrode, calomel was used as the reference electrode, and the electrolyte was 0.5MH ₂ SO ₄ placed in a three-electrode system to evaluate the OER, HER and total water splitting of the electrocatalyst electrochemical performance. The electrochemical window of OER test is 0.9～1.6V (vs SCE), and the scan rate is 0.005～0.1V/s; the electrochemical window of HER test is -0.8～-0.2V (vs SCE), and the scan rate is 0.005～0.1V/s; The electrochemical window of total water splitting is 0.8-2.0V (vs SCE), and the scan rate is 0.005-0.1V/s.

The vanadium-doped iridium dioxide electrocatalyst prepared by the method of the present invention has the following characteristics: small particle diameter, many edge active sites, and high activity. ₂ Activity in alkaline and acidic media and advantages in acidic large-scale applications.

The vanadium-doped _IrO2 nanocomposite material prepared by the sol-gel pyrolysis method of the present invention has uniform appearance and controllable particle size (realized by adjusting the content of doped V and the temperature of pyrolysis), and finally through adjusting the crystallinity of the catalyst. It shows that the amorphous vanadium-doped iridium dioxide has higher activity. The obtained vanadium-doped iridium dioxide has relatively efficient catalytic activity in electrocatalytic hydrogen evolution and oxygen evolution. It can be used as a good bifunctional electrolysis water catalyst.

The innovation mechanism of the present invention has:

The vanadium-doped iridium dioxide prepared by the invention has high catalytic activity and good electrochemical performance. Compared with ordinary IrO ₂ , the OER performance of the vanadium-doped IrO ₂ in alkaline and acidic media is significantly improved. The morphology of the catalyst is controllable, and it has the characteristics of controllable particle size and adjustable crystallinity. The preparation method of the catalyst prepared by the invention is simple, the operation is practical, and it has a good application prospect in electrolysis of water for oxygen evolution and application of electrocatalytic materials. This provides an idea for catalyst design ideas and research methods and lays a solid foundation for the synthesis and preparation of materials.

In addition, according to the inventor's experimental and analytical research, it is believed that vanadium and iridium have a synergistic effect, and vanadium has a multivalent state that is beneficial to regulating the electronic structure of IrO ₂ , so that the octahedral structure of IrO ₂ undergoes a singular change, thereby optimizing the performance of the catalyst. By doping IrO ₂ , the amount of noble metal iridium used can be greatly reduced (the performance is best when the molar ratio of doped vanadium is 25% to 30%), thereby reducing the cost of the catalyst. The doped catalyst not only maintains good stability (the test potential under acidic conditions can be kept stable for more than 200 hours), but also its activity is significantly improved (the overpotential of acidic iridium dioxide is about 320mV, and the optimized performance can reach 264mV) . The particle size and crystallinity of the catalyst are closely related to the performance through transmission electron microscopy analysis. The amorphous vanadium-doped iridium dioxide nano-particle pair is obtained by doping with different vanadium content (25%) and temperature control (350°C). The oxygen evolution reaction exhibited the best electrochemical performance. This invention solves the problem of IrO ₂ activity and stability maintenance by reducing the content of noble metal iridium, and provides valuable experience for the research of amorphous materials, and provides a feasible strategy for the synthesis and structure design of electrochemical catalytic materials.

The benefits of the present invention are reflected in:

(1), the prepared catalyst doped with vanadium can effectively reduce the content of noble metal Ir and the preparation method is simple and convenient to reduce the catalyst cost;

(2) The morphology, particle size and crystallinity of the prepared vanadium-doped iridium dioxide catalyst are controllable;

(3) The prepared doped material has many edge active sites; it has excellent durability, which can reach more than 200h

(4) The resistance of the prepared material is small, which is conducive to the efficient transmission of electrons and the improvement of the synergistic effect between materials, so as to better exert their activity.

In summary, the vanadium-doped iridium dioxide provided by the present invention is used in electrocatalyst research methods. On the one hand, it is easy to prepare, strong in practicability, mild in reaction conditions, high in reaction yield, easy in large-scale production, and has no pollution to the environment. In line with green sustainable chemical production; on the other hand, through appropriate condition control, vanadium can be doped into iridium dioxide, and vanadium can be doped into iridium dioxide to adjust the electronic structure of iridium dioxide and by increasing iridium dioxide The disordered structure and amorphous layer, thereby increasing the activity of the catalyst. The prepared doped material has better electrochemical performance in catalyzing electrolysis of water, and has better performance than commercial iridium dioxide in oxygen evolution reaction, and has lower overpotential; it also has good electrochemical performance in hydrogen evolution ; The materials used in the electrolysis of water also showed a lower decomposition voltage.

See the experimental data of the examples for specific effects.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, obtaining other drawings based on these drawings still belongs to the scope of the present invention without any creative effort.

Figure 1 (a), (b) is the TEM image of IrO ₂ before doping vanadium at 350°C, (c), (d) is the TEM image of V _0.25 IrO ₂ after doping at 350°C, as can be seen from Figure 1, According to the TEM image analysis, under the same synthesis conditions, it was observed that the particle contrast between vanadium-doped and undoped was smaller, and the crystallinity was significantly reduced; indicating that doping changed the particle size of IrO ₂ and then optimized the structure to improve the crystallinity of vanadium-doped IrO ₂ catalytic performance;

Figure 2 is the cross-XRD pattern of vanadium-doped iridium dioxide catalytic materials prepared under different doping content and different temperature conditions. From Figure 2, it can be seen that the analysis of the XRD pattern can prove that vanadium is successfully doped into the IrO ₂ lattice. When the content of vanadium occurs, the crystal lattice shifts, and when the temperature is adjusted, the crystallinity will also change;

The electrochemical performance diagram of the vanadium-doped iridium dioxide electrocatalytic material prepared in Fig. 3; as can be seen from Fig. 3, the regulation and control of different contents of doped vanadium proves that there is the best OER activity when doped with a molar ratio of 25%; regulation of different temperatures It shows that at 350°C, there is the best OER activity, and it shows the minimum overpotential at 350°C doped with 25% vanadium in both alkaline and acidic media, d) e) shows that the vanadium-doped IrO ₂ composite material is greatly Reducing the content of precious metal iridium also has significant advantages in hydrogen evolution and water electrolysis applications. (f) The picture is an electrochemical impedance spectrum, which shows that the vanadium-doped IrO2 composite catalyst and IrO2 have very small impedance and good conductivity;

Figure 4: Stability test chart, the durability test of vanadium-doped IrO ₂ through the acid test can reach more than 200h.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

Example 1: Synthesis of vanadium-doped iridium dioxide catalytic material and electrochemical performance characterization

(1) Synthesis of vanadium-doped iridium dioxide catalyst: IrCl ₃ .xH ₂ O and VCl ₃ .xH ₂ O were added to deionized water, citric acid, and ethylene glycol at a molar ratio of 3:1, stirred, heated and mixed for uniform reaction, Stir for approx. until gelled. Then it is transferred to a muffle furnace for pyrolysis, and then a powdery vanadium-doped catalyst is obtained. The reactants IrCl _{3.xH 2} O and VCl _{3.xH 2} O are not limited thereto, and compounds H ₂ IrCl ₆ , K ₂ IrCl ₆ , (NH ₄ ) ₃ IrCl ₆ , (NH ₄ ) ₂ IrCl6, Ir ₄ (CO) _12, etc., and the molar ratio of the iridium compound to the vanadium compound is 1 to 10;

(2) Preparation of the working electrode: Weigh 4.0 mg of the vanadium-doped iridium dioxide catalyst, ultrasonicate at 40KHz for 1 hour to form a suspension, and use a pipette gun to take a certain volume and drop-coat it on 0.5X5 cm carbon paper (or glass Carbon electrode), after drop-coating, let it dry at room temperature, then add a layer of 0.2% nafion solution dropwise, and leave it to dry to obtain a vanadium-doped iridium dioxide catalyst-modified working electrode.

(3) Electrolyte configuration: add 13.3mL concentrated sulfuric acid to 500mL deionized water, stir evenly and cool to room temperature to obtain 0.5MH ₂ SO ₄ electrolyte.

(4) Electrochemical test: test the electrochemical performance of oxygen evolution in the three-electrode system and test the electrochemical performance of electrolyzed water in the two-electrode system. In the three-electrode system, in the 0.5MH ₂ SO ₄ electrolyte, the platinum mesh is used as the counter electrode, calomel is used as the reference electrode, and the self-provided catalyst is used as the working electrode. The above system was connected to an electrochemical workstation to test its linear voltammetry curve (LSV) to test its electrochemical performance. Also in the two-electrode system, the above-mentioned reference electrode and the counter electrode are replaced by the same electrode, which is the self-prepared working electrode. In this system, the electrolytic water decomposition voltage is tested by linear voltammetry scanning.

Embodiment ₂ : Electrochemical performance control of different contents of vanadium-doped IrO

The electrochemical performance in alkaline and acidic media can be adjusted by different molar ratios of vanadium compounds. On the basis of the synthesis conditions and tests in Example 1, the electrochemical properties of different vanadium doping contents (mainly IrO ₂ , 5%, 15%, 25%, and 30%) were synthesized and controlled.

Embodiment 3: the regulation and control of different temperatures

On the basis of Example 2, the synthesis temperature was regulated for the content with the best performance (25%), and then the electrochemical performance of the catalyst was tested.

The above experiments and the description of the accompanying drawings show that doping with 25% vanadium has the best oxygen evolution catalytic activity when the synthetic pyrolysis temperature is 350°C.

Example 4: Applying vanadium-doped oxide composite _IrO2 material to hydrogen evolution and electrolysis of water

The Vx/IrO2 composite was subjected to linear voltammetry sweep tests for hydrogen evolution and electrolytic water.

Example 5: Morphology and object image characterization of doped vanadium iridium dioxide material

Transmission electron microscope (TEM) analysis and X-ray diffraction (XRD) analysis were carried out on the doped Vx/IrO2.

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (6)

1. A preparation method of a vanadium-doped iridium dioxide electrocatalyst is characterized by comprising the following steps of:

preparing a vanadium doped iridium dioxide electrocatalyst from an iridium compound and a vanadium compound by a sol-gel method, wherein the molar ratio of the iridium compound to the vanadium compound is 1-10;

heating and stirring an iridium compound and a vanadium compound to dissolve in deionized water, then adding citric acid and ethylene glycol, stirring to gel microbubbles in a heating state, and then performing high-temperature pyrolysis;

the molar ratio of the added citric acid to the iridium compound is 0.3-40, and the molar ratio of the glycol to the citric acid is 2-1;

the stirring temperature in the heating state is 100-150 ℃, and the stirring rotating speed range is 100-600 r/min.

2. The method for preparing the vanadium-doped iridium dioxide electrocatalyst according to claim 1, wherein the method comprises the following steps: the iridium compound is iridium trichloride hydrate, H ₂ IrCl ₆ 、K ₂ IrCl ₆ 、(NH ₄ ) ₃ IrCl ₆ 、(NH ₄ ) ₂ IrCl ₆ Or Ir ₄ (CO) ₁₂ 。

3. The method for preparing the vanadium-doped iridium dioxide electrocatalyst according to claim 1, wherein the method comprises the following steps: the vanadium compound adopts vanadium trichloride hydrate.

4. The method for preparing the vanadium-doped iridium dioxide electrocatalyst according to claim 1, wherein the method comprises the following steps: the pyrolysis temperature is 300-700 ℃, and the heating rate is 1.5-10 ℃/min.

5. A vanadium doped iridium dioxide electrocatalyst obtainable by a process according to any one of claims 1 to 4.

6. Use of the vanadium doped iridium dioxide electrocatalyst according to claim 5 as a catalyst for the electrolytic water oxygen and hydrogen evolution reactions.

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