Composite comprising a platinum-alkaline earth metal alloy, fuel cell comprising the composite, and water electrolysis cell and methods for their production

Abstract

The present invention relates to a composite having the advantages of economy, excellent catalyst activity, and significantly improved stability compared to conventional pure platinum catalysts, and specifically, the composite according to the present invention includes: a carbon support; and a binary alloy loaded on the carbon support and containing platinum (Pt) and an alkaline earth metal, wherein, in a Pt 4f XPS spectrum of the binary alloy based on X-ray photoelectron spectroscopy (XPS), E1 and E2 defined by the following Formula 1 and Formula 2 satisfy the following Formula 3. (Formula 1) E1 = E0 - E0(ref) (Formula 2) E2 = EII - EII(ref) (Formula 3) E1 / E2 ≤ 0.85, in Formula 1 and Formula 2, E0(ref) and EII(ref) are binding energies (centers) of a Pt(0) peak and a Pt(II) peak, respectively, in a Pt 4f XPS spectrum of pure platinum (Pt), and E0 and EII are binding energies (centers) of a Pt(0) peak and a Pt(II) peak, respectively, in a Pt 4f XPS spectrum of the binary alloy.

Description

Technical Field

[0001] This invention relates to a composite comprising a platinum-alkaline earth metal alloy, a fuel cell comprising the composite, a water electrolysis battery, and a method for preparing the same. Specifically, it relates to a composite comprising a platinum alloy with excellent catalytic activity and significantly improved durability for oxygen reduction reaction or hydrogen evolution reaction, a fuel cell comprising the composite, a water electrolysis battery, and a method for preparing the same. Background Technology

[0002] Fuel cells and water electrolysis batteries, which are used for environmentally friendly energy conversion, must use catalysts to improve energy conversion efficiency.

[0003] As an example, in the case of proton exchange membrane fuel cells, platinum (Pt) is primarily used as a catalyst to promote the oxygen reduction reaction (ORR) at the cathode and the hydrogen oxidation reaction (HOR) at the anode. In particular, the oxygen reduction reaction at the cathode is slower than the hydrogen oxidation reaction at the anode, and its reaction rate determines the overall formation of the fuel cell. Therefore, pure platinum catalysts are currently mainly used to promote the oxygen reduction reaction at the cathode.

[0004] However, the high price and scarcity of platinum as a precious metal limit its large-scale application. To overcome these problems, research is actively underway on platinum-based catalysts that alloy platinum with second metals such as cobalt, nickel, iron, manganese, or copper.

[0005] While Korean Patent Publication No. 10-2020-0023080 provides an alloy nanoparticle catalyst alloyed with platinum and over-metals, its actual performance still requires improvement in terms of activity, durability, and cost-effectiveness.

[0006] Therefore, in order to improve the efficiency of fuel cells, there is a need to provide a catalyst that is both more active and more durable while also being more economical.

[0007] Although alkaline earth metals are abundant in nature and relatively inexpensive compared to other metals, their high negative reduction potential and the large reduction potential difference between platinum and alkaline earth metals make them difficult to synthesize for alloying with platinum, especially platinum-alkaline earth metal alloys. Therefore, particulate alloys are rarely reported in the literature. Conversely, if a new synthetic method can be developed to overcome this reduction potential difference to prepare particulate alloys, the resulting alloy would require a very large amount of energy during dealloying, thus potentially becoming a new platinum-based alloy material that simultaneously possesses stability and activity.

[0008] Therefore, there is a need to develop platinum alloy catalysts that not only possess catalytic activity and durability but are also economical, thus enabling their practical application in fuel cells.

[0009] [Existing Technology]

[0010] [Patent Documents]

[0011] Korean Patent Publication No. 10-2020-0023080 Summary of the Invention

[0012] Technical issues

[0013] The purpose of this invention is to provide a composite material with excellent catalyst activity and stability and is economical.

[0014] Another object of the present invention is to provide a catalyst for oxygen reduction reaction and water electrolysis battery, comprising the composite of the present invention, and a cathode for fuel cell and water electrolysis battery.

[0015] Another object of the present invention is to provide a fuel cell and a water electrolysis cell that include the cathode of the present invention for use in fuel cells and water electrolysis cells.

[0016] Another object of the present invention is to provide a method for preparing a composite according to the present invention.

[0017] Technical solution

[0018] According to one aspect of the invention, the composite comprises: a carbon support; and a binary alloy supported on the carbon support and containing platinum (Pt) and an alkaline earth metal, wherein, in the Pt 4f XPS spectrum of the binary alloy based on X-ray photoelectron spectroscopy (XPS), E1 and E2, as defined by Equations 1 and 2 below, satisfy Equation 3 below.

[0019] (Equation 1)

[0020] E1 = E0 - E0(ref)

[0021] (Equation 2)

[0022] E2 = EⅡ - EⅡ (ref)

[0023] (Equation 3)

[0024] E1 / E2≤0.85

[0025] In Equations 1 and 2, E0(ref) and EⅡ(ref) are the binding energies (centers) of the Pt(0) peak and the Pt(Ⅱ) peak in the Pt 4f XPS energy spectrum of pure platinum (Pt), respectively. E0 and EⅡ are the binding energies (centers) of the Pt(0) peak and the Pt(Ⅱ) peak in the Pt 4f XPS energy spectrum of the binary alloy, respectively.

[0026] In a composite according to an embodiment of the present invention, the alkaline earth metal may be selected from one or more of calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), radium (Ra) and beryllium (Be).

[0027] In a composite according to an embodiment of the present invention, the atomic ratio of alkaline earth metal to platinum (Pt) included in the binary alloy may be from 1:1 to 5.

[0028] In a composite according to an embodiment of the present invention, the binary alloy may be one or more selected from particulate PtSr, Pt2Ca, Pt3Mg and Pt5Ba.

[0029] In a composite according to an embodiment of the present invention, the size of the particulate binary alloy particles can be from 3 nm to 300 nm.

[0030] In a composite according to an embodiment of the present invention, the binary alloy may be a cubic crystalline phase.

[0031] In a composite according to an embodiment of the present invention, the binary alloy may further include a platinum coating on the alloy surface.

[0032] According to another aspect of the present invention, a catalyst comprising the above-described composite for use in oxygen reduction reaction (ORR) or hydrogen evolution reaction (HER) is provided.

[0033] According to another aspect of the present invention, a cathode for a fuel cell or a water electrolysis cell comprising the above-described composite is provided.

[0034] According to another aspect of the present invention, an energy conversion device is provided as a fuel cell or a water electrolysis cell including the above-described cathode.

[0035] According to another aspect of the present invention, a method for preparing the above-described composite is provided.

[0036] The method for preparing the composite according to the present invention includes the following steps: a) preparing a mixture comprising a platinum precursor, an alkaline earth metal precursor, a first reducing agent, and an aprotic organic solvent; b) subjecting the mixture to a first heat treatment at a temperature above the boiling point of the organic solvent, followed by natural cooling, thereby preparing a colloid containing the composite; c) centrifuging the colloid to obtain the composite; d) coating the composite onto a carbon support, then mixing it with a powdered second reducing agent, and subjecting it to a second heat treatment in an inert reducing atmosphere to induce alloying between platinum and the alkaline earth metal; and e) removing impurities contained in the alloyed composite by acid treatment.

[0037] In a method for preparing a composite according to an embodiment of the present invention, steps a), b), and d) can be performed under anhydrous and oxygen-free conditions.

[0038] In a method for preparing a composite according to an embodiment of the present invention, the first heat treatment in step b) can be performed for 11 to 30 hours.

[0039] In a method for preparing a composite according to an embodiment of the present invention, the composite of step b) may include crystalline platinum (Pt) and amorphous alkaline earth metals.

[0040] In a method for preparing a composite according to an embodiment of the present invention, the second heat treatment may be performed at a temperature of 300°C to 1000°C.

[0041] In a method for preparing a composite according to an embodiment of the present invention, the alkaline earth metal precursor may be a chloride selected from one or more of calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), radium (Ra) and beryllium (Be).

[0042] In a method for preparing a composite according to an embodiment of the present invention, the aprotic organic solvent may be selected from one or more of acetonitrile, dimethyl acetamide (DMAc), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), methyl ethyl ketone, methyl n-propylketone, N-methylpyrrolidone (NMP), propylene carbonate, nitromethane, sulforane, and hexamethylphosphoramide (HMP).

[0043] In a method for preparing a composite according to an embodiment of the present invention, a platinum coating layer can be formed on the surface of the alloyed composite by acid treatment in step e).

[0044] Beneficial effects

[0045] The composite according to the present invention comprises: a carbon support; and a binary alloy supported on the carbon support and containing platinum (Pt) and an alkaline earth metal. In the Pt 4f XPS spectrum of the binary alloy based on X-ray photoelectron spectroscopy (XPS), under certain conditions, it can exhibit economic efficiency, excellent catalytic activity, and significantly improved stability compared to conventional pure platinum catalysts in oxygen reduction reactions or hydrogen evolution reactions.

[0046] Furthermore, a simple process of solvothermal synthesis and heat treatment can be used to provide particulate composites of platinum and alkaline earth metals. Attached Figure Description

[0047] Figure 1 This is a schematic diagram illustrating a series of processes for preparing a composite according to an embodiment of the present invention.

[0048] Figure 2 (a) and Figure 2 Figure (b) shows TEM images of Example 1 at low magnification (scale bar 100 nm) and high magnification (scale bar 50 nm), respectively. Figure 2 (c) is shown as being in Figure 2 The portion marked with dashed lines in (b) corresponds to the HR-TEM image and the Fast Fourier Transform (FFT) pattern image. Figure 2 (d) is a graph showing an HR-TEM image (scale bar 50 nm) of the platinum alloy portion of Example 1. Figure 2 (e) is to show that it will be Figure 2 The enlarged image of the portion marked with a dashed line in (d).

[0049] Figure 3 (a) and Figure 3 (b) are diagrams showing the XRD patterns of Example 1 and Comparative Example 2, respectively.

[0050] Figure 4 (a) shows Example 1 before the second heat treatment. Figure 4 (a) lower end) and Example 2 ( Figure 4 The image shows the XRD pattern at the top of (a). Figure 4 (b) is a graph showing the XRD patterns measured before and after acid treatment in Example 1.

[0051] Figure 5 (a) and Figure 5 (b) shows the compositional distribution of Pt and Ca based on line scans in the high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image of a platinum alloy particle and the EDS elemental mapping image of a platinum alloy particle obtained by energy dispersive X-ray spectroscopy (EDS).

[0052] Figure 6 (a) and Figure 6 (b) are graphs showing the high-resolution Pt 4f XPS profiles of Comparative Example 3 and Example 1, respectively.

[0053] Figure 7 of (a), Figure 7 (b) and Figure 7 (c) shows the cyclic voltammetry (CV) curves measured in nitrogen-saturated 0.1M HClO4 solutions of Examples 1 and Comparative Example 3, the ORR polarization curves measured by linear sweep voltammetry (LSV) in oxygen-saturated 0.1M HClO4 solutions, and the Tafel plots, respectively.

[0054] Figure 8 (a) and Figure 8 (b) shows the electrochemical active surface area (ECSA) determined by the charge of hydrogen desorption according to cyclic voltammetry in Example 1 and Comparative Example 3, as well as the mass activity and specific activity per unit mass measured at 0.9 V (relative to RHE).

[0055] Figure 9 (a) and Figure 9 (b) shows the linear sweep voltammetry (LSV) curves measured at the beginning of Example 1 (before the accelerated durability test (ADT)) and after 10k cycles of ADT, and the LSV curves of Example 1 measured at the beginning of Comparative Example 3 and after 30k cycles of ADT. Figure 9 (c) and Figure 9 (d) shows the cyclic voltammetry (CV) curves and electrochemical active surface area (ECSA) at the beginning of Example 1, after 10k, 20k, and 30k cycles of ADT.

[0056] Figure 10 (a) and Figure 10 (b) shows the polarization and power density curves of the fuel cells using Example 1 and Comparative Example 3 as cathode catalysts before and after 30k cycles in the accelerated durability test. Figure 10 (c) and Figure 10 (d) are graphs showing the changes in maximum power density and mass activity per unit mass before and after 30k cycles of accelerated durability testing.

[0057] Figure 11 of (a), Figure 11 (b) and Figure 11 (c) are diagrams showing the XRD patterns of the particulate composites of Example 4 (PtSr / C), Example 5 (PtBa / C), and Example 6 (PtMg / C) prepared according to an embodiment of the present invention.

[0058] Figure 12 (a) and Figure 12 (b) is a diagram showing the TEM images at low magnification (scale bar 10 nm), high magnification (scale bar 5 nm), lattice space of the crystal plane, and Fast Fourier Transform (FFT) pattern images of the composite of Example 6.

[0059] Figure 13 (a) and Figure 13 (b) are high-resolution Pt 4f XPS profiles of Example 6 (PtMg / C) and Comparative Example 3 (commercially available Pt / C), respectively.

[0060] Figure 14 (a) and Figure 14 (b) are graphs showing the polarization and power density curves before and after 30k cycles of accelerated durability testing of fuel cells used as cathode catalysts in Example 6 (PtMg / C) and Comparative Example 3 under H2-O2 conditions. Figure 14 (c) and Figure 14 (d) are graphs showing the polarization and power density curves before and after 30k cycles of accelerated durability testing of fuel cells used as cathode catalysts in Example 6 (PtMg / C) and Comparative Example 3 under H2-Air conditions. Detailed Implementation

[0061] The present invention will now be described in detail with reference to the accompanying drawings. The drawings provided below are provided as examples to fully convey the concept of the invention to those skilled in the art. Therefore, the invention is not limited to the drawings shown below, and may be embodied in other forms. The drawings shown below may be exaggerated to clarify the concept of the invention. Unless otherwise defined, the technical and scientific terms used here have the meanings commonly understood by those skilled in the art to which this invention pertains. In the following description and drawings, descriptions of well-known functions and structures that may unnecessarily obscure the essence of the invention will be omitted.

[0062] Furthermore, unless the context otherwise requires, the singular form used in the specification and appended claims may refer to the plural form.

[0063] In this specification and the appended claims, terms such as "comprising" or "having" refer to the presence of the features or structural elements described in the specification, and unless otherwise specified, do not preclude the possibility of adding more than one other feature or structural element.

[0064] According to one aspect of the invention, the composite comprises: a carbon support; and a binary alloy supported on the carbon support and containing platinum (Pt) and an alkaline earth metal, wherein E1 and E2, as defined by Equations 1 and 2 below, satisfy Equation 3 below in the Pt 4f XPS spectrum of the binary alloy based on X-ray photoelectron spectroscopy (XPS).

[0065] (Equation 1)

[0066] E1 = E0 - E0(ref)

[0067] (Equation 2)

[0068] E2 = EⅡ - EⅡ(ref)

[0069] (Equation 3)

[0070] E1 / E2≤0.85

[0071] In Equations 1 and 2, E0(ref) and EⅡ(ref) are the binding energies (centers) of the Pt(0) peak and the Pt(Ⅱ) peak in the Pt 4f XPS energy spectrum of pure platinum (Pt), respectively. E0 and EⅡ are the binding energies (centers) of the Pt(0) peak and the Pt(Ⅱ) peak in the Pt 4f XPS energy spectrum of the binary alloy, respectively.

[0072] The composite according to the present invention comprises: a carbon support; and a binary alloy supported on the carbon support and containing platinum (Pt) and an alkaline earth metal. When specific conditions are met in the Pt 4f XPS spectrum of the binary alloy based on X-ray photoelectron spectroscopy (XPS), it can have the advantages of economy, excellent catalytic activity and significantly improved stability compared with conventional pure platinum catalysts in oxygen reduction reactions or hydrogen evolution reactions.

[0073] Specifically, binary alloys contain platinum and alkaline earth metals. Because they contain inexpensive alkaline earth metals, the amount of platinum used can be substantially reduced. Therefore, composites including binary alloys have an economic advantage.

[0074] Furthermore, conventional platinum and late transition metal alloys suffer from the following drawback: during electrochemical reactions (for example, the oxygen reduction reaction (ORR) or the hydrogen evolution reaction (HER), catalyst degradation occurs due to transitions in the alloy composition, resulting in instability. However, the binary alloy comprising the composite according to an embodiment of the present invention requires a high cathode alloying energy to form the alloy, and therefore exhibits excellent stability by suppressing dealloying.

[0075] Meanwhile, the durability of the catalyst may be reduced due to poisoning of reaction intermediates generated during the electrochemical reaction, but the composite according to an embodiment of the present invention can effectively suppress poisoning, thereby providing further improved stability.

[0076] More specifically, in the Pt 4f XPS spectrum of a binary alloy based on X-ray photoelectron spectroscopy (XPS) according to an embodiment of the present invention, E1 and E2 as specified by the above formulas 1 and 2 satisfy the above formula 3, thereby minimizing the poisoning phenomenon caused by reaction intermediates.

[0077] Among them, the Pt 4f XPS energy spectrum can be obtained using the energy corresponding to Pt 4f 5 / 2 and Pt 4f 7 / 2 The peaks are composed of doublet peaks, and the Pt(0) and Pt(II) peaks can be deconvolved peaks from each doublet. That is, the Pt(0) peak is divided from Pt 4f 5 / 2 Peak deconvolution of Pt(0)-Pt 4f 5 / 2 Peak and from Pt 4f 7 / 2 Peak deconvolution of Pt(0)-Pt 4f 7 / 2 Each peak is independent of the others.

[0078] Similarly, the Pt(II) peak can be divided from the independent Pt 4f peaks. 5 / 2 Peak deconvolution of Pt(II)-Pt4f 5 / 2 Peak and from Pt 4f 7 / 2 Peak deconvolution of Pt(II)-Pt 4f 7 / 2 .

[0079] E1, as specified in Equation 1, can be the Pt(0) peak (Pt(0)-Pt4f) located at the same position in the XPS energy spectrum of each binary alloy and pure platinum. 5 / 2 or Pt(0)-Pt 4f 7 / 2 The difference in binding energy between the centers of the two elements, E2 as specified in Equation 2, can be the Pt(II) peak (Pt(II)-Pt4f) located at the same point in the XPS spectra of each binary alloy and pure platinum. 5 / 2 or Pt(II)-Pt 4f 7 / 2 The difference in binding energy between the centers.

[0080] At this point, the binding energy at the center of the independent Pt(0) peak and Pt(II) peak in the binary alloy can be higher than the binding energy at the center of the same Pt(0) peak and Pt(II) peak in pure platinum.

[0081] This shift in binding energy indicates a downward shift in the d-band center relative to the Fermi level, but this change in chemical structure affects the binding strength between the d-band center and the reaction intermediates formed during the catalytic reaction with platinum atoms located on the surface of the binary alloy.

[0082] As an example, in oxygen reduction reactions or hydrogen evolution reactions, the binding strength of reaction intermediates such as O, OH groups OOH formed during the reaction process to Pt atoms is weakened to minimize poisoning caused by the aforementioned reaction intermediates, thereby significantly improving durability.

[0083] As a specific example, E1 / E2 in Equation 3 can be less than 0.85, less than 0.8, less than 0.75, less than 0.70, less than 0.65, less than 0.60, or less than 0.55, but in reality, it can be greater than 0.3.

[0084] Typically, in the oxygen reduction reaction, the catalyst activity is as follows: the supplied oxygen molecules (O2) are adsorbed onto the reduction electrode and react with hydrogen ions to generate reaction intermediates such as O, OH, and OOH, ultimately producing H2O.

[0085] During the process of generating the final product H2O, the intermediate reactants generated organically undergo formation (adsorption) and disappearance (desorption). The improvement in catalyst activity achieved by smooth adsorption and the maintenance of catalyst activity achieved by easy desorption are in a trade-off relationship.

[0086] Therefore, in terms of the trade-off between catalyst activity and durability, it is advantageous for E1 / E2 of Formula 3 to satisfy the above range in order to have excellent catalyst activity and durability in terms of the generation (adsorption) and disappearance (desorption) of intermediate reactants.

[0087] In one embodiment, the alkaline earth metal included in the binary alloy may be one or more selected from magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra) and beryllium (Be). Advantageously, it may be one or more selected from calcium (Ca), barium (Ba), magnesium (Mg) and strontium (Sr). More powerfully, it may be one or more selected from calcium (Ca), magnesium (Mg) and strontium (Sr).

[0088] As described above, binary alloys containing alkaline earth metals with oxyphilic properties and platinum can suppress dealloying. In particular, the composites of the present invention, which include binary alloys containing calcium and platinum, magnesium and platinum, or strontium and platinum, can satisfy Formula 3 (E1 / E2 ≤ 0.85) in the Pt 4f XPS energy spectrum. Therefore, when used as catalysts for oxygen reduction reactions, they have advantages in terms of economy, catalyst activity, and stability.

[0089] In one embodiment, the binary alloy may also include a platinum overlayer on the alloy surface.

[0090] In this case, the platinum coating can represent a situation where the intensity of platinum, measured in a high-angle annular dark-field scanning transmission electron microscope (HAA DF-STEM) image, is more than three times the intensity of the alkali metals in the compositional distribution of platinum and alkaline earth metals based on line scan.

[0091] As an example, the binary alloy may include a platinum capping layer, which is based on a monoatomy layer made up of platinum atoms, with 1 to 10, specifically 1 to 6, more specifically 1 to 3 monoatomy layers stacked on the surface of the binary alloy.

[0092] The platinum capping layer on the surface of the binary alloy can promote charge transfer by means of the electronegativity difference between platinum and alkaline earth metals, thereby improving the catalyst activity. At the same time, the difference in atomic radius between platinum and alkaline earth metals can induce strain in the platinum lattice, thereby changing the electronic structure compared with pure platinum and improving the durability of the catalyst.

[0093] In one embodiment, the atomic ratio of alkaline earth metal to platinum (Pt) included in the binary alloy can be from 1:1 to 5, substantially from 1:1.6 to 3, and more substantially from 1:1.7 to 2.5.

[0094] As a specific example, the binary alloy may be selected from one or more of the following: granular PtSr, Pt2Ca, Pt3Mg, and Pt5Ba.

[0095] In one implementation example, the binary alloy can be a cubic crystalline phase.

[0096] As an example, the particle size can be from 3 nm to 300 nm, advantageously from 5 nm to 200 nm, more advantageously from 5 nm to 100 nm, further advantageously from 5 nm to 50 nm, and even more advantageously from 5 nm to 30 nm.

[0097] In one embodiment, the carbon support included in the composite can be used without limitation as long as it is a carbon support containing carbon with excellent chemical stability and conductivity that is known in the art. As an example, the carbon support can be selected from one or more of Vulcan carbon, carbon paper, carbon felt, carbon fiber, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and timcal, but the present invention is not limited thereto.

[0098] As an advantageous example, the BET surface area of ​​the carbon support can be 200 m². 2 g -1 Above, 500m 2 g -1 Above, 800m 2g -1 Above, 1000m 2 g -1 Above, 1200m 2 g -1 The above, and the upper limit is unlimited, but can be 2000m. 2 g -1 the following.

[0099] In the case where the carbon support included in the composite according to one embodiment of the present invention is a porous structure with a high BET surface area, it has the advantage of being beneficial in terms of catalyst activity by effectively suppressing the aggregation of particulate binary alloys supported on the carbon support.

[0100] As an example, based on the total weight of the composite, the content of the binary alloy loaded on the carbon support can be from 5 wt% to 50 wt%, practically from 10 wt% to 30 wt%, and more practically from 15 wt% to 25 wt%.

[0101] According to another aspect of the present invention, a catalyst comprising the above-described composite for use in oxygen reduction reaction or hydrogen evolution reaction (for water electrolysis cells) is provided.

[0102] As described above, for composites including carbon supports and binary alloys supported on carbon supports containing platinum (Pt) and alkaline earth metals, and for composites that meet specific conditions in the Pt 4f XP S energy spectrum of binary alloys based on X-ray photoelectron spectroscopy (XPS), they can be used as catalysts with excellent activity and significantly improved stability in oxygen reduction reactions or hydrogen evolution reactions compared with conventional pure platinum catalysts.

[0103] Furthermore, compared to pure platinum catalysts, it can reduce the amount of platinum used, thus offering economic advantages.

[0104] According to another aspect of the invention, a cathode for a fuel cell or a water electrolysis cell comprising the above-described composite is provided.

[0105] At this point, the cathode can represent the electrode where electrons enter or where oxygen reduction or hydrogen evolution occurs.

[0106] In a fuel cell that has a fuel electrode (anode) that generates hydrogen ions and electrons through the oxidation of fuel substances, an air electrode (cathode) that undergoes reduction of oxygen or other oxidizing agents through the reaction with hydrogen ions and electrons, and an electrolyte layer (membrane) that can efficiently transport hydrogen ions from the fuel electrode to the air electrode, the above-mentioned cathode is used as the air electrode (cathode) of the fuel cell, thereby having the advantage of improving the efficiency and stability of the fuel cell.

[0107] According to another aspect of the present invention, an energy conversion device is provided as a fuel cell or water electrolysis cell including the above-described cathode.

[0108] Examples of fuel cells include polymer electrolyte membrane fuel cells (PEMFC), direct methanol fuel cells (DMFC) using ethanol as fuel, direct ethanol fuel cells (DEFC), alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCF C), and solid oxide fuel cells (SOFC), but the present invention is not limited thereto.

[0109] As an advantageous example, a polymer electrolyte membrane fuel cell can operate at low temperatures and is suitable for use in transportation vehicles.

[0110] Polymer electrolyte membrane fuel cells, also known as proton exchange membrane fuel cells (PEMFCs), may include a first gas diffusion layer, an anode, a polymer electrolyte membrane, a cathode, and a second gas diffusion layer.

[0111] At this time, hydrogen, as a fuel substance, is supplied to the anode through the first gas diffusion layer. The supplied hydrogen is oxidized at the anode, and hydrogen ions are transported to the cathode through the polymer electrolyte membrane. As described above, at the cathode, hydrogen ions react with oxygen supplied to the cathode through the second gas diffusion layer to generate water. At this time, the catalyst activity for the oxygen reduction reaction can be improved by means of the composite included in the cathode according to the invention, and the stability of the fuel cell can be improved by means of the composite with significantly excellent durability.

[0112] The first and second gas diffusion layers can be formed using materials known in the art, but the invention is not limited thereto. The material is capable of supplying fuel, air, or oxygen smoothly and is conductive.

[0113] The polymer electrolyte membrane can be applied without restriction as long as it is a polymer material known in the field of fuel cells. Examples of polymer materials include sulfonated benzimidazoles, sulfonated polyimides, sulfonated polyetherimides, sulfonated polyphenylene sulfides, sulfonated polysulfones, sulfonated polyethers, sulfonated polyether ketones, sulfonated polyether-ether ketones, sulfonated polyether sulfones, sulfonated polyphenylquinoxalines, and polymers with sulfonated partial fluorine, but are not limited to these.

[0114] According to another aspect of the present invention, a method for preparing the above-described composite is provided.

[0115] A method for preparing a composite according to an embodiment of the present invention includes the following steps: a) preparing a mixture comprising a platinum precursor, an alkaline earth metal precursor, a first reducing agent, and an aprotic organic solvent; b) subjecting the mixture to a first heat treatment at a temperature above the boiling point of the organic solvent, followed by natural cooling, thereby preparing a colloid containing the composite; c) centrifuging the colloid to obtain the composite; d) coating the composite onto a carbon support, then mixing it with a powdered second reducing agent, and subjecting it to a second heat treatment in an inert reducing atmosphere to induce alloying between platinum and the alkaline earth metal; and e) removing impurities contained in the alloyed composite by acid treatment.

[0116] The method for preparing the composite according to the present invention can provide a composite comprising platinum and alkaline earth metal alloys by using a simple method of so-called solvothermal synthesis and heat treatment.

[0117] The following describes in detail, step by step, a method for preparing a composite according to another aspect of the present invention.

[0118] In one embodiment of the present invention, the method for preparing the composite may include the step of preparing a mixture comprising a platinum precursor, an alkaline earth metal precursor, a first reducing agent and an aprotic organic solvent.

[0119] As an example, the molar ratio of platinum precursor to alkaline earth metal precursor in the mixture may be 1:2 to 10, specifically, 1:2 to 8, and more specifically, 1:3 to 6.

[0120] In all metal precursors including platinum alkaline earth metals contained in the mixture, the molar ratio of metal precursor to first reducing agent can be from 1:5 to 25, advantageously from 1:5 to 20, and more advantageously from 1:8 to 15.

[0121] In order to effectively alloy platinum and alkaline earth metals through the first and second heat treatments described below, it is advantageous for the molar ratio of platinum precursor to alkaline earth metal precursor and the molar ratio of metal precursor to first reducing agent to satisfy the above-mentioned ranges.

[0122] In one embodiment, the platinum precursor may be platinum chloride, and as a specific example, the platinum precursor may be one or more selected from PtCl2, PtCl4, H2PtCl6, K2(PtCl4), [Pt(NH3)4]Cl2 and (NH3)2PtCl6.

[0123] Alkaline earth metal precursors can be chlorides of one or more metals selected from magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra) and beryllium (Be), specifically, they can be one or more selected from calcium chloride (CaCl2), strontium chloride (SrCl2) and magnesium chloride (MgCl2).

[0124] In one specific example, the first reducing agent may be one or more selected from sodium hydride (NaH), sodium borohydride (NaBH4), lithium aluminum hydride (LiAlH4), hydrazine (N2H4), diisobutylaluminum hydride (DIBALH), and potassium triethylborohydride (KEt3BH).

[0125] In this case, preferably, the first reducing agent is readily soluble in the aprotic organic solvent described later, and reduces the metal ions included in the metal precursor with strong reducing power. From this perspective, as a preferred example, the first reducing agent can be sodium borohydride (NaBH4).

[0126] In the step of preparing the mixture, by dissolving the platinum precursor, the alkaline earth metal precursor and the first reducing agent in an aprotic organic solvent, the oxidation of the reduced alkaline earth metal can be effectively suppressed, thereby improving the alloying efficiency between platinum and alkaline earth metal.

[0127] As an example, based on the total weight of the mixture, the content of aprotic organic solvents included in the mixture can be from 60 wt% to 99 wt%, substantially from 70 wt% to 99 wt%, and more substantially from 80 wt% to 99 wt%.

[0128] In one specific example, the aprotic organic solvent may be one or more selected from acetonitrile, dimethyl acetamide (DMAc), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), methyl ethyl ketone, methyl n-propylketone, N-methylpyrrolidone (NMP), propylene carbonate, nitromethane, sulforane, and hexamethylphosphoramide (HMP), preferably dimethyl formamide (DMF).

[0129] At this point, the aprotic organic solvent can be a solvent that is degassed to remove dissolved oxygen from the organic solvent.

[0130] As a specific example, the step of preparing a mixture comprising a platinum precursor, an alkaline earth metal precursor, a first reducing agent, and an aprotic organic solvent can be performed under anhydrous and oxygen-free conditions.

[0131] As a specific example, the steps for preparing the mixture described above can be performed in a glove box filled with an inert atmosphere of argon, but any method that can meet the requirements of being moisture-free and oxygen-free can be used without restriction. As mentioned above, by preparing the mixture under anhydrous and oxygen-free conditions, the alloying efficiency between platinum and alkaline earth metals can be improved.

[0132] In one embodiment, the prepared mixture can be subjected to a first heat treatment and then naturally cooled to room temperature (15°C to 25°C) to prepare a colloid comprising the compound.

[0133] At this point, with the aim of improving the alloying efficiency between platinum and alkaline earth metals, the first heat treatment can be performed in a high-pressure reactor under vacuum. That is, the preparation of the colloid of the composite and the steps for manufacturing the above-mentioned mixture can be performed under anhydrous and oxygen-free conditions, in the same manner.

[0134] As a specific example, the temperature of the first heat treatment can be a temperature above the boiling point of the aforementioned aprotic organic solvent, and as a specific example, it can be 50°C to 300°C, advantageously, it can be 80°C to 250°C, and more advantageously, it can be 100°C to 200°C.

[0135] As an example, the first heat treatment can be performed for 11 to 40 hours, in fact, for 11 to 30 hours, and more in fact, for 11 to 25 hours.

[0136] By solvothermal synthesis according to the heat treatment conditions described above (i.e., the first heat treatment temperature and time), a composite including crystalline platinum and amorphous alkali metal can be prepared.

[0137] Under the first heat treatment temperature conditions, if the execution time of the first heat treatment is less than 11 hours, after the second heat treatment described later, platinum and alkaline earth metals may not be able to achieve alloying, or the alloying efficiency may decrease. If the execution time of the first heat treatment exceeds 40 hours, the particle size of the platinum-alkaline earth metal alloy prepared after the second heat treatment described later will become larger, which may reduce the catalyst activity. Therefore, in the step of preparing the colloid including the compound, it is preferable to satisfy the above-mentioned first heat treatment conditions.

[0138] In one implementation, the composite colloid, including the above-mentioned composite, is centrifuged to obtain the composite, then coated onto a carbon support, and then mixed with a powdered second reducing agent. After that, a second heat treatment is performed in an inert reducing atmosphere, thereby enabling the induction of alloying between platinum and alkaline earth metals.

[0139] As an example, the second reducing agent mixed in the obtained synthesis may be 20 wt% to 90 wt% by weight relative to the total weight of the mixture of the synthesis and the second reducing agent, specifically, it may be 40 wt% to 80 wt% by weight, and more specifically, it may be 50 wt% to 70 wt% by weight.

[0140] Here, the second reducing agent can be one or more selected from sodium hydride (NaH), sodium borohydride (NaBH4), lithium aluminum hydride (LiAlH4), hydrazine (N2H4), diisobutylaluminum hydride (DIBALH), and potassium triethylborohydride (KEt3BH), and can be the same as or different from the first reducing agent described above. As a preferred example, the second reducing agent can be potassium triethylborohydride (KEt3BH).

[0141] At this point, the second reducing agent can have a stronger reducing power than the first reducing agent. After mixing the second reducing agent, which is stronger than the first reducing agent, with the obtained composite, a second heat treatment is performed in an inert reducing atmosphere, which can further improve the reduction efficiency of the alkaline earth metals included in the composite, thereby improving the alloying efficiency between platinum and alkaline earth metals.

[0142] As an example, it is evident that a second heat treatment for inducing alloying between platinum and alkaline earth metals can be performed after the second reducing agent is mixed with the composite and then a mixed carbon support is attached to it or coated onto a carbon support.

[0143] At this point, the physical properties of the final product (i.e., the composite) obtained by the second heat treatment can be the same as or similar to those of the composite generated after the above-mentioned induced alloying.

[0144] That is, obviously, in order to induce alloying between platinum and alkaline earth metals, the mixing order of the composite obtained by centrifugation, the carbon support, and the second reducing agent can be freely adjusted before performing the second heat treatment. In this case, the carbon support can be the same as described above, and its detailed description will be omitted.

[0145] As an example, a method for coating a composite or a composite mixed with a second reducing agent onto a carbon carrier can be used, such as a spraying method, a casting method, or a powder spraying device, but the present invention is not limited thereto.

[0146] As an example, the processes of mixing the obtained compound with the carbon support, mixing with the second reducing agent, or mixing the obtained compound with the second reducing agent, as well as coating the mixed product onto the carbon support or mixing it with the carbon support, can all be performed under anhydrous and oxygen-free conditions.

[0147] In one implementation, for a composite mixed with a carbon support or a composite mixed with a second reducing agent coated on a carbon support, alloying between platinum and an alkaline earth metal can be induced by a second heat treatment in an inert reducing atmosphere.

[0148] An inert reducing atmosphere can be an atmosphere containing an inert gas such as hydrogen, helium, argon, or neon, but is not limited to these.

[0149] At this point, the hydrogen contained in the inert gas can be from 1% to 10% by volume, specifically from 3% to 8% by volume.

[0150] In one embodiment, the second heat treatment temperature for alloying platinum with alkaline earth metals can be from 300°C to 1000°C, substantially from 600°C to 1000°C, and more substantially from 800°C to 1000°C.

[0151] As an example, the second heat treatment can be performed for 2 to 10 hours, in fact, it can be performed for 2 to 6 hours.

[0152] In order to induce alloying between platinum and alkaline earth metals with excellent alloying efficiency, the temperature and execution time of the second heat treatment preferably meet the above-mentioned ranges.

[0153] In one embodiment, the alloyed composition may be acid-treated to remove impurities included in the alloyed composition.

[0154] Acid treatment can be carried out at temperatures ranging from 40°C to 100°C, essentially from 60°C to 80°C, by immersing the alloyed compound in an acid solution for 2 to 10 hours, advantageously, 4 to 6 hours.

[0155] At this point, the acid solution can be a solution including hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid. In order to effectively remove impurities, the concentration of the acid solution can be from 0.05M to 5M, specifically from 0.1M to 3M, and more specifically from 0.5M to 1.5M.

[0156] In one implementation, a platinum coating layer can be formed on the surface of the alloyed composite obtained by the above-mentioned acid treatment.

[0157] Here, the platinum coating can be formed by removing the thermodynamically unstable alkaline earth metal from the surface of the alloy between platinum and the alkaline earth metal during an acid treatment process.

[0158] After acid treatment to remove impurities, the alloy between platinum and alkaline earth metal can be granular Pt2Ca.

[0159] After acid treatment, the granular platinum-alkaline earth metal alloy can be obtained as a composite supported on a carbon support. The weight of the alloy supported on the carbon support relative to the total weight of the composite can be from 5 wt% to 80 wt%, practically from 10 wt% to 40 wt%, and more practically from 15 wt% to 25 wt%, depending on the conditions of use.

[0160] As described above, the advantage of the composite prepared by the above preparation method (i.e., the composite comprising a carbon support and a binary alloy supported on the carbon support and containing platinum and alkaline earth metals) is that the binary alloy included in the composite satisfies specific conditions in the above-mentioned Pt 4f XPS energy spectrum, thereby being used as a catalyst with excellent activity and significantly superior stability in oxygen reduction reaction or hydrogen evolution reaction compared with existing pure platinum catalysts.

[0161] The present invention will now be described in more detail through embodiments. However, the following embodiments are merely for the purpose of illustrating the invention in detail, and the invention is not limited thereto but can be implemented in various forms.

[0162] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this application is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

[0163] (Example 1)

[0164] In an inert atmosphere glove box, platinum chloride (PtCl4), calcium chloride (CaCl2), and sodium borohydride (NaBH4) were dissolved in 15 mL of degassing N,N'-dimethylformamide solvent in a vial at a molar ratio of 1:4.5:62.6. The vial was then sealed with Teflon tape and subjected to ultrasonic treatment for 2 hours to prepare the mixture.

[0165] The prepared mixture was subjected to a first heat treatment at 165°C for 12 hours in a 25 mL Teflon-lined autoclave, followed by natural cooling to room temperature to prepare a colloid containing the synthesized compound. The synthesized compound was then obtained by centrifugation.

[0166] The composite obtained in an inert atmosphere glove box was coated with 80 mg of commercially available carbon (Ket jenBlack EC 600JD) and then mixed with 80 mg of powdered potassium triethylborohydride (KEt3BH). Following alloying induction by a second heat treatment at 900 °C for 4 hours in an inert reducing atmosphere (5% H₂ / Ar), an acid treatment was performed at 70 °C for 5 hours to remove impurities, followed by drying, thus preparing a composite comprising a carbon-supported platinum alloy (PtCa / C). The metal content of the composite could be 20.41 wt%.

[0167] Figure 1 A schematic diagram of a series of processes for preparing a composite material consisting of a carbon-supported platinum alloy (PtCa / C) is shown.

[0168] (Example 2)

[0169] Except that the first heat treatment is performed for 24 hours, it is performed in the same manner as in Example 1.

[0170] (Example 3)

[0171] In addition to coating the compound obtained after the first heat treatment onto a surface with approximately 300m... 2 / g to 400m 2 / g of low surface area Vulcan carbon (Vulcan XC72) rather than coated on a substrate with approximately 1400m 2Apart from this, the same procedure was performed as in Example 1 on commercially available carbon (Ketjen Black EC 600JD) with a high surface area of ​​ / g.

[0172] (Example 4)

[0173] Except that strontium chloride (SrCl2) was used instead of calcium chloride (CaCl2) to prepare the mixture, it was carried out in the same manner as in Example 1.

[0174] (Example 5)

[0175] Except that barium chloride (BaCl2) was used instead of calcium chloride (CaCl2) to prepare the mixture, it was carried out in the same manner as in Example 1.

[0176] (Example 6)

[0177] Except that magnesium chloride (MgCl2) was used instead of calcium chloride (CaCl2) to prepare the mixture, it was carried out in the same manner as in Example 1.

[0178] (Comparative Example 1)

[0179] Except for the fact that the first heat treatment is performed for 10 hours, it is performed in the same manner as in Example 1.

[0180] (Comparative Example 2)

[0181] A mixture was prepared by dispersing a Pt solution (100 mg / ml) and 80 mg of commercially available carbon (Ketjen Black EC 600JD) in water. At this point, the platinum content was 20 wt% (20 wt% Pt / C) of the total weight of platinum and carbon.

[0182] The prepared mixture was ultrasonically treated for 30 minutes, then heated and evaporated under magnetic stirring to form a thick slurry, and then dried in a vacuum oven at 70°C for 4 hours.

[0183] A mixed powder was prepared by mixing 13 mg of metallic Ca particles (Alfa Aesar Korea) with dry 20 wt% Pt / C and then pulverizing it in a mortar.

[0184] Next, the final powdered mixture was placed in a tube and then heat-treated at 900°C for 5 hours in an inert reducing atmosphere (5% H2 / Ar), followed by drying.

[0185] (Comparative Example 3)

[0186] Commercially available Pt / C (20wt% Pt, Tanaka Kikinzoku Kogyo, Japan) was purchased.

[0187] (Experimental Example 1) Morphology and Structural Characteristics

[0188] Using transmission electron microscopy (TEM, Hitachi HF-3300), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD, Rigaku Smartlab, 40kV, 30mA, 4°min) -1 The morphology and structural properties of the prepared platinum alloys were observed by analyzing Cu-Kα radiation (λ = 0.15406 nm).

[0189] Figure 2 (a) and Figure 2 (b) are TEM images of PtCa / C of Example 1 at low magnification (scale bar 100 nm) and high magnification (scale bar 50 nm), respectively. Figure 2 (c) is shown as being in Figure 2 The portion marked with dashed lines in (b) corresponds to the HR-TEM image and the Fast Fourier Transform (FFT) pattern image. Figure 2 (d) is a graph showing an HR-TEM image (scale bar 50 nm) of the platinum alloy portion of Example 1. Figure 2 (e) is to show that it will be Figure 2 The enlarged image of the portion marked with a dashed line in (d).

[0190] like Figure 2 (a) and Figure 2 As shown in (b), nanoparticles with sizes ranging from 10 nm to 25 nm are uniformly dispersed on the carbon support (commercially available carbon, Ketjen Black EC600JD). Although not shown, in Example 3, where Vulcan carbon with a low surface area was used as the carbon support, nanoparticles with sizes ranging from 50 nm to 200 nm were observed, which is believed to be due to particle aggregation that occurred during the second heat treatment.

[0191] That is, it has been confirmed that the second heat treatment process performed at high temperature effectively suppressed particle aggregation in a carbon support with a high surface area.

[0192] Furthermore, through Figure 2 (c) to Figure 2(e) confirms that the nanoparticles uniformly dispersed on the carbon support possess high crystallinity, and as... Figure 2 As shown in (e), the interplanar spacing (lattice spacing) of the (111) facet of the nanoparticle is 0.41 nm, which is an increase compared to the interplanar spacing (0.23 nm) of the (111) facet of Pt. This indicates that Ca is incorporated into the Pt lattice, and the observed interplanar spacing of the (111) facet of the nanoparticle is very similar to that of the (111) facet of Pt2Ca (0.44 nm). Furthermore, the interplanar spacing (0.27 nm) of the (220) facet of the nanoparticle is also very similar to that of the (220) facet of Pt2Ca (0.269 nm).

[0193] Figure 3 (a) and Figure 3 (b) are diagrams showing the XRD patterns of Example 1 and Comparative Example 2, respectively. At this time, in Figure 3 In (b), the upper XRD pattern was measured after acid treatment, and the lower XRD pattern was measured before acid treatment.

[0194] observe Figure 3 In Example (a), peaks appear at 2θ values ​​of 20.14, 33.19, 39.13, 40.95, 47.64, 52.22, 63.29, and 69.66, which are consistent with specific peaks (PDF#030651744) on the (111), (220), (311), (222), (400), (331), (511), and (440) planes of the Pt2Ca alloy, respectively. Furthermore, the lattice spacing in the aforementioned HR-TEM images confirms that the nanoparticles are an alloy similar to Pt2Ca. This crystallographic structure is consistent with the cubic structure of space group Fd-3m (#227).

[0195] Meanwhile, based on the high-intensity peak at 2θ value of 39.13 observed in the XRD pattern of Example 1 and the peaks of pure Pt corresponding to the (200), (220) and (222) planes, it can be known that the Pt2Ca alloy and Pt exist in the form of a mixed phase.

[0196] On the contrary, such as Figure 3As shown in (b), in Comparative Example 2, after acid treatment, no significant peaks corresponding to Pt2Ca were observed except for the peaks corresponding to the pure Pt XRD pattern. This indicates that even if an alloy was formed, its degree was very low. Furthermore, although not shown, in the case of Comparative Example 1, the alloying rate was also significantly reduced, and therefore no significant XRD pattern corresponding to Pt2Ca was observed.

[0197] Figure 4 (a) shows Example 1 before the second heat treatment. Figure 4 (a) lower end) and Example 2 ( Figure 4 The image shows the XRD pattern at the top of (a). Figure 4 (b) is a graph showing the XRD patterns measured before and after acid treatment in Example 1.

[0198] Reference Figure 4 In Example 1 and Example 2, which were subjected to a first heat treatment at 165°C for 12 hours before the second heat treatment, peaks corresponding to the (111), (200), (220), and (222) planes of pure Pt were observed. The position of the (111) peak was observed at a position that moved with a 2θ value higher than that of pure Pt (2θ = 39.76), and no crystalline peak corresponding to calcium chloride or calcium was observed.

[0199] Therefore, it can be seen that Pt forms crystalline form through the first heat treatment, while Ca exists in an amorphous phase or as a doped Pt phase within the crystalline form. Furthermore, as... Figure 4 As shown in (a), Ca can exist in the form of oxide (CaO) or can be hydrogenated to exist in the form of CaH2. However, it can be seen that the position of the above-mentioned (111) peak is located at a 2θ value shifted relative to pure Pt.

[0200] In particular, the CaO formed during the first heat treatment protects the crystalline Pt that has formed during the second heat treatment performed at a high temperature (900°C), thereby inhibiting particle aggregation and thus expanding the active surface area of ​​the platinum alloy catalyst (PtCa / C), which is advantageous.

[0201] Figure 4(b) is a comparison of the XRD patterns before and after acid treatment following the second heat treatment according to Example 1. It can be seen that the calcium hydroxide (Ca(OH)2) formed during the second heat treatment is completely removed by acid treatment. As mentioned above, the reason why Pt2Ca alloy and Pt exist in the form of a mixed phase after acid treatment is that the thermodynamically unstable Ca located on the surface of the platinum alloy catalyst is removed during the acid treatment, thus forming a Pt capping layer.

[0202] Figure 5 (a) and Figure 5 (b) shows the compositional distribution of Pt and Ca based on line scans in the high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image of a platinum alloy particle and the EDS elemental mapping image of a platinum alloy particle obtained by energy dispersive X-ray spectroscopy (EDS).

[0203] like Figure 5 (a) and Figure 5 As shown in (b), the formation of the Pt capping layer is evident, and it is also evident that Pt and Ca elements are uniformly dispersed throughout the platinum alloy particles, especially from... Figure 5 (b) confirms that the area of ​​the region containing Pt is larger than the area of ​​the region containing Ca, and that Ca is concentrated in the center of the particle.

[0204] Furthermore, the atomic percentages of Pt and Ca included in Example 1, as observed from EDS energy dispersive spectroscopy, were 65.8% and 32.2%, respectively. This result is consistent with the XRD pattern data of the platinum alloy and Pt2Ca alloy confirmed by XRD analysis described above.

[0205] (Experimental Example 2) Chemical Structure and Electronic Structure Properties

[0206] The chemical and electronic structure of the prepared platinum alloy catalyst was analyzed by X-ray photoelectron spectroscopy (XPS).

[0207] Figure 6 (a) and Figure 6 (b) are high-resolution Pt 4f XPS profiles of Comparative Example 3 (commercially available Pt / C) and Example 1 (PtCa / C), respectively.

[0208] like Figure 6 (a) and Figure 6 As shown in (b), the Pt 4f XPS spectra of both Example 1 and Comparative Example 3 are derived from the Pt 4f... 5 / 2 and Pt 4f 7 / 2 It consists of doublet peaks. Furthermore, it can be known that this corresponds to Pt 4f. 5 / 2 and Pt 4f 7 / 2 The bimodal structure consists of the Pt(0) peak and the Pt(II) peak, which are deconvolved with respect to each peak.

[0209] Compared with the binding energy of the double peaks (including the deconvolutioned Pt(0) peak and Pt(II) peak) in Comparative Example 3, it was observed that the binding energy of the double peaks (including the deconvolutioned Pt(0) peak and Pt(II) peak) in Example 1 shifted in the positive direction (i.e., to higher binding energies).

[0210] Specifically, in Pt 4f of Example 1 5 / 2 and Pt 4f 7 / 2 The binding energies of the deconvolutioned Pt(0) peaks in Comparative Example 3 are 74.8 eV and 71.5 eV, respectively. 5 / 2 and Pt 4f 7 / 2 The binding energies of the deconvolutioned Pt(0) peaks were 74.2 eV and 70.9 eV, respectively, and it was confirmed that the binding energies in Pt 4f were... 5 / 2 and Pt 4f 7 / 2 The deconvolution of the Pt(0) peaks in Example 1 was located at a binding energy equivalent to 0.6 eV higher than that in Comparative Example 3.

[0211] If we observe at Pt 4f 5 / 2 and Pt 4f 7 / 2 The binding energies of the deconvoluted Pt(II) peaks in Example 1 were confirmed to be 76.9 eV and 73.2 eV, respectively, and those in Comparative Example 3 were confirmed to be 75.3 eV and 72.1 eV, respectively. This confirms that the binding energies of the Pt 4f peaks are... 5 / 2 and Pt4f 7 / 2 The deconvolution of the Pt(II) peak in Example 1 was located at a binding energy equivalent to 1.6 eV and 1.1 eV higher than that in Comparative Example 3, respectively.

[0212] At this point, the XPS spectrum of commercially available Pt / C corresponds to Pt 4f. 5 / 2 and Pt 4f 7 / 2 Based on the binding energies of the deconvolutioned Pt(0) and Pt(II) peaks of the double peaks, the corresponding Pt 4f peaks in the XPS energy spectrum of PtCa / C (Example 1) are... 5 / 2 and Pt 4f 7 / 2The difference in binding energies between the deconvolved Pt(0) and Pt(II) peaks of the bimodal graph, i.e., the ratio (E1 / E2) of the binding energy difference between the Pt(0) peak (E1) and the Pt(II) peak (E2), in Pt 4f 5 / 2 The peak was identified as 0.37, and in Pt4f 7 / 2 The peak value was confirmed to be 0.54.

[0213] This shift in binding energy means a downward shift in the d-bandcenter relative to the Fermi level. This change in chemical structure affects the binding strength of reaction intermediates formed through catalytic reactions with Pt atoms located on the surface of a platinum alloy catalyst (PtCa / C).

[0214] As an example, in the oxygen reduction reaction (ORR), the binding strength between reaction intermediates such as OH or -OOH formed during the reaction and Pt atoms is weakened, thereby minimizing the poisoning of platinum catalysts caused by the aforementioned reaction intermediates and significantly increasing durability.

[0215] (Experimental Example 3) Electrochemical Characteristics Analysis

[0216] To analyze the electrocatalytic properties of the oxygen reduction reaction, the electrochemical characteristics of each sample were measured in 0.1 M HClO4 solution using a rotating disk electrode system comprising a three-electrode system (glassy carbon coated with the samples of Example 1 and Comparative Example 3 as the working electrode, Pt wire as the counter electrode, and silver / silver chloride (Ag / AgCl) in 1.0 M potassium chloride (KCl) solution as the reference electrode).

[0217] At this point, 2.5 mg of the catalyst powder prepared according to Example 1 and Comparative Example 3 was ultrasonically treated for 1 hour in a mixed solution of 4 mL of deionized water, 0.95 mL of isopropanol, and 0.5 mL of 5 wt% perfluorosulfonic acid polymer solution (NaFi-ON solution) to prepare dispersed catalyst ink. Then, 1.5 μL of catalyst ink was drop-cast onto glassy carbon and dried to prepare catalyst ink loaded with 5 μg of NaFi-ON. Pt / cm 2 The working electrode of a certain amount of catalyst.

[0218] The oxygen reduction reaction (ORR) characteristics were measured at a scan rate of 10 mV / s and a working electrode rotating at 1600 rpm.

[0219] Figure 7 of (a), Figure 7 (b) and Figure 7 (c) shows the cyclic voltammetry (CV) curves measured in nitrogen-saturated 0.1M HClO4 solutions of Examples 1 and Comparative Example 3, the ORR polarization curves measured by linear sweep voltammetry (LSV) in oxygen-saturated 0.1M HClO4 solutions, and the Tafel plots, respectively.

[0220] like Figure 7 As shown in (a), it can be confirmed that in the case of Example 1 (PtCa / C), compared with Comparative Example 3 (commercially available Pt / C), the adsorption peaks of oxides and hydroxides shift towards the positive voltage direction. This is because, as described above, by means of the Pt and Ca alloy formed in Example 1, the d-band center of Pt shifts towards the decreasing direction, thereby weakening the Pt-O bonding strength. Similarly, referring to... Figure 7 (a) is a magnified graph in the range of 0.4V to 1.0V. It is observed that, compared with Comparative Example 3, the reduction peak of Example 1 shifts towards the positive voltage direction. In particular, it can be seen that, compared with Comparative Example 3, the overpotential of Example 1 is reduced by about 55mV. This confirms that the catalyst activity of Example 1 is superior compared with Comparative Example 3.

[0221] Another indicator of catalyst activity is the half-wave potential in the ORR polarization curve obtained by linear sweep voltammetry. The half-wave potential is the potential at which the current reaches its midpoint under the diffusion-limiting current density; a higher half-wave potential indicates better catalyst activity. (Observation) Figure 7 From the ORR polarization curve in (b), it can be seen that the half-wave potential of Example 1 is 0.87V, which is 35mV higher than that of Comparative Example 3 (0.835V).

[0222] Furthermore, if in Figure 7 By observing the Tafel slope in (c) of the Tafel plot, it can be seen that the slope of Example 1 is 60.8 mV / dec, which is lower than that of Comparative Example 3 (76.8 mV / dec). Therefore, it can be seen that the active reaction rate of Example 1 is superior to that of Comparative Example 3.

[0223] Figure 8 (a) and Figure 8 (b) shows the electrochemical active surface area (ECSA) determined by the charge of hydrogen desorption according to cyclic voltammetry in Example 1 and Comparative Example 3, as well as the mass activity and specific activity per unit mass measured at 0.9 V (relative to RHE).

[0224] It was confirmed that the ECSA values ​​of Example 1 and Comparative Example 3 were 47.03 m. 2 / g and 53.99m 2 / g, and it was confirmed that the activity per unit mass of Example 1 was 0.67A / mg. Pt Compared with Comparative Example 3 (0.17A / mg) Pt Compared to Comparative Example 3, Example 1 exhibited approximately 4 times the superior activity, and similarly, in terms of surface activity, Example 1 exhibited approximately 4.5 times the superior activity compared to Comparative Example 3.

[0225] Additionally, accelerated durability tests (ADT) were performed in an oxygen-saturated 0.1M HClO4 solution at 10k, 20k, and 30k cycles, with cyclic voltages applied over a voltage range of 0.6V to 1.1V (relative to RHE) and a scan rate of 50mV / s.

[0226] Figure 9 (a) and Figure 9 (b) shows the linear sweep voltammetry (LSV) curves measured at the beginning of Example 1 (before the accelerated durability test (ADT)) and after 10k cycles of ADT, and the LSV curves of Example 1 measured at the beginning of Comparative Example 3 and after 30k cycles of ADT. Figure 9 (c) and Figure 9 (d) shows the cyclic voltammetry (CV) curves and electrochemical active surface area (ECSA) at the beginning of Example 1, after 10k, 20k, and 30k cycles of ADT.

[0227] like Figure 9 As shown in (a), even after 10k cycles of ADT, the LSV curve of Example 1 remains active, with the LSV curve almost overlapping the initial LSV curve. That is, it can be confirmed that the platinum alloy catalyst (PtCa / C) of Example 1 has excellent durability. Furthermore, from... Figure 9As shown in (b), the durability of Example 1 is once again confirmed to be so excellent that the activity of Example 1 after 30k cycles of ADT is similar to that of Comparative Example 3. In contrast, in the LSV curve of Comparative Example 3, it was confirmed that the half-wave potential decreased by approximately 33mV after 30k cycles of ADT compared to the initial value.

[0228] like Figure 9 As shown in (d), it was confirmed that there was almost no loss of electrochemical active surface area even after ADT was performed for 10k, 20k and 30k cycles.

[0229] (Experimental Example 4) Characteristics of a fuel cell containing a platinum alloy catalyst (PtCa / C)

[0230] The prepared platinum alloy catalyst was used as the cathode catalyst in a membrane electrode assembly (MEA) to evaluate the performance of the fuel cell.

[0231] A slurry was prepared by mixing the catalysts of Example 1 and Comparative Example 3 with 5 wt% Nafion ionomer solution, isopropanol and deionized water, respectively. The prepared slurry was then sprayed onto a Nafion 211 membrane (DuPont) to prepare a membrane electrode assembly.

[0232] To conduct performance testing of the proton exchange membrane fuel cell (PEMFC), commercially available Pt / C (TKK, 19.4 wt% Pt) was used as the anode catalyst. The anode and cathode areas were maintained at 5 cm². 2 .

[0233] The membrane electrode assembly was then assembled with a commercially available gas diffusion layer (GDL, SG L 39BC) without thermocompression.

[0234] The proton exchange membrane fuel cell supplies pure hydrogen with 100% relative humidity to the anode at a flow rate of 300 mL / min and pure oxygen with 100% relative humidity to the cathode at a flow rate of 1000 mL / min, thereby operating at 80°C and 0.5 bar back pressure.

[0235] According to the U.S. Department of Energy (DOE) protocol, cyclic sweeps were applied with a rise time of 0.5 s and a voltage range of 0.6 V to 0.95 V, and accelerated durability testing was performed at 10 k, 20 k, and 30 k cycles.

[0236] Figure 10 (a) and Figure 10 (b) shows the polarization and power density curves of the fuel cells using Example 1 and Comparative Example 3 as cathode catalysts before and after 30k cycles in the accelerated durability test. Figure 10 (c) and Figure 10 (d) are graphs showing the changes in maximum power density and mass activity per unit mass before and after 30k cycles of accelerated durability testing.

[0237] from Figure 10 of (a), Figure 10 (b) and Figure 10 As can be seen from (c), the initial maximum power density of the fuel cell including Example 1 is 1380 mW / cm². 2 Slightly lower than the initial maximum power density (1465 mW / cm³) of the fuel cell including Comparative Example 3. 2 It has been confirmed that, in the fuel cell including Example 1, the maximum power density is actually quite high after the accelerated durability test of 30k cycles.

[0238] For the fuel cell using Example 1 as the cathode catalyst, the maximum power density after the accelerated durability test of 30k cycles decreased by 11% compared to the initial power density. In contrast, the fuel cell using Comparative Example 3 as the cathode catalyst decreased by 30%. This is consistent with the results of the accelerated durability test performed in Experimental Example 3 above, which means that the fuel cell using Example 1 as the cathode catalyst has significantly better durability than the fuel cell using Comparative Example 3 (commercially available Pt / C (20wt% Pt)) as the cathode catalyst.

[0239] Furthermore, referring to Figure 10 (d) It was confirmed that, at 0.9V, the initial unit mass activity of the fuel cell, including that of Example 1, was 0.45 A / mg. Pt And the activity per unit mass after performing an accelerated durability test of 30k cycles (0.29A / mg) Pt The activity per unit mass of the fuel cell, including Comparative Example 3, decreased by approximately 35.6% compared to the initial state after undergoing an accelerated durability test of 30k cycles.

[0240] This result for the fuel cell, including Example 1, means that, with respect to activity per unit mass, it has an initial activity per unit mass exceeding the U.S. Department of Energy's 2020-2025 target (beginning-of-life, 0.44 A / mg). Pt And the activity per unit mass after the 30k accelerated durability test (end-of-life (EOL)) was 0.26A / mg. Pt It exhibits exceptional durability at a level exceeding 40% of the initial unit mass activity (based on the standard).

[0241] (Experimental Example 5) Comparison of Particulate PtMg / C, PtSr / C and PtBa / C Catalysts and Their Characteristics

[0242] Figure 11 of (a), Figure 11 (b) and Figure 11 (c) are diagrams showing the XRD patterns of the particulate composites of Example 4 (PtSr / C), Example 5 (PtBa / C), and Example 6 (PtMg / C) prepared according to an embodiment of the present invention.

[0243] like Figure 11 (a) to Figure 11 As shown in (c), all synthesized Pt-alkaline earth metal alloys exhibit high crystallinity, and this synthesis method is a universally effective approach that provides a new breakthrough for the synthesis of particulate Pt-alkaline earth metal alloys, which are difficult to achieve due to large reduction potential differences. Furthermore, although not shown in this invention, it is also generally applicable to early transition metals and alloys between lanthanides and platinum, which are also difficult to achieve due to large reduction potential differences, and demonstrates an excellent synthesis method that can be generalized in almost all syntheses.

[0244] In particular, it was confirmed that the complex of Example 5 was consistent with the specific peak (PDF#00-023-0830) data of Pt5Ba / C, and the complex of Example 6 was consistent with Pt3Mg / C. 0.17 The specific peak data (PDF#00-028-0626) is consistent. Furthermore, it has been confirmed that Examples 4 to 6 all possess a cubic crystal phase.

[0245] Figure 12 (a) and Figure 12(b) is a diagram showing the TEM images at low magnification (scale bar 10 nm), high magnification (scale bar 5 nm), lattice space of the crystal plane, and Fast Fourier Transform (FFT) pattern images of the composite of Example 6.

[0246] Reference Figure 12 (a) and Figure 12 As shown in (b), the average size of the PtMg nanoparticles loaded on the carbon support (commercially available carbon, Ketje n Black EC600JD) is approximately 5 nm, and the crystalline plane of the particles exhibits a lattice size of 0.256 nm, which is equivalent to the (111) plane of PtMg, larger than the lattice size of the pure Pt (111) plane (0.230 nm). This is because Mg with a size larger than Pt enters the lattice, causing lattice expansion and thus increasing the lattice size. Interestingly, it is known that most of the PtMg particles are encapsulated in a thin carbon layer, consistent with the XRD pattern of Pt3MgC. 0.17 The structure is consistent.

[0247] Figure 13 (a) and Figure 13 Figure (b) shows high-resolution Pt 4f XPS profiles of Example 6 (PtMg / C) and Comparative Example 3 (commercially available Pt / C), respectively. For Pt3Mg / C and Pt / C, in Pt4f... 7 / 2 The binding energies of the deconvolutioned Pt(0) peaks in the peaks are 71.4 eV and 70.9 eV, respectively, as in Example 1 (PtCa / C). This confirms that the peaks in Example 6 (PtMg / C) are located at binding energies that are 0.5 eV higher than those of Pt / C.

[0248] If we observe from Pt 4f 7 / 2 The binding energies of the deconvolutioned Pt(II) peaks were confirmed to be 72.8 eV in Example 6 and 72.1 eV in Comparative Example 3 (i.e., Pt / C). It was confirmed that the binding energy of Pt 4f... 7 / 2 The deconvolutioned Pt(II) peak in PtMg / C is located at a binding energy equivalent to 0.7 eV higher than that of Comparative Example 3.

[0249] At this point, based on the XPS energy distribution of commercially available Pt / C corresponding to Pt 4f... 7 / 2 The binding energies of the deconvolutioned Pt(0) and Pt(II) peaks, corresponding to Pt 4f in the XPS energy spectrum of PtMg / C. 7 / 2The difference in binding energies between the deconvolutioned Pt(0) and Pt(II) peaks, i.e., the ratio (E1 / E2) of the binding energy difference (E1) of the Pt(0) peak to the binding energy difference (E2) of the Pt(II) peak, in Pt 4f 7 / 2 The peak value was confirmed to be 0.71, which is greater than the Pt4f value of PtCa / C. 7 / 2 The ratio (E1 / E2) at the peak (0.54) was determined to be related to the severe lattice strain caused by the larger atomic size of Ca than that of Mg.

[0250] Figure 14 (a) and (b) of 14 respectively show the conditions under H2-O2, Figure 14 (c) and Figure 14 (d) are graphs showing the polarization and power density curves before and after 30k cycles of accelerated durability testing of fuel cells used as cathode catalysts in Example 6 (PtMg / C) and Comparative Example 3 under H2-Air conditions.

[0251] from Figure 14 (a) and Figure 14 As shown in (b), under H2-O2 conditions, the initial maximum power density of the fuel cell including PtMg / C is 1580 mW / cm³. 2 The initial maximum power density (1465 mW / cm³) is higher than that of the fuel cell including Comparative Example 3. 2 This demonstrates excellent activity. After an accelerated durability test with 30k cycles, the maximum power density decreased by only 6% compared to Comparative Example 3, which had a 30% reduction. Therefore, it can be confirmed that it exhibits very good activity and excellent stability.

[0252] Under H2-Air conditions, almost identical phenomena were observed to those under H2-O2 conditions; that is, under H2-Air conditions, the initial maximum power density of the PtMg / C fuel cell (740 mW / cm³) was significantly higher. 2 It is also higher than the initial maximum power density (655 mW / cm³) of the fuel cell including Comparative Example 3. 2 This results in excellent activity; after an accelerated durability test at 30 kJ, the maximum power density decreased by only 5% compared to Comparative Example 3, which showed a 29% reduction. Therefore, it can be confirmed that the fuel cell exhibits very excellent activity and stability. This means that, compared to the fuel cell using Comparative Example 3 (commercially available Pt / C (20 wt% Pt)) as the cathode catalyst, the fuel cell using the PtMg / C composite prepared according to an embodiment of the present invention as the cathode catalyst exhibits significantly superior durability.

[0253] As described above, the present invention has been illustrated by specific details and limited embodiments, but this is only provided to help to understand the present invention more fully. The present invention is not limited to the above embodiments, and any modifications and variations can be made from such description by those skilled in the art.

[0254] Therefore, the concept of the present invention is not limited to the illustrated embodiments, nor to the claims; all contents that are equivalent or modified to the claims fall within the scope of the present invention.

Claims

1. A method for preparing a composite, comprising the following steps: a) Prepare a mixture comprising a platinum precursor, an alkaline earth metal precursor, a first reducing agent and an aprotic organic solvent; b) The mixture is subjected to a first heat treatment at a temperature above the boiling point of the organic solvent, followed by natural cooling, to prepare a colloid containing the compound; c) Centrifuge the colloid to obtain the composite; d) The composite is mixed with a powdered second reducing agent, coated onto a carbon support, and subjected to a second heat treatment in an inert reducing atmosphere to induce alloying between platinum and the alkaline earth metal; and e) Remove impurities from the alloyed composite by acid treatment. in, The aprotic organic solvent is selected from acetonitrile, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, methyl n-propyl ketone, N-acetonitrile, dimethyl ethyl ketone, dimethyl methyl sulfoxide, dimethyl ethyl ketone, dimethyl ... One or more of methylpyrrolidone, propylene carbonate, nitromethane, sulfolane, and hexamethylphosphoric triamine. The synthesized product of step b) includes crystalline platinum and amorphous alkaline earth metals.

2. The method for preparing the composite according to claim 1, wherein, Steps a), b), and d) are performed under anhydrous and oxygen-free conditions.

3. The method for preparing the composite according to claim 1, wherein, The first heat treatment in step b) is performed for 11 to 30 hours.

4. The method for preparing the composite according to claim 1, wherein, The second heat treatment is performed at a temperature of 300°C to 1000°C.

5. The method for preparing the composite according to claim 1, wherein, The alkaline earth metal precursor is a chloride selected from one or more of calcium, magnesium, strontium, barium, radium and beryllium.

6. The method for preparing the composite according to claim 1, wherein, A platinum coating is formed on the surface of the alloyed composite by means of the acid treatment in step e).

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