FeP-embellished carbon-coated cobalt zinc carbide electrocatalyst constructed based on pore confinement and preparation method of FeP-embellished carbon-coated cobalt zinc carbide electrocatalyst

Abstract

The invention discloses a FeP-decorated carbon-coated cobalt zinc carbide electrocatalyst constructed based on a pore confinement and a preparation method thereof, and belongs to the technical field of electrocatalytic materials. The preparation method comprises the following steps: dissolving a zinc-containing nitrate hydrate and a cobalt-containing nitrate hydrate in methanol to obtain a solution A; dissolving a proper amount of 2-methylimidazole in methanol to obtain a solution B; adding the solution B into the solution A while stirring at room temperature, standing after stirring, centrifugally drying to obtain ZnCo-ZIF, and calcining the ZnCo-ZIF to obtain a Co / Co3ZnC-CN precursor; dissolving the precursor in n-ethane to obtain a solution C; dissolving the iron-containing nitrate hydrate in methanol to obtain a solution D; dropwise adding the solution D into the solution C, stirring, centrifuging, drying to obtain a black precipitate, then carrying out calcination treatment twice, adding a phosphorus source during second-stage calcination, and cooling to obtain a black target product. The electrocatalytic material obtained by the method can show excellent water electrolysis performance, electrochemical activity and long-term stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and in particular relates to a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst constructed based on pore confinement and a preparation method thereof. Background Art

[0002] The essence of hydrogen production by water electrolysis is to convert electrical energy into chemical energy. In addition to electricity provided by non-renewable energy, the required electricity can also be supplied by renewable energy sources such as wind energy, solar energy, nuclear energy and hydropower. The decomposition of water involves two half reactions. One end undergoes a reduction reaction at the cathode to obtain electrons to produce hydrogen, which is called the hydrogen evolution reaction; the other end undergoes an oxidation reaction at the anode to lose electrons to produce oxygen, which is called the oxygen evolution reaction. As an emerging electrocatalyst, transition metal phosphides (TMPs) have shown excellent performance in the field of electrocatalytic water splitting. Materials such as single metal phosphides CoP and FeP have attracted widespread attention from researchers due to their unique electronic structure and excellent catalytic activity. These catalysts not only perform well in catalyzing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), but also show excellent performance in stability and durability.

[0003] Then, single metal phosphides have poor stability in strong alkaline environments and are prone to dissolution or structural collapse, resulting in a decrease in catalytic activity; in addition, the existing methods for preparing electrocatalysts mostly adopt traditional high-pressure and high-heat methods, which have high energy consumption and are not conducive to large-scale industrial production. Summary of the invention

[0004] The purpose of the present invention is to provide a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst constructed based on pore confinement and a preparation method thereof. The preparation method is simple and efficient, and can reduce energy consumption and equipment requirements; the prepared FeP-Co / Co3ZnC@CN electrocatalyst can exhibit excellent water electrolysis performance, electrochemical activity and long-term stability.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a preparation method of FeP dotted carbon coated cobalt zinc carbide electrocatalyst based on pore confinement, comprising the following steps: S1. Preparation of Co / Co3ZnC@CN precursor; S1-1, dissolving zinc nitrate hydrate and cobalt nitrate hydrate in methanol, recorded as solution A; dissolving an appropriate amount of 2-methylimidazole in methanol, recorded as solution B; S1-2, adding the solution B prepared in step S1-1 to the solution A under stirring at room temperature, and continuing stirring for a period of time, then standing at room temperature, centrifuging with methanol several times, and then drying to obtain ZnCo-ZIF; S1-3, calcining the ZnCo-ZIF powder in an inert gas to obtain a Co / Co3ZnC@CN precursor; S2, dissolving the Co / Co3ZnC@CN precursor prepared in step S1 in n-hexane, recorded as solution C; dissolving the iron-containing nitrate hydrate in methanol, recorded as solution D; adding solution D dropwise to solution C, stirring for a period of time, centrifuging with deionized water several times, and drying to obtain a black precipitate; S3. The black precipitate prepared in step S2 is calcined twice in an inert gas, a phosphorus source is added in the second calcination for phosphating, and black FeP-Co / Co3ZnC@CN is obtained after natural cooling, which is a FeP-dotted carbon-coated cobalt zinc carbide electrocatalyst constructed based on pore confinement.

[0006] Preferably, in step S1-1, in solution A, the concentrations of zinc nitrate hydrate and cobalt nitrate hydrate are 0.067 mol / L and 0.017 mol / L, respectively; in solution B, the concentration of 2-methylimidazole is 1.25 mol / L.

[0007] Preferably, in step S1-2, the volume ratio between solution A and solution B is 1.5:1.

[0008] Preferably, in step S1-3, the calcination temperature is 900°C, the calcination time is 2h, the heating rate is 2-5°C / min, and the gas working pressure is 0.1-5000Pa.

[0009] Preferably, in step S2, in solution C, the concentration of the Co / Co3ZnC@CN precursor is 7.14 g / L; and in solution D, the concentration of the iron-containing nitrate hydrate is 1.01 mol / L.

[0010] Preferably, in step S2, the volume ratio between solution C and solution D is 35:1.

[0011] Preferably, in step S3, the calcination temperature of the first stage is 600°C, the calcination time is 2h, the heating rate is 2~5°C / min, and the gas working pressure is 0.1~5000 Pa; the calcination temperature of the second stage is 350°C, the calcination time is 2h, the heating rate is 2~5°C / min, and the gas working pressure is 0.1~5000 Pa.

[0012] Preferably, in step S3, the amount of the phosphorus source added is three times the mass of the black precipitate, and the phosphorus source is sodium hypophosphite or sodium hypophosphite.

[0013] Preferably, in step S1-2 and step S2, vacuum drying is performed at 60° C.; in step S1-3 and step S3, the inert gas is nitrogen or argon.

[0014] In order to achieve the purpose of the invention, the present invention also provides a FeP-Co / Co3ZnC@CN electrocatalytic material prepared by the above preparation method.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The present invention utilizes the large specific surface area and moderate pore size distribution of the ZIF structure to introduce FeP doping into the CoZn-ZIF structure for the first time, and has a 3 nm carbon layer coating on the outside of the CN framework and 10 nm cobalt nanoparticles on the inside. The electron transfer between the composite structure is conducive to the HER and OER reactions.

[0016] (2) The present invention only adopts the method of co-precipitation (stirring) and calcination. The preparation process is simple and efficient, the equipment requirements are simple, the energy consumption is low, and it meets the requirements of green chemistry. It is suitable for large-scale industrial production and has great application potential.

[0017] (3) The present invention uses Co / Co3ZnC@CN as a matrix, embeds FeP through liquid-liquid co-doping-co-precipitation, and explores the synergistic effect between FeP and Co / Co3ZnC@CN. The nano-confinement effect of the porous structure of the CN skeleton is used to achieve confined growth of the precipitate, and the FeP-Co / Co3ZnC@CN composite material is obtained by further oxidation and phosphating; the FeP-Co / Co3ZnC@CN carbon-nitrogen skeleton porous structure shows a large specific surface area and good chemical stability, which is conducive to the effective diffusion of catalytic reactants and the full exposure of active sites. In addition, due to the presence of FeP, electrons are transferred from FeP to Co / Co3ZnC@CN, which changes the electron cloud density around Co / Co3ZnC@CN, effectively reduces the energy required in the HER and OER reactions, and improves the HER / OER activity of Co / Co3ZnC@CN; and the carbon layer enhances the acid and alkali resistance of the FeP-Co / Co3ZnC@CN catalyst and improves the stability of the catalyst.

[0018] (4) The FeP-Co / Co3ZnC@CN electrocatalyst prepared in the present invention has an OER current density of 10 mA·cm under alkaline conditions. -2 and 50 mA·cm -2 The overpotentials of 346 mV and 389 mV are required, and the overpotentials are 5 mA·cm -2 The potential can be kept stable for more than 80 h.

[0019] (5) The FeP-Co / Co3ZnC@CN electrocatalyst prepared in this invention has a HER current density of 10 mA·cm under alkaline conditions. -2 and 100 mA·cm -2The overpotentials of 293 mV and 411 mV are required, and the overpotentials are 15 mA·cm -2 The potential can be kept stable for more than 40 h.

[0020] (6) Electrochemical impedance spectroscopy (EIS) tests show that the FeP-Co / Co3ZnC@CN electrode prepared in the present invention has a smaller electron migration resistance and a higher electron mobility than the single Co / Co3ZnC@CN electrode, which is consistent with the Tafel curve results obtained by converting the linear voltammetric curve. The heterostructure has better catalytic performance and reaction kinetics.

[0021] In summary, the test results of the present invention show that the FeP-Co / Co3ZnC@CN heterogeneous composite structure has excellent OER and HER performance and is a potential practical material as an electrocatalytic hydrogen and oxygen evolution catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1; Figure 2 XRD pattern of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1; Figure 3 TEM images of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1, (a) scale is 50 nm, (b) scale is 10 nm; Figure 4 HRTEM image of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1; Figure 5 The STEM-mapping image of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1; Figure 6 This is the XPS spectrum of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1; Figure 7 Polarization curve of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 as an OER catalyst; Figure 8 Polarization curve of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 as a HER catalyst; Fig. 9 The Tafel slope obtained by converting the polarization curve of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 as an OER catalyst; Fig.10The Tafel slope obtained by converting the polarization curve of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 as a HER catalyst; Fig.11 The electrochemical impedance spectroscopy of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 as an OER catalyst; Fig.12 The electrochemical impedance spectroscopy of the FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 as a HER catalyst; Fig.13 The FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 is -2 Stability curve under potential; Fig.14 The FeP-Co / Co3ZnC@CN composite structure prepared in Example 1 is -15 mA·cm -2 Stability curve under potential; Fig.15 This is a SEM image of the NiP-Co / Co3ZnC@CN composite structure prepared in Comparative Example 1; Fig.16 XRD pattern of the NiP-Co / Co3ZnC@CN composite structure prepared in Comparative Example 1; Fig.17 Polarization curves of FeP-Co / Co3ZnC@CN and NiP-Co / Co3ZnC@CN composite structures prepared in Example 1 and Comparative Example 1 as OER catalysts; Fig.18 Polarization curves of the FeP-Co / Co3ZnC@CN and NiP-Co / Co3ZnC@CN composite structures prepared in Example 1 and Comparative Example 1 as HER catalysts; Fig.19 This is the SEM image of the Co / Co3ZnC@CN composite structure prepared in Comparative Example 2; Fig. 20 XRD pattern of the Co / Co3ZnC@CN composite structure prepared in Comparative Example 2; Fig.21 Polarization curves of FeP-Co / Co3ZnC@CN, NiP-Co / Co3ZnC@CN, and Co / Co3ZnC@CN composite structures prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively, as OER catalysts; Fig. 22Polarization curves of FeP-Co / Co3ZnC@CN, NiP-Co / Co3ZnC@CN, and Co / Co3ZnC@CN composite structures prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively, as HER catalysts. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] In the following examples, unless otherwise specified, all reagents used can be purchased from commercial sources or obtained according to known literature reports. Example 1

[0025] A preparation method of FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement, comprising the following steps: S1. Preparation of Co / Co3ZnC@CN precursor; S1-1, dissolve 2.98 g Zn(NO3)2·6H2O and 0.73 g Co(NO3)2·6H2O in 150 mL methanol, and the mixed solution is recorded as solution A; dissolve 10.26 g 2-methylimidazole in 100 mL methanol, and the mixed solution is recorded as solution B; S1-2, adding the solution B prepared in step S1-1 to the solution A under stirring at room temperature, and continuously stirring for 1 h, then standing at room temperature for 24 h, centrifuging with methanol several times, and vacuum drying at 60 °C to obtain ZnCo-ZIF; S1-3, heating the ZnCo-ZIF powder to 900 °C at a heating rate of 5 °C / min in an Ar atmosphere, keeping the temperature for 2 h, and the gas working pressure is 0.1~5000 Pa to obtain a Co / Co3ZnC@CN precursor; S2, disperse 0.25 g of the Co / Co3ZnC@CN precursor prepared in step S1 into 35 mL of n-hexane, recorded as solution C; dissolve 0.41 g of Fe(NO3)3·9H2O in 1 mL of methanol, recorded as solution D; add solution D dropwise into solution C and stir for 6 h, centrifuge with deionized water several times, and dry in vacuum at 60 °C to obtain a black precipitate; S3. The black precipitate prepared in step S2 was calcined twice under an Ar atmosphere. In the first calcination, the temperature was increased to 600°C at a heating rate of 5°C / min and kept warm for 2 h. In the second calcination, sodium hypophosphite three times the mass of the black precipitate was placed in the upwind of the tubular furnace, and the temperature was increased to 350°C at a heating rate of 5°C / min under an Ar atmosphere. The temperature was kept warm for 2 h, and the gas working pressure was 0.1~5000 Pa. After cooling, it was taken out and named FeP-Co / Co3ZnC@CN.

[0026] The SEM test was performed using a FEI Quanta FEG250 high-resolution field emission scanning electron microscope. The FeP-Co / Co3ZnC@CN obtained in this example was adhered to a black conductive adhesive and then subjected to gold spraying to prepare for SEM testing. SEM results ( Figure 1 ) showed that FeP-Co / Co3ZnC@CN is composed of Co nanoparticles of about 10 nm located inside the CN framework and Co3ZnC coated with a carbon layer of about 3 nm located outside the CN framework. It shows the feasibility of synthesizing FeP-Co / Co3ZnC@CN using the co-precipitation and calcination method. The porous structure of the CN framework provides a large specific surface area and good chemical stability, which is conducive to the effective diffusion of catalytic reactants and the full exposure of active sites. The role of the carbon layer can further enhance the corrosion resistance of the catalyst and improve the stability of the catalyst.

[0027] The XRD test uses a Bruker D8 advance X-ray diffractometer and adopts the grazing incidence method to analyze the phase composition and crystal structure of the material surface. Figure 2 The results show that the main components of the material are Co3ZnC and Co. The morphology and phase distribution of the material were further analyzed using a JEOL-JEM 2100 F transmission electron microscope. Figure 3 It shows that the thickness of the carbon layer is about 3 nm and the size of the Co nanoparticles is about 10 nm. Figure 4 It shows that the interplanar spacing of Co3ZnC is 0.37 nm.

[0028] Element distribution by STEM-mapping ( Figure 5 ) It can be seen that the uniform distribution of Fe, Co, Zn, P, and N elements confirms that the FeP-Co / Co3ZnC@CN composite material is uniformly distributed, and the Fe content is very small, which also explains why the FeP peak in XRD cannot be distinguished.

[0029] XPS (Thermo SCIENTIFIC ESCALAB) was used to analyze the valence state of elements in the material. Figure 6 The XPS results shown in the FeP-Co / Co3ZnC@CN composite material indicate that due to the presence of FeP, electrons are transferred from FeP to Co / Co3ZnC@CN, which changes the electron cloud density around Co / Co3ZnC@CN and is beneficial to the HER and OER reactions.

[0030] FeP-Co / Co3ZnC@CN was measured using a three-electrode system. The specific steps are as follows: The FeP-Co / Co3ZnC@CN obtained in this example is clamped on a platinum electrode clamp as a working electrode, Hg / HgO as a reference electrode, and a carbon rod as a counter electrode, and HER and OER tests are performed in a 1 mol KOH solution. The polarization curve tests are all performed at a scanning rate of 5 mV / s, except that the scanning range of HER is -0.95~-2 V, and the scanning range of OER is 0.3~1.5 V. The electrochemical impedance spectroscopy test range is 100kHz~0.01Hz, the voltage for HER is -0.1V vs. RHE, and the voltage for OER is 1.5V vs. RHE.

[0031] Depend on Figure 7 The polarization curve of OER shows that the material can -2 and 50 mA·cm -2 Overpotentials of 346 mV and 389 mV are required. Figure 8 The polarization curve of HER shows that the HER current density reaches 10 mA cm -2 and 100 mA·cm -2 The overpotentials of 293 mV and 411 mV are required. Based on the Tafel slope ( Fig. 9 and Fig.10 ), this material has excellent kinetic properties in OER and HER reactions. Fig.11 and Fig.12 The charge transfer resistance of this material and other comparative materials is shown. This material has a small charge transfer resistance, indicating that it has good catalytic kinetic properties. Fig.13 and Fig.14 The excellent stability of FeP-Co / Co3ZnC@CN was demonstrated at 5 mA·cm -2 (OER) and -15 mA cm -2 (HER) remained stable for more than 80 h and 40 h, respectively.

[0032] Comparative Example 1 The “0.41 g Fe(NO3)3·9H2O” in step S2 of Example 1 was replaced with “0.29 g Ni(NO2)2·6H2O”, and the other steps remained consistent with Example 1.

[0033] The material obtained in this comparative example was subjected to SEM test, and the results were as follows: Fig.15As shown, NiP-Co / Co3ZnC@CN is composed of a CN framework, Co nanoparticles located inside the CN framework, and Co3ZnC located outside the CN framework, which once again demonstrates the feasibility of the one-step co-precipitation-calcination preparation method. Fig.16 The XRD results of the material are shown, indicating the formation of NiP-Co / Co3ZnC@CN. The same electrochemical test method as in Example 1 was used. Fig.17 and Fig.18 The OER and HER polarization curves of Example 1 and Comparative Example 1 are shown. It can be seen from the figure that Comparative Example 1 has worse catalytic performance.

[0034] Comparative Example 2 Comparative Example 2 is the Co / Co3ZnC@CN precursor prepared in step S1 of Example 1.

[0035] The Co / Co3ZnC@CN precursor was tested by SEM, and the results are as follows Fig.19 , which is composed of a CN framework, Co nanoparticles located inside the CN framework, and Co3ZnC located outside the CN framework, once again demonstrating the feasibility of the one-step co-precipitation-calcination preparation method. Fig. 20 The XRD results of the material are shown, indicating the formation of Co / Co3ZnC@CN. The same electrochemical test method as in Example 1 was used. Fig.21 and Fig. 22 The OER and HER polarization curves of Example 1, Comparative Example 1, and Comparative Example 2 are shown. It can be seen from the figure that Comparative Example 2 has worse catalytic performance.

Claims

1. A method for preparing FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement, characterized in that: The following steps are involved: S1. Preparation of Co / Co3ZnC@CN precursor; S1-1, dissolving zinc nitrate hydrate and cobalt nitrate hydrate in methanol, recorded as solution A; dissolving an appropriate amount of 2-methylimidazole in methanol, recorded as solution B; S1-2, adding the solution B prepared in step S1-1 to the solution A under stirring at room temperature, and continuing stirring for a period of time, then standing at room temperature, centrifuging with methanol several times, and then drying to obtain ZnCo-ZIF; S1-3, calcining the ZnCo-ZIF powder in an inert gas to obtain a Co / Co3ZnC@CN precursor; S2, dissolving the Co / Co3ZnC@CN precursor prepared in step S1 in n-ethane, recorded as solution C; dissolving the iron-containing nitrate hydrate in methanol, recorded as solution D; Solution D was added dropwise to solution C and stirred for a period of time. After multiple centrifugation with deionized water, a black precipitate was obtained after drying. S3. The black precipitate prepared in step S2 is calcined twice in an inert gas, a phosphorus source is added in the second calcination for phosphating, and black FeP-Co / Co3ZnC@CN is obtained after natural cooling, which is a FeP-dotted carbon-coated cobalt zinc carbide electrocatalyst constructed based on pore confinement.

2. The method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1, characterized in that: In step S1-1, in solution A, the concentrations of zinc nitrate hydrate and cobalt nitrate hydrate are 0.067 mol / L and 0.017 mol / L, respectively; in solution B, the concentration of 2-methylimidazole is 1.25 mol / L.

3. The method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1, characterized in that: In step S1-2, the volume ratio between solution A and solution B is 1.5:

1.

4. The method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1, characterized in that: In step S1-3, the calcination temperature is 900°C, the calcination time is 2h, the heating rate is 2~5°C / min, and the gas working pressure is 0.1~5000Pa.

5. A method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1 or 2, characterized in that: In step S2, in solution C, the concentration of the Co / Co3ZnC@CN precursor is 7.14 g / L; in solution D, the concentration of the iron-containing nitrate hydrate is 1.01 mol / L.

6. A method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1 or 2, characterized in that: In step S2, the volume ratio between solution C and solution D is 35:

1.

7. A method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1 or 2, characterized in that: In step S3, the calcination temperature of the first stage is 600°C, the calcination time is 2h, the heating rate is 2~5°C / min, and the gas working pressure is 0.1~5000 Pa; the calcination temperature of the second stage is 350°C, the calcination time is 2h, the heating rate is 2~5°C / min, and the gas working pressure is 0.1~5000 Pa.

8. A method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 1 or 2, characterized in that: In step S3, the amount of the phosphorus source added is three times the mass of the black precipitate, and the phosphorus source is sodium hypophosphite or sodium hypophosphite.

9. The method for preparing a FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement according to claim 2, characterized in that: In step S1-2 and step S2, vacuum drying is performed at 60° C.; in step S1-3 and step S3, the inert gas is nitrogen or argon.

10. A FeP-dotted carbon-coated cobalt-zinc carbide electrocatalyst based on pore confinement prepared by the preparation method according to any one of claims 1 to 9.

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