阅读说明：本技术 一种利用多羟基醛酮还原制备低贵金属壳层催化剂及其制备方法 (Low-noble metal shell catalyst prepared by reduction of polyhydroxy aldehyde ketone and preparation method thereof ) 是由 赵卿 王诚 王建龙 孙连国 张泽坪 于 2019-10-09 设计创作，主要内容包括：本发明属能源催化技术领域,尤其涉及一种利用多羟基醛酮还原制备低贵金属壳层催化剂及其制备方法。本发明提供了一种低贵金属壳层合金催化剂和方法。本发明催化剂制备步骤如下：1)将核心金属离子鳌合分散,冷冻稳定；加入还原剂结合,进一步冷冻处理,获得还原性前驱体；2)碳载体超声分散在表面活性剂稳定的溶液里,加入还原性前驱体,升温还原,制备核心金属；3)进行稳定金属过渡层的包覆；4)壳层金属的多羟基醛酮还原；5)晶体陈化生长；6)离心干燥热处理。所获得的催化剂具有优于商业化Pt/C的氧还原活性,制备方法简单,在氧还原催化体系、电催化和燃料电池等领域具有重要价值。(The invention belongs to the technical field of energy catalysis, and particularly relates to a low-noble metal shell catalyst prepared by reduction of polyhydroxy aldehyde ketone and a preparation method thereof. The invention provides a low-noble metal shell alloy catalyst and a method. The preparation steps of the catalyst are as follows: 1) chelating and dispersing core metal ions, and freezing for stabilization; adding a reducing agent for combination, and further freezing to obtain a reducing precursor; 2) ultrasonically dispersing a carbon carrier in a solution with stable surfactant, adding a reducing precursor, and heating for reducing to prepare a core metal; 3) coating a stable metal transition layer; 4) reducing polyhydroxy aldehyde ketone of shell metal; 5) aging and growing the crystal; 6) and (4) centrifugal drying and heat treatment. The obtained catalyst has oxygen reduction activity superior to that of commercial Pt/C, is simple in preparation method, and has important value in the fields of oxygen reduction catalytic systems, electrocatalysis, fuel cells and the like.)

1. A low platinum shell alloy catalyst is characterized in that the carbon atom percentage in the catalyst is 80-93 at.%, and the O element atom percentage is 7-20 at.%; the Pt loading on the surface is 5-18 wt.%, the metal particle size is 0.5-5 nm, and the cluster size is 8-20 nm.

2. A method for preparing a low-noble metal shell catalyst by using polyhydroxy aldehyde ketone reduction is characterized by comprising the following steps:

(1) preparing a core metal ion reductive precursor;

(2) heating and reducing core metal;

(3) preparing a stable metal transition coating layer;

(4) reducing the metal polyhydroxy aldehyde ketone of the shell layer;

(5) aging and growing the crystal;

(6) and (6) heat treatment.

3. The method of claim 2, wherein step (1) comprises stabilizing the core metal ions by chelating with polyhydroxy organic compounds at a low temperature, adding a reducing agent for the core ions at a low temperature after the stabilizing treatment at a low temperature, and further treating at a low temperature to obtain the pre-reduced reducing precursor.

4. The method according to claim 3, wherein the step (1) comprises stabilizing at a reaction temperature of-10 to 10 ℃ for 20 to 100min, and further stabilizing at a low temperature of-10 to 3 ℃ for 20 to 100 min.

5. The method of claim 2, wherein step (2) comprises dispersing the carbon support in a surfactant-stabilized solution by sonication, adding the pre-reduced reducing precursor, and reducing at elevated temperature.

6. The method of claim 2, wherein step (3) comprises adding a strong oxidatively stable metal to produce the transition cladding layer by displacement.

7. The method of claim 2, wherein step (4) comprises adding a strongly oxidizing shell metal to produce a stable active shell structure under the action of a polyhydroxy aldehyde ketone reducing agent.

8. The method of claim 2, wherein step (5) comprises adjusting the pH of the solution and performing crystal-aging growth under constant-temperature heat treatment conditions.

9. The method as claimed in claim 2, wherein the step (6) comprises centrifuging, drying to obtain the catalyst to be treated, and performing high-temperature heat treatment to obtain the product.

10. The method of any of claims 2-9, wherein the core metal ions are soluble ions of a 3d, 4d non-noble metal transition element; the polyhydroxy organic chelating agent is one or more selected from pectin, xylitol, sucrose, lignin, coumaryl alcohol, coniferyl alcohol, sinapyl alcohol, pentaerythritol and polyethylene glycol; the core ion reducing agent is selected from NaBH₄、KBH₄、LiAlH₄And one or more of hydrazine.

Technical Field

The invention belongs to the technical field of energy catalysis, and particularly relates to a low-noble metal shell catalyst prepared by reduction of polyhydroxy aldehyde ketone and a preparation method thereof.

Background

Energy and environmental problems are important problems influencing world development at present, and the efficient utilization of renewable energy is an important development direction for realizing sustainable development of energy and effectively solving the problem of environmental pollution. Hydrogen is the most widely distributed substance in the universe and is a clean secondary energy source. Hydrogen energy in the 21 st century becomes a very important clean energy form on the world energy stage, and the development and utilization of the hydrogen energy are bound to be concerned (jin-Xiao Tang et al, j. mater. chem.a, 2018). The hydrogen has the advantages of high combustion heat value, no pollution of products, rich resources and sustainable utilization. Hydrogen fuel cells are an important hydrogen energy utilization device, which can realize clean and efficient conversion of hydrogen energy, but their widespread use is limited by the oxygen reduction reaction of the fuel cell cathode lag, which requires the use of a large amount of expensive platinum catalyst (Xiao Xia Wang et al, naturecatalyst, 2019). Research shows that the catalytic efficiency can be effectively improved by regulating and controlling the microstructure of the platinum-based alloy catalyst (Falk Muench et al, catalysis, 2018).

Classical electrocatalysis theory shows that the excellent ORR catalyst has moderate oxygen binding energy, and the control of the stress on the surface of the catalyst is one of the effective ways to regulate and control the oxygen binding energy (Mingchuan Luo et al, nature reviews materials, 2017). For most Pt bimetallic catalysts, there are generally several structural relationships that dominate the performance of the catalyst, namely ligand effect, electronic effect, stress effect, synergistic effect. Stress effects between different metals are one of the currently known means of effective and controllable regulation of catalytic properties (Jianping Lai et al, Small, 2017). Compared with the synergistic effect and the electronic effect, the stress effect has wider action range, thereby being capable of existing in the complex operation environment of the electrocatalyst for a long time and having very high practical application value. When the metal surface is compressed or stretched, the center position of the d-band of the metal surface is correspondingly changed, so that the adsorption bond energy of the metal surface to oxygen or oxygen-containing intermediates is influenced. The stress regulation and control means of the metal surface comprises: preparing a core-shell structure catalyst, wherein a metal interface generates compressive stress on metal with a larger lattice constant and generates tensile stress on metal with a smaller lattice constant; polycrystalline metal catalysts were prepared (Kezhu Jiang et al, sci. adv., 2017). Compared to single crystal structures, polycrystals have unique grain boundaries to mitigate excessive specific surface energies while altering the stress distribution at their surface (LingzhengBu et al, adv.mater, 2015); and introducing external force to introduce stress to the metal catalyst on the surface of the metal catalyst. The expansion and compression phenomena generated when the electrode material is embedded and removed. The polycrystalline grain boundaries have obvious influence on the surface stress distribution and the catalytic activity, and a high-activity alloy catalyst can be prepared, so that the cost is reduced, and the commercialization progress of a fuel cell is promoted (Wei Wang et al, adv. It is an effective means to adjust the crystal face stress between nano particles to improve the metal catalytic ability and electrochemical reaction conversion efficiency (Mufan Li et al, science, 2016). Therefore, the preparation of the alloy shell-core structure catalyst has important significance.

Disclosure of Invention

Technical problem to be solved by the invention

The oxygen reduction activity of the catalyst is one of the key factors determining the performance of the hydrogen fuel cell, the ORR catalyst with excellent performance needs to have relatively moderate oxygen binding energy, and generally, the control of the stress on the surface of the catalyst is one of the effective ways for regulating the oxygen binding energy and the catalytic activity of the catalyst. Therefore, alloying and preparing a catalyst with a shell-core structure are important research directions. The invention aims to provide a technology for preparing a low-noble metal shell catalyst by a polyhydroxy aldehyde ketone reduction method.

Means for solving the technical problem

Aiming at the problems, the invention provides a low-noble metal shell alloy catalyst and a method.

According to one embodiment of the invention, a low platinum shell alloy catalyst is provided, wherein the carbon atom percentage in the catalyst is 80 to 93 at.%, and the oxygen atom percentage in the catalyst is 7 to 20 at.%; the Pt loading on the surface is 5-18 wt.%, the metal particle size is 0.5-5 nm, and the cluster size is 8-20 nm.

According to a second aspect of the present invention, there is provided a method for preparing a low noble metal shell catalyst by reduction of a polyhydroxy aldehyde ketone, comprising the steps of:

(1) preparing a core metal ion reductive precursor;

(2) heating and reducing core metal;

(3) preparing a stable metal transition coating layer;

(4) reducing the metal polyhydroxy aldehyde ketone of the shell layer;

(5) aging and growing the crystal;

(6) and (6) heat treatment.

In one embodiment, step (1) comprises stabilizing the core metal ions by chelating with polyhydroxy organic compounds at low temperature, adding reducing agent for the core ions at low temperature after stabilizing at low temperature, and further treating at low temperature to obtain the pre-reduced reducing precursor.

One embodiment is that the step (1) comprises stabilizing at-10 deg.C for 20-100 min, and further stabilizing at-10-3 deg.C for 20-100 min.

In one embodiment, the step (2) comprises dispersing the carbon carrier in a surfactant-stabilized solution by ultrasonic waves, adding the pre-reduced reducing precursor, and heating for reduction.

In one embodiment, step (3) comprises adding a strong oxidatively stable metal to produce the transition cladding by displacement.

In one embodiment, step (4) comprises adding a strongly oxidizing shell metal to prepare a stable active shell structure under the action of a polyhydroxy aldehyde ketone reducing agent.

In one embodiment, the step (5) comprises adjusting the pH value of the solution, and performing crystal aging growth under the condition of constant-temperature heat treatment.

In one embodiment, the step (6) comprises centrifuging, drying to obtain the catalyst to be treated, and performing high-temperature heat treatment to obtain the product.

In one embodiment, the core metal ions are soluble ions of 3d, 4d non-noble metal transition elements; the organic chelating agent is selected from pectin, xylitol, sucrose, lignin, coumaryl alcohol, coniferyl alcohol, sinapyl alcohol, pentaerythritol, and polyethylene glycolOne or more of (a); the core ion reducing agent is selected from NaBH₄、KBH₄、LiAlH₄And one or more of hydrazine. In the image forming apparatus according to the first aspect,

the invention has the advantages of

The invention relates to a low-noble metal shell catalyst prepared by a polyhydroxy aldehyde ketone reduction method. Firstly, chelating and dispersing core metal ions to obtain a loaded pre-reduction reducing precursor; then, heating to reduce the precursor to prepare dispersed non-noble metal nuclei; then, coating a stable metal transition layer; then polyhydroxy aldehyde ketone reduction of shell metal is carried out; controlling the pH value of the system, and carrying out crystal aging growth; finally, the high-performance catalyst is obtained by heat treatment. The catalyst has the advantages of simple preparation method, easily controlled preparation conditions, easily amplified reaction system and wide application prospect in the fields of fuel cells and oxygen reduction catalysis.

(2) The isoelectrochemical test proves that the catalyst has high-efficiency ORR catalytic performance, can be comparable to commercial Pt/C catalysts, and has important significance for reducing the cost of the catalyst and reducing the use of noble metals such as Pt and the like.

(3) A series of physical representations prove that the catalyst is a cluster-shaped structure which is formed by further self-assembling alloy nanoparticles and has high activity and good stability, the consumption of noble metal of the catalyst is low, the shell layer coating microstructure increases the exposed area of the noble metal, and the utilization rate of the noble metal is improved.

In a word, the low platinum shell alloy catalyst is prepared by a method for controlling reduction by a polyhydroxy aldehyde ketone reducing agent, and the low platinum shell alloy catalyst shows excellent oxygen reduction activity and electrocatalytic performance under an acidic condition.

Further features of the present invention will become apparent from the following description of exemplary embodiments.

Drawings

FIGS. 1(a) - (c) are low magnification TEM topography of the catalyst prepared in example 1 of the present invention. (a) And (b) and (c) observing the morphology graph of the catalyst at different magnifications.

Figure 2 is an XRD pattern of the catalyst prepared in example 1 of the present invention.

FIGS. 3(a) - (d) are XPS plots of catalysts prepared according to example 1 of the present invention, with a surface carbon percentage of 85.75 atomic percent, 12.73 atomic percent O, 0.78 atomic percent Pt, and 0.74 atomic percent Ni. (a) C1s peak processing graph; (b) o1s peak processing plot; (c) pt4f peak processing diagram; (d) a peak processing graph of Ni2 p; .

FIGS. 4(a) - (b) are test charts of electrochemical performance of catalysts prepared in example 1 of the present invention; (a) cyclic voltammogram; (b) oxygen reduction comparative plot.

FIGS. 5(a) - (b) are comparative plots of electrochemical activity of conditioned experimental samples of catalysts prepared in examples 2, 3 of the present invention; (a) cyclic voltammetry versus (b) oxygen reduction versus.

FIG. 6 core metal ion reductive precursor preparation state, no significant metal precipitation;

Detailed Description

One embodiment of the present disclosure will be specifically described below, but the present disclosure is not limited thereto.

The surface element analysis of the low platinum shell alloy catalyst prepared by the method is as follows: the surface carbon atom percentage is 80-93 at.%, and the O element atom percentage is 7-20 at.%; the Pt loading on the surface is 5-18 wt.%, the metal particle size is 0.5-5 nm, and the cluster size is 8-20 nm. The catalyst has low Pt consumption and superior oxygen reduction activity to commercial Pt/C catalyst, and has important significance for reducing the catalyst cost and reducing the use of noble metals such as Pt and the like. The percentage of total doped metal on the surface of the catalyst is 0.1-3 at.%.

According to the method for preparing the low-noble-metal shell catalyst by utilizing the polyhydroxy aldehyde ketone for reduction, the catalyst is further self-assembled by alloy nano particles, a cluster structure with high activity and good stability exists, the using amount of noble metal of the catalyst is low, the exposed area of the noble metal is increased by a shell coating microstructure, the utilization rate of the noble metal is improved, and the specific preparation steps of the catalyst are as follows:

1) pre-reducing core metal ions: stabilizing the core metal ions through the chelating action of polyhydroxy organic matters, freezing, adding a reducing agent of the core ions, and further processing at low temperature to obtain a pre-reduced reducing precursor; the reaction temperature is-10 ℃, the pre-cooling treatment time is 20-100 min, the further freezing treatment temperature is-10-3 ℃, and the further freezing treatment time is 20-100 min;

2) heating and reducing core metal: dispersing a carbon carrier in a solution with stable surfactant by ultrasonic, dripping the pre-reduced reducing precursor, and heating for reduction; the ultrasonic treatment time is 30-90 min, the temperature rise reduction reaction temperature is 60-130 ℃, and the reaction time is 0.5-3 h;

3) preparing a stable metal transition coating layer: adding a metal with strong oxidizing property and stability, and preparing a transition coating layer by replacement; the reaction temperature in the replacement coating process is 60-130 ℃, and the reaction time is 0.5-3 h;

4) reducing the shell metal polyhydroxy aldehyde ketone: adding shell metal with strong oxidizing property, and preparing a stable active shell structure under the action of a polyhydroxy aldehyde ketone reducing agent; the reduction reaction temperature of polyhydroxy aldehyde ketone is 60-130 ℃, and the reaction time is 1-6 h;

5) aging and growing of crystals: adjusting the pH value of the solution, and carrying out crystal aging growth under the condition of constant-temperature heat treatment; performing aging growth and hydrothermal crystallization of metal, wherein the reaction temperature is 60-120 ℃, and the growth time is 8-16 h;

6) and (3) heat treatment: centrifuging and drying to obtain the catalyst to be treated, and carrying out high-temperature heat treatment to obtain the product. The drying temperature is 40-100 ℃, and the drying time is 6-16 h; the high-temperature treatment temperature ranges from 200 ℃ to 550 ℃, the high-temperature treatment time is 1-6 h, and the temperature rise speed is 1-10 ℃/min.

Further, the core metal ions are soluble ions of 3d and 4d non-noble metal transition elements, such as: fe. Soluble ionic salts of Co, Ni, Cu, Zn, Mn, Mo, Zr, Sn, Ce and other elements; the polyhydroxy organic chelating agent is one or more of hydroxyl-rich organic substances such as pectin, xylitol, sucrose, lignin, coumaryl alcohol, coniferyl alcohol, sinapyl alcohol, pentaerythritol, polyethylene glycol, etc.; the core ion reducing agent comprises one or more of NaBH4, KBH4, LiAlH4, hydrazine and other fast reducing agents to obtain a pre-reduced reducing precursor;

the concentration of the core metal ions is 0.01-0.15 mol/L, and the addition amount is 2-20 vt%; the adding amount of the chelating polyhydroxy organic matter is 0.01-0.1 wt.%; the volume of the dispersing solvent is 30-60 vt%; the addition amount of the pre-reducing agent is 0.01-0.1 wt.%, and the addition amount of the alkali is 0.01-0.1 wt.%;

further, the supported carbon carrier is one or more of high-conductivity and high-specific-surface-area carbon conductive carbon materials such as Vulcan XC-72, Ketjenblack, BP2000, EC300J, acetylene black, carbon nanotubes and graphene; the stabilizing surfactant is one or more of polyacrylamide, acrylamide, P123, F127, PVP, CTAB, CTAC, polyethylene glycol or polyethylene oxide. The addition amount of the carbon carrier is 0.03-0.1 wt.%; the addition amount of the surfactant is 0.01-0.1 wt.%;

further, the strong oxidizing metal ions for preparing the transition coating layer are from AgF and AgNO₃、AgClO₄、Na₂PdCl₄、(NH₄)₂PdCl₆、PdCl₂One or more of strongly oxidizing noble metal ions such as chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, chloroiridic acid, chloroauric acid, iridium chloride, ruthenium chloride and the like; the ion concentration of the coating layer is 0.005-0.1 mol/L, and the addition amount is 2-10 mL;

furthermore, the added shell metal with strong oxidizing property is the same as the transition coating metal or has stronger ionic oxidizing property, and is one or more of high-activity and high-stability noble metal strong oxidizing ions such as chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, chloroiridic acid, chloroauric acid, iridium chloride and the like; the polyhydroxy aldone reducing agent is mainly selected from one or more of hydroxy aldone-rich organic substances such as glucose, mannose, allose, aldosterone, maltose, pyranose, cinnamaldehyde, vanillin, citral, citronellal, hydroxycitronellal, perillaldehyde, furfural, benzaldehyde, formaldehyde, acetaldehyde, hydroxyacetaldehyde, vitamins, oxalic acid, sodium citrate, citric acid, etc.; the concentration of the metal ions of the strong oxidizing shell is 0.005-0.1 mol/L, and the addition amount is 2-10 vt%; the adding amount of the reducing polyhydroxy aldehyde ketone is 0.5-3 wt.%;

the reagent for adjusting the pH value of the solution is ammonia water, NaOH, KOH or K₂CO₃、KHCO₃、Na₂CO₃、NaHCO₃One or more of common inorganic alkali such as ammonium carbonate; adjusting the pH range to 8-14;

further, the heat treatment atmosphere is a reducing atmosphere, and the adopted protective gas is H₂、CO、NH₃Or H₂、CO、NH₃And N₂、Ar、CO₂One or more of mixed gas of He and the like;

the shell oxygen reduction catalyst is prepared by reducing polyhydroxy aldehyde ketone organic matters, the carrying range of metal components is 2-40%, and the mass fraction of carbon carriers is 60-98%. The noble metal shell catalyst prepared by the polyhydroxy aldehyde ketone reduction method is a catalyst with a spherical cluster structure formed by aggregating small alloy nano particles, has better catalytic activity and stability, and has electrocatalytic performance superior to oxygen reduction activity of commercial Pt/C.