CN108110265B

CN108110265B - Au @ Au/Pt core-shell structure nano catalyst for alcohol fuel cell

Info

Publication number: CN108110265B
Application number: CN201711361538.5A
Authority: CN
Inventors: 赵振路; 曹琳; 冯煜; 王建荣; 杨萍
Original assignee: University of Jinan
Current assignee: University of Jinan
Priority date: 2017-12-18
Filing date: 2017-12-18
Publication date: 2020-07-07
Anticipated expiration: 2037-12-18
Also published as: CN108110265A

Abstract

An Au @ Au/Pt core-shell structure nano catalyst for alcohol fuel cells is in a shape of a concave cube, and the size of the Au @ Au/Pt core-shell structure nano catalyst is 29 +/-4 nm; the inside is a gold core, and the outside is a gold/platinum shell; the catalyst is prepared by the following method: firstly, preparing gold nanoparticles; depositing silver on the surface of the gold nanoparticles to form a nanocube with an Au @ Ag core-shell structure; and then preparing the nano cube with the Au @ Ag/Au core-shell structure by adopting an in-situ growth method, and finally adding chloroplatinic acid to replace silver to obtain the product. The catalyst of the invention changes a pure platinum shell into a shell composed of platinum, thereby further reducing the platinum load and the cost. Meanwhile, the catalyst has a unique core-shell structure, has richer atomic arrangement and larger surface area, has a plasmon resonance effect when interacting with a gold core, and can effectively enhance the catalytic activity and weaken the poisoning effect; the stability and the catalytic activity are better for the oxidation reaction of ethanol under the alkaline condition.

Description

Au @ Au/Pt core-shell structure nano catalyst for alcohol fuel cell

Technical Field

The invention belongs to the field of fuel cell catalysts, and relates to an Au @ Au/Pt nano catalyst for an alcohol fuel cell and a preparation method thereof.

Background

The alcohol fuel cell has the advantages of rich fuel source, low price, safety and convenience in carrying and storage and the like, and among the methanol fuel cells, the research is more. However, methanol has certain toxicity, which limits its application in mobile power supply fields such as mobile phones, notebooks, computers, etc. Ethanol, as the simplest small organic molecule in the chain alcohol, has the following advantages compared with methanol: firstly, the price is low, the safety is realized, and the toxicity is avoided; secondly, the transportation is easy, and the volatility is small; thirdly, the theoretical specific energy is high; and fourthly, the source is wide, and the energy is renewable green energy. Therefore, the research on the direct alcohol fuel cell taking ethanol as fuel not only has theoretical significance, but also has very wide application prospect. The mechanism of the anode reaction of the ethanol fuel cell is as follows:

CH₃CH₂OH+·OH^-→H₂O + CO₃ ^2-

as can be seen from the above reaction equation, ethanol has 12 electrons generated during the complete oxidation process, which means that C-C must be broken during the oxidation process of ethanol compared with 6 electrons of methanol, so that the complete oxidation process of ethanol is very difficult due to the condition. Noble metal catalysts in methanol fuel cells may not be suitable for use in ethanol fuel cells.

Pt is a high-efficiency proton exchange membrane fuel cell catalyst (Nature 2001, 414, 345-352), however, a pure Pt catalyst is easily poisoned by a fuel oxidation intermediate product CO, resulting in reduced catalytic activity, poor stability, slow kinetics, less Pt storage and high price, which limits its application. To this end, researchers have constructed unitary nanostructured Pt (J.Am. chem. Soc. 2007, 129, 6974-. For example, Zhu H et al (International journal of Hydowgen Energy 2011, 6, 9151-9154) report that Vulcan XC-72R is used as a carrier material, a two-step reduction method is adopted to synthesize a Cu @ Pt/C core-shell structure catalyst to be applied to a fuel cell, the Cu @ Pt/C core-shell structure catalyst shows particularly high activity for cathode oxygen reduction, and the catalyst with low platinum content is developed to improve the utilization rate of precious metals and reduce the cost. Nevertheless, it is still a challenge to further reduce the amount of Pt, enhance the catalytic activity and stability of the Pt-based noble metal catalyst, and reduce the poisoning effect during the catalytic process.

Platinum-based nanocatalysts have received great attention because of their unique catalytic properties. However, due to the scarcity of platinum resources and its strong commercial demand, platinum-based catalysts are very expensive. In order to reduce the amount of platinum and the amount of platinum, the Au @ Au/Pt nano-particle with the core-shell structure is a novel nano-material with wide application prospect, but because the mixing and dissolving temperature of Au and Pt is high, the preparation of the AuPt alloy nano-particle generally needs higher temperature, for example, Xu and the like (J. Phys. chem. Lett.,2010,1: 2514-2518) report that metal inorganic salt is used as a precursor, oleylamine is used as a solvent, a stabilizer and a reducing agent, and the reaction is carried out for 2 hours at the high temperature of 160 ℃ to prepare the AuPt nano-alloy. The Chinese patent application with the application number of 201310667345.8, namely the preparation method of the Au @ AuPt alloy nano particles and the colloid dispersion system, adopts the technical scheme that part of Au ions are reduced into gold nano particles by ascorbic acid, Pt ions and the rest Au ions in the system are simultaneously reduced into an AuPt alloy by hydrazine hydrate aqueous solution which is added subsequently, and the AuPt alloy is deposited on the surfaces of the gold nano particles which serve as new phase seeds to form the Au @ Au/Pt alloy nano particles with the core-shell structure, so that the Au @ Au/Pt alloy nano particles are synthesized by one-pot two-step reduction under the room temperature condition. However, the preparation method of the invention uses toxic hydrazine hydrate, although the preparation method is faster, the toxicity is inevitable, and the prepared material is structurally not suitable for the plasmonic to enhance the action of the catalytic active sites.

Disclosure of Invention

Aiming at the problems that the ethanol fuel cell is easy to be poisoned and the catalytic efficiency is low when the precious metal nano-catalyst is used for catalyzing the ethanol fuel cell at present, the invention provides the Au @ Au/Pt core-shell structure nano-catalyst for the alcohol fuel cell, which has the advantages of higher catalytic efficiency, no catalyst poisoning phenomenon and high precious metal use efficiency.

The invention also provides a preparation method of the catalyst.

In order to achieve the purpose, the invention adopts the following technical scheme.

An Au @ Au/Pt core-shell structure nano catalyst for alcohol fuel cells is in a shape of a concave cube, and the size of the Au @ Au/Pt core-shell structure nano catalyst is 29 +/-4 nm; the inner part is a gold core (Au core) and the outer part is a gold/platinum shell (Au/Pt shell).

The Au @ Au/Pt core-shell structure nano catalyst is prepared by adopting the following method: firstly, preparing gold nanoparticles; depositing silver on the surface of the gold nanoparticles to form a nanocube with an Au @ Ag core-shell structure; and then preparing the Au @ Ag/Au core-shell structure nanocubes by adopting an in-situ growth method, and finally adding chloroplatinic acid to replace silver to obtain the Au @ Au/Pt core-shell concave nanocubes.

The preparation method of the Au @ Au/Pt core-shell structure nano catalyst comprises the following steps:

(1) adding a mixed solution of chloroauric acid, CTAB (cetyl trimethyl ammonium bromide) and sodium borohydride into a mixed solution containing CTAC (cetyl trimethyl ammonium chloride), AA (ascorbic acid) and chloroauric acid, and stirring to obtain a red transparent solution;

(2) mixing the precipitate obtained after the solution in the step (1) is centrifuged with CTAC, stirring in a water bath at 60 ℃, and simultaneously adding silver nitrate, AA and CTAC to change the solution into brown yellow;

(3) adding hydroxylamine hydrochloride and chloroauric acid into the solution obtained in the step (2) after centrifugation and stirring, boiling, and changing the solution into red;

(4) and (3) dispersing the solution obtained in the step (3) in a mixed solution of CTAB and PVP (polyvinylpyrrolidone), heating at 100 ℃, slowly adding chloroplatinic acid, and centrifuging after the solution becomes purple to obtain the Au @ Au/Pt core-shell structure nano catalyst.

In the step (1), the preferred molar ratio of chloroauric acid, CTAB and sodium borohydride is 37:50000: 5000.

In step (1), the preferred molar ratio of chloroauric acid, CTAC and AA is 1:400: 200.

In step (2), the preferred molar ratio of silver nitrate, AA and CTAC is 1:25: 20.

In step (4), the preferable molar ratio of PVP and CTAB is 9:3125, wherein the molar amount of PVP is based on the molar amount of its polymerized monomers.

Preferably, step (1) chloroauric acid, CTAB and sodium borohydride are mixed and stored at 27 ℃ for 3 hours.

Preferably, the red transparent solution obtained in step (1) is centrifuged at 15000rpm for 20min, and the precipitate is washed once and dissolved for the next reaction.

Preferably, after the solution of step (2) is stirred in a water bath at 60 ℃ for 3h when it turns brown yellow, it is centrifuged at 15000rpm for 15min, and the precipitate is washed once and dissolved for the next reaction.

Preferably, the purple solution obtained in the step (4) is centrifuged at 10000rmp for 10min, and the precipitate is washed twice to obtain the Au @ Au/Pt core-shell structure nano catalyst.

The Au @ Au/Pt core-shell structure nano catalyst is applied to methanol or ethanol fuel cells.

The invention has the following advantages:

the invention provides an Au @ Au/Pt core-shell structure nano catalyst for an alcohol fuel cell, wherein a pure platinum shell is replaced by a shell jointly composed of platinum, so that the platinum load is further reduced, and the cost is reduced. Meanwhile, the catalyst has a unique core-shell structure, has richer atomic arrangement and larger surface area, has a plasmon resonance effect when interacting with a gold core, and can effectively enhance the catalytic activity and weaken the poisoning effect; the stability and the catalytic activity are better for the oxidation reaction of ethanol under the alkaline condition. The method is feasible and effective, and the preparation method is simple, the raw materials are easy to obtain, and the catalyst is an anode catalyst of a proton exchange membrane fuel cell with good performance.

The method for synthesizing the Au @ Au/Pt core-shell concave nano particles is simple, convenient and effective, and comprises the steps of firstly synthesizing gold nano particles, then depositing silver on the surfaces of the gold nano particles to form Au @ Ag core-shell nanocubes, adding chloroauric acid and hydroxylamine hydrochloride to synthesize the Au @ Ag/Au core-shell nanocubes, then adding chloroplatinic acid and the Au @ Ag/Au core-shell nanocubes to perform reaction by utilizing a displacement reaction, and adding excessive chloroplatinic acid to completely displace silver to form the Au @ Ag/Pt core-shell concave nanocubes with gold cores and gold platinum alternated.

Drawings

Fig. 1 is a transmission electron microscope photograph of each nanoparticle synthesized, in which (a) gold/silver core-shell nanocubes, (b) gold/platinum core-shell nanoparticles; (c) gold/gold platinum core-shell nanoparticles;

FIG. 2 is a UV-VIS spectrum of gold nanoparticles, gold/silver core-shell nanocubes, gold/platinum core-shell nanoparticles, gold/gold platinum core-shell nanoparticles;

FIG. 3 is a plot of the timing current for gold nanoparticles, gold/silver core-shell nanocubes, gold/gold platinum core-shell nanocubes in a mixed solution of 1.0M sodium hydroxide and 1.0M ethanol with a sweep rate of 50 mV/s;

FIG. 4 is a plot of cyclic voltammetry characteristics of gold nanoparticles, gold/silver core-shell nanocubes, gold/platinum core-shell nanoparticles, gold/gold platinum core-shell nanocubes in a mixed solution of 1M sodium hydroxide and 1M ethanol with a sweep rate of 50 mV/s;

fig. 5 is a cyclic voltammetry characteristic curve of an electrode modified by gold/platinum core-shell nanoparticles and gold/gold platinum core-shell nanocubes after electrochemical surface active area normalization in a mixed solution of 1.0M sodium hydroxide and 1.0M ethanol and a time current curve after electrochemical surface active area normalization.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, but the present invention is not limited to the following examples.

Example 1 preparation of Au @ AuPt core-shell nanostructures

1.1 preparation of Au nanoparticles

(1) Before the experiment, a plurality of 25mL beakers, medicine spoons, 50 mL beakers, 2 magnetic stirrers and 50 mL measuring cylinders are prepared, and the beakers are soaked in aqua regia, cleaned and dried for later use. And 5-50 μ L of pipette, 100-.

(2) A clean beaker is taken, a small amount of deionized water is poured into the beaker, and the beaker is put into a freezing chamber of a refrigerator for freezing for standby. After the medicine spoon is washed and dried by deionized water and ethanol, 0.364 g of hexadecyl trimethyl ammonium bromide is weighed by an electronic balance, 10mL of deionized water is removed by a liquid removing gun and added into a beaker for dissolution. 0.033 g of sodium borohydride was weighed by an electronic balance, 10mL of ice water was measured, and the ice water was poured into a 25mL beaker to dissolve. 42.5. mu.L of chloroauric acid (1%) was slowly added to 5mL of prepared cetyltrimethylammonium bromide CTAB (100 mM) by using a 5-50. mu.L pipette at 27 ℃, after uniform mixing, 0.3 mL of ice-cold freshly prepared sodium borohydride (100 mM) solution was rapidly added thereto, and after 2 minutes of rapid counter-rotation shaking, the mixture was stored at 27 ℃ for 3 hours to ensure complete decomposition of the unreacted sodium borohydride.

(3) Using a 100-charge 1000-microliter pipetting gun to pipette 290 microliter of chloroauric acid (1%) to prepare 12mL of chloroauric acid (0.5 mM) solution, weighing 0.768 g of cetyltrimethylammonium chloride CTAC by an electronic balance, measuring 12mL of deionized water by a measuring cylinder to prepare 12mL of cetyltrimethylammonium chloride CTAC (200 mM) solution, weighing 0.288 g of ascorbic acid by the electronic balance, measuring 10mL of deionized water by the measuring cylinder, and pouring the deionized water into a 25mL beaker for dissolution. 12mL of chloroauric acid solution (0.5 mM), 12mL of CTAC solution (200 mM), 9 mL of ascorbic acid (100 mM) were mixed well in a 50 mL beaker, and 0.6 mL of gold seed was added to the above mixed solution with stirring, and the solution turned from colorless to red for about 1 minute, indicating that large-particle gold nanoparticles had formed. After 1 hour, the product was purified by centrifugation several times and finally dispersed in 2mL of water.

1.2 preparation of Au @ Ag core-shell cube

Prepare 20 mM CTAC solution, weigh 0.640 g of cetyltrimethylammonium chloride CTAC with an electronic balance, weigh 10mL of deionized water with a measuring cylinder, pour into a 25mL beaker and mix. 0.144 g of ascorbic acid is weighed by an electronic balance, 10mL of deionized water is weighed by a measuring cylinder, and the mixture is poured into a beaker for mixing. The gold nanoparticle dispersion was added to 9 mL of an aqueous CTAC solution, and after adding a magnetic stirrer and vigorously stirring, 1 mL of a silver nitrate (2 mM) solution and 1 mL of a mixed solution of ascorbic acid (50 mM) and CTAC (40 mM) were simultaneously added at a rate of 0.2 mL/min after maintaining the temperature of 60 ℃ in a water bath on a constant temperature magnetic stirrer for 20 minutes. The silver concentration in the solution after addition of silver nitrate was 0.17 mM. During the addition of the two solutions, the reaction turned from red to brown-yellow. After 4 hours of reaction, the reaction mixture was cooled in an ice-water bath, and the product was purified by centrifugation several times and dispersed in 2mL of water.

1.3 preparation of in-situ grown Au on Ag Shell

5mL of the Au/Ag nano solution (nanoparticles or nanocubes) prepared newly was diluted in 5mL of water, 0.126 g of hydroxylamine hydrochloride was weighed by an electronic balance, 10mL of deionized water was measured in a measuring cylinder, and mixed in a 25mL beaker. Then 0.1 mL of hydroxylamine hydrochloride (0.02M) and 100. mu.L of chloroauric acid (0.1%) were added under vigorous stirring, and the solution turned red, then boiled for several minutes and cooled to room temperature.

1.4 preparation of Au @ AuPt core-shell nanostructure

This step is carried out by a metathesis reaction. Weigh 0.040 g PVP with 0.364 g CTAB, measure 10mL deionized water with a graduated cylinder, mix in a beaker. 0.8 mL of Au/Ag-Au core-shell nanocubes were dispersed into a mixed solution of 8 mL of polyvinylpyrrolidone (0.5%) and CTAB (0.1M), the solution was heated to 100 deg.C, and after 2 minutes 140. mu.L of chloroplatinic acid (0.01%) diluted to 10mL was added, ensuring that the silver was completely replaced. The solution turned purple in color. After cooling to room temperature, the purified product was dispersed in water several times by centrifugation.

Comparative example 1 preparation of Au @ Pt nanoparticles

1.1 same as in example 1.1

1.2 same as in example 1.2

1.3 preparation of concave Au @ Pt nanotube

By Au @ Ag core-shell cubes and K₂PtCl₆An electro-substitution reaction between aqueous solutions to prepare Au @ Pt nanoparticles. In a typical procedure, 0.8 mL of Au @ Ag was redispersed in 8 mL of PVP (0.5 wt%) and CTAB (0.1M) solution. The Au @ Ag core-shell cubes were then heated at 100 ℃ for 2 minutes, followed by the addition of 20. mu.L of 0.1% K₂PtCl₆And (3) solution. The color of the mixture turned dark blue. The final product was mixed with the same volume of 6M HNO₃Mix to remove AgCl precipitate and unreacted silver. After that, the product was collected by centrifugation (10000 rpm, 10 minutes) and then washed twice with water.

Example 2 preparation of core-shell Structure physicochemical Properties characterization

2.1 form

Transmission electron microscopy images of the gold nanoparticles, Au @ Ag core-shell nanocubes, Au @ AuPt core-shell nanostructures in example 1 and the Au @ Pt core-shell nanoparticles in comparative example 1 are shown in fig. 1 (a) - (c). As can be seen from the figure, the obtained Au @ AuPt core-shell nano structure is a concave cube, and the average particle size is 29 +/-4 nm. The gold nanoparticles and the Au @ Ag core-shell nanocubes are monodisperse, the average particle size is 10 +/-2 nm, and the average particle size of the Au @ Pt core-shell nanoparticles is 33 +/-3 nm.

2.2 ultraviolet-visible Spectrum

The gold nanoparticles, Au @ Ag core-shell nanocubes, Au @ AuPt core-shell nanostructures in example 1 and the Au @ Pt core-shell nanoparticles in comparative example 1 were subjected to uv-vis spectral scanning, and the spectra are shown in fig. 2. As can be seen from FIG. 2, the UV-visible absorption peak of the gold nanoparticles is about 520 nm, the Au @ Ag core-shell nanocube has two characteristic absorption peaks at 410 nm and 490 nm, the UV-additional absorption peak of the Au @ Au/Pt core-shell nanocube is about 530 nm, and the UV-visible absorption peak of the gold nanoparticles disappears due to the fact that the gold nanoparticles are completely wrapped by platinum due to the gold/platinum core-shell structure.

Example 3 catalytic Effect of core-shell Structure preparation on ethanol Fuel cells

3.1 chronoamperometric and cyclic voltammetric characteristics

The Au @ Ag core-shell nanocubes, Au @ AuPt core-shell nanostructures in example 1 and the Au @ Pt core-shell nanoparticles in comparative example 1 were tested for chronoamperometric and voltammetric properties. The detection conditions are as follows: mixing 1.0M sodium hydroxide and 1.0M ethanol mixed solution, wherein the scanning voltage is-1V-0.6V, and the scanning speed is 50 mV/s.

The result of the timing current is shown in fig. 3, which illustrates that the Au @ AuPt core-shell nanocube has the characteristics of better catalytic performance and higher stability.

The voltammetric cycling results are shown in figure 4: the peak potential of the Au @ Pt core-shell nanoparticles (approximately-0.3V) was lower than the peak potential of the gold nanoparticles (approximately 0.2V), indicating that the platinum shell enhanced the catalytic effect on ethanol; the oxidation peak of the Au @ Au/Pt core-shell nanocube is higher than that of the Au @ Pt core-shell nanocube, which shows that the Au @ Pt core-shell nanocube has better electrocatalytic performance. Compared with other catalysts, Au @ Au/Pt has lower peak potential and higher oxidation peak, and the oxidation peak is obviously weaker in the flyback process, which indicates that the poisoning effect is weak and is superior to other catalysts. Because the catalytic effect of silver on ethanol is poor, the reduction peak of the Au @ Ag oxidation peak is not obvious.

For more accurate reaction electrocatalytic performance, we normalized the electrocatalytic activity curve to the electrochemically active area, with the results shown in fig. 5 (a) and (b). In the process of catalyzing ethanol, the Au @ Au/Pt core-shell nanocubes have lower peak potential in a cyclic voltammetry characteristic curve with electrochemical surface active area normalization (figure 5 (a)), which shows that the Au @ Au/Pt core-shell nanocubes have better effect on the catalysis of ethanol, and in the flyback process, the oxidation peak is obviously weaker, which shows that the poisoning effect is weak. In the electrochemically surface active area normalized time current curve (fig. 5 (b)), the Au @ Au/Pt core-shell plasma nanocubes have higher currents. This demonstrates that the stability and activity of the Au @ Au/Pt core-shell plasma nanocubes are higher than those of Au @ Pt core-shell nanoparticles.

Claims

1. A preparation method of an Au @ Au/Pt core-shell structure nano catalyst is characterized by comprising the following steps:

(1) adding a mixed solution of chloroauric acid, CTAB and sodium borohydride into a mixed solution containing CTAC, AA and chloroauric acid, and stirring to obtain a red transparent solution;

2. The method according to claim 1, wherein in the step (1), the molar ratio of chloroauric acid, CTAB and sodium borohydride is 37:50000: 5000; the molar ratio of chloroauric acid, CTAC and AA was 1:400: 200.

3. The method according to claim 1, wherein in the step (2), the molar ratio of silver nitrate, AA and CTAC is 1:25: 20.

4. The method according to claim 1, wherein in the step (4), the molar ratio of PVP to CTAB is 9:3125, wherein the molar amount of PVP is based on the molar amount of the polymerized monomers.

5. The method according to claim 1, wherein the chloroauric acid, CTAB and sodium borohydride in step (1) are mixed and then stored at 27 ℃ for 3 hours.

6. The method according to claim 2, wherein the red transparent solution obtained in step (1) is centrifuged at 15000rpm for 20min, and the precipitate is washed once and dissolved for the next reaction.

7. The method according to claim 1, wherein the solution of step (2) is stirred in a water bath at 60 ℃ for 3 hours after turning to brown, centrifuged at 15000rpm for 15 minutes, and the precipitate is washed once and dissolved for the next reaction.

8. The preparation method of claim 1, wherein the purple solution obtained in the step (4) is centrifuged at 10000rmp for 10min, and the precipitate is washed twice to obtain the Au @ Au/Pt core-shell structured nano-catalyst.

9. An Au @ Au/Pt core-shell structured nanocatalyst obtained by the preparation method according to any one of claims 1 to 8, characterized in that it is in the shape of a concave cube and has a size of 29 ± 4 nm; the inside is a gold core and the outside is a gold/platinum shell.

10. Use of the Au @ Au/Pt core-shell structured nanocatalyst of claim 9 in a methanol or ethanol fuel cell.