KR102156218B1 - Pt nanoparticles having high areal density synthesized on 2-dimensional conducting polymers and a manufacturing method thereof - Google Patents

Abstract

The present invention relates to a platinum nanoparticle and a conductive polymer composite, and a method for producing the same, and more particularly, to a platinum nanoparticle-conductive polymer composite having a high areal density and a method for producing the same.
The composite according to the present invention is prepared by dispersing platinum nanoparticles in a two-dimensional polyaniline nanosheet, placing a two-dimensional polyaniline nanosheet at the interface between a solution containing a platinum precursor and a gas, and heating a solution containing the platinum precursor. do.

Description

Pt nanoparticles having high areal density synthesized on 2-dimensional conducting polymers and a manufacturing method thereof

The present invention relates to a platinum nanoparticle and a conductive polymer composite, and a method for producing the same, and more particularly, to a platinum nanoparticle-conductive polymer composite having a high areal density and a method for producing the same.

In addition, the present invention has priority to Korean Patent Application No. 10-2017-003156563 "Synthesis of platinum nanoparticles two-dimensional conductive polymer composite having high areal density", and the application is incorporated by reference in this application as a whole.

Platinum nanoparticles are known as the most effective electrochemical catalyst for oxidation reactions. ^{It has} been known that platinum nanoparticles using ^1-3 carbon as a support are the most widely studied form of these catalysts, and their catalytic activity is greatly influenced by the size and shape of the platinum nanoparticles. ^4-7 However, the carbon support does not prevent agglomeration of particles, and eventually leads to loss of catalytic activity over time. ^{8,9 In} addition, the fact that a high reaction temperature is required to prepare platinum nanoparticles with carbon as a support ^10,11 and the fact that expensive carbon chemical structures ^12,13 are used are considered as limitations.

Therefore, eco-friendly and cost-effective synthesis of platinum nanoparticles is a major focus. In view of this, much attention has been paid to platinum nanoparticles having a conductive polymer as a support. ^{14 In} particular, polylinalin has been studied the most because of its high reduction potential and the amine part in the polymer skeleton structure. ^15-17 These factors enabled the nucleation and growth of platinum nanoparticles in polyaniline, even at room temperature, to be reliably fixed to the structure of the conductive polymer. ^17-19

Considering that the electrical conductivity and electrochemical stability of polyaniline are greatly affected by its shape, ^20-22 nanostructured polyaniline will be a promising method to improve the catalytic activity of nanoparticles by making platinum nanoparticles uniformly dispersed. I can. In addition, nanostructured polyaniline having a large surface area can help reduce the carbon monoxide poisoning phenomenon of platinum nanoparticles, which has been considered an urgent task in the field of platinum-based electrochemical catalysts for decades. ^18,23 However, there is no known method of suppressing agglomeration while increasing the ^areal density of platinum nanoparticles in the polyaniline system. The reason is that when platinum ions come into contact with polyaniline, there is a lack of control over nucleation/reduction of platinum ions.

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The problem to be solved in the present invention is to provide a platinum nanoparticle-conductive polymer composite having a high areal density.

The problem to be solved in the present invention is to provide a method of manufacturing a platinum nanoparticle-conductive polymer composite having a high areal density.

Another problem to be solved in the present invention is to provide an electrochemical catalyst including a platinum nanoparticle-conductive polymer composite having a high areal density.

In order to solve the above problems, the present invention provides a two-dimensional polyaniline nanosheet, characterized in that the platinum nanoparticles are dispersed.

In the present invention, the platinum nanoparticles may have a size of 10 nm or less, more preferably 5 nm or less, and most preferably 2 to 4 nm to have a high areal density.

In the present invention, the platinum nanoparticles may be 80% or more, more preferably 90% or more, more preferably 95% or more, and most preferably 99% of zero-valent nanoparticles.

In one aspect, the present invention provides an electrochemical catalyst, characterized in that platinum nanoparticles are dispersed in a two-dimensional polyaniline nanosheet. In the practice of the present invention, the electrochemical catalyst may be a catalyst in the oxidation reaction of alcohol, for example methanol.

The present invention in another aspect,

Providing a solution comprising platinum ions;

Providing a two-dimensional polyaniline nanosheet;

Positioning the two-dimensional polyaniline nanosheets on the surface of the solution; And

It provides a platinum nanoparticle-conductive polymer composite manufacturing method comprising the step of heating the solution.

In the present invention, the solution containing platinum ions may be a solution of a platinum precursor.

In the present invention, the solution containing platinum ions has a surface tension of 50 mN/m or more, preferably 60 mN/m or more, and more preferably 70 mN/m or more, so that the platinum nanoparticles have a high areal density. It is preferable to have. In a preferred embodiment of the present invention, the solution containing platinum ions may be an aqueous solution of a platinum precursor.

In the present invention, the platinum precursor is a compound capable of dissolving to provide platinum ions. As long as the platinum precursor can provide platinum ions, a particular limitation is No, for example, the platinum precursor solution may be a K ₂ PtCl ₄ solution. The solution may have a concentration of 0.1 to 1 mM so as to have an appropriate reaction rate.

In the present invention, the two-dimensional polyaniline nanosheet may be prepared by polymerizing aniline on an ice surface. In the practice of the invention, the nanosheet may have a thickness of 100 nm or less, more preferably 50 nm or less, and most preferably 30 nm or less. In a preferred embodiment of the present invention, the two-dimensional polyaniline nanosheets are orthorhombic in which quinoid rings are arranged in a substantially vertical direction, and conjugated rings form an edge-on π-π arrangement. ) It is a highly conductive crystalline nanosheet of the structure, and has a conductivity of 10 S/cm or more, preferably 20 S/cm or more, more preferably 30 S/cm or more at 1 V, for example, a conductivity of 35 S/cm. It is a highly conductive aniline nanosheet. For the preparation and characteristics of the nanosheet, reference may be made to Korean Patent Publication No. 2016-0114399, which is fully incorporated as a reference in the present invention.

In the present invention, the surface of the solution may be an interface between a solution containing a platinum precursor and a gas. In the practice of the present invention, the interface may be an interface between a solution and air.

In the present invention, the contact on the surface may be made by floating the two-dimensional polyaniline nanosheets by the surface tension of the solution. In the practice of the present invention, the floating may be performed in a state in which a nanosheet having an area of several cm2 or more is spread.

In the invention, the heating is quick and spontaneous rising ² PtCl ₄ in order to reduce the surface tension of water it is ^preferred to achieve a platinum nano-particles for high-density surface derived ion cluster, and through this, the formed without stirring.

In the present invention, it is preferable that the heating is performed at a temperature lower than the boiling point, for example, 10° C. or less, more preferably 20° C. or less, so as to prevent excessive fluctuation of the nanosheets. In the practice of the present invention, when the aqueous solution containing a platinum precursor is heated under 1 atmosphere of pressure, 80° C. or less, more preferably 75° C., and even more preferably 50 so as to prevent excessive oscillation of the nanosheets. It can be heated at ~70℃.

In the present invention, the solution may further contain a reducing agent so that platinum ion clusters optionally bonded to the amine group of the two-dimensional polyaniline nanosheets can be easily reduced to zero valence. In the practice of the present invention, it may be an acid component.

According to the present invention, a new approach for synthesizing platinum nanocrystals having a uniform and high areal density using a conductive polymer as a support has been provided. Its core strategy is to use ice-based polyaniline as a platform for platinum nucleation at the air-water interface.

Pt nanoparticles having high crystallinity, small size distribution of 2.68 ± 0.27 nm, and high electrochemical activity area of 94.57 m ² /g were obtained.

Platinum nanoparticles were strongly immobilized on polyaniline nanosheets, demonstrating an unprecedented high current density, good durability, and excellent carbon monoxide resistance against methanol oxidation reactions. The idea proposed in this study can be applied as a catalyst with improved catalytic activity against various other reactions.

1 is a schematic illustration of the synthesis of platinum nanoparticles (PANI-supported Pt NPs) using polyaniline nanosheets as a support at a water-air interface.
FIG. 2 is a TEM photograph of (a) finely dispersed and uniform platinum nanoparticles supported on polyaniline nanosheets. The inserted magnified TEM image and bar graph show the average particle diameter of 2.68 ± 0.27 nm. (b) XRD patterns and HRTEM images of highly crystalline platinum nanoparticles stacked in a face-centered cubic lattice structure as shown in the photograph. (c) XPS spectrum of platinum ion clusters on polyaniline and platinum nanoparticles on polyaniline taken out after synthesis. (d) FT-IR spectrum of polyaniline nanosheets before and after synthesis of platinum nanoparticles. The characteristic peaks of polyaniline are shown in the picture.
Figure 3 is a typical CV curve of (a) platinum nanoparticles supported on polyaniline nanosheets, (b) platinum nanoparticles supported on carbon, 50 mV s in a 0.1 M aqueous perchloric acid solution containing 1 M methanol at 25°C. ^{It was} measured for 50 cycles with a scan rate of ^1. (c) TEM photograph of platinum nanoparticles supported on polyaniline nanosheets synthesized when air was saturated with heptane vapor and the surface tension of water decreased. (d) Representative CV curves of platinum nanoparticles supported on polyaniline according to the change of the surface tension of water, in 0.1 M perchloric acid aqueous solution containing 1 M methanol at 25 ℃ for 50 cycles at a scanning rate of 50 mV s ^{- 1} Was measured.
Figure 4 is a HRTEM photograph of platinum nanoparticles supported on PANI nanosheets. A two-dimensional Fourier transform is inserted. HRTEM photographs confirm that the highly crystalline platinum nanoparticles supported by PANI are in the form of spheres.
5 is a time-current curve of PANI-supported platinum nanoparticles (red) and Pt/C (black), measured for 7200 seconds at 0.4 V in 0.1 M perchloric acid and 1 M methanol aqueous solution at 25°C. Time current curves run at 0.4 V for 7200 s are shown to demonstrate the improved electrochemical stability of PANI-supported platinum nanoparticles. The PANI-supported platinum nanoparticles clearly observed a slower current density reduction and higher steady state current density than commercial Pt/C. It should be noted that the initial decrease in the current density is caused by the formation of intermediates such as -(CO) _ads , -(OH) _ads , and -(CH ₃ OH) _ads .
Figure 6 is a supported platinum to the polyaniline nanoparticles (red) and cyclic voltammetry curves of Pt / C (black), at 25 ℃ in 0.1 M perchloric acid aqueous solution of 50 mV s ^- was measured with a scanning rate of ^1. Figure 6 shows the circulating current voltage curve of platinum nanoparticles supported on PANI measured in 0.1 M aqueous perchloric acid solution. In addition, the circulating current voltage curve of Pt/C is shown as a control. Hydrogen adsorption/desorption regions (-0.2-0.1 V), double layer regions (0.1-0.4 V), and oxide formation/removal regions (> 0.4 V) were observed. The electrochemically active area (ECSA) was calculated from the total amount of charge (Q _H ) of the baseline corrected hydrogen adsorption region based on the bilayer region, according to equation (1):
ECSA = Q _H / ( m _Pt x 210 x 10 ^-6 ) [m ² g ^-1 ] (1)
Here, m _Pt is the content of Pt, and 210 x 10 ^-6 is the theoretical value of the formation of a single layer of hydrogen in a smooth surface area. The calculated ECSA value of PANI-supported platinum nanoparticles was 94.57 m ² g ^-1 , while the commercial Pt/C (40%) was 41.73 m ² g ^-1 .

Hereinafter, the present invention will be described in detail through examples. It should be noted that the following examples are not intended to limit the present invention, but are intended to illustrate the present invention.

Example

We report a simple and environmentally friendly synthesis method of high areal density platinum nanoparticles immobilized on polyaniline nanostructures. First, high conductivity two-dimensional polyaniline nanosheets were synthesized on ice with a thickness of about 30 nm and a size of several square centimeters, and transferred to an aqueous solution containing 0.5 mM K ₂ PtCl ₄ . The solution was heated at 70° C. for 5 minutes without stirring. The process is fast emerging PtCl voluntarily to reduce the surface tension of water ^{₄₂ -} were induced ion clusters, it was critical to get the platinum nano-particles of high surface density. This resulted in the formation of a complex with the secondary amine (or tertiary imine) of the polyaniline nanosheet. The addition of formic acid to the complex resulted in the formation of platinum nanoparticles fixed to the polyaniline nanosheets. 1 schematically illustrates the synthesis of platinum nanoparticles using polyaniline as a support at an air-water interface.

The morphology of the platinum nanoparticles in the two-dimensional polyaniline nanosheets was investigated by transmission electron microscopy (TEM). As shown in FIG. 2A, platinum nanoparticles using polyaniline nanosheets as a support could be obtained with remarkably high areal density. It was confirmed that it had an average particle diameter of 2.68±0.27 nm through TEM photo analysis displayed on the bar graph inserted in FIG. 2A. The enlarged TEM image shown in FIG. 2A is also finely dispersed without agglomeration, and the formation of regular platinum nanoparticles is described. Additional TEM images are shown in FIG. 4.

The crystal structure of platinum nanoparticles supported by polyaniline nanosheets was investigated by powder X-ray diffraction (XRD) experiments. As shown in Figure 2b, the XRD pattern showed the presence of (111), (200), (220), (311), and (222) planes of platinum nanocrystals stacked in a face-centered cubic lattice structure. The average size of platinum nanoparticles was predicted to be 4.36 nm through Scherrer equation ²⁴ . The other peaks at 2θ = 24.8° and 27.9° corresponded to the (002) and (020) planes of the orthorhombic polyaniline nanocrystals in P222 space group ²² . The high-resolution transmission electron microscope (HRTEM) image inserted in FIG. 2B confirms that the highly crystalline platinum nanoparticles in the polyaniline support have a spherical shape.

X-ray photoelectron spectroscopy was used to better understand the underlying mechanism of platinum nanoparticle synthesis at the air-water interface. When the polyaniline nanosheets were heated on the surface of water containing K ₂ PtCl ₄ for 5 minutes and then taken out, as shown in FIG. 2c, the Pt(II) ion clusters migrated to polyaniline from the presence of two peaks of 72.8 and 76.0 eV. It turned out. The chemical reduction of formic acid resulted in a clear peak shift to 71.5 eV and 74.8 eV corresponding to Pt4f _{7 /2} and Pt4f _{5 /2} for the two peaks, respectively. The separated peak shows that 83.8% of Pt(II) ions were reduced to Pt(0). Therefore, it is believed that a large number of well-ordered molecular bonding positions throughout the crystalline polyaniline nanosheets located at the air-water interface effectively nucleated platinum ion clusters to form only 2.7 nm of platinum nanoparticles without aggregation. Is inferred.

It should be noted that the Fourier transform infrared spectra (FT-IR) shows the change in the vibration state of the polyaniline nanosheets according to the synthesis result of the platinum nanoparticles. As shown in FIG. 2D, after binding of the platinum nanoparticles, the characteristic peak of polyaniline shifted to a high wavenumber. The large blue shift (26 cm ^-1 ) of the N=Q=N stretching vibration peak is particularly noteworthy. This can be said to be due to the phenomenon of electron delocalization between the platinum d-orbital and the p-conjugated polyaniline, which causes the formation of Pt-N bonds, helping to reduce the decomposition and desorption of platinum during electrocatalysis. Gives ^{16, 25}

3A is a cyclic voltage-current curve (CVs, cyclic voltammograms) of platinum nanoparticles supported on polyaniline nanosheets measured at a scanning rate of 50 mV/s in a 0.1 M aqueous perchloric acid solution containing 1 M methanol at 25°C. ). The peak current density ( I _f ) appearing at approximately 0.7 V in the forward scanning corresponds to methanol oxidation, and the peak current density ( I _b ) appearing at approximately 0.5 V in the reverse scanning is associated with the oxidation of the carbon intermediate. Hydrogen adsorption/desorption was observed in the -0.2-0.1 V range. Interestingly, the I _f / I _b value at the first injection was very high at 2.45, which maintained a high value of 1.84 after 50 cycles. It is also noteworthy that the current density decreased by only 8% after 50 cycles. This indicates good carbon monoxide resistance and high durability of the polyaniline-supported platinum nanoparticles against methanol oxidation, all due to the platinum nanoparticles finely dispersed and strongly fixed in the polyaniline nanosheets.

These results contrast visibly with commercial Pt/C catalysts (containing 40% platinum by mass). As shown in Fig. 3b, the peak current density obtained in Pt/C was approximately two times lower than that of platinum nanoparticles supported on polyaniline. The current decreases significantly with the progress of the cycle, keeping only 60% of the initial value after 50 cycles. The I _f / I _b value of Pt/C was 0.92, which was well agreed with the literature. ^26-28 improved electrochemical of platinum nanoparticles supported on a polyaniline for methanol oxidation stability was identified to be added, by the time the current method as shown in Fig.

Therefore, the results obtained so far can conclude that the two-dimensional polyaniline nanosheets at the air-water interface can be a new platform for the synthesis of platinum nanoparticles having a uniform and high areal density.

It should be noted that the electrochemically active area (ECSA) of platinum nanoparticles supported on polyaniline is 94.57 m ² /g in 0.1 M aqueous perchloric acid solution, whereas that of commercial Pt/C is 41.73 m ² /g (Fig. 6).

We conclude by referring to the role of the surface tension of water in contact with air in determining the size and distribution of platinum nanoparticles. We carried out a control experiment in the condition that the surface tension of water was reduced by saturating air with heptane vapor while leaving the other conditions the same.

This was expected to reduce the surface tension of water from 72 to 52 mN/m at 25 °C. ²⁹ Therefore, there were fewer clusters of platinum ions on the polyaniline nanosheets, and thus, as shown in FIG. 3, a significantly low areal density was observed along with the agglomeration of a significant amount of platinum nanoparticles. This inevitably lowered peak current (more than twice) and their durability deteriorated against methanol oxidation can be confirmed in FIG. 3D. However, it is interesting to see I _f / I _b values of 1.7 to 1.9, which are still higher than commercial Pt/C catalysts, signaling the importance of the use of two-dimensional polyaniline for good catalytic activity.

In summary, platinum nanoparticles having a size of 2.7 nm, uniform, high crystallinity, and very catalytically active, were synthesized in a two-dimensional conductive polymer having a large area.

The spontaneous and rapid clustering of platinum ions at the location of the polyaniline molecule at the air-water interface was the key to achieving this. The I _f / I _b value of the platinum nanoparticles supported on polyaniline was very high at 2.45, and high catalytic activity was well maintained at 50 cycles or more. In addition, the new catalyst had a peak current density that was twice as high as that of commercial Pt/C catalysts, along with more than twice the ECSA and improved carbon monoxide tolerance.

matter.

Aniline (>99.5%), perchloric acid (HClO ₄ , 70%), and 5% Nafion ^TM 117 in a mixture of low aliphatic alcohol and water were purchased from Sigma Aldrich. Ammonium persulfate (APS, 98.0%), hydrochloric acid (HCl, 36%), formic acid (97%), potassium tetrachloride (II) acid (K ₂ PtCl ₄ , 99.9%), commercial Pt/C (40 wt% loading) on carbon black) was purchased from Alfa Aesar. Methanol (99.9%, HPLC grade) and absolute ethanol (99.9%, HPLC grade) were purchased from JT Baker and Fisher, respectively. Water in all experiments was purified through the Millipore system.

Polyaniline ( PANI ) Nanosheet synthesis.

The PANI nanosheets were synthesized according to the procedure described in our previously published work. ^{[ 1]} 0.25 M aniline in 1 M hydrochloric acid and 0.25 M APS in 1 M hydrochloric acid were continuously dropped onto ice at 0°C. After 5 minutes of reaction, a green PANI nanosheet was obtained in a size of several centimeters. [1] IY Choi, J. Lee, H. Ahn, J. Lee, HC Choi, MJ Park, Angew . Chem . Int . Ed. 2015, 54, 10497-10501.

PANI Supported Synthesis of platinum nanoparticles.

The PANI nanosheets were transferred to the surface of 50 mL water containing 10.4 mg of K ₂ PtCl ₄ . With the PANI nanosheets maintained at the air-water interface, the solution was heated to 70° C. for 5 minutes, followed by 1.5 mL of formic acid. After further heating for 30 minutes, the solution was cooled to room temperature, and the resulting platinum nanoparticles supported by PANI at the water-air interface were transferred to the target substrate, and then washed repeatedly with distilled water.

In addition, the other conditions were the same, and the surface tension of water was changed by saturating the air with heptane vapor.

On carbon Supported Preparation of Pt/C catalyst.

5 mg of Pt/C was suspended in 1 mL of ethanol containing 50 L of Nafion ^TM 117 solution. A uniform ink was prepared by dispersing the mixture under sonication. 5 μl of the resulting Pt/C ink was dropped onto the surface of a glass carbon electrode (CHI 104, diameter of 3 mm) to confirm the electrochemical catalyst properties.

Molecular and structural properties.

Transmission electron microscopy (TEM) pictures of platinum nanoparticles supported on PANI were taken through a JEOL-JEM-1011 electron microscope. High-resolution transmission electron microscope (HR-TEM) was taken through a JEOL-JEM-2100F electron microscope. For the measurement of TEM and HRTEM, a 200 mesh copper TEM grid without a formvar coating was used. X-ray photoelectron spectroscopy was measured with a monochromatic Al Kα source on a VG Scientific ESCALAB 250 (Thermo Scientific) instrument. Powder X-ray diffraction (XRD) data of the sample was measured on a 9B beamline of Pohang Accelerator Laboratory (PAL) using synchrotron radiation. XPS and XRD samples were prepared by transferring platinum nanoparticles supported on PANI from the water-air interface to a silicon wafer. Fourier transform infrared spectroscopy was measured using potassium bromide (KBr) (Aldrich) pellets.

Electrochemical catalyst properties.

The electrochemical catalytic properties of platinum nanoparticles and Pt/C supported on PANI were investigated using a three-electrode system at room temperature. A glass carbon electrode, a platinum wire, and a silver/silver chloride electrode were used as a working electrode, a counter electrode, and a reference electrode, respectively. The free carbon electrode was carefully wiped with 0.05 μm d of aluminum oxide powder and then washed with distilled water. Cyclic voltage current measurement (VersaSTAT3, Princeton Applied Research, AMETEK, Inc.) was performed in a 0.1 M aqueous perchloric acid solution containing 1.0 M methanol at a scanning speed of 50 mV s ^{- 1} based on a silver/silver chloride electrode of -0.2 to 1.0 V. Was implemented in scope. The electrochemically active area (ECSA) of platinum nanoparticles supported on polyaniline and Pt/C was calculated from the sum of the amount of charge in the hydrogen adsorption region measured in 0.1 M aqueous perchloric acid solution. The time amperometric test was run at 0.4 V for 7200 seconds. Prior to all measurements, the electrolyte solution was purged with argon for 20 minutes to remove residual oxygen. The content of platinum in each catalyst was obtained through inductively coupled plasma atomic emission spectroscopy (ICP-AES, iCAP 7400, Thermo Scientific).

Claims (11)

delete delete delete delete delete delete Providing a solution comprising platinum ions;
Providing a two-dimensional polyaniline nanosheet;
Positioning the two-dimensional polyaniline nanosheets on the surface of the solution; And
Heating the solution
Composite manufacturing method comprising a. The method of claim 7, wherein the solution has a surface tension of 70 mN/m or more. The method of claim 7 or 8, wherein the solution is an aqueous solution. The method of claim 7 or 8, wherein the heating is performed in an unstirred state. The method of claim 7 or 8, wherein in the step of heating the solution, the solution contains a reducing agent.

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