阅读说明：本技术 一种纳米结构可控的电催化剂合成方法 (Method for synthesizing electrocatalyst with controllable nano structure ) 是由 刘征 宋晨辉 王正罗 乔红艳 陈启章 于 2020-05-15 设计创作，主要内容包括：本发明公开了一种纳米结构可控的电催化剂合成方法。本发明采用聚酰胺-胺树形分子为模版剂,通过对贵金属离子的至少一次络合和还原,制备粒径稳定可控、粒径分布均匀的所述树形分子包覆贵金属纳米粒子；将导电炭黑研磨,依次经酸化和酯化、或酸酐化预处理,形成表面功能化的碳颗粒；将所述树形分子包覆贵金属纳米粒子与预处理后的导电炭黑混合制备导电碳黑包覆贵金属电催化剂。本发明通过模版剂、金属离子反复络合和还原技术,控制和稳定贵金属纳米粒径范围且形成均匀的粒径分布；功能化的导电碳黑通过与所述树形分子共价交联形成导电碳黑包覆贵金属电催化剂,提高了电催化剂的导电性能；本发明采用水溶剂作为反应助剂,污染小,环境友好。(The invention discloses a method for synthesizing an electrocatalyst with a controllable nano structure. The method adopts polyamide-amine dendrimer as a template agent, and prepares the dendrimer-coated noble metal nano-particles with stable and controllable particle size and uniform particle size distribution through at least one complexing and reduction of noble metal ions; grinding conductive carbon black, and sequentially carrying out acidification and esterification or anhydride pretreatment to form surface functionalized carbon particles; and mixing the dendrimer coated noble metal nano particles with the pretreated conductive carbon black to prepare the conductive carbon black coated noble metal electrocatalyst. The invention controls and stabilizes the noble metal nanometer particle size range and forms uniform particle size distribution by the template agent and the metal ion repeated complexing and reducing technology; the functionalized conductive carbon black and the dendrimer are covalently crosslinked to form a conductive carbon black coated noble metal electrocatalyst, so that the conductivity of the electrocatalyst is improved; the invention adopts hydrosolvent as reaction auxiliary agent, has little pollution and is environment-friendly.)

1. A method for synthesizing an electrocatalyst with controllable nano-structure is characterized in that:

preparing polyamide-amine dendrimer coated noble metal nano particles with stable and controllable particle size and uniform particle size distribution by adopting polyamide-amine dendrimer as a template agent and complexing and reducing noble metal ions at least once;

grinding conductive carbon black to obtain a particle size smaller than 1 micron, and sequentially carrying out acidification and esterification pretreatment or acidification and anhydrization pretreatment to form surface functionalized carbon particles;

and mixing the polyamide-amine dendrimer coated noble metal nano particles with the pretreated conductive carbon black to prepare the conductive carbon black coated noble metal electrocatalyst.

2. The method of claim 1, wherein the complexing and reductive preparation of the polyamidoamine dendrimer coated noble metal nanoparticles comprises: dispersing polyamide-amine dendrimer into deionized water, adjusting the pH to 2-7, adding a solution prepared from noble metal-containing acid or noble metal salt according to the molar ratio of noble metal to polyamide-amine dendrimer being greater than 30 under stirring to completely complex noble metal ions by the polyamide-amine dendrimer to form a solution of polyamide-amine dendrimer coated with noble metal ions; then dropwise adding excessive NaBH at the temperature of between 0 and room temperature under the condition of vigorous stirring₄Continuously stirring the solution to ensure that metal ions are completely reduced, separating, washing and drying the solution to obtain polyamide-amine dendrimer coated noble metal nanoparticles prepared by primary complexation and reduction; wherein, NaBH₄The solution is 0.3-0.5M NaBH₄Mixed with 0.1-0.3M NaOH.

3. A method of synthesising an electrocatalyst with controllable nanostructures according to claim 2 characterised in that: the conductive carbon black acidification pretreatment is to grind the conductive carbon black into particles smaller than 1 micron, and then carry out acidification in a concentrated acid solution to form surface carboxylic acid groups.

4. A method of synthesising an electrocatalyst with controllable nanostructures according to claim 3 characterised in that: the conductive carbon black esterification pretreatment is that the conductive carbon black after acidification pretreatment is ultrasonically dispersed in 2- (N-morpholine) ethanesulfonic acid buffer aqueous solution, a coupling agent synthesized by peptide is dripped under the condition of violent stirring, and N-hydroxysuccinimide is added to form the surface functionalized conductive carbon black.

5. A method of synthesising an electrocatalyst with controllable nanostructures according to claim 3 characterised in that: the conducting carbon black anhydrization pretreatment is to transfer the conducting carbon black subjected to acidification pretreatment to a dimethylformamide solution containing ethyl chloroformate and N-methylmorpholine to obtain the anhydride functionalized conducting carbon black.

6. A method of synthesising an electrocatalyst with controllable nanostructures according to claim 4 or 5 characterised in that: the noble metal nano particles coated by the polyamide-amine dendrimer and the pretreated conductive carbon black are mixed according to the mass ratio of the prepared noble metal nano particles coated by the polyamide-amine dendrimer to the conductive carbon black of 0.01-0.1 percent, and the mixture is stirred and mixed at room temperature to prepare the conductive carbon black coated noble metal electrocatalyst.

Technical Field

The invention belongs to the technical field of catalyst design and preparation, particularly belongs to a preparation method of an electrocatalyst in a high-performance low-precious metal membrane electrode for a proton exchange membrane fuel cell, relates to the field of new energy materials and application in fuel cell automobiles, and particularly relates to a synthesis method of the electrocatalyst with a controllable nano structure.

Background

Proton Exchange Membrane Fuel Cells (PEMFC) can be operated at room temperature to 100 ℃ due to their low operating temperature, are safe and pollution-free, and do not use corrosive electrolyte or high-temperature molten salt characteristics; compared with an internal combustion engine, the energy density and the power density are high, the application prospect of the new generation energy technology is wide, and the market potential is huge. However, the key component of the fuel cell, the Membrane Electrode Assembly (MEA), the key component of the electrocatalyst, is the biggest obstacle to the commercial application of the pem fuel cell due to its low electrochemical activity and noble metal utilization rate, and high cost. In recent decades, the academia and industry have been working on exploring and developing new electrocatalysts to meet the requirements of commercial catalysts for high efficiency, durability and low cost.

The traditional preparation method of the electrocatalyst, such as wet impregnation, coprecipitation method, sol-gel method, etc., is widely applied to the production of industrial catalysts due to simple preparation process and low cost, but the traditional method is often difficult to control the particle size and uniform distribution of the active components of the catalyst, thereby causing that the dispersion degree can not meet the requirement, the utilization rate of the precious metals of the effective active components is low, and the cost is greatly increased.

The polyamide-amine dendrimer (PAMAM dendrimer) has a nano-scale cavity inside and is a very effective template agent for synthesizing and stabilizing nano metal particles. In recent years, the polyamide-amine dendrimer coated metal electrocatalyst has received extensive attention from basic research due to its controllable particle size and uniformity, but its application in fuel cell industrialization is limited due to low electrochemical activity. The low activity mainly comes from two aspects: firstly, the surface electrical property is poor because the active noble metal is formed inside the polyamide-amine dendrimer; the second is that the nanoparticles produced by this method are small, on average less than 2nm, and are not the optimal particle size for cathodic Oxygen Reduction Reaction (ORR) activity, which is typically 3nm, resulting in poor electrochemical activity.

The current fuel cell catalyst has the following defects: 1) the catalytic activity of the cathode oxygen reduction reaction is poor; 2) precious metal (PGM) nanoparticles are not uniformly distributed, and the particle size is difficult to control and is stable in a high activity range; 3) for the catalyst with noble metal nano particles (PGM-DENs) wrapped by polyamide-amine dendrimer, the conductivity is poor, so that the electrochemical activity is poor; 4) the noble metal active component has low dispersity and low utilization rate, so that the catalyst has high cost; 5) the preparation process is complex and is not environment-friendly.

The following are the english abbreviations referred to herein:

PAMAM, polyamidoamine;

PAMAM dendrimer, polyamidoamine dendrimer;

PEMFCs, proton exchange membrane fuel cells;

MEA, membrane electrode assembly;

PGM, noble metals;

ORR, cathodic oxygen reduction reaction;

DENs, dendrimer coated (or stabilized) nanoparticles;

PGM-DENs, polyamide-amine dendrimer wraps the noble metal nanoparticles;

pgm (c) -DENs, conductive carbon black coated noble metal electrocatalyst;

MES, 2- (N-morpholine) ethanesulfonic acid;

EDC, coupling agent for peptide synthesis;

NHS, N-hydroxysuccinimide;

EFC, ethyl chloroformate;

NMM, N-methylmorpholine;

DMF, dimethylformamide.

Disclosure of Invention

The invention discloses an electrocatalyst synthesis method with controllable nano-structure according to the deficiency of the prior art. The invention aims to provide a simple and environment-friendly method for synthesizing a high-efficiency fuel cell catalyst with controllable nano particle size and uniformity by utilizing a special tree-shaped structure of a polyamide-amine dendrimer, and the conductivity of the catalyst is improved by covalently crosslinking the surface of the polyamide-amine dendrimer by conductive carbon particles.

The invention is realized by the following technical scheme:

the method for synthesizing the electrocatalyst with controllable nano structure is characterized in that:

preparing polyamide-amine dendrimer coated noble metal nano particles with stable and controllable particle size and uniform particle size distribution by adopting polyamide-amine dendrimer as a template agent and complexing and reducing noble metal ions at least once;

grinding conductive carbon black to obtain a particle size smaller than 1 micron, and sequentially carrying out acidification and esterification pretreatment or acidification and anhydrization pretreatment to form surface functionalized carbon particles;

and mixing the polyamide-amine dendrimer coated noble metal nano particles with the pretreated conductive carbon black to prepare the conductive carbon black coated noble metal electrocatalyst.

The complexing and reducing preparation of the polyamide-amine dendrimer coated noble metal nanoparticles comprises the following steps: dispersing polyamide-amine dendrimer into deionized water, adjusting the pH to 2-7, adding a solution prepared from noble metal-containing acid or noble metal salt according to the molar ratio of noble metal to polyamide-amine dendrimer being greater than 30 under stirring to completely complex noble metal ions by the polyamide-amine dendrimer to form a solution of polyamide-amine dendrimer coated with noble metal ions; then dropwise adding excessive NaBH at the temperature of between 0 and room temperature under the condition of vigorous stirring₄Continuously stirring the solution to ensure that metal ions are completely reduced, separating, washing and drying the solution to obtain polyamide-amine dendrimer coated noble metal nanoparticles prepared by primary complexation and reduction; wherein, NaBH₄The solution is 0.3-0.5M NaBH₄Mixed with 0.1-0.3M NaOH.

The conductive carbon black acidification pretreatment is to grind the conductive carbon black into particles smaller than 1 micron, and then carry out acidification in a concentrated acid solution to form surface carboxylic acid groups.

The conductive carbon black esterification pretreatment is that the conductive carbon black after acidification pretreatment is ultrasonically dispersed in 2- (N-morpholine) ethanesulfonic acid buffer aqueous solution, a coupling agent synthesized by peptide is dripped under the condition of violent stirring, and N-hydroxysuccinimide is added to form the surface functionalized conductive carbon black.

The conducting carbon black anhydrization pretreatment is to transfer the conducting carbon black subjected to acidification pretreatment to a dimethylformamide solution containing ethyl chloroformate and N-methylmorpholine to obtain the anhydride functionalized conducting carbon black.

The noble metal nano particles coated by the polyamide-amine dendrimer and the pretreated conductive carbon black are mixed according to the mass ratio of the prepared noble metal nano particles coated by the polyamide-amine dendrimer to the conductive carbon black of 0.01-0.1 percent, and the mixture is stirred and mixed at room temperature to prepare the conductive carbon black coated noble metal electrocatalyst.

The invention controls the nanometer particle size of the catalyst by the metal ion repeated complexing and reducing technology, and meets the size and structure required by the cathode Oxygen Reduction Reaction (ORR); the functionalized conductive carbon black is covalently crosslinked with polyamide-amine dendrimer (PAMAM dendrimer) to form a conductive carbon black coated noble metal electrocatalyst (PGM (C) -DENs), so that the conductivity of the electrocatalyst is improved, and the electrochemical activity of the catalyst is improved; the invention provides a proper process technical route for future high-efficiency macro production of the fuel cell catalyst; the invention adopts hydrosolvent as reaction auxiliary agent, has little pollution and is environment-friendly.

The invention provides a new synthesis method of a noble metal nano electrocatalyst, which is used for improving the electrochemical activity of the noble metal electrocatalyst; the method controls and stabilizes the noble metal nano particle size in the optimal range and forms uniform particle size distribution by taking polyamide-amine dendrimer (PAMAM dendrimer) as a template agent and repeatedly complexing and reducing metal ions; the conductive carbon black is subjected to acidification pretreatment and esterification or anhydrization treatment to form carboxyl functional groups on the surface, and further forms covalent crosslinking with the surfaces of the polyamide-amine dendrimer coated noble metal nano particles (PGM-DENs) so as to improve the conductivity of the prepared conductive carbon black coated noble metal electro-catalyst (PGM (C) -DENs).

Drawings

FIG. 1 is a schematic diagram of the synthetic route of the polyamide-amine dendrimer-coated noble metal nanoparticles (PGM-DENs) according to the present invention.

FIG. 2 is a schematic diagram of the synthesis route of the conductive carbon black coated noble metal electrocatalysts (PGM (C) -DENs) of the present invention.

FIG. 3 is a TEM image of conductive carbon black-coated platinum electrocatalyst (Pt (C) -DENs1) prepared in example 1 of the present invention.

FIG. 4 is a normal distribution diagram of the average particle size of the corresponding nanoparticles of the conductive carbon black-coated platinum electrocatalyst (Pt (C) -DENs1) prepared in example 1 according to the present invention. In the figure, the average particle size of the nanoparticles is about 2.1nm with the highest distribution, the main range being 1-2.6 nm.

FIG. 5 is a TEM image of conductive carbon black-coated platinum electrocatalyst (Pt (C) -DENs2) prepared by re-complexing and reduction according to example 1 of the present invention.

FIG. 6 is a normal distribution diagram of the average particle size of the corresponding nanoparticles of the conductive carbon black-coated platinum electrocatalyst (Pt (C) -DENs2) prepared by re-complexing and reduction according to example 1 of the present invention. In the figure, the average particle size of the nanoparticles is about 3.2nm with the highest distribution, the main range being 2-3.5 nm.

FIG. 7 is a transmission electron micrograph of a Pt/C electrocatalyst prepared according to the comparative example.

FIG. 8 is a normal distribution diagram of the average particle size of the metal particles corresponding to the Pt/C electrocatalyst prepared in the comparative example. In the figure, the average particle size of the nanoparticles is about 3.5nm with the highest distribution, ranging from 1.5 to 6.5 nm.

FIG. 9 is a linear voltage sweep (LSV) plot of the electrochemical performance of the conductive carbon black coated platinum electrocatalysts (Pt (C) -DENs) prepared in accordance with the present invention versus Pt/C catalysts.

FIG. 10 is a comparison of specific mass activities of Pt (C) -DENs and Pt/C redox catalysts (ORR) prepared according to the present invention, where the ordinate is the specific mass activity measured by RDE (Rolling-disk-electrode).

Detailed Description

The present invention is further described below in conjunction with the following detailed description, which is intended to further illustrate the principles of the invention and is not intended to limit the invention in any way, but is equivalent or analogous to the present invention without departing from its scope.