Porous carbon-coated heterostructure material, preparation method and application thereof to her, oer and full-hydrolysis trifunctional reaction

Abstract

The application provides a porous carbon-coated heterostructure material, a preparation method and application to HER, OER and full hydrolysis three-function reaction. First, a carbon material carrier is immersed in a mixed solution of a cobalt source and a nickel source, taken out and dried; then high-temperature carbonization is performed to obtain a porous carbon-coated CoNi-Co3O4 heterostructure. The porous carbon limits the size of the CoNi-Co3O4 heterostructure and prevents it from polymerization. In the same amount of substance, more active sites can be provided. In addition, the interface effect of the porous carbon and the CoNi-Co3O4 heterostructure significantly improves the catalytic activity of the catalyst, and the catalyst has high efficient catalytic activity for hydrogen evolution reaction, oxygen evolution reaction and full water splitting.

Description

Technical Field

[0001] This invention belongs to the research field of high-performance water electrolysis catalyst preparation, specifically involving the preparation of porous carbon-coated CoNi-Co3O4 heterostructure electrocatalysts and their use to promote HER, OER and total hydrolysis trifunctional reactions. Background Technology

[0002] Water electrolysis technology, due to its enormous energy conversion potential with zero pollution, has become one of the most promising methods for solving the energy crisis and environmental problems. The water electrolysis process involves two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. It is well known that oxygen production requires multiple reaction steps, and OER requires overcoming a high activation barrier, resulting in slow kinetics. Therefore, developing highly active electrocatalysts to effectively lower the energy barrier in the water splitting process, thereby improving energy conversion efficiency, is of great significance. Furthermore, in practical applications, both the anode and cathode reactions should take place in the same electrolyte to support the overall water splitting reaction. Undoubtedly, highly efficient bifunctional electrocatalysts capable of simultaneously catalyzing HER and OER on the electrodes in the same electrolyte are essential.

[0003] To date, Pt-based and Ir / Ru-based noble metal nanostructures have been the main electrocatalysts for HER / OER. However, their scarcity and high cost have severely limited their large-scale utilization in practical and commercial applications. More importantly, due to their different activity compatibility across different pH ranges, they cannot exhibit excellent electrocatalytic performance in the same electrolyte for HER and OER. Therefore, exploring non-noble metal nanostructures as efficient bifunctional electrocatalysts for HER and OER activation remains imperative.

[0004] In recent years, various transition metals have been developed as bifunctional electrocatalysts, including metal alloys, metal oxides, nitrides, carbides, and chalcogenides. Among them, Co and Ni-based electrocatalysts have attracted much attention due to their variable valence states and excellent catalytic activity. In particular, alloys or oxides have been used as catalysts for both anodes and cathodes. However, developing highly active electrocatalysts to reduce the dynamic overpotential of transition metal-based electrocatalysts in HER, OER, and overall water splitting in the same electrolyte remains a significant challenge. Summary of the Invention

[0005] The purpose of this invention is to provide porous carbon-coated heterostructure materials and their preparation methods. By utilizing the synergistic effect between CoNi alloy, Co3O4 and carbon substrate, porous carbon-coated CoNi-Co3O4 heterostructures are prepared by impregnation and high-temperature carbonization methods. The preparation method is safe, efficient and low-cost, and can be carried out on a large scale.

[0006] Another objective of this invention is to provide a porous carbon-coated heterostructure material for use in HER, OER and total water electrolysis trifunctional reactions. The prepared porous carbon-coated heterostructure material reduces the overpotential of OER and HER and is an excellent water electrolysis catalyst.

[0007] The specific technical solution of this invention is as follows:

[0008] A method for preparing porous carbon-coated heterostructured materials includes the following steps:

[0009] 1) Immerse the carbon material carrier in a mixed solution of cobalt and nickel sources, remove it, and dry it;

[0010] 2) The carbon material carrier treated in step 1) is carbonized at high temperature to prepare a porous carbon-coated CoNi-Co3O4 heterostructure.

[0011] In step 1), the carbon material carrier refers to filter paper;

[0012] The impregnation described in step 1) is carried out at room temperature. The mixed solution should just cover the carrier. Once the carrier is wetted, it can be removed.

[0013] In step 1), the molar ratio of the cobalt source to the nickel source is 1:3-3:1; more preferably 2:1.

[0014] In step 1), the cobalt source is selected from soluble cobalt salts, preferably any one or both of cobalt nitrate and cobalt chloride, and more preferably cobalt nitrate nonahydrate.

[0015] In step 1), the nickel source is selected from soluble nickel salts, preferably one or both of nickel nitrate and nickel chloride, and more preferably nickel nitrate nonahydrate.

[0016] In step 1), the molar ratio of cobalt nitrate nonahydrate to nickel nitrate nonahydrate is 1:3-3:1; more preferably 2:1.

[0017] In step 1), the solvent for the mixed solution of cobalt source and nickel source is one or both of water and ethanol;

[0018] In step 1), the concentration of the cobalt source in the mixed solution is 0.1-0.2 g / mL;

[0019] In step 1), drying refers to drying at a temperature of 20-60°C for 12-24 hours.

[0020] In step 2), the carbon material carrier treated in step 1) is placed in a covered quartz boat and carbonized at high temperature in a tube furnace under a protective atmosphere.

[0021] In step 2), the protective atmosphere refers to argon or nitrogen.

[0022] In step 2), the high-temperature carbonization is as follows: the heating rate is 2-10℃ / min, the carbonization temperature is 400-800℃, and the holding time is 1-5h; more preferably, the carbonization temperature is 500℃ and the holding time is 2h.

[0023] The porous carbon-coated heterostructure material provided by this invention is a CoNi-Co3O4 heterostructure with a specific surface area of ​​75-90 m² prepared by the above method. 2 / g, mesopore volume is 0.020-0.030cm³ 3 / g, with pore size distribution concentrated in the range of 1.5nm to 5nm.

[0024] The application of the porous carbon-coated heterostructure material provided by this invention in the hydrogen evolution reaction (HER) of water electrolysis.

[0025] The application of the porous carbon-coated heterostructure material provided by this invention in the oxygen evolution reaction (OER) of water electrolysis.

[0026] The application of the porous carbon-coated heterostructure material provided by this invention in the complete water splitting process.

[0027] The porous carbon-coated heterostructure material of this invention exhibits significantly lower overpotentials for hydrogen evolution and oxygen evolution reactions in 1M KOH electrolyte solution compared to commercial Pt / C and RuO2 (lower overpotential indicates better catalytic performance); it also demonstrates highly efficient catalytic activity for total water splitting.

[0028] The porous carbon-coated CoNi-Co3O4 heterostructure prepared in this invention allows the porous carbon to spatially restrict the size of the CoNi-Co3O4 heterostructure, preventing its aggregation, increasing the active sites of the electrocatalyst, and enhancing its catalytic activity. Furthermore, the interfacial effects between CoNi and Co3O4, between CoNi and porous carbon, and between Co3O4 and porous carbon can alter the electron cloud distribution of the active sites, effectively improving the elution and adsorption energy of intermediate products, and significantly enhancing the catalytic activity of the electrocatalyst.

[0029] This invention prepares porous carbon-coated CoNi-Co3O4 heterostructures via impregnation and high-temperature carbonization. The porous carbon restricts the size of the CoNi-Co3O4 heterostructure, preventing its polymerization and providing more active sites for the same amount of material. Furthermore, the interfacial effect between the porous carbon and the CoNi-Co3O4 heterostructure significantly enhances the catalytic activity of the catalyst.

[0030] Compared with the prior art, the present invention has the following advantages: the catalyst preparation process is safe and efficient, with low cost, and can be prepared on a large scale; the catalyst has high catalytic activity for hydrogen evolution reaction, oxygen evolution reaction and total water splitting; and the catalyst of the present invention has excellent stability and mass transfer performance. Attached Figure Description

[0031] Figure 1 The image shows a scanning electron microscope image of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1; the 200nm indicated by the arrow refers to the two-dimensional sheet-like carbon sheet after the filter paper is carbonized, with a thickness of approximately 200nm.

[0032] Figure 2 Transmission electron microscope image of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1;

[0033] Figure 3 The XRD patterns of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1 and Comparative Examples 1 and 2 are shown.

[0034] Figure 4 The Raman spectrum of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1 is shown.

[0035] Figure 5 X-ray photoelectron spectroscopy (XPS) of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1.

[0036] Figure 6 The image shows the mapping diagram of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1.

[0037] Figure 7 The image shows the BET spectrum of the porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared in Example 1, with the inset showing the pore size distribution.

[0038] Figure 8 Transmission electron microscope image of the Ni / CFP electrocatalyst prepared in Comparative Example 1;

[0039] Figure 9 Transmission electron microscope image of the Co3O4 / CFP electrocatalyst prepared in Comparative Example 2;

[0040] Figure 10 Transmission electron microscope image of the CFP electrocatalyst prepared in Comparative Example 3;

[0041] Figure 11 Polarization curves of the nanomaterials prepared in Example 1 and Comparative Examples 1, 2, and 3, and commercial Pt / C (5%) in 1M KOH solution for HER catalysis;

[0042] Figure 12 Polarization curves of commercial RuO2 nanomaterials prepared in Example 1 and Comparative Examples 1, 2, and 3 for OER catalysis in 1M KOH solution;

[0043] Figure 13 Polarization curves of the overall water decomposition of Pt / C and RuO2 in 1M KOH solution in Example 1 and commercial Pt / C and RuO2.

[0044] Figure 14 The HER stability of Example 1 in 1M KOH solution;

[0045] Figure 15 The OER stability of Example 1 in 1M KOH solution;

[0046] Figure 16 The stability of the total hydrolysis of Example 1 in 1M KOH solution;

[0047] Figure 17 Polarization curves of HER catalysis for catalysts with different Co / Ni ratios in 1M KOH solution;

[0048] Figure 18 Polarization curves of OER catalysis for catalysts with different Co / Ni ratios in 1M KOH solution;

[0049] Figure 19 Polarization curves of catalysts prepared at different carbonization temperatures for HER catalysis in 1M KOH solution;

[0050] Figure 20 Polarization curves of OER catalysis for catalysts prepared at different carbonization temperatures in 1M KOH solution. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0052] Example 1

[0053] A method for preparing a high-performance water electrolysis catalyst with a porous carbon-coated CoNi-Co3O4 heterostructure includes the following steps:

[0054] 1) Solution preparation: Dissolve 0.5g of cobalt nitrate nonahydrate and 0.25g of nickel nitrate nonahydrate in 3mL of deionized water, stir well, and the solution turns red to obtain a mixed solution; the molar ratio of Co:Ni in this example is 2:1.

[0055] 2) Impregnation reaction: The filter paper cut to a size of 15mm×3mm was impregnated in the above-prepared mixed solution. The mixed solution did not cover the filter paper. The impregnation process was carried out at room temperature. Once the filter paper was wetted, it was removed and placed in a clean petri dish. It was then dried at 35℃ for 12 hours for later use.

[0056] 3) High-temperature carbonization reaction: The dried impregnated filter paper is placed in a covered quartz boat and carbonized at high temperature in a tube furnace under the protection of argon atmosphere. The heating rate is 5℃ / min, and the temperature is raised to 500℃ and held for 2 hours.

[0057] The porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst prepared according to the preparation method in Example 1 above is named CoNi-Co3O4 / CFP. Its microstructure was determined by scanning electron microscopy and transmission electron microscopy. Figure 1 , Figure 2 Its morphology is a porous carbon-coated CoNi-Co3O4 heterostructure. Figure 1 The scanning electron microscope image of Example 1 (CoNi-Co3O4 / CFP) shows that the filter paper formed a carbon sheet with a thickness of approximately 200 nm after carbonization. The transmission electron microscope image of Example 1 (CoNi-Co3O4 / CFP) is also shown. Figure 2 It can be seen that CoNi-Co3O4 nanoparticles are embedded in porous carbon, with uniform particle size and distribution, providing numerous catalytic sites for the catalytic reaction. The phase composition of the catalyst was determined by XRD and Raman spectroscopy. Figure 3 and Figure 4 ), Figure 3 XRD analysis confirmed the material composition of Example 1, Comparative Example 1, and Comparative Example 2. Example 1 consisted of a CoNi alloy and Co3O4, Comparative Example 1 consisted of elemental Ni, and Comparative Example 2 consisted of Co3O4. XPS analysis was performed on CoNi-Co3O4 / CFP, Co3O4 / CFP, and Ni / CFP. Figure 5By comparing the XPS spectra of Example 1 (a) and Example 2 (b), the valence states of each element were determined. It was found that the Co 2p and Ni 2p spectra of Example 1 shifted compared to those of Comparative Examples 1 and 2. This indicates that the CoNi alloy in Example 1 formed a heterostructure with Co3O4, and the interface formation facilitated electron transfer, resulting in the shift in the XPS spectra. The interface formation is beneficial for electron transfer and also improves the adsorption energy of the active intermediates at the active sites, thereby enhancing the catalytic activity of the catalytic sites. Mapping tests were conducted... Figure 6 By determining the distribution of each element, it can be observed that the distribution of each element is very uniform. This can be achieved through the BET test. Figure 7 The specific surface area and pore size distribution of the catalyst were determined. The results showed that the catalyst phases were CoNi, Co3O4, and carbon, and the distribution was very uniform, with mesopores present in the carbon substrate; the specific surface area of ​​Example 1 was 81.5 m². 2 / g, mesopore volume is 0.025cm³ 3 / g, with a pore size distribution concentrated in the range of 1.5nm to 5nm. The large specific surface area and numerous mesopores provide the catalyst with a larger contact area and mass transfer channels, further enhancing the catalyst's catalytic performance.

[0058] Comparative Example 1

[0059] Following the preparation method of Example 1, except that only nickel nitrate nonahydrate was added to the precursor solution, porous carbon-coated Ni nanoparticles were prepared using the same method and named Ni / CFP.

[0060] The porous carbon-coated Ni nanoparticles prepared according to the above method were observed to have a microstructure using transmission electron microscopy. Figure 8 The results showed that the microstructure consisted of porous carbon-coated Ni nanoparticles. While the Ni nanoparticles were uniform in size, their distribution was highly uneven, leading to agglomeration. This reduced the number of catalytic sites and consequently decreased catalytic activity.

[0061] Comparative Example 2

[0062] Following the preparation method of Example 1, except that only cobalt nitrate nonahydrate was added to the precursor solution, porous carbon-coated Co3O4 nanoparticles were prepared using the same method and named Co3O4 / CFP. Their microstructure, observed under a transmission electron microscope, is as follows: Figure 9 It can be seen that the Co element is evenly distributed on the carbon sheet, but the morphology of the particles is not clear, which indicates that its electrical conductivity is poor, and thus its catalytic performance is also poor.

[0063] Comparative Example 3

[0064] Following the preparation method of Example 1, except that no salt was added to the precursor solution, carbonized filter paper was prepared using the same method and named CFP.

[0065] The carbonized filter paper prepared according to the above method was observed to have its microstructure using a transmission electron microscope. Figure 10 The results showed that its microstructure was layered carbon.

[0066] Application Example 1

[0067] The application of porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst in the hydrogen evolution reaction is as follows:

[0068] Electrochemical tests were conducted on an electrochemical workstation (CHI-760E) using a graphite rod as the counter electrode and an Ag / AgCl (saturated KCl) electrode as the reference electrode. The working electrodes were nickel foams, each 1 cm × 1 cm in size, coated with inks containing different electrocatalytic materials. To prepare the working electrodes, the nickel foams were first ultrasonically cleaned in hydrochloric acid, deionized water, and ethanol, respectively. They were then dried in a vacuum drying oven at 60°C. A mixture of 7 mg of different electrocatalysts, 2 mg of carbon black, and 1 mg of polyvinylidene fluoride was uniformly mixed, and 50 μL of N-methylpyrrolidone (NMP) was added dropwise to form an ink. This ink was then uniformly coated onto the nickel foams and dried at room temperature. The electrodes were then tested in a nitrogen-saturated 1 M KOH solution at 5 mV s⁻¹. -1 The electrocatalytic performance of the electrocatalyst for HER was measured at a scan rate of 10 mA / cm². -2 At that time, the polarization curve for HER catalysis was as follows: Figure 11 As shown, the overpotential of the CoNi-Co3O4 / CFP prepared in Example 1 as an electrocatalyst is 35 mV, the overpotential of the Ni / CFP catalyst prepared in Comparative Example 1 is 67 mV, the overpotential of the Co3O4 / CFP catalyst prepared in Comparative Example 2 is 74 mV, the overpotential of the Pt / C (5% Pt mass fraction) catalyst is 39 mV, and the overpotential of the CFP prepared in Comparative Example 3 is 237 mV. The lower the overpotential, the better the catalytic performance. The catalytic performance of the CoNi-Co3O4 / CFP prepared in Example 1 of this invention is significantly higher than that of the comparative examples and the commercially available Pt / C catalyst.

[0069] Application Example 2

[0070] The application of porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst in the oxygen evolution reaction includes the following steps:

[0071] Electrochemical tests were performed on an electrochemical workstation (CHI-760E) using a platinum sheet as the counter electrode and an Ag / AgCl (saturated KCl) electrode as the reference electrode. The working electrode was a nickel foam (1 cm × 1 cm) coated with different electrocatalyst inks. To prepare the working electrode, the nickel foam was first ultrasonically cleaned in hydrochloric acid, deionized water, and ethanol, respectively. It was then dried in a vacuum drying oven at 60 °C. 7 mg of different electrocatalysts, 2 mg of carbon black, and 1 mg of polyvinylidene fluoride were uniformly mixed, and 50 μL of NMP was added dropwise to form an ink, which was then uniformly coated onto the nickel foam and dried at room temperature. The electrode was then tested at 1 mV s⁻¹ in a nitrogen-saturated 1 M KOH solution. -1 The electrocatalytic performance of the electrocatalyst for OER was measured at a scan rate of 10 mA cm⁻¹. -2 At that time, the polarization curve for OER catalysis is as follows: Figure 12 As shown, the overpotential of the CoNi-Co3O4 / CFP prepared in Example 1 as an electrocatalyst is 189 mV, the overpotential of the Ni / CFP catalyst prepared in Comparative Example 1 is 213 mV, the overpotential of the Co3O4 / CFP catalyst prepared in Comparative Example 2 is 284 mV, the overpotential of the RuO2 catalyst is 259 mV, and the overpotential of the CFP prepared in Comparative Example 3 is 418 mV. The CoNi-Co3O4 / CFP prepared in Example 1 of this invention has the lowest overpotential and its catalytic performance is significantly higher than that of the materials prepared in Comparative Examples 1-3 and the commercially available RuO2 catalyst.

[0072] Application Example 3

[0073] The application of porous carbon-coated CoNi-Co3O4 heterostructure high-performance water electrolysis catalyst in total water splitting is as follows: Similar to the sample preparation method in Application Example 1, two pieces of CoNi-Co3O4 / CFP electrocatalyst with nickel foam were used as the cathode and anode, respectively. Total water splitting curves were obtained using linear sweep voltammetry (LSV). For comparison, Pt / C and RuO2 were used as the cathode and anode, respectively, and total water splitting curves were obtained under the same conditions using LSV. In total water splitting, at a current density of 10 mA / cm²... -2 At that time, the polarization curve of the overall water splitting is as follows: Figure 13 As shown, the potential of the CoNi-Co3O4 / CFP electrocatalyst prepared in Example 1 is 1.45V, and the overpotential of the Pt / C (5%) and RuO2 catalysts is 1.61V.

[0074] Example 1: The HER stability, OER stability, and total hydrolysis stability of the product in 1M KOH solution were tested as follows: Figures 14-16As shown, the test conditions were consistent with those described above for testing overpotential, with a fixed current value and changes in test voltage to characterize the catalyst's stability. It can be seen that the porous carbon-coated CoNi-Co3O4 heterostructure prepared in Example 1 exhibits stable catalytic performance, remaining stable even after 20 hours of cycling.

[0075] Comparative Example 4

[0076] Prepared using the same method as in Example 1, except that the molar ratio of Co:Ni was changed to 3:1, 1:1, 1:2, and 1:3. The prepared materials were tested in 1M KOH solution using the same method to obtain the polarization curves for HER catalysis. Figure 17 ) and polarization curves of OER catalysis ( Figure 18 The HER catalytic overpotentials for Co:Ni ratios of 3:1, 1:1, 1:2, and 1:3 were 39 mV, 37 mV, 39 mV, and 46 mV, respectively; the OER overpotentials for Co:Ni ratios of 3:1, 1:1, 1:2, and 1:3 were 257 mV, 228 mV, 234 mV, and 231 mV, respectively. It can be seen that only under the condition of Co:Ni = 2:1 did the overpotential be lower and the catalytic performance be the best. The porous carbon-coated CoNi-Co3O4 heterostructure prepared under other molar ratios showed poor HER and OER catalytic performance.

[0077] Comparative Example 5

[0078] Prepared using the same method as in Example 1, except that the high-temperature carbonization temperatures were changed to 400, 600, 700, and 800°C, the prepared materials were tested in 1M KOH solution using the same method to obtain the polarization curves of HER catalysis. Figure 19 ) and polarization curves of OER catalysis ( Figure 20 The HER overpotentials at temperatures of 400, 600, 700, and 800 °C were 80 mV, 70 mV, 76 mV, and 129 mV, respectively; the OER overpotentials at temperatures of 400, 600, 700, and 800 °C were 249 mV, 267 mV, 287 mV, and 277 mV, respectively. It can be seen that only at a high-temperature carbonization temperature of 500 °C did the overpotentials be low and the catalytic performance be optimal. The HER and OER catalytic performance of porous carbon-coated CoNi-Co3O4 heterostructures prepared under other high-temperature carbonization conditions was poor.

[0079] The above detailed description of a high-performance water electrolysis catalyst with a porous carbon-coated CoNi-Co3O4 heterostructure is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing porous carbon-coated heterostructured materials, characterized in that, The preparation method includes the following steps: 1) Immerse the carbon material carrier in a mixed solution of cobalt and nickel sources, remove it, and dry it; 2) The carbon material carrier treated in step 1) is carbonized at high temperature to prepare a porous carbon-coated CoNi-Co3O4 heterostructure. In step 1), the molar ratio of the cobalt source to the nickel source is 1:3-3:1; the carbon material carrier refers to filter paper; in step 2), the high-temperature carbonization is: carbonization temperature is 400-800℃, and holding time is 1-5h.

2. The preparation method according to claim 1, characterized in that, In step 1), the cobalt source is selected from soluble cobalt salts, and the nickel source is selected from soluble nickel salts.

3. The preparation method according to claim 1, characterized in that, In step 1), the concentration of the cobalt source in the mixed solution is 0.1-0.2 g / mL.

4. The preparation method according to claim 1, characterized in that, In step 1), the solvent for the mixed solution of cobalt source and nickel source is either water or ethanol, or both.

5. The preparation method according to claim 1, characterized in that, In step 2), high-temperature carbonization is carried out under a protective atmosphere.

6. The porous carbon-coated heterostructure material prepared by the preparation method according to any one of claims 1-5.

7. The porous carbon-coated heterostructure material prepared by the preparation method according to any one of claims 1-5 is used for HER, OER or total hydrolysis trifunctional reactions.

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