Sulfur-doped nickel platinum nitrogen carbon material as well as preparation method and application thereof

Abstract

The invention belongs to the field of electrocatalysis, and particularly relates to a sulfur-doped nickel platinum nitrogen carbon material and a preparation method and application thereof. The material is of a spherical shell structure and comprises a sulfur-containing conductive substrate and nickel and platinum which are loaded on the sulfur-containing conductive substrate and are in a monatomic dispersion state. A hollow spherical precursor material is prepared by introducing a silicon dioxide template and a re-etching method, and nickel and platinum are dispersed in an atomic scale. The specific surface area and the atomic dispersion degree of the material are increased. In the obtained f-etch-NiNC-S-Pt material, the ORR performance is enhanced through the bi-metal synergistic effect of Pt and Ni.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis, specifically to a sulfur-doped nickel-platinum-nitrogen-carbon material, its preparation method, and its applications. Background Technology

[0003] Hydrogen energy, as a clean and pollution-free renewable energy source, boasts abundant reserves, high energy utilization efficiency, and convenient storage and transportation. Fuel cells, as energy conversion devices that effectively utilize hydrogen energy, can convert the chemical energy contained in fuel into electrical energy through a chemical reaction. Generally, fuel loses electrons and is oxidized at the anode, while oxygen gains electrons and is reduced at the cathode. Electrons flow from the negative to the positive electrode through an external circuit, while ions migrate between the anode and cathode inside the cell, forming a closed loop. Unlike the energy conversion process of a heat engine, the energy conversion within a fuel cell is a one-step process, eliminating the need for multiple conversion steps (from chemical energy to thermal energy to mechanical energy to electrical energy). This allows it to bypass the limitations of the Carnot cycle, theoretically achieving an energy conversion rate as high as 85%–90%.

[0004] Proton exchange fuel cells, as a novel energy device, possess numerous advantages such as being pollution-free, having renewable energy, and high energy conversion efficiency. However, their high cost is a major drawback due to the sluggish ORR (oxygen reduction) kinetics at the cathode, requiring large amounts of precious metal catalysts. Therefore, the development of novel electrocatalysts to replace traditional precious metal catalysts is imperative.

[0005] Noble metal catalysts refer to catalysts containing a single noble metal or multi-metal catalysts with noble metals as the main component. For ORR, Pt exhibits the highest activity among noble metals, which is attributed to the suitable binding energy of Pt for the O* of the ORR intermediate.

[0006] Non-precious metal catalysts, mostly composed of transition metals, are relatively inexpensive to prepare due to their high abundance. Non-precious metal catalysts, primarily composed of sulfides and oxides, exhibit high activity under alkaline conditions but insufficient activity under acidic conditions. Atomically dispersed MNC (metal nitrogen-carbon) catalysts, whose precursors undergo high-temperature pyrolysis, generate highly active metal sites on a nitrogen-carbon substrate. These catalysts achieve high activity and stability while also exhibiting high atom utilization due to the atomically dispersed catalytic sites. However, these MNC catalysts obtained solely through pyrolysis still have some drawbacks, such as uneven distribution of active sites, low active site density, and severe degradation of active sites under acidic conditions. Bimetallic single-atom catalysts or diatomic catalysts, doped with two metals, can further regulate the coordination environment of the metal active sites compared to single-atom catalysts. Furthermore, due to the interaction between the orbitals of different metals, their electronic structure is improved, thus achieving higher ORR activity and stability. Summary of the Invention

[0007] To obtain a highly active and stable low-platinum ORR catalyst, this paper introduces S through a two-stage high-temperature pyrolysis, anchors Cu on S via underpotential deposition, and then replaces Cu with Pt through chemical substitution, successfully preparing a highly dispersed platinum-based bimetallic catalyst f-etch-NiNC-S-Pt. This catalyst exhibits high activity and stability, with a half-wave potential exceeding 0.90 V in 0.1 M KOH and a decay of only 14 mV after 10,000 cycles, demonstrating a mass activity of 483.83 mA / mg. Pt The specific activity is 0.85 mA / cm. 2 The mass activity and specific activity were 6.42 times and 8.33 times that of 20% Pt / C, respectively.

[0008] The first aspect of the present invention provides a sulfur-doped nickel-platinum-nitrogen-carbon material, the material having a spherical shell structure, comprising a sulfur-containing conductive substrate and nickel and platinum in a single-atom dispersed state supported on the sulfur-containing conductive substrate.

[0009] Preferably, the spherical shell of the material has a thickness of 7–9 nm and a diameter of 240–260 nm.

[0010] Preferably, the sulfur-containing conductive substrate is a sulfur-nitrogen-carbon material; the material contains Ni-N bonds and Pt-S bonds.

[0011] The second aspect of this application provides a method for preparing the sulfur-doped nickel-platinum-nitrogen-carbon material described in the first aspect, the method comprising the following steps:

[0012] (a) Add zinc precursor, nickel precursor and silicon dioxide to formamide solution, load into reaction vessel, react at 160-180℃ for 9-15h to obtain precursor material, separate solid and liquid, dry and grind the obtained solid.

[0013] (b) The precursor material after grinding in step (a) is heated to 900-950°C in an inert atmosphere and held at this temperature for 1-3 hours to obtain a silicon dioxide-coated nickel-nitrogen-carbon material, namely f-SiO2@NiNC;

[0014] (c) The above f-SiO2@NiNC is stirred in a strong alkali at 40-80℃ for 4-10h, dried, and then stirred in a strong acid at 60-85℃ for 4-10h. The solid-liquid separation yields hollow spherical nickel-nitrogen-carbon material f-etch-NiNC.

[0015] (d) The above f-etch-NiNC and sulfur-containing precursor were added to water, stirred and then rotary evaporated. The temperature was raised to 900-950℃ in an inert atmosphere and maintained at this temperature for 1-3 hours to obtain sulfur-doped nickel nitrogen carbon f-etch-NiNC-S.

[0016] (e) F-etch-NiNC-S is placed in a copper precursor solution for underpotential deposition to obtain f-etch-NiNC-S-Cu, and then chemical substitution is performed in a platinum precursor solution to obtain the sulfur-doped nickel-platinum-nitrogen-carbon material f-etch-NiNC-S-Pt.

[0017] Preferably, in step (a): the molar ratio of the zinc precursor and the nickel precursor is 20:1 to 30:1, the molar concentration of the zinc precursor in the formamide is 0.10 mol / L (13.63 g / L) to 0.15 mol / L (20.45 g / L), the molar concentration of the nickel precursor in the formamide is 0.005 mol / L (0.65 g / L), and the silica mass concentration is 26.7 to 33 g / L of formamide solution.

[0018] Preferably, in step (b): the inert gas used for the sample in the tube furnace is Ar, and the heating rate is 5-10℃ / min.

[0019] Preferably, in step (c): the strong base is 6 mol / L KOH or 6 mol / L NaOH, the strong acid is 0.5 mol / L H2SO4 or 1M HCl, and the heating rate is 5–10 °C / min.

[0020] Preferably, in step (d): the sulfur-containing precursor is thiourea, the mass ratio of f-etch-NiNC to thiourea is 3:1 to 1:1, and the heating rate is 5 to 10 °C / min.

[0021] Preferably, in step (e): the solution concentration of the copper precursor is 0.005–0.015 mol / L, the underpotential deposition potential is 0.10–0.20 V vs saturated Ag / AgCl electrode, and the deposition time is 30–60 s;

[0022] The concentration of the platinum precursor solution was 0.005-0.08 mol / L, and the displacement time was 10-30 min.

[0023] Both the copper precursor solution and the platinum precursor solution must be maintained at a pH of 1.

[0024] The concentrations of the copper precursor solution and the platinum precursor solution are such that both copper precursor solutions must be kept in an N2 saturated state.

[0025] The third aspect of this application provides the use of the sulfur-doped nickel-platinum-nitrogen-carbon material described in the first aspect as a catalyst for oxygen reduction reactions to improve reaction activity and stability. In particular, it improves the stability of the oxygen reduction four-electron reaction.

[0026] In step (a) above: the solid-liquid separation method is vacuum filtration, during which the sample is washed three times with deionized water and then with ethanol. Drying is performed by vacuum freeze drying for more than 12 hours.

[0027] In step (b) above: a tube furnace is used, and the inert gas used for the sample in the tube furnace is Ar, with a heating rate of 5 to 10 °C / min.

[0028] In step (c) above: the solid-liquid separation method is centrifugation, the centrifugation speed is 11000 r / min, the duration is 10 min, and the solid obtained after centrifugation needs to be washed with water three times and with ethanol three times.

[0029] Underpotential deposition (UPD) refers to the phenomenon where a metal deposits on a foreign metal at a potential more positive than its Nernst reversible potential, forming a monolayer. This phenomenon differs from bulk deposition of the metal itself. First, bulk deposition occurs when the metal deposits on itself, requiring a potential more negative than the Nernst reversible potential. With prolonged deposition, the metal develops a three-dimensional morphology. In contrast, underpotential deposition remains a monolayer regardless of deposition time. Second, while metal ions form metallic bonds with free electrons to stabilize the metal, depositing a metal on a foreign metal does not create these bonds. This deposition between dissimilar metals inevitably involves stronger intermetallic interactions. Underpotential deposition can occur before bulk deposition, but not every two metals can undergo underpotential deposition. This involves the work function. A metal with a smaller work function can underpotentially deposit on a metal with a larger work function, but the reverse is not true. The work function is the electron work function; the larger the electron work function, the more difficult it is for the metal to lose electrons. Therefore, in underpotential deposition, the deposited monolayer atoms are mostly non-noble metals, while the metal used as the deposition substrate is mostly noble metal. Underpotential deposition is currently mainly used to study the deposition kinetics of electrode surfaces under different conditions, and to modify metal surfaces to synthesize highly efficient electrocatalysts.

[0030] Galvanic replacement (chemical replacement) refers to the process of immersing a metal M (mostly non-precious metals) in a solution containing another metal M. noble In a solution containing (mostly noble metals), if the Nernst redox potential of the noble metal is greater than that of the non-noble metal, and the ionic form of M is stable under given experimental conditions (temperature, pH, complexing agent, etc.), then M... noble The displacement reaction of M is thermodynamically permissible, as shown below:

[0031]

[0032] This type of reaction is actually a coupling of two half-reactions, namely the oxidation of M and the oxidation of M. noble The reduction reaction results in M ​​completely or partially dissolving into M. n+ And M noble Then, at the surface site where M was previously located, M has already been deposited. noble Deposits may occur at other sites on or near the substrate. This is M. noble The displacement reaction of M.

[0033] The key feature of this application is the combination of underpotential deposition and chemical substitution. One metal is pre-deposited as a sacrificial template onto sulfur sites using an underpotential method, followed by substitution of one metal with the template metal. This allows for precise control over the metal sites.

[0034] The beneficial effects of this invention are:

[0035] 1. This invention utilizes a silica template and re-etching method to prepare hollow spherical precursor materials with atomically dispersed nickel and platinum. This increases the specific surface area and atomic dispersion of the material. The bimetallic synergistic effect of Pt and Ni in the obtained f-etch-NiNC-S-Pt material enhances ORR performance. In particular, f-etch-NiNC-S-2 and f-etch-NiNC-S-2-Pt exhibit electron transfer numbers of 3.2 and 3.4 at 0.6V, respectively, and H2O2 yields of 39% and 29%, respectively. This indicates that platinum loading tends the oxygen reduction reaction towards four-electron transfer, and the lower hydrogen peroxide yield is beneficial for reducing the Fenton effect, thereby improving catalyst stability.

[0036] 2. This invention introduces sulfur and utilizes the strong interaction between sulfur and copper, as well as the characteristics of underpotential deposition monolayer deposition, to achieve precise deposition of copper. Then, through chemical substitution, copper is replaced with platinum. This synthesis method not only obtains low-load atomically dispersed platinum, but also achieves precise control of the platinum coordination environment.

[0037] 3. This invention introduces platinum into the catalytic system through a clean and efficient electrochemical method, which reduces environmental pollution during the preparation process, while also greatly reducing preparation time and cost.

[0038] 4. In this invention, the atomically dispersed nickel and platinum have a high atomic utilization rate. The interaction between nickel and platinum can effectively regulate their electronic structure, thereby obtaining excellent ORR performance. Attached Figure Description

[0039] Figure 1 The image is a scanning electron microscope (SEM) image of f-etch-NiNC-S-1-Pt from Example 1.

[0040] Figure 2 The image shows a transmission high-resolution transmission electron microscope (TEM, HRTEM) image of f-etch-NiNC-S-1-Pt from Example 1.

[0041] Figure 3 The image shows a transmission high-resolution transmission electron microscope (TEM, HRTEM) image of f-etch-NiNC-S-2-Pt from Example 2.

[0042] Figure 4 The X-ray diffraction (XRD) patterns of f-etch-NiNC-S-1, f-etch-NiNC-S-1-Cu, and f-etch-NiNC-S-1-Pt in Example 1 are shown.

[0043] Figure 5XPS spectra of N1s for f-etch-NiNC-S-1 and S2p for f-etch-NiNC-S-1-Pt in Example 1.

[0044] Figure 6 The oxygen reduction linear scanning polarization curves of the 20% Pt / C, f-etch-NiNC-S-1, f-etch-NiNC-S-1-Pt material in Example 1 at 1600 rpm are shown.

[0045] Figure 7 The oxygen reduction linear scanning polarization curves of the 20% Pt / C, f-etch-NiNC-S-2, f-etch-NiNC-S-2-Pt material in Example 2 at 1600 rpm are shown.

[0046] Figure 8 The oxygen reduction linear scanning polarization curves of f-etch-NC-S-2-Pt and f-etch-NiNC-S-2-Pt materials in Example 2 at 1600 rpm are shown.

[0047] Figure 9 The oxygen reduction polarization curves of the f-etch-NiNC-S-2-Pt material in Example 2 before and after 10,000 cycles of operation.

[0048] Figure 10 The graph shows the mass activity and specific activity of 20% Pt / C, f-etch-NiNC-S-2-Pt in Example 2.

[0049] Figure 11 Tafel slope plot for 20% Pt / C, f-etch-NiNC-S-2, f-etch-NiNC-S-2-Pt in Example 2.

[0050] Figure 12 The H2O2 yield and electron transfer number of f-etch-NiNC-S-2-Pt in Example 2 are shown.

[0051] Figure 13 The oxygen reduction linear scanning polarization curves of the 20% Pt / C, f-etch-NiNC-S-3, f-etch-NiNC-S-3-Pt material in Example 3 at 1600 rpm are shown.

[0052] Figure 14 The oxygen reduction linear scanning polarization curves of the 20% Pt / C, f-etch-FeNC-S-2, and f-etch-FeNC-S-2-Pt materials in Comparative Example 1 at 1600 rpm are shown. Detailed Implementation

[0053] The present invention will be further described below through embodiments, but is not limited to these embodiments. (The embodiments do not include...)

[0054] Experimental methods that specify specific conditions are generally performed under standard conditions and as described in the manual, or under conditions recommended by the manufacturer. The general equipment, materials, reagents, etc. used are all commercially available unless otherwise specified.

[0055] Example 1

[0056] The preparation method of sulfur-doped nickel-platinum-nitrogen-carbon materials includes the following steps:

[0057] 1. First, measure 30 ml of formamide into a 100 ml beaker using a graduated cylinder. Weigh 0.8 g of silica and add it to the formamide. Then weigh the zinc precursor and nickel precursor and add them to the formamide. Sonicate for 30 minutes until the anhydrous zinc chloride is fully dissolved in the formamide. Then place the beaker on a magnetic stirrer and stir for 30 minutes. The molar ratio of zinc precursor to nickel precursor is 20:1. The zinc precursor is anhydrous zinc chloride, and the molar concentration of zinc chloride in the formamide is 0.10 mol / L. The nickel precursor is anhydrous nickel chloride, and the molar concentration of zinc chloride in the formamide is 0.005 mol / L.

[0058] 2. Pour the mixed formamide solution obtained in step 1 into the lining of a 40ml reactor, place it into the high-pressure reactor, and tighten it. Put the reactor into an oven and maintain it at 160℃ for 12 hours. After the reaction is complete, remove the reactor and allow it to cool naturally.

[0059] 3. Pour out the solution obtained from the reactor lining, filter, wash three times with water, and three times with ethanol. Place the filtered sample into a vacuum freeze-drying apparatus and dry overnight.

[0060] 4. Grind the dried sample into powder, place it in a porcelain boat, insert a quartz tube, and place the quartz tube on a tube furnace. Seal both ends with flanges and sealing rings, and purge with Ar for 30 minutes. After the air in the tube has been expelled by Ar, start the heating program, raising the temperature to 950℃ at 10℃ / min and maintaining it at 950℃ for 2 hours, while continuously purging with Ar. After the temperature drops to room temperature, remove the sample from the quartz tube to obtain the silica-coated nickel-nitrogen-carbon material f-SiO2@NiNC.

[0061] 5. The prepared f-SiO2@NiNC was stirred in 6M NaOH at 60℃ for 8 hours to etch silicon dioxide. The etched product was centrifuged, washed three times with water, and three times with ethanol. It was then placed in a vacuum freeze dryer and dried overnight.

[0062] 6. The product after alkali washing was placed in 1M HCl solution and stirred in a metal bath at 80℃ for 8 hours. After stirring, the solution was allowed to cool naturally, filtered, washed three times with water, and washed three times with ethanol. It was then dried overnight in a vacuum freeze-drying apparatus to obtain hollow spherical nickel-nitrogen-carbon material f-etch-NiNC.

[0063] 7. Weigh f-etch-NiNC and sulfur-containing small molecules in a 3:1 mass ratio and place them in 60 ml of deionized water. Sonicate for 20 min, stir for 8 h, and then rotary evaporate. The sulfur-containing small molecule mentioned above is thiourea, with f-etch-NiNC weighing 30 mg and thiourea weighing 10 mg.

[0064] 8. Place the obtained sample in a tube furnace, introduce Ar, raise the temperature to 950℃ at 10℃ / min and maintain it at 950℃ for 2 hours. After the temperature drops to room temperature, take the sample out of the quartz tube to obtain the sulfur-doped nickel-nitrogen-carbon material f-etch-NiNC-S-1.

[0065] 9. The obtained f-etch-NiNC-S-1 was drop-coated onto a glassy carbon electrode. After the reaction, the electrode was rinsed with deionized water. Underpotential deposition was then performed in a copper precursor solution to obtain the sulfur-doped nickel-copper bimetallic material f-etch-NiNC-S-1-Cu. The copper precursor was copper sulfate with a molar concentration of 0.015 mol / L. The pH of the copper sulfate solution was controlled at 1, the deposition potential was 0.20 V vs Ag / AgCl, the deposition time was 30 s, and an H-type electrolytic cell was used. The two single cells were separated by a proton exchange membrane. Ar saturation was maintained during the deposition process. The counter electrode was a platinum sheet electrode, the reference electrode was saturated Ag / AgCl, and the working electrode loading was 0.5 mg / cm.

[0066] 10. Immerse the prepared f-etch-NiNC-S-1-Cu in a platinum-containing precursor aqueous solution and stir for 10 min to obtain the sulfur-doped nickel-platinum bimetallic material f-etch-NiNC-S-1-Pt. The above platinum precursor is potassium tetrachloroplatinate, with a molar concentration of 0.08 mol / L. The pH of the potassium tetrachloroplatinate aqueous solution is controlled at 1, and Ar saturation is maintained during stirring.

[0067] Material characterization and performance testing are as follows:

[0068] Figure 1 Scanning electron microscope (SEM) image of f-etch-NiNC-S-1-Pt. Figure 1 It can be seen that f-etch-NiNC-S-1-Pt has a hollow spherical structure.

[0069] Figure 2Transmission high-resolution transmission electron microscopy (TEM, HRTEM) image of f-etch-NiNC-S-1-Pt. Figure 2 It can be seen that the average spherical shell thickness of f-etch-NiNC-S-1-Pt is about 7 nm and the diameter is about 240 nm. No metal nanoparticle agglomeration was found on it, indicating that nickel and platinum are in an atomically dispersed state.

[0070] Figure 4 X-ray diffraction (XRD) patterns of f-etch-NiNC-S-1, f-etch-NiNC-S-1-Cu, and f-etch-NiNC-S-1-Pt. Figure 4 It can be seen that f-etch-NiNC-S-1, f-etch-NiNC-S-1-Cu, and f-etch-NiNC-S-1-Pt all show broad diffraction peaks of graphite carbon, but no metal diffraction peaks, indicating that nickel and platinum are in an atomically dispersed state.

[0071] Figure 5 X-ray photoelectron spectra (XPS) of N1s for f-etch-NiNC-S-1 and S2p for f-etch-NiNC-S-1-Pt. Figure 5 This indicates that there is a Ni-N bond portion in f-etch-NiNC-S-1 and a Metal-S (Pt-S bond) portion in f-etch-NiNC-S-1-Pt.

[0072] Performance testing:

[0073] The performance of the above-obtained f-etch-NiNC-S-1-Pt, 20% Pt / C, and f-etch-NiNC-S-1 was tested. The test conditions were CHI three-electrode system, linear sweep (LSV) test at O2 saturated 0.1M KOH and 1600 rpm.

[0074] Figure 6 The oxygen reduction linear scanning polarization curves of 20% Pt / C, f-etch-NiNC-S-1, and f-etch-NiNC-S-1-Pt materials at 1600 rpm. Figure 6 It can be seen that in 0.1M KOH, the half-wave potential of f-etch-NiNC-S-1-Pt is 0.881V, which is much better than that of unloaded platinum f-etch-NiNC-S-1 (half-wave potential is 0.807V) and basically the same as that of 20% Pt / C (half-wave potential is 0.883V). Figure 6 This indicates that f-etch-NiNC-S-1-Pt has better oxygen reduction activity than f-etch-NiNC-S-1.

[0075] Example 2

[0076] The preparation method of sulfur-doped nickel-platinum-nitrogen-carbon includes the following steps:

[0077] 1. First, measure 30 ml of formamide into a 100 ml beaker using a graduated cylinder. Weigh 1.0 g of silica and add it to the formamide. Then weigh the zinc precursor and nickel precursor and add them to the formamide. Sonicate for 30 minutes until the anhydrous zinc chloride is fully dissolved in the formamide. Then place the beaker on a magnetic stirrer and stir for 30 minutes. The ratio of zinc precursor to nickel precursor is 20:1. The zinc precursor is anhydrous zinc chloride with a molar concentration of 0.15 mol / L, and the nickel precursor is anhydrous nickel chloride with a molar concentration of 0.005 mol / L.

[0078] 2. Pour the mixed formamide solution obtained in step 1 into the lining of a 40ml reactor, place it into the high-pressure reactor, and tighten it. Put the reactor into an oven and maintain it at 180℃ for 12 hours. After the reaction is complete, remove the reactor and allow it to cool naturally.

[0079] 3. Pour out the solution obtained from the reactor lining, filter, wash three times with water, and three times with ethanol. Place the filtered sample into a vacuum freeze-drying apparatus and dry overnight.

[0080] 4. Grind the dried sample into powder, place it in a porcelain boat, insert a quartz tube, and place the quartz tube on a tube furnace. Seal both ends with flanges and sealing rings, and purge with Ar for 30 minutes. After the air in the tube has been expelled by Ar, start the heating program, raising the temperature by 5°C per minute to 900°C and maintaining it at 900°C for 2 hours, while continuously purging with Ar. Once the temperature has cooled to room temperature, remove the sample from the quartz tube to obtain the silica-coated nickel-nitrogen-carbon material f-SiO2@NiNC.

[0081] 5. The prepared f-SiO2@NiNC was stirred in 6M KOH at 60℃ for 8 hours to etch silicon dioxide. The etched product was centrifuged, washed three times with water, and three times with ethanol. It was then placed in a vacuum freeze dryer and dried overnight.

[0082] 6. The alkaline-washed product obtained in step 5 was placed in a 0.5M H2SO4 solution and stirred in a metal bath at 80℃ for 8 hours. After stirring, the solution was allowed to cool naturally, filtered, washed three times with water, and washed three times with ethanol. It was then dried overnight in a vacuum freeze-drying apparatus to obtain hollow spherical nickel-nitrogen-carbon material f-etch-NiNC.

[0083] 7. Weigh f-etch-NiNC and sulfur-containing small molecules in a 3:2 mass ratio and place them in 60 ml of deionized water. Sonicate for 20 min, stir for 8 h, and then rotary evaporate. The sulfur-containing small molecule is thiourea, with f-etch-NiNC weighing 30 mg and thiourea weighing 20 mg.

[0084] 8. Place the obtained sample in a tube furnace, introduce Ar, raise the temperature to 900℃ at 5℃ per minute and maintain it at 900℃ for 2 hours. After the temperature drops to room temperature, take the sample out of the quartz tube to obtain the sulfur-doped nickel-nitrogen-carbon material f-etch-NiNC-S-2.

[0085] 9. The obtained f-etch-NiNC-S-2 was drop-coated onto a glassy carbon electrode. After the reaction, the electrode was rinsed with deionized water. Underpotential deposition was then performed in a copper precursor solution to obtain the sulfur-doped nickel-copper metal material f-etch-NiNC-S-2-Cu. The copper precursor was copper sulfate with a molar concentration of 0.005 mol / L. The pH of the copper sulfate solution was controlled at 1, the deposition potential was 0.10 V vs Ag / AgCl, the deposition time was 60 s, and an H-type electrolytic cell was used. The two single cells were separated by a proton exchange membrane. Ar saturation was maintained during the deposition process. The counter electrode was a platinum sheet electrode, the reference electrode was saturated Ag / AgCl, and the working electrode loading was 0.5 mg / cm². 2 .

[0086] 10. Immerse the prepared f-etch-NiNC-S-2-Cu in a platinum-containing precursor solution and stir for 30 min to obtain the sulfur-doped nickel-platinum-nitrogen-carbon material f-etch-NiNC-S-2-Pt. The platinum precursor is potassium tetrachloroplatinate, with a molar concentration of 0.005 mol / L. The pH of the potassium tetrachloroplatinate aqueous solution is controlled at 1, and Ar saturation is maintained during stirring.

[0087] Material characterization and performance testing are as follows:

[0088] Figure 3 Transmission high-resolution transmission electron microscopy (TEM, HRTEM) image of f-etch-NiNC-S-2-Pt. Figure 3 It can be seen that the average spherical shell thickness of f-etch-NiNC-S-2-Pt is about 9 nm and the diameter is about 260 nm. No metal nanoparticle agglomeration was found on it, indicating that nickel and platinum are in an atomically dispersed state.

[0089] Performance testing:

[0090] The performance of the above-obtained f-etch-NiNC-S-2-Pt, 20% Pt / C, and f-etch-NiNC-S-2 was tested. The test conditions were CHI three-electrode system, linear sweep (LSV) test was performed at O2 saturated 0.1M KOH and 1600 rpm.

[0091] Figure 7The oxygen reduction linear scanning polarization curves of 20% Pt / C, f-etch-NiNC-S-2, and f-etch-NiNC-S-2-Pt materials at 1600 rpm.

[0092] Figure 7 It can be seen that in 0.1M KOH, the half-wave potential of f-etch-NiNC-S-2-Pt is 0.903V, which is much better than that of unloaded platinum f-etch-NiNC-S-2 (half-wave potential is 0.804V) and also exceeds that of 20% Pt / C (half-wave potential is 0.883V). Figure 7 This indicates that f-etch-NiNC-S-2-Pt has better oxygen reduction activity than f-etch-NiNC-S-2 and 20%Pt / C.

[0093] Figure 8 The oxygen reduction linear scanning polarization curves of f-etch-NC-S-2-Pt and f-etch-NiNC-S-2-Pt materials at 1600 rpm are shown. Figure 8 It can be seen that in 0.1M KOH, the half-wave potential of f-etch-NC-S-2-Pt is 0.857V, which is about 40mV lower than that of f-etch-NiNC-S-2-Pt. Figure 8 This indicates that for this synthesis method, the synergistic effect of platinum and nickel makes the oxygen reduction performance superior to simply loading platinum.

[0094] The preparation method of f-etch-NC-S-2-Pt is as follows: the method of Example 2 is adopted, except that the nickel precursor is not added in step 1.

[0095] Figure 9 Oxygen reduction polarization curves of f-etch-NiNC-S-2-Pt material before and after 10,000 cycles. Figure 9 It can be seen that the half-wave potential of the f-etch-NiNC-S-2-Pt material decreases by only 14mV after 10,000 cycles, indicating its good stability.

[0096] Figure 10 Mass activity versus specific activity of f-etch-NiNC-S-2-Pt with 20% Pt / C.

[0097] Figure 10 It can be seen that the mass activity of f-etch-NiNC-S-2-Pt is 483.83 mA / mg. Pt The specific activity is 0.85 mA / cm. 2 The mass activity and specific activity were 6.42 times and 8.33 times that of 20% Pt / C, respectively, indicating that f-etch-NiNC-S-2-Pt has high intrinsic activity.

[0098] Figure 11 Tafel slope plots for 20% Pt / C, f-etch-NiNC-S-2, f-etch-NiNC-S-2-Pt.

[0099] Figure 11 It can be seen that the Tafel slope of f-etch-NiNC-S-2-Pt is 73.6 mV·dec -1 Lower than f-etch-NiNC-S-2 (394mV·dec) -1 ) and 20% Pt / C (81.1 mV·dec -1 This indicates that platinum loading effectively improves the sluggish oxygen reduction kinetics.

[0100] Figure 12 The H2O2 yield and electron transfer number of f-etch-NiNC-S-2-Pt are given.

[0101] Figure 12 It can be seen that the electron transfer numbers of f-etch-NiNC-S-2 and f-etch-NiNC-S-2-Pt at 0.6V are 3.2 and 3.4, respectively, and the H2O2 yields are 39% and 29%, respectively. This indicates that the platinum loading tends the oxygen reduction reaction towards four-electron transfer, and the lower hydrogen peroxide yield is beneficial to reducing the Fenton effect, thereby improving the stability of the catalyst.

[0102] Example 3

[0103] The preparation method of sulfur-doped nickel-platinum-nitrogen-carbon includes the following steps:

[0104] 1. First, measure 30 ml of formamide into a 100 ml beaker using a graduated cylinder. Weigh 0.9 g of silica and add it to the formamide. Then weigh out the zinc and nickel precursors and add them to the formamide. Sonicate for 30 minutes until the anhydrous zinc chloride is fully dissolved in the formamide. Then place the beaker on a magnetic stirrer and stir for 30 minutes. The ratio of zinc to nickel precursor is 25:1. The zinc precursor is anhydrous zinc chloride with a molar concentration of 0.125 mol / L, and the nickel precursor is anhydrous nickel chloride with a molar concentration of 0.005 mol / L.

[0105] 2. Pour the formamide solution into the 40ml liner of the reaction vessel, place it into the high-pressure reaction vessel, and tighten it. Put the reaction vessel into an oven and maintain it at 170℃ for 12 hours. After the reaction is complete, remove the reaction vessel and allow it to cool naturally.

[0106] 3. Pour out the solution obtained from the reactor lining, filter, wash three times with water, and three times with ethanol. Place the filtered sample into a vacuum freeze-drying apparatus and dry overnight.

[0107] 4. Grind the dried sample into powder, place it in a porcelain boat, insert a quartz tube, and place the quartz tube on a tube furnace. Seal both ends with flanges and sealing rings, and purge with Ar for 30 minutes. After the air in the tube has been expelled by Ar, start the heating program, raising the temperature from 8°C per minute to 925°C and maintaining it at 925°C for 2 hours, while continuously purging with Ar. Once the temperature has cooled to room temperature, remove the sample from the quartz tube to obtain the silica-coated nickel-nitrogen-carbon material f-SiO2@NiNC.

[0108] 5. The prepared f-SiO2@NiNC was stirred in 6M KOH at 60℃ for 8 hours to etch silicon dioxide. The etched product was centrifuged, washed three times with water, and three times with ethanol. It was then placed in a vacuum freeze dryer and dried overnight.

[0109] 6. The product after alkali washing was placed in 0.5M H2SO4 solution and stirred in a metal bath at 80℃ for 8 hours. After stirring, the solution was allowed to cool naturally, filtered, washed three times with water, and washed three times with ethanol. It was then dried overnight in a vacuum freeze dryer to obtain hollow spherical nickel-nitrogen-carbon material f-etch-NiNC.

[0110] 7. Weigh f-etch-NiNC and sulfur-containing small molecules in a 1:1 mass ratio and place them in 60 ml of deionized water. Sonicate for 20 min, stir for 8 h, and then rotary evaporate. The sulfur-containing small molecule mentioned above is thiourea, with f-etch-NiNC weighing 30 mg and thiourea weighing 30 mg.

[0111] 8. Place the obtained sample in a tube furnace, introduce Ar, raise the temperature to 925°C at 8°C per minute and maintain it at 925°C for 2 hours. After the temperature drops to room temperature, remove the sample from the quartz tube to obtain the sulfur-doped nickel-nitrogen-carbon material f-etch-NiNC-S-3.

[0112] 9. The obtained f-etch-NiNC-S-3 was drop-coated onto a glassy carbon electrode. After the reaction, the electrode was rinsed with deionized water. Underpotential deposition was then performed in a copper precursor solution to obtain the sulfur-doped nickel-copper metal material f-etch-NiNC-S-3-Cu. The copper precursor was copper sulfate with a molar concentration of 0.010 mol / L. The pH of the copper sulfate solution was controlled at 1, the deposition potential was 0.15 V vs Ag / AgCl, the deposition time was 50 s, and an H-type electrolytic cell was used. The two single cells were separated by a proton exchange membrane. Ar saturation was maintained during the deposition process. The counter electrode was a platinum sheet electrode, the reference electrode was saturated Ag / AgCl, and the working electrode loading was 0.5 mg / cm³. 2 .

[0113] 10. Immerse the prepared f-etch-NiNC-S-3-Cu in a platinum-containing precursor solution and stir for 20 min to obtain the sulfur-doped nickel-platinum-nitrogen-carbon material f-etch-NiNC-S-3-Pt. The platinum precursor is potassium tetrachloroplatinate, with a molar concentration of 0.04 mol / L. The pH of the potassium tetrachloroplatinate aqueous solution is controlled at 1, and Ar saturation is maintained during stirring.

[0114] Performance tests are as follows:

[0115] The performance of the f-etch-NiNC-S-3-Pt obtained above was tested under the following conditions: a CHI three-electrode system was used, and linear sweep (LSV) tests were performed at 0.1M KOH saturated with O2 and a rotation speed of 1600 rpm.

[0116] Figure 13 The oxygen reduction linear scanning polarization curves of 20% Pt / C, f-etch-NiNC-S-3, and f-etch-NiNC-S-3-Pt materials at 1600 rpm.

[0117] Figure 13 It can be seen that in 0.1M KOH, the half-wave potential of f-etch-NiNC-S-3-Pt is 0.882V, which is much better than that of unplatinum-loaded f-etch-NiNC-S-3 (half-wave potential is 0.800V) and basically the same as that of 20% Pt / C (half-wave potential is 0.883V). This indicates that for this synthesis method, the synergistic effect of platinum and nickel makes the oxygen reduction performance better than that of simply loading platinum.

[0118] Comparative Example 1 - Sulfur-doped iron-platinum-nitrogen-carbon materials

[0119] Preparation method of sulfur-doped iron-platinum-nitrogen-carbon material: The only difference from Example 1 is that the anhydrous nickel chloride in step 1 is replaced with an equimolar amount of anhydrous ferric chloride, finally obtaining the sulfur-doped iron-platinum-nitrogen-carbon material, namely f-etch-FeNC-S-3-Pt. Simultaneously, f-etch-FeNC-S-3 is obtained in step 8.

[0120] Performance tests are as follows:

[0121] The performance of the f-etch-FeNC-S-3-Pt and f-etch-FeNC-S-3 obtained above was tested. The test conditions were CHI three-electrode system, linear sweep (LSV) test at O2 saturated 0.1M KOH and 1600 rpm.

[0122] Figure 14 The linear scanning polarization curves of oxygen reduction for f-etch-FeNC-S-3 and f-etch-FeNC-S-3-Pt materials at 1600 rpm are shown.

[0123] Figure 14 It can be seen that in 0.1M KOH, the half-wave potential of f-etch-FeNC-S-3 is 0.866V, which is only about 6mV lower than that of f-etch-FeNC-S-3-Pt (half-wave potential is 0.872V), and slightly lower than that of 20% Pt / C (half-wave potential is 0.883V). This indicates that the activity of sulfur-doped iron-platinum-nitrogen-carbon material (f-etch-FeNC-S-3-Pt) in catalyzing the ORR reaction is far inferior to that of sulfur-doped nickel-platinum-nitrogen-carbon material (f-etch-NiNC-S-1-Pt). Furthermore, it can be seen that the activity of f-etch-FeNC-S-3-Pt is basically not improved compared to f-etch-FeNC-S-3.

Claims

1. A sulfur-doped nickel-platinum-nitrogen-carbon material, characterized in that, The material has a spherical shell structure, comprising a sulfur-containing conductive substrate and nickel and platinum, which are in a single-atom dispersed state and loaded on the sulfur-containing conductive substrate.

2. The sulfur-doped nickel-platinum-nitrogen-carbon material according to claim 1, characterized in that, The spherical shell of the material has a thickness of 7–9 nm and a diameter of 240–260 nm.

3. The sulfur-doped nickel-platinum-nitrogen-carbon material according to claim 1, characterized in that, The sulfur-containing conductive substrate is a sulfur-nitrogen-carbon material; the material contains Ni-N bonds and Pt-S bonds.

4. The method for preparing sulfur-doped nickel-platinum-nitrogen-carbon material according to claim 1, characterized in that, The preparation method includes the following steps: (a) Add zinc precursor, nickel precursor and silicon dioxide to formamide solution and react at 160-180℃ for 9-15h to obtain precursor material. Separate solid and liquid, dry and grind the obtained solid. (b) The precursor material after grinding in step (a) is heated to 900-950°C in an inert atmosphere and held at this temperature for 1-3 hours to obtain a silicon dioxide-coated nickel-nitrogen-carbon material, namely f-SiO2@NiNC; (c) The above f-SiO2@NiNC is stirred in a strong alkali at 40-80℃ for 4-10h, dried, and then stirred in a strong acid at 60-85℃ for 4-10h. After solid-liquid separation, hollow spherical nickel-nitrogen-carbon material f-etch-NiNC is obtained. (d) The above f-etch-NiNC and sulfur-containing precursor were added to water, stirred and then rotary evaporated. The temperature was raised to 900-950℃ in an inert atmosphere and maintained at this temperature for 1-3 hours to obtain sulfur-doped nickel nitrogen carbon, i.e. f-etch-NiNC-S. (e) f-etch-NiNC-S is placed in a copper precursor solution for underpotential deposition to obtain f-etch-NiNC-S-Cu, and then chemical substitution is performed in a platinum precursor solution to obtain the sulfur-doped nickel-platinum-nitrogen-carbon material f-etch-NiNC-S-Pt.

5. The preparation method according to claim 4, characterized in that, In step (a): the molar ratio of the zinc precursor and the nickel precursor is 20:1 to 30:1, the molar concentration of the zinc precursor in the formamide is 0.10 mol / L to 0.15 mol / L, the molar concentration of the nickel precursor in the formamide is 0.005 mol / L, and the mass concentration of silica is 26.7 to 33 g / L of formamide solution.

6. The preparation method according to claim 4, characterized in that: In step (b): the inert gas used for the sample in the tube furnace is Ar, and the heating rate is 5-10℃ / min.

7. The preparation method according to claim 4, characterized in that: In step (c): the strong base is 6 mol / L KOH or 6 mol / L NaOH, the strong acid is 0.5 mol / L H2SO4 or 1M HCl, and the heating rate is 5-10℃ / min.

8. The preparation method according to claim 4, characterized in that: In step (d): the sulfur-containing precursor is thiourea, the mass ratio of f-etch-NiNC to thiourea is 3:1 to 1:1, and the heating rate is 5 to 10 °C / min.

9. The preparation method according to claim 4, characterized in that: In step (e): the concentration of the copper precursor solution is 0.005-0.015 mol / L, the concentration of potassium tetrachloroplatinate is 0.005-0.08 mol / L, the underpotential deposition potential is 0.10-0.20 V vs saturated Ag / AgCl electrode, the deposition time is 30-60 s, and the replacement time is 10-30 min.

10. The use of the sulfur-doped nickel-platinum-nitrogen-carbon material of claim 1 as an oxygen reduction reaction catalyst to improve reaction activity and stability.

Images