A palladium-platinum bimetallic core-shell heterostructure nanocrystal, a preparation method and applications thereof

Abstract

The application belongs to the technical field of functional nanometer material, and discloses a heterostructure nanocrystal of palladium@platinum bimetallic core-shell heterostructure, a preparation method and application. The preparation method is that palladium is photo-deposited on reduced graphene oxide to form metal nanocrystals with regular morphology as crystal seeds, and then platinum is photo-driven to form epitaxial coating on the formed metal nanocrystal seeds to form palladium@platinum bimetallic core-shell heterostructure nanocrystals supported by reduced graphene oxide. The palladium@platinum bimetallic core-shell heterostructure nanocrystals prepared by the above method have specific crystal faces and morphology and are uniformly dispersed, and the nucleation and growth coating process of the bimetallic nanocrystals is controlled. The nanocrystals can be directly used as electrode materials, and due to the synergistic effect between the bimetals, the palladium@platinum bimetallic core-shell heterostructure nanocrystal composite catalyst supported by reduced graphene oxide has good application in electrocatalytic water decomposition.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional nanomaterials, and particularly relates to a heterostructure nanocrystal of a reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure and a preparation method thereof, and application of the same as an electrode material and a carbon-based composite catalyst. BACKGROUND

[0002] Large-scale social and economic development and rapid depletion of non-renewable fossil fuels have drawn increasing attention to energy issues, and there is an urgent need to develop large-scale carbon-neutral fuels to achieve sustainable development strategies. Hydrogen, as a new energy source, has the advantages of high energy density, large combustion heat value, and no pollution byproducts, and is currently considered an effective way to obtain clean and renewable energy through water electrolysis. Heterogeneous bimetallic core-shell heterostructure nanocrystals have tunable electronic structures, various synergistic effects such as ligand groups, and special phase boundaries or interfaces, and are widely used in catalysis and other fields. With the development of nanomaterial phase engineering technology, the controllable preparation of nanomaterials and the exploration of the structure-activity relationship between morphology and electrocatalysis are still great challenges faced by researchers in this field. In addition to structure, composition, and morphology, the characteristics and performance of core-shell heterostructure nanocrystals are also closely related to the carrier. Rational design and preparation of high-activity and durable composite catalysts of specific morphology supported metal heterostructure nanocrystals are of great significance for driving the pH-universal electrocatalytic hydrogen evolution reaction (HER).

[0003] To date, various types of core-shell heterostructures have made significant achievements in production and application, among which the most fruitful is the liquid-phase seed epitaxial growth strategy, i.e., epitaxially depositing the shell material on the surface of the pre-existing core material to form a core-shell heterostructure. However, compared with the separate synthesis of core-shell nanoparticles in solution, there are few reports on the direct growth of bimetallic core-shell nanocrystals on carriers in liquid phase. Moreover, with the introduction of the carrier, the nucleation and growth process of the core-shell heterostructure becomes more complex. In addition, the preparation of most bimetallic core-shell nanoparticles also requires the addition of capping reagents, surfactants, coordination ligands, etc. to prevent the agglomeration of the second metal in the solution, ensuring the controlled growth of the second metal on the crystal seed. However, these reagents attached to the surface of the core-shell heterostructure may cause material dysfunction and hinder further application, or need to be removed through complex post-processing.

[0004] Therefore, it is of great significance to study a synthesis strategy for a reduced graphene oxide-based composite catalyst of core-shell heterostructure that can accurately control the nucleation and growth of metal nanocrystals, develop core-shell heterostructures with specific structures, combinations, and interfaces, and does not require the introduction of more surfactants, foreign ions, or molecules. However, the prior art cannot achieve this goal. SUMMARY

[0005] The present application aims to provide a reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal, a preparation method and an application, which can accurately control the nucleation and growth coating process of the palladium-platinum bimetallic nanocrystal, and prepare a reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal composite catalyst which is uniformly dispersed and has a specific crystal face and morphology, and which avoids introducing additional capping reagents, surfactants, foreign ions or molecules, so as to solve the above technical problems existing in the prior art or related art.

[0006] In order to achieve the above-mentioned purpose, the technical scheme provided by the present application is as follows:

[0007] A preparation method and an application of a reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal, characterized in that: palladium is photo-deposited on reduced graphene oxide to form a metal nanocrystal with regular morphology as a seed, and the platinum is epitaxially coated on the formed metal nanocrystal seed by photo-driving to form a reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal, which has a good application in the electrocatalytic decomposition of water to produce hydrogen.

[0008] S610: uniformly mixing the nanosemiconductor and the graphene oxide solution to obtain a semi-finished product composite substrate solution;

[0009] S620: placing the semi-finished product composite substrate solution in a photo-reactor, adding a sacrificial reagent, and stirring and introducing gas throughout the process;

[0010] S630: obtaining a reduced graphene oxide-semiconductor composite substrate by irradiation of an internal light source;

[0011] S640: adding a palladium metal precursor solution to the reduced graphene oxide-semiconductor composite substrate to obtain a semi-finished product palladium seed;

[0012] S650: obtaining a composite substrate supported palladium tetrahedral seed by irradiating the semi-finished product seed with an internal light source;

[0013] S660: adding a platinum metal precursor solution to the composite substrate supported palladium tetrahedral seed to obtain a semi-finished product catalyst;

[0014] S670: irradiating the semi-finished product catalyst with an internal light source to obtain a composite substrate supported palladium-platinum core-shell nanocrystal catalyst;

[0015] S680: application of the composite substrate supported palladium-platinum core-shell nanocrystal catalyst in the electrocatalytic decomposition of water to produce hydrogen.

[0016] The step S610 specifically comprises the following steps:

[0017] S611: After adding the nano-semiconductor to the solution of the graphene oxide, ultrasonically disperse for 10 to 30 minutes to obtain a mixture of graphene oxide and semiconductor;

[0018] S612: The mixture is magnetically stirred at room temperature at a stirring speed of 1000-2000 rpm to obtain a semi-finished composite base solution.

[0019] In step S620, the sacrificial reagent is at least one of methanol, ethanol, and lactic acid, and the amount used is from 0.0 mL to 20.0 mL.

[0020] The entire stirring process is performed using magnetic stirring at a speed of 1000-2000 rpm.

[0021] At least one inert gas, consisting of argon and nitrogen, is introduced into the photoreactor.

[0022] In step S630, the controlled light source includes either a mercury lamp or a xenon lamp; the irradiation time of the controlled light source is 10 to 20 minutes; the power of the controlled light source is 500W to 700W; and the illuminance of the controlled light source is 100mW / cm². 2 Up to 220mW / cm 2 .

[0023] In step S640, the nano-semiconductor comprises: TiO2 (rutile, anatase, P...) 25 (Rutile anatase mixed crystal), at least one of ZnO, ZrO2, CeO2, and g-C3N4.

[0024] In step S640, the metal precursor liquid includes one of Pd(NH3)4Cl2 or an aqueous solution of PdCl2.

[0025] In step S640, the mass ratio of the metal in the metal precursor solution to the reduced graphene oxide-semiconductor composite is 7:(90-92).

[0026] In step S640, the reduced graphene oxide-semiconductor composite is prepared from reduced graphene oxide and semiconductor in a mass ratio of (15-16):1.

[0027] In step S650, the controlled light source includes either a mercury lamp or a xenon lamp; the irradiation time of the controlled light source is 20 to 40 minutes; the power of the controlled light source is 600 W to 1000 W; and the illuminance of the controlled light source is 120 mW / cm². 2 Up to 360mW / cm 2 .

[0028] The mass ratio of the metal in the palladium metal precursor solution to the metal in the platinum metal precursor solution is 7:1-3.

[0029] The controlled light source comprises one of a mercury lamp or a xenon lamp, the irradiation time of the controlled light source is 30-120 min, the power of the controlled light source is 600-1000 W, and the light intensity of the controlled light source is 120-360 mW / cm 2 . 2 .

[0030] The palladium@platinum core-shell nanocrystal catalyst supported by the composite substrate can be directly coated on a gas diffusion electrode, and the hydrogen is produced by electrocatalytic decomposition of water at a voltage of 0.2-1.2 V after reversible hydrogen electrode conversion.

[0031] A reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal composite catalyst is prepared by the above method, and the palladium@platinum bimetallic core-shell heterostructure nanocrystal synthesized by controllable light deposition on the reduced graphene oxide is uniformly dispersed on the reduced graphene oxide and has a specific morphology and exposed crystal face.

[0032] (a) the Pd7@Pt1 bimetallic nanocrystal is a tetrahedron with exposed {111} crystal faces, and the Pt shell is a layered structure of the coating layer;

[0033] (b) the Pd7@Pt3 bimetallic nanocrystal is a tetrahedron with exposed {111} crystal faces, and the Pt shell is a semi-island layered structure of the coating layer;

[0034] (c) the Pd7@Pt5 bimetallic nanocrystal is a tetrahedron with exposed {111} crystal faces, and the Pt shell is an island layered structure of the coating layer;

[0035] The beneficial effects of the present application are:

[0036] 1. The application provides a reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal, a preparation method and an application, and provides a new technical concept. A general photochemical synthesis strategy is provided, in which platinum is precisely grown on a palladium tetrahedron loaded on a reduced graphene oxide (rGO) composite base through seed-mediated growth, and the palladium-platinum bimetallic core-shell heterostructure nanocrystal has a customized morphology. The application first successfully prepares a Pd tetrahedron with {111} crystal face exposure on the reduced graphene oxide, and then controls the growth mode of the Pt shell by adjusting the irradiation intensity to change the ratio between the deposition rate and the surface diffusion rate, so that the unique hybrid structure can associate the platinum shell morphology with the performance of HER. The palladium-platinum bimetallic core-shell heterostructure nanocrystal with a Pt shell in a Stranski-Krastanov morphology exhibits excellent HER performance in a pH-universal medium, and has an excellent overpotential.

[0037] 2. The palladium-platinum bimetallic core-shell heterostructure nanocrystal prepared by the application can affect the surface strain generated by the electronic interaction between the Pt shell layer of different morphologies and the Pd core, can change the surface charge state, can change the binding energy of the adsorbate on the Pt, and can generate more efficient active sites, which is of great significance to improve the pH-universal electrocatalytic water splitting hydrogen production activity.

[0038] 3. The application provides a preparation method of the reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal. The method uses reduced graphene oxide as a storage layer for rapid transfer of photoelectrons, can effectively control the rapid accumulation of photoelectrons on the metal, does not need to add additional components such as surfactants and end-capping reagents, can accurately control the nucleation and core-shell heterostructure growth process of the palladium-platinum bimetallic core-shell heterostructure nanocrystal on the reduced graphene oxide. Controlling the thermodynamic and kinetic crystal growth process through controllable photo deposition is the key to controlling the shape of the metal nanocrystal, and the size, chemical state and geometric distribution of the bimetallic core-shell heterostructure nanocrystal can also be conveniently adjusted. The process conditions are easy to control, the operation steps are few, the materials, energy and equipment used are few, the operation is simple, and the cost is saved.

[0039] 4. The application of the reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystal prepared by the application as a composite catalyst has the advantages of specific crystal face and morphology and uniform dispersion on the reduced graphene oxide, and has good application in electrocatalytic water splitting hydrogen production, has a lower overpotential and can efficiently produce H2. BRIEF DESCRIPTION OF DRAWINGS

[0040] The above and / or additional aspects and advantages of the application will become apparent and be readily understood by considering the following detailed description, including the appended drawings, in which:

[0041] Figure 1A schematic flow chart of a method for preparing reduced graphene oxide-based supported Pd@Pt bimetallic core-shell heterostructure nanocrystals according to the present application is shown;

[0042] Figure 2 Reduced graphene oxide-based supported tetrahedral Pd nanoseeds according to the present application are shown. Wherein (a) is a low magnification transmission electron microscopy image (TEM), (b) is a high resolution transmission electron microscopy image (HRTEM), and the inset is a Fourier transform of the diffraction spots and a crystal 3D model of the tetrahedral Pd nanoseed;

[0043] Figure 3 Reduced graphene oxide-based supported Pd7@Pt1 bimetallic core-shell heterostructure nanocrystals according to the present embodiment 1 of the present application are shown. Wherein (a) is a crystal 3D model of the Pd7@Pt1 bimetallic core-shell heterostructure of the present embodiment 1, (a1) is a low magnification transmission electron microscopy image (TEM) of the catalyst of the present embodiment 1 and (a2) is a high resolution transmission electron microscopy image (HRTEM) of the catalyst of the present embodiment 1, (a3) is a Pd elemental energy dispersive plane scanning analysis image of the catalyst of the present embodiment 1, (a4) is a Pt elemental energy dispersive plane scanning analysis image of the catalyst of the present embodiment 1, and (a5) is a Pd and Pt elemental energy superimposed plane scanning analysis image of the catalyst of the present embodiment 1;

[0044] Figure 4 Reduced graphene oxide-based supported Pd7@Pt3 bimetallic core-shell heterostructure nanocrystals according to the present embodiment 2 of the present application are shown. Wherein (b) is a crystal 3D model of the Pd7@Pt3 bimetallic core-shell heterostructure of the present embodiment 2, (b1) is a low magnification transmission electron microscopy image (TEM) of the catalyst of the present embodiment 2 and (b2) is a high resolution transmission electron microscopy image (HRTEM) of the catalyst of the present embodiment 2, (b3) is a Pd elemental energy dispersive plane scanning analysis image of the catalyst of the present embodiment 2, (b4) is a Pt elemental energy dispersive plane scanning analysis image of the catalyst of the present embodiment 2, and (b5) is a Pd and Pt elemental energy superimposed plane scanning analysis image of the catalyst of the present embodiment 2;

[0045] Figure 5The diagram illustrates a reduced graphene oxide-supported Pd7@Pt5 bimetallic core-shell heterostructure nanocrystal according to Specific Embodiment 3 of the present invention. (c) is a 3D model of the Pd7@Pt5 bimetallic core-shell heterostructure crystal of Specific Embodiment 3; (c1) is a low-magnification transmission electron microscope (TEM) image of the catalyst of Specific Embodiment 3; (c2) is a high-resolution transmission electron microscope (HRTEM) image of the catalyst of Specific Embodiment 3; (c3) is a scanning electron microscope (SEM) image of the Pd element in the catalyst of Specific Embodiment 3; (c4) is a scanning electron microscope (SEM) image of the Pt element in the catalyst of Specific Embodiment 3; and (c5) is a scanning electron microscope (SEM) image of the superposition of Pd and Pt elements in the catalyst of Specific Embodiment 3.

[0046] Figure 6 The application of the reduced graphene oxide-supported palladium@platinum bimetallic core-shell heterostructure nanocrystalline catalyst prepared according to specific embodiments 1, 2, and 3 of the present invention in electrocatalytic water splitting for hydrogen production is shown, wherein (a) polarization curve of HER in acidic electrolyte, (b) polarization curve of HER in neutral electrolyte, (c) polarization curve of HER in alkaline electrolyte, (d) Tafel slope diagram of HER in acidic electrolyte, (e) Tafel slope diagram of HER in neutral electrolyte, (f) Tafel slope diagram of HER in alkaline electrolyte, (g) comparison diagram of normalized mass activity per unit mass at different potentials in acidic electrolyte, (h) comparison diagram of normalized mass activity per unit mass at different potentials in neutral electrolyte, (i) comparison diagram of normalized mass activity per unit mass at different potentials in alkaline electrolyte, and (j) stability test diagram of fixed potential in full pH electrolyte;

[0047] Figure 7 Pd7@Pt of reduced graphene oxide-supported layered Pt according to Comparative Example 1 of the present invention is shown. 3-U Bimetallic core-shell heterostructure nanocrystals. Among them, (a) is a low-magnification transmission electron microscope (TEM) image of Comparative Example 1, (b) is a high-resolution transmission electron microscope (HRTEM) image of Comparative Example 1, (c) is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of Comparative Example 1, (d) is a scanning electron microscope (SEM) image of the energy distribution surface of Pd element in Comparative Example 1, (e) is a scanning electron microscope (SEM) image of the energy distribution surface of Pt element in Comparative Example 1, and (f) is a scanning electron microscope (SEM) image of the superposition of Pd and Pt elements in Comparative Example 1.

[0048] Figure 8 The application of the composite catalyst prepared according to Specific Example 2 and Comparative Example 1 in electrocatalytic water splitting for hydrogen production is shown, wherein (a) is the polarization curve of HER in acidic electrolyte, and (b) is a comparison graph of normalized mass activity per unit mass at different potentials in acidic electrolyte. Detailed Implementation

[0049] The application provides a preparation method and application of reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystals.

[0050] The application will be further described in detail below with reference to the drawings Figures 1-8 The application focuses on depositing palladium-platinum bimetallic core-shell heterostructure nanocrystals with specific morphology and uniform dispersion on reduced graphene oxide through a metal nanocrystal core-shell heterostructure and a morphology-controlled photodeposition process.

[0051] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0052] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the application can be purchased from the market or prepared by existing methods.

[0053] Embodiment 1:

[0054] The application provides a preparation method of reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystals, which is a photodeposition method for controlled growth of metal morphology seed epitaxy, and the method is used for photodeposition of palladium on reduced graphene oxide to form metal nanocrystals with regular morphology as seeds, and then photodriven epitaxial coating of platinum on the formed metal nanocrystal seeds to form reduced graphene oxide-based supported palladium-platinum bimetallic core-shell heterostructure nanocrystals.

[0055] S610: uniformly mixing the nanosemiconductor and the graphene oxide solution to obtain a semi-finished composite substrate solution; specifically,

[0056] S611: adding the nanosemiconductor to the graphene oxide solution and ultrasonically dispersing for 10-30 minutes to obtain a mixture of graphene oxide and semiconductors;

[0057] S612: magnetically stirring the mixture at room temperature at a stirring rate of 1000-2000 rpm to obtain a semi-finished composite substrate solution.

[0058] Ultrasonic dispersion and magnetic stirring can uniformly mix the nanosemiconductor with the graphene oxide, and the subsequent nucleation and growth in the photochemical deposition process of the metal nanocrystals will be more uniform and sufficient.

[0059] S620: Put the semi-finished composite substrate solution into the photo-reactor, add the sacrificial reagent, stir throughout and introduce the gas; specifically:

[0060] Put the semi-finished composite substrate solution into the photo-reactor, add the sacrificial reagent, magnetically stir throughout and introduce at least one inert gas of nitrogen and argon, the stirring rate is 1000-2000 rpm; the function of the sacrificial reagent is to capture holes, in the process of photo-deposition, the conduction band and the valence band of the semiconductor oxide respectively generate electrons and holes under the irradiation of the light source, the light source excites the semiconductor, the electron goes from the ground state to the excited state, the electron can reduce the metal precursor on the semiconductor to form metal nanocrystals, while the remaining holes have oxidizing properties, the electron and the hole are prone to recombination, and need to be captured by the sacrificial reagent to slow down the recombination of the electron and the hole, thereby controlling the reduction degree of the reduced graphene oxide. The above-mentioned sacrificial reagent is at least one of methanol, ethanol and lactic acid, and the amount is 0.0 mL to 20.0 mL. In specific implementation, at least one of methanol, ethanol and lactic acid with reducing property can be generally selected as the reducing agent. And the amount of the reducing agent is selected according to the quality of the prepared catalyst, the type of the semiconductor nanometer and the metal loaded on the graphene oxide, and the amount of the reducing agent is 0.0 mL to 20.0 mL. The magnetic stirring throughout provides a uniform reaction environment, and too fast or too slow stirring rate will lead to uneven reaction, and 1500 rpm just meets the reaction requirement. Introduce at least one inert gas of nitrogen and argon into the photo-reactor, in specific implementation, introduce the inert gas such as nitrogen or argon while magnetically stirring throughout, the function is to avoid oxygen from being dissolved into the reaction solution during the reaction, causing the generation of metal oxides or other valence state metals except zero-valence, leading to the phenomena of decreased catalytic efficiency, low catalyst utilization rate, etc.

[0061] S630: Obtain the reduced graphene oxide-semiconductor composite substrate by irradiation of the internal light source;

[0062] The controlled light source includes one of a mercury lamp or a xenon lamp; the irradiation time of the controlled light source is 10 min to 20 min; the power of the controlled light source is 500 W to 700 W, and the light intensity of the controlled light source is 100 mW / cm 2 to 220 mW / cm 2 ; specifically:

[0063] A reduced graphene oxide-semiconductor composite substrate is obtained by irradiation with a controlled light source. This controlled light source includes either a mercury lamp or a xenon lamp. The irradiation duration is 10 to 20 minutes, and the power of the controlled light source is 500 W to 700 W. In the specific implementation process, the type of light source is selected based on the types of metal ions on the nano-semiconductor and the reduced graphene oxide. The light source is either a mercury lamp or a xenon lamp. The light source irradiates the semi-finished composite substrate solution, which is uniformly mixed with nano-semiconductor and graphene oxide solutions, in a photoreactor. Specifically, a light source is added inside the photoreactor to better irradiate the uniformly mixed semi-finished composite substrate solution. A quartz cooling well separates the light source from the reaction solution. A light source with a power of 500 W to 700 W irradiates the uniformly mixed semi-finished composite substrate solution of nano-semiconductor and graphene oxide solutions in the photoreactor for 10 to 20 minutes. The reduced graphene oxide-semiconductor composite substrate is obtained by irradiation with a controlled light source. This can be understood as the nano-semiconductor reducing graphene oxide to reduced graphene oxide to form the reduced graphene oxide-semiconductor composite substrate. The purpose is that reduced graphene oxide is superior to graphene oxide as a reservoir for rapid photoelectron transfer, so that the growth process caused by the rapid accumulation of photoelectrons on the metal can be precisely controlled.

[0064] S640: Palladium metal precursor solution is added to a reduced graphene oxide-semiconductor composite substrate to obtain semi-finished palladium seed crystals; specifically:

[0065] Under the conditions of introducing at least one inert gas, namely nitrogen and argon, into the photoreactor and magnetic stirring at a stirring rate of 1500 rpm, palladium metal precursor solution is added to the reduced graphene oxide-semiconductor composite substrate to obtain semi-finished palladium seed crystals.

[0066] The aforementioned nano-semiconductors include: TiO2 (specifically, rutile, anatase, or P2O3 can be selected). 25 (one of the following) ZnO, ZrO2, CeO2, g-C3N4.

[0067] The aforementioned metal precursor solution includes one of Pd(NH3)4Cl2 or an aqueous solution of PdCl2, wherein the aqueous solution containing the metal ions corresponding to the catalyst to be prepared is selected as the metal precursor solution.

[0068] The mass ratio of the metal in the metal precursor solution to the reduced graphene oxide-semiconductor composite group is 7:(90-92);

[0069] The aforementioned reduced graphene oxide-semiconductor composite is prepared from reduced graphene oxide and semiconductor in a mass ratio of (15-16):1.

[0070] S650: irradiating the semi-finished seed crystal by the internal light source to obtain a palladium tetrahedral seed crystal supported by a composite substrate; specifically:

[0071] The semi-finished palladium seed crystal is irradiated by the internal light source to obtain a palladium seed crystal supported by a composite substrate. Specifically, the controlled light source is one of a mercury lamp and a xenon lamp; the irradiation time of the controlled light source is 20 min to 40 min; the power of the controlled light source is 600 W to 1000 W, and the light intensity of the controlled light source is 120 mW / cm 2 to 360 mW / cm 2 Under the conditions of passing at least one inert gas of nitrogen and argon into the photoreactor and magnetic stirring at a stirring speed of 1500 rpm, the semi-finished seed crystal is irradiated by the controlled light source to obtain a palladium seed crystal supported by a reduced graphene oxide substrate. The conduction band and the valence band of the semiconductor respectively generate electrons and holes under ultraviolet or visible light irradiation. The light source excites the electrons from the ground state to the excited state. The electrons can reduce the metal precursor on the semiconductor to form palladium metal nanocrystals, while the holes need to be captured by a sacrificial reagent such as methanol to slow down the recombination time of the electrons and holes, thereby controlling the nucleation and growth rate of the palladium metal.

[0072] S660: adding a platinum metal precursor solution to the palladium tetrahedral seed crystal supported by the composite substrate to obtain a semi-finished catalyst; specifically:

[0073] The mass ratio of the palladium metal precursor solution to the metal in the platinum metal precursor solution is 7:1-3.

[0074] S670: irradiating the semi-finished catalyst by the internal light source to obtain a palladium@platinum core-shell nanocrystal catalyst supported by a composite substrate; specifically:

[0075] The semi-finished catalyst is irradiated by the internal light source to obtain a catalyst supported by a composite substrate. Specifically, the controlled light source includes one of a mercury lamp or a xenon lamp; the irradiation time of the controlled light source is 30 min to 60 min; the power of the controlled light source is 600 W to 1000 W, and the light intensity of the controlled light source is 120 mW / cm 2 to 360 mW / cm 2 . The photoelectrons generated by the light excitation of the nanosemiconductor by one of a mercury lamp or a xenon lamp are used to reduce the platinum metal precursor to the surface of the palladium metal seed crystal to form a palladium@platinum bimetallic core-shell heterostructure nanocrystal catalyst supported by a reduced graphene oxide substrate.

[0076] S680: application of the palladium@platinum core-shell nanocrystal catalyst supported by a composite substrate in the electrocatalytic decomposition of water to produce hydrogen. Specifically:

[0077] The reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal catalyst can be directly coated on a gas diffusion electrode, and the electrocatalytic decomposition of water to produce hydrogen is carried out at a voltage of 0.2-1.2 V after reversible hydrogen electrode conversion. The Tafel slope, mass activity and other parameters of the conversion rate are calculated to evaluate the conversion efficiency of the composite substrate supported catalyst, and durability evaluation test is carried out.

[0078] The application of a reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal as a composite catalyst, wherein the palladium@platinum bimetallic core-shell heterostructure nanocrystal is prepared by the aforementioned method, and the bimetallic core-shell heterostructure nanocrystal synthesized by controllable photodeposition on the reduced graphene oxide is uniformly dispersed on the reduced graphene oxide and has a specific crystal face and morphology. Specifically, there are three forms:

[0079] (a) The Pd7@Pt1 bimetallic nanocrystal is a tetrahedron exposing a {111} crystal face, and the Pt shell is a layered structure of the coating layer;

[0080] (b) The Pd7@Pt3 bimetallic nanocrystal is a tetrahedron exposing a {111} crystal face, and the Pt shell is a half-island layered structure of the coating layer;

[0081] (c) The Pd7@Pt5 bimetallic nanocrystal is a tetrahedron exposing a {111} crystal face, and the Pt shell is an island layered structure of the coating layer;

[0082] The reduced graphene oxide-based supported palladium@platinum bimetallic core-shell structure nanocrystal prepared by the above method has a specific crystal face and morphology and is uniformly dispersed, without the need to add additional surfactants, capping reagents, etc., and the nucleation and growth coating process of the palladium@platinum bimetallic core-shell structure nanocrystal on the reduced graphene oxide base can be accurately controlled.

[0083] In order to more clearly understand the objects, technical solutions and advantages of the present application, the present application will be further described in detail below in conjunction with examples. The specific data involved in the specific examples described herein are only used to explain the present application and do not limit the present application. Specific example 1

[0085] The present application embodiment is based on example 1, and specifically provides a palladium@platinum bimetallic core-shell heterostructure-graphene oxide-based nanocrystal (composite catalyst) TiO2-rGO-Pd7@Pt1 and a preparation method thereof. The preparation of the palladium@platinum bimetallic core-shell heterostructure-graphene oxide-based nanocrystal (composite catalyst) TiO2-rGO-Pd7@Pt1 comprises the following steps:

[0086] Select a reduced graphene oxide-semiconductor composite base carrier: TiO2(rutile)-rGO;

[0087] The first metal precursor solution is Pd(NH3)4Cl2 solution;

[0088] The second metal precursor solution is H2PtCl6 solution;

[0089] 2.0 mg of TiO2(rutile) and 3.75 mL of graphene oxide solution with a concentration of 8 mg / mL were dispersed in a sample bottle containing 260.0 mL of ultrapure water and ultrasonically treated for 15 min. The mixed solution was transferred into a photo-reactor, 15.0 mL of anhydrous methanol was added, and the whole process was magnetically stirred and argon-purged. After irradiation for 15 min with a 650 W (130 mW / cm2) mercury lamp, the mercury lamp was turned off. 620.0 μL of Pd(NH3)4Cl2 solution with a concentration of 1.0 g / 100 mL was added, and after irradiation for 30 min with a 910 W (320 mW / cm2) mercury lamp, the mercury lamp was turned off. Then, 94 μL of H2PtCl6 solution with a concentration of 1.0 g / 100 mL was added, and after irradiation for 30 min with a 910 W (320 mW / cm2) mercury lamp, the mercury lamp was turned off. Subsequently, irradiation was performed for 90 min with a 1000 W (360 mW / cm2) mercury lamp, and the product was suction-filtered and dried to obtain a reduced graphene oxide-based palladium@platinum bimetallic core-shell structure nanocrystal composite catalyst TiO2-rGO-Pd7@Pt1 with uniform dispersion and specific crystal faces and morphology, which was sealed and stored in the dark. 2 2 2 2

[0090] The mass ratio of the palladium@platinum bimetallic core-shell structure nanocrystal in the TiO2-rGO-Pd7@Pt1 to the reduced graphene oxide-semiconductor composite base is 8:92, the mass ratio of the reduced graphene oxide to the semiconductor in the reduced graphene oxide-semiconductor composite base is 15:1, and the amount of the sacrificial reagent is 15.0 mL. The Pd seed is described in Figure 2 The 3D model, low-magnification transmission electron microscopy (TEM) image, and high-resolution TEM image of the reduced graphene oxide-based palladium@platinum bimetallic core-shell structure nanocrystal composite catalyst TiO2-rGO-Pd7@Pt1 are described in Figure 3 (a), 3(a1), and Figure 3 (a2), and it can be seen from the transmission electron microscopy images in Figure 3 (a1) and 3(a2) that the Pd7@Pt1 bimetallic core-shell heterostructure with specific morphology is uniformly distributed on the reduced graphene oxide, and it can be seen from the element and superimposed energy distribution area scanning analysis images in Figure 3 (a3)-(a5) that the layered Pt is orientedly coated on the surface of the regular Pd tetrahedral seed. Specific embodiment 2

[0092] ​​​​​​​The embodiment of the present application is based on the embodiment 1, and specifically provides a palladium-platinum bimetallic core-shell heterostructure-graphene oxide-based nanocrystal (composite catalyst) TiO2-rGO-Pd7@Pt3 and a preparation method thereof.

[0093] The reduced graphene oxide-semiconductor composite carrier TiO2(rutile)-rGO is selected.

[0094] The first metal precursor solution Pd(NH3)4Cl2 solution is selected.

[0095] The second metal precursor solution H2PtCl6 solution is selected.

[0096] 2.0 mg of TiO2(rutile) and 3.75 mL of graphene oxide solution with a concentration of 8 mg / mL are dispersed in a sample bottle containing 260.0 mL of ultrapure water for ultrasonic treatment for 15 min, and the mixed solution is transferred into a photo reactor, 15.0 mL of anhydrous methanol is added, and the whole process is magnetically stirred and argon is blown. After irradiation with a 650 W (130 mW / cm 2 ) mercury lamp for 15 min, the mercury lamp is turned off. 630.0 μL of Pd(NH3)4Cl2 solution with a concentration of 1.0 g / 100 mL is added, and after irradiation with a 910 W (320 mW / cm 2 ) mercury lamp for 30 min, the mercury lamp is turned off, and then 286.6 μL of H2PtCl6 solution with a concentration of 1.0 g / 100 mL is added, and after irradiation with a 910 W (320 mW / cm 2 ) mercury lamp for 30 min, irradiation is performed with a 1000 W (360 mW / cm 2 ) mercury lamp for 90 min, and then the composite catalyst TiO2-rGO-Pd7@Pt3 with reduced graphene oxide-based support and palladium-platinum bimetallic core-shell structure nanocrystals with specific crystal faces and morphology is obtained by suction filtration and drying, and is stored in a sealed and light-proof manner.

[0097] The mass ratio of the palladium-platinum bimetallic core-shell structure nanocrystals in the TiO2-rGO-Pd7@Pt3 and the reduced graphene oxide-semiconductor composite carrier is 10:90, the mass ratio of the reduced graphene oxide and the semiconductor contained in the reduced graphene oxide-semiconductor composite carrier is 15:1, and the amount of the sacrificial reagent is 15.0 mL. The Pd seed is described in Figure 2 , and the 3D model, low-magnification transmission electron microscopy (TEM) image and high-resolution TEM image of the reduced graphene oxide-based support palladium-platinum bimetallic core-shell structure nanocrystal composite catalyst TiO2-rGO-Pd7@Pt3 are described in Figure 4 (b), 4(b1) and Figure 4 (b2), from Figure 4(b1) and 4(b2) Transmission Electron Microscope images can be seen: Pd7@Pt3 bimetallic core-shell heterostructure with specific morphology is uniformly distributed on reduced graphene oxide, from Figure 4 (b3)-(b5) Element and superimposed energy distribution surface scanning analysis images can be seen: Peninsula layer Pt is orientedly coated on the surface of regular Pd tetrahedral seed. Specific embodiment 3

[0099] The embodiment of the application is based on embodiment 1, and specifically provides a palladium@platinum bimetallic core-shell heterostructure-reduced graphene oxide-based nanocrystal (composite catalyst) TiO2-rGO-Pd7@Pt5 and a preparation method thereof, which comprises the following steps:

[0100] Select a reduced graphene oxide-semiconductor composite base carrier: TiO2(rutile)-rGO;

[0101] Select a first metal precursor solution: Pd(NH3)4Cl2 solution;

[0102] Select a second metal precursor solution: H2PtCl6 solution;

[0103] Disperse 2.0 mg of TiO2(rutile) and 3.75 mL of graphene oxide solution with a concentration of 8 mg / mL in a sample bottle containing 260.0 mL of ultrapure water and ultrasonic for 15 min, transfer the mixed solution into a photo reactor, add 15.0 mL of anhydrous methanol, and then the whole process is magnetically stirred and argon is blown. After irradiation with a 650 W (130 mW / cm 2 ) mercury lamp for 15 min, turn off the mercury lamp. Add 644.5 μL of Pd(NH3)4Cl2 solution with a concentration of 1.0 g / 100 mL, irradiate with a 910 W (320 mW / cm 2 ) mercury lamp for 30 min, then add 488.3 μL of H2PtCl6 solution with a concentration of 1.0 g / 100 mL, irradiate with a 910 W (320 mW / cm 2 ) mercury lamp for 30 min, and then irradiate with a 1000 W (360 mW / cm 2 ) mercury lamp for 90 min, and then filter, dry to obtain a reduced graphene oxide-based supported palladium@platinum bimetallic core-shell structure nanocrystal composite catalyst TiO2-rGO-Pd7@Pt5 with uniform dispersion and specific crystal face and morphology, and store in a sealed and light-proof manner.

[0104] In the TiO2-rGO-Pd7@Pt5 composite, the mass ratio of the palladium@platinum bimetallic core-shell nanocrystals to the reduced graphene oxide-semiconductor composite is 12:88, the mass ratio of reduced graphene oxide to semiconductor in the reduced graphene oxide-semiconductor composite is 15:1, and the amount of sacrificial reagent is 15.0 mL. See Pd seed crystals for details. Figure 2 For the 3D model, low-magnification transmission electron microscope (TEM) image, and high-resolution transmission electron microscope (TEM) image of the reduced graphene oxide-supported palladium@platinum bimetallic core-shell nanocrystalline composite catalyst TiO2-rGO-Pd7@Pt5, please refer to [the original text]. Figure 5 (c), 5(c1) and Figure 5 (c2), from Figure 5 Transmission electron microscopy images (c1) and (c2) show that a specific morphology of the Pd7@Pt5 bimetallic core-shell heterostructure is uniformly distributed on the reduced graphene oxide. Figure 5 The surface scanning analysis of the (c3)-(c5) elements and superimposed energy distribution shows that: island-like Pt is oriented and coated on the surface of regular Pd tetrahedral seed crystals. Specific Implementation Example 4

[0106] The nanocrystalline (composite catalyst) obtained in Specific Examples 1, 2, and 3 above was tested for hydrogen production through electrochemical water splitting. Figure 6 The application of the reduced graphene oxide-supported palladium@platinum bimetallic core-shell heterostructure nanocrystalline catalyst prepared according to specific embodiments 1, 2, and 3 of the present invention in the electrocatalytic splitting of water to produce hydrogen is shown, and compared with palladium seed crystals and commercial platinum-carbon catalysts with the same loading. The figures include: (a) polarization curves of HER in acidic electrolyte; (b) polarization curves of HER in neutral electrolyte; (c) polarization curves of HER in alkaline electrolyte; (d) Tafel slope diagram of HER in acidic electrolyte; (e) Tafel slope diagram of HER in neutral electrolyte; (f) Tafel slope diagram of HER in alkaline electrolyte; (g) comparison of normalized mass activity per unit mass at different potentials in acidic electrolyte; (h) comparison of normalized mass activity per unit mass at different potentials in neutral electrolyte; (i) comparison of normalized mass activity per unit mass at different potentials in alkaline electrolyte; and (j) stability test diagram at a fixed potential in a full pH electrolyte.

[0107] Comparative Example 1

[0108] A palladium@platinum bimetallic core-shell heterostructure-graphene oxide-based composite catalyst TiO2-rGO-Pd7@Pt is provided. 3-U The preparation method thereof includes the following steps:

[0109] The reduced graphene oxide-semiconductor composite carrier is selected as TiO2(rutile)-rGO;

[0110] The first metal precursor solution is selected as Pd(NH3)4Cl2 solution;

[0111] The second metal precursor solution is selected as H2PtCl6 solution;

[0112] 2.0 mg of TiO2(rutile) and 3.75 mL of graphene oxide solution with a concentration of 8 mg / mL are dispersed in a sample bottle containing 260.0 mL of ultrapure water for ultrasonic treatment for 15 min, and the mixed solution is transferred into a photo reactor, 5.0 mL of anhydrous methanol is added, and the whole process is magnetically stirred and argon purged. After irradiation for 15 min with a 650 W (130 mW / cm 2 ) mercury lamp, the mercury lamp is turned off. 630.0 μL of Pd(NH3)4Cl2 solution with a concentration of 1.0 g / 100 mL is added, and after irradiation for 30 min with a 910 W (320 mW / cm 2 ) mercury lamp, the mercury lamp is turned off, and then 286.6 μL of H2PtCl6 solution with a concentration of 1.0 g / 100 mL is added, and after irradiation for 30 min with a 910 W (320 mW / cm 2 ) mercury lamp, irradiation is performed for 90 min with a 1000 W (360 mW / cm 2 ) mercury lamp, and the product is obtained by suction filtration and drying. The reduced graphene oxide-based supported palladium@platinum bimetallic core-shell structure nanocrystal composite catalyst TiO2-rGO-Pd7@Pt 3-U is obtained, and is sealed and stored in the dark.

[0113] The mass ratio of the palladium@platinum bimetallic core-shell structure nanocrystal in the TiO2-rGO-Pd7@Pt 3-U to the reduced graphene oxide-semiconductor composite base is 10:90, the mass ratio of the reduced graphene oxide and the semiconductor contained in the reduced graphene oxide-semiconductor composite base is 15:1, and the amount of the sacrificial reagent is 5.0 mL. The Pd seed is described in Figure 2 The low-magnification transmission electron microscopy (TEM) image and the high-resolution transmission electron microscopy (HRTEM) image of the reduced graphene oxide-based supported palladium@platinum bimetallic core-shell structure nanocrystal composite catalyst TiO2-rGO-Pd7@Pt 3-U are shown in Figure 6 (a) and Figure 6 (b), respectively. As can be seen from the transmission electron microscopy (TEM) images in Figure 6 (a) and Figure 6 (b), the Pd7@Pt 3-U bimetallic core-shell heterostructure with regular morphology is uniformly distributed on the reduced graphene oxide. Figure 6(c)-(f) elements and superimposed energy distribution mapping analysis diagram can be seen: by weakening the light source radiation intensity of the platinum reduction stage, the peninsula layered Pt is completely converted into the layered Pt oriented coating on the regular Pd tetrahedron seed surface. Embodiment 5

[0115] Figure 8 The application of the composite catalyst prepared according to the embodiment 2 of the present application and the comparative example 1 in the electrocatalytic decomposition of water to produce hydrogen is shown, wherein (a) is the polarization curve of HER in an acidic electrolyte, and (b) is a comparison diagram of the mass-normalized mass activity of the composite catalyst at different potentials.

[0116] Test results of the comparative electrocatalytic decomposition of water to produce hydrogen

[0117] The composite catalysts prepared in the embodiment 2 and the comparative example 1 are subjected to the comparative test of the electrocatalytic decomposition of water to produce hydrogen, and the test results are shown in Figure 8 It can be seen that the polarization curve of HER at different potentials and the mass-normalized mass activity of the composite catalyst prepared in the embodiment 2 are much higher than those of the comparative example 1, which indicates that the bimetallic core-shell heterostructure nanocrystal catalyst with the peninsula layered platinum shell coating structure is superior to the bimetallic core-shell structure nanocrystal catalyst with only the layered platinum shell coating in the electrocatalytic decomposition of water to produce hydrogen under the same loading amount.

[0118] The present application focuses on providing a preparation method and application of a reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal, which can accurately control the nucleation and platinum shell growth coating process of the palladium@platinum bimetallic core-shell heterostructure nanocrystal, prepare a reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal composite catalyst which is uniformly dispersed and has a specific crystal face and morphology, and avoid introducing additional capping reagents, surfactants, foreign ions or molecules, so as to solve the above technical problems in the prior art or related art. The palladium@platinum bimetallic core-shell heterostructure of the composite catalyst prepared by the above method has a specific crystal face and morphology and is uniformly dispersed, is simple to operate, and saves cost. The reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal can be directly used as an electrode material. Due to the synergistic effect between the palladium and platinum bimetals, the reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystal composite catalyst has good application in the electrocatalytic decomposition of water to produce hydrogen.

[0119] It should be particularly pointed out that, within the range of the components, the ratio and the process parameters described in the present application, other technical solutions obtained by specific selection can achieve the technical effects of the present application, so they will not be listed one by one. At the same time, other technical solutions obtained by using similar components such as semiconductors, metals and solvents described in the present application are included in the protection scope of the present application. In the description of the present application, the description of the terms "one embodiment", "some embodiments", "a specific embodiment" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing palladium@platinum bimetallic core-shell heterostructure nanocrystals, characterized in that, It employs a photodeposition method for the epitaxial growth of metal morphology using seed crystals. Palladium is photodeposited onto reduced graphene oxide to form metal nanocrystals with regular morphologies, which serve as seed crystals. Platinum is then photo-driven to be epitaxially coated onto the formed metal nanocrystals to form reduced graphene oxide-based supported palladium@platinum bimetallic core-shell heterostructure nanocrystals. The method includes the following steps: S610: Uniformly mix nano-semiconductor and graphene oxide solution to obtain semi-finished composite substrate solution; S620: Place the semi-finished composite substrate solution in the photoreactor, add the sacrificial reagent, stir throughout the process and introduce gas; S630: Obtaining reduced graphene oxide-semiconductor composite substrates through internal light source irradiation; S640: Add palladium metal precursor solution to reduced graphene oxide-semiconductor composite substrate to obtain semi-finished palladium seed crystals; S650: Obtain palladium tetrahedral seed crystals supported by a composite substrate by irradiating semi-finished palladium seed crystals with an internal light source; S660: Platinum metal precursor solution is added to palladium tetrahedral seed crystals supported by a composite substrate to obtain a semi-finished catalyst. S670: An internal light source irradiates a semi-finished catalyst to obtain a palladium@platinum core-shell nanocrystalline catalyst supported by a composite substrate, wherein the platinum shell is a layered, peninsula-layered, or island-layered coating layer. This preparation method requires no addition of surfactants, capping reagents, or foreign ions; The mass ratio of the palladium metal precursor solution to the platinum metal precursor solution is 7:1~3. The reduced graphene oxide-semiconductor composite substrate is prepared from reduced graphene oxide and semiconductor in a mass ratio of (15~16):

1. The palladium tetrahedral seed crystal has an exposed {111} crystal facet.

2. The method for preparing palladium@platinum bimetallic core-shell heterostructure nanocrystals according to claim 1, characterized in that, In step S620, the sacrificial reagent is at least one of methanol, ethanol, and lactic acid, and the amount used is from 0.0 mL to 20.0 mL. The entire stirring process is performed using magnetic stirring at a speed of 1000-2000 rpm. At least one inert gas, consisting of argon and nitrogen, is introduced into the photoreactor.

3. The method for preparing palladium@platinum bimetallic core-shell heterostructure nanocrystals according to claim 1, characterized in that, In steps S630, S650, and S670, the controlled light source includes either a mercury lamp or a xenon lamp; the irradiation time of the controlled light source is 10 to 120 minutes; the power of the controlled light source is 500 W to 1000 W; and the illuminance of the controlled light source is 100 mW / cm². 2 Up to 360 mW / cm 2 .

4. The method for preparing palladium@platinum bimetallic core-shell heterostructure nanocrystals according to claim 1, characterized in that, The nano-semiconductor in step S640 includes at least one of TiO2, ZnO, ZrO2, CeO2, and g-C3N4; the metal precursor solution in step S640 includes one of Pd(NH3)4Cl2 or an aqueous solution of PdCl2; the mass ratio of the metal in the metal precursor solution to the reduced graphene oxide-semiconductor composite group is 7:(90~92).

5. A palladium@platinum bimetallic core-shell heterostructure nanocrystal, characterized in that: It is prepared by the method of any one of claims 1 to 4, which is a palladium@platinum bimetallic core-shell heterostructure nanocrystal synthesized by controllable photodeposition on reduced graphene oxide. The crystals are uniformly dispersed on the reduced graphene oxide and have specific morphology and thermodynamically stable exposed crystal faces.

6. The palladium@platinum bimetallic core-shell heterostructure nanocrystal according to claim 5, characterized in that: It has a specific morphology and exposed crystal faces, specifically: (a) Pd7@Pt1 bimetallic nanocrystals are tetrahedra with exposed {111} crystal planes, and the Pt shell is a layered coating layer. (b) Pd7@Pt3 bimetallic nanocrystals are tetrahedrons with exposed {111} crystal planes, and the Pt shell is a peninsula-like layered coating. (c) Pd7@Pt5 bimetallic nanocrystals are tetrahedrons with exposed {111} crystal planes, and the Pt shell is an island-like layered coating.

7. An application of palladium@platinum bimetallic core-shell heterostructure nanocrystals, wherein the palladium@platinum bimetallic core-shell heterostructure nanocrystals according to any one of claims 5 to 6 are used as electrode materials.

8. An application of palladium@platinum bimetallic core-shell heterostructure nanocrystals, wherein the palladium@platinum bimetallic core-shell heterostructure nanocrystals according to any one of claims 5 to 6 are used as carbon-based composite catalysts for electrocatalytic water splitting to produce hydrogen.

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