KR101263762B1 - OXYGEN-REDUCTION ELECTROCATALYST CONTAINING BIMETALLIC AuPd NANOPARTICLE, AND PRODUCING METHOD OF THE SAME - Google Patents

Abstract

The present application relates to an oxygen-reducing electrode catalyst comprising bimetallic AuPd nanoparticles supported on a carbon-based support, and a method for preparing the same, and a fuel cell including the oxygen-reducing electrode catalyst. The oxygen-reducing electrocatalyst according to this shows stability and / or alcohol tolerance with good oxygen-reducing activity under acidic conditions.

Description

OXYGEN-REDUCTION ELECTROCATALYST CONTAINING BIMETALLIC AuPd NANOPARTICLE, AND PRODUCING METHOD OF THE SAME}

The present invention relates to an oxygen-reducing electrode catalyst comprising bimetallic AuPd nanoparticles and a method for preparing the same, and a fuel cell including the oxygen-reducing electrode catalyst.

In recent years, research on an electrocatalyst material to replace platinum in the fuel cell field is continuously required. In particular, the fuel cell oxygen cathode catalyst for ORR is considered to be one of the most important research areas because it is mainly reduced by a sluggish oxygen reduction reaction (ORR) requiring high overvoltage in the fuel cell cathode. Currently, Pt or Pt-based electrocatalysts are most widely used as cathode catalysts in fuel cells due to their high activity against ORR, but do not contain low Pt-based or Pt content due to the high unit cost and limited supply of Pt. A lot of spurs are being put into developing efficient alternative catalysts. In addition, several methods have been used to introduce microstructures such as nanoparticles or to alloy other metals with Pt to improve catalytic activity with very low Pt loading. For example, as a non-platinum electrocatalyst, nanostructured materials based on relatively inexpensive transition metals (eg Pd), carbon-based nanomaterials with modified surfaces (eg nitrogen-doped carbon nanotubes) ) And combinations thereof are generally studied.

As one of the more economical and abundant metals compared to Pt, the electrocatalytic activity of Au has been studied, but due to its poor chemisorption properties, it generally exhibits low catalytic activity. In recent years, in order to improve electrocatalytic activity, methods of increasing the surface ratio to volume using nanoparticles or porous structures and surface modification or alloying with other metals have been mainly attempted. However, catalysts based on pure Au exhibit lower activity than Pt-based catalysts for ORR, and Pt is generally selected as a modified or alloying metal for Au for good catalytic activity. In fact, AuPt alloy nanoparticles have been reported to have high catalytic activity against ORR and methanol oxidation reaction (MOR). Recently, a study has been reported to evaluate Au nanoparticles having Pt introduced for ORR and formic acid by using a spontaneous deposition method as Au containing Pt nanoparticles. Synthesis of sponge-type Au / Pt (core / shell) electrode catalysts with hollow cavities using a modified galvanic replacement reaction has been suggested, resulting in increased catalytic activity for ORR and MOR. Reported.

On the other hand, Pd has received much attention because it is cheaper and richer than Pt while having very similar characteristics to Pt (for example, the same group on the periodic table, the same FCC crystal structure and similar atomic size). Indeed, many Pd-based electrocatalysts have been studied much in recent years as one of the candidate Pt-free catalysts. Due to the significant similarity between Pd and Pt, Au catalyst systems coated or alloyed with Pd instead of Pt were introduced. For example, Pd-coated nanoporous Au and nanoporous Au-Pd alloys were synthesized and evaluated for ORR and MOR, respectively. In addition, it has been reported that Pd-modified Au nanoparticles for ethanol oxidation under basic conditions show increased catalytic activity for methanol, ethanol and formic acid oxidation. However, such catalysts include substitution of Pd after underpotential deposition (UPD) of a Cu template on nanoporous Au; Dealloying after production of the multicomponent metal glass; There is a problem that requires a rather complex synthesis process, such as Pd precursor reduction, on a nanostructured Au template using a reducing agent (eg, ascorbic acid). In addition, such Au-Pd dimetallic catalysts have a problem of being active only in neutral or basic environments due to the relatively low stability of Pd under acidic environments.

Accordingly, the present application is to provide an oxygen-reduction electrode catalyst having excellent oxygen-reduction activity and stability without containing Pt, and specifically, an oxygen-reduction electrode including bimetallic AuPd nanoparticles. The present invention provides a fuel cell including a catalyst, a method for preparing the same, and an electrode catalyst for reducing oxygen.

However, the problems to be solved by the present invention are not limited to the problems described above, and other problems not described can be clearly understood by those skilled in the art from the following description.

One aspect of the present application provides an oxygen-reducing electrode catalyst comprising bimetallic AuPd nanoparticles supported on a carbon-based support.

Another aspect of the present application provides a fuel cell comprising a cathode containing the oxygen-reduction electrode catalyst according to the present application.

Another aspect of the present application is to form Au nanoparticles supported on a carbon-based support; Forming a bimetallic AuPd nanoparticles by depositing Pd by spontaneous reduction of the palladium cation on the surface of the Au nanoparticles supported on the carbon-based support: a method for producing an oxygen-reduction electrode catalyst according to the present application To provide.

The present application enables easy and simple preparation of an oxygen-reducing electrode catalyst comprising bimetallic AuPd nanoparticles supported on a carbon-based support through spontaneous reduction of palladium without further reducing agent treatment, in particular the oxygen-reduction according to the present application. The electrocatalyst has a form including an Au nanoparticle core supported on a carbon-based support and a porous Pd shell formed on the Au nanoparticle core, thereby surpassing the activity of commercially available Pt / C in an acidic environment. It shows excellent stability and alcohol resistance together with activity, and can be usefully applied as a cathode in a fuel cell.

1 shows TEM images of (A) Au nanoparticles and (B) AuPd (1: 0.61) / C nanoparticles synthesized by spontaneous reduction reaction, and HAADF-STEM of (C) AuPd (1: 0.61) / C. Images and elemental mapping images are shown: The magnified portions of (A) and (B) are magnified TEM images and HAADF-STEM images of single Au NPs on carbon, respectively, and (C) is AuPd (1: 0.61) / Representative HAADF-STEM image of C (left top panel) and its Pd (red) and Au (green) atomic mapping images, the blue of the right top panel corresponding to the carbon support of AuPd (1: 0.61) / C will be.
2 is (a) Au, (b) AuPd (0.5 mM PdCl ₂ ), (c) AuPd (5 mM PdCl ₂ ), (d) AuPd (10 mM PdCl ₂ ), and (e) AuPd (20 mM PdCl ₂ ) Representative UV-vis spectra including nanoparticles are shown: Magnification shows absorbance spectra for aqueous PdCl ₂ solution.
FIG. 3 shows the cyclic voltammetry curves obtained from AuPd / C-modified GC electrodes in Ar-saturated 0.1 M HClO ₄ solution at a scanning rate of 10 mV s ⁻¹ : Arrows represent Au / C and AuPd (1: 0.15) ) / C shows the expanded cyclic voltage current curve for each.
FIG. 4 shows a graph of integrated reduced charge (Δ) of surface Pd oxide with Pd / Au wt% ratio (O) and Pd precursor concentration measured by SEM-EDS, and charge density is normalized to GSA Obtained).
5 is a rotation speed and 10 mV s of 1600 rpm ^- bulk Pt, Pt / C in the ^first scan rate, Au / C, AuPd (1 : 0.15) / C, AuPd (1: 0.49) / C, AuPd (1 : 0.61) / C, and AuPd (1: 0.73) / C RDE Voltamograms for Oxygen Reduction at O ₂ -Saturated 0.5 MH ₂ SO ₄ of Each Electrode, and Current Density by Normalization of Electrode GSA Obtained.
FIG. 6 shows a Koutecky-Levich plot for oxygen reduction obtained from the RDE data of FIG. 5: (Δ) Pt / C, (O) AuPd (1: 0.61) / C, and (□) AuPd (1: 0.73) / C.
Figure 7 shows the stability test results of AuPd (1: 0.61) / C.
FIG. 8 shows (a) Pt / C, (b) AuPd in a deoxygenated 0.5 MH ₂ SO ₄ solution in the presence (solid line) and absence (dashed line) of 0.5 M methanol at a scan rate of 10 mV s ⁻¹ . 1: 0.61) / C, and (c) cyclic voltammograms of AuPd (1: 0.73) / C catalysts.

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

As used herein, the terms "about", "substantially", and the like, are used at, or in close proximity to, numerical values when manufacturing and material tolerances inherent in the meanings indicated are provided to aid the understanding herein. In order to prevent the unfair use of unscrupulous infringers. In addition, throughout this specification, "step to" or "step of" does not mean "step for."

Hereinafter, a fuel cell including the oxygen-reduction electrode catalyst of the present application, a method of manufacturing the same, and the oxygen-reduction electrode catalyst will be described in detail with reference to embodiments, examples, and drawings. However, the present application is not limited to these embodiments, examples and drawings.

Oxygen-reduction electrode catalyst according to an aspect of the present application may be to include a bimetallic AuPd nanoparticles supported on a carbon-based support, but is not limited thereto.

In one embodiment, the dimetallic AuPd nanoparticles may be formed including an Au core and a Pd shell surrounding the Au core, but is not limited thereto.

In one embodiment, the Pd shell may be to include a porous Pd layer, but is not limited thereto.

In one embodiment, the porous Pd layer may be deposited by a spontaneous reduction reaction by a galvanic replacement reaction of palladium cations on the surface of the Au nanoparticles, but is not limited thereto.

In one embodiment, the weight ratio of Au: Pd in the dimetallic AuPd nanoparticles may be about 1: about 0.1 to about 1, but is not limited thereto.

In one embodiment, the weight ratio of Au: Pd in the bimetallic AuPd nanoparticles may be about 1: about 0.15 to about 0.8, but is not limited thereto.

In one embodiment, the weight ratio of Au: Pd in the bimetallic AuPd nanoparticles may be about 1: about 0.5 to about 0.7, but is not limited thereto.

In one embodiment, the dimetallic AuPd nanoparticles may have a size of about 1 nm to about 20 nm, but is not limited thereto. For example, the dimetallic AuPd nanoparticles may have a size of about 1 nm to about 20 nm, or about 5 nm to about 20 nm, or about 10 nm to about 20 nm, but is not limited thereto.

In one embodiment, the carbon-based support may include one selected from the group consisting of carbon black, graphite carbon, carbon nanotubes, carbon fibers, and combinations thereof, but is not limited thereto. It is not.

In one embodiment, the oxygen-reduction electrode catalyst may be stable under acidic conditions, but is not limited thereto.

In one embodiment, the oxygen-reduction electrode catalyst may be alcohol resistant under acidic conditions, but is not limited thereto. For example, the oxygen-reduction electrode catalyst may be resistant to alcohols such as methanol and ethanol even under acidic conditions, but is not limited thereto.

A fuel cell according to an aspect of the present application may include, but is not limited to, a cathode containing the oxygen-reducing electrode catalyst.

Method for producing an oxygen-reduction electrode catalyst according to an aspect of the present application, to form Au nanoparticles supported on a carbon-based support; Deposition of Pd by spontaneous reduction of the palladium cation on the surface of the Au nanoparticles supported on the carbon-based support to form a bimetallic AuPd nanoparticles: may be, but is not limited thereto.

In one embodiment, depositing Pd by spontaneous reduction of the palladium cation, the precursor solution containing the palladium cation and the Au nanoparticles supported on the carbon-based support is mixed, and supported on the carbon-based support The palladium cation is reduced and deposited to Pd by the galvanic replacement reaction on the Au nanoparticle surface by oxidizing and etching Au into a gold cation from the Au nanoparticle surface to form the dimetallic AuPd nanoparticle. It may include, but is not limited to.

In one embodiment, the Pd deposited by the galvanic substitution reaction on the surface of the Au nanoparticles supported on the carbon-based support may be to form a porous Pd layer, but is not limited thereto.

In one embodiment, the precursor containing the palladium cation may be one containing PdCl ₂ , but is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present application is not limited thereto.

[ Example ]

In this embodiment, hydrogen tetrachloroaurate trihydrate (HAuCl ₄ H ₂ O), sodium citrate (Na ₃ C ₆ H ₅ O ₇ H ₂ O), 5.0 wt% Nafion, and Potassium hexacyanoferrate (K ₃ [Fe ₃ (CN) ₆ ]) was obtained from Sigma Aldrich (St. Louis, Mo.). Palladium chloride (PdCl ₂ ) and carbon black were obtained from Alfa Aesar (Ward Hill, Mass.). Sulfuric acid (H ₂ SO ₄ ) and perchloric acid (HClO ₄ ) used as electrolytes are described in Dae Jung Co. (KCl) was purchased from Duksan Co. From Korea. A commercial Pt / C (20 wt% Pt loading on carbon Vulcan XC-72) catalyst was from E-TEK and methyl alcohol was obtained from Hayman (Witham, Essex, UK). All solvents and chemicals were analytical-reagent grade and all solutions were prepared using 18 MΩcm ^-1 deionized water.

< Example  1> carbon-supported AuPd Preparation of A / C Catalyst

Au Manufacture of A / C

Au nanoparticles were synthesized by methods similar to those described in McFarland et al. (McFarland, AD; Haynes, CL; Mirkin, CA; Van Duyne, RP; Godwin, HAJ Chem. Edu. 2004, 81, 544A-544B). . First, 20 mL of 1.0 mM HAuCl ₄ aqueous solution was heated until boiling, then 2 mL of 38.8 mM citrate solution was added to the boiling solution with vigorous stirring. The color of the solution changed gradually to light yellow, purple, and dark red, and when it was dark red, the stirring was stopped and stored under dark conditions until the solution was used. The Au nanoparticle solution was mixed with the carbon carrier (2.0 mg / mL) dispersed in water with stirring for 5 hours, and the resulting carbon-supported Au nanoparticles (Au / C) were filtered and washed sufficiently with distilled water. It was. The Au / C was separated from the wash by centrifugation at 4000 rpm for 20 minutes, and this washing was repeated at least three times. Thereafter, washed Au / C that settled to the bottom of the centrifuge cell was used after complete drying in a vacuum environment.

Au On nanoparticles Pd Spontaneous deposition of

AuPd / C was prepared as follows.

The Au / C solution (1 mg / mL) dispersed in water was mixed with PdCl ₂ at various concentrations (0.5, 5, 10, and 20 mM) and stirred at room temperature for 5 hours to form a thin film of Pd on the Au nanoparticle surface. Was deposited. AuPd / C prepared in the suspended state was filtered and washed thoroughly with distilled water to remove unreacted Pd precursor. The AuPd / C catalyst was completely dried under vacuum and stored in a refrigerator until use.

< Experimental Example  1> Analysis of Electrocatalyst

In order to confirm the surface form and composition of the catalyst prepared as in Example 1, a high resolution transmission electron microscope (HR-TEM; JEOL JEM-3010, 300 kV) image was obtained. Elemental mapping images were obtained using a FEI Tecnai F20 Scanning Transmission Electron Microscope (STEM). UV-vis spectra of the Au / C and AuPd / C hydrosols were obtained using an HP-8452A spectrophotometer equipped with quartz cells. The atomic composition ratio of the AuPd / C catalyst was analyzed using energy dispersive X-ray spectroscopy (EDS) with a scanning electron microscope (SEM) (Jeol JSM-6700F). .

< Experimental Example  2> Electrochemical Measurement

Glassy carbon (GC) disk electrode surface [diameter = 3 mm, Bioanalytical Systems, Inc. (BAS)] was independently loaded with each of Pt / C, Au / C, and AuPd / C catalysts as follows. First, each catalyst suspension was prepared by mixing the catalyst of Example 1 with deionized water (2.0 mg / mL). 10 μL of each of these suspensions was pipetted onto a GC disc, applied and then dried. This step was repeated three times to prepare a GC disk electrode. Then 10 μL of Nafion solution (0.05 wt%) was applied on the dried electrode and dried at room temperature. Bulk Pt (bPt) electrodes (diameter = 3 mm, Bioanalytical Systems, Inc.) were used as comparative examples. The activity of the catalyst of Example 1 on ORR was assessed by rotating disk electrode (RDE) voltammetry. All electrochemical experiments were performed using a RDE-1 rotor and BAS 100 B / W electrochemical analyzer (Bioanalytical Systems Inc.) with a saturated calomel reference electrode (SCE) and Au wire counter electrode. The RDE experiment was performed in 0.5 MH ₂ SO ₄ aqueous solution saturated with oxygen or nitrogen (Dong-A gas Co.) at a scan rate of 10 mV s ⁻¹ . Cyclic voltammetry (CV) was performed using a 900B bipotentiostat (CH Instrument, Inc.). Normalization to the geometric surface area (GSA) of each modified electrode determined by chronocoulometry (CC) in 10 mM K ₃ Fe (CN) ₆ aqueous solution containing 0.1 M KCl as supported electrolyte The normalization converts the measured current into a current density.

<Characteristic analysis result>

AuPd Characteristics of / C

The shape and size of Au NP and AuPd / C prepared above were confirmed by TEM image. Figure 1a shows a typical TEM image of Au nanoparticles before and after loading on the carbon carrier (magnified view of Figure 1), where Au nanoparticles (about 13 mm in diameter) have a nearly spherical narrow particle distribution. (narrow size distribution) was confirmed. Once loaded, the Au nanoparticles were well dispersed on the carbon support without changing the size distribution (not shown). After spontaneous deposition of Pd on Au nanoparticles, the resulting AuPd nanoparticles also showed a similar size to the parent Au nanoparticles and were evenly dispersed on the carbon support (FIG. 1 b). Indeed, no significant size difference was observed between the Au nanoparticles and the AuPd nanoparticles (see also amplification of a and b in FIG. 1), indicating that spontaneous Pd layer deposition is associated with Au etching. In other words, Pd coating on Au cores probably occurred through mechanisms similar to galvanic substitution reactions (GRR). ^{_{Au (III) (AuCl 4 -}} / Au, +1.002 V vs. NHE) is Pd (II) compared to ^{(Pd 2 + / Pd, 0.951} V vs. NHE) which is slightly more positive (positive) the standard reduction potential Considering this, the GRR between Au and Pd (II) (Scheme 1) is not expected to be very advantageous, and it is expected to produce AuPd nanoparticles only when the chlorine ion concentration is rather high. On the other hand, the wt% ratio of Pd / Au evaluated by SEM-EDS suggests a fairly advantageous Pd layer deposition on the Au core. Indeed, the average Pd / Au wt% ratio (measured at 10 different positions of each catalyst) increased with Pd precursor concentration as follows: 0.15 ± respectively for 0.5, 5, 10, and 20 mM PdCl ₂ . 0.06, 0.49 ± 0.08, 0.61 ± 0.11, and 0.73 ± 0.11. In the following examples, a series of prepared AuPd / C catalysts were designated as AuPd (Au: Pd wt% ratio) / C depending on the composition. In addition, the molar ratio of Pd increase to Au decrease is about 1.5: 1, which is in good agreement with the GRR ratio between Au / Au (III) and Pd (II) / Pd, especially when the Pd precursor concentration is ≧ 10 mM. On the other hand, the substitution molar ratio of Au (III) / Pd was determined to be greater than 1.5 when the Pd precursor concentration was low, that is, at 3.5 (0.5 mM PdCl ₂ ) and 2.4 (5 mM PdCl ₂ ). It suggests that other processes, such as underpotential deposition (UPD), may be involved in Pd layer formation. The reason why PRR deposition similar to GRR is observed in connection with Au etching is that, contrary to the thermodynamic projections from the reduction potential, chlorine anions from PdCl ₂ adsorb on the Au nanoparticle surface, leading to increased local chlorine anion concentrations. This may be because the oxidation of Au to AuCl ₄ ⁻ and the reduction of Pd ²⁺ can be promoted by shifting the equilibrium state to the right side of the following Scheme 1:

[Reaction Scheme 1]

The total average wt% of Au and Pd measured by EDS was about 10 wt% for all catalysts prepared. The deposited Pd layer is not easily distinguished from the Au cores in the TEM image, suggesting epitaxial growth of the Pd layer on the surface of the Au nanoparticles. On the other hand, high-angle annular dark-field scanning TEM (HAADF-STEM) analysis indicated contrast differences around the Au nanosphere core and Pd shell. Indeed, a close-up examination of a single AuPd (1: 0.61) NP loaded on carbon in the HAADF-STEM image makes it possible to distinguish brighter cores from darker shells (magnification of b in FIG. 1). This indicates that the nanoparticles are formed into shells containing elements Pd that are lighter than the core Au because the change in contrast in HAADF-STEM is proportional to the square of the number of atoms of the element. Elemental mapping of Au and Pd clearly shows the AuPd nanoparticle structure formed of Au cores encapsulated into a uniformly deposited Pd thin film shell (FIG. 1C).

The nanoparticles were further analyzed by UV-vis absorption spectroscopy. In addition to the TEM analysis, the size of the parent Au nanoparticles could be successfully measured by UV-vis absorption spectra. A strong absorbance at ˜520 nm due to surface plasmon resonance (SPR) of Au nanoparticles prepared using citrate reductase was observed in the Au nanoparticle colloid solution (FIG. 2 a). ). The color of the Au nanoparticle containing solution depends on the size and shape of the nanoparticles. The absorbance peak at 520 nm is closely related to the Au nanoparticle size (about 13 nm) measured in the TEM image. On the other hand, Au SPR at 520 nm decreased with increasing concentration of the Pd precursor used and disappeared when the concentration of the Pd precursor was ≧ 10 mM (FIG. 2 b to e). These observations further demonstrate that the Pd layer completely covers the Au NP core. UV-vis including by from carbon interference and a solution of at absorbance measured due to a difficult to collect the nanoparticles being without carbon support, the nano-particles in the absence of the carbon support state catalyst, and unreacted residual Pd precursor (Pd ^{2 +)} It should be noted that UV-vis spectra were obtained for the solution. Therefore, increased PdCl ₂ According to the concentration To the 415 nm absorbance intensity that increases in a stepwise manner is due to the Pd ^{+ 2.} In fact, the absorption spectrum of the solution containing only the PdCl ₂ is in proportion to the concentration increase of the absorption intensity (an enlarged view of FIG. 2), which is also the absorbance at 2, c to e to 415 nm by the residual Pd ^{2 +} It is implied.

The electrochemical properties of Au / C and AuPd / C catalysts were confirmed by CV in Ar-saturated 0.1 M HClO ₄ solution. In this example, all electrochemical results for the catalyst, including the CV shown in FIG. 3, are shown as current density after normalization to the corresponding GSA. GSAs of the electrodes were determined by chronocoulometry (CC), as described in JH Shim et al. (JH Shim, J. Kim, C. Lee and Y. Lee, J. Phys . Chem . C , 2011, 115, 305). Evaluation was made in 10 mM K ₃ Fe (CN) ₆ solution containing 0.1 M KCl. CC vs. ¹ time ^/ from the slope of a linear plot of charge measured at ^2, it was GSAs is larger than the crystal substrate at the GC electrode (0.071 cm ²⁾ (about 0.080 ~ 0.110 cm ^2, depending on the catalyst loading). This indicates that the AuPd / C catalyst is evenly loaded on the insulator of the GC electrode resulting in increased GSA.

The normalized cyclic voltammogram from each catalyst loaded GC electrode showed three specific regions: double layer capacitive region, hydrogen adsorption / desorption region, and metal oxide formation / Reduction zone. In particular, it was observed that the capacitance background current density between the hydrogen adsorption / desorption region and the metal oxide formation / reduction region increased from Au / C to AuPd / C and also increased as the Pd: Au ratio in AuPd / C increased. . Since the particle size measured from the TEM image is not different regardless of the nanoparticles, the change in capacitance current indicates a somewhat porous Pd layer formed on the Au NP core, which increases the actual surface area.

Hydrogen adsorption / desorption at a negative potential range of more than ˜0.0 V was not observed in Au / C. On the other hand, well-defined hydrogen peaks appear in AuPd / C and increase with increasing Pd: Au ratio, supporting the successful deposition of Pd shells on Au cores. It is well known that no hydrogen adsorption occurs at the gold electrode. The anodic scan from 0.55 V corresponds to the formation of Pd surface oxides and ends at the cathodic scan at 0.30 V corresponding to their reduction. In AuPd / C catalysts with a high Pd: Au ratio, the integrated charge amount passed for the cathodic peak, more precisely, for surface Pd oxide reduction at 0.39 V, than in AuPd / C catalysts with a lower Pd: Au ratio, Large, indicating an increased Pd surface area, consistent with that observed at the capacitance current density.

4 shows the charge amount for surface Pd oxide reduction according to the Pd: Au wt% ratio and Pd precursor concentration of a series of AuPd / C catalysts. As described above, in general, as the precursor concentration increases, the Pd: Au wt% ratio and charge amount also increase, while the Pd: Au ratio increases stepwise, while the charge corresponding to the actual surface area of Pd is increased from 0.5 mM to 5 mM. PdCl ₂ There was a slight increase in concentration followed by a significant increase in PdCl ₂ concentrations up to 10 mM. This suggests that the most effective porosity of the Pd layer on the Au core, believed to be related to catalytic activity, appeared at a concentration of 10 mM among the tested precursor concentrations.

<Electrochemical Measurement Results>

On the catalyst ORR

Pt/C > AuPd(1:0.61)/C > AuPd(1:0.49)/C

AuPd(1:0.15)/C > 벌크 Pt >> Au/C. 반파 전위(E _{1 /2}) 역시 ORR 시작 전위와 유사한 것으로 관찰되었다. AuPd(1:0.61)/C (0.53 V vs. SCE)에서의 E _1/2 수치가, 훨씬 더 가파른 RDE 곡선 형태에 의한 시작 전위와 반대로, AuPd(1:0.73)/C (0.52 V vs. SCE) 및 Pt/C (0.49 V vs. SCE) 둘 다에서보다 좀더 양(positive)의 값을 나타내고 있으며, 이는 AuPd(1:0.61)/C에서의 좀더 신속한 ORR 동역학을 나타낸 것이다. 실제로, 혼합된 반응-확산 조절 영역에서의 RDE 곡선 모양은 한계 전류 밀도의 중간 90% 변화에 대한 △E 수치로부터 좀더 분명하게 확인할 수 있다(즉, 더 적은 △E에 대하여, 더 가파른 곡선 기울기): 측정된 △E 수치는 AuPd(1:0.61)/C에서 0.087 V; AuPd(1:0.73)/C에서 0.15 V; 및 Pt/C에서 0.22 V이었다. 게다가, 다른 촉매에 비해 높은, 유사한 확산-한계 전류 밀도가 AuPd(1:0.61)/C 및 AuPd(1:0.73)/C에서 관찰되었다. The catalytic activity of Au / C and a series of AuPd / C catalysts on ORR was investigated using RDE voltammetry under oxidizing conditions. FIG. 5 shows normalized RDE voltammetry curves of each catalyst-loaded GC electrode recorded in O ₂ -saturated 0.5 MH ₂ SO ₄ solution at 1600 rpm. For comparison, ORR activities of commercial Pt / C catalyst-loaded GC and bulk Pt disk electrodes were also evaluated. ORR started at slightly more positive potentials for AuPd (1: 0.73) / C and Pt / C, followed by near proximity at AuPd (1: 0.61) / C. Indeed, the ORR onset potential showed more positive values in the following order: AuPd (1: 0.73)

Pt / C> AuPd (1: 0.61) / C> AuPd (1: 0.49) / C

AuPd (1: 0.15) / C> Bulk Pt >> Au / C. Half-wave potential (E _1/2) also was observed that similar ORR starting potential. The value of E _1/2 at AuPd (1: 0.61) / C (0.53 V vs. SCE) is the AuPd (1: 0.73) / C (0.52 V vs. SCE) and Pt / C (0.49 V vs. SCE) are more positive values than in both, indicating faster ORR kinetics in AuPd (1: 0.61) / C. Indeed, the shape of the RDE curve in the mixed response-diffusion control region can be seen more clearly from the ΔE values for the median 90% change in the marginal current density (ie, steeper curve slope for less ΔE ). ΔE values measured were 0.087 V at AuPd (1: 0.61) / C; 0.15 V at AuPd (1: 0.73) / C; And 0.22 V at Pt / C. In addition, similar diffusion-limiting current densities were observed at AuPd (1: 0.61) / C and AuPd (1: 0.73) / C compared to other catalysts.

Transition during ORR course for two good AuPd / C catalysts (1: 0.73 and 1: 0.61) and commercial Pt / C from RDE voltammetry results obtained at various electrode rotation rates using Koutecky-Levich (KL) equation Calculated number of electrons ( n ):

Where j is the total current density, j _k is the reaction current density, j _d is the diffusion current density. n is the number of electrons transitioned from the ORR, F is the Faraday constant, C _O2 (1.1 × 10 ^-6 mol cm ^-3 ) is the saturated concentration of oxygen, D _O2 (1.4 × 10 ^-5 cm ² s ^-1 ) Is the diffusion coefficient of oxygen and v is the kinematic viscosity of the solution (1.0 × 10 ^-2 cm ²⁾ s ⁻¹ ), and ω is the electrode rotation rate. The parameters for calculation are K.-L. Hsueh et al., K.-L. Hsueh, D.-T. Chin, S. Srinivasan, J. Electroanal. Chem. 153 (1983) 79-95.

FIG. 6 shows a KL plot of the ORR ( j _d ⁻¹ vs. ω ^1/2 ) using RDE current density at 0.10 V (vs. SCE). Plots are completely straight, meaning that ORR kinetics have priority in reactant concentrations. The n values calculated from the slope of the KL plot were 3.94, 4.01, and 4.09 for the Pt / C, AuPd (1: 0.61) / C, and AuPd (1: 0.73) / C catalysts, respectively. Direct ORR pathways through 4-electron migration are preferred over 2-electron transition pathways that produce hydrogen peroxide, which negatively affects the stability of the catalyst. Indeed, the four-electron transition ORR pathway, which produces water as the main ORR product, predominates on all three catalysts.

All aspects tested in the above examples (e.g., ORR start and half wave potentials, limit current density levels, RDE curve shapes, and n values) are AuPd / C (especially AuPd with an optimal Au: Pt ratio of 1: 0.61). / C) supports high ORR activity, even activity over that of commercial Pt / C. The slightly higher ORR catalytic activity of AuPd (1: 0.61) / C with a slightly lower Pd content compared to AuPd (1: 0.73) results in a good porosity of the Pd layer formed on Au as described above (FIG. 4). It is related. At least 50 repeated RDEs in O ₂ saturated 0.5 MH ₂ SO ₄ solution yielded nearly identical RDE voltamogram results for ORR starting potential, curve shape, and limit current, indicating that the catalyst has satisfactory stability. (FIG. 7). High ORR activity of AuPd (1: 0.61) / C under acidic conditions, considering previous reports that most Au-Pd dimetallic catalysts are active only in neutral or basic conditions because of the low stability of Pd in acidic environments In addition, high stability is considered to be a notable characteristic of AuPd / C catalysts.

Methanol Tolerance of Catalyst

When ORR catalysts are used directly in the cathode of a methanol fuel cell, the methanol crossover problem commonly occurs in catalysts where fuel cell efficiency is lowered. CV was performed in oxygen-free 0.5 MH ₂ SO ₄ solution to measure the AuPd / C catalyst's resistance to methanol. Commercial Pt / C catalysts, in the presence of methanol, exhibit an anode peak corresponding to methanol oxidation up to 0.58 V in the forward scan and other peaks corresponding to the oxidation of carbon species adsorbed up to 0.40 V in the reverse scan. It was typical (Fig. 8a). On the other hand, high resistance to methanol was observed in AuPd / C catalysts (b and d in FIG. 8). In particular, AuPd (1: 0.61) / C showed a fairly similar CV in the presence and absence of methanol, suggesting better methanol resistance than AuPd (1: 0.73) / C.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (16)

Bimetallic AuPd nanoparticles supported on a carbon-based support,
The dimetallic AuPd nanoparticles are formed including an Au core and a Pd shell surrounding the Au core,
Wherein said Pd shell comprises a porous Pd layer.
delete delete The method of claim 1,
The porous Pd layer is deposited by a spontaneous reduction reaction by galvanic replacement reaction of palladium cations on the surface of Au nanoparticles, oxygen-reduction electrode catalyst.
The method of claim 1,
The weight ratio of Au: Pd in the bimetallic AuPd nanoparticles is 1: 0.1 to 1, oxygen-reduction electrode catalyst.
The method of claim 5, wherein
The weight ratio of Au: Pd in the bimetallic AuPd nanoparticles is 1: 0.15 to 0.8, oxygen-reduction electrode catalyst.
The method according to claim 6,
The weight ratio of Au: Pd in the bimetallic AuPd nanoparticles is 1: 0.5 to 0.7, oxygen-reduction electrode catalyst.
The method of claim 1,
The dimetallic AuPd nanoparticles will have a size of 1 nm to 20 nm, oxygen-reduction electrode catalyst.
The method of claim 1,
The carbon-based support is carbon black, graphite carbon, carbon nanotubes (carbon nanotube), carbon fiber (carbon fiber) and the one comprising a combination consisting of a combination thereof, oxygen-reduction electrode catalyst.
The method of claim 1,
Oxygen-reduction electrode catalyst, which is stable under acidic conditions.
The method of claim 1,
Oxygen-reducing electrode catalyst, which is resistant to alcohol under acidic conditions.
12. A fuel cell comprising a cathode containing the oxygen-reducing electrode catalyst according to any one of claims 1 and 4.
Forming Au nanoparticles supported on the carbon-based support;
Forming bimetallic AuPd nanoparticles by depositing Pd by spontaneous reduction of palladium cations on the surface of the Au nanoparticles supported on the carbon-based support:
A method for producing an oxygen-reducing electrode catalyst according to any one of claims 1 and 4 to 11 comprising a.
The method of claim 13,
Deposition of Pd by spontaneous reduction of the palladium cation comprises mixing the precursor solution containing the palladium cation and the Au nanoparticles supported on the carbonaceous support, and galvanic on the surface of the Au nanoparticles supported on the carbonaceous support. The palladium cation is reduced to Pd and deposited by oxidizing and etching Au into a gold cation from the surface of the Au nanoparticles by a galvanic replacement reaction to form the bimetallic AuPd nanoparticles. That is,
Method for preparing an oxygen-reduction electrode catalyst.
15. The method of claim 14,
Pd deposited by the galvanic substitution reaction on the surface of the Au nanoparticles supported on the carbon-based support to form a porous Pd layer,
Method for preparing an oxygen-reduction electrode catalyst.
15. The method of claim 14,
Where the precursor containing the palladium cation contains PdCl ₂ ,
Method for preparing an oxygen-reduction electrode catalyst.

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