Preparation method of three-dimensional self-supporting Rh nanosheets

Abstract

The present invention discloses a preparation method of three-dimensional self-supporting Rh nanosheets. This method uses ethylenediamine as a complexing agent and a structure-directing agent, formaldehyde as a reducing agent, and water as a solvent. Under the condition of no surfactant, Rh<supgt;3+< / supgt; can be reduced to obtain three-dimensional self-supporting Rh nanosheets. This preparation method is simple, green, and economical, and is suitable for large-scale industrial production. The three-dimensional self-supporting Rh nanosheets prepared by the present invention are composed of ultrathin two-dimensional Rh nanosheet subunits, showing the characteristics of a three-dimensional interconnected structure, high atomic utilization rate, and large specific surface area; they have high catalytic reactivity towards the model reaction of methanol electrooxidation and have good application prospects in the field of catalysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and specifically relates to a method for preparing three-dimensional self-supporting Rh nanosheets. This Rh nanomaterial exhibits high catalytic activity as a catalyst for methanol electrocatalytic oxidation reaction. Background Art

[0002] Metallic Rh is a noble metal catalyst with good catalytic performance. The nanostructured Rh nanocrystals have a larger active surface area, which can improve the utilization rate of Rh and expose more catalytic active sites, making it have extremely high application value in the field of catalysis. Currently, due to the high surface energy of Rh, the controllable synthesis of three-dimensional self-supporting Rh nanosheet materials with a high specific surface area is still challenging. The three-dimensional self-supporting structure constructed by the interconnection of two-dimensional nanosheets can not only ensure that the Rh nanocrystals have a fully exposed active surface, but its self-supporting property can also prevent the stacking of the nanosheets themselves, further improving its practicality in catalytic applications. In addition, during the catalytic process, the interconnected structure of the nanosheets can not only better promote the mass transfer and diffusion of reactants and products on the Rh surface, accelerate the reaction kinetics, but also promote the electron transfer in its electrocatalytic applications, reduce the resistance and improve the catalytic efficiency.

[0003] Recent research has shown that Rh nanocrystals have good application prospects in the field of electrocatalysis. It exhibits a lower oxidation potential for methanol electrooxidation reaction in alkaline media than Pt catalysts and has become a research hotspot. Therefore, the design and synthesis of three-dimensional self-supporting Rh nanosheets can significantly increase their electrochemically active surface area and thus improve their methanol electrooxidation activity. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing three-dimensional self-supporting Rh nanosheets with controllable morphology by wet chemical reduction of RhCl3.

[0005] For the above purpose, the technical solution adopted by the present invention is: RhCl3, ethylenediamine and formaldehyde are added to deionized water. After mixing evenly, the obtained mixed solution is transferred to a polytetrafluoroethylene reaction kettle, and a reduction reaction is carried out at 130 - 160 °C for 2 - 8 hours. After the reaction, it is centrifugally washed with deionized water and ethanol and dried under vacuum to obtain three-dimensional self-supporting Rh nanosheets.

[0006] In the above preparation method, it is preferred that the molar ratio of RhCl3 to ethylenediamine and formaldehyde is 1:10 - 20:150 - 300.

[0007] In the above preparation method, it is further preferred that the molar ratio of RhCl3 to ethylenediamine and formaldehyde is 1:12 - 17:200 - 250.

[0008] Further, in the above preparation method, it is preferred that the concentration of RhCl3 in the obtained mixed solution is 2-7 mmol / L.

[0009] Further, in the above preparation method, it is preferred to carry out the reduction reaction at 140-160 °C for 3-5 hours.

[0010] The beneficial effects of the present invention are as follows:

[0011] 1. Compared with other preparation methods, the present invention does not require the participation of surfactants and can be carried out in an aqueous solution, with less pollution, high yield, and easy to achieve gram-scale preparation. At the same time, in the present invention, ethylenediamine acts as a complexing agent and a structure-directing agent during the preparation process, and under the combined action of it and the reducing agent formaldehyde, it can efficiently induce the formation of three-dimensional self-supporting Rh nanosheets.

[0012] 2. The present invention uses ethylenediamine as a complexing agent and a structure-directing agent, and formaldehyde as a reducing agent. Through a hydrothermal reduction method in an aqueous solution, a three-dimensional self-supporting structure composed of ultrathin Rh nanosheets can be prepared from the precursor RhCl3. This method is simple and easy to operate, has a low preparation temperature, is environmentally friendly, and is suitable for large-scale industrial production.

[0013] 3. The three-dimensional self-supporting Rh nanosheets prepared by the present invention have a high specific surface area and abundant low-coordinated active Rh atoms, significantly improving the utilization rate and catalytic reactivity of Rh atoms. Therefore, the three-dimensional self-supporting Rh nanosheets exhibit excellent electrocatalytic methanol oxidation activity, and the peak oxidation potential is shifted negatively by more than 0.2 V compared with the commercial SigmaAldrich Pt black catalyst, and the oxidation peak current is also comparable to that of Pt black. Description of the Drawings

[0014] Figure 1 is the XRD pattern of the three-dimensional self-supporting Rh nanosheets prepared in Example 1.

[0015] Figure 2 is the high-magnification SEM image of the three-dimensional self-supporting Rh nanosheets prepared in Example 1.

[0016] Figure 3 is the SEM image of the three-dimensional self-supporting Rh nanosheets prepared in Example 1.

[0017] Figure 4 is the TEM image of the three-dimensional self-supporting Rh nanosheets prepared in Example 1.

[0018] Figure 5 is the SEM image of the three-dimensional self-supporting Rh nanosheets prepared in Example 2.

[0019] Figure 6 is the SEM image of the three-dimensional self-supporting Rh nanosheets prepared in Example 3.

[0020] Figure 7 It is the cyclic voltammogram of the three-dimensional self-supporting Rh nanosheets prepared in Example 1.

[0021] Figure 8 It is the cyclic voltammogram of the electrocatalytic methanol oxidation of the three-dimensional self-supporting Rh nanosheets prepared in Example 1 and the commercial Sigma Aldrich Pt black catalyst. Detailed implementation manners

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments only.

[0023] Example 1

[0024] 0.25 mL of 0.08 mol / L RhCl3 aqueous solution, 45 μL (0.34 mmol) of ethylenediamine, and 0.75 mL (4.94 mmol) of formaldehyde were added to 6 mL of deionized water. After stirring and mixing evenly, the obtained mixed solution was transferred to a polytetrafluoroethylene reaction kettle and subjected to a reduction reaction at 140 °C in an oven for 5 hours. After the reaction, it was centrifuged, separated, washed 4 - 6 times with deionized water and ethanol, and vacuum dried at 40 °C to obtain three-dimensional self-supporting Rh nanosheets. From Figure 1 the XRD pattern, it can be seen that the obtained product is a face-centered cubic structure Rh nanocrystal. From Figure 2 and Figure 3 it can be seen that the obtained product is a three-dimensional self-supporting structure composed of Rh nanosheets with a thickness of about 2 nm, and these Rh nanosheets show an interpenetrating assembly morphology, fully exposing the surface active sites and edge low-coordination active Rh atoms. In addition, from Figure 4 it can be seen that the interior of the three-dimensional self-supporting Rh nanosheets shows obvious characteristics of a hollow structure, which is beneficial to further improving the utilization rate of Rh atoms.

[0025] Example 2

[0026] 0.5 mL of 0.08 mol / L RhCl3 aqueous solution, 75 μL (0.57 mmol) of ethylenediamine, and 1.5 mL (9.87 mmol) of formaldehyde were added to 6 mL of deionized water. After stirring and mixing evenly, the obtained mixed solution was transferred to a polytetrafluoroethylene reaction kettle and subjected to a reduction reaction at 150 °C in an oven for 4 hours. After the reaction, it was centrifuged, separated, washed 4 - 6 times with deionized water and ethanol, and vacuum dried at 40 °C to obtain three-dimensional self-supporting Rh nanosheets (see Figure 5 ).

[0027] Example 3

[0028] Add 0.75 mL of 0.08 mol / L RhCl3 aqueous solution, 90 μL (0.68 mmol) of ethylenediamine, and 2 mL (13.16 mmol) of formaldehyde to 6 mL of deionized water. After stirring and mixing evenly, transfer the resulting mixture to a polytetrafluoroethylene reaction kettle, and carry out a reduction reaction at 160 °C in a water bath for 3 hours. After the reaction, centrifuge and separate with deionized water and ethanol, wash 4 - 6 times, and dry in vacuo at 40 °C to obtain three-dimensional self-supporting Rh nanosheets (see Figure 6 ).

[0029] To prove the beneficial effects of the present invention, the three-dimensional self-supporting Rh nanosheets prepared in Example 1 were subjected to electrochemical cyclic voltammetry tests and electrocatalytic methanol oxidation tests in an alkaline electrolyte at 30 °C. The results are shown in Figure 7 and Figure 8 .

[0030] As can be seen from Figure 7 , the three-dimensional self-supporting Rh nanosheets show a large hydrogen adsorption / desorption peak. By calculating the integral of the hydrogen desorption charge, it has an electrochemically active surface area as high as 105.0 m 2 / g.

[0031] As can be seen from Figure 8 , due to the large electrochemically active surface area and abundant low-coordinated active Rh atoms of the three-dimensional self-supporting Rh nanosheets prepared by the present invention, the three-dimensional self-supporting Rh nanosheets exhibit a mass activity of 390 A / g; at the same time, the peak oxidation peak potential is negatively shifted by more than 0.2 V compared with the commercial Sigma Aldrich Pt black catalyst, showing excellent methanol electrooxidation kinetics.

Claims

1. A preparation method of three-dimensional self-supporting Rh nanosheets, characterized in that: RhCl3, ethylenediamine, and formaldehyde were added to deionized water. After mixing evenly, the resulting mixture was transferred to a polytetrafluoroethylene reaction kettle and subjected to a reduction reaction at 130-160 °C for 2-8 hours. After the reaction, it was centrifugally washed with deionized water and ethanol and dried under vacuum to obtain three-dimensional self-supporting Rh nanosheets; The molar ratio of the RhCl3 to ethylenediamine and formaldehyde is 1:10-20:150-300; The concentration of RhCl3 in the resulting mixture is 2-7 mmol / L.

2. The preparation method of the three-dimensional self-supporting Rh nanosheets according to claim 1, wherein: The molar ratio of the RhCl3 to ethylenediamine and formaldehyde is 1:12-17:200-250.

3. The preparation method of the three-dimensional self-supporting Rh nanosheets according to claim 1, wherein: The reduction reaction was carried out at 140-160 °C for 3-5 hours.

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