Mxene-palladium multilayer thin film formed by electrostatic layer-by-layer assembly and method for manufacturing same

Abstract

The present invention relates to a MXene-palladium multilayer thin film by electrostatic interlayer assembly and a method for manufacturing the same. The technical gist of the invention is that the MXene-palladium multilayer thin film by electrostatic interlayer assembly according to one aspect of the present invention comprises negatively charged MXene nanosheets and positively charged palladium nanoparticles, has a multilayer thin film structure in which the MXene nanosheets and palladium nanoparticles are alternately stacked by electrostatic interaction, and is capable of simultaneously performing a methanol oxidation reaction and a hydrogen evolution reaction.

Description

Technology Field

[0001] The present invention relates to an electrocatalytic multilayer thin film and a method for manufacturing the same, and more specifically, to a nanocomposite multilayer thin film capable of performing methanol oxidation and hydrogen generation reactions and a method for manufacturing the same. Background Technology

[0002] Hydrogen is attracting attention as a next-generation energy carrier due to its high energy density and clean combustion characteristics; however, most current commercial hydrogen production relies on fossil fuel-based processes, which poses a problem of emitting large amounts of carbon dioxide.

[0003] Electrochemical water splitting is considered a more sustainable alternative, but it has limitations in that it requires a voltage higher than the theoretical voltage (1.23 V) (approximately 1.5 V or higher) due to the slow reaction rate of the anodic oxygen evolution (OER). To overcome this problem, an electrochemical reforming method has been proposed that replaces the anodic reaction with the oxidation reaction of small molecules such as methanol.

[0004] Methanol oxidation (MOR) is characterized by a low oxidation potential and a fast reaction rate, but realizing this requires not only catalytic activity but also the efficient design of charge transfer and mass transfer within the electrode.

[0005] Palladium-based catalysts exhibit excellent activity in MOR and HER, but the role of the support is crucial for ensuring structural stability and electrical conductivity. Conventionally, palladium multilayer thin films using graphene oxide as a support have been proposed, but due to low electrical conductivity (approximately 10 -3 There is a problem in that charge transfer is insufficient due to (below S / cm), and diffusion resistance increases sharply above a certain thickness, limiting the achievement of high catalytic performance.

[0006] Therefore, there is a need to develop new multilayer thin-film electrode manufacturing technologies that can precisely control electrode structures at the nanoscale while providing high electrical conductivity and structural stability. Prior art literature

[0007] Korean Patent Publication No. 10-1764923, published on August 4, 2017. Korean Patent Publication No. 10-2373455, published on March 6, 2020. The problem to be solved

[0008] The present invention was developed to resolve the aforementioned problems, and aims to provide a dual-functional nanocomposite multilayer thin film capable of efficiently performing methanol oxidation and hydrogen generation reactions simultaneously.

[0009] In addition, another objective is to provide a method for manufacturing a nanocomposite multilayer thin film that can be produced simply and reproducibly by applying an electrostatic layer-by-layer (LbL) method.

[0010] In addition, the present invention aims to realize a system capable of efficient hydrogen production even at low potential by providing an electrocatalytic electrode comprising the above-mentioned multilayer thin film.

[0011] The objectives of the present invention are not limited to those mentioned above, and other unmentioned objectives may be clearly understood from the descriptions below and may be sufficiently included in the objectives of the present invention. means of solving the problem

[0012] A MXene-palladium nanocomposite multilayer thin film according to one aspect of the present invention for achieving the above objective comprises negatively charged MXene nanosheets and positively charged palladium nanoparticles, and has a multilayer thin film structure in which the MXene nanosheets and palladium nanoparticles are alternately stacked by electrostatic interaction, and can be configured to simultaneously perform methanol oxidation reaction and hydrogen evolution reaction.

[0013] A method for manufacturing a MXene-palladium nanocomposite multilayer thin film according to another aspect of the present invention for achieving the above objective may comprise the steps of: modifying the surface of a substrate with a positive charge; immersing the substrate in a negatively charged MXene nanosheet solution to form a MXene layer; immersing the substrate with the formed MXene layer in a positively charged palladium nanoparticle solution to form a palladium layer; and repeating the MXene layer formation step and the palladium layer formation step 3 to 25 times to form a multilayer thin film structure. Effects of the invention

[0014] The MXene-palladium nanocomposite multilayer thin film and the method for manufacturing the same according to the embodiment of the present invention based on the above-described configuration can enhance the catalytic activity of palladium nanoparticles by using MXene, which has high electrical conductivity and hydrogen storage capacity, as a support. In addition, by applying an electrostatic interlayer assembly method, the structure of each layer is easily controlled, and charge transport pathways and mass transfer characteristics can be improved, thereby exhibiting excellent electrochemical performance in methanol oxidation and hydrogen evolution reactions.

[0015] The present invention enables the achievement of a high current density of 3 to 15 mA / cm2 in the methanol oxidation reaction by alternately stacking MXene nanosheets and palladium nanoparticles in an electrostatic interlayer assembly manner, which is more than three times higher than that of conventional graphene oxide. As a dual-functional electrocatalyst capable of simultaneously performing methanol oxidation and hydrogen evolution reactions, it achieves a low onset potential of -0.15 V (vs. Ag / AgCl) in a 15-layer double-layer structure in the hydrogen evolution reaction, thereby enabling the production of hydrogen with an overpotential 0.35 V lower than that of a bare electrode.

[0016] In addition, when the present invention is applied to a two-electrode electrochemical modification system, the multilayer thin film of the present invention is used on both the anode and the cathode to operate at a low operating potential of 0.65 V, which is half the level of the theoretical water splitting voltage (1.23 V), thereby significantly improving energy efficiency. The present invention facilitates the manufacturing of large-area electrodes using a simple manufacturing method utilizing an electrostatic interlayer assembly method, and offers excellent flexibility in the manufacturing process as performance can be optimized by adjusting the number of layers. Furthermore, the present invention [possesses] the high electrical conductivity (10) of MXene 3 ~10 4 By simultaneously utilizing the excellent catalytic activity of S / cm and palladium, the problem of low electrical conductivity in conventional polymer support-based electrodes was solved. Brief explanation of the drawing

[0017] FIG. 1 is a flowchart showing the manufacturing process of a MXene-palladium nanocomposite multilayer thin film according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the concept of manufacturing a MXene-palladium multilayer thin film using an electrostatic interlayer assembly method according to an embodiment of the present invention. Figure 3 is a graph showing the results of the analysis of the formation process of a multilayer thin film according to an embodiment of the present invention. Figure 4 is a graph showing the results of the methanol oxidation reaction performance evaluation of a multilayer thin film according to an embodiment of the present invention. FIG. 5 is a schematic diagram showing the hydrogen generation reaction mechanism of a multilayer thin film according to an embodiment of the present invention. Figure 6 is a graph showing the results of evaluating the hydrogen generation reaction performance of a multilayer thin film and a comparison electrode according to an embodiment of the present invention. Figure 7 shows a two-electrode electrochemical modification system using a multilayer thin film according to an embodiment of the present invention and the results of the performance evaluation thereof. Figure 8 is a graph showing the results of the electrochemical surface area analysis of a multilayer thin film according to an embodiment of the present invention. Figure 9 is a graph showing the Tafel analysis results of a multilayer thin film and a comparison electrode according to an embodiment of the present invention. Specific details for implementing the invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms, and the embodiments described herein are not limited.

[0019] Similar parts in this specification are denoted by the same reference numerals.

[0020] In this specification, when a part is described as "comprising" a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0021] Where a numerical range is described in this specification, it should be understood that it includes both upper and lower limits of the range, and that all values ​​and partial ranges within the range are also specifically disclosed. For example, if "3 to 25 times" is described, it includes not only 3 times, 4 times, 5 times, ... 25 times, but also partial ranges such as 3 to 20 times, 5 to 25 times, 10 to 20 times, etc.

[0022] In this specification, the description "A and / or B" means "A or B, or A and B".

[0023] In this specification, the size or thickness of nanostructures, such as nanosheets and nanoparticles, refers to the average value measured by conventional measurement methods, such as electron microscopy, atomic force microscopy, and dynamic light scattering, and includes conventional tolerances depending on manufacturing and measurement conditions.

[0024] In this specification, electrochemical and physical properties such as current density, potential, and thickness refer to values ​​measured under measurement methods and conditions commonly used in the field, and include the typical range of measurement error depending on the measurement equipment and environment.

[0026] The present invention relates to a MXene-palladium nanocomposite multilayer thin film and a method for manufacturing the same.

[0027] In particular, the MXene-palladium nanocomposite multilayer film (10) according to an embodiment of the present invention is characterized by the fact that negatively charged MXene nanosheets (100) and positively charged palladium nanoparticles (200) are alternately stacked in an electrostatic layer-by-layer (LbL) manner, thereby enabling efficient simultaneous methanol oxidation reaction and hydrogen generation reaction.

[0029] Hereinafter, a MXene-palladium nanocomposite multilayer film (10) and a method for manufacturing the same (S10) according to a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[0031] A MXene-palladium nanocomposite multilayer film (10) according to a preferred embodiment of the present invention may be composed of MXene nanosheets (100) and palladium nanoparticles (200).

[0033] In this invention, 'MXene' is Ti3C2T X (T x represents one or more surface termination groups selected from the group consisting of -OH, -F, and =O, and is a negatively charged transition metal carbide in the form of a two-dimensional nanosheet. For convenience, it may be referred to as a 'MXene nanosheet (100)' below.

[0035] In this specification, the term "palladium nanoparticle (200)" refers to a palladium nanoparticle surface modified with a cationic ligand (210), as indicated by reference numeral 200 in the drawings. At this time, "palladium nanoparticle," "Pd nanoparticle," "positively charged palladium," etc., all refer to the same concept and mean a palladium nanoparticle (200) that carries a positive charge due to the cationic ligand (210). Therefore, for convenience, these terms may be used interchangeably below, but they should be understood as having the same meaning.

[0037] Additionally, the term 'cationic ligand (210)' in this specification refers to an organic molecule that binds to the surface of palladium nanoparticles (200) and imparts a positive charge, and any compound capable of forming a coordinate bond or an electrostatic bond with palladium can be used without limitation.

[0038] Specific examples include pyridine derivatives (e.g., 4-dimethylaminopyridine (DMAP), 4-methylpyridine, pyridine), quaternary ammonium compounds (e.g., tetraalkylalmonium salts), imidazolium compounds, and cationic polymers (e.g., polyethyleneimine derivatives).

[0039] Most preferably, 4-dimethylaminopyridine (DMAP) can be used, and in all embodiments of the present invention, DMAP was used as the cationic ligand (210).

[0040] DMAP forms a strong coordination bond with the palladium surface while maintaining a stable positive charge in an aqueous solution, thereby effectively performing electrostatic interlayer assembly with negatively charged MXene nanosheets (100). For convenience, even if 'DMAP-Pd' is written in the examples and drawings, it should be understood that this refers to palladium nanoparticles (200) modified with a cationic ligand (210).

[0042] The MXene-palladium nanocomposite multilayer film (10) according to an embodiment of the present invention may have a multilayer structure in which MXene nanosheets (100) and palladium nanoparticles (200) are alternately stacked by electrostatic interaction.

[0044] At this time, it is preferable to have a structure in which the alternating stacking of MXene nanosheets (100) and palladium nanoparticles (200) is repeated 3 to 25 times. More preferably, it may have a structure in which the stacking is repeated 5 to 20 times, and most preferably 10 to 15 times. If the number of stacking times is less than 3, the thickness of the multilayer thin film (10) is insufficient, resulting in a lack of catalytic active sites and low electrical conductivity, which significantly reduces the methanol oxidation current density. Conversely, if it exceeds 25 times, the mass transfer resistance increases rapidly due to excessive thickness, and access to the active sites of the inner layer is restricted, which tends to reduce performance. Therefore, the above range of 3 to 25 times is a condition that can simultaneously optimize catalytic activity, electrical conductivity, and mass transfer efficiency.

[0046] A MXene-palladium nanocomposite multilayer thin film (10) according to an embodiment of the present invention has an electrolyte comprising 1.0 mol methanol and 0.1 mol potassium hydroxide, with an amperage of 3 to 15 mA / cm² 2 It can exhibit a methanol oxidation current density of 5 to 12 mA / cm². Preferably, 5 to 12 mA / cm² 2 , most preferably 9~10 mA / cm 2 It can exhibit a current density of. This is comparable to conventional graphene oxide-based palladium electrodes (maximum approximately 3 mA / cm²). 2 This figure is more than three times higher than the value, and is the result of the high electrical conductivity of the MXene nanosheet (100) and the excellent catalytic activity of the palladium nanoparticle (200) showing a synergistic effect.

[0048] The MXene-palladium nanocomposite multilayer film (10) according to an embodiment of the present invention exhibits excellent catalytic activity in a hydrogen evolution reaction (HER).

[0049] The combination of MXene and palladium exhibits a synergistic effect in the hydrogen evolution reaction. MXene is 10 3 ~10 4 It provides an efficient electron transfer pathway with high electrical conductivity of S / cm and has hydrogen adsorption-desorption capabilities of its own, thereby assisting the catalytic activity of palladium nanoparticles (200). Palladium effectively promotes the reduction of hydrogen ions as a major catalytic active site. Thanks to these structural advantages, it exhibits significantly improved hydrogen generation performance compared to using a polymer support with low conductivity or using MXene alone.

[0050] Specifically, in a 0.1 molar sulfuric acid electrolyte, the hydrogen evolution reaction onset potential is in the range of -0.25 V (vs. Ag / AgCl) to -0.10 V (vs. Ag / AgCl), preferably -0.20 to 0.12 V, and most preferably 0.15 V. This is an overpotential about 0.35 V lower than that of the bare electrode, meaning that energy efficiency is significantly improved.

[0051] In addition, the hydrogen generation current density at around -0.3V is -3.0mA / cm² 2 Up to -3.5 mA / cm 2 It achieves this, which is the electrical conductivity of polymer support-based Pd electrodes (e.g., PSS / Pd electrode, approx. -1.0 mA / cm²). 2 It exhibits excellent hydrogen generation capability by having a reduction current that is more than three times larger than that of ).

[0053] The MXene-palladium multilayer film (10) of the present invention is a bifunctional electrocatalyst capable of performing both methanol oxidation and hydrogen generation reactions.

[0054] Performance evaluation of each reaction was performed under their respective optimal conditions.

[0055] The methanol oxidation reaction was measured in an alkaline electrolyte containing 0.1 M potassium hydroxide (KOH) and 1.0 M methanol, because methanol oxidation is favorable under alkaline conditions.

[0056] On the other hand, the hydrogen generation reaction was measured in a 0.1M sulfuric acid (H2SO4) electrolyte. This is because in an alkaline electrolyte, the reduction current of the ITO substrate itself overlaps with the hydrogen generation reaction potential region, making it difficult to accurately evaluate the intrinsic hydrogen generation catalytic activity of the MXene-palladium multilayer film (10).

[0057] Meanwhile, when applied to an actual electrochemical reforming system (Experimental Example 4), a two-electrode configuration can be used to simultaneously perform methanol oxidation at the anode and hydrogen generation at the cathode in an electrolyte containing 0.1M KOH and 1.0M methanol. This two-electrode system operates efficiently at a low operating potential of 0.65 to 0.9V.

[0059] A method (S10) for manufacturing a MXene-palladium nanocomposite multilayer thin film according to an embodiment of the present invention is described with reference to FIGS. 1 and 2.

[0061] First, a substrate (300) is prepared (S100). The substrate (300) may be one of an indium tin oxide (ITO) substrate, a glass carbon electrode (GCE), a silicon wafer, and a quartz substrate, and for electrochemical measurement, it is preferable to use a conductive substrate such as ITO or a glass carbon electrode (GCE).

[0063] Next, the surface of the substrate (300) is modified with a positive charge (S200). Specifically, the substrate (300) can be treated with an aminosilane compound, for example, 3-aminopropyltriethoxysilane (APTES) to impart a positive charge.

[0064] More specifically, by immersing the substrate (300) in a 1.0 vol% APTES ethanol solution for 2 hours, then washing with ethanol and deionized water and drying under a nitrogen atmosphere, positively charged amino groups (-NH3) on the surface + ) can be introduced.

[0066] Next, a MXene layer is formed (S300). The substrate (300) is immersed in a solution containing negatively charged MXene nanosheets (100) for 5 to 15 minutes, preferably 10 minutes, and then washed with deionized water to form the MXene layer. Loosely adsorbed MXene can be removed by washing three times for 1 minute each in deionized water.

[0068] MXene nanosheet (100) is Ti3C2T X (T X is one or more surface terminators selected from the group consisting of -OH, -F, and =O, and carries a negative charge due to the surface terminators. The MXene nanosheet solution can be prepared as an aqueous dispersion with a concentration of 0.5 to 1.5 mg / mL, preferably 1.0 mg / mL. The immersion time may be 5 to 15 minutes, preferably 10 minutes. If the immersion time is less than 5 minutes, sufficient electrostatic adsorption does not occur, making it difficult to form a uniform layer, and if it exceeds 15 minutes, the additional adsorption effect is negligible, resulting in reduced process efficiency.

[0070] In addition, to prevent oxidation of the MXene nanosheet (100), it is preferable that the MXene nanosheet solution contains 5 to 6 mM of a reducing antioxidant, for example, L-ascorbic acid. The MXene nanosheet solution can be stored in the dark at 4°C to minimize oxidation.

[0072] Next, a palladium layer is formed (S400). A substrate (300) with a MXene layer formed thereon is immersed in a solution containing palladium nanoparticles (200) surface-modified with a cationic ligand (210), for example, 4-dimethylaminopyridine (DMAP), for 5 to 15 minutes, preferably 10 minutes, and then washed with deionized water to form a palladium layer. Loosely adsorbed palladium nanoparticles can be removed by washing three times for 1 minute each in deionized water.

[0074] Palladium nanoparticles (200) are positively charged by DMAP and are adsorbed onto the surface of a negatively charged MXene nanosheet (100) by electrostatic attraction. The palladium nanoparticle solution can be prepared at a concentration of 0.5 to 1.5 mg / mL, preferably 1.0 mg / mL. The immersion time can be 5 to 15 minutes, preferably 10 minutes, the same as the MXene layer.

[0076] One bilayer is formed by performing the above MXene layer formation step (S300) and palladium layer formation step (S400) once. The above process is repeated until the target number of bilayers (3 to 25 times) is reached (S500). When the target number of bilayers is reached, a MXene-palladium nanocomposite multilayer film (10) is completed in which MXene nanosheets (100) and palladium nanoparticles (200) are alternately stacked by electrostatic interaction (S600).

[0078] Example 1. (MXene / Palladium) n Manufacture of multilayer thin film (10) (n=5, 10, 15, 20)

[0079] A glass carbon electrode (GCE, diameter 3 mm) was used as a substrate (300). The substrate (300) was immersed in a 1.0 vol% APTES ethanol solution for 2 hours, then washed with ethanol and dried under a nitrogen atmosphere to modify the surface to a positive charge (S200).

[0081] The MXene nanosheet solution was prepared as follows. 1 g of Ti3AlC2MAX phase powder was added to a mixed solution of 10 mL of 10 M LiF and 10 mL of 9 M HCl and stirred at 35°C for 24 hours. After the reaction, the solution was washed by centrifugation (3500 rpm, 5 min) and the process was repeated until the pH was 6 or higher. The obtained MXene nanosheet (100) was redispersed in deionized water, exfoliated by sonication (1 hour) in an Ar atmosphere, and the supernatant was recovered by centrifugation (3500 rpm, 1 hour). The final concentration was adjusted to 1.0 mg / mL, and 5 mM L-ascorbic acid was added to prevent oxidation.

[0083] The palladium nanoparticle solution was prepared as follows.

[0084] First, 80 mL of a 25 mM TOAB (tetraoctylammonium bromide) solution dissolved in toluene was prepared, and a 30 mM Na2PdCl4 aqueous solution was added to it and mixed at room temperature. Then, 25 mL (0.4 M) of an aqueous NaBH4 solution was slowly added dropwise while the reduction reaction was carried out, and the mixture was stirred for 1 hour.

[0085] After the reaction was completed, the organic phase, the toluene layer, was separated and dried using anhydrous Na2SO4 to remove residual moisture. An aqueous DMAP solution (0.1M) was added to the dried toluene solution in a 1:1 (v / v) ratio, and the mixture was aged for at least 6 hours to induce phase separation.

[0086] Afterward, the aqueous solution of the lower layer was recovered and redispersed to a final concentration of 1.0 mg / mL for use in subsequent processes. Through this process, positively charged palladium nanoparticles (200) surface-modified with DMAP are prepared in an aqueous solution state.

[0088] A positively charged substrate (300) was immersed in a MXene nanosheet solution for 10 minutes, then washed with deionized water and dried in a nitrogen atmosphere to form a MXene layer (S300). Subsequently, a palladium layer was formed by immersing in a palladium nanoparticle solution for 10 minutes, then washing with deionized water and drying in a nitrogen atmosphere (S400).

[0090] By varying the number of repetitions of the above MXene layer formation step (S300) and palladium layer formation step (S400) to 5, 10, 15, and 20 times, respectively, (MXene / Pd)5, (MXene / Pd) 10 , (Maxine / Pd) 15 , (Maxine / Pd) 20 A multilayer thin film was manufactured (S500, S600).

[0092] Comparative Example 1. Preparation of (MXene / Pd)1 multilayer thin film

[0093] A (MXene / Pd)1 multilayer thin film was prepared by proceeding in the same manner as in Example 1, but performing the MXene layer formation step (S400) and the palladium layer formation step (S400) only once each.

[0095] Comparative Example 2. Bare glass carbon electrode (Bare GCE)

[0096] The glass carbon electrode that did not form a multilayer thin film (10) was used as is.

[0098] Comparative Example 3. MXene-coated electrode

[0099] A thin film composed solely of MXene was prepared by drop-casting a MXene nanosheet solution onto the electrode of Comparative Example 2.

[0101] Comparative Example 4. (PSS / Palladium) n Fabrication of multilayer thin films (n=5, 10, 15, 20)

[0102] The procedure was carried out in the same manner as in Example 1, but a polystyrene sulfonate solution (PSS, Mw 60,000~80,000, 1.0 mg / mL) was used as the negative charge support instead of the MXene nanosheet solution. This was done to evaluate the performance of a polymer support with low electrical conductivity.

[0104] Comparative Example 5. (MXene / PEI) n Fabrication of multilayer thin films (n=5, 10, 15, 20)

[0105] The procedure was carried out in the same manner as in Example 1, but a polyethyleneimine solution (PEI, Mw 20,000~30,000, 1.0 mg / mL) was used as the positively charged material instead of a palladium nanoparticle solution. This is to evaluate the electrochemical activity of only the MXene nanosheet (100) without a catalytic active material.

[0107] <Experimental Example 1> Analysis of Multilayer Thin Film Formation Process and Characteristics

[0108] The formation process and characteristics of the multilayer thin film (10) prepared in Example 1 were analyzed. The results are shown in FIG. 3.

[0110] Figure 3(a) shows the UV-Vis absorbance spectrum according to the number of double layers, and as the number of double layers increases, the absorbance at 280 nm increases linearly (see Figure 3(b)). This indicates that the MXene nanosheet (100) and palladium nanoparticles (200) are uniformly stacked.

[0112] FIG. 3(c) shows a mass deposition profile measured by a QCM (Quartz Crystal Microbalance), which allowed real-time confirmation of the alternating stacking of MXene nanosheets (100) and palladium nanoparticles (200). The mass increased stepwise at each immersion step, indicating that the interlayer assembly proceeded sequentially. The average adsorption amount of the individual layers was 5.72 μg / cm² for the MXene nanosheets (100). 2 , palladium nanoparticles (200) at 2.84 μg / cm 2 It was measured as.

[0114] FIG. 3(d) shows the thin film thickness measured by a surface profilometer, and the thickness increased linearly in proportion to the number of double layers. The average thicknesses measured in 5, 10, 15, and 20 double layers were approximately 50.5 nm, 52.9 nm, 68.7 nm, and 107.4 nm, respectively. This indicates that the MXene nanosheets (100) and palladium nanoparticles (200) are stacked uniformly and densely layer by layer, and suggests that a stable multilayer thin film is formed due to strong interlayer electrostatic interactions.

[0116] <Experimental Example 2> Evaluation of Methanol Oxidation Reaction Performance

[0117] The electrodes prepared in Example 1 and Comparative Example 1 were evaluated in a three-electrode system. Each multilayer thin-film electrode was used as the working electrode, a platinum wire as the counter electrode, and Hg / HgO as the reference electrode. An aqueous solution of 0.1 M KOH + 1.0 M CH3OH was used as the electrolyte, and cyclic voltammetry (CV) was set in the range of -0.7 to 0.7 V (vs. Hg / HgO), with a scan rate 20It was performed at mV / s. The results are shown in Figure 4 and Table 1.

[0119] Fig. 4(a) is (MXene / Pd) 15 As shown in the surface SEM image of the multilayer thin film (10), it can be confirmed that palladium nanoparticles (200) are uniformly dispersed on the surface of the MXene nanosheet (100). This uniform dispersion contributes to maximizing the catalytic active sites.

[0121] FIG. 4(b) shows the cyclic voltammetry (CV) curves of the (MXene / Pd)n multilayer film (10) (n=5, 10, 15, 20) of Example 1 and Comparative Example 1 (n=1). A distinct oxidation peak due to methanol oxidation was observed at 0.4 V (vs. Hg / HgO). As the number of double layers increased, the oxidation current increased, and the maximum current density was observed at 15 BL.

[0123] FIG. 4(c) compares the maximum current density at each double layer number. Comparative Example 1 (1BL) is 1.8 mA / cm² 2 While it showed a low current density, Example 1 (5~20BL) was 5 mA / cm 2 The above high current densities were observed. In particular, the highest value of 9.38 mA / cm² was recorded at 15 BL. 2 It achieved, and at 20BL, it decreased slightly to 9.0 mA / cm² due to increased diffusion resistance. 2 It was shown. This suggests that 15BL is the optimal balance point for catalytic activity and mass transfer.

[0125] FIG. 4(d) shows the Tafel analysis results, and Example 1 showed a lower Tafel slope compared to Comparative Example 1, confirming excellent reaction kinetic characteristics. The smaller the slope in the Tafel region, the lower the reaction resistance, which is advantageous for increasing current density, and this is the combined effect of the high electrical conductivity of the MXene nanosheet (100) and the catalytic activity of the palladium nanoparticle (200).

[0127] Comparison of methanol oxidation current densities (Example 1, Comparative Example 1) Sample Number of double layers (n) Maximum current density (mA / cm²) 2 ) Comparative Example 1 1 1.8 Example 1 5 5.5 10 9.0 15 9.38 20 9.0

[0129] As can be seen in Table 1, in Example 1, the current density increased with increasing double layer number, reaching 9.38 mA / cm² at 15 BL. 2 The maximum value was achieved. On the other hand, Comparative Example 1 (1BL) was 1.8 mA / cm 2 It showed a low value. This indicates that a multilayer thin film structure is essential for improving methanol oxidation reaction performance. Specifically, the 1BL electrode of Comparative Example 1 did not provide sufficient catalytic active sites with only a single double layer, and the electrical conduction pathways were limited. In the 5BL electrode of Example 1, the current density was 5.5 mA / cm² 2 It increased sharply, which is a result of the increase in active sites due to the formation of a multilayer structure and the improvement of electron transport pathways. As the value increased from 10BL to 15BL, the current density increased from 9.0 to 9.38 mA / cm². 2 It reached a peak, which is the result of an optimal balance of catalytic activity, electrical conductivity, and mass transfer. The current density at 20 BL was 9.0 mA / cm². 2 The slight decrease is interpreted as being due to the increased diffusion resistance of methanol and products caused by the excessive thickness (107 nm), and the limited accessibility to the palladium active sites in the inner layer.

[0131] <Experimental Example 3> Evaluation of Hydrogen Generation Reaction Performance

[0132] The electrodes prepared in Example 1 and Comparative Examples 1 to 5 were evaluated in a three-electrode system. The electrolyte was 0.1 M H 2 SO 4 An aqueous solution was used, and a linear scanning voltammetry (LSV) range of -0.4–0.1 V (vs. Ag / AgCl) was performed at a scanning rate of 20 mV / s. In addition, cyclic voltammetry (CV) was performed at the same scanning rate to verify hydrogen adsorption-desorption characteristics. The results are shown in Figures 5 and 6 and Table 2.

[0134] Figure 5 is a schematic diagram showing the hydrogen evolution reaction mechanism. (MXene / Pd) of Example 1 n At the electrode, the MXene nanosheet (100) provides an excellent electron transfer pathway, and the palladium nanoparticle (200) acts as a major catalytic active site to promote the reduction reaction of hydrogen ions. In particular, the MXene nanosheet (100) has hydrogen adsorption-desorption capabilities, which further enhances the catalytic activity of the palladium nanoparticle (200), thereby efficiently generating hydrogen gas. On the other hand, the (PSS / Pd) of Comparative Example 4 n The electrode's electron transfer is limited due to the polystyrene sulfonate having low electrical conductivity, resulting in reduced HER performance, and Comparative Example 5 (MXene / PEI) n The electrode does not have palladium nanoparticles (200) with catalytic activity, so HER hardly occurs. These comparative results demonstrate that the combination of MXene nanosheets (100) and palladium nanoparticles (200) exhibits a very important synergistic effect in the hydrogen evolution reaction.

[0136] Figure 6(a) shows the LSV curves of the (MXene / Pd)n electrodes of Example 1 (n=5, 10, 15, 20) and Comparative Example 1 (n=1), where the hydrogen generation onset potential decreased and the current density increased as the number of double layers increased.

[0137] In particular, the 20BL electrode is -3.0 mA / cm² at approximately -0.3 V (vs. Ag / AgCl). 2 Up to -3.5 mA / cm 2 The hydrogen generation current density was shown, which indicates that a reduction current more than three times greater in absolute value flows compared to the (PSS / Pd)15 electrode of Comparative Example 4 (approx. -1.0 mA / cm2), resulting from the combined action of the excellent electrical conductivity of MXene and the high catalytic activity of palladium. The best HER performance was observed at 15–20 BL.

[0139] FIG. 6(b) is the (PSS / Pd) of Comparative Example 4 nElectrode, FIG. 6(c) is the (MXene / PEI) of Comparative Example 5 n The LSV curve of the electrode was shown, exhibiting a significantly lower current density compared to Example 1. This demonstrates that both the electrical conductivity of the MXene nanosheet (100) and the catalytic activity of the palladium nanoparticle (200) are required.

[0141] FIG. 6(d) shows the LSV curves of Comparative Example 2 (Bare GCE) and Comparative Example 3 (MXene-coated electrode). The bare electrode showed a negligible level of HER activity, whereas the MXene-coated electrode showed a certain level of hydrogen generation current. This means that the MXene nanosheet (100) itself has hydrogen adsorption-desorption ability.

[0143] Figure 6(e) shows the cyclic voltammetry curves of Comparative Example 2 and Comparative Example 3, where underpotential deposition (UPD) characteristics of hydrogen were observed in the range of -0.4 to 0.6 V on the MXene-coated electrode. This confirms that MXene alone can perform hydrogen adsorption and desorption.

[0145] FIG. 6(f) shows the cyclic voltammetry curves of Comparative Example 1 and Example 1, which showed a hydrogen adsorption-desorption peak shape distinctly different from that of the MXene-only electrode when palladium nanoparticles (200) were included. It was confirmed that as the number of double layers increased, the peak intensity increased, indicating an increase in electrochemically active sites. This means that palladium nanoparticles (200) act as the main HER active sites and exhibit excellent HER performance in combination with the hydrogen storage capacity of the MXene nanosheets (100).

[0147] Comparison of hydrogen generation reaction initiation potentials Sample Number of double layers (n) HER onset potential (V vs. Ag / AgCl) Example 1 15 -0.15 Example 1 20 -0.15 Comparative Example 1 1 -0.35 Comparative Example 2 (Bare) - -0.50 Comparative Example 3 (Maxine) 10 (fault) -0.40 Comparative Example 4 (PSS) 15 -0.30 Comparative Example 5 (PEI) 15 -0.45

[0149] As can be seen in Table 2, Example 1 exhibited superior hydrogen generation performance by displaying a lower onset potential compared to Comparative Examples 1 to 5. Upon closer examination, the bare electrode of Comparative Example 2 required a very high overpotential of -0.50 V, indicating that HER is very difficult without a catalyst. The MXene-only electrode of Comparative Example 3 showed an improvement over the bare electrode at -0.40 V, but a high overpotential was still required due to the absence of palladium. Comparative Example 4's (PSS / Pd) 15 Although the catalytic activity of palladium was exhibited at the electrode at -0.30V, the low electrical conductivity of PSS (10 -6 Due to the limitation of electron transfer caused by S / cm, an overvoltage 0.15V higher than that of Example 1 (-0.15V) was required. Comparative Example 5 (MXene / PEI) 15 The electrode showed -0.45V, indicating that the HER performance is limited by the hydrogen adsorption capacity of MXene alone. In contrast, the 15BL electrode of Example 1 achieved the lowest onset potential of -0.15V, which is due to the excellent electrical conductivity of MXene (10 3 This is the result of the combined effect of S / cm), the high catalytic activity of palladium, and the hydrogen storage capacity of MXene.

[0151] <Experimental Example 4> Performance Evaluation of Electrochemical Modification System

[0152] (MXene / Pd) of Example 1 15 Use platinum or (MXene / Pd) electrode as the anode 20 A two-electrode system was constructed using the electrode as the cathode. An aqueous solution of 0.1M KOH + 1.0M CH3OH was used as the electrolyte, and the test was performed with an LSV in the range of 0–2.0V and a scan rate of 5mV / s. The results are shown in Figure 7.

[0154] FIG. 7(a) is a schematic diagram of an electrochemical modification system, wherein the (MXene / Pd) of the present invention is at the anode n A multilayer thin film (10) is placed to perform a methanol oxidation reaction, and platinum or (MXene / Pd) is placed on the cathode nA hydrogen generation reaction is performed by placing a multilayer thin film (10).

[0156] Figure 7(b) shows the LSV curves of two electrode combinations. (MXene / Pd) 15 In the ∥Pt combination, hydrogen generation began at 0.9V, and (MXene / Pd) 15 ∥(Maxine / Pd) 20 The combination operated at 0.65V. This is a low potential, approximately half the level of the conventional water splitting voltage (1.23V), which means that energy efficiency can be significantly improved by replacing the oxygen evolution reaction with the methanol oxidation reaction.

[0158] In particular, when the multilayer thin film (10) of the present invention is applied to the anode even when a platinum cathode is used, the operating potential is lowered, thereby reducing energy consumption. Furthermore, when the multilayer thin film (10) of the present invention is used for both the anode and the cathode, the use of precious metal platinum can be completely replaced, resulting in excellent economic efficiency.

[0160] <Experimental Example 5> Electrochemical Surface Area Analysis

[0161] The electrochemical surface area (ECSA) of the electrodes prepared in Example 1 and Comparative Example 1 was analyzed. The ECSA was calculated from the charging current measured in the non-Faraday region using cyclic voltammetry. The results are shown in Fig. 8.

[0163] Figure 8 shows the results of the electrochemical surface area (ECSA) analysis. The ECSA of Example 1 (5–20 BL) increased significantly compared to Comparative Example 1 (1 BL), which means that the catalytic active site increases with increasing double layer number. Specifically, the ECSA of the 1 BL electrode is 0.02 cm 2 It was at a very low level, but at 5BL it was 3.47cm 2 It increased rapidly to . The 10BL electrode is 9.45cm 2 It showed ECSA, and the 15BL electrode was 19.73 cm 2 The maximum active surface area was achieved at 15.25 cm² on the 20BL electrode.2 It decreased slightly, which is interpreted as being due to the limited accessibility of the inner layer caused by excessive thickness.

[0165] <Experimental Example 6> Tafel Analysis

[0166] Tafel analysis was performed on the hydrogen evolution reaction of the electrodes prepared in Example 1 and Comparative Examples 1, 4, and 5. The results are shown in Fig. 9.

[0168] FIG. 9(a) is the (MXene / Pd) of Example 1 n Figure 9(b) shows the electrode and the Tafel plot of Comparative Example 1, and the (PSS / Pd) of Comparative Example 4 n Electrode, FIG. 9(c) is the (MXene / PEI) of Comparative Example 5 n The Tafel plot of the electrodes is shown, and Example 1 showed the lowest Tafel slope, confirming the excellent HER reaction rate.

[0170] As described above, the MXene-palladium nanocomposite multilayer film (10) and the method for manufacturing the same (S10) according to the embodiment of the present invention secure high electrical conductivity and excellent catalytic activity simultaneously by stacking MXene nanosheets (100) and palladium nanoparticles (200) 3 to 25 times in an electrostatic interlayer assembly manner. A high current density of 3 to 15 mA / cm2 was achieved in the methanol oxidation reaction, and when applied to an electrochemical reforming system, hydrogen can be efficiently produced at a low operating potential of 0.65 to 0.9 V.

[0172] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

[0173] Therefore, the true technical scope of protection of the present invention should include not only the above embodiments but also other embodiments that are variously modified according to the technical concept of the invention described in the following claims. Explanation of the symbols

[0174] 10: MXene-palladium nanocomposite multilayer thin film 100: MXene nanosheet 200: Palladium nanoparticles 210: Cationic ligand 300: Substrate S10: Method for manufacturing a MXene-palladium nanocomposite multilayer thin film S100: Substrate preparation step S200: Substrate surface positive charge modification step S300: MXene layer formation step S400: Palladium layer formation step S500: Repeat determination step S600: Multilayer thin film structure formation completion stage

Claims

Claim 1 A MXene-palladium nanocomposite multilayer thin film comprising: negatively charged MXene nanosheets; and positively charged palladium nanoparticles; wherein the palladium nanoparticles are surface-modified with cationic ligands, and the MXene nanosheets and the palladium nanoparticles are alternately stacked by electrostatic interaction, and the MXene-palladium nanocomposite multilayer thin film is characterized by being capable of simultaneously performing methanol oxidation and hydrogen evolution reactions. Claim 2 In claim 1, the MXene is Ti3C2T x and, the above T x A MXene-palladium nanocomposite multilayer thin film characterized by having one or more surface termination groups selected from the group consisting of -OH, -F and =O. Claim 3 delete Claim 4 A MXene-palladium nanocomposite multilayer thin film according to claim 1, characterized in that the alternating stacking of the MXene nanosheets and the palladium nanoparticles is repeated 3 to 25 times. Claim 5 In claim 1, 3 to 15 mA / cm² in an electrolyte comprising 1.0 mol methanol and 0.1 mol potassium hydroxide 2 MXene-palladium nanocomposite multilayer thin film characterized by exhibiting a methanol oxidation current density. Claim 6 A MXene-palladium nanocomposite multilayer thin film according to claim 1, characterized by exhibiting a hydrogen evolution reaction initiation potential of -0.25V to -0.10V (vs. Ag / AgCl) in an electrolyte containing 0.1 mol sulfuric acid. Claim 7 A MXene-palladium nanocomposite electrocatalyst electrode characterized by having a multilayer thin film of any one of claims 1, 2, 4 to 6 formed on a substrate. Claim 8 A method for manufacturing a MXene-palladium nanocomposite multilayer thin film, comprising: a step of modifying the surface of a substrate with a positive charge; a step of forming a MXene layer by immersing the substrate in a negatively charged MXene nanosheet solution; a step of forming a palladium layer by immersing the substrate with the formed MXene layer in a positively charged palladium nanoparticle solution; and a step of forming a multilayer thin film structure by repeating the MXene layer formation step and the palladium layer formation step 3 to 25 times. Claim 9 A method for manufacturing a MXene-palladium nanocomposite multilayer thin film according to claim 8, wherein the MXene nanosheet solution comprises 5 to 6 mM of a reducing antioxidant, the immersion time is 5 to 15 minutes each, and further comprises a step of washing with deionized water after each immersion step. Claim 10 A method for manufacturing a MXene-palladium nanocomposite multilayer thin film, wherein, in claim 8, the step of modifying the surface of the substrate with a positive charge is to treat the substrate with an aminosilane compound, and the substrate is selected from the group consisting of an indium tin oxide substrate, a glassy carbon electrode, a silicon wafer, and a quartz substrate.

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