Preparation method and application of MnO-Ru / NFs catalyst

Abstract

The invention relates to a preparation method and application of a MnO-Ru / NFs catalyst. The preparation method disclosed by the invention comprises the following steps: dissolving an organic carbon source, a manganese source and a ruthenium source in a mixed solvent of DMF (Dimethyl Formamide) and ethanol to obtain a precursor solution; performing electrostatic spinning on the precursor solution to prepare precursor nanofibers; the preparation method comprises the following steps: pre-oxidizing precursor nanofibers in an air atmosphere, and carbonizing and roasting the precursor nanofibers in an inert atmosphere to obtain the MnO-Ru / NFs catalyst. In the invention, MnO can optimize the electronic environment of Ru sites and reduce the electron density of Ru nanoparticles to facilitate the desorption of H, so that the catalyst shows excellent electro-catalysis full water splitting performance and improved stability.

Description

Technical Field

[0001] The invention relates to the field of water electrolysis catalysts; in particular, to a preparation method of a MnO-Ru / NFs catalyst and application of the catalyst in electrocatalytic water decomposition reactions. Background Art

[0002] As a clean energy carrier, the production of hydrogen mainly depends on the electrolysis of water. With the transformation of the global energy structure and the growing demand for renewable energy, efficient and economical water electrolysis technology is particularly important. Traditional water electrolysis hydrogen production technology mostly uses precious metals such as platinum (Pt), ruthenium (Ru) and iridium (Ir) as electrocatalysts. However, the scarcity and high cost of these precious metals severely limit their popularity in large-scale commercial applications.

[0003] In order to overcome these limitations, it is urgent to seek more economical and sustainable alternative materials. Transition metal-based catalysts have become a research hotspot in this field due to their abundant reserves and low cost, especially manganese (Mn), which is not only low in cost but also shows good catalytic activity. In addition, in the selection of catalyst carriers, carbon nanofibers (CNFs) have become ideal carrier materials due to their high specific surface area, good electrical conductivity and chemical stability. Loading active metal particles on CNFs is conducive to the exposure of catalytic active sites and rapid electron transfer, thereby improving the activity and stability of the catalyst. Summary of the invention

[0004] To further develop the prior art, the first aspect of the present invention provides a method for preparing a MnO-Ru / NFs catalyst, comprising the following steps:

[0005] dissolving an organic carbon source, a manganese source and a ruthenium source in a mixed solvent of DMF and ethanol to obtain a precursor solution;

[0006] Electrospinning the precursor solution to prepare precursor nanofibers;

[0007] The precursor nanofibers are firstly pre-oxidized in an air atmosphere, and then carbonized and calcined in an inert atmosphere to obtain the MnO-Ru / NFs catalyst.

[0008] Furthermore, the pre-oxidation temperature is 150-300° C. and the time is 1-3 hours.

[0009] Furthermore, the carbonization calcination is carried out at a temperature of 600 to 800° C. and for a time of 2 to 5 hours.

[0010] Furthermore, the organic carbon source is PVP.

[0011] Furthermore, the manganese source is manganese acetylacetonate, and the ruthenium source is ruthenium chloride.

[0012] Furthermore, the molar ratio of the manganese source to the ruthenium source is 5 to 15:1.

[0013] Furthermore, the volume ratio of DMF to ethanol in the mixed solvent is 1:1.

[0014] The second aspect of the present invention discloses the use of the MnO-Ru / NFs catalyst obtained by the above-mentioned preparation method in the electrocatalytic decomposition of water under alkaline conditions.

[0015] The technical solution of the present invention has the following beneficial effects:

[0016] 1. The present invention obtains a MnO-Ru / NFs catalyst by electrospinning and calcination carbonization, wherein MnO and Ru are highly dispersed on a carbon nanofiber carrier, and part of Ru is incorporated into the lattice of MnO, so that MnO can more effectively adjust the electronic structure of Ru, optimize the adsorption energy of reaction intermediates, thereby improving the activity of the catalyst for water electrolysis reaction, which helps to improve the hydrogen generation rate and overall energy efficiency.

[0017] 2. In the present invention, after the high-temperature carbonization and calcination step, the Ru and MnO nanoparticles have a strong interaction with the carbon nanofiber support while maintaining a high degree of dispersibility, so that the catalyst exhibits excellent structural stability.

[0018] 3. The MnO-Ru / NFs catalyst prepared in the present invention exhibits excellent HER (hydrogen evolution reaction) and OER (oxygen evolution reaction) catalytic performance under alkaline conditions, and at 100 mA cm -2 The electrolyzer can operate stably for at least 250 h at a current density of 500 mA cm -2 Only 1.88V cell voltage is required at industrial current density.

[0019] 4. The present invention significantly reduces the total cost of the catalyst by using lower-cost manganese and a relatively small amount of ruthenium to replace traditional precious metals such as platinum or iridium, which makes the large-scale production and application of the catalyst economically feasible.

[0020] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the XRD pattern of the catalysts of the embodiment and the comparative example;

[0022] Figure 2In the figure: a is the Ru 3p XPS spectra of the catalysts of Example MnO-Ru / NFs and Comparative Example 1 Ru / NFs, b is the XPS spectra of the Mn 2p of the catalysts of Example and Comparative Example 2 MnO / NFs, c is the O1s XPS spectra of the catalyst of Example, and d is the N1s XPS spectra of the catalyst of Example;

[0023] Figure 3 In: a is a SEM image of the MnO-Ru / NFs catalyst of Example, and b, c and d are TEM images thereof;

[0024] Figure 4 In the figure: a is a comparison of the HER linear sweep voltammetry (LSV) curves of the embodiment, the comparative example and the commercial Pt / C catalyst, b is a comparison of its Tafel slope, and c is a comparison of its double layer capacitance (C dl ) is a comparison diagram, d is a HER chronovoltage curve (CP) diagram of the MnO-Ru / NFs catalyst of the embodiment;

[0025] Figure 5 In the figure: a is a comparison of the OER linear sweep voltammetry (LSV) curves of the embodiment, the comparative example and the commercial RuO2 catalyst, b is a comparison of its Tafel slope, and c is its double layer capacitance (C dl ) is a comparison diagram, d is an OER chronovoltage curve (CP) diagram of the MnO-Ru / NFs catalyst of the embodiment;

[0026] Figure 6 In the figure: a is a comparison diagram of the overall water splitting LSV of the MnO-Ru / NFs catalyst of the embodiment and the commercial catalyst, and b is a Faraday efficiency diagram (FE) of the MnO-Ru / NFs catalyst of the embodiment calculated by the hydrogen production efficiency test system;

[0027] Figure 7 It is a chronovoltage curve (CP) of the complete water splitting of the MnO-Ru / NFs catalyst of the embodiment. DETAILED DESCRIPTION

[0028] The embodiment of the present invention discloses a method for preparing a MnO-Ru / NFs catalyst by combining electrospinning and high temperature carbonization, comprising the following steps:

[0029] An organic carbon source such as PVP (polyvinyl pyrrolidone), a manganese source such as manganese acetylacetonate, and a ruthenium source such as ruthenium chloride are dissolved in a mixed solvent of DMF (N,N-dimethylformamide) and ethanol in a predetermined ratio to obtain a precursor solution. Exemplarily, the degree of polymerization of PVP is ˜1300000, the volume ratio of DMF and ethanol is 1:1, and the molar ratio of manganese acetylacetonate and ruthenium chloride is 10:1.

[0030] Electrospinning the precursor solution to prepare precursor nanofibers;

[0031] The precursor nanofibers are firstly pre-oxidized in an air atmosphere and then carbonized and calcined in an inert atmosphere to obtain a MnO-Ru / NFs catalyst.

[0032] The pre-oxidation temperature may be 150-300° C. (eg, 200° C.) and the time may be 1-3 h (eg, 2 h); the carbonization calcination temperature may be 600-800° C. (eg, 700° C.) and the time may be 2-5 h (eg, 2 h).

[0033] Hereinafter, the present invention is described in more detail based on specific examples and comparative examples.

[0034] Example: Preparation of MnO-Ru / NFs catalyst

[0035] (1) Dissolve 0.5 g PVP in a mixed solvent of 3 mL DMF and 3 mL ethanol and stir magnetically for 12 h to obtain a transparent solution.

[0036] (2) Dissolve 0.5 mmol of manganese acetylacetonate and 0.05 mmol of ruthenium chloride in the above transparent solution to obtain a precursor solution.

[0037] ⑶ The precursor solution was electrospinned to prepare precursor nanofibers. The electrospinning voltage was 17 kV and the syringe push speed was 0.8 mL h -1 , the syringe needle is 21 gauge, and the distance between the syringe and the receiver is 16 cm.

[0038] (4) Pre-oxidize the precursor nanofibers in an air atmosphere at 200°C for 2 hours; then, raise the temperature to 700°C in a nitrogen atmosphere and keep calcining for 2 hours to obtain a MnO-Ru / NFs catalyst.

[0039] Comparative Example 1: Preparation of Ru / NFs catalyst

[0040] The difference between Comparative Example 1 and the embodiment is that in step (2), only 0.05 mmol of ruthenium chloride is added to the transparent solution.

[0041] Comparative Example 2: Preparation of MnO / NFs catalyst

[0042] The difference between Comparative Example 2 and the embodiment is that in step (2), only 0.5 mmol of manganese acetylacetonate was added to the transparent solution.

[0043] Morphology and Phase Analysis of Examples and Comparative Examples

[0044] Figure 1The X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1 was used to verify the crystal structure and composition. Figure 1 It can be seen from a that the XRD spectrum of MnO-Ru / NFs prepared in Example 1 has no other impurities, that is, it does not contain other impurities, and the position of the diffraction peak corresponds to the PDF card of standard MnO. Figure 1 b It can be seen that the peak of MnO-Ru / NFs has a certain degree of negative shift relative to the peak of MnO / NFs, indicating that part of Ru is incorporated into the MnO lattice. No Ru peak is found in the spectrum, which may be due to the low content of Ru and its incorporation into the MnO lattice.

[0045] Figure 2 It is the XPS spectrum of the catalyst of Example and Comparative Example. Figure 2 a shows the Ru 3pXPS spectra of Example 1 and Comparative Example 1. There are two peaks at 484.0 and 461.8 eV, corresponding to the 3p1 / 2 and 3p3 / 2 orbitals of zero-valent Ru. The other two peaks with binding energies of 487.1 and 463.5 eV correspond to Ru 4+ 3p1 / 2 and 3p3 / 2 orbitals. Figure 2 b shows the Mn 2p XPS spectra of the catalysts of Example 2 and Comparative Example 2. The peaks with binding energies of 653.4 and 641.7 eV correspond to the Mn 2+ The remaining peak belongs to the satellite peak. Figure 2 The comparison between a and 2b shows that the MnO-Ru / NFs 2+ The peak relative to MnO / NFs 2+ The peak shifted negatively by about 0.41 eV, while Ru 0 The peak shifted positively by about 0.21 eV, indicating that part of the electrons were transferred from Ru to Mn sites, and the decrease in the electron density of Ru nanoparticles was beneficial to the desorption of H and promoted the HER and OER reactions.

[0046] Figure 2 c shows the O1s XPS spectrum of the MnO-Ru / NFs catalyst, in which the three peaks correspond to the MO bonds, chemisorbed hydroxyl groups (-OH), and carboxyl groups (-COO). Figure 2 d shows the N1s XPS spectrum of the MnO-Ru / NFs catalyst, where the peaks correspond to three N configurations: pyridinic N (398.5 eV), pyrrolic N (399.5 eV), and graphitic N (400.7 eV). The presence of multiple N and O species in MnO-Ru / NFs can produce defects on the surface of carbon nanofibers and improve their reactivity.

[0047] Figure 3a and b are the field emission scanning electron microscope (FE-SEM) images and transmission electron microscope (TEM) images of the MnO-Ru / NFs catalyst of the example, and it can be clearly seen that the nanoparticles are very evenly distributed on the carbon nanofiber morphology. Figure 3 The high-resolution transmission electron microscopy (HRTEM) images in c and d show two different lattice fringes with lattice spacings of 0.255 nm and 0.442 nm, corresponding to the (111) crystal plane of MnO and the (201) crystal plane of Ru, respectively.

[0048] Electrocatalytic performance test of examples and comparative examples

[0049] The three-electrode system test conditions are as follows: the test is conducted in a 1 mol / L KOH solution saturated with N2; the reference electrode is an Ag / AgCl electrode, and the counter electrode is a Pt sheet electrode.

[0050] The conditions for the complete water splitting test were as follows: the test was conducted in a 1 mol / L KOH solution saturated with N2; wherein the reference electrode and the counter electrode were both the catalysts prepared in Example 1.

[0051] Figure 4 The HER performance comparison of different catalysts is shown. Figure 4 The HER linear sweep voltammetry (LSV) curve of a shows that the MnO-Ru / NFs catalyst has a -2 The overpotential at a current density of only 16 mV is -2 The overpotential is 216 mV, which is the lowest, and it shows significant activity in HER. Figure 4 As shown in the Tafel slope diagram (b), the Tafel slope of MnO-Ru / NFs is 27.5 mV dec. -1 , this lower value indicates its fast kinetic characteristics in the HER reaction. Figure 4 c shows the double layer capacitance (Cdl) that can be used to evaluate the electrochemically active surface area (ECSA). The Cdl of MnO-Ru / NFs reaches 502.3 mF cm -2 , which is significantly higher than other comparative samples, indicating that MnO-Ru / NFs can provide more active sites during the reaction. Figure 4 The chronovoltage curve (CP) of d shows that at 100 mA cm -2 At a constant current density of , the MnO-Ru / NFs catalyst showed stability for more than 50 h, with almost no attenuation of HER catalytic activity, demonstrating its excellent durability.

[0052] Figure 5 The electrochemical performance of different catalysts in OER is demonstrated. Figure 5As shown in the comparison of OER linear sweep voltammetry (LSV) curves of a, the MnO-Ru / NFs catalyst has a -2 The overpotential at the current density is only 265mV, while at 500mAcm -2 The overpotential is 396 mV, which is the lowest among all samples and has superior OER catalytic activity than Ru / NFs, MnO / NFs and commercial Ru2O. Figure 5 As shown in the Tafel slope diagram (b), the Tafel slope of the MnO-Ru / NFs catalyst is 48.1 mV dec -1 , this lowest value indicates that it has faster reaction kinetics in OER, which is better than other tested samples. Figure 5 c The electrochemically active surface area (ECSA) of each sample was evaluated by measuring the double layer capacitance (Cdl). The Cdl value of MnO-Ru / NFs was 17.9 mF cm -2 , which is higher than other comparison samples, indicating that it can provide more active sites in the OER process. Figure 5 The chronovoltage curve (CP) of d shows that at 100 mA cm -2 Long-term stability tests under current density showed that the OER catalytic activity of the MnO-Ru / NFs catalyst showed almost no attenuation after more than 50 hours of continuous operation, demonstrating excellent durability.

[0053] Figure 6 The data in show the performance comparison of the example MnO-Ru / NFs catalyst and commercial catalyst in the overall hydrolysis reaction. Figure 6 a, at 10 mA cm -2 and 500mAcm -2 In the current density test, the MnO-Ru / NFs catalyst of the embodiment only needs 1.53V and 1.84V voltage to reach these current densities, showing that it far exceeds the performance of commercial catalysts. The Faraday efficiency (FE) of MnO-Ru / NFs was evaluated using a hydrogen production efficiency test system. Figure 6 As shown in (b), by comparing the theoretical gas production with the measured gas production, the volume ratio of H2 to O2 is 2:1. This result shows that the Faraday efficiency of MnO-Ru / NFs in the overall electrolysis of water is close to 100%, proving its excellent catalytic activity in overall water splitting.

[0054] Figure 7 The chronopotentiometry curve (CP) of water splitting shows that at 100 mA cm -2At a current density of 2.5 Å, the MnO-Ru / NFs catalyst exhibited a continuous working ability of more than 250 h, and its catalytic activity showed almost no decay.

[0055] In summary, the present invention combines electrospinning technology with carbonization and calcination steps to prepare MnO-Ru / NFs catalysts. The use of electrospinning technology makes the production process of the catalyst easy to control and scale up, which helps to meet the needs of industrial large-scale production. The adjustability of this technology also allows the performance of the catalyst to be carefully adjusted to meet different application requirements. Further, the preparation method of the present invention can evenly load Ru and MnO particles on carbon nanofibers, and significantly improve the efficiency of electrocatalytic water decomposition through the synergistic effect of Mn and Ru. In addition, the catalyst exhibits high stability and excellent electrocatalytic performance, providing an effective technical solution to solve the problems of high cost and resource limitations of traditional precious metal catalysts.

Claims

1. A method for preparing a MnO-Ru / NFs catalyst, comprising the following steps: dissolving an organic carbon source, a manganese source and a ruthenium source in a mixed solvent of DMF and ethanol to obtain a precursor solution; Electrospinning the precursor solution to prepare precursor nanofibers; The precursor nanofibers are firstly pre-oxidized in an air atmosphere, and then carbonized and calcined in an inert atmosphere to obtain the MnO-Ru / NFs catalyst.

2. The preparation method according to claim 1; wherein The pre-oxidation temperature is 150-300° C. and the time is 1-3 hours.

3. The preparation method according to claim 1; wherein The carbonization calcination temperature is 600-800° C. and the time is 2-5 hours.

4. The preparation method according to claim 1; wherein The organic carbon source is PVP.

5. The preparation method according to claim 1; wherein The manganese source is manganese acetylacetonate, and the ruthenium source is ruthenium chloride.

6. The preparation method according to claim 1; wherein The molar ratio of the manganese source to the ruthenium source is 5 to 15:

1.

7. The preparation method according to claim 1; wherein The volume ratio of DMF to ethanol in the mixed solvent is 1:

1.

8. Use of the MnO-Ru / NFs catalyst obtained according to the preparation method according to any one of claims 1 to 7 in electrocatalytic water decomposition under alkaline conditions.

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