KR102076979B1 - A water-soluble catalyst for hydrogen evolution reaction and a method for manufacturing thereof - Google Patents

Abstract

One embodiment of the present invention provides a hydrogen gas generating water-soluble catalyst comprising a complex represented by the formula (1):
[Formula 1]
M _x Au _25-x (L) ₁₈
In Chemical Formula 1,
M is Pt or Ag,
L is a thiol ligand having a hydrophilic functional group,
x is one of integers from 0 to 13.

Description

Hydrogen gas generation water-soluble catalyst and its manufacturing method {A WATER-SOLUBLE CATALYST FOR HYDROGEN EVOLUTION REACTION AND A METHOD FOR MANUFACTURING THEREOF}

The present invention relates to a hydrogen gas generating water-soluble catalyst and a method for producing the same.

As economic growth continues, fossil fuels are rapidly depleted, and as a countermeasure, there is an increasing interest in developing new renewable energy and high performance catalysts for their effective use. Among them, the development of an electrochemical catalyst for a hydrogen evolution reaction (HER), which decomposes water that is not depleted and obtains hydrogen energy, is drawing particular attention.

The main focus of the catalyst development is to lower the overpotential of the catalytic reaction and to improve the reactivity and selectivity. Much research is being conducted in the field of heterogeneous solid catalysts based on metals and metal oxides and homogeneous molecular catalysts based on organometallic compounds. The field of solid catalysts has been remarkable in the design of theoretical catalysts that optimize the adsorption energy of substrates using computational chemical methodologies such as density functional theory (DFT), but due to the inherent nonuniformity of solid surfaces, There are many problems with the use of the catalyst. In the field of molecular catalysts, research is being conducted to design and manufacture HER customized catalysts based on the uniformity of catalysts and the control of central metal ions and ligands. Recently, by utilizing a metal complex coordinated with a ligand functionalized with a functional group such as sulfonic acid, carboxylic acid or amine as a molecular catalyst, the excess hydrogen ions are collected around the catalyst. At the same time, a technology for promoting a catalytic reaction by inducing a hydrogen ion relay reaction that effectively moves hydrogen ions to a reaction point has been developed.

Since this technique is implemented through a homogeneous catalyst using a water soluble ligand, no elementization step is required, and hydrogen energy can be obtained from water in an environmentally friendly manner. However, due to the nature of the molecular catalyst, the chemical structure and the synthesis process are complicated, and there is a limit that is unstable in aqueous solution. One of the methods to fundamentally solve the limitations of the existing catalyst is to prepare a reaction tailored catalyst optimally designed for HER based on metal clusters that are uniform, easy to design, and stable in aqueous solution.

Metal clusters are particles composed of a very small core (<2 nm) core composed of up to 200 metal atoms and a metal-ligand shell that stabilizes them. Similar to the molecular catalyst, there is a characteristic that the physical properties expressed according to the number and composition of constituent atoms change significantly. That is, if the size, composition, structure and ligand of the metal cluster can be controlled at the atomic level, it is possible to prepare a catalyst of the structure and physical properties according to the purpose.

Specifically, Au ₂₅ (is composed of a cosahedral core metal (Au ₁₃ ) consisting of 13 gold atoms and six pairs of ligand-gold-ligand-gold-ligand films (Au ₂ (L) ₃ ) surrounding them). L) ₁₈ complexes can be used as electrocatalysts with precise control of unique physicochemical properties, with only 13 and 18 central metal atoms and ligands, respectively.

Unlike conventional metal nanoparticles containing ligands, Au ₂₅ (L) ₁₈ complex provides open structure and flexibility of metal-ligand membranes, allowing hydrogen ions to easily access the core metals, which can be used to facilitate Hydrogen ion transport and multiple catalytic effects. The Au ₃₈ (L) ₂₄ complex, which can be obtained together during the preparation of Au ₂₅ (L) ₁₈ , consists of a central metal (Au ₂₃ ) connected by two icosahedrons sharing three gold atoms, and a pair of three surrounding them Consists of a ligand-gold-ligand membrane (Au (L) ₂ ) and six pairs of ligand-gold-ligand-gold-ligand membranes (Au ₂ (L) ₃ ) with twice the number of reaction points and more pronounced ligand control effects Has

Patent Literature 1 uses hexanethiol (C ₆ S) ligand as a ligand such as Pd ₂ Au ₃₆ (C ₆ S) ₂₄ in a gold-based nanocluster catalyst, and dichloromethane, acetonitrile, acetone, and the like. A hydrogen gas generating water-soluble catalyst having a structure of PdAu ₂₄ (MPS) ₁₈ and Cu _x Au _25-x (MPS) ₁₈ is disclosed by alloying a hydrogen gas generating non-aqueous catalyst used as a solvent, palladium or copper. The present invention improves and develops Patent Document 1, and has produced a hydrogen gas generating water-soluble catalyst having a remarkably excellent effect by doping a ligand or metal different from the prior art.

Korea Patent Registration No. 10-1759433

 Huifeng Qian et al. 6, Monoplatinum Doping of Gold Nanoclusters and Catalytic Application, J. Am. Chem. Soc., Vol. 134, Issue. 39, pp. 16159-16162 (2012.09.19.)  Peili Zhang et al. 4, A Molecular Copper Catalyst for Electrochemical Water Reduction with a Large Hydrogen-Generation Rate Constant in Aqueous Solution, Angew. Chem. Int. Ed., 2014, 53, pp. 13803-13807 (2014.10.14.)

The present invention is to solve the above-mentioned problems of the prior art, an object of the present invention is to provide a hydrogen gas generation catalyst that is excellent in the reaction rate, water-soluble.

One aspect of the present invention provides a hydrogen gas generating water-soluble catalyst comprising a complex represented by the following formula (1):

[Formula 1]

M _x Au _25-x (L) ₁₈

In Formula 1, M is Pt or Ag, L is a thiol ligand having a hydrophilic functional group, and x is one of integers from 0 to 13.

In one embodiment, x is 0, and L may be mercaptopropionic acid or mercaptopropanesulfonic acid.

In one embodiment, x is 1, M is Pt, and L may be glutathione or mercaptopropanesulfonic acid.

In one embodiment, M is Ag and L may be mercaptopropanesulfonic acid.

Another aspect of the invention provides a hydrogen gas water-soluble generating catalyst comprising a complex represented by the following formula (2):

[Formula 2]

Au ₃₈ (L) ₂₄ or M ₂ Au ₃₆ (L) ₂₄

In Formula 2, M is Ag and L is a thiol ligand having a hydrophilic functional group.

In one embodiment, L may be mercaptopropanesulfonic acid or glutathione.

In addition, another aspect of the invention, (a) adding an aqueous solution containing L to a solution containing M and Au; (b) reacting an aqueous solution comprising sodium borohydride with the product of step (a); And (c) obtaining a complex represented by the following Chemical Formula 1 or 2 from the product of step (b); providing a method for producing a hydrogen gas water-soluble generating catalyst comprising:

[Formula 1]

M _x Au _25-x (L) ₁₈

[Formula 2]

Au ₃₈ (L) ₂₄ or M ₂ Au ₃₆ (L) ₂₄

In Formula 1 or 2, M is Pt or Ag, L is a thiol-based ligand having a hydrophilic functional group, x is one of integers from 0 to 13.

In one embodiment, the molar ratio of M and Au may be 0:50 to 10:40, respectively.

In one embodiment, the solution of step (a) further comprises acetonitrile, wherein L may be mercaptopropanesulfonic acid.

In one embodiment, the solution of step (a) further comprises methanol, wherein L may be glutathione.

In one embodiment, the M is Pt, wherein step (c) comprises the steps of (i) phase shifting the complex to an organic solvent by adding tetraoctylammonium cation to the product of step (b); (ii) removing impurities by adding hydrogen peroxide solution to the organic solvent; And (iii) adding tetramethylammonium decanoate to the product of step (ii) to phase transfer the complex to an aqueous solution.

In one embodiment, in step (c) the product of step (b) may be centrifuged after desalting to obtain the complex.

According to one aspect of the present invention, it is possible to prepare a hydrogen gas water-soluble generating catalyst with excellent reaction rate.

According to another aspect of the present invention, by alloying the metal it is possible to control the activity of the hydrogen gas generation reaction of the catalyst.

It is to be understood that the effects of the present invention are not limited to the above effects, and include all effects deduced from the configuration of the invention described in the detailed description or claims of the present invention.

1 illustrates the structure of a ligand that may form part of a complex according to an embodiment or comparative example of the present invention.
FIG. 2 shows negative-mode electrospray ionization mass spectra in the negative charge detection mode of a complex having a structure of Au ₂₅ (MPA) ₁₈ (red) or Au ₂₅ (MPS) ₁₈ (blue). In one embodiment, x, y, and z represent hydrogen ions (H ⁺ ), sodium ions (Na ⁺ ), and the charge state of the composite, respectively.
Figure 3 compares the prior art (Patent Document 1, Au ₂₅ (C ₆ S) ₁₈ ) and the catalyst (Au ₂₅ (MPA) ₁₈ , Au ₂₅ (MPS) ₁₈ ) prepared in the present invention, (A) dichloro Ultraviolet-visible-near infrared rays of Au ₂₅ (C ₆ S) ₁₈ (black) dissolved in dichloromethane solution, Au ₂₅ (MPA) ₁₈ (red) or Au ₂₅ (MPS) ₁₈ (blue) dissolved in water UV-vis NIR absorption spectra, (B) 1 mM Au ₂₅ (C ₆ S) ₁₈ , 0.1 M tetrabutylammonium hexafluorophosphate (Bu ₄ NPF ₆ ) dichloro Square-wave voltammograms (SWVs) of 0.1 M aqueous potassium chloride solution containing methane solution (black), 10 mM Au ₂₅ (MPA) ₁₈ (red) or 10 mM Au ₂₅ (MPS) ₁₈ (blue) ) Is shown.
4 is linear in 180 mM acetic acid and 0.1 M potassium chloride (KCl) mixture with or without 1 mM Au ₂₅ (MPA) ₁₈ (red) or 1 mM Au ₂₅ (MPS) ₁₈ (blue). Linear-sweep voltammograms (LSVs) were used to measure the potential with Ag / AgCl reference electrodes and were expressed on the basis of reversible hydrogen electrodes (RHEs) using acid dissociation constants of acetic acid (10 ^-4.76 ).
FIG. 5 shows -0.7 V (RHE) versus scan rate (v) in 180 mM acetic acid and 0.1 M KCl solution containing 1 mM Au ₂₅ (MPA) ₁₈ (red) or 1 mM Au ₂₅ (MPS) ₁₈ (blue). I _c / I _p in reference).
6 is LSVs measured by dropwise adding acetic acid from 0 mM to 180 mM in 0.1 M KCl mixture containing (A) 1 mM Au ₂₅ (MPA) ₁₈ or (B) 1 mM Au ₂₅ (MPS) _18. FIG. Based on A (red) of 6 and B (blue) of 6, the catalytic current at -0.7 V (RHE basis) is shown according to the hydrogen ion concentration.
7 is a comparison of the prior art (Patent Document 1, Au ₂₅ (C ₆ S) ₁₈ ) and the catalyst (Au ₂₅ (MPA) ₁₈ , Au ₂₅ (MPS) ₁₈ ) prepared in the present invention, 1mM Au ₂₅ (MPA), ₁₈ (red) or 1mM of Au ₂₅ (MPS) of ₁₈ (blue) with a 180mM acetic acid and 0.1M KCl and 1mM aqueous solution containing the Au ₂₅ (C ₆ S) ₁₈ of 0.1M Bu ₄ NPF ₆ contains the Shows the catalytic reaction rate constant (k _obs ) versus the applied voltage measured in 1M trifluoroacetic acid (TFA) dichloromethane solution (black). Ag / AgCl or RHE were expressed in reference with the acid dissociation constant of acetic acid (10 ^-12.7) with Ag / AgNO ₃ reference electrode and measured acid (10 ^-4.76), or trifluoromethyl with the potential.
8 is a comparison of the prior art (Patent Document 1, Au ₂₅ (GS) ₁₈ ) and the catalyst (Au ₂₅ (MPA) ₁₈ , Au ₂₅ (MPS) ₁₈ ) prepared in the present invention, 1mM Au ₂₅ (MPA ) -0.7 V (depending on pH and hydrogen ion concentration in 0.1M KCl mixture containing ₁₈ (red), 1 mM Au ₂₅ (MPS) ₁₈ (blue) or 1 mM Au ₂₅ (GS) ₁₈ (green) The catalytic current diagram in RHE reference) is shown.
FIG. 9 shows (A) electrospray mass spectrometry in the negative charge detection mode of PtAu ₂₄ (MPS) ₁₈ , where x and z represent sodium ions (Na ⁺ ) and the charged amounts of the complexes, respectively (B ) Ultraviolet-visible-near infrared absorption spectroscopy of Au ₂₅ (MPS) ₁₈ (blue) or PtAu ₂₄ (MPS) ₁₈ (green) dissolved in water, (C) 10 mM Au ₂₅ (MPS) ₁₈ (blue) Or SWVs of 0.1 M aqueous KCl solution containing ₁₀ mM PtAu ₂₄ (MPS) ₁₈ (green).
10 shows (A) LSVs and (B) applied voltage in 180 mM acetic acid and 0.1 M KCl mixture with 1 mM Au ₂₅ (MPS) ₁₈ (blue) or 1 mM PtAu ₂₄ (MPS) ₁₈ (green) The relative catalytic reaction rate constant (k _obs ) is shown, and the potential is measured using an Ag / AgCl reference electrode and is expressed based on RHE using an acid dissociation constant of acetic acid (10 ^-4.76 ).
11 shows 0.1 M KCl with 5 μM of Au ₂₅ (MPA) ₁₈ (red), Au ₂₅ (MPS) ₁₈ (blue) or PtAu ₂₄ (MPS) ₁₈ (green) on a glassy carbon plate Shows the turnover frequency (TOF), which is the number of moles of hydrogen gas obtained by constant potential electrolysis (CPE) in 180 mM acetic acid solution, divided by the number of moles of the composite used. The potential was measured and ^expressed on a RHE basis using an acid dissociation constant of acetic acid (10 ^-4.76 ).
FIG. 12 shows (A) ultraviolet-rays of PdAu ₂₄ (C ₆ S) ₁₈ (black), PdAu ₂₄ (GS) ₁₈ (red) or PdAu ₂₄ (MPS) ₁₈ (blue) dissolved in dichloromethane solution. Visible-near infrared absorption spectroscopy is shown (B) Au ₂₅ (GS) ₁₈ (black), PdAu ₂₄ (GS) ₁₈ (red) (C) Au ₂₅ (MPS) ₁₈ (black) or PdAu ₂₄ ( MPS) Electrospray mass spectrometry spectroscopy in negative charge detection mode of ₁₈ (blue).
FIG. 13 shows (A) Au ₂₅ (C ₆ S) ₁₈ (grey) dissolved in dichloromethane solution, Cu _x Au _25-x (C ₆ S) ₁₈ (black), Cu _x Au _25-x dissolved in water Ultraviolet-visible-near infrared absorption spectroscopy of (GS) ₁₈ (red) or Cu _x Au _25-x (MPS) ₁₈ (blue), (B) Au ₂₅ (GS) ₁₈ , Cu _x Au ₂₅ Electrospray mass spectrometry spectroscopy in negative charge detection mode of _-x (GS) ₁₈ (red), (C) Au ₂₅ (MPS) ₁₈ or Cu _x Au _25-x (MPS) ₁₈ (blue).
14 shows Ag _x Au _25-x (MPS) prepared when the molar ratios of silver and gold salts were 0:50 (black), 3:47 (red), 6:44 (blue), and 10:40 (green), respectively. (A) UV-Visible-Near Absorption Spectroscopy and (B) Electrospray Mass Spectrometry in the negative charge detection mode of the ₁₈ alloy composite.

Hereinafter, with reference to the accompanying drawings will be described the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 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 the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "indirectly connected" with another member in between. . In addition, when a part is said to "include" a certain component, it means that it may further include other components, without excluding the other components unless otherwise stated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Hydrogen gas generation water-soluble catalyst according to an aspect of the present invention may include a complex represented by the formula (1).

[Formula 1]

M _x Au _25-x (L) ₁₈

In Formula 1, M is Pt or Ag, L is a thiol-based ligand having a hydrophilic functional group, x may be one of integers from 0 to 13.

The catalyst may be used in the hydrogen gas generation reaction represented by the following Scheme 1.

Scheme 1

(1) M _x Au _25-x (L) ₁₈ + xH ⁺ → M _x Au _25-x (LH ⁺ ) _n (L) _18-n

(2) M _x Au _25-x (LH ⁺ ) _n (L) _18-n ↔ (H ⁺ -M) M _x-1 Au _25-x (LH ⁺ ) _n-1 (L) _18-n

(3) (H ⁺ -M) M _x-1 Au _25-x (LH ⁺ ) _n-1 (L) _18-n + H ⁺ → M _x Au _25-x (LH ⁺ ) _n-1 (L) _18-n + H ₂ (g)

(4) M _x Au _25-x (LH ⁺ ) _n-1 (L) _18-n + H ⁺ → M _x Au _25-x (LH ⁺ ) _n (L) _18-n

(In the above scheme, n may be an integer of 1 to 18.)

The thiol-based ligand may have a hydrophilic functional group, and when the acidity of the ligand is high, the activity of the catalyst may be improved.

1 is hexanethiol (C ₆ S) used as a ligand in Patent Document 1, mercaptopropionic acid (MPA) and mercaptopropanesulfonic acid (3-mercaptopropionic acid, used as a ligand in the present invention (3- mercapto-1-propanesulfonic acid (MPS) is shown in order.

Referring to FIG. 1, when x is 0 and L is MPA or MPS, the complex may be Au ₂₅ (MPA) ₁₈ or Au ₂₅ (MPS) ₁₈ . When the complex is Au ₂₅ (MPA) ₁₈ , the reaction rate may be 8 times higher than that of the conventional Au ₂₅ (C ₆ S) ₁₈ complex, and when the complex is Au ₂₅ (MPS) ₁₈ , the conventional Au ₂₅ ( C ₆ S) _{18 The} reaction rate may be 23 times better than the complex. This may be a result of the sulfonic acid group or carboxyl group of the ligand promoting hydrogen ion relay reaction. In addition, while the Au ₂₅ (C ₆ S) ₁₈ complex is water-insoluble, Au ₂₅ (MPA) ₁₈ or Au ₂₅ (MPS) ₁₈ complex may be dissolved in an aqueous solution.

The composite may be in the form of an alloy comprising Pt atoms, for example PtAu ₂₄ (GS) ₁₈ or PtAu ₂₄ (MPS) ₁₈ . If the composite is in the form of a Pt alloy, the reaction rate may be five times faster than the catalyst composed of Au alone. The PtAu ₂₄ (GS) ₁₈ or PtAu ₂₄ (MPS) ₁₈ complex prepared according to Example 2 or 3 can be dissolved in an aqueous solution, unlike the conventional PtAu ₂₄ (C6S) ₁₈ complex, which is not water-soluble, and further improves the reaction rate. Can be.

The complex may be Ag _x Au _25-x (MPS) ₁₈ . X may be 1 to 12.

Hydrogen gas generation catalyst according to another aspect of the present invention may include a complex represented by the formula (2).

[Formula 2]

Au ₃₈ (L) ₂₄ or M ₂ Au ₃₆ (L) ₂₄

In Formula 2, M may be Ag, and L may be a thiol ligand having a hydrophilic functional group. L may be mercaptopropanesulfonic acid or glutathione.

The catalyst may be used for the hydrogen gas generation reaction represented by the following Scheme 2.

Scheme 2

(1) M ₂ Au ₃₆ (L) ₂₄ + xH ⁺ → M ₂ Au ₃₆ (LH ⁺ ) _k (L) _24-k

(2) M ₂ Au ₃₆ (LH ⁺ ) _k (L) _24-k ↔ (H ⁺ -M) MAu ₃₆ (LH ⁺ ) _k-1 (L) _24-k

(3) (H ⁺ -M) MAu ₃₆ (LH ⁺ ) _k-1 (L) _24-k + H ⁺ → M ₂ Au ₃₆ (LH ⁺ ) _k-1 (L) _24-k + H ₂ (g )

(4) M ₂ Au ₃₆ (LH ⁺ ) _k-1 (L) _24-k + H ⁺ → M ₂ Au ₃₆ (LH ⁺ ) _k (L) _24-k

(In the above scheme, k may be an integer of 1 to 24.)

The complex represented by Chemical Formula 2 may have an increased active point than the complex represented by Chemical Formula 1, thereby improving the effect of the ligand by 4/3 times.

The complex represented by Formula 2 may be, for example, Au ₃₈ (MPS) ₂₄ , Au ₃₈ (GS) ₂₄ , Ag ₂ Au ₃₆ (MPS) ₂₄ , Ag ₂ Au ₃₆ (GS) ₂₄ .

In the hydrogen gas generating catalyst of the present invention, M and L are mutually dependent components, and M is applicable to L, and the preparation method thereof may also be dependent on each configuration. Specific manufacturing method for this is as follows.

In addition, the method for producing a hydrogen gas generating catalyst according to another aspect of the present invention, (a) adding an aqueous solution containing L to a solution containing M and Au; (b) reacting an aqueous solution comprising sodium borohydride with the product of step (a); And (c) obtaining a complex represented by the following Chemical Formula 1 or 2 from the product of step (b).

[Formula 1]

M _x Au _25-x (L) ₁₈

[Formula 2]

Au ₃₈ (L) ₂₄ or M ₂ Au ₃₆ (L) ₂₄

In Formula 1 or 2, M is Pt or Ag, L is a thiol-based ligand having a hydrophilic functional group, x may be one of integers from 0 to 13.

The molar ratio of M and Au may be 0:50 to 10:40, respectively. Preferably, the molar ratio may be 0:50, 3:47, 6:44 or 10:40. If the molar ratio is 0:50, it means that x is 0 or the complex is Au ₃₈ (L) ₂₄ . By adjusting the molar ratio, it is possible to control the alloy ratio of the resulting composite.

The product of step (a) may further include sodium hydroxide, acetonitrile or methanol according to the type of the ligand.

For example, when L is MPA, the aqueous solution of step (a) and the aqueous solution of step (b) may further include sodium hydroxide, and the concentration ratio of Au, MPA and sodium borohydride is Each may be 2: 1: 2, and the aqueous solution of step (b) may have a molar ratio of sodium hydroxide and sodium borohydride of 1: 2, but is not limited thereto.

If L is MPS, the solution of step (a) further comprises acetonitrile, step (b) may be repeated twice, step (c) is a solution using a mixed solution of water and methanol It may be carried out by fractionation. In this case, the ratio of the solution and the aqueous solution of the step (a) may be 1: 2, the step (b) is the sodium borohydride each 3 equivalents based on the total of M and Au at 1 hour intervals, It may be to react two equivalents, the molar ratio of water and methanol in the step (c) is 3: 8 to 10, respectively, when obtaining the complex represented by the formula (1) to obtain a complex represented by the formula (2) Cases may be 3: 4 to 6, respectively.

When L is GS, the solution of step (a) further includes methanol, and step (c) may be performed by a solution fraction separation method using a mixed solution of water and methanol. In this case, the ratio of the solution and the aqueous solution of step (a) may be 1: 1, the step (b) may be to react the sodium borohydride 10 equivalents based on the total of M and Au The molar ratio of water and methanol in step (c) is 3:10 to 14 when obtaining the complex represented by Formula 1, and 3: 6 to 8 when obtaining the complex represented by Formula 2, respectively. Can be.

In step (c), the product of step (b) may be centrifuged after desalting, or the complex may be obtained by a phase transfer method.

In the case of centrifugation after the desalination treatment, for example, Au ₂₅ (L) ₁₈ complexes are prepared and then desalted with a desalting column, and purified in a centrifuge to obtain the high purity complex. Can be.

In the case of obtaining the complex by the phase transfer method, for example, a PtAu ₂₄ (L) ₁₈ or a PdAu ₂₄ (L) ₁₈ complex is prepared, and then (i) tetraoctylammonium cation is added to the organic compound. Phase shift with a solvent, (ii) hydrogen peroxide (H ₂ O ₂ ) is added and stirred to remove impurities, and (iii) tetraoctylammonium decanoate is added to phase transfer the complex to an aqueous solution. It may be a method obtained by. Including the step (iii), it is possible to prepare a water-soluble catalyst different from the prior art.

Hereinafter, embodiments of the present invention will be described in more detail. However, the following experimental results are only representative of the experimental results of the above examples, and the scope and contents of the present invention may be reduced or limited by the examples and the like and thus cannot be interpreted. The effects of each of the various embodiments of the invention, which are not explicitly set forth below, will be described in detail in that section.

Example 1

0.25 mL of 20 mM gold (III) chloride trihydrate aqueous solution, 2 mL of 5 mM 3-mercaptopropionic acid aqueous solution and 2.4 mL of water were mixed and stirred, and 0.25 mL of 1M sodium hydroxide aqueous solution was added. When the solution turned from opaque yellow to transparent yellow, 20 mL of sodium borohydride 0.1 mL was added slowly to change into a brown solution. The solution was stirred vigorously for 3 hours and then treated with 3 kDa desalting column, and purified at 4,000 rpm for 10 minutes or more in a centrifuge to obtain a high purity Au ₂₅ (MPA) ₁₈ complex. Purity was confirmed by absorbance and mass spectrometry of the complex.

Example 2

A mixture was prepared by dissolving 0.20 mmol of metal (M) salt and 0.80 mmol of gold (III) chloride trihydrate in 50 mL of methanol, and then slowly mixing with 50 mL of water in which 3.0 mmol of glutathione was dissolved. The mixture was stirred for 60 minutes and cooled to 0 ° C. To the cooled mixture was added 10 mL of an aqueous solution of 5.0 mmol of sodium borohydride and stirred for 90 minutes. After the reaction was completed, the solvent was completely removed from the rotary evaporator, dissolved in 9 mL of water, and 2 mL of nonsolvent methanol was added thereto. The resulting solids were precipitated using a centrifuge, and 2 mL of methanol was added to the detachment solution from which the solids were separated, followed by repeated precipitation of the solids using a centrifuge. The precipitated solid was added to excess methanol to remove impurities, and the obtained complex was confirmed to be M _x Au _25-x (GS) ₁₈ or M ₂ Au ₃₆ (GS) ₁₈ .

Example 3

0.20 mmol of metal (M) salt and 0.80 mmol of gold (III) chloride trihydrate are dissolved in 40 mL of acetonitrile, and then slowly with 50 mL of water in which 3.0 mmol of sodium 3-mercapto-1-propanesulfonate is dissolved. Mixing gave a mixture. The mixture was stirred for 30 minutes and cooled to 0 ° C. To the cooled mixture, 6 mL of an aqueous solution containing 3.0 mmol of sodium borohydride was added and stirred vigorously at 0 ° C. for 60 minutes, and an additional 4 mL of an aqueous solution of 2.0 mmol of sodium borohydride was added thereto for 30 minutes. Was stirred. After the reaction was completed, the solvent was completely removed from the rotary evaporator, dissolved in 9 mL of water, and 2 mL of nonsolvent methanol was added thereto. The resulting solids were precipitated using a centrifuge, and 2 mL of methanol was added to the detachment solution from which the solids were separated, followed by repeated precipitation of the solids using a centrifuge. The precipitated solid was added to excess methanol to remove impurities, and the obtained complex was confirmed to be M _x Au _25-x (MPS) ₁₈ or M ₂ Au ₃₆ (MPS) ₁₈ obtained by absorbance and mass spectrometry.

The metal (M) salt consists of dihydrogen hexachloroplatinate (IV) hydrate (H ₂ PtCl ₆ .xH ₂ O,> 99%) and silver (I) acetate (CH ₃ COOAg,> 99%). It is one selected from the group, the composition of the solvent, the mole ratio of the metal salt and gold salt, the mole ratio of the total metal salt and ligand can be adjusted according to the purity and yield of the final product.

Comparative Example 1

0.10 mmol dihydrogenhexachloroplatinate (IV) hydrate, sodium tetrachloropalladate (II) hydrate, cadmium chloride hydrate or mercury (II) chloride, 0.40 mmol gold (III) chloride trihydrate, and 0.58 A mmol of tetraoctylammonium bromide is dissolved in 15 mL of tetrahydrofuran and stirred for 60 minutes.

2.5 mmol of hexane thiol was added to the dark red mixed solution for 1 minute, followed by stirring for 5 minutes so that the color of the solution became orange. Into this solution, add 5 mL of an aqueous solution of 5.0 mmol of sodium borohydride, and stir vigorously.

Further, the stirred solution at room temperature was evaporated using a rotary evaporator to obtain a black complex in the form of a slurry. The obtained complex is washed 10 times with methanol and ethanol each to remove impurities, and then the excess solvent is removed using a rotary evaporator.

PtAu ₂₄ (C ₆ S) ₁₈ , PdAu ₂₄ (C ₆ S) ₁₈ , CdAu ₂₄ (C ₆ S) ₁₈ or HgAu ₂₄ (C ₆ S) ₁₈ were obtained separately in the washed complex.

Comparative Example 2

For the preparation, 0.20 mmol of sodium tetrachloropalladate (II) hydrate and 0.80 mmol of gold (III) chloride trihydrate were dissolved in 40 mL of acetonitrile and 3.0 mmol of sodium 3-mercapto- dissolved in 80 mL of water. Slowly and slowly mix with 1-propanesulfonate, then stir and cool for 30 minutes.

6mL aqueous solution of 3.0mmol sodium borohydride dissolved in the cooled mixture was stirred vigorously at 0 ° C for 60 minutes, and then 4mL aqueous solution of 2.0mmol sodium borohydride dissolved was added. Stir for minutes. Alternatively, 10 mL of an aqueous solution of 5.0 mmol of sodium borohydride is added thereto, followed by vigorous stirring at 0 ° C. for 90 minutes.

After completion of the reaction, the solvent was completely evaporated by rotary evaporation, dissolved in 9 mL of water, and 2 mL of nonsolvent methanol was added to precipitate a solid produced by centrifugation. In addition, 2 mL of methanol was added to the solution which was not settled again. Repeat the centrifugation and settling.

Through this process, the ligand-protected complex is separated, and the precipitated solid is added with excess methanol to remove impurities, and the PdAu ₂₄ (MPS) ₁₈ complex is obtained by absorbance analysis and mass spectrometry.

Comparative Example 3

(1) Cu _{1 ~ 8} Au _{24 ~ 17} (C ₆ S) ₁₈

0.10 mmol of copper (II) chloride dihydrate, 0.40 mmol of gold (III) chloride trihydrate, and 0.58 mmol of tetraoctyl ammonium bromide are dissolved in 15 mL of tetrahydrofuran and stirred for 60 minutes.

2.5 mmol hexane thiol was added to the reddish brown mixed solution for 1 minute, followed by stirring for 60 minutes so that the color of the solution became green. Into this solution, add 5 mL of an aqueous solution of 5.0 mmol of sodium borohydride, and stir vigorously.

Further, the stirred solution at room temperature was evaporated using a rotary evaporator to obtain a black complex in the form of a slurry. The obtained complex is washed 10 times with methanol and ethanol each to remove impurities, and then the excess solvent is removed using a rotary evaporator.

Next, put excess acetonitrile and acetone mixture (volume ratio = 1: 1) to the washed complex to extract the Cu _x Au _25-x (C ₆ S) ₁₈ (x = 1 ~ 8) complex.

(2) Cu ₁₆ Au ₉ (GS) ₁₈

After dissolving 0.20 mmol of copper (II) chloride dihydrate and 0.80 mmol of gold (III) chloride trihydrate in 50 mL of methanol, slowly and slowly mixing with 3.0 mmol of glutathione dissolved in 50 mL of water, followed by 60 minutes Stir and cool to 0 ° C. To the cooled mixture is added 10 mL of an aqueous solution of 5.0 mmol of sodium borohydride and stirred for 90 minutes.

After completion of the reaction, the solvent was completely evaporated by rotary evaporation, dissolved in 9 mL of water, and 2 mL of nonsolvent methanol was added to precipitate a solid formed by centrifugation. The process of centrifugation and precipitation is repeated.

This process separates the complex protected with small particle glutathione, removes the precipitated solids by adding excess methanol and removes the Cu ₁₆ Au ₉ (GS) ₁₈ complex by absorbance analysis and mass spectrometry. Get

_{(3) Cu 11 ~ 12 Au} 14 ~ 13 (MPS) 18

0.20 mmol of copper (II) chloride dihydrate and 0.80 mmol of gold (III) chloride trihydrate were dissolved in 40 mL of acetonitrile and 3.0 mmol of sodium 3-mercapto-1-propanesulfonate dissolved in 80 mL of water. After slowly and slowly mixing with, stirred for 30 minutes and cooled to 0 ℃.

6mL aqueous solution of 3.0mmol sodium borohydride dissolved in the cooled mixture was stirred vigorously at 0 ° C for 60 minutes, and then 4mL aqueous solution of 2.0mmol sodium borohydride dissolved was added. Stir for minutes.

After completion of the reaction, the solvent was completely evaporated by rotary evaporation, dissolved in 9 mL of water, and 2 mL of nonsolvent methanol was added to precipitate a solid formed by centrifugation. Repeat the centrifugation and settling.

Through this process, the complex protected with small particle ligand was separated, and the precipitated solid was added with excess methanol to remove impurities, and absorbance and mass spectrometry were used to detect Cu ₁₁ Au ₁₄ (MPS) ₁₈ and Cu ₁₂ Au _13. (MPS) ₁₈ complex is obtained.

Experimental Example

Water soluble MPA and MPS were used as ligand (L) to prepare Au ₂₅ (L) ₁₈ , and hexane thiol dissolved in the conventional organic solvent described in Patent Document 1 to understand the effect of ligand in HER catalysis. Au ₂₅ (C ₆ S) ₁₈ complex using 1-hexanethiol, C ₆ S) was prepared and compared. The structure of each of the ligands is shown in FIG. Referring to FIG. 1, MPA and MPS ligands are functionalized with carboxylic acid and sulfonic acid, respectively, while C ₆ S has no functional group.

Purity of the prepared Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ was confirmed by electrospray ionization mass spectrometry of negative charge mode, each composition Au ₂₅ containing hydrogen ions (H ⁺ ) It was confirmed that Au ₂₅ (S ₂ C ₃ H ₆ O ₃ ) ₁₈ containing (SC ₃ H ₄ O ₂ ) ₁₈ and sodium ion (Na ⁺ ). Detailed analysis results are shown in Tables 1 and 2, respectively.

Au count MPA ^- Count H ⁺ count Charge Calculated Value
m / z (Da) Measures
m / z (Da) Relative error
(%) 25 18 15 -4 1707.92 1702.79 -0.30 25 18 15 -4 1681.38 1676.54 -0.29 25 18 15 -4 1605.60 1601.05 -0.28 25 18 15 -4 1556.36 1551.81 -0.29 25 18 15 -4 1529.83 1525.56 -0.28 25 18 15 -4 1366.13 1362.03 -0.30 25 18 15 -4 1344.90 1341.03 -0.29 25 18 15 -4 1284.28 1280.64 -0.28 25 18 15 -4 1244.89 1241.24 -0.29 25 18 15 -4 1223.66 1220.24 -0.28 25 18 15 -4 1138.27 1134.86 -0.30 25 18 15 -4 1120.58 1117.36 -0.29 25 18 15 -4 1070.07 1067.03 -0.28 25 18 15 -4 1037.24 1034.20 -0.29 25 18 15 -4 1019.55 1016.70 -0.28 25 18 15 -4 975.52 972.59 -0.30 25 18 15 -4 960.36 957.59 -0.29

Au count MPS ^- Count Na ⁺ count Charge Calculated Value
m / z (Da) Measures
m / z (Da) Relative error
(%) 25 18 12 -7 1139.41 1139.09 -0.028 25 17 11 -7 1114.10 1113.81 -0.026 24 16 10 -7 1060.64 1060.39 -0.024 25 18 11 -8 994.11 993.83 -0.029 25 17 10 -8 971.96 971.71 -0.026 24 16 9 -8 925.19 924.96 -0.024 23 16 9 -8 900.57 900.34 -0.025 23 15 8 -8 878.42 878.22 -0.022 25 18 10 -9 881.10 880.85 -0.029 25 17 9 -9 861.41 861.18 -0.026 24 16 8 -9 819.84 819.64 -0.024 23 16 8 -9 797.95 797.75 -0.025 23 15 7 -9 778.26 778.09 -0.022 25 18 9 -10 790.69 790.46 -0.029 25 17 8 -10 772.97 772.77 -0.026 24 16 7 -10 735.55 735.37 -0.024 23 16 7 -10 715.86 715.68 -0.025 23 15 6 -10 698.14 697.98 -0.022 25 18 8 -11 716.72 716.51 -0.029 25 17 7 -11 700.61 700.43 -0.026 24 16 6 -11 666.59 666.43 -0.025

Referring to Table 1 or 2, it can be confirmed that the composite prepared according to the embodiment of the present invention is a high purity nano cluster having a low relative error. Referring to A of FIG. 2, mass analysis of Au ₂₅ (MPA) ₁₈ was performed. Spectra were observed in the range from 900 to 1,800 Da, revealing a set of Au ₂₅ (MPA) ₁₈ peaks of -7, -6, -5, and -4 whose charge phase was determined by hydrogen ions.

Referring to B of FIG. 2, the mass spectrometry spectra of Au ₂₅ (MPS) ₁₈ were observed in the range of 600 to 1,200 Da, -11, -10, -9, -8, and -7 in which the charged phase was determined by sodium ions. A peak set of appeared.

Since the central metal charge phase of Au ₂₅ (L) ₁₈ is -1, the charge contributed by the ligand to the charge phase is -3 to -6 for Au ₂₅ (MPA) ₁₈ , and Au ₂₅ (MPS) ₁₈ is -6 to -10 to be. 12 to 15 hydrogen ions are bound to 18 carboxylic acids in the ligand of Au ₂₅ (MPA) ₁₈ and 8 to 12 sodium ions are bound to 18 sulfonic acids in the ligand of Au ₂₅ (MPS) ₁₈ to form this charged phase. Can have.

This means that MPA ligands are unlikely to dissociate and dissociate hydrogen ions at a given time, but MPS ligands easily dissociate hydrogen ions and more often exist as anions, which means that the acidity of sulfonic acid (pKa <1) Is due to the difference between the two ligands in that the acidity of the carboxylic acid (pKa = 3.8). This result suggests that the acidity difference of the ligands alters the ligand's ability to retain protons in aqueous solution and may affect the electrochemical catalyst HER.

3A shows ultraviolet-visible rays of Au ₂₅ (C ₆ S) ₁₈ , Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ which are comparative examples prepared according to the prior art (Patent Document 1). Near-infrared (UV-vis-NIR) absorption spectra are shown. In order to more clearly observe the trend of the spectrum in the near infrared range, it is shown by the photon energy axis. Au ₂₅ (C ₆ S) ₁₈ , Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ all exhibited typical energy bands of Au ₂₅ (L) ₁₈ complexes observed at 1.8, 2.8 and 3.1 eV. It can be seen that all of the prepared composites have a typical Au ₂₅ (L) ₁₈ structure, and the electronic structure due to the change of the ligand is difficult to observe in the absorption spectrum.

Voltamograms of each complex can be determined by square-wave voltammetry (SWV), which is one of the most effective methods for experimentally identifying the electronic structure of microscopically changing complexes. (voltammograms) were obtained and shown in B of FIG. 3. Referring to B of FIG. 3, the calibration line is a voltamogram of Au ₂₅ (C ₆ S) _{18 as} a comparative example, and 0.31 (O 1), -0.04 (O 2), and -1.7 V (R 1) (based on Ag / AgCl). The peaks observed at are Au ₂₅ ^{+ / 0} , Au ₂₅ ^{0 /} -and Au _25- ^{/ 2-} . The HOMO-LUMO energy gap of Au ₂₅ (C ₆ S) ₁₈ can be determined by subtracting the charging energy (O2-O1) from the difference between the first oxide peak (O1) and the reducing peak (R1). , 1.3V.

Referring to B of FIG. 3, the potential at which the complex is reduced is changed depending on the ligand. The reduction potential (R1) of Au ₂₅ (MPA) ₁₈ moves to a more positive position (-1.6 V) relative to the reduction potential of Au ₂₅ (C ₆ S) ₁₈ , with the result that the energy bandgap decreases slightly to 1.2 V. It was. The reduction potential of Au ₂₅ (MPS) ₁₈ shifted to a more positive position and was observed at -1.2V, and the energy bandgap was further reduced to 0.8V.

This shift in reduction potential can be explained by the electrostatic field effect of carboxylic acid functionalized on MPA ligand and sulfonic acid functionalized on MPS ligand. Acidic ligands such as MPA and MPS have high electron densities, resulting in non-uniform electron densities in the metal-ligand films, thereby facilitating the reduction reaction of the complex, thereby shifting the reduction potential in the positive direction. In addition, since the acidity of sulfonic acid is higher than that of carboxylic acid, the electrostatic field effect in sulfonic acid acted more strongly than in carboxylic acid. These results indicate that acidic ligands can be used to change the electronic structure of the complex.

To determine what role the ligand changes play in the HER catalysis of Au ₂₅ (L) ₁₈ , 1 mM Au ₂₅ (MPA) ₁₈ (red) or 1 mM Au ₂₅ (MPS) ₁₈ (blue) Linear-sweep voltammograms (LSVs) in a 180 mM acetic acid and 0.1 M potassium chloride (KCl) mixture not included (grey) are shown in FIG. 4, and the potentials were measured using an Ag / AgCl reference electrode. The acid dissociation constant of acetic acid (10 ^-4.76 ) is ^{expressed on the} basis of reversible hydrogen electrode (RHE).

Referring to FIG. 4, the current in the absence of a catalyst was 0.35 mA at −1.3 V (RHE reference), and when Au ₂₅ (C ₆ S) ₁₈ was introduced as a catalyst, the current increased to 1.6 mA. The catalytic current increased further to 1.9 and 4.1 mA when Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ were added as catalysts, respectively. Au ₂₅ (C ₆ S) ₁₈ was introduced and the observed catalytic current confirmed that the Au ₂₅ (L) ₁₈ complex was fully catalyzed by HER. The increase in catalytic current observed in complexes with MPA or MPS as a ligand suggests that the change of ligand is effective for HER catalysis.

Kinetic constants were derived to quantitatively evaluate the ligand effect on HER of Au ₂₅ (L) ₁₈ complex. The following equation is applied as an approximation model for the first-order reaction in which hydrogen gas is generated by a freely diffused catalyst in a solution, and predicts the apparent rate constant (k _obs ) for HER. Was used.

[Equation]

In the above equation, I _c is the current generated as a result of the catalytic reaction, I _p is the current generated when the catalytic reaction does not occur (reduction current of Au ₂₅ ^{0 /} -flowing in the absence of hydrogen ions in the present invention), R is the gas constant Where T is the temperature in Kelvin, F is the Faraday constant, ν is the scan rate, and k _obs is the observed first reaction rate constant. The catalytic reaction rate constant (k _obs ) for the reduction of hydrogen ions is a graph plotting the ratio of the current flowing in the catalytic reaction (I _c / I _p ) to the square root of ν versus the current when no catalytic reaction occurs at a specific potential. It can be determined from the slope of. The graph of ν and I _c / I _p is shown in FIG. 5.

6 shows the results of LSV dropwise adding HOAc to Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ aqueous solution. Referring to FIG. 6, I _c gradually increases with increasing concentration of acid in the solution. It can be seen that an environment is provided in which sufficient hydrogen ions are supplied to the catalyst near 180 mM where the value becomes constant. At this time, the k _obs at -1.3V of Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ are calculated to be 200,000 and 559,000 s ^-1 , respectively, and this value is known as Au ₂₅ (C ₆ S). ₁₈ times higher for k _obs (24,000 s ⁻¹ ) in the organic phase of the ₁₈ complex catalyst.

Au ₂₅ (C ₆ S) ₁₈ prepared in the prior art (Patent Document 1) and Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ prepared in the present invention to determine what the source of the reaction rate varies depending on the ligand K _obs of each of the potentials were compared as shown in FIG. 7, and the pure catalyst reaction rates were compared except for the fast electron transfer rate of Au ₂₅ (C ₆ S) ₁₈ dissolved in the organic solvent.

First, the catalytic reaction rates of Au ₂₅ (MPA) ₁₈ of the present invention and Au ₂₅ (C ₆ S) ₁₈ of the prior art were compared. Au ₂₅ (MPA) k _obs for the catalytic reaction of ₁₈ is always greater than the k _obs of the _{Au 25 (C 6 S) 18} , was from -1.3 V a k _obs of Au ₂₅ (MPA) ₁₈ check 8 misappropriation . The fact that the reaction in Au ₂₅ (MPA) ₁₈ with a carboxylic acid group is significantly faster than the reaction in Au ₂₅ (C ₆ S) ₁₈ without any functional group indicates that carboxylic acid plays a role in promoting HER. .

This is a result of the hydrogen ion relay reaction occurring in the ligand of the molecular catalyst. In order for HER to proceed, hydrogen ions in the solution must approach the central metal, so a large activation energy is required in this process. Even when approaching only HER proceeds, the activation energy is significantly lowered, and as a result, the effect of the catalytic reaction can be improved.

Next, the catalytic reaction rates of Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ of the present invention were compared. Referring to FIG. 7, the k _obs of Au ₂₅ (MPS) ₁₈ is significantly larger than that due to the catalytic reaction of Au ₂₅ (MPA) ₁₈ , and the k _obs (559,000s ⁻¹ ) at −1.3 V represents Au ₂₅ (MPA). 2.8 times larger than ₁₈ k _obs (200,000s ^-1 ). These k _obs are more than three times larger than the nickel composite molecular catalyst that has recorded the fastest k _obs (170,000 s ^-1 ) to date and are based on commonly used nickel (1,850 s ^-1 ) or cobalt (10,673 s ^-1 ) composites. Is 300 or 50 times larger than the molecular catalyst of. The good catalytic reaction rate of Au ₂₅ (MPS) ₁₈ was due to the MPS ligand, which is more acidic than MPA.

In order to prove this, the concentration of Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ of the present invention was fixed at 1 mM, and a small amount of HOAc was added to observe the catalytic current. It shows in FIG. 8 compared with Au ₂₅ (GS) ₁₈ of a prior art (patent document 1). When Au ₂₅ (MPS) ₁₈ was used as a catalyst (blue), it was confirmed that as the concentration of hydrogen ions was increased due to the addition of HOAc, the catalytic current increased constantly. Catalytic reaction of Au ₂₅ (MPA) ₁₈ (red) is similar to the catalytic current of Au ₂₅ (MPS) ₁₈ at concentrations lower than the concentration of hydrogen ions that form the same pH as pKa of MPA, but with higher hydrogen ions. At the concentration, a limited catalytic reaction was observed with a 49% decrease in the increase in catalytic current.

In the case of Au ₂₅ (MPS) ₁₈ , sulfonic acid is very small in pKa, so hydrogen ions are easily dissociated regardless of pH, so it is believed that hydrogen ions quickly move to the central metal and a continuous increase in current by HER is observed. However, in the case of Au ₂₅ (MPA) ₁₈ , in a solution with a concentration of hydrogen ions whose pH is greater than the pKa of MPA, carboxylic acids readily dissociate hydrogen ions like sulfonic acids, resulting in a catalytic current similar to Au ₂₅ (MPS) ₁₈ . However, when the pH of the solution is lower than the pKa of MPA due to the increase in the concentration of hydrogen ions, the hydrogen ion dissociation reaction of carboxylic acid is lowered and a small catalytic current by limited HER is observed. In other words, the conditions of observing k _obs MPS is a ligand environment capable of more smoothly relaying hydrogen ions to the core metal than MPA was found to have the effect of a ligand that promotes unprecedented rapid HER.

The effect of the ligands described above was also observed in the case of the prior art employing glutathione (GS) having multiple functional groups as ligands (Au ₂₅ (GS) ₁₈ ). The concentration of Au ₂₅ (GS) ₁₈ was fixed at 1 mM, and a small amount of HOAc was added to observe the catalytic current. The catalyst current with respect to the pH change was shown in green in FIG. 8. The functional pKa of glutathione having two carboxylic acids and one amino acid as a functional group is 2.1, 3.5, and 8.7 in turn, and Au ₂₅ (MPA) at the boundary at which pH becomes larger or smaller than pKa of two carboxylic acids. _The tendency was very similar to the HER reaction of ₁₈ . In other words, the results show that the ligand or ligand's environment in which hydrogen ions are easily dissociated is an important factor that can facilitate the transfer of hydrogen ions from solution to the active site, thereby promoting an effective HER reaction.

In addition, referring to Figure 8, Au ₂₅ (MPA) ₁₈ of the present invention has a hydrogen ion relaying effect of a similar level to the prior art, Au ₂₅ (MPS) ₁₈ shows a significantly superior hydrogen ion relaying effect compared to the prior art You can check it.

Ligand's effect on HER, in addition to promoting the relaying effect of hydrogen ions has the effect of reducing the overpotential by changing the electronic structure of the complex. Referring to FIG. 6, upon addition of HOAc to Au ₂₅ (MPA) ₁₈ and Au ₂₅ (MPS) ₁₈ , an increase in the catalytic current at R1 was observed for both complex catalysts, which is a reaction in which the complex catalyst reduces hydrogen ions. It means to act as a medium for. This can be explained by the following scheme.

_{[Au 25 (L) 18]} - + e - → [Au 25 (L) 18] 2-

[Au ₂₅ (L) ₁₈ ] ^2- + H ⁺ → [Au ₂₅ (L) ₁₈ -H] ^-

[Au ₂₅ (L) ₁₈ -H] ^- + H ⁺ → [Au ₂₅ (L) ₁₈ ] ⁰ + H ₂

[Au ₂₅ (L) ₁₈ ] ⁰ + [Au ₂₅ (L) ₁₈ ] ^2- → 2 [Au ₂₅ (L) ₁₈ ] ^-

The result of the catalytic reaction product _{[Au 25 (L) 18]} - has increased the back of the R1 current, so reducing accept electrons. At this time, due to the electrostatic field effect of the ligand, R 1 of Au ₂₅ (MPA) ₁₈ is generated at a potential of 0.1 V more than that of Au ₂₅ (C ₆ S) ₁₈ , and Au ₂₅ (MPS) ₁₈ having high acidity is Au _It was observed at a potential of 0.4 V more than that of ₂₅ (MPA) ₁₈ . As the current at R1 increases, the starting point of the catalytic current is determined by the potential of R1, so the overpotential at the starting point of the catalytic reaction is 0.43V, which is the smallest of Au ₂₅ (MPS) ₁₈ where R1 is at the most positive potential. Was decided. That is, the ligand of the complex catalyst not only induces rapid HER reaction by hydrogen ion relay reaction, but also causes rapid change of electronic structure that was not observed in the conventional molecular catalyst, and thus can proceed fast HER with a small amount of energy input. .

The PtAu ₂₄ (MPS) ₁₈ complex was prepared by substituting a platinum atom with a central metal of Au ₂₅ (MPS) ₁₈ having excellent ligand effect, thereby preparing a HER catalyst having excellent performance by controlling the ligand and the central metal simultaneously.

According to Example 3, a PtAu ₂₄ (MPS) ₁₈ complex having one platinum atom introduced into the MPS ligand was prepared. Purity of the prepared PtAu ₂₄ (MPS) ₁₈ was confirmed by electrospray mass spectrometry of the negative charge mode, the composition was confirmed as PtAu ₂₄ (S ₂ C ₃ H ₆ O ₃ ) ₁₈ containing sodium ions.

Referring to FIG. 9, mass spectrometry spectra were observed in the range of 700 to 1,400 Da, and PtAu ₂₄ (MPS) ₁₈ peak sets of -10, -9, -8, -7 and -6, each of which had been charged with sodium ions, were determined. Confirmed. Thus, the peaks represented by (12,6), (11,7), (10,8), (9,9) and (8,10) in FIG. 9A are [PtAu ₂₄ (MPS) ₁₈ Na ⁺ _y ]. _Z means a composite particle having y sodium ions and a z-charged phase, respectively. In addition, fragments of ligand (L) -gold (Au) -L, L-Au-L-Au and L-Au-L-Au-L were observed at each peak. Detailed analysis results are shown in Table 3 below.

The peak observed at 991 Da matches the isotope pattern of [PtAu ₂₄ (MPS) ₁₈ Na ⁺ ₁₀ ] ^8- exactly, which is observed in [Au ₂₅ (MPS) ₁₈ Na ⁺ observed at 994 Da in the Au ₂₅ (MPS) ₁₈ spectrum. ₁₁ ] and ^8- . This means that one gold atom in the central metal of Au ₂₅ (MPS) ₁₈ was successfully converted to a platinum atom. PtAu ₂₄ (MPS) ₁₈ is significant for the first time successfully manufactured alloy composites using water-soluble ligands.

Pt Count Au count MPS ^- Count Na ⁺ count Charge Calculated Value
m / z (Da) Measures
m / z (Da) Relative error
(%) One 24 18 12 -6 1329.00 1328.60 -0.030 One 24 17 11 -6 1299.46 1299.11 -0.028 One 23 16 10 -6 1237.10 1236.78 -0.026 One 22 16 10 -6 1204.28 1203.96 -0.027 One 22 15 9 -6 1174.74 1174.46 -0.024 One 24 18 11 -7 1135.86 1135.66 -0.018 One 24 17 10 -7 1110.54 1110.24 -0.028 One 23 16 9 -7 1057.09 1056.82 -0.026 One 22 16 9 -7 1028.95 1028.68 -0.027 One 22 15 8 -7 1003.64 1003.40 -0.024 One 24 18 10 -8 991.00 990.70 -0.030 One 24 17 9 -8 968.85 968.58 -0.028 One 23 16 8 -8 922.08 921.84 -0.026 One 22 16 8 -8 897.46 897.22 -0.027 One 22 15 7 -8 875.31 875.10 -0.024 One 24 18 9 -9 878.34 878.07 -0.030 One 24 17 8 -9 858.65 858.52 -0.015 One 23 16 7 -9 817.07 816.86 -0.026 One 22 16 7 -9 795.19 794.97 -0.027 One 22 15 6 -9 775.50 775.31 -0.024 One 24 18 8 -10 788.20 787.96 -0.030 One 24 17 7 -10 770.48 770.27 -0.028 One 23 16 6 -10 733.07 732.87 -0.026

Referring to Table 3, the PtAu ₂₄ (MPS) ₁₈ complex prepared according to the embodiment of the present invention can be confirmed that the relative error of the nano clusters of high purity with a magnitude of 0.03% or less, purity of 99.97% or more. When the ligands of the Au ₂₅ (L) ₁₈ complex were not changed, the optical properties were not observed, whereas the substitution of heterogeneous metal atoms significantly changed the electrical and optical properties of the complex. Referring to B of FIG. 9, the introduction of platinum creates a new band at 2.1 eV and a new absorption band at 1.1 eV, which is a near infrared region. This change in absorption spectrum occurs when the platinum atom is substituted at the position of the gold atom in the center metal of Au ₂₅ (L) _18. The absorption band disappeared at 1.8 eV and two new bands appear in the complex. It means that the electronic structure has changed.

In order to clarify the electronic structure of the composite in detail, a square wave voltage-current method was performed and the results are shown in FIG. 9. As a result, the two oxidation peaks, PtAu ₂₄ ^{+ / 0} and PtAu ₂₄ ^{2 + / +} , based on the Ag / AgCl reference electrode were 0.33 (O1) and 0.64V (O2), and two reduction peaks, PtAu ₂₄ ^{0 / -} with PtAu ₂₄ ^{- / 2-} it was observed at -0.31 (R1) and -0.55V (R2). The HOMO-LUMO energy difference calculated from this result is 0.32V.

The above results confirm that the electronic structure is substantially changed even though only one Pt atom is substituted for one Au atom. Furthermore, the reduction peak of the metal complex is shifted by an amount of 0.65V to reduce the reaction even at a smaller overpotential. It was confirmed that the catalytic reaction can proceed effectively.

The PtAu LSV of when the ₂₄ (MPS) for containing the PtAu ₂₄ (MPS) ₁₈ of a 1mM solution in 180mM acetic acid is added to demonstrate the superior catalytic activity of the ₁₈ is shown in Fig. At -0.7V, the catalytic current of PtAu ₂₄ (MPS) ₁₈ was 4.1 times higher than that of Au ₂₅ (MPS) ₁₈ before the alloy was formed at -0.7V, and the overpotential for the catalytic reaction to start was 360 mV. The decrease was confirmed to be 40mV. The catalytic reaction rate was also calculated in the same way, recording 628,000 s ^−1, which is five times faster than before the alloy was formed. The reaction rate was found to be significantly faster than the most effective molecular catalyst (170,000 s ⁻¹ ) or a typical hydrogenase (21,000 s ⁻¹ ).

The catalytic performance of the composite was evaluated in an application environment where substantial hydrogen energy was obtained by quantifying the amount of hydrogen gas generated by constant potential electrolysis (CPE) by gas chromatography. Au ₂₅ (MPA) ₁₈ (red), Au ₂₅ (MPS) ₁₈ (blue) or PtAu ₂₄ (MPS) ₁₈ (green) at _2.5 μM on a glassy carbon plate was 180 mM with 0.1 M KCl. A turnover frequency (TOF) value measured by dividing the number of moles of hydrogen gas generated by constant voltage reaction in an acetic acid aqueous solution by the number of moles of the complex used is shown for each reaction voltage in FIG. 11.

Referring to FIG. 11, catalytic results of Au ₂₅ (MPA) ₁₈ , Au ₂₅ (MPS) ₁₈ , and PtAu ₂₄ (MPS) ₁₈ resulted in hydrogen for the first time in a constant voltage reaction of −0.5, −0.4, and −0.1 V (based on RHE). The gas was detected, and the higher the potential, the higher the amount of hydrogen gas generated, which coincided with LSV and k _obs of FIGS. 4, 7, and 10. The results show that the catalytic reaction rate for HER has a direct effect on the actual hydrogen gas generation.

Particularly, the PtAu ₂₄ (MPS) ₁₈ composite has a TOF of 127 mol H ₂ (mol cat) ⁻¹ s ⁻¹ at -0.7 V, which is the highest performance copper-based molecular catalyst that can be used as a control disclosed in Non-Patent Document 2. It was confirmed that it has an effect of generating hydrogen energy significantly superior to TOF (4.1 mol H ₂ (mol cat) ^-1 s ^-1 ).

9 to 11 to confirm the structure of the PtAu ₂₄ (MPS) ₁₈ composite was analyzed based on the data of the following PdAu ₂₄ (L) ₁₈ alloy composite.

The PdAu ₂₄ (L) ₁₈ alloy composite was manufactured by the method of the comparative example 2 similar to the prior art (patent document 1), and was named PdAu ₂₄ (MPS) ₁₈ or PdAu ₂₄ (GS) ₁₈ , respectively, according to the ligand contained. Referring to A of FIG. 12, which shows the results of absorption spectroscopy, it showed a similar tendency to PdAu ₂₄ (C ₆ S) _18, and it was confirmed that only one Pd atom was introduced into the center of the central metal. Purity of the material was confirmed by electrospray mass spectrometry.

12B and 12C show purified Au ₂₅ (GS) ₁₈ (black) and PdAu ₂₄ (GS) ₁₈ (red) or Au ₂₅ (MPS) ₁₈ (black) and PdAu ₂₄ (MPS) ₁₈ (blue) ) Is the mass spectrum. Referring to Figure 12, Au ₂₅ (GS) ₁₈ compared PdAu ₂₄ (GS) ₁₈ peak and Au ₂₅ of (MPS) ₁₈ compared PdAu ₂₄ (MPS) The difference between the ₁₈ peak is gold (Au) and palladium (Pd) atom Equal to the mass difference of, which means that the prepared alloy composite is monodisperse and consists of PdAu ₂₄ (GS) ₁₈ or PdAu ₂₄ (MPS) ₁₈ .

Next, an alloy composite was prepared in which x was able to act as an excess reaction point as an integer of 2 or more, instead of only one metal atom being substituted. The water-soluble ligand was added to the mixed solution of silver salt and gold salt to form a complex and then reduced. The number of atoms introduced (x) was controlled by adjusting the molar ratio of silver salt to gold salt.

Cu _x Au _25-x (C ₆ S) ₁₈ , Cu _x Au _25-x (GS) ₁₈ , Cu _x Au prepared by fixing the molar ratio of copper salt: gold salt to 1: 24 as a control group Absorption spectroscopy of _25-x (MPS) ₁₈ is shown in FIG. 13A. In FIG. 13B and FIG. 13C, electrospray mass spectroscopy spectra of Cu _x Au _25-x (GS) ₁₈ and Cu _x Au _25-x (MPS) ₁₈ are shown by comparison with those before the introduction of copper, respectively. As a result of quantification of x, it was confirmed that Cu ₁₆ Au ₉ (GS) ₁₈ or Cu ₁₂ Au ₁₃ (MPS) ₁₈ was formed on average.

Absorption spectral diagram of Ag _x Au _25-x (MPS) ₁₈ prepared by changing the molar ratio of silver salt to gold salt according to Example 2 from 0:50 to 10:40 is shown in FIG. In FIG. 14B, x was quantified by showing the electrospray mass spectrometry of Ag _x Au _25-x (MPS) ₁₈ compared with the alloy nanocomposite prepared by changing the molar ratio of silver salt to gold salt. As a result, when the molar ratio of silver salt: gold salt is 0: 50, 3: 47, 6: 44, 10: 40 on average, Ag ₀ Au ₂₅ (MPS) ₁₈ and Ag _{0 ~ 5} Au _{25 ~ 20} (MPS) ₁₈ It was confirmed that Ag, _{5 ~ 9} Au _{20 ~ 16} (MPS) ₁₈ , Ag _{7 ~ 12} Au _{18 ~ 13} (MPS) ₁₈ . That is, by increasing the content of the silver salt in preparation can be controlled to sequentially increase the composition of Ag alloyed in Ag _x Au _25-x (MPS) ₁₈ , wherein the silver atoms can be controlled to 1 to 12. In agreement with the absorption graph of Comparative Example 3 described in the prior art (Patent Document 1), it can be inferred that the alloyed silver atom is located in the icosahedral center metal of M _x Au _25-x (MPS) ₁₈ . .

In another method, a catalyst for generating hydrogen gas having an M ₂ Au ₃₆ (L) ₂₄ structure was prepared by expanding an alloy composite system in which x was an integer of 1. The alloy composite of the structure may have two times more active sites than M ₁ Au ₂₄ (L) ₁₈ and may improve the effect of the ligand 24/18 times.

It is possible to control the activity of the HER according to the adsorption energy between M and hydrogen introduced in the alloy composites prepared by the above method, the present content is generally understood. The HER performance of all alloy composites is expected to be improved by functional ligands as described above, and the role of the catalyst for hydrogen gas generation in the water-soluble alloy composite of M _x Au _25-x (L) ₁₈ structure is There is no doubt about it.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the invention is indicated by the following claims, and it should be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalents are included in the scope of the invention.

Claims (12)

Hydrogen gas generation water-soluble catalyst comprising a complex represented by the formula (1):
[Formula 1]
M _x Au _25-x (L) ₁₈
In Chemical Formula 1,
M is Pt or Ag,
L is one selected from the group consisting of glutathione, mercaptopropionic acid, mercaptopropanesulfonic acid, and combinations thereof,
x is one of integers from 0 to 13. The method of claim 1,
X is 0,
Wherein L is mercaptopropionic acid or mercaptopropanesulfonic acid, hydrogen gas generation water-soluble catalyst. The method of claim 1,
X is 1,
M is Pt,
Wherein L is glutathione or mercaptopropanesulfonic acid, hydrogen gas generation water-soluble catalyst. The method of claim 1,
M is Ag,
L is a hydrogen gas generating water-soluble catalyst, which is mercaptopropanesulfonic acid. Hydrogen gas water-soluble generating catalyst comprising a complex represented by the formula (2):
[Formula 2]
Au ₃₈ (L) ₂₄ or M ₂ Au ₃₆ (L) ₂₄
In Chemical Formula 2,
M is Ag,
L is one selected from the group consisting of glutathione, mercaptopropanesulfonic acid and combinations thereof. delete (a) adding an aqueous solution comprising L to a solution comprising M and Au;
(b) reacting an aqueous solution comprising sodium borohydride with the product of step (a); And
(c) obtaining a complex represented by the following Chemical Formula 1 or 2 from the product of step (b);
[Formula 1]
M _x Au _25-x (L) ₁₈
In Chemical Formula 1,
M is Pt or Ag,
L is one selected from the group consisting of glutathione, mercaptopropionic acid, mercaptopropanesulfonic acid, and combinations thereof,
[Formula 2]
Au ₃₈ (L) ₂₄ or M ₂ Au ₃₆ (L) ₂₄
In Chemical Formula 2,
M is Ag,
L is one selected from the group consisting of glutathione, mercaptopropanesulfonic acid, and combinations thereof,
x is one of integers from 0 to 13. The method of claim 7, wherein
The molar ratio of M and Au is 0:50 to 10:40, respectively. The method of claim 7, wherein
The solution of step (a) further comprises acetonitrile,
Wherein L is mercaptopropanesulfonic acid, the method of producing a hydrogen gas generating water-soluble catalyst. The method of claim 7, wherein
The solution of step (a) further comprises methanol,
Wherein L is glutathione, the method of producing a hydrogen gas generating water-soluble catalyst. The method of claim 7, wherein
M is Pt,
In step (c),
(i) phase shifting the complex to an organic solvent by adding tetraoctylammonium cation to the product of step (b);
(ii) removing impurities by adding hydrogen peroxide solution to the organic solvent; And
(iii) adding tetramethylammonium decanoate to the product of step (ii) to transfer the complex to an aqueous solution. The method of claim 7, wherein
Process for producing a hydrogen gas generating water-soluble catalyst in the step (c) to obtain the complex by centrifugation after desalting the product of step (b).

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