A manganese-doped ruthenium dioxide nanofiber material, a preparation method thereof, and applications thereof in alkaline electrocatalytic hydrogen evolution and oxygen evolution

Abstract

A manganese-doped ruthenium dioxide nanofiber material, a preparation method thereof, and an application thereof in alkaline electrocatalytic hydrogen evolution and oxygen evolution at industrial-level current intensity belong to the technical field of controllable preparation of doped metal oxide nanomaterials. In the present invention, a manganese-doped ruthenium dioxide nanofiber material is prepared by two steps of electrospinning technology and calcination in an air atmosphere. The material exists in a uniform fiber morphology as a whole, and the surface is rough. This method is simple and efficient and can be applied to large-scale industrialization. The manganese-doped ruthenium dioxide nanofiber material prepared in the present invention, as a bifunctional electrocatalyst for electrocatalytic water splitting, exhibits excellent hydrogen evolution and oxygen evolution catalytic activities and stability at industrial-level current density, realizes the efficient and stable preparation of clean and green hydrogen energy, solves the disadvantages of low catalyst activity and poor stability in current industry, and provides an efficient solution to the increasingly serious environmental problems, having high practical application and economic value.

Description

Technical Field

[0001] The present invention belongs to the technical field of controllable preparation of doped metal oxide nanomaterials, and particularly relates to a manganese-doped ruthenium dioxide nanofiber material, a preparation method thereof, and an application thereof in alkaline electrocatalytic water hydrogen evolution and oxygen evolution at industrial-level current intensity. Background Art

[0002] Nowadays, electrochemical water splitting devices are considered as a high-performance and convenient method for producing hydrogen, which can significantly solve environmental pollution and fossil fuel consumption with high-density energy carriers. However, the low activity and low energy efficiency of traditional alkaline water electrolyzers are difficult to meet the current industrial requirements. At the same time, currently, most hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts only drive the electrocatalytic process at a small current density, still far from meeting the industrial requirements (≥500 mA / cm 2 ). And the poor stability always makes these catalysts difficult to withstand a large current density, becoming a stumbling block to their practical application. Therefore, advanced alkaline water electrolyzers not only need to have good activity for HER and OER, but also can withstand ohmic losses at a large current density.

[0003] Metal doping is an effective method to improve the intrinsic activity of catalysts. Introducing foreign atoms into the lattice of metal oxides can reasonably adjust the atomic coordination and electronic structure, thereby improving their catalytic ability. For example, in iron-doped cobalt ferrite (Fe-Co3O4), the isolated Fe atoms in the Co3O4 lattice can well adjust the adsorption ability of reaction intermediates, thereby improving the catalytic activity (Advanced Materials., 2020, 32, 2002235). However, non-precious metal-based materials still have difficulty breaking through the bottleneck of low activity. Therefore, it is urgent to further improve the catalytic activity and stability of precious metal-based materials to meet the industrial production requirements. Ruthenium dioxide (RuO2) has excellent OER catalytic activity and a lower price compared to platinum and iridium-based catalysts, but its stability and catalytic activity at high current density are low. Currently, there are literature reports that its OER stability can be effectively adjusted by metal doping, but there is still no report on the improvement of its activity and stability as a bifunctional catalyst at high current density. As a multivalent element, Mn can greatly improve the activity and oxidation resistance of RuO2 at high current density. At the same time, Mn doping can also optimize the hydrogen adsorption energy of HER reaction intermediates, thereby significantly improving its HER performance. Therefore, in view of the above problems, the present invention combines the advantages of the two to prepare a high-activity and high-stability bifunctional electrocatalyst for alkaline water electrolysis at industrial-level current intensity. Summary of the Invention

[0004] The object of the present invention is to provide a manganese-doped ruthenium dioxide nanofiber material with high efficiency and high stability at high current density, a preparation method thereof, and its application in alkaline electrocatalytic hydrogen evolution and oxygen evolution at industrial-level current intensity.

[0005] The present invention prepares a manganese-doped ruthenium dioxide nanofiber material by combining electrospinning technology with calcination in an air atmosphere. The material exists as a uniform fibrous morphology as a whole, and the surface is rough. By optimizing the preparation process and material ratio, a suitable formulation is determined. The prepared catalyst has excellent catalytic activity. In 1 mol / L KOH electrolyte, when the current density reaches 1 A / cm 2 the overpotentials required for hydrogen evolution reaction and oxygen evolution reaction are 269 mV and 461 mV respectively.

[0006] A preparation method of a manganese-doped ruthenium dioxide nanofiber material according to the present invention comprises the following steps:

[0007] (1) Prepare a nanofiber membrane by electrospinning method: First, dissolve 0.4 - 0.7 g of polyvinylpyrrolidone (PVP), 0.01 - 0.05 g of manganese salt and 0.4 - 0.5 g of ruthenium salt in 4 - 8 mL of a mixed solution of N,N-dimethylformamide and water. The amount of N,N-dimethylformamide or water can be 0. Stir overnight to obtain a uniform viscous spinning solution precursor. Inject the viscous spinning solution precursor into the syringe of the electrospinning device, and perform electrospinning under the conditions of a spinning distance of 15 - 30 cm and a spinning voltage of 12 - 25 kV, so as to obtain a nanofiber membrane on an aluminum foil receiving plate;

[0008] (2) Calcinate the nanofiber membrane obtained in step (1) in air at 400 - 600 °C for 2 - 4 h to obtain the manganese-doped ruthenium dioxide nanofiber material of the present invention, and the product presents a dark green film shape; the manganese-doped ruthenium dioxide nanofiber is a one-dimensional material with a diameter of 100 - 250 nm and a length greater than 5 μm.

[0009] The manganese salt in step (1) can be manganese nitrate, manganese chloride, manganese sulfate, manganese acetate, etc.; the ruthenium salt can be potassium chlororuthenate, ruthenium chloride or ammonium chlororuthenate, etc.; the molecular weight of PVP is 800000 - 2000000.

[0010] The beneficial effects of the present invention:

[0011] 1. The method of the present invention is simple and easy to implement, the experimental procedure is controllable, the preparation period is short, and industrial large-scale production can be realized.

[0012] 2. The ruthenium dioxide nanofiber material doped with manganese prepared by the present invention is used as a bifunctional electrocatalyst for electrocatalytic water splitting at a high current density. By adjusting the doping amount of manganese, it exhibits excellent catalytic activity, which can greatly reduce the overpotential required for the water splitting reaction at a high current density and extend its stability. The electrocatalytic hydrogen evolution and oxygen evolution current densities reach 1 A / cm 2 When it reaches 2 , only the overpotentials of 269 mV and 461 mV are required, and the catalytic stabilities reach 500 h and 170 h, respectively, which has important practical application value. Description of the Drawings

[0013] Figure 1 : Scanning electron microscope (SEM) image of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1.

[0014] Figure 2 : X-ray diffraction (XRD) pattern of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1.

[0015] Figure 3 : Raman spectrum of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1.

[0016] Figure 4 : Polarization curve of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1 during the hydrogen evolution process.

[0017] Figure 5 : Polarization curve of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1 during the oxygen evolution process.

[0018] Figure 6 : Time-current curve of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1 for the hydrogen evolution process.

[0019] Figure 7 : Time-current curve of the ruthenium dioxide nanofiber material doped with manganese prepared in Example 1 for the oxygen evolution process. Detailed Embodiments

[0020] The present invention will be further described below through examples in combination with the drawings. However, the protection scope of the present invention is not limited to the following examples. Those skilled in the art are aware that the present invention can be changed or adjusted without departing from the gist and scope of the present invention, and these changes or adjustments are also included in the protection scope of the present invention.

[0021] 1. Preparation method of the ruthenium dioxide nanofiber material doped with manganese

[0022] Example 1

[0023] Preparation of nanofiber membrane by electrospinning method: First, 0.5 g of polyvinylpyrrolidone (PVP, molecular weight 1,300,000), 0.03 g of manganese nitrate and 0.47 g of ruthenium chloride were dissolved in a mixed solution of 3 mL of N,N-dimethylformamide (DMF) and 3 mL of water, and then stirred overnight to obtain a homogeneous viscous spinning solution precursor; The spinning solution precursor was injected into the syringe of the electrospinning device, and electrospinning was carried out under the conditions of a spinning distance of 20 cm and a spinning voltage of 16 kV to obtain a nanofiber membrane on the aluminum foil receiving plate; The obtained nanofiber membrane was calcined in air at 500 °C for 2 h to obtain a manganese-doped ruthenium dioxide nanofiber material catalyst. The product presented a dark green film shape and was named manganese-doped ruthenium dioxide-1.

[0024] Some structural studies were carried out on the materials prepared by the above method. Figure 1 Figure 5 is the scanning electron microscope (SEM) image of the obtained manganese-doped ruthenium dioxide-1. From Figure 1 it can be seen that the material is a one-dimensional nanofiber with a rough surface and uniform diameter, with a diameter of 100 - 250 nm and a length greater than 5 μm.

[0025] Figure 2 Figure 6 is the X-ray diffraction (XRD) pattern of the material. It can be seen that the obtained main body is a pure phase of ruthenium dioxide.

[0026] Figure 3 Figure 7 is the Raman spectrum of the material. It can be seen that the peak at 565 cm -1 is attributed to the manganese-oxygen bond, confirming the successful doping of manganese.

[0027] Example 2

[0028] Same as Example 1, except that in the preparation of manganese-doped ruthenium dioxide-1, the contents of manganese nitrate and ruthenium chloride were changed to 0.012 g and 0.488 g, and the amounts and conditions of other reactants remained unchanged, to obtain the product manganese-doped ruthenium dioxide-2.

[0029] Example 3

[0030] Same as Example 1, except that in the preparation of manganese-doped ruthenium dioxide-1, the contents of manganese nitrate and ruthenium chloride were changed to 0.048 g and 0.452 g, and the amounts and conditions of other reactants remained unchanged, to obtain the product manganese-doped ruthenium dioxide-3.

[0031] Example 4

[0032] Same as Example 1, except that in the preparation of manganese-doped ruthenium dioxide-1, manganese nitrate was replaced with manganese chloride, and the amounts and conditions of other reactants remained unchanged, to obtain the product manganese-doped ruthenium dioxide-4.

[0033] Example 5

[0034] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, ruthenium chloride was replaced with ammonium chlororuthenate, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-5.

[0035] Example 6

[0036] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, the calcination temperature was increased to 600 °C and the calcination time was extended to 4 h, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-6.

[0037] Example 7

[0038] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, the calcination temperature was reduced to 400 °C, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-7.

[0039] Example 8

[0040] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, the voltage was increased to 20 kV during the electrospinning process, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-8.

[0041] Example 9

[0042] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, 3 mL of N,N-dimethylformamide (DMF) and 3 mL of water were all replaced with 6 mL of water, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-9.

[0043] Example 10

[0044] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, 3 mL of N,N-dimethylformamide (DMF) and 3 mL of water were all replaced with 6 mL of N,N-dimethylformamide (DMF), and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-10.

[0045] Example 11

[0046] Same as Example 1, except that in the preparation of ruthenium manganese dioxide-1, the amounts of N,N-dimethylformamide (DMF) and water were both reduced to 2 mL, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium manganese dioxide-11.

[0047] Example 12

[0048] Same as Example 1, except that in the preparation of manganese-doped ruthenium dioxide-1, the content of polyvinylpyrrolidone (PVP, molecular weight 1,300,000) was increased to 0.6 g, and the amounts and conditions of other reactants remained unchanged, to obtain the product manganese-doped ruthenium dioxide-12.

[0049] Comparative Example 1

[0050] Same as Example 1, except that in the preparation of manganese-doped ruthenium dioxide-1, manganese nitrate was not added, but 0.5 g of ruthenium chloride was added, and the amounts and conditions of other reactants remained unchanged, to obtain the product ruthenium dioxide. This product is nanofibers with the same morphology as in Example 1.

[0051] 2. Study on the electrocatalytic hydrogen evolution and oxygen evolution properties of manganese-doped ruthenium dioxide nanofiber materials

[0052] Example 13

[0053] Specifically, the manganese-doped ruthenium dioxide-1 prepared in Example 1 was dispersed in a mixed solution of water, ethanol, and Nafion (mass ratio of water, ethanol, and Nafion is 495:495:10) to prepare a dispersion with a concentration of 2 mg / mL; then 60 μL of the dispersion was dropped on a carbon paper with an area of 9 mm 2 and air-dried naturally to obtain the carbon paper loaded with the catalyst; the prepared carbon paper was tested in an electrolytic cell, and the test system was a three-electrode system (the carbon paper loaded with the catalyst was the working electrode, a carbon rod (for hydrogen evolution test) or a platinum wire (for oxygen evolution test) was the counter electrode, and a mercury oxide electrode (Hg / HgO) was the reference electrode), and the electrolyte was 1 mol / L KOH solution. Before the test, Ar was bubbled into the electrolytic cell until saturation, and the Ar atmosphere was maintained throughout the test. To evaluate the hydrogen evolution and oxygen evolution activities, linear sweep voltammetry (LSV) tests were carried out with a scan rate of 1 mV / s. At the same current density, the higher the overpotential, the lower the hydrogen production and oxygen production ability. It should be noted that all the potentials obtained with the mercury oxide reference electrode in the electrocatalytic tests were converted to the reversible hydrogen electrode potential in the property diagram, and the external power supply was the main battery of the electrochemical workstation.

[0054] Some properties of the modified electrode prepared by the above process were studied. Figure 4 Linear sweep voltammetry polarization curve of the manganese-doped ruthenium dioxide-1 nanofiber material catalyst prepared in Example 1 for hydrogen evolution reaction (HER) in potassium hydroxide (1 M KOH) solution. The overpotentials at current densities of 10 mA / cm 2 and 1 A / cm 2 are 29 mV and 269 mV, respectively. It shows that the material of the present invention has excellent hydrogen evolution catalytic activity.

[0055] Figure 5Linear sweep voltammetry polarization curve of the manganese-doped ruthenium dioxide-1 nanofiber material catalyst prepared in Example 1 for oxygen evolution reaction (OER) in potassium hydroxide (1 M KOH) solution. At current densities of 10 mA / cm 2 and 1 A / cm 2 the overpotentials are 236 mV and 461 mV, respectively, indicating that the material of the present invention has excellent oxygen evolution catalytic activity.

[0056] Figure 6 Time-current curve of the manganese-doped ruthenium dioxide-1 nanofiber material catalyst prepared in Example 1 for hydrogen evolution reaction (HER) in potassium hydroxide (1 M KOH) solution. At a current density of 1 A / cm 2 the catalyst can be stable for 500 h with almost no obvious decay in current density, indicating that the material of the present invention has excellent stability for the hydrogen evolution process at high current densities at the industrial level.

[0057] Figure 7 Time-current curve of the manganese-doped ruthenium dioxide-1 nanofiber material catalyst prepared in Example 1 for oxygen evolution reaction (OER) in potassium hydroxide (1 M KOH) solution. At a current density of 1 A / cm 2 the catalyst can be stable for 170 h with almost no obvious decay in current density, indicating that the material of the present invention has excellent stability for the oxygen evolution process at high current densities at the industrial level.

[0058] Example 14

[0059] The test conditions and the method for preparing the modified electrode are the same as those in Example 13, except that the catalyst is replaced with the material prepared in Example 2, and thus the electrocatalytic tests of hydrogen evolution and oxygen evolution properties are carried out. The overpotentials for hydrogen evolution and oxygen evolution of the prepared catalyst are 86 mV and 241 mV, respectively, at 10 mA / cm 2 and 406 mV and 631 mV, respectively, at 1 A / cm 2

[0060] Example 15

[0061] The test conditions and the method for preparing the modified electrode are the same as those in Example 13, except that the catalyst is replaced with the material prepared in Example 3, and thus the electrocatalytic tests of hydrogen evolution and oxygen evolution properties are carried out. The overpotentials for hydrogen evolution and oxygen evolution of the prepared catalyst are 76 mV and 262 mV, respectively, at 10 mA / cm 2 and 539 mV and 616 mV, respectively, at 900 mA / cm 2

[0062] Comparative Example 2

[0063] ​​The test conditions and the means for preparing the modified electrode were the same as those in Example 13, except that the catalyst was replaced with the material prepared in Comparative Example 1, and thus the electrocatalytic tests of hydrogen evolution and oxygen evolution properties were carried out. The overpotentials for hydrogen evolution and oxygen evolution of the prepared catalyst were 256 mV and 282 mV respectively at 10 mA / cm 2 , and the overpotentials for hydrogen evolution and oxygen evolution were 585 mV and 499 mV respectively at 200 mA / cm 2 . Compared with Examples 13, 14, and 15, the electrocatalytic hydrogen evolution and oxygen evolution properties of Comparative Example 2 were significantly reduced, and it was difficult to reach a higher current density.

Claims

1. A preparation method of a manganese-doped ruthenium dioxide nanofiber material applied in alkaline electrocatalytic hydrogen evolution and oxygen evolution at industrial-level current intensity, the steps are as follows: (1) Prepare a nanofiber membrane by electrospinning: First, dissolve 0.4 - 0.7 g of polyvinylpyrrolidone, 0.01 - 0.05 g of manganese salt and 0.4 - 0.5 g of ruthenium salt in 4 - 8 mL of a mixed solution of N,N-dimethylformamide and water. The amount of N,N-dimethylformamide or water can be 0. Stir overnight to obtain a uniform viscous spinning solution precursor. Inject the spinning solution precursor into the syringe of the electrospinning device and electrospin under the conditions of a spinning distance of 15 - 30 cm and a spinning voltage of 12 - 25 kV, so as to obtain a nanofiber membrane on an aluminum foil receiving plate; (2) Calcinate the nanofiber membrane obtained in step (1) in air at 400 - 600 °C for 2 - 4 h to obtain a one-dimensional manganese-doped ruthenium dioxide nanofiber material with a diameter of 100 - 250 nm and a length greater than 5 μm; Among them, The manganese salt is manganese nitrate, manganese chloride, manganese sulfate or manganese acetate; the ruthenium salt is potassium ruthenium chloride, ruthenium chloride or ammonium ruthenium chloride; the molecular weight of polyvinylpyrrolidone is 800000 - 2000000.

2. A ruthenium manganese dioxide nanofiber material applied in alkaline electrocatalytic hydrogen evolution and oxygen evolution at industrial-level current intensity, characterized in that: It is prepared by the method described in claim 1.

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