Simple preparation method of high-performance low-Pt-loading oxygen reduction / hydrogen evolution bifunctional electrocatalyst

Abstract

The invention relates to the field of fuel cell catalysts, and provides a preparation method of a high-performance low-Pt-loading bifunctional electrocatalyst which can be used as a key electrochemical reaction of a fuel cell and a metal-air cell, namely an oxygen reduction reaction and a hydrogen evolution reaction of electrolyzed water. The preparation method comprises the following steps: firstly, preparing a non-noble metal and / or non-metal doped small-size carbon-based carrier material with rich defect structures by combining a hydrothermal method with a high-temperature pyrolysis method, wherein the rich defect structures and highly dispersed heteroatoms provide a large number of anchoring sites for subsequent Pt loading; on the basis, a small amount of Pt is loaded on the carbon-based carrier through a rapid chemical reduction method, and the well-dispersed loaded low-Pt catalyst material with the particle size being only 2 nm is obtained. The catalyst shows excellent bifunctional catalytic activity due to the synergistic effect of rich catalytic active sites and different active sites. The invention provides a simple and feasible method for preparing the multifunctional catalyst which saves precious metal, is low in cost and has high performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a simple preparation method of a high-performance, low-Pt-loaded bifunctional electrocatalyst that can be used for oxygen reduction reactions in fuel cells and metal-air batteries, as well as electrolysis of water to produce hydrogen. Background Art

[0002] New generation energy storage and conversion devices such as fuel cells, metal-air batteries and water electrolysis for hydrogen production have gradually developed into promising new energy technologies due to their advantages such as easy availability of raw materials, high energy density, clean and environmentally friendly. The application of these new energy technologies involves two key electrochemical reactions - oxygen reduction and hydrogen evolution reaction. How to effectively catalyze these processes on the electrode surface to obtain the lowest overpotential and the highest current density to ensure the efficient output performance of energy conversion technology is an important scientific issue. At present, oxygen reduction / hydrogen evolution reactions usually use highly active precious metal Pt-based catalysts. How to improve the utilization rate of Pt, reduce the amount of Pt used and thus reduce the catalyst cost is of great significance to promote the development of clean energy technology.

[0003] Carbon-supported Pt (Pt / C or PtM / C) is currently the most important Pt-based electrocatalyst. This type of catalyst is obtained by loading Pt or Pt-based alloys onto carbon carrier materials with high specific surface area. Among them, the type of carbon-based carrier material and the reduction method of the Pt precursor have an important influence on the dispersion degree, electronic / geometric structure, and Pt-C interaction of the active component Pt, and are the key control factors for obtaining low-Pt and high-efficiency electrocatalysts.

[0004] Studies have shown that using the high specific surface area and highly dispersed heteroatoms of carbon-based carrier materials as anchoring sites is an effective method to achieve good dispersion of Pt, but the preparation process of such carbon materials is usually cumbersome. Here we provide a simple method to obtain highly dispersed heteroatom-doped small-sized carbon-based carrier materials with rich defects, which provides conditions for promoting good dispersion of Pt particles.

[0005] Compared with other reduction methods, the liquid phase chemical reduction method for preparing supported Pt-based catalysts requires relatively simple equipment conditions, relatively mild reaction conditions, strong controllability, and is easier to achieve large-scale production. Sodium borohydride is often used as a reducing agent in this method, but the uniformity of the resulting catalyst is poor and the performance is not ideal. Through our exploration, we found that by shortening the reaction time of sodium borohydride reduction, the growth degree of Pt particles can be controlled, and a high-performance, low Pt-loaded oxygen reduction / hydrogen evolution bifunctional electrocatalyst material with small and uniformly distributed Pt particles can be obtained. Summary of the invention

[0006] The present invention aims to overcome the shortcomings of the prior art and provide a method for preparing a high-efficiency, low-Pt-loaded oxygen reduction / hydrogen evolution bifunctional electrocatalyst. The platinum nanoparticle catalyst prepared by the method has high catalytic activity, simple reaction operation, low production cost, and can be mass-produced. To achieve the above purpose, the technical solution adopted by the present invention includes the following steps.

[0007] 1) The carbon precursor (and non-precious metal salt) is prepared into a solution of a certain concentration and ultrasonically stirred to obtain a uniform precursor solution.

[0008] 2) The precursor solution is transferred to a reactor for hydrothermal reaction, and the product is dried to obtain a carrier precursor.

[0009] 3) The carrier precursor is subjected to high-temperature pyrolysis under the protection of an inert atmosphere to obtain a heteroatom-doped composite carbon-based carrier material.

[0010] 4) The platinum precursor is prepared into a solution of a certain concentration, and stirred and ultrasonicated to obtain a uniform platinum precursor solution.

[0011] 5) A certain amount of composite carbon-based carrier material is dispersed in a Pt metal precursor solution, and after sufficient stirring, sodium borohydride rapid reduction is performed at room temperature to obtain a reaction product, and the reaction product is filtered, washed and dried to obtain a final catalyst product.

[0012] As a further preferred embodiment, the carbon precursor used in step (1) is one or two of chitosan, glucose, citric acid, and ascorbic acid, which are stirred until completely dissolved. The concentration of the carbon precursor solution is 1 g / L to 100 g / L.

[0013] As a further preferred embodiment, the method specifically comprises the following steps: (1) the metal in the non-precious metal salt precursor is one of Fe, Co, Ni, Cu and Mn.

[0014] Preferably, the non-precious metal salt is one of the hydrochloride, nitrate and acetate of Fe, Co, Ni, Cu and Mn.

[0015] As a further preferred embodiment, the method specifically comprises: step (2) transferring the precursor solution to a reaction kettle for hydrothermal reaction, wherein the reaction temperature is 120°C to 200°C and the reaction time is 10 h to 24 h.

[0016] As a further preferred embodiment, the method specifically comprises: step (3) pyrolyzing the carrier precursor under the protection of an inert atmosphere at high temperature, wherein the inert gas is N2 or Ar, the heating rate is 1 to 10 °C / min, the heating temperature is 500 °C to 1000 °C, and the reaction time is 0.5 h to 8 h.

[0017] As a further preferred embodiment, the platinum precursor solution used in step (4) has a solvent selected from the group consisting of methanol, ethanol, isopropanol and ethylene glycol, and is ultrasonically treated until the solution is completely dissolved.

[0018] As a further preferred embodiment, the method specifically includes: in step (4), the platinum precursor is one of Pt(acac)2, K2PtCl6, K2PtCl4, and H2PtCl6, and the concentration of the platinum precursor solution is 0.1 g / L to 20 g / L.

[0019] As a further preferred embodiment, the method specifically comprises the following steps: Step (5) dispersing a certain amount of the composite carbon-based carrier material obtained by pyrolysis in a Pt metal precursor solution, wherein the Pt loading amount is 1 wt% to 5 wt%.

[0020] As a further preferred embodiment, the method specifically comprises: step (5) performing rapid reduction of sodium borohydride at room temperature to obtain a reaction product, wherein the concentration of the sodium borohydride solution is 0.01 mol / L to 5 mol / L, and the reaction time is 1 s to 600 s.

[0021] The beneficial effects of the present invention are mainly reflected in the use of small-sized, defect-rich and highly dispersed heteroatom-containing carbon carrier materials, which provide a large number of anchoring sites for the Pt active component, which is conducive to its good dispersion and increases the catalyst performance at a lower metal loading. At the same time, sodium borohydride is used for rapid reduction to control the particle size of the nanoparticles. The shorter reaction time is conducive to the rapid nucleation of Pt and the growth process is limited, so as to obtain small-sized and uniformly distributed Pt particles and improve the catalyst performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 (a) and Figure 1 (b) is the TEM images of the catalyst samples prepared in Example 1 and Example 2, respectively, and the corresponding Pt nanoparticle size distribution diagram.

[0023] Figure 2 The LSV curves of the catalyst samples prepared in Example 1 and Example 2 in an O2-saturated 0.1 M KOH solution are shown in Figure 1. The electrochemical test conditions are: a linear scan rate of 5 mV / s, a potential scan range of 0.0 V to 1.0 V, a negative scan, and a rotating disk electrode speed of 1600 rpm.

[0024] Figure 3 The LSV curves of HER were measured in a 1 M KOH solution saturated with N2 using the catalysts prepared in Example 1 and Example 2. The electrochemical test conditions were: a linear scan rate of 5 mV / s, a potential scan range of -1 V to 0 V, and a negative scan. Implementation Example 1

[0025] Accurately weigh 1 g of chitosan and 1 g of citric acid and dissolve them in 20 mL of distilled water. Stir them ultrasonically to obtain a uniform precursor solution.

[0026] The precursor solution was transferred to a reactor and subjected to hydrothermal reaction at 160 °C for 10 h. After the product was dried, a carrier precursor was obtained.

[0027] The carrier precursor was placed under N2 atmosphere and heated at 900 °C for 2 h at a heating rate of 5 °C / min to obtain a pyrolysis product.

[0028] Accurately weigh 1 g of H2PtCl6 and dissolve it in 20 mL of ethylene glycol to prepare chloroplatinic acid solution.

[0029] Accurately weigh 50 mg of the pyrolysis product, disperse it in 30 mL of distilled water, add 0.35 mL of chloroplatinic acid solution and stir thoroughly, then quickly add 2 mL of freshly prepared 0.1 M sodium borohydride solution at room temperature, and quickly reduce it for 15 s to obtain the reaction product. The reaction product is filtered, washed and dried to obtain the final catalyst product, and the theoretical Pt loading of the product is 5 wt%. Example 2

[0030] Accurately weigh 1 g of chitosan, 1 g of citric acid and 40 mg of NiCl2 and dissolve them in 20 mL of distilled water. Stir ultrasonically to obtain a uniform precursor solution.

[0031] The precursor solution was transferred to a reactor and subjected to hydrothermal reaction at 160 °C for 10 h. After the product was dried, a carrier precursor was obtained.

[0032] The carrier precursor was placed under N2 atmosphere and heated at 900 °C for 2 h at a heating rate of 5 °C / min to obtain a pyrolysis product.

[0033] Accurately weigh 1 g of H2PtCl6 and dissolve it in 20 mL of ethylene glycol to prepare chloroplatinic acid solution.

[0034] Accurately weigh 50 mg of the pyrolysis product, disperse it in 30 mL of distilled water, add 0.35 mL of chloroplatinic acid solution and stir thoroughly, then quickly add 2 mL of freshly prepared 0.1 M sodium borohydride solution at room temperature, and quickly reduce it for 15 s to obtain the reaction product. The reaction product is filtered, washed and dried to obtain the final catalyst product, and the theoretical Pt loading of the product is 5 wt%. Example 3

[0035] Accurately weigh 1 g of chitosan, 1 g of citric acid and 60 mg of CoCl2 and dissolve them in 20 mL of distilled water. Stir ultrasonically to obtain a uniform precursor solution.

[0036] The precursor solution was transferred to a reactor and subjected to hydrothermal reaction at 160 °C for 10 h. After the product was dried, a carrier precursor was obtained.

[0037] The carrier precursor was placed under N2 atmosphere and heated at 900 °C for 2 h at a heating rate of 5 °C / min to obtain a pyrolysis product.

[0038] Accurately weigh 1 g of H2PtCl6 and dissolve it in 20 mL of ethanol to prepare chloroplatinic acid solution.

[0039] Accurately weigh 50 mg of the pyrolysis product, disperse it in 30 mL of distilled water, add 0.21 mL of chloroplatinic acid solution and stir thoroughly, then quickly add 2 mL of freshly prepared 0.1 M sodium borohydride solution at room temperature, and quickly reduce it for 300 s to obtain the reaction product. The reaction product is filtered, washed and dried to obtain the final catalyst product, and the theoretical Pt loading of the product is 3 wt%.

[0040] Example 4 Accurately weigh 2 g of chitosan, 2 g of ascorbic acid and 200 mg of Cu(AC)2 and dissolve them in 50 mL of distilled water. Stir ultrasonically to obtain a uniform precursor solution.

[0041] The precursor solution was transferred to a reactor and subjected to hydrothermal reaction at 180 °C for 6 h. After the product was dried, a carrier precursor was obtained.

[0042] The carrier precursor was placed under N2 atmosphere and heated at 800 °C for 2 h at a heating rate of 5 °C / min to obtain a pyrolysis product.

[0043] Accurately weigh 1 g of K2PtCl6 and dissolve it in 20 mL of ethanol to prepare chloroplatinic acid solution.

[0044] 50 mg of the pyrolysis product was accurately weighed and dispersed in 30 mL of distilled water. 0.1 mL of chloroplatinic acid solution was added and stirred thoroughly. Then, 2 mL of freshly prepared 0.2 M sodium borohydride solution was quickly added at room temperature and the reaction product was quickly reduced for 60 s. The reaction product was filtered, washed and dried to obtain the final catalyst product, with a theoretical Pt loading of 1 wt%.

[0045] Example 5 Accurately weigh 1 g of chitosan, 1 g of citric acid, and 60 mg of MnCl2 and dissolve them in 20 mL of distilled water. Stir ultrasonically to obtain a uniform precursor solution.

[0046] The precursor solution was transferred to a reactor and subjected to hydrothermal reaction at 160 °C for 10 h. After the product was dried, a carrier precursor was obtained.

[0047] The carrier precursor was placed under N2 atmosphere and heated at 900 °C for 2 h at a heating rate of 5 °C / min to obtain a pyrolysis product.

[0048] Accurately weigh 1 g of K2PtCl6 and dissolve it in 20 mL of ethylene glycol to prepare chloroplatinic acid solution.

[0049] 50 mg of the pyrolysis product was accurately weighed and dispersed in 30 mL of distilled water. 0.2 mL of chloroplatinic acid solution was added and stirred thoroughly. Then, 2 mL of freshly prepared 1 M sodium borohydride solution was quickly added at room temperature and the reaction product was quickly reduced for 500 s. The reaction product was filtered, washed and dried to obtain the final catalyst product with a Pt loading of 2 wt%.

[0050] Example 6 Accurately weigh 10 g of chitosan, 10 g of ascorbic acid and 500 mg of Co(NO3)2 and dissolve them in 180 mL of distilled water, stirring with ultrasound to obtain a uniform precursor solution.

[0051] The precursor solution was transferred to a reactor and subjected to hydrothermal reaction at 160 °C for 10 h. After the product was dried, a carrier precursor was obtained.

[0052] The carrier precursor was placed under N2 atmosphere and heated at 900 °C for 3 h at a heating rate of 2 °C / min to obtain a pyrolysis product.

[0053] Accurately weigh 1 g of H2PtCl6 and dissolve it in 20 mL of ethylene glycol to prepare chloroplatinic acid solution.

[0054] 100 mg of the pyrolysis product was accurately weighed and dispersed in 80 mL of distilled water. 0.35 mL of chloroplatinic acid solution was added and stirred thoroughly. Then, 2 mL of freshly prepared 2 M sodium borohydride solution was quickly added at room temperature and the reaction product was quickly reduced for 600 s. The reaction product was filtered, washed and dried to obtain the final catalyst product, with a theoretical Pt loading of 2.5 wt%.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

[0056] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and to form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present invention and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a low Pt loading catalyst that can be used in fuel cells, metal air batteries and water electrolysis processes, characterized in that: The preparation method comprises the following steps. 2.1) Prepare a carbon precursor (and non-precious metal salt) into a solution of a certain concentration, stir ultrasonically, and obtain a uniform precursor solution. 2) Move the precursor solution to a reactor for hydrothermal reaction, and after the product is dried, obtain a carrier precursor. 3) The carrier precursor is subjected to high-temperature pyrolysis under the protection of an inert atmosphere to obtain a heteroatom-doped composite carbon-based carrier material. 4) Prepare a platinum precursor into a solution of a certain concentration, stir ultrasonically, and obtain a uniform platinum precursor solution. 5) Disperse a certain amount of composite carbon-based carrier material in the Pt metal precursor solution, stir thoroughly, and use sodium borohydride to quickly reduce it at room temperature to obtain a reaction product. The reaction product is filtered, washed, and dried to obtain the final catalyst product.

3. The preparation method according to claim 1, characterized in that: The carbon precursor used in step (1) is one or two of chitosan, glucose, citric acid, and ascorbic acid, which are stirred until completely dissolved. The concentration of the carbon precursor solution is 1 g / L ~ 100 g / L.

4. The preparation method according to claim 1, characterized in that: The metal in the non-precious metal salt precursor of step (1) is one of Fe, Co, Ni, Cu, and Mn. Preferably, the non-precious metal salt is one of the hydrochloride, nitrate, and acetate of Fe, Co, Ni, Cu, and Mn.

5. The preparation method according to claim 1, characterized in that Step (2) The precursor solution is transferred to a reactor for hydrothermal reaction at a reaction temperature of 120°C to 200°C and a reaction time of 10 h to 24 h.

6. The preparation method according to claim 1, characterized in that Step (3) The carrier precursor is subjected to high-temperature pyrolysis under the protection of an inert atmosphere, wherein the inert gas is N2 or Ar, the heating rate is 1 to 10 °C / min, the heating temperature is 500 °C to 1000 °C, and the reaction time is 0.5 h to 8 h.

7. The preparation method according to claim 1, characterized in that: The platinum precursor solution used in step (4) has a solvent selected from the group consisting of methanol, ethanol, isopropanol and ethylene glycol, and is ultrasonically treated until the solution is completely dissolved.

8. The preparation method according to claim 1, characterized in that In step (4), the platinum precursor is one of Pt(acac)2, K2PtCl6, K2PtCl4, H2PtCl6, and the concentration of the platinum precursor solution is 0.1 g / L ~ 20 g / L.

9. The preparation method according to claim 1, characterized in that Step (5) A certain amount of composite carbon-based carrier material is dispersed in the Pt metal precursor solution, and the Pt loading amount is 1 wt% to 5wt%.

10. The preparation method according to claim 1, characterized in that In step (5), sodium borohydride is rapidly reduced at room temperature to obtain a reaction product, the concentration of the sodium borohydride solution is 0.01 mol / L to 5 mol / L, and the reaction time is 1 s to 600 s.

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