Fe3C-Ru / NFs catalyst as well as preparation method and application thereof

Abstract

The invention relates to a Fe3C-Ru / NFs catalyst as well as a preparation method and application thereof. Wherein the Fe3C-Ru / NFs catalyst comprises carbon nanofibers NFs, and Fe3C and sub-nanoscale Ru particles which are loaded on the carbon nanofibers NFs, and the average particle size of the Ru particles is less than 3nm. The preparation method of the catalyst comprises the following steps: dissolving PVP (Polyvinyl Pyrrolidone), an iron source and a ruthenium source in a mixed solvent of DMF (Dimethyl Formamide) and ethanol to obtain a precursor solution; and preparing FeRu / PVP nanofibers from the precursor solution through an electrostatic spinning method, and then carrying out pre-oxidation and high-temperature carbonization to obtain the Fe3C-Ru / NFs catalyst. According to the invention, Fe3C and sub-nanoscale Ru particles are highly dispersed on the carbon nanofibers, and the Fe3C particles enable the electronic environment of Ru sites to be changed and to be in an electron-deficient state, so that the generation of a catalytic reaction is facilitated, and the catalyst has extremely high electro-catalysis full-water-splitting performance and stability.

Description

Technical Field

[0001] The present invention relates to the field of water electrolysis catalysts; in particular, to a Fe 3 C-Ru / NFs catalyst, preparation method thereof and application in electrocatalytic water decomposition reaction. Background Art

[0002] As a zero-carbon emission energy carrier, hydrogen energy has become a perfect solution to meet the growing energy demand. Among them, electrochemical water splitting is considered to be a highly respected large-scale hydrogen production method due to its outstanding advantages such as zero carbon emissions, ecological sustainability, and simple process. However, the large-scale application of electrochemical water splitting is hindered by the sluggish kinetics and high energy barriers of the cathode hydrogen evolution reaction (HER) and especially the anode oxygen evolution reaction (OER). Platinum (Pt)-based catalysts are well-known for their excellent performance in electrochemical water splitting. However, the high cost and limited natural abundance pose a great obstacle to its scalable application, so there is an urgent need to explore suitable alternatives to Pt metal.

[0003] Since Ru has similar metal hydrogen bond strength and strong water dissociation ability as Pt, and its price is only 1 / 4 of Pt, it is considered to be one of the most promising platinum substitutes. In the existing technology, in order to optimize the HER and OER electrocatalytic performance of Ru-based catalysts and achieve efficient utilization of the precious metal Ru, the strategy of regulating transition metal carbides (TMCs) is widely used. TMCs generally have the characteristics of clear structure, good thermal stability, corrosion resistance, high conductivity and metal-like electronic interaction, and have attracted much attention. However, the intrinsic activity of TMCs is a major obstacle to its application. Considering the advantages of the above two materials, the reasonable combination of Ru and TMCs is expected to be an effective strategy to utilize their respective advantages, which is expected to significantly improve the HER and OER activities of Ru. Summary of the invention

[0004] The first aspect of the present invention discloses an Fe 3 C-Ru / NFs catalyst, comprising carbon nanofiber NFs and Fe supported on the carbon nanofiber NFs 3 C and sub-nanometer Ru particles; wherein the average particle size of the Ru particles is less than 3 nm.

[0005] Furthermore, the average particle size of the Ru particles is 1 to 2 nm.

[0006] The second aspect of the present invention discloses the aforementioned Fe 3 The preparation method of C-Ru / NFs catalyst comprises the following steps:

[0007] PVP (polyvinyl pyrrolidone) as a carbon source, an iron source, and a ruthenium source are dissolved in a mixed solvent of DMF (N,N-dimethylformamide) and ethanol to obtain a precursor solution;

[0008] Electrospinning the precursor solution to obtain FeRu / PVP nanofibers;

[0009] The FeRu / PVP nanofibers are first pre-oxidized and calcined in an air atmosphere, and then carbonized and calcined in an inert atmosphere to obtain FeRu / PVP nanofibers. 3 C-Ru / NFs catalyst.

[0010] Furthermore, the molar ratio of the iron source to the ruthenium source is 3 to 10:1.

[0011] Furthermore, the iron source is ferric nitrate, and the ruthenium source is ruthenium chloride.

[0012] Furthermore, the pre-oxidation temperature is 150-300° C. and the time is 1-3 hours.

[0013] Furthermore, the carbonization calcination is carried out at a temperature of 600 to 800° C. and for a time of 2 to 5 hours.

[0014] Furthermore, the volume ratio of DMF to ethanol in the mixed solvent is 1:1.

[0015] The third aspect of the present invention discloses the aforementioned Fe 3 Application of C-Ru / NFs catalyst in electrocatalytic water splitting reaction.

[0016] Furthermore, the electrocatalytic water decomposition reaction is carried out under alkaline conditions.

[0017] The technical solution of the present invention has the following beneficial effects:

[0018] 1. Fe of the present invention 3 C-Ru / NFs catalysts 3 C optimizes the electronic structure of Ru, causing part of the electrons to transfer from Ru to the Fe site and reduce the electron density on the Ru side, which can optimize the adsorption energy of the reaction intermediates, thereby promoting the HER and OER reactions and achieving efficient HER and OER catalysis in water electrolysis. Among them, the average particle size of sub-nanometer Ru particles is less than 3nm, which realizes the efficient utilization of precious metal Ru and can reduce the amount of precious metal Ru.

[0019] 2. Fe of the present invention 3 C-Ru / NFs catalyst is prepared by electrospinning-high temperature carbonization reduction method. The carbon nanofibers obtained by electrospinning not only have the advantages of large specific surface area, short material diffusion distance, fast electron transmission, but also can realize Fe3 The highly dispersed distribution of C and sub-nanoscale Ru particles on the carbon nanofibers and their strong interaction with the carbon nanofibers reduce the dissolution of metals into the electrolyte, thereby making the catalyst have higher stability.

[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 Example 5 3 XRD pattern of C-Ru / NFs catalyst;

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

[0023] Figure 3 Middle: a and b are SEM images of the catalyst of the embodiment, and c and d are TEM images thereof;

[0024] Figure 4 Middle: a and b are SEM images of the catalyst of Example 1, and c and d are SEM images of the catalyst of Example 2;

[0025] Figure 5 1 is a Raman spectrum of the catalysts of the embodiment and the comparative example;

[0026] Figure 6 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 catalyst of the embodiment;

[0027] Figure 7 In: a is an example and a comparative example and commercial RuO 2 The OER linear sweep voltammetry (LSV) curves of the catalysts are compared, b is the Tafel slope comparison, and c is the double layer capacitance (C dl ) is a comparison diagram, d is an OER timing voltage curve (CP) diagram of the catalyst of the embodiment;

[0028] Figure 8 In the figure: a is a comparison diagram of the LSV of the complete water splitting of the catalyst of the embodiment and the commercial catalyst, and b is a Faraday efficiency diagram (FE) of the catalyst of the embodiment calculated by the hydrogen production efficiency test system;

[0029] Fig. 9 It is the chronovoltage curve (CP) diagram of the complete water splitting of the example catalyst and the commercial catalyst. DETAILED DESCRIPTION

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other variations or replacements made on this basis. Therefore, other possible implementation methods that may be known to those skilled in the art based on the embodiments described in this application all belong to the protection scope of the present invention.

[0031] The embodiment of the present invention discloses a Fe 3 C-Ru / NFs catalyst, including carbon nanofiber NFs and Fe supported on carbon nanofiber NFs 3 C and sub-nanometer Ru particles. 3 C-Ru / NFs catalyst can be obtained by electrospinning-high temperature carbonization reduction method. The specific preparation method includes the following steps:

[0032] (1) PVP is used as a carbon source, and PVP is dissolved in a mixed solvent of DMF and ethanol in a predetermined ratio, and a transparent solution is obtained after magnetic stirring. For example, the degree of polymerization of PVP is ˜1,300,000; the volume ratio of DMF and ethanol is 1:1.

[0033] (2) dissolving an iron source such as ferric nitrate and a ruthenium source such as ruthenium chloride in the transparent solution to obtain a precursor solution, wherein the molar ratio of ferric nitrate to ruthenium chloride can be 3 to 10:1, for example 5:1.

[0034] ⑶ Electrospinning the precursor solution to prepare FeRu / PVP nanofibers.

[0035] (4) Pre-oxidation and calcination of FeRu / PVP nanofibers in air atmosphere to obtain p-FeRu / PVP precursor, wherein the pre-oxidation and calcination temperature can be 150-300° C., and the time can be 1-3 hours, for example, calcination at 200° C. for 2 hours.

[0036] (5) Carry out carbonization calcination of the p-FeRu / PVP precursor in an inert atmosphere such as nitrogen to obtain Fe 3 C-Ru / NFs catalyst. The carbonization calcination temperature may be 600-800°C, and the calcination time may be 2-5 hours, for example, calcination at 700°C for 3 hours.

[0037] Hereinafter, the present invention is described in more detail based on specific examples and comparative examples.

[0038] Example: Fe 3C-Ru / NFs catalyst

[0039] (1) Dissolve 0.5 g of PVP with a degree of polymerization of 1300000 in a mixed solvent of 3 mL of DMF and 3 mL of ethanol, and stir magnetically for 12 h to obtain a transparent solution.

[0040] (2) Dissolve 0.25 mmol of ferric nitrate and 0.05 mmol of ruthenium chloride in the above transparent solution to obtain a precursor solution.

[0041] ⑶ The above precursor solution was used to prepare FeRu / PVP nanofibers by electrospinning.

[0042] The electrospinning voltage was 16 kV and the syringe push speed was 0.8 mL h -1 , the syringe needle model is 21 gauge, and the distance between the syringe and the receiver is 16 cm.

[0043] (4) Calcine the FeRu / PVP nanofibers at 200°C in an air atmosphere for 2 h to obtain a p-FeRu / PVP precursor.

[0044] ⑸ The p-FeRu / PVP precursor was calcined at 700℃ in a nitrogen atmosphere for 3h to obtain Fe 3 C-Ru / NFs catalyst.

[0045] Comparative Example 1: Ru / NFs catalyst

[0046] The difference between Comparative Example 1 and Example 1 is that in step (2), only 0.05 mmol of ruthenium chloride is added to the transparent solution.

[0047] Comparative Example 2: Fe 3 C / NFs catalyst

[0048] The difference between Comparative Example 2 and Example 1 is that in step (2), only 0.25 mmol of ferric nitrate is added to the transparent solution.

[0049] Morphology, size and phase analysis of examples and comparative examples

[0050] Figure 1 The crystal structure and composition of the catalyst in the embodiment were verified by X-ray diffraction (XRD) patterns. Figure 1 It can be seen that Fe 3 The diffraction peak position in the XRD spectrum of C-Ru / NFs is consistent with that of standard Fe 3 The PDF card of C corresponds to the PDF card of C, and there are no other impurities, that is, it does not contain other impurities. No diffraction peak of Ru was found in the spectrum, which may be due to the low content of Ru and extremely small grains. Fe 3The content of precious metal Ru in C-Ru / NFs catalyst is 3.11wt%, and the content of Fe is 6.85wt%.

[0051] 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 484.1 and 461.9 eV, corresponding to the 3p1 / 2 and 3p3 / 2 orbitals of zero-valent Ru. The other two peaks at 486.9 and 463.7 eV correspond to Ru 4+ 3p1 / 2 and 3p3 / 2 orbitals. Figure 2 b shows the Fe2p XPS spectra of Example 2 and Comparative Example 2. The peaks with binding energies of 721.8 and 707.2 eV correspond to the 2p1 / 2 and 2p3 / 2 orbitals of zero-valent Fe, and 724.5 and 709.3 eV correspond to Fe 2+ The 2p1 / 2 and 2p3 / 2 orbitals of Fe, 726.3 and 711.2 eV 3+ The 2p1 / 2 and 2p3 / 2 orbitals, and the remaining two peaks are satellite peaks. Figure 2 From a and b, we know that Fe 3 Fe of C-Ru / NFs 3+ Peak relative to Fe 3 Fe of C / NFs 3+ The peak shifted negatively by about 0.43 eV, while Ru 0 The peak shifted positively by about 0.12 eV, indicating that part of the electrons were transferred from Ru to the Fe site. The reduction in the electron density on the Ru side can optimize the adsorption energy of the reaction intermediates, thereby promoting the HER and OER reactions.

[0052] Figure 2 c shows Fe 3 N1s XPS spectrum of C-Ru / NFs, where the peaks correspond to three N configurations: pyridinic N (398.3 eV), pyrrolic N (399.2 eV) and graphitic N (400.9 eV). Figure 2 d shows Fe 3 O1s XPS spectrum of C-Ru / NFs, in which the three peaks correspond to MO bonds, chemically adsorbed hydroxyl groups (-OH) and carboxyl groups (-COO). 3 The presence of various N and O species in C-Ru / NFs can generate defects on the surface of carbon nanofibers and improve their reactivity.

[0053] Figure 3 ac is Example 1Fe 3Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images of the C-Ru / NFs catalyst clearly show that the carbon nanofibers have highly dispersed nanoscale Fe 3 C particles ( Figure 3 b) and sub-nanometer Ru particles ( Figure 3 c); among which, Fe 3 The average diameter of the C particles is 64.4 nm, and the average diameter of the Ru particles is 1.67 nm. Figure 3 The high-resolution transmission electron microscopy (HRTEM) image in (d) shows two different lattice fringes with lattice spacings of 0.191 nm and 0.205 nm, corresponding to Fe 3 The (200) crystal plane of C and the (101) crystal plane of Ru. In addition, Figure 3 Obvious curved graphite lattice fringes can be observed in d, indicating that Fe 3 C and Ru are embedded in the surface of carbon nanofibers, which can produce stronger interactions with carbon nanofibers, effectively avoid the corrosion of metals in alkaline environments, and ensure the stability of the catalyst.

[0054] Figure 4 a and 4b are field emission scanning electron microscope (FE-SEM) images of the catalyst of Example 1, in which almost no fiber structure is observed. This is due to the thermoplasticity of PVP and the low metal content in Ru / NFs, which causes PVP to fuse during pyrolysis to form a cross-linked structure. Figure 4 c and 4d are field emission scanning electron microscope (FE-SEM) images of the catalyst of Example 2. It is observed that the catalyst of Example 2 also exhibits the same nanofiber shape as the catalyst of Example 1, indicating that the introduction of Ru does not affect the Fe 3 Nanofibrous structure of C-Ru / NFs.

[0055] Figure 5 The Raman spectra of the catalysts of the embodiment and the comparative example are shown in FIG. D band (disordered carbon, 1350 cm -1 ) and G band (sp2 graphitized carbon, 1580cm -1 ) intensity ratio (I D / I G ) reflects the degree of defects and graphitization of the carbon matrix. 3 I of C-Ru / NFs D / I G The strength ratio is 1.01, which is higher than 0.97 of Ru / NFs and 0.97 of Fe / NFs. 3 C / NFs is 0.99, indicating that Fe 3C-Ru / NFs has the highest degree of defects and graphitization, can provide the most active sites and has the best conductivity.

[0056] Electrocatalytic performance test of examples and comparative examples

[0057] Three-electrode system test conditions: 2 The test was conducted in a saturated 1 mol / L KOH solution; the reference electrode was an Ag / AgCl electrode, and the counter electrode was a Pt sheet electrode.

[0058] Fully decomposed water test conditions: in N 2 The test was conducted in a saturated 1 mol / L KOH solution; wherein the reference electrode and the counter electrode were both the catalysts prepared in Example 1.

[0059] Figure 6 a is a comparison of the HER linear sweep voltammetry (LSV) curves of the embodiment, comparative example and commercial Pt / C catalyst, where Fe 3 C-Ru / NFs showed the lowest overpotential at 10 mA cm -2 The HER overpotential is 18 mV at 500 mA cm -2 The HER overpotential under the condition of 202 mV is significantly enhanced, which is significantly better than Ru / NFs and Fe 3 C / NFs and commercial Pt / C. Figure 6 b is the Tafel comparison diagram, where Fe 3 C-Ru / NFs exhibited a lower Tafel slope (37.1 mV dec -1 ), which indicates that Fe 3 C-Ru / NFs have fast reaction kinetics; Figure 6 c is a comparison of the double layer capacitance (Cdl) used to evaluate the electrochemical surface area (ECSA), Fe 3 The Cdl of C-Ru / NFs is 351.3 mF cm -2 , which is much higher than that of other samples, indicating that it can provide more active sites in the HER process. Figure 6 d is Fe 3 HER chronovoltage curve (CP) of C-Ru / NFs at 500 mA cm -2 The current density of Fe 3 The catalytic activity of C-Ru / NFs showed almost no decay, indicating its excellent HER stability.

[0060] Figure 7 a is the embodiment, comparative example and commercial Ru 2 Comparison of OER linear sweep voltammetry (LSV) curves of Fe O catalysts.3 C-Ru / NFs has the lowest overpotential at 10 mA cm -2 The OER overpotential is 263 mV at 500 mA cm -2 The OER overpotential under the condition is 382 mV, which indicates that its OER performance is significantly better than that of Ru / NFs and Fe / NFs. 3 C / NFs and commercial Ru 2 O. 7b is its Tafel comparison diagram, Fe 3 C-Ru / NFs exhibited the lowest Tafel slope (39.7 mV dec -1 ), which indicates that Fe 3 C-Ru / NFs have faster reaction kinetics; Figure 7 c is a comparison of the double layer capacitance (Cdl) used to evaluate the electrochemical surface area (ECSA), Fe 3 C-Ru / NFs dl 6.75mF cm -2 , indicating that it can provide more active sites in the OER process. Figure 7 d is Fe 3 OER chronovoltage curve (CP) of C-Ru / NFs at 500 mA cm -2 The current density of Fe 3 The catalytic activity of C-Ru / NFs showed almost no decay, indicating its excellent OER stability.

[0061] Figure 8 a is embodiment FE 3 Comparison of LSV of complete water splitting between C-Ru / NFs and commercial catalysts, Fe 3 The C-Ru / NFs catalysts only required 1.53 V and 1.83 V to achieve 10 mA cm -2 and 500mA cm -2 The current density is much higher than that of commercial catalysts. Figure 8 b is calculated by the hydrogen production efficiency test system to obtain Fe 3 The Faraday efficiency (FE) of C-Ru / NFs was measured by comparing the theoretical gas production and the actual gas production at different times. 2 With O 2 The volume ratio is 2:1, and Fe is calculated. 3 The overall FE of C-Ru / NFs for water splitting is close to 100%, showing excellent catalytic activity for overall water splitting.

[0062] Fig. 9 Example 5 3The chronopotentiometry (CP) curves of the complete water splitting of C-Ru / NFs catalyst and commercial catalyst, where Fe 3 C-Ru / NFs at 500 mA cm -2 It can work continuously for more than 150 hours at a current density of 1.500 W with almost no attenuation of catalytic activity, and has a stability that is significantly better than that of commercial catalysts.

[0063] In summary, the present invention adopts electrospinning-high temperature carbonization reduction method to obtain Fe 3 C-Ru / NFs catalyst realizes efficient HER and OER catalysis in water electrolysis under alkaline conditions. The preparation process is suitable for large-scale industrial production and has high economic value and application prospects.

Claims

1. A Fe3C-Ru / NFs catalyst, comprising carbon nanofibers NFs and Fe3C and sub-nanometer Ru particles supported on the carbon nanofibers NFs; wherein: The average particle size of the Ru particles is less than 3 nm.

2. The Fe3C-Ru / NFs catalyst according to claim 1; wherein The average particle size of the Ru particles is 1 to 2 nm.

3. The method for preparing the Fe3C-Ru / NFs catalyst according to claim 1 or 2, comprising the following steps: PVP as a carbon source, an iron source, and a ruthenium source are dissolved in a mixed solvent of DMF and ethanol to obtain a precursor solution; Electrospinning the precursor solution to obtain FeRu / PVP nanofibers; The FeRu / PVP nanofibers are firstly pre-oxidized and calcined in an air atmosphere, and then carbonized and calcined in an inert atmosphere to obtain a Fe3C-Ru / NFs catalyst.

4. The preparation method according to claim 3; wherein The molar ratio of the iron source to the ruthenium source is 3 to 10:

1.

5. The preparation method according to claim 3; wherein, The iron source is ferric nitrate, and the ruthenium source is ruthenium chloride.

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

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

8. The preparation method according to claim 3; wherein The volume ratio of DMF to ethanol in the mixed solvent is 1:

1.

9. Use of the Fe3C-Ru / NFs catalyst according to claim 1 or 2 in electrocatalytic water decomposition reaction.

10. The use according to claim 9; wherein: The electrocatalytic water splitting reaction is carried out under alkaline conditions.

Images