Platinum nano oxygen reduction catalyst, and preparation method and application thereof

Abstract

The present disclosure belongs to the technical field of catalysts, and provides a platinum nano oxygen reduction catalyst, a preparation method and application thereof, the preparation method of the platinum nano oxygen reduction catalyst comprising the following steps: dispersing a MOF derived carbon material in a mixed solution of deionized water and ethanol, selecting a compound containing a negatively charged or positively charged platinum coordination unit according to the positive or negative of the Zeta potential, stirring at room temperature, and using electrostatic force to make the two fully adsorb to obtain a reaction solution; evaporating the reaction solution to dryness, and then performing a reduction reaction in a hydrogen reduction atmosphere at 300-600 DEG C to obtain the platinum nano oxygen reduction catalyst. The obtained catalyst is applied to a proton exchange membrane fuel cell, on the one hand, the micropore confinement effect improves the stability of platinum nanoparticles and avoids the poisoning of high molecular electrolytes such as perfluorosulfonic acid, and on the other hand, the interconnection of the pores effectively enhances mass transfer, so that the confined catalyst exhibits excellent catalytic activity.

Description

Technical Field

[0001] This disclosure belongs to the field of catalyst technology, and relates to a platinum nano-oxygen reduction catalyst, its preparation method and application. Background Technology

[0002] Platinum / carbon (Pt / C) catalysts are widely used in the oxygen reduction reaction (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs) due to their excellent electrocatalytic performance. However, in conventional Pt / C catalysts, platinum nanoparticles are exposed on the outer surface of the support, making them susceptible to poisoning reactions with functional groups of polymeric electrolytes (such as sulfonate groups in perfluorosulfonic acid (PFSA) electrolytes). Furthermore, platinum nanoparticles are prone to dissolution, aggregation, and growth, leading to decreased catalytic performance and shortened lifespan. Summary of the Invention

[0003] This disclosure provides a platinum nano-oxygen reduction catalyst, its preparation method, and its application, which can effectively solve the above-mentioned problems.

[0004] This disclosure is implemented as follows:

[0005] On the one hand, this disclosure provides a method for preparing a platinum nano-oxygen reduction catalyst, comprising the following steps:

[0006] MOF-derived carbon material is dispersed in a mixed solution of deionized water and ethanol, wherein the measured Zeta potential of the MOF-derived carbon material is negative. A compound containing a positively charged platinum coordination unit is added, and the mixture is stirred at room temperature to allow both to be fully adsorbed, thus obtaining a reaction solution.

[0007] The reaction solution was evaporated to dryness, and then a reduction reaction was carried out in a reducing atmosphere at 300~600℃ to obtain the platinum nano oxygen reduction catalyst.

[0008] Alternatively, the MOF-derived carbon material is dispersed in a mixed solution of deionized water and ethanol, wherein the measured Zeta potential of the MOF-derived carbon material is positive. A compound containing a negatively charged platinum-containing coordination unit is added, and the mixture is stirred at room temperature to allow both to be fully adsorbed, thereby obtaining a reaction solution.

[0009] The reaction solution was evaporated to dryness, and then a reduction reaction was carried out in a reducing atmosphere at 300~600℃ to obtain the platinum nano oxygen reduction catalyst.

[0010] On the other hand, this disclosure provides a platinum nano-oxygen reduction catalyst, which is prepared by the above-described method for preparing platinum nano-oxygen reduction catalysts.

[0011] Furthermore, this disclosure provides the application of the aforementioned platinum nano-oxygen reduction catalyst in the oxygen reduction reaction at the cathode of a proton exchange membrane fuel cell.

[0012] The beneficial effects of this disclosure are:

[0013] This disclosure provides a method for preparing platinum nano-oxygen reduction catalysts. By controlling the electrostatic interaction between the charge properties of the platinum precursor and the Zeta potential of the carbon support, the confined distribution of platinum nanoparticles in the microporous channels of MOF-derived carbon materials is achieved, and the particle size of the platinum nanoparticles is 1~2 nm.

[0014] The prepared platinum nano-oxygen reduction catalyst, when applied to the cathode of PEMFC, exhibits excellent ORR performance and possesses high stability and resistance to poisoning. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram illustrating the preparation of platinum nanoparticles in MOF-derived carbon materials under zeta potential regulation, as provided in an embodiment of this disclosure.

[0017] Figure 2 In the figure (a), the N2 adsorption-desorption isotherm of the MOF-derived carbon support in Example 1 of this disclosure is shown. Figure 2 (b) in the figure represents its aperture distribution.

[0018] Figure 3 (a) is a TEM image of the confined Pt@C catalyst in Example 1 of this disclosure; Figure 3 (b) is a TEM image of the surface Pt / C catalyst in Comparative Example 1 of this disclosure; Figure 3 (c) is a TEM image of the confined Pt@Mn-NC catalyst in Example 3 of this disclosure; Figure 3 (d) is a TEM image of the surface Pt / Mn-NC catalyst in Comparative Example 3 of this disclosure.

[0019] Figure 4 (a) is the polarization curve of the confined Pt@C catalyst in 0.1 M HClO4 saturated with oxygen in Example 1 of this disclosure, and the polarization curve after adding Nafion to the catalyst; Figure 4 (b) is the polarization curve of the surface Pt / C catalyst in Comparative Example 1 of this disclosure in oxygen-saturated 0.1 M HClO4, and the polarization curve after the addition of Nafion to the catalyst.

[0020] Figure 5 (a) is the CO desorption cyclic voltammetry curve of the confined Pt@C catalyst in 0.1 M HClO4 saturated with nitrogen in Example 1 of this disclosure, and the CO desorption cyclic voltammetry curve after adding PVP to the catalyst. Figure 5 (b) is the CO desorption cyclic voltammetry curve of the surface Pt / C catalyst in Comparative Example 1 of this disclosure in 0.1 M HClO4 saturated with nitrogen, and the CO desorption cyclic voltammetry curve after adding PVP to the catalyst.

[0021] Figure 6 (a) is the polarization curve of PEMFC in the initial state and after 5000 accelerated decay tests, when the confined Pt@C catalyst in Example 1 of this disclosure is applied to the cathode of PEMFC as an ORR catalyst. Figure 6 (b) is a polarization curve of PEMFC in the initial state and after 5000 accelerated decay tests, in which the surface Pt / C catalyst of Comparative Example 1 of this disclosure is applied to the cathode of PEMFC as an ORR catalyst. Figure 6 (c) is a TEM image of the confined Pt@C catalyst in Example 1 of this disclosure after 5000 accelerated degradation tests; Figure 6 (d) is a TEM image of the surface Pt / C catalyst in Comparative Example 1 of this disclosure after 5000 accelerated degradation tests.

[0022] Figure 7 (a) is the polarization curve of PEMFC in the initial state and after 5000 accelerated decay tests, when the confined Pt@Fe-NC catalyst in Example 2 of this disclosure is applied to the cathode of PEMFC as an ORR catalyst. Figure 7 (b) shows the polarization curves of PEMFC in the initial state and after 5000 accelerated decay tests, when the surface Pt / Fe-NC catalyst in Comparative Example 2 of this disclosure is applied to the cathode of PEMFC as an ORR catalyst.

[0023] Figure 8 (a) is the polarization curve of PEMFC in the initial state and after 25,000 accelerated decay tests, when the confined Pt@Mn-NC catalyst in Example 3 of this disclosure is applied to the cathode of PEMFC as an ORR catalyst. Figure 8 (b) shows the polarization curves of PEMFC in the initial state and after 25,000 accelerated decay tests, when the surface Pt / Fe-NC catalyst in Comparative Example 3 of this disclosure is applied to the cathode of PEMFC as an ORR catalyst.

[0024] Figure 9The confined Pt@Co-NC catalyst in Example 4 of this disclosure is used in the cathode of PEMFC as an ORR catalyst. The polarization curves of PEMFC in the initial state and after 25,000 accelerated decay tests are shown. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0026] This disclosure provides a method for preparing a platinum nano-oxygen reduction catalyst, which is prepared by using MOF-derived carbon material with a negative Zeta potential and a compound containing positively charged platinum coordination units.

[0027] The method includes the following steps:

[0028] MOF-derived carbon material is dispersed in a mixed solution of deionized water and ethanol, wherein the measured Zeta potential of the MOF-derived carbon material is negative. A compound containing a positively charged platinum coordination unit is added, and the mixture is stirred at room temperature to allow both to be fully adsorbed, thus obtaining a reaction solution.

[0029] The reaction solution was evaporated to dryness, and then a reduction reaction was carried out in a reducing atmosphere at 300~600℃ to obtain the platinum nano oxygen reduction catalyst.

[0030] This disclosure utilizes an electrostatic adsorption confinement strategy based on zeta potential to ensure that compounds containing positively charged platinum coordination units, i.e., platinum precursors, preferentially enter the microporous channels of the carbon support, resulting in the formation of ultra-small, highly dispersed platinum particles of 1–2 nm after reduction. The platinum nanoparticles confined within the microporous channels avoid direct contact with the polymeric electrolyte, preventing poisoning of its functional groups and enhancing the ORR activity of the confined platinum nanocatalyst. Furthermore, the pore walls physically restrict the platinum nanoparticles like "nanocages," inhibiting their migration, growth, and aggregation, thus improving the catalyst's stability.

[0031] This disclosure uses MOF-derived carbon materials as carbon supports. Compared with materials such as graphene and two-dimensional carbon, metal-organic framework (MOF)-derived carbon materials have the advantages of abundant micropores and interconnected pore channels. On the one hand, the micropores limit the poisoning caused by direct contact between the polymer electrolyte and the platinum catalyst. On the other hand, the interconnected pore channels effectively enhance mass transfer, so that the confined platinum catalyst exhibits excellent ORR activity.

[0032] The platinum nanocatalyst preparation method disclosed herein is based on a dual mechanism of "MOF self-limited pore + electrostatic directional adsorption". It does not require the introduction of template agents, the process is simple, and it can achieve large-scale continuous production. It is particularly suitable for high-efficiency catalysis of ORR in PEMFC cathodes.

[0033] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be -5 to -40 mV.

[0034] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be -5 to -25 mV.

[0035] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be -10 to -40 mV.

[0036] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be -10 to -20 mV.

[0037] The zeta potential measurement value of the MOF-derived carbon material is specifically the zeta potential measurement value of the MOF-derived carbon material in the mixed solution.

[0038] Zeta potential is an important parameter for measuring the surface charge of particles and is often used to characterize the charge properties and stability of materials in solution.

[0039] In some embodiments, the positively charged platinum-containing coordination unit is a tetraammineplatinum complex [(Pt(NH3)4)] 2+ .

[0040] In some embodiments, the compound containing a positively charged platinum-containing coordination unit is tetraammineplatinum nitrate [(Pt(NH3)4](NO3)2.

[0041] The basis for selecting platinum precursors is that the platinum-containing coordination units and the measured Zeta potential of MOF-derived carbon materials carry opposite charges. Adsorption through Coulomb attraction between the two is an important strategy for achieving efficient and uniform loading of platinum particles on carbon supports by utilizing electrostatic interactions.

[0042] MOF-derived carbon supports have a negatively charged surface (negative zeta potential measurement), which preferentially adsorbs positively charged platinum-containing coordination units into the pores via electrostatic interactions. Conversely, the negatively charged surface of MOF-derived carbon supports repels negatively charged platinum-containing coordination units (such as [PtCl6)). 2- This prevents the precursor from entering the pores and allows it to be adsorbed onto the surface only through weak interactions such as van der Waals forces. Therefore, spatially selective distribution, i.e., confined distribution, of the platinum precursor can be achieved based on Zeta potential modulation.

[0043] This disclosure provides a method for preparing a platinum nano-oxygen reduction catalyst, which is prepared by using a MOF-derived carbon material with a positive Zeta potential and a compound containing negatively charged platinum coordination units.

[0044] The method includes the following steps:

[0045] MOF-derived carbon material is dispersed in a mixed solution of deionized water and ethanol, wherein the measured Zeta potential of the MOF-derived carbon material is positive. A compound containing a negatively charged platinum coordination unit is added, and the mixture is stirred at room temperature to allow both to be fully adsorbed, thus obtaining a reaction solution.

[0046] The reaction solution was evaporated to dryness, and then a reduction reaction was carried out in a reducing atmosphere at 300~600℃ to obtain the platinum nano oxygen reduction catalyst.

[0047] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be +5 to +40 mV.

[0048] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be +10 to +40 mV.

[0049] In some embodiments, the zeta potential of the MOF-derived carbon material is measured to be +35 to +40 mV.

[0050] In some embodiments, the negatively charged platinum-containing coordination unit is a platinum hexachlorocyclohexane complex [PtCl6]. 2- .

[0051] In some embodiments, the compound containing a negatively charged platinum-containing coordination unit is hexachloroplatinum(IV) acid.

[0052] The MOF-derived carbon support has a positively charged surface (positive zeta potential measurement), which preferentially adsorbs negatively charged platinum-containing coordination units into the pores via electrostatic interactions. Conversely, the positively charged surface of the MOF-derived carbon support repels positively charged platinum-containing coordination units (such as [(Pt(NH3)4)]). 2+This prevents the precursor from entering the pores and allows it to be adsorbed onto the surface only through weak interactions such as van der Waals forces. Therefore, spatially selective distribution, i.e., confined distribution, of the platinum precursor can be achieved based on Zeta potential modulation.

[0053] In some embodiments, the method for preparing the MOF-derived carbon material includes the following steps:

[0054] MOF precursors were carbonized in an argon atmosphere at 800–1200 °C to obtain MOF-derived carbon materials.

[0055] In some implementations, carbonization is carried out at 900~1100°C.

[0056] Carbonization decomposes organic ligands in MOF precursors, causing metal nodes to volatilize and transform into metal oxides / carbides, which then firmly bond with the carbon framework, forming a carbon framework with structural defects (providing anchoring sites and active sites). Simultaneously, it largely preserves the original ordered microporous channel framework of the MOF or forms new, stable microporous structures. However, excessively high carbonization temperatures can lead to over-graphitization of the MOF-derived carbon material, resulting in the loss of numerous defect sites, pore collapse or closure, and the loss of the microporous structure. Insufficient carbonization temperatures may prevent complete pyrolysis of organic ligands in the MOF, and residual organic matter may clog the pores of the MOF-derived carbon material, affecting the entry of platinum precursors. Insufficient carbonization temperatures may also result in an incomplete carbon framework, poor conductivity, and inability to serve as an electrocatalyst support.

[0057] In some embodiments, the MOF-derived carbon material is a zeolite imidazole ester framework-8 derived carbon material (ZIF-8 derived carbon material). That is, the MOF precursor is ZIF-8. ZIF-8 derived carbon material is an ideal support for achieving highly dispersed and highly active platinum catalysts. ZIF-8 contains imidazole ligands, and carbonization allows for nitrogen doping of the carbon support, enhancing the negative charge on the surface of the ZIF-8 derived carbon material. The cavities left by zinc volatilization after ZIF-8 carbonization increase porosity, and the resulting 1-2 nm microporous structure has a pore confinement effect, preventing the aggregation of platinum nanoparticles. Furthermore, these pores are interconnected, and this interconnected pore structure facilitates the diffusion and transport of reactant molecules, allowing reactants to contact the platinum catalyst more fully, thereby improving the overall efficiency of the catalytic reaction.

[0058] In some embodiments, the MOF-derived carbon material is prepared by ZIF-8.

[0059] In some embodiments, the method for preparing ZIF-8 includes:

[0060] 2-Methylimidazole was dissolved in methanol to obtain solution A. Zinc nitrate hexahydrate Zn(NO3)2·6H2O was dissolved in methanol to obtain solution B.

[0061] After mixing solutions A and B thoroughly, the mixture was reacted in an oil bath at 60°C. After the reaction was complete, the product was centrifuged, washed, and dried to obtain ZIF-8.

[0062] In some embodiments, the MOF-derived carbon material is an undoped transition metal MOF-derived carbon material, or the MOF-derived carbon material is a transition metal-doped MOF-derived carbon material.

[0063] MOF-derived carbon materials doped with transition metals (including Fe, Co, Mn, etc.) are a class of atomically dispersed catalysts prepared by high-temperature carbonization of MOF precursors containing transition metals. Their core characteristic is that metal atoms are anchored as single atoms at coordination sites on the nitrogen-doped carbon framework (e.g., M-N4 structure). Metal salts (e.g., Fe(Ac)2) are anchored by nitrogen atoms during carbonization.

[0064] In some embodiments, the MOF-derived carbon material is an undoped transition metal ZIF-8-derived carbon material, or the MOF-derived carbon material is a transition metal-doped ZIF-8-derived carbon material.

[0065] In some embodiments, the reducing atmosphere is a mixture of hydrogen and argon.

[0066] In some embodiments, the volume fraction of hydrogen in the mixed atmosphere of hydrogen and argon is 10%.

[0067] A reducing atmosphere was used to reduce the platinum precursor in situ to platinum nanoparticles, which were then confined within a microporous structure.

[0068] In some embodiments, the reduction reaction is carried out in a reducing atmosphere at 450~550°C.

[0069] This disclosure also provides a platinum nano-oxygen reduction catalyst prepared by the method described in any of the above embodiments.

[0070] This disclosure also provides the application of the above-described platinum nano-oxygen reduction catalyst in the oxygen reduction reaction at the cathode of a proton exchange membrane fuel cell.

[0071] Platinum nanoparticles are confined within micropores, preventing the sulfonate groups (size > 4 nm) of the PFSA proton exchange membrane from entering. Platinum nanoparticles confined within micropores can avoid direct contact with the PFSA proton exchange membrane and prevent the poisoning of its functional groups.

[0072] This disclosure provides a platinum nano-oxygen reduction catalyst and its preparation method. Based on the positive or negative value of the Zeta potential measured by MOF-derived carbon material in a mixed solution of deionized water and ethanol, a compound containing platinum-containing coordination units with opposite charges is selected. Taking advantage of the abundant micropores and interconnected channels of MOF-derived carbon material, it is used as a support to confine platinum nanoparticles within the channels. Electrostatic forces are used to fully adsorb both, and the platinum nano-oxygen reduction catalyst is prepared after reduction.

[0073] The platinum nano-oxygen reduction catalyst is used in the cathode of PEMFC as an ORR catalyst. Its platinum nanoparticles are confined within microporous channels, which can avoid the poisoning of functional groups of polymeric electrolytes. Moreover, the stability of platinum nanoparticles is improved through the confinement effect, and the interconnection of the support channels effectively enhances mass transfer, so that this type of catalyst exhibits excellent ORR performance.

[0074] Example 1

[0075] This disclosure provides a method for synthesizing a confined Pt@C catalyst. Specifically, it includes the following steps:

[0076] Step 1: Dissolve 6.3 g of 2-methylimidazole in 160 mL of methanol to obtain solution A. Dissolve 5.4 g of Zn(NO3)2·6H2O in 100 mL of methanol to obtain solution B.

[0077] Step 2: Mix solutions A and B from Step 1 thoroughly and react in an oil bath at 60°C for 24 h. After the reaction is complete, centrifuge and wash the product obtained from the reaction, and dry it at 70°C for 12 h to obtain the MOF precursor ZIF-8.

[0078] Step 3: Carbonize the MOF precursor from Step 2 at 1000℃ for 1 h in an argon atmosphere to obtain MOF-derived carbon material.

[0079] Step 4: Disperse 91.0 mg of the MOF-derived carbon material from Step 3 in a 40 mL mixed solution of ethanol and water, then add dropwise a solution containing a positively charged platinum-containing coordination unit. The amount of platinum-containing compound added is 3.5 μmol, and the expected platinum loading is approximately 7%. wt. The adsorption was carried out at room temperature with stirring for 2 h to obtain a reaction solution. The volume ratio of ethanol to water was 1:1, and the platinum-containing compound was [(Pt(NH3)4](NO3)2.

[0080] Step 5: Evaporate the reaction solution from Step 4 to dryness, and then carry out a reduction reaction at 500°C for 10 min in a hydrogen atmosphere to obtain the confined Pt@C catalyst.

[0081] The Zeta potential of the MOF precursor in Example 1 is approximately -20 mV. The Zeta potential was detected using a nanoparticle size and Zeta potential analyzer (model: NanoBrook Omni). Principle: Based on the directional migration of charged particles excited by an external electric field, the electromigration velocity of the particles is accurately calculated using laser Doppler interferometry or phase-modulated light scattering. This migration rate has a quantitative relationship with the potential value (i.e., Zeta potential) of the sliding interface (shear plane) of the electric double layer on the particle surface. By combining parameters such as the dielectric constant and viscosity of the medium, and using a theoretical model for numerical conversion, the specific value of the Zeta potential can be obtained.

[0082] The confined Pt@C catalyst in Example 1, as measured by inductively coupled plasma mass spectrometry (ICP-MS), showed an actual platinum loading of 5.3%. wt. %.

[0083] Comparative Example 1

[0084] This disclosure provides a method for synthesizing a surface Pt / C catalyst, which differs from the method for synthesizing a confined Pt@C catalyst in Example 1 in that:

[0085] Step 4 contains a platinum precursor solution containing a negatively charged platinum complex, wherein the platinum precursor is hexachloroplatinum(IV) acid.

[0086] The surface-mount Pt / C catalyst of Comparative Example 1, as determined by ICP-MS, showed an actual platinum loading of 6.8%. wt. %.

[0087] The remaining steps are the same as in Example 1.

[0088] The preparation processes of platinum nanoparticles in MOF-derived carbon materials under different Zeta potential regulation in Example 1 and Comparative Example 1 are as follows: Figure 1 As shown.

[0089] Example 2

[0090] This disclosure provides a method for synthesizing platinum nanoparticles confined within Fe-doped MOF-derived carbon materials (confined Pt@Fe-NC catalyst), which differs from the method for synthesizing confined Pt@C catalyst in Example 1 in that:

[0091] Step 3: 742.0 mg of the MOF precursor from Step 2 and 45.0 mg of ferrous acetate (Fe(Ac)2) were added to 130 mL of anhydrous methanol, mixed thoroughly, evaporated to dryness, and then kept at 1000 °C for 1 hour in a nitrogen atmosphere to obtain Fe-doped MOF-derived carbon material.

[0092] The confined Pt@Fe-NC catalyst in Example 2, as determined by ICP-MS, showed an actual platinum loading of 6.1%. wt. %.

[0093] The remaining steps are the same as in Example 1.

[0094] The zeta potential of the Fe-doped MOF-derived carbon material in Example 2 is approximately -10 mV.

[0095] Comparative Example 2

[0096] This disclosure provides a method for synthesizing a surface Pt / Fe-NC catalyst, which differs from the method for synthesizing the confined Pt@Fe-NC catalyst in Example 2 in that:

[0097] Step 4 contains a platinum precursor solution containing a negatively charged platinum complex, wherein the platinum precursor is hexachloroplatinum(IV) acid.

[0098] The surface-mount Pt / Fe-NC catalyst of Comparative Example 2, as determined by ICP-MS, showed an actual platinum loading of 6.2%. wt. %.

[0099] The remaining steps are the same as in Example 2.

[0100] Example 3

[0101] This disclosure provides a method for synthesizing platinum nanoparticles confined within Mn-doped MOF-derived carbon materials (confined Pt@Mn-NC catalyst), which differs from the method for synthesizing confined Pt@C catalyst in Example 1 in that:

[0102] Step 3: 240.0 mg of the MOF precursor from Step 2 and 5.9 mg of manganese acetate (Mn(Ac)2) were added to 130 mL of anhydrous methanol, mixed thoroughly and evaporated to dryness, and then kept at 1000 °C for 1 hour in a nitrogen atmosphere to obtain Mn-doped MOF-derived carbon material.

[0103] Step 4: Disperse 91.0 mg of the Mn-doped MOF-derived carbon material from Step 3 in a 40 mL mixed solution of ethanol and water. Then, add dropwise a compound solution containing positively charged platinum-containing coordination units. The amount of platinum-containing compound added is 5.2 μmol, and the expected platinum loading is approximately 10 μmol. wt. The mixture was stirred at room temperature for 2 hours to adsorb the platinum-containing compound, yielding a reaction solution. The volume ratio of ethanol to water was 1:1, and the platinum-containing compound was [(Pt(NH3)4](NO3)2.

[0104] The Zeta potential of the Mn-doped MOF-derived carbon material in Example 3 is approximately -15 mV.

[0105] The confined Pt@Mn-NC catalyst in Example 3, as determined by ICP-MS, showed an actual platinum loading of 9.5%. wt. %. The remaining steps are the same as in Example 1.

[0106] Comparative Example 3

[0107] This disclosure provides a method for synthesizing a surface Pt / Mn-NC catalyst, which differs from the method for synthesizing the confined Pt@Mn-NC catalyst in Example 3 in that:

[0108] Step 4 contains a platinum precursor solution containing a negatively charged platinum complex, wherein the platinum precursor is hexachloroplatinum(IV) acid.

[0109] The surface-mount Pt / Mn-NC catalyst of Comparative Example 3, as determined by ICP-MS, showed an actual platinum loading of 9.7%. wt. %.

[0110] The remaining steps are the same as in Example 3.

[0111] Example 4

[0112] This disclosure provides a method for synthesizing platinum nanoparticles confined within Co-doped MOF-derived carbon materials (confined Pt@Co-NC catalyst), which differs from the method for synthesizing confined Pt@C catalyst in Example 1 in that:

[0113] Step 3: 240 mg of the MOF precursor from Step 2 and 18.2 mg of cobalt acetylacetonate (Co(acac)3) were added to 130 mL of anhydrous methanol, mixed thoroughly and evaporated to dryness, and then kept at 1000 °C for 1 hour in a nitrogen atmosphere to obtain Co-doped MOF-derived carbon material.

[0114] Step 4: Disperse 91.0 mg of the MOF-derived carbon material from Step 3 in a 40 mL mixed solution of ethanol and water. Then, add dropwise a solution containing a negatively charged platinum-containing coordination unit. The amount of platinum-containing compound added is 8.2 μmol, and the expected loading is approximately 15 μmol. wt. The mixture was stirred at room temperature for 2 hours to adsorb the platinum, yielding a reaction solution. The volume ratio of ethanol to water was 1:1, and the platinum-containing compound was hexachloroplatinum(IV) acid.

[0115] The remaining steps are the same as in Example 1. The confined Pt@Co-NC catalyst of Example 4 was tested by ICP-MS, and the actual platinum loading was 14.0 g / L. wt. %.

[0116] The Zeta potential of the Co-doped MOF-derived carbon material in Example 4 is approximately +37 mV.

[0117] The N2 adsorption-desorption isotherms and pore size distribution of the MOF-derived carbon support in Example 1 are as follows: Figure 2 As shown in the figure, the MOF-derived carbon support is a carbon material with micropores as the main component.

[0118] Please refer to Figure 3 The distribution and particle size of platinum nanoparticles in the confined Pt@C catalyst of Example 1, the surface Pt / C catalyst of Comparative Example 1, the confined Pt@Mn-NC catalyst of Example 3, and the surface Pt / Mn-NC catalyst of Comparative Example 3 were analyzed by transmission electron microscopy (TEM). Figure 3 As shown in (a) and (c), platinum nanoparticles are confined within a microporous structure. Figure 3 In (a), the green circles mark several typical platinum nanoparticles. These particles are encapsulated in carbon material. Due to their confinement in the carbon support, the platinum nanoparticles have weak contrast in the image and are not clearly visible. Their particle size is 1~2 nm. Figure 3 As shown in (b) and (d), platinum nanoparticles are distributed on the surface of the carbon material. Figure 3 In (b) of the diagram, the green circles mark several typical platinum nanoparticles that are directly exposed on the surface of the carbon material. Specifically... Figure 3 In (d), the platinum nanoparticles appear as concentrated distributions at the edges of carbon particles in a two-dimensional plane, while in a three-dimensional structure they should be distributed on the surface of the dodecahedral structure of the MOF-derived carbon material.

[0119] The ORR activities of the confined Pt@C catalyst in Example 1 and the surface Pt / C catalyst in Comparative Example 1 were tested in oxygen-saturated 0.1 M HClO4, and the changes in ORR activity after the addition of Nafion to the catalyst were also investigated.

[0120] Figure 4 (a) shows that the activity of the confined Pt@C catalyst did not change significantly after the addition of Nafion. Figure 4 (b) shows that the activity of the surface Pt / C catalyst significantly decreased after the addition of Nafion. The above comparison demonstrates that the confined platinum nanocatalyst in the embodiments of this disclosure can avoid poisoning by polymeric electrolytes and has excellent resistance to Nafion electrolyte poisoning.

[0121] Furthermore, using polyvinylpyrrolidone (PVP) polymer as a probe, the electrochemical area changes of the confined Pt@C catalyst in Example 1 and the surface Pt / C catalyst in Comparative Example 1 before and after the addition of PVP polymer in nitrogen-saturated 0.1 M HClO4 were compared. Figure 5 As shown in the CO desorption curve in (a) of the confined Pt@C catalyst, the hydrogen region and CO desorption capacity remained almost unchanged after the addition of PVP, indicating that the platinum nanoparticles were distributed within the pores and did not interact with PVP. Figure 5 As shown in (b) of the figure, the CO desorption curve reveals that the addition of PVP to the surface Pt / C catalyst significantly reduces both hydrogen and CO desorption capacities, indicating that the platinum nanoparticles are distributed on the surface and interact with PVP. This comparison confirms that confined platinum nanocatalysts can avoid polymer poisoning and also verifies that platinum nanoparticles in the confined Pt@C catalyst are distributed within the pores.

[0122] The confined Pt@C catalyst from Example 1 and the surface Pt / C catalyst from Comparative Example 1 were applied to the PEMFC cathode as ORR catalysts. (Comparison) Figure 6 PEMFC using confined Pt@C catalyst in (a) and Figure 6 In (b) of the paper, the voltammograms of the PEMFC using the surface Pt / C catalyst in the initial state show that, at the same current density, the cell using the confined Pt@C catalyst has a higher voltage, indicating better cell performance. This may be because the confined Pt@C catalyst is protected from Nafion poisoning, thus exhibiting higher ORR activity.

[0123] Meanwhile, each of the two types of batteries was subjected to 5000 accelerated degradation tests. The accelerated degradation test conditions were: potential step 0.6V (held for 3s) - 0.95V (held for 3s) cycle, temperature 80℃, anolyte flow rate 200 sccm, and back pressure 150 kPa.

[0124] The performance changes of PEMFC were characterized by polarization curves. Figure 6 As can be seen in (a), the relationship between battery voltage and current density remains almost unchanged after 5000 cycles compared to the initial state, indicating that the performance of PEMFC using the confined Pt@C catalyst shows almost no degradation, demonstrating excellent stability and durability. This can be attributed to the excellent ORR performance of the confined Pt@C catalyst, which possesses high stability and resistance to poisoning. Figure 6 As shown in (b), the performance of PEMFCs using surface Pt / C catalysts is significantly degraded. This may be because the platinum nanoparticles in the surface Pt / C catalysts are exposed on the surface of the carbon support, making them prone to migration, aggregation, growth, and dissolution, leading to a decrease in catalytic performance and a shortened lifespan.

[0125] After accelerated degradation testing, the two catalysts were analyzed by TEM. Figure 6 As shown in (c), no significant changes were observed in the platinum nanoparticles within the confined Pt@C catalyst. Figure 6 As shown in (d), most of the platinum nanoparticles in the surface Pt / C catalyst exhibited significant agglomeration, which led to a decrease in its catalytic performance.

[0126] The confined Pt@Fe-NC catalyst from Example 2 and the surface Pt / Fe-NC catalyst from Comparative Example 2 were applied to the cathode of a PEMFC as ORR catalysts. The PEMFC was subjected to 5000 accelerated decay cycles. The accelerated decay test conditions were: potential step 0.6V (hold for 3s) - 0.95V (hold for 3s) cycle, temperature 80°C, anolyte flow rate 200 sccm, and back pressure 150 kPa.

[0127] pass Figure 7 The comparison of curves (a) and (b) shows that the PEMFC using the confined Pt@Fe-NC catalyst exhibits a smaller performance degradation and better stability.

[0128] The confined Pt@Mn-NC catalyst from Example 3 and the surface Pt / Mn-NC catalyst from Comparative Example 3 were applied to the cathode of a PEMFC as ORR catalysts. The PEMFC was subjected to 25,000 accelerated decay cycles. The accelerated decay test conditions were: potential step 0.6V (hold for 3s) - 0.95V (hold for 3s) cycling, temperature 80°C, anolyte flow rate 200 sccm, and back pressure 150 kPa.

[0129] pass Figure 8 The curves in (a) and (b) show that the PEMFC using the confined Pt@Mn-NC catalyst exhibits a smaller performance degradation and better stability.

[0130] The confined Pt@Co-NC catalyst from Example 4 was used as an ORR catalyst in the cathode of a PEMFC. The PEMFC underwent 25,000 accelerated degradation cycles. The accelerated degradation test conditions were: potential step 0.6V (hold for 3s) - 0.95V (hold for 3s) cycling, temperature 80°C, anolyte flow rate 200 sccm, and back pressure 150 kPa.

[0131] like Figure 9 As shown, PEMFC exhibits relatively small performance degradation after 25,000 accelerated degradation tests, demonstrating good stability.

[0132] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for preparing a platinum nano-oxygen reduction catalyst, characterized in that, Includes the following steps: MOF-derived carbon material is dispersed in a mixed solution of deionized water and ethanol, wherein the measured Zeta potential of the MOF-derived carbon material is negative. A compound containing a positively charged platinum coordination unit is added, and the mixture is stirred at room temperature to allow both to be fully adsorbed, thus obtaining a reaction solution. The reaction solution was evaporated to dryness, and then a reduction reaction was carried out in a reducing atmosphere at 300~600℃ to obtain the platinum nano oxygen reduction catalyst. The positively charged platinum-containing coordination units were preferentially adsorbed into the pores through electrostatic interaction. Alternatively, the MOF-derived carbon material is dispersed in a mixed solution of deionized water and ethanol, wherein the measured Zeta potential of the MOF-derived carbon material is positive. A compound containing a negatively charged platinum-containing coordination unit is added, and the mixture is stirred at room temperature to allow both to be fully adsorbed, thereby obtaining a reaction solution. The reaction solution is evaporated to dryness, and then a reduction reaction is carried out in a reducing atmosphere at 300~600℃ to obtain the platinum nano oxygen reduction catalyst, which is applied to the cathode of a proton exchange membrane fuel cell.

2. The method as described in claim 1, characterized in that, The positively charged platinum-containing coordination unit is a tetraammineplatinum complex; the negatively charged platinum-containing coordination unit is a hexachloroplatinum complex.

3. The method as described in claim 1, characterized in that, The MOF-derived carbon material is a ZIF-8-derived carbon material.

4. The method as described in claim 1, characterized in that, The MOF-derived carbon material is either an undoped transition metal MOF-derived carbon material or a transition metal-doped MOF-derived carbon material.

5. The method as described in claim 1, characterized in that, The measured zeta potential of the MOF-derived carbon material is +5 to +40 mV, or -5 to -40 mV.

6. The method as described in claim 1, characterized in that, The preparation method of the MOF-derived carbon material includes the following steps: The MOF precursor was carbonized in an argon atmosphere at 800-1200°C to obtain the MOF-derived carbon material.

7. The method as described in claim 1, characterized in that, The reducing atmosphere is a mixture of hydrogen and argon.

8. A platinum nano-oxygen reduction catalyst, characterized in that, The platinum nano-oxygen reduction catalyst was prepared using the preparation method described in any one of claims 1-7.

9. The application of the platinum nano-oxygen reduction catalyst as described in claim 8 in the oxygen reduction reaction at the cathode of a proton exchange membrane fuel cell.

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