Preparation method and application of hollow sphere structure chlorine-free ptcu / c catalyst

Abstract

This invention relates to a method for preparing a hollow spherical, chlorine-free PtCu / C catalyst and its application. The preparation method includes the following steps: calcining a carbon support in a reducing atmosphere; dispersing the calcined carbon support in an alcohol-water mixture and adding an oxidant for a hydrothermal reaction; uniformly dispersing the hydrothermally reacted carbon support in the alcohol-water mixture and adjusting the pH to acidic to obtain a carbon support suspension; and adding Pt(NH4+)4 to the carbon support. 3 ) 4 (OH) 2 Solution and Cu(NH4) 3 ) 4 (OH) 2 A carbon-supported suspension was added to the solution, followed by reduction with a reducing agent to obtain a chlorine-free PtCu / C catalyst, wherein the PtCu is a nano-hollow sphere structure. This invention eliminates the contamination caused by residual Cl ions in existing catalysts; the synergistic and ligand effects between Pt and Cu atoms weaken the adsorption strength of oxygen-containing intermediates at Pt sites during the ORR process, lowering the reaction energy barrier of the catalyst in the oxygen reduction process; the high atomic utilization and large electrochemical active surface area of ​​the hollow sphere structure also facilitate the catalytic reaction, resulting in excellent ORR electrocatalytic activity and stability of the catalyst.

Description

Preparation method and application of a hollow spherical chlorine-free PtCu / C catalyst Technical Field

[0001] This invention relates to the field of fuel cell catalysts; more specifically, it relates to a method for preparing a hollow spherical chlorine-free PtCu / C catalyst and its application. Background Technology

[0002] The ever-increasing global energy demand and environmental challenges have driven the development of sustainable energy conversion and storage technologies. Proton exchange membrane fuel cells (PEMFCs) have attracted significant attention as a highly efficient and pollution-free green hydrogen conversion technology. Pt-based catalysts are a crucial component of PEMFCs, significantly reducing reaction overpotential and accelerating the kineticly slow oxygen reduction reaction (ORR) at the cathode. However, the scarcity, high cost, and low stability of Pt severely hinder the large-scale commercial application of PEMFCs. Therefore, developing Pt-based catalysts with low Pt loading, high activity, and high stability is essential for accelerating the kinetics of the cathode ORR and improving the energy conversion efficiency of PEMFCs.

[0003] Alloying Pt with transition metals (Fe, Co, Ni, Cu) is an effective strategy to reduce catalyst costs. The resulting lattice strain and ligand effects can further optimize the electronic structure of Pt, improve the adsorption strength of oxygen-containing intermediates, and thus enhance ORR catalytic activity. However, in the oxidative chemistry of acidic electrolytes and at higher reaction potentials, the dissolution of transition metals (Fe or Co) often occurs, leading to the destruction of the initial morphology and lattice structure, as well as the loss of catalytic activity, thereby drastically reducing the lifespan of the membrane electrode assembly (MEA). In contrast, Cu... 2+ The anodic dissolution potential of Cu (+0.3V vs NHE) is higher than that of Fe. 2+ / Fe(-0.5V vs NHE), Co 2+ / Co(-0.2V vs NHE) and Ni 2+ / Ni(+0.1V vs NHE), indicating that Cu is more stable in ORR potential cycling and is difficult to dissolve in acidic electrolytes.

[0004] Furthermore, chlorides can poison the performance of PEMFCs. Because commercial Pt / C catalysts use Cl-containing Pt precursors such as chloroplatinic acid or potassium chloroplatinate in their preparation, residual Cl remains after batch production. -1 The presence of [something] can poison the active sites of the catalyst, causing more H2O2 to be generated during the ORR process, and can also lead to catalyst dissolution, thereby reducing the electrochemical active surface area.

[0005] To address the aforementioned issues, the inventors of this application disclosed a method for preparing a chlorine-free PtCu alloy nanocatalyst in Chinese Invention Patent Application No. CN202111084983.8. This application is a further study and improvement by the inventors based on the aforementioned application. Summary of the Invention

[0006] The first aspect of this invention discloses a method for preparing a chlorine-free PtCu / C catalyst with a hollow sphere structure, comprising the following steps:

[0007] (1) The carbon support is calcined in a reducing atmosphere;

[0008] (2) The calcined carbon support is dispersed in an alcohol-water mixture and an oxidant is added to carry out a hydrothermal reaction;

[0009] (3) The carbon support after hydrothermal reaction is evenly dispersed in an alcohol-water mixed solution and the pH is adjusted to acidity to obtain a carbon support suspension.

[0010] (4) Add Pt(NH3)4(OH)2 solution and Cu(NH3)4(OH)2 solution to the carbon support suspension, and then add a reducing agent to obtain a chlorine-free PtCu / C catalyst, wherein PtCu is a nano-hollow sphere structure.

[0011] In this invention, calcining the carbon support under a reducing atmosphere removes the uneven oxygen-containing functional groups on its surface, which is beneficial for increasing the graphitization degree of the carbon support and thus improving its corrosion resistance. Subsequent hydrothermal reaction with an oxidant introduces more negatively charged oxygen-containing functional groups onto the carbon support surface and also introduces carbon defects based on the calcination process, providing numerous anchoring sites for metal particles. Adjusting the pH to acidic provides a favorable environment for the adsorption of metal precursors. During the impregnation process, positively charged Pt[NH3]4... 2+ / Cu[NH3]4 2+ Strong electrostatic adsorption between the metal precursor ions and the negatively charged oxygen-containing functional groups on the carbon support can effectively anchor the metal precursor ions onto the carbon support. Finally, a reducing agent is added to reduce the metal precursor ions and form a chlorine-free PtCu / C catalyst with a nano-hollow sphere structure.

[0012] Furthermore, Pt atoms are located on the outer layer of the hollow nanospheres, while Cu atoms are mainly distributed on the inner side of the hollow nanospheres. This structure can expose more Pt active sites, thereby improving the performance of the catalyst.

[0013] Furthermore, the size of the hollow nanospheres is less than 20 nm.

[0014] Furthermore, in step (1), the calcination temperature is 750–850℃, and the calcination time is 1–3 hours. If the calcination temperature is too low, the carbon support in the catalyst will have a low degree of graphitization, poor conductivity and corrosion resistance, which is not conducive to ORR electrocatalysis. If the calcination temperature is too high, the carbon support may have a low degree of defect, lacking metal particle anchoring sites, thus reducing catalytic performance.

[0015] Furthermore, the alcohol-water mixture is a mixture of ethanol and water, wherein the volume ratio of ethanol to water is 0.5 to 2:1.

[0016] Furthermore, in step (2), the hydrothermal reaction temperature is 180–200℃, and the hydrothermal time is 4–6 hours.

[0017] Furthermore, in step (3), HNO3 is used to adjust the pH to 2-3.

[0018] Furthermore, the oxidant is H2O2, and the reducing agent is NaBH4.

[0019] Furthermore, the mass ratio of Pt to Cu in the chlorine-free PtCu / C catalyst is 1–3:1–3.

[0020] The second aspect of the present invention relates to the application of the chlorine-free PtCu / C catalyst obtained by the aforementioned preparation method in the ORR reaction.

[0021] The technical solution of the present invention has at least the following beneficial effects:

[0022] The electrocatalytic ORR activity of Pt-based catalysts is closely related to their microstructure. Among various morphologies, hollow or porous structures can significantly enhance the catalytic activity of the catalyst. This invention uses Pt(NH3)4(OH)2 and Cu(NH3)4(OH)2 as metal precursors. On the one hand, this eliminates the contamination of Cl ions in existing chlorine-containing precursors. On the other hand, combined with a carbon support pretreatment step, hollow spherical PtCu nanoparticles can be obtained without the addition of template agents or morphology control components. The Pt atoms are located in the outer layer of the hollow spheres, which is beneficial for improving atom utilization and exposing a large number of catalytic sites, thereby increasing the electrochemical active surface area and improving the electrocatalytic activity of the catalyst.

[0023] To more clearly illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0024] Figure 1 shows the example PtCu(N) / C R-F Comparative Example 1: Pt(N) / C R-F Comparative Example 2Cu(N) / C R-FCatalyst and comparative example 3PtCu(Cl) / C R-F XRD characterization pattern of the catalyst;

[0025] Figure 2a shows the example PtCu(N) / C R-F TEM image of the catalyst, Figure 2b is its STEM image;

[0026] Figure 3a shows the example PtCu(N) / C R-F Figure 3b shows the HR-TEM image of the catalyst and its HAADF-STEM image.

[0027] In Figure 4: a is the comparative example 1Pt(N) / C R-F TEM image of the catalyst, b is its HR-TEM image;

[0028] In Figure 5: a is the comparative example 2Cu(N) / C R-F TEM image of the catalyst, b is its HR-TEM image;

[0029] In Figure 6: a is the comparative example 3PtCu(Cl) / C R-F TEM image of the catalyst, b is its HR-TEM image;

[0030] Figure 7 shows C0 and C. F C R C R-F The support, and [Pt(NH3)4](OH)2 / [Cu(NH3)4](OH)2 with C R-F Fourier transform infrared (FTIR) spectrum of freeze-dried powder after the carrier is mixed in aqueous solution;

[0031] Figure 8 shows C0 and C. F C R-F The support, and [Pt(NH3)4](OH)2+[Cu(NH3)4](OH)2 and [Pt(NH3)4](OH)2+[Cu(NH3)4](OH)2+C R-F Zeta potential diagram;

[0032] Figure 9 shows the example PtCu(N) / C R-F Comparative Example 1Pt(N) / C R-F Pt 4f XPS plot of the catalyst;

[0033] Figure 10 is a cyclic voltammetry (CV) curve of the examples, comparative examples 1-3 and the commercial Pt / C catalyst under N2 saturation conditions;

[0034] Figure 11 is a comparison of the linear sweep voltammetry (LSV) curves of the Examples, Comparative Examples 1-3 and the commercial Pt / C catalyst;

[0035] Figure 12 shows the Tafel slope curves of the examples, comparative examples 1-3, and commercial Pt / C catalysts;

[0036] Figure 13 is a graph showing the number of electrons transferred and the H2O2 yield of the Examples, Comparative Example 1, and the commercial Pt / C catalysts;

[0037] Figure 14 shows the example PtCu(N) / C R-F LSV curves and KL plots of the catalyst at different rotational speeds;

[0038] Figure 15 shows the example PtCu(N) / C R-F LSV curves of the catalyst and a commercial Pt / C catalyst in a GDE half-cell;

[0039] Figure 16 shows the example PtCu(N) / C R-F EIS impedance plots of the catalyst and a commercial Pt / C catalyst;

[0040] Figure 17 shows the example PtCu(N) / C R-F Comparison of chronoamperometry (it) curves of the catalyst and a commercial Pt / C catalyst. Detailed Implementation

[0041] This invention provides a method for preparing a hollow spherical chlorine-free PtCu / C catalyst. This method uses a chlorine-free metal precursor and leverages the strong electrostatic adsorption between positively charged metal precursor ions and negatively charged oxygen-containing functional groups on a carbon support. Combined with an impregnation reduction method, a hollow spherical PtCu / C catalyst is obtained. The hollow spherical structure of the PtCu particles in the catalyst improves atom utilization and exposes a large number of catalytic sites, resulting in extremely high electrocatalytic activity and stability.

[0042] The preparation method of the embodiment includes the following steps:

[0043] (1) Place an appropriate amount of carbon support, such as carbon powder BP2000, under an H2 / Ar atmosphere for calcination; wherein the calcination temperature is 750-850℃ (e.g., 800℃), the calcination time is 1-3h (e.g., 2h), and the volume ratio of H2 in the H2 / Ar gas is 5%.

[0044] (2) The calcined carbon support is dispersed in an alcohol-water mixed solution, and an oxidant is added to carry out a hydrothermal reaction. Specifically, the alcohol-water mixed solution can be a mixture of ethanol and water, with a volume ratio of ethanol to water of 0.5–2:1, preferably 1:1; the hydrothermal reaction temperature is 180–200℃ (e.g., 200℃), and the hydrothermal time is 4–6 h (e.g., 6 h). The oxidant can be nitric acid, nitric acid-sulfuric acid, H2O2, etc., with H2O2 being preferred.

[0045] (3) Disperse the carbon support after hydrothermal reaction evenly in an alcohol-water mixed solution and adjust the pH to 2-3 to obtain a black carbon support suspension; specifically, adjust the pH with 0.1 mol / L HNO3.

[0046] (4) After mixing Pt(NH3)4(OH)2 solution and Cu(NH3)4(OH)2 solution in a predetermined ratio, add the above black suspension dropwise, then add an appropriate amount of reducing agent such as NaBH4, wash with pure water and filter, freeze dry to obtain a chlorine-free PtCu / C catalyst with a hollow sphere structure.

[0047] The present invention will now be described in more detail with reference to specific embodiments and comparative examples.

[0048] Example: Preparation of PtCu(N) / CR-F catalyst

[0049] (1) First, place 100 mg of carbon powder BP2000 (CO) in a tube furnace and calcine it at 800 °C under an Ar / H2 atmosphere for 2 h to obtain C. R .

[0050] (2) C R The mixture was ultrasonically dispersed in a solution of 25 mL pure water and 25 mL anhydrous ethanol for 1 h. Then, 2 mL of H₂O₂ was added to the resulting black suspension, and the mixture was stirred for 10 min. The mixture was then transferred to a 100 mL polytetrafluoroethylene-sealed autoclave and heated at 200 °C for 6 h. After cooling to room temperature, the mixture was filtered and washed with pure water, and finally dried in a vacuum drying oven for 2 h to obtain C. R-F C R Replace with C0, and follow the same steps to obtain vector C. F .

[0051] (3) Weigh out 10mg of C R-F Add the solution to a mixture of 40 mL of pure water and 40 mL of ethanol and sonicate for 3 hours. Then, add 0.1 mol / L HNO3 solution to adjust the pH to 2-3 to obtain a black suspension.

[0052] (4) Add 60 μL of 0.05 g / mL [Pt(NH3)4](OH)2 solution and 100 μL of 0.05 g / mL [Cu(NH3)4](OH)2 solution to 10 mL of aqueous solution, mix well, and then add dropwise to the above black suspension. Stir well, sonicate for 30 min and stir for 2 h. Then add 20 mL of 20 mmol / L NaBH4 solution to the solution, let stand for 30 min, stir for 4 h, wash with pure water, filter, freeze-dry after 48 h to obtain the catalyst PtCu(N) / C. R-F .

[0053] Comparative Example 1: Preparation of Pt(N) / CR-F catalyst

[0054] The difference between this comparative example and the original example is that only [Pt(NH3)4](OH)2 solution was added to this comparative example.

[0055] (1) First, place 100 mg of BP2000 (CO) carbon powder in a tube furnace and calcine it at 800 °C under an Ar / H2 atmosphere for 2 hours to obtain C. R .

[0056] (2) C R The solution was dispersed in a mixture of 25 mL pure water and 25 mL anhydrous ethanol and sonicated for 1 h. Then, 2 mL of H₂O₂ was added to the resulting black suspension, and the mixture was stirred for 10 min. The mixture was then transferred to a 100 mL polytetrafluoroethylene-sealed autoclave and heated at 200 °C for 6 h. After cooling to room temperature, the mixture was filtered and washed with pure water, and finally dried in a vacuum drying oven for 2 h to obtain C. R-F .

[0057] (3) Weigh out 10mg of C R-F Add the solution to a mixture of 40 mL of pure water and 40 mL of ethanol and sonicate for 3 hours. Then, add 0.1 mol / L HNO3 solution to adjust the pH to 2-3 to obtain a black suspension.

[0058] (4) Add 60 μL of a 0.05 g / mL [Pt(NH3)4](OH)2 solution to 10 mL of aqueous solution, mix well, and then add dropwise to the above black suspension. After stirring evenly, sonicate for 30 min and stir for 2 h. Then add 20 mL of a 20 mmol / L NaBH4 solution to the solution, let stand for 30 min, stir for 4 h, wash with pure water, filter, and freeze-dry for 48 h to obtain the catalyst Pt(N) / C. R-F .

[0059] Comparative Example 2: Preparation of Cu(N) / CR-F catalyst

[0060] The difference between this comparative example and the original example is that only [Cu(NH3)4](OH)2 solution was added to this comparative example.

[0061] (1) First, place 100 mg of BP2000 (CO) carbon powder in a tube furnace and calcine it at 800 °C under an Ar / H2 atmosphere for 2 hours to obtain C. R .

[0062] (2) C RThe solution was dispersed in a mixture of 25 mL pure water and 25 mL anhydrous ethanol and sonicated for 1 h. Then, 2 mL of H₂O₂ was added to the resulting black suspension, and the mixture was stirred for 10 min. The mixture was then transferred to a 100 mL polytetrafluoroethylene-sealed autoclave and heated at 200 °C for 6 h. After cooling to room temperature, the mixture was filtered and washed with pure water, and finally dried in a vacuum drying oven for 2 h to obtain C. R-F .

[0063] (3) Weigh out 10mg of C R-F Add the solution to a mixture of 40 mL of pure water and 40 mL of ethanol and sonicate for 3 hours. Then, add 0.1 mol / L HNO3 solution to adjust the pH to 2-3 to obtain a black suspension.

[0064] (4) Add 100 μL of a 0.05 g / mL [Cu(NH3)4](OH)2 solution to 10 mL of aqueous solution, mix well, and then add dropwise to the above black suspension. After stirring evenly, sonicate for 30 min and stir for 2 h. Then add 20 mL of a 20 mmol / L NaBH4 solution to the solution, let stand for 30 min, stir for 4 h, wash with pure water, filter, and freeze-dry for 48 h to obtain the catalyst Cu(N) / C. R-F .

[0065] Comparative Example 3: Preparation of PtCu(Cl) / CR-F catalyst

[0066] The difference between this comparative example and the embodiment is that the [Pt(NH3)4](OH)2 solution is replaced with 495 μL of H2PtCl6 solution with a concentration of 0.0075 g / mL.

[0067] (1) First, place 100 mg of BP2000 (CO) carbon powder in a tube furnace and calcine it at 800 °C under an Ar / H2 atmosphere for 2 hours to obtain C. R .

[0068] (2) C R The solution was dispersed in a mixture of 25 mL pure water and 25 mL anhydrous ethanol and sonicated for 1 h. Then, 2 mL of H₂O₂ was added to the resulting black suspension, and the mixture was stirred for 10 min. The mixture was then transferred to a 100 mL polytetrafluoroethylene-sealed autoclave and heated at 200 °C for 6 h. After cooling to room temperature, the mixture was filtered and washed with pure water, and finally dried in a vacuum drying oven for 2 h to obtain C. R-F .

[0069] (3) Weigh out 10mg of C R-F Add the solution to a mixture of 40 mL of pure water and 40 mL of ethanol and sonicate for 3 hours. Then, add 0.1 mol / L HNO3 solution to adjust the pH to 2-3 to obtain a black suspension.

[0070] (4) Add 495 μL of 0.0075 g / mL H2PtCl6 solution and 100 μL of 0.05 g / mL [Cu(NH3)4](OH)2 solution to 10 mL of aqueous solution. After mixing thoroughly, add the mixture dropwise to the above black suspension. Stir until homogeneous, sonicate for 30 min and stir for 2 h. Then add 20 mL of 20 mmol / L NaBH4 solution to the solution, let stand for 30 min, stir for 4 h, wash with pure water, filter, freeze-dry for 48 h to obtain the catalyst PtCu(Cl) / C R-F .

[0071] Morphology, dimensions and phase analysis of the examples and comparative examples

[0072] Figure 1 shows the example PtCu(N) / C R-F Comparative Example 1: Pt(N) / C R-F Comparative Example 2Cu(N) / C R-F Comparative example 3PtCu(Cl) / C R-F The XRD patterns of the catalysts, compared with the PDF cards, show that the XRD diffraction peaks of all four catalysts exhibit typical face-centered cubic (FCC) characteristics. PtCu(N) / C R-F The diffraction peaks of the catalyst shift to a higher 2θ angle because the introduction of Cu causes some atoms to form an alloy, resulting in a decrease in the lattice constant.

[0073] Figures 2a and 2b show the PtCu(N) / C example. R-F TEM and STEM images of the catalyst show that the carbon support is loaded with many interconnected hollow spherical PtCu particles, with particle sizes ranging from 5 to 12 nm. Figures 3a and 3b are from the example PtCu(N) / C. R-F The HR-TEM and HAADF-STEM images of the catalyst are shown in Figure 3a. It can be seen that the hollow spherical nanoparticles have lattice fringes in different directions. The lattice fringes with a spacing of 0.202 nm correspond to the (111) crystal plane of Cu, and the lattice fringes with a spacing of 0.224 nm correspond to the (111) crystal plane of Pt. Figure 3b shows that the brightest region on the outer layer of the hollow sphere is Pt atoms, the darker region on the inner side is Cu atoms, and the small central region is a PtCu alloy. This is consistent with the XRD characterization results.

[0074] Figure 4 shows a and b as comparative examples 1Pt(N) / C R-F TEM and HR-TEM images of the catalyst show that the Pt morphology in the catalyst is flower-like and non-hollow. The lattice fringe spacing of 0.197 nm corresponds to the (200) crystal plane of Pt, and the lattice fringe spacing of 0.227 nm corresponds to the (111) crystal plane of Pt. Figures 5a and b are comparative examples 2Cu(N) / C.R-F The TEM and HR-TEM images of the catalyst show that the Cu in the catalyst has a non-hollow spherical morphology, and the 0.199 nm lattice fringe spacing corresponds to the (111) crystal plane of Cu.

[0075] Based on the test results of inductively coupled plasma atomic emission spectrometry (ICP-OES), the example PtCu(N) / C R-F The catalyst contains 6.51% Pt and 5.75% Cu by mass. Comparative Example 1: Pt(N) / C R-F The mass ratio of Pt in the catalyst is 10.8%, compared to the comparative example 2Cu(N) / C. R-F The mass ratio of Cu in the catalyst is 10.6%.

[0076] Figure 6a and b are comparative examples 3PtCu(Cl) / C R-F TEM and HR-TEM images of the catalyst show that non-hollow spherical PtCu nanoparticles are loaded on the carbon support. The 0.201 nm lattice fringe spacing corresponds to the (111) crystal plane of Cu, and the 0.225 nm lattice fringe spacing corresponds to the (111) crystal plane of Pt. Therefore, it can be inferred that PtCu(N) / C R-F With PtCu(Cl) / C R-F The differences in morphology and dispersibility among catalysts are mainly attributed to the different chemical structures of the Pt precursors.

[0077] Figure 7 shows C0 and C. F C R C R-F The support, and [Pt(NH3)4](OH)2 / [Cu(NH3)4](OH)2 with C R-F Fourier transform infrared (FTIR) spectrum of the lyophilized powder after mixing in aqueous solution. C0 in the figure is at 3625 cm⁻¹. -1 1567cm -1 1100cm -1 The characteristic peaks on the left and right are the hydroxyl (-OH) peak, the C=C stretching vibration peak, and the CO single bond peak, respectively. R At 3600cm -1 The disappearance of the -OH peaks on the left and right indicates that the oxygen-containing functional groups on CO were basically reduced after heat treatment. R-F At 3500cm -1 A stronger -OH peak reappeared at the point, indicating that surface functionalization with H2O2 after heat treatment can introduce more oxygen-containing functional groups into the carbon support. [Pt(NH3)4](OH)2 and C R-F The lyophilized powder mixed in the aqueous solution was at 1373 cm⁻¹. -1The characteristic peak appearing at 3500 cm⁻¹ is due to the tensile vibration of CN. -1 The left and right -OH peaks and 1100 cm⁻¹ -1 The CO single bonds on the left and right sides have basically disappeared, indicating that the [Pt(NH3)4](OH)2 precursor and C R-F Strong electrostatic adsorption exists between the oxygen-containing functional groups on [Cu(NH3)4](OH)2 and C. R-F The lyophilized powder mixed in the aqueous solution was heated to 1100 cm⁻¹. -1 The characteristic peaks of the CO single bonds on both sides weakened, and their positions shifted, confirming that the [Cu(NH3)4](OH)2 precursor and C R-F There is also strong electrostatic adsorption between the oxygen-containing functional groups on it.

[0078] Figure 8 shows C0 and C. F C R-F The support, and [Pt(NH3)4](OH)2+[Cu(NH3)4](OH)2 and [Pt(NH3)4](OH)2+[Cu(NH3)4](OH)2+C R-F The Zeta potential diagram shows that the potential of C0 is -4.7mV, and C... F The potential is -6.8mV, C R-F The potential is -7.3mV, indicating that functionalization with H2O2 after heat treatment / calcination is beneficial for C. R-F More negatively charged functional groups are introduced onto the carrier surface. Additionally, the potential of [Pt(NH3)4](OH)2+[Cu(NH3)4](OH)2 is 5.6 mV, and when added to C... R-F The potential measured in the dispersion of Pt(NH3)4 was -2.9 mV, further indicating that... 2+ / Cu(NH3)4 2+ With C R-F There is a strong electrostatic adsorption between the negatively charged oxygen-containing functional groups.

[0079] Figure 9 shows the example PtCu(N) / C R-F Comparative Example 1Pt(N) / C R-F The Pt 4f XPS plot of the catalyst shows that PtCu(N) / C R-F The peak of Pt 4f is compared to that of Pt(N) / C R-F The shift towards lower binding energy is likely due to the ligand effect between Pt and Cu. Since Cu is less electronegative than Pt, there is a charge transfer from Cu to Pt between Pt and Cu, which increases the electron density of Pt atoms, thus leading to a decrease in binding energy.

[0080] Catalytic performance testing

[0081] RDE testing conditions: The test was conducted using a three-electrode system in an O2-saturated 0.5 mol / L H2SO4 solution; the reference electrode was an Ag / AgCl electrode, and the counter electrode was a platinum electrode. The rotation speed was 1600 rpm, and the catalyst loading was 2 mg / cm³. -2 .

[0082] GDE half-cell testing conditions: A three-electrode system was used. A GDE was prepared by coating catalyst ink onto carbon cloth as the working electrode, a Pt sheet connected to a carbon rod was used as the counter electrode, and an Ag / AgCl (saturated KCl solution) electrode was used as the reference electrode. The catalyst loading was 2 mg / cm³. -2 The electrolyte is a 0.5 mol / L H2SO4 solution.

[0083] Figure 10 shows the cyclic voltammetry (CV) curves of the Examples, Comparative Examples 1-3, and the commercial Pt / C catalyst under N2 saturation conditions. The peaks in the 0.4–0.8 V range are attributed to the redox peaks of Pt, and the PtCu(N) / C catalysts exhibit this characteristic. R-F The catalyst exhibits the largest H adsorption / desorption peak area, indicating that the PtCu(N) / C R-F The hollow spherical structure can provide a larger electrochemically active surface area for ORR.

[0084] Figure 11 is a comparison of the linear sweep voltammetry (LSV) curves of the Examples, Comparative Examples 1-3, and the commercial Pt / C catalyst. Among them, PtCu(N) / C... R-F The catalyst exhibits a higher limiting current density (j L =4.8mAcm -2 ), initial potential (E) onset =0.961V) and half-wave potential (E 1 / 2 =0.827V), significantly higher than Comparative Examples 1-3 and commercial Pt / C catalysts, indicating that PtCu(N) / C R-F The hollow sphere structure of the PtCu alloy catalyst is beneficial to improving the catalytic activity of ORR.

[0085] Figure 12 shows the Tafel slope curves of the examples, comparative examples 1-3, and commercial Pt / C catalysts, where the PtCu(N) / C catalysts of the examples are shown. R-F The catalyst exhibits the smallest slope, indicating that it has the fastest ORR catalytic reaction rate and demonstrates the best ORR reaction activity.

[0086] Figure 13 shows the electron transfer number and H2O2 yield of the examples, Comparative Example 1, and commercial Pt / C catalysts, PtCu(N) / C R-F The H2O2 yield of the catalyst is almost zero, PtCu(N) / C R-F Pt(N) / CR-F The number of electrons transferred is slightly higher than that of commercial Pt / C catalysts, particularly PtCu(N) / C. R-F The electron transfer number of the catalyst is closest to 4, further indicating that PtCu(N) / C R-F The catalyst exhibits higher catalytic activity for ORR.

[0087] Figure 14 shows the example PtCu(N) / C R-F The LSV curves and KL plots of the catalyst at different rotational speeds show that the ORR current density increases with increasing rotational speed, indicating that the ORR process is controlled by O2 diffusion. The PtCu(N) / C ratio was calculated using the Koutecky-Levich (KL) equation. R-F The catalyst has an electron transfer number of 4. This indicates that PtCu(N) / C R-F The ORR on the catalyst follows a four-electron reaction pathway, and O2 is directly reduced to H2O on the surface of the PtCu(N) / CR-F catalyst, which is consistent with the test results of RRDE.

[0088] Figure 15 shows the example PtCu(N) / C R-F LSV curves of the catalyst and a commercial Pt / C catalyst in GDE half-cells. PtCu(N) / C R-F The LSV curve of the [specific material] exhibits better performance at high current densities, with an initial potential significantly higher than that of commercial Pt / C, and at 250 mA / cm². -2 The overpotential difference was 137mV, and the lower overpotential was beneficial to promoting mass transfer efficiency.

[0089] Figure 16 shows the example PtCu(N) / C R-F EIS impedance plots of the catalyst and a commercial Pt / C catalyst. From the plots, it can be seen that PtCu(N) / C... R-F The radius of the arc is significantly smaller than that of commercial Pt / C, indicating that PtCu(N) / C R-F Its charge transfer resistance is lower than that of commercial Pt / C, and its mass transfer conductivity is faster.

[0090] Figure 17 shows the PtCu(N) / C prepared in the example. R-F Comparison of chronoamperometry (it) curves of the catalyst and a commercial Pt / C catalyst. PtCu(N) / C R-F After a 20,000-s stability test, the catalyst's current decreased by 15.8%, while that of the commercial Pt / C catalyst decreased by 20.8%, indicating that the PtCu(N) / C catalyst... R-F The catalyst has better stability.

[0091] In summary, the hollow spherical structure of the PtCu nanoparticles in the chlorine-free PtCu / C catalyst prepared in this invention provides high atomic utilization and a large electrochemical active surface area, thereby enhancing the catalyst's electrocatalytic activity. As reactive active sites, the synergistic and ligand effects between Pt and Cu atoms significantly regulate the reaction, altering the electronic structure of Pt and causing a negative shift in the d-band center. This weakens the adsorption strength of oxygen-containing intermediates at Pt sites during the ORR process, lowers the reaction energy barrier in the oxygen reduction reaction, and ultimately results in higher electrocatalytic activity and stability for the ORR reaction.

[0092] Although the present invention has been described above through specific embodiments, it should be understood that any equivalent improvements made by those skilled in the art in accordance with the present invention without departing from the scope of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a chlorine-free PtCu / C catalyst with a hollow spherical structure, characterized in that... The process includes the following steps: (1) calcining the carbon support in a reducing atmosphere; (2) dispersing the calcined carbon support in an alcohol-water mixture and adding an oxidant for a hydrothermal reaction; (3) dispersing the hydrothermally reacted carbon support evenly in the alcohol-water mixture and adjusting the pH to acidic to obtain a carbon support suspension; (4) adding Pt(NH3)4(OH)2 solution and Cu(NH3)4(OH)2 solution to the carbon support suspension, and then adding a reducing agent to obtain a chlorine-free PtCu / C catalyst, wherein PtCu is a nano-hollow sphere structure; the calcination temperature in step (1) is 750~850℃ and the calcination time is 1~3 h; the hydrothermal reaction temperature in step (2) is 180~200℃ and the time is 4~6 h.

2. The preparation method according to claim 1, characterized in that: Pt atoms are located in the outer layer of the hollow nanospheres.

3. The preparation method according to claim 1, characterized in that: The size of the hollow nanospheres is less than 20 nm.

4. The preparation method according to claim 1, characterized in that: The alcohol-water mixture is a mixture of ethanol and water, wherein the volume ratio of ethanol to water is 0.5 to 2:

1.

5. The preparation method according to claim 1, characterized in that: In step (3), the pH is adjusted to 2-3 using HNO3.

6. The preparation method according to claim 1, characterized in that: The oxidant is H2O2, and the reducing agent is NaBH4.

7. The preparation method according to claim 1, characterized in that: The mass ratio of Pt to Cu in the chlorine-free PtCu / C catalyst is 1~3:1~3.

8. The application of the chlorine-free PtCu / C catalyst obtained by the preparation method according to any one of claims 1-7 in the ORR reaction.

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