ORR catalyst with flexible structure as well as preparation method and application of ORR catalyst

Abstract

The invention discloses an ORR catalyst with a flexible structure as well as a preparation method and application of the ORR catalyst, and relates to the field of electro-catalysis. The structure of the electrocatalyst is that supramolecules or macromolecules with flexible structures are anchored on the surfaces of noble metal alloy nanoparticles loaded on a carbon black carrier, which is attributed to the entropy change of anchored molecules caused by oxygen adsorption, so that the desorption of key species in the oxygen reduction process is accelerated, and the reaction activity is obviously improved compared with that of a noble metal alloy catalyst. When the catalyst is used for a cathode of a proton membrane fuel cell, the output power of the catalyst is up to 2.07 W cm <-2 > under the condition that the use amount of the noble metal is as low as 0.1 mg cm <-2 >.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysis, and particularly to an ORR catalyst with a flexible structure, a preparation method thereof, and an application thereof. Background Art

[0002] Proton exchange membrane fuel cells have the advantages of high efficiency, low pollution, and being unrestricted by the Carnot cycle, and are an important part of the future energy structure. However, the cathode and anode catalysts thereof highly rely on precious metals. To achieve high power output with low precious metal usage is the key to further promoting proton exchange membrane fuel cells. Among these, the most important is to develop catalyst materials for the cathode oxygen reduction reaction (ORR).

[0003] To achieve the above goal, researchers have developed a series of highly active platinum-based catalysts, especially Pt-M (M = Fe, Co, Ni, etc.) alloys or metal compounds, to increase the ORR activity. The article titled "Stabilizing Pt-Based Electrocatalysts for Oxygen Reduction Reaction: Fundamental Understanding and Design Strategies" (Adv. Mater. 2021, 33 (20), e2006494.) summarizes a large number of platinum-based alloy catalysts.

[0004] Theoretically, the volcano plot is used to determine more excellent active centers or catalytic materials, which summarizes the linear relationship between the adsorption energy of key intermediates on the surfaces of different materials and their catalytic activities. However, these calculations usually consider the local surface conditions of the catalyst and ignore the role of entropy. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems of high platinum usage and low output power in existing proton exchange membrane fuel cells, and aims to provide an ORR catalyst with a flexible structure, a preparation method thereof, and an application thereof.

[0006] To achieve the above purpose, the present invention specifically adopts the following technical solutions: An ORR catalyst with a flexible structure, wherein the ORR catalyst is a noble metal-M alloy nanoparticle loaded on the surface of a carbon source, and a flexible structure macromolecule or supramolecule is coordinated and anchored on the surface of the noble metal-M alloy catalyst; Wherein, the carbon source is conductive carbon black; The noble metal includes one or more mixtures of Pt, Ru, Pd, and Au; The M includes one or more mixtures of Co, Fe, Ni, Cu, Zn, Cr, Mo, Sn, Ce, and Pd; The flexible structure macromolecules or supramolecules described above include one or more mixtures of calixarenes, cyclodextrins, and cetylsulfonic acid.

[0007] Preferably, the noble metals described above include one or more mixtures of Pt and Pd; the M includes one or more mixtures of Co, Fe, Ni, and Pd; the flexible structure macromolecules or supramolecules include calixarenes.

[0008] Preferably, the ORR catalyst is a calixarene-modified PtCo / C, a cyclodextrin-modified PdNi / C, a cetylsulfonic acid-modified RuFe / C, a calixarene-modified -AuCu / C catalyst, a cyclodextrin-modified PdZn / C catalyst, a cetylsulfonic acid-modified RuCr / C catalyst, a calixarene-modified -PtMo / C catalyst, a cyclodextrin-modified PtSn / C catalyst, or a cetylsulfonic acid-modified PtCe / C catalyst.

[0009] Preferably, the noble metal is 5% - 60% of the mass of the ORR catalyst.

[0010] A preparation method of an ORR catalyst includes the following steps: S1, loading noble metal-M alloy nanoparticles on the surface of a carbon source by an impregnation-H2 reduction method or a liquid-phase reduction method; S2, mixing the product obtained in S1 with a flexible structure macromolecule or supramolecule to obtain a flexible structure ORR catalyst.

[0011] Preferably in S1, a carbon source, a noble metal salt, and an M metal salt are mixed, stirred, filtered, and washed to obtain a catalyst with noble metal-M alloy nanoparticles loaded on the surface of the carbon source; The addition amounts of the carbon source, the noble metal salt, the M metal salt, and DMF are as follows: adding 50 mg of conductive carbon black, 50 mg of palladium acetylacetonate, 20 mg of nickel acetylacetonate, and 50 ml of DMF.

[0012] Preferably, the carbon source is conductive carbon black; the noble metal salt is palladium acetylacetonate; the M metal salt is nickel acetylacetonate.

[0013] Preferably in S2, the product obtained in S1 and a flexible structure molecule are dissolved in a solution, stirred, and dried to obtain a flexible structure ORR catalyst; The flexible structure molecule is anchored on the surface of the product obtained in S1 through a coordination effect; the anchoring means that the O in the flexible structure molecule combines with the M metal in the product obtained in S1 through a coordination effect.

[0014] The preparation method of the present invention was prepared with reference to the following literature: Zhao, Z., Liu, Z., Zhang, A. et al. Graphene-nanopocket-encaged PtCo nanocatalysts for highly durable fuel cell operation under demanding ultralow-Pt-loading conditions. Nat. Nanotechnol. 17, 968–975 (2022). An ORR catalyst with a flexible structure is applied to the field of electrocatalysis.

[0015] Specifically, the ORR catalyst is used for the cathode of a proton exchange membrane fuel cell. Beneficial effects

[0016] The electrocatalyst structure of the present invention is that supramolecules or macromolecules with a flexible structure are anchored on the surface of noble metal alloy nanoparticles supported on a carbon black carrier. Due to the entropy change of the anchored molecules caused by oxygen adsorption, that is, the entropy change of the modified molecules significantly promotes the adsorption of O2 and the desorption of OH in the reaction, thus accelerating the desorption of key species in the oxygen reduction process, and the reaction activity is significantly improved compared with noble metal alloy catalysts. When such a catalyst is used for the cathode of a proton exchange membrane fuel cell, under the condition that the noble metal dosage is as low as 0.1 mg cm -2 its output power is as high as 2.07 W cm -2 . Description of the drawings

[0017] Figure 1 It is a schematic structural diagram of the tBu[4]-PtCo / C catalyst prepared in Example 1 of the present invention; Figure 2 It is a comparison diagram of polarization curves and power curves when the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention are used as the cathodes of proton exchange membrane fuel cells respectively; Figure 3 It is a comparison diagram of in-situ Raman spectra of the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention during the ORR process; Figure 4 It is a comparison diagram of in-situ infrared spectra of the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention during the ORR process; Figure 5 It is a step diagram of the model ORR process of the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention; Figure 6The extended X-ray absorption fine structure spectra of Co-k edge in the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention. Detailed implementation mode

[0018] The present invention will be described in detail below with reference to the accompanying drawings to facilitate those skilled in the art to understand the present invention.

[0019] The noble metal loading of the cathode catalyst for fuel cell testing is 0.1 mg cm -2 , and the cathode feed is high-purity oxygen with a humidity of 100%. In-situ Raman spectroscopy was measured by LabRAM HR Evolution, and the electrolyte was an oxygen-saturated 0.1 M HClO4 solution. In-situ infrared spectroscopy was measured by PerkinElmer Spectrum, the electrolyte was an oxygen-saturated 0.1 M HClO4 solution, and the reference spectrum was measured at the open circuit potential in a nitrogen-saturated 0.1 M HClO4 solution.

[0020] Example 1 S1. Take a carbon source, a noble metal salt, and an M metal salt, mix them and disperse them in an organic solvent. After ultrasonic treatment for 1 h, perform rotary evaporation treatment, and load noble metal-M alloy nanoparticles catalyst on the surface of the carbon source by the impregnation-H2 reduction method; Among them, the carbon source is conductive carbon black; The noble metal salt is platinum acetylacetonate; The M metal salt is cobalt acetylacetonate; The organic solvent is methanol; The addition amounts of the carbon source, noble metal salt, M metal salt, and organic solvent are: add 80 mg of conductive carbon black, 30 mg of platinum acetylacetonate, 20 mg of cobalt acetylacetonate, and 100 ml of methanol The impregnation-H2 reduction method is to place the rotary evaporation treatment product in a 5% H2 / N2 atmosphere and reduce it for 6 h; The product obtained in S1 is labeled as PtCo / C-1; S2. Take the product obtained in S1 and dissolve it with a flexible structure molecule in an organic solvent. After stirring for 12 h, filter, wash with methanol, and dry to obtain a flexible structure ORR catalyst; The flexible structure molecule is anchored on the surface of the product obtained in S1 through coordination; the anchoring means that O in the flexible structure molecule combines with M metal in the product obtained in S1 through coordination; The flexible structure molecule is calixarene; the organic solvent is a mixed solution of DMF and triethylamine (DMF and triethylamine are mixed according to a volume ratio of 9:1); The added amounts of the product obtained in S1, the flexible structure molecule, and the organic solvent are as follows: 50 mg of the product obtained in S1, 200 mg of calixarene, and 20 ml of a mixed solution of DMF and triethylamine; The product obtained in S2 is labeled as tBu[4]-PtCo / C catalyst.

[0021] The physical and chemical properties of the PtBu[4]-PtCo / C catalyst prepared by S2 were measured.

[0022] The PtBu[4]-PtCo / C catalyst obtained in S2 was ultrasonically dispersed in a mixed solution of isopropanol and perfluorosulfonic acid oligomer to prepare a catalyst slurry, which was sprayed on the surface of carbon paper to keep the platinum content at 0.1 mg. Pt cm -2 The graphite flow field was assembled with the proton membrane and the anode catalyst layer by hot pressing to form a proton membrane fuel cell. The polarization curve and power curve were tested at 80 °C after oxygen and hydrogen were introduced into the anode and cathode respectively (gas rate was 500 mL min -1 , back pressure is 250 kPa).

[0023] Figure 1 The schematic diagram is a structural diagram of the tBu[4]-PtCo / C catalyst prepared in Example 1 of the present invention. The calixarene is anchored on the Co atom, and the Pt atom serves as the active site for ORR.

[0024] Figure 2 The polarization curve and power curve comparison of tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention when used as cathodes of proton membrane fuel cells. The output power of tBu[4]-PtCo / C reaches 2.07 W cm -2 , while PtCo / C only has 1.48 W cm -2 .

[0025] Figure 3 The in-situ Raman spectra of the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention during the ORR process are compared. RHE There was obvious O2 adsorption and at 0.8 V RHE and then disappears, while PtCo / C at 0.8 V RHE It appears and at 0.7 V RHESubsequently, it disappeared, indicating that the tBu[4]-PtCo / C surface is more prone to adsorb oxygen and increase its concentration to a level that can be captured by in-situ Raman, which demonstrates the promotion of the entropy synergy effect on reactant adsorption. Moreover, the Raman shift of oxygen on the tBu[4]-PtCo / C surface decreased significantly, indicating that the O-O bond in the adsorbed oxygen became larger, suggesting that oxygen is more easily activated on the tBu[4]-PtCo / C surface.

[0026] Figure 4 This is a comparison chart of in-situ infrared spectra of the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention during the ORR process. The vibration wavenumber of the OH species on the tBu[4]-PtCo / C surface is higher than that of PtCo / C at each potential. The larger the vibration wavenumber, the greater the O-H bond energy (or the chemical bond force constant), and thus the weaker the adsorption of OH to the catalyst, which indicates the promotion of the entropy synergy effect on the desorption of the intermediate OH.

[0027] Figure 5 This is a Gibbs free energy step diagram of the model ORR process of the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention. The Gibbs free energy of the reaction process was obtained based on DFT calculations. The DFT calculations were performed using the VASP software. The ion-electron interaction was described by the projector augmented wave (PAW). The exchange-correlation functional was represented by the Perdew-Burke-Ernzerhof (PBE) functional under the generalized gradient approximation (GGA). Spin polarization was considered during the calculation. The initial magnetic moments of Co and Pt were set to 3 and 0 respectively, and on this basis, the magnetic moments were automatically optimized to the minimum energy. The kinetic energy cutoff value for geometric optimization was set to 400 eV, and the sampling of the Brillouin zone used (3×3×1) k-points. To avoid any interlayer interaction, a 20 Å vacuum layer was set along the Z direction, and the structure was optimized on this basis until the energy and force reached 10-5 eV and 0.02 eV Å respectively. -1Convergence threshold. The dispersion correction of DFT-D3 was introduced throughout the calculation process. The VSPKIT software package and VESTA software were used to assist in analyzing the calculation results. Due to the entropy effect of the nearby calix[4]arene, the adsorption energies of OOH*, O*, and OH* on the PtCo surface decreased by 68.6%, 39.1%, and 40.5%, respectively. The free energy change of OOH*→O*+OH* changed from positive to negative, indicating that the cleavage of the O-O bond became more favorable. The adsorption free energy of O2 on the tBu[4]-PtCo surface reached 1.64 eV, an increase of 0.44 eV compared to PtCo. In addition to the electronic regulation brought about by the modification of calix[4]arene, the additional improvement will be attributed to the entropy increase of the nearby calix[4]arene caused by the adsorption of O2 on the PtCo surface, which leads to an additional compensation of -TΔS, reaching 0.1 - 0.2 eV. The free energy barrier for the desorption of OH* from the tBu[4]-PtCo surface was 0.223 eV, a decrease of 0.152 eV compared to the PtCo catalyst, significantly reducing the rate-determining step of the reaction.

[0028] Figure 6 This is the extended X-ray absorption fine structure spectrum of the Co - k edge in the tBu[4]-PtCo / C and PtCo / C catalysts prepared in Example 1 of the present invention. Compared with PtCo / C, the Co - O coordination in tBu[4]-PtCo / C increased significantly, which is the key evidence for the coordination and anchoring of the hydroxyl O in calixarene with Co atoms.

[0029] Example 2 S1. A carbon source, a noble metal salt, and an M metal salt were mixed and dispersed in DMF. After stirring at 160 °C for 12 h, the mixture was filtered and washed with methanol to load noble metal - M alloy nanoparticles catalyst on the surface of the carbon source; Among them, the carbon source is conductive carbon black; The noble metal salt is palladium acetylacetonate; The M metal salt is nickel acetylacetonate; The addition amounts of the carbon source, the noble metal salt, the M metal salt, and DMF are as follows: 50 mg of conductive carbon black, 50 mg of palladium acetylacetonate, 20 mg of nickel acetylacetonate, and 50 ml of DMF; The product obtained in S1 was labeled as PdNi / C - 1; S2. The product obtained in S1 and a flexible structure molecule were dissolved in a solution and stirred for 12 h, and then dried to obtain a flexible structure ORR catalyst; The flexible structure molecule was anchored on the surface of the product obtained in S1 through coordination; the anchoring means that the O in the flexible structure molecule is combined with the M metal in the product obtained in S1 through coordination; The flexible structure molecule is cyclodextrin; the solution is 1 M aqueous NaOH solution; The addition amounts of the product obtained from S1, the flexible structure molecule, and the organic solvent are as follows: 50 mg of the product obtained from S1, 300 mg of cyclodextrin, and 10 ml of 1 M NaOH aqueous solution; The product obtained from S2 is labeled as cyclodextrin-modified PdNi / C catalyst.

[0030] Example 3 S1: A carbon source, a noble metal salt, and an M metal salt are mixed and dispersed in an ethylene glycol solution. After stirring at 180 °C for 12 h, the noble metal-M alloy nanoparticle catalyst is loaded on the carbon source surface through filtration and methanol washing; Among them, the carbon source is conductive carbon black; The noble metal salt is ruthenium acetylacetonate; The M metal salt is iron acetylacetonate; The addition amounts of the carbon source, the noble metal salt, the M metal salt, and ethylene glycol are as follows: 100 mg of conductive carbon black, 100 mg of ruthenium acetylacetonate, 50 mg of iron acetylacetonate, and 50 ml of ethylene glycol; The product obtained from S1 is labeled as RuFe / C-1; S2: The product obtained from S1 and the flexible structure molecule are dissolved in water. After stirring for 12 h and drying, the flexible structure ORR catalyst is obtained; The flexible structure molecule is anchored on the surface of the product obtained from S1 through coordination; the anchoring means that the O in the flexible structure molecule combines with the M metal in the product obtained from S1 through coordination; The flexible structure molecule is cetylsulfonic acid; The addition amounts of the product obtained from S1, the flexible structure molecule, and the organic solvent are as follows: 50 mg of the product obtained from S1 and 100 mg of cetylsulfonic acid; The product obtained from S2 is labeled as cetylsulfonic acid-modified RuFe / C catalyst.

[0031] Example 4 The same preparation method as in Example 1 is adopted, with only the following modifications: In S1, The noble metal salt is gold chloride; The M metal salt is copper chloride; The addition amounts of the carbon source, the noble metal salt, the M metal salt, and the organic solvent are as follows: 80 mg of conductive carbon black, 60 mg of gold chloride, 40 mg of copper chloride, and 100 ml of methanol The product obtained from S1 is labeled as AuCu / C; In S2, The addition amounts of the product obtained from S1, the flexible structure molecule, and the organic solvent are as follows: 60 mg of the product obtained from S1, 150 mg of calixarene, and a total of 30 ml of a mixed solution of DMF and triethylamine; The product obtained in S2 is labeled as calixarene-modified -AuCu / C catalyst.

[0032] Example 5 The same preparation method as in Example 2 is adopted, with only the following modifications: In S1, The noble metal salt is palladium chloride; The M metal salt is zinc chloride; The addition amounts of the carbon source, noble metal salt, M metal salt, and DMF are as follows: 50 mg of conductive carbon black, 40 mg of platinum chloride, 15 mg of zinc chloride, and 50 ml of DMF are added; The product obtained in S1 is labeled as PdZn / C; In S2, The addition amounts of the product obtained in S1, flexible structure molecule, and organic solvent are as follows: 40 mg of the product obtained in S1, 300 mg of cyclodextrin, and 10 ml of 1 M NaOH aqueous solution are added; The product obtained in S2 is labeled as cyclodextrin-modified PdZn / C catalyst.

[0033] Example 6 The same preparation method as in Example 3 is adopted, with only the following modifications: In S1, The noble metal salt is ruthenium chloride; The M metal salt is chromium chloride; The addition amounts of the carbon source, noble metal salt, M metal salt, and ethylene glycol are as follows: 100 mg of conductive carbon black, 80 mg of ruthenium chloride, 50 mg of chromium chloride, and 50 ml of ethylene glycol are added; The product obtained in S1 is labeled as RuCr / C; In S2, The addition amounts of the product obtained in S1, flexible structure molecule, and organic solvent are as follows: 40 mg of the product obtained in S1 and 100 mg of cetylsulfonic acid are added; The product obtained in S2 is labeled as cetylsulfonic acid-modified RuCr / C catalyst. Example 7

[0034] The same preparation method as in Example 1 is adopted, with only the following modifications: In S1, The noble metal salt is platinum acetylacetonate; The M metal salt is molybdenum acetylacetonate; The addition amounts of the carbon source, noble metal salt, M metal salt, and organic solvent are as follows: 100 mg of conductive carbon black, 40 mg of platinum acetylacetonate, 50 mg of molybdenum acetylacetonate, and 100 ml of methanol The product obtained in S1 is labeled as PtMo / C; In S2, The addition amounts of the product obtained from S1, the flexible structure molecule, and the organic solvent are as follows: add 80 mg of the product obtained from S1, 100 mg of calixarene, and a total of 30 ml of a mixed solution of DMF and triethylamine; The product obtained from S2 is labeled as calixarene-modified -PtMo / C catalyst. Example 8

[0035] The same preparation method as in Example 2 is adopted, with only the following modifications: In S1, The noble metal salt is platinum chloride; The M metal salt is tin chloride; The addition amounts of the carbon source, noble metal salt, M metal salt, and DMF are as follows: add 50 mg of conductive carbon black, 40 mg of platinum chloride, 40 mg of tin chloride, and 50 ml of DMF; The product obtained from S1 is labeled as PtSn / C; In S2, The addition amounts of the product obtained from S1, the flexible structure molecule, and the organic solvent are as follows: add 60 mg of the product obtained from S1, 300 mg of cyclodextrin, and 10 ml of 1 M NaOH aqueous solution; The product obtained from S2 is labeled as cyclodextrin-modified PtSn / C catalyst. Example 9

[0036] The same preparation method as in Example 3 is adopted, with only the following modifications: In S1, The noble metal salt is platinum chloride; The M metal salt is cerium chloride; The addition amounts of the carbon source, noble metal salt, M metal salt, and ethylene glycol are as follows: add 100 mg of conductive carbon black, 80 mg of platinum chloride, 70 mg of cerium chloride, and 50 ml of ethylene glycol; The product obtained from S1 is labeled as PtCe / C; In S2, The addition amounts of the product obtained from S1, the flexible structure molecule, and the organic solvent are as follows: add 60 mg of the product obtained from S1, 100 mg of cetylsulfonic acid; The product obtained from S2 is labeled as cetylsulfonic acid-modified PtCe / C catalyst.

Claims

1. An ORR catalyst with a flexible structure, characterized in that: The ORR catalyst is noble metal-M alloy nanoparticles supported on the surface of a carbon source, and flexible structure macromolecules or supramolecules are coordinated and anchored on the surface of the noble metal-M alloy catalyst; Among them, the carbon source is conductive carbon black; The noble metal includes one or more mixtures of Pt, Ru, Pd, and Au; The M includes one or more mixtures of Co, Fe, Ni, Cu, Zn, Cr, Mo, Sn, Ce, and Pd; The flexible structure macromolecules or supramolecules include one or more mixtures of calixarene, cyclodextrin, and cetylsulfonic acid.

2. The ORR catalyst according to claim 1, characterized in that: The noble metal includes one or more mixtures of Pt and Pd; The M includes one or more mixtures of Co, Fe, Ni, and Pd; The flexible structure macromolecules or supramolecules include calixarene.

3. The ORR catalyst according to claim 1, characterized in that: The ORR catalyst is calixarene-modified PtCo / C, cyclodextrin-modified PdNi / C, cetylsulfonic acid-modified RuFe / C, calixarene-modified -AuCu / C catalyst, cyclodextrin-modified PdZn / C catalyst, cetylsulfonic acid-modified RuCr / C catalyst, calixarene-modified -PtMo / C catalyst, cyclodextrin-modified PtSn / C catalyst, cetylsulfonic acid-modified PtCe / C catalyst.

4. The ORR catalyst according to claim 1, characterized in that: The noble metal is 5%-60% of the mass of the ORR catalyst.

5. A method for preparing an ORR catalyst according to any one of claims 1-4, characterized in that: It includes the following steps: S1, using the impregnation-H2 reduction method or the liquid-phase reduction method to support noble metal-M alloy nanoparticles on the surface of the carbon source; S2, mixing the product obtained in S1 with flexible structure macromolecules or supramolecules to obtain an ORR catalyst with a flexible structure.

6. The preparation method according to claim 5, characterized in that: S1, mixing the carbon source, noble metal salt, and M metal salt, stirring, filtering, and washing to obtain a noble metal-M alloy nanoparticle catalyst supported on the surface of the carbon source.

7. The preparation method according to claim 6, characterized in that: Among them, The carbon source is conductive carbon black; the noble metal salt is palladium acetylacetonate; the M metal salt is nickel acetylacetonate; the molar ratio of the carbon source, noble metal salt, and M metal salt is 1:1:2.

5.

8. An ORR catalyst according to any one of claims 1-4 and an ORR catalyst obtained by the preparation method according to any one of claims 5-7 are applied in the field of electrocatalysis.

9. Use of the ORR catalyst according to claim 8, characterized in that: The ORR catalyst is used for the cathode of a proton exchange membrane fuel cell.

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